"make tinyconfig" Configure the tiniest possible kernel.
You can find more information on using the Linux kernel config tools
- in Documentation/kbuild/kconfig.txt.
+ in Documentation/kbuild/kconfig.rst.
- NOTES on ``make config``:
--- /dev/null
+=============================================
+Exporting kernel headers for use by userspace
+=============================================
+
+The "make headers_install" command exports the kernel's header files in a
+form suitable for use by userspace programs.
+
+The linux kernel's exported header files describe the API for user space
+programs attempting to use kernel services. These kernel header files are
+used by the system's C library (such as glibc or uClibc) to define available
+system calls, as well as constants and structures to be used with these
+system calls. The C library's header files include the kernel header files
+from the "linux" subdirectory. The system's libc headers are usually
+installed at the default location /usr/include and the kernel headers in
+subdirectories under that (most notably /usr/include/linux and
+/usr/include/asm).
+
+Kernel headers are backwards compatible, but not forwards compatible. This
+means that a program built against a C library using older kernel headers
+should run on a newer kernel (although it may not have access to new
+features), but a program built against newer kernel headers may not work on an
+older kernel.
+
+The "make headers_install" command can be run in the top level directory of the
+kernel source code (or using a standard out-of-tree build). It takes two
+optional arguments::
+
+ make headers_install ARCH=i386 INSTALL_HDR_PATH=/usr
+
+ARCH indicates which architecture to produce headers for, and defaults to the
+current architecture. The linux/asm directory of the exported kernel headers
+is platform-specific, to see a complete list of supported architectures use
+the command::
+
+ ls -d include/asm-* | sed 's/.*-//'
+
+INSTALL_HDR_PATH indicates where to install the headers. It defaults to
+"./usr".
+
+An 'include' directory is automatically created inside INSTALL_HDR_PATH and
+headers are installed in 'INSTALL_HDR_PATH/include'.
+
+The command "make headers_install_all" exports headers for all architectures
+simultaneously. (This is mostly of interest to distribution maintainers,
+who create an architecture-independent tarball from the resulting include
+directory.) You also can use HDR_ARCH_LIST to specify list of architectures.
+Remember to provide the appropriate linux/asm directory via "mv" or "ln -s"
+before building a C library with headers exported this way.
+
+The kernel header export infrastructure is maintained by David Woodhouse
+<dwmw2@infradead.org>.
+++ /dev/null
-Exporting kernel headers for use by userspace
-=============================================
-
-The "make headers_install" command exports the kernel's header files in a
-form suitable for use by userspace programs.
-
-The linux kernel's exported header files describe the API for user space
-programs attempting to use kernel services. These kernel header files are
-used by the system's C library (such as glibc or uClibc) to define available
-system calls, as well as constants and structures to be used with these
-system calls. The C library's header files include the kernel header files
-from the "linux" subdirectory. The system's libc headers are usually
-installed at the default location /usr/include and the kernel headers in
-subdirectories under that (most notably /usr/include/linux and
-/usr/include/asm).
-
-Kernel headers are backwards compatible, but not forwards compatible. This
-means that a program built against a C library using older kernel headers
-should run on a newer kernel (although it may not have access to new
-features), but a program built against newer kernel headers may not work on an
-older kernel.
-
-The "make headers_install" command can be run in the top level directory of the
-kernel source code (or using a standard out-of-tree build). It takes two
-optional arguments:
-
- make headers_install ARCH=i386 INSTALL_HDR_PATH=/usr
-
-ARCH indicates which architecture to produce headers for, and defaults to the
-current architecture. The linux/asm directory of the exported kernel headers
-is platform-specific, to see a complete list of supported architectures use
-the command:
-
- ls -d include/asm-* | sed 's/.*-//'
-
-INSTALL_HDR_PATH indicates where to install the headers. It defaults to
-"./usr".
-
-An 'include' directory is automatically created inside INSTALL_HDR_PATH and
-headers are installed in 'INSTALL_HDR_PATH/include'.
-
-The command "make headers_install_all" exports headers for all architectures
-simultaneously. (This is mostly of interest to distribution maintainers,
-who create an architecture-independent tarball from the resulting include
-directory.) You also can use HDR_ARCH_LIST to specify list of architectures.
-Remember to provide the appropriate linux/asm directory via "mv" or "ln -s"
-before building a C library with headers exported this way.
-
-The kernel header export infrastructure is maintained by David Woodhouse
-<dwmw2@infradead.org>.
--- /dev/null
+:orphan:
+
+===================
+Kernel Build System
+===================
+
+.. toctree::
+ :maxdepth: 1
+
+ kconfig-language
+ kconfig-macro-language
+
+ kbuild
+ kconfig
+ makefiles
+ modules
+
+ headers_install
+
+ issues
+
+.. only:: subproject and html
+
+ Indices
+ =======
+
+ * :ref:`genindex`
--- /dev/null
+Recursion issue #1
+------------------
+
+ .. include:: Kconfig.recursion-issue-01
+ :literal:
+
+Recursion issue #2
+------------------
+
+ .. include:: Kconfig.recursion-issue-02
+ :literal:
--- /dev/null
+======
+Kbuild
+======
+
+
+Output files
+============
+
+modules.order
+-------------
+This file records the order in which modules appear in Makefiles. This
+is used by modprobe to deterministically resolve aliases that match
+multiple modules.
+
+modules.builtin
+---------------
+This file lists all modules that are built into the kernel. This is used
+by modprobe to not fail when trying to load something builtin.
+
+modules.builtin.modinfo
+--------------------------------------------------
+This file contains modinfo from all modules that are built into the kernel.
+Unlike modinfo of a separate module, all fields are prefixed with module name.
+
+
+Environment variables
+=====================
+
+KCPPFLAGS
+---------
+Additional options to pass when preprocessing. The preprocessing options
+will be used in all cases where kbuild does preprocessing including
+building C files and assembler files.
+
+KAFLAGS
+-------
+Additional options to the assembler (for built-in and modules).
+
+AFLAGS_MODULE
+-------------
+Additional module specific options to use for $(AS).
+
+AFLAGS_KERNEL
+-------------
+Additional options for $(AS) when used for assembler
+code for code that is compiled as built-in.
+
+KCFLAGS
+-------
+Additional options to the C compiler (for built-in and modules).
+
+CFLAGS_KERNEL
+-------------
+Additional options for $(CC) when used to compile
+code that is compiled as built-in.
+
+CFLAGS_MODULE
+-------------
+Additional module specific options to use for $(CC).
+
+LDFLAGS_MODULE
+--------------
+Additional options used for $(LD) when linking modules.
+
+HOSTCFLAGS
+----------
+Additional flags to be passed to $(HOSTCC) when building host programs.
+
+HOSTCXXFLAGS
+------------
+Additional flags to be passed to $(HOSTCXX) when building host programs.
+
+HOSTLDFLAGS
+-----------
+Additional flags to be passed when linking host programs.
+
+HOSTLDLIBS
+----------
+Additional libraries to link against when building host programs.
+
+KBUILD_KCONFIG
+--------------
+Set the top-level Kconfig file to the value of this environment
+variable. The default name is "Kconfig".
+
+KBUILD_VERBOSE
+--------------
+Set the kbuild verbosity. Can be assigned same values as "V=...".
+
+See make help for the full list.
+
+Setting "V=..." takes precedence over KBUILD_VERBOSE.
+
+KBUILD_EXTMOD
+-------------
+Set the directory to look for the kernel source when building external
+modules.
+
+Setting "M=..." takes precedence over KBUILD_EXTMOD.
+
+KBUILD_OUTPUT
+-------------
+Specify the output directory when building the kernel.
+
+The output directory can also be specified using "O=...".
+
+Setting "O=..." takes precedence over KBUILD_OUTPUT.
+
+KBUILD_DEBARCH
+--------------
+For the deb-pkg target, allows overriding the normal heuristics deployed by
+deb-pkg. Normally deb-pkg attempts to guess the right architecture based on
+the UTS_MACHINE variable, and on some architectures also the kernel config.
+The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
+architecture.
+
+ARCH
+----
+Set ARCH to the architecture to be built.
+
+In most cases the name of the architecture is the same as the
+directory name found in the arch/ directory.
+
+But some architectures such as x86 and sparc have aliases.
+
+- x86: i386 for 32 bit, x86_64 for 64 bit
+- sh: sh for 32 bit, sh64 for 64 bit
+- sparc: sparc32 for 32 bit, sparc64 for 64 bit
+
+CROSS_COMPILE
+-------------
+Specify an optional fixed part of the binutils filename.
+CROSS_COMPILE can be a part of the filename or the full path.
+
+CROSS_COMPILE is also used for ccache in some setups.
+
+CF
+--
+Additional options for sparse.
+
+CF is often used on the command-line like this::
+
+ make CF=-Wbitwise C=2
+
+INSTALL_PATH
+------------
+INSTALL_PATH specifies where to place the updated kernel and system map
+images. Default is /boot, but you can set it to other values.
+
+INSTALLKERNEL
+-------------
+Install script called when using "make install".
+The default name is "installkernel".
+
+The script will be called with the following arguments:
+ - $1 - kernel version
+ - $2 - kernel image file
+ - $3 - kernel map file
+ - $4 - default install path (use root directory if blank)
+
+The implementation of "make install" is architecture specific
+and it may differ from the above.
+
+INSTALLKERNEL is provided to enable the possibility to
+specify a custom installer when cross compiling a kernel.
+
+MODLIB
+------
+Specify where to install modules.
+The default value is::
+
+ $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
+
+The value can be overridden in which case the default value is ignored.
+
+INSTALL_MOD_PATH
+----------------
+INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
+relocations required by build roots. This is not defined in the
+makefile but the argument can be passed to make if needed.
+
+INSTALL_MOD_STRIP
+-----------------
+INSTALL_MOD_STRIP, if defined, will cause modules to be
+stripped after they are installed. If INSTALL_MOD_STRIP is '1', then
+the default option --strip-debug will be used. Otherwise,
+INSTALL_MOD_STRIP value will be used as the options to the strip command.
+
+INSTALL_HDR_PATH
+----------------
+INSTALL_HDR_PATH specifies where to install user space headers when
+executing "make headers_*".
+
+The default value is::
+
+ $(objtree)/usr
+
+$(objtree) is the directory where output files are saved.
+The output directory is often set using "O=..." on the commandline.
+
+The value can be overridden in which case the default value is ignored.
+
+KBUILD_SIGN_PIN
+---------------
+This variable allows a passphrase or PIN to be passed to the sign-file
+utility when signing kernel modules, if the private key requires such.
+
+KBUILD_MODPOST_WARN
+-------------------
+KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
+symbols in the final module linking stage. It changes such errors
+into warnings.
+
+KBUILD_MODPOST_NOFINAL
+----------------------
+KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
+This is solely useful to speed up test compiles.
+
+KBUILD_EXTRA_SYMBOLS
+--------------------
+For modules that use symbols from other modules.
+See more details in modules.txt.
+
+ALLSOURCE_ARCHS
+---------------
+For tags/TAGS/cscope targets, you can specify more than one arch
+to be included in the databases, separated by blank space. E.g.::
+
+ $ make ALLSOURCE_ARCHS="x86 mips arm" tags
+
+To get all available archs you can also specify all. E.g.::
+
+ $ make ALLSOURCE_ARCHS=all tags
+
+KBUILD_ENABLE_EXTRA_GCC_CHECKS
+------------------------------
+If enabled over the make command line with "W=1", it turns on additional
+gcc -W... options for more extensive build-time checking.
+
+KBUILD_BUILD_TIMESTAMP
+----------------------
+Setting this to a date string overrides the timestamp used in the
+UTS_VERSION definition (uname -v in the running kernel). The value has to
+be a string that can be passed to date -d. The default value
+is the output of the date command at one point during build.
+
+KBUILD_BUILD_USER, KBUILD_BUILD_HOST
+------------------------------------
+These two variables allow to override the user@host string displayed during
+boot and in /proc/version. The default value is the output of the commands
+whoami and host, respectively.
+
+KBUILD_LDS
+----------
+The linker script with full path. Assigned by the top-level Makefile.
+
+KBUILD_VMLINUX_OBJS
+-------------------
+All object files for vmlinux. They are linked to vmlinux in the same
+order as listed in KBUILD_VMLINUX_OBJS.
+
+KBUILD_VMLINUX_LIBS
+-------------------
+All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and KBUILD_VMLINUX_LIBS
+together specify all the object files used to link vmlinux.
+++ /dev/null
-Output files
-
-modules.order
---------------------------------------------------
-This file records the order in which modules appear in Makefiles. This
-is used by modprobe to deterministically resolve aliases that match
-multiple modules.
-
-modules.builtin
---------------------------------------------------
-This file lists all modules that are built into the kernel. This is used
-by modprobe to not fail when trying to load something builtin.
-
-modules.builtin.modinfo
---------------------------------------------------
-This file contains modinfo from all modules that are built into the kernel.
-Unlike modinfo of a separate module, all fields are prefixed with module name.
-
-
-Environment variables
-
-KCPPFLAGS
---------------------------------------------------
-Additional options to pass when preprocessing. The preprocessing options
-will be used in all cases where kbuild does preprocessing including
-building C files and assembler files.
-
-KAFLAGS
---------------------------------------------------
-Additional options to the assembler (for built-in and modules).
-
-AFLAGS_MODULE
---------------------------------------------------
-Additional module specific options to use for $(AS).
-
-AFLAGS_KERNEL
---------------------------------------------------
-Additional options for $(AS) when used for assembler
-code for code that is compiled as built-in.
-
-KCFLAGS
---------------------------------------------------
-Additional options to the C compiler (for built-in and modules).
-
-CFLAGS_KERNEL
---------------------------------------------------
-Additional options for $(CC) when used to compile
-code that is compiled as built-in.
-
-CFLAGS_MODULE
---------------------------------------------------
-Additional module specific options to use for $(CC).
-
-LDFLAGS_MODULE
---------------------------------------------------
-Additional options used for $(LD) when linking modules.
-
-HOSTCFLAGS
---------------------------------------------------
-Additional flags to be passed to $(HOSTCC) when building host programs.
-
-HOSTCXXFLAGS
---------------------------------------------------
-Additional flags to be passed to $(HOSTCXX) when building host programs.
-
-HOSTLDFLAGS
---------------------------------------------------
-Additional flags to be passed when linking host programs.
-
-HOSTLDLIBS
---------------------------------------------------
-Additional libraries to link against when building host programs.
-
-KBUILD_KCONFIG
---------------------------------------------------
-Set the top-level Kconfig file to the value of this environment
-variable. The default name is "Kconfig".
-
-KBUILD_VERBOSE
---------------------------------------------------
-Set the kbuild verbosity. Can be assigned same values as "V=...".
-See make help for the full list.
-Setting "V=..." takes precedence over KBUILD_VERBOSE.
-
-KBUILD_EXTMOD
---------------------------------------------------
-Set the directory to look for the kernel source when building external
-modules.
-Setting "M=..." takes precedence over KBUILD_EXTMOD.
-
-KBUILD_OUTPUT
---------------------------------------------------
-Specify the output directory when building the kernel.
-The output directory can also be specified using "O=...".
-Setting "O=..." takes precedence over KBUILD_OUTPUT.
-
-KBUILD_DEBARCH
---------------------------------------------------
-For the deb-pkg target, allows overriding the normal heuristics deployed by
-deb-pkg. Normally deb-pkg attempts to guess the right architecture based on
-the UTS_MACHINE variable, and on some architectures also the kernel config.
-The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
-architecture.
-
-ARCH
---------------------------------------------------
-Set ARCH to the architecture to be built.
-In most cases the name of the architecture is the same as the
-directory name found in the arch/ directory.
-But some architectures such as x86 and sparc have aliases.
-x86: i386 for 32 bit, x86_64 for 64 bit
-sh: sh for 32 bit, sh64 for 64 bit
-sparc: sparc32 for 32 bit, sparc64 for 64 bit
-
-CROSS_COMPILE
---------------------------------------------------
-Specify an optional fixed part of the binutils filename.
-CROSS_COMPILE can be a part of the filename or the full path.
-
-CROSS_COMPILE is also used for ccache in some setups.
-
-CF
---------------------------------------------------
-Additional options for sparse.
-CF is often used on the command-line like this:
-
- make CF=-Wbitwise C=2
-
-INSTALL_PATH
---------------------------------------------------
-INSTALL_PATH specifies where to place the updated kernel and system map
-images. Default is /boot, but you can set it to other values.
-
-INSTALLKERNEL
---------------------------------------------------
-Install script called when using "make install".
-The default name is "installkernel".
-
-The script will be called with the following arguments:
- $1 - kernel version
- $2 - kernel image file
- $3 - kernel map file
- $4 - default install path (use root directory if blank)
-
-The implementation of "make install" is architecture specific
-and it may differ from the above.
-
-INSTALLKERNEL is provided to enable the possibility to
-specify a custom installer when cross compiling a kernel.
-
-MODLIB
---------------------------------------------------
-Specify where to install modules.
-The default value is:
-
- $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
-
-The value can be overridden in which case the default value is ignored.
-
-INSTALL_MOD_PATH
---------------------------------------------------
-INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
-relocations required by build roots. This is not defined in the
-makefile but the argument can be passed to make if needed.
-
-INSTALL_MOD_STRIP
---------------------------------------------------
-INSTALL_MOD_STRIP, if defined, will cause modules to be
-stripped after they are installed. If INSTALL_MOD_STRIP is '1', then
-the default option --strip-debug will be used. Otherwise,
-INSTALL_MOD_STRIP value will be used as the options to the strip command.
-
-INSTALL_HDR_PATH
---------------------------------------------------
-INSTALL_HDR_PATH specifies where to install user space headers when
-executing "make headers_*".
-The default value is:
-
- $(objtree)/usr
-
-$(objtree) is the directory where output files are saved.
-The output directory is often set using "O=..." on the commandline.
-
-The value can be overridden in which case the default value is ignored.
-
-KBUILD_SIGN_PIN
---------------------------------------------------
-This variable allows a passphrase or PIN to be passed to the sign-file
-utility when signing kernel modules, if the private key requires such.
-
-KBUILD_MODPOST_WARN
---------------------------------------------------
-KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
-symbols in the final module linking stage. It changes such errors
-into warnings.
-
-KBUILD_MODPOST_NOFINAL
---------------------------------------------------
-KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
-This is solely useful to speed up test compiles.
-
-KBUILD_EXTRA_SYMBOLS
---------------------------------------------------
-For modules that use symbols from other modules.
-See more details in modules.txt.
-
-ALLSOURCE_ARCHS
---------------------------------------------------
-For tags/TAGS/cscope targets, you can specify more than one arch
-to be included in the databases, separated by blank space. E.g.:
-
- $ make ALLSOURCE_ARCHS="x86 mips arm" tags
-
-To get all available archs you can also specify all. E.g.:
-
- $ make ALLSOURCE_ARCHS=all tags
-
-KBUILD_ENABLE_EXTRA_GCC_CHECKS
---------------------------------------------------
-If enabled over the make command line with "W=1", it turns on additional
-gcc -W... options for more extensive build-time checking.
-
-KBUILD_BUILD_TIMESTAMP
---------------------------------------------------
-Setting this to a date string overrides the timestamp used in the
-UTS_VERSION definition (uname -v in the running kernel). The value has to
-be a string that can be passed to date -d. The default value
-is the output of the date command at one point during build.
-
-KBUILD_BUILD_USER, KBUILD_BUILD_HOST
---------------------------------------------------
-These two variables allow to override the user@host string displayed during
-boot and in /proc/version. The default value is the output of the commands
-whoami and host, respectively.
-
-KBUILD_LDS
---------------------------------------------------
-The linker script with full path. Assigned by the top-level Makefile.
-
-KBUILD_VMLINUX_OBJS
---------------------------------------------------
-All object files for vmlinux. They are linked to vmlinux in the same
-order as listed in KBUILD_VMLINUX_OBJS.
-
-KBUILD_VMLINUX_LIBS
---------------------------------------------------
-All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and KBUILD_VMLINUX_LIBS
-together specify all the object files used to link vmlinux.
--- /dev/null
+================
+Kconfig Language
+================
+
+Introduction
+------------
+
+The configuration database is a collection of configuration options
+organized in a tree structure::
+
+ +- Code maturity level options
+ | +- Prompt for development and/or incomplete code/drivers
+ +- General setup
+ | +- Networking support
+ | +- System V IPC
+ | +- BSD Process Accounting
+ | +- Sysctl support
+ +- Loadable module support
+ | +- Enable loadable module support
+ | +- Set version information on all module symbols
+ | +- Kernel module loader
+ +- ...
+
+Every entry has its own dependencies. These dependencies are used
+to determine the visibility of an entry. Any child entry is only
+visible if its parent entry is also visible.
+
+Menu entries
+------------
+
+Most entries define a config option; all other entries help to organize
+them. A single configuration option is defined like this::
+
+ config MODVERSIONS
+ bool "Set version information on all module symbols"
+ depends on MODULES
+ help
+ Usually, modules have to be recompiled whenever you switch to a new
+ kernel. ...
+
+Every line starts with a key word and can be followed by multiple
+arguments. "config" starts a new config entry. The following lines
+define attributes for this config option. Attributes can be the type of
+the config option, input prompt, dependencies, help text and default
+values. A config option can be defined multiple times with the same
+name, but every definition can have only a single input prompt and the
+type must not conflict.
+
+Menu attributes
+---------------
+
+A menu entry can have a number of attributes. Not all of them are
+applicable everywhere (see syntax).
+
+- type definition: "bool"/"tristate"/"string"/"hex"/"int"
+ Every config option must have a type. There are only two basic types:
+ tristate and string; the other types are based on these two. The type
+ definition optionally accepts an input prompt, so these two examples
+ are equivalent::
+
+ bool "Networking support"
+
+ and::
+
+ bool
+ prompt "Networking support"
+
+- input prompt: "prompt" <prompt> ["if" <expr>]
+ Every menu entry can have at most one prompt, which is used to display
+ to the user. Optionally dependencies only for this prompt can be added
+ with "if".
+
+- default value: "default" <expr> ["if" <expr>]
+ A config option can have any number of default values. If multiple
+ default values are visible, only the first defined one is active.
+ Default values are not limited to the menu entry where they are
+ defined. This means the default can be defined somewhere else or be
+ overridden by an earlier definition.
+ The default value is only assigned to the config symbol if no other
+ value was set by the user (via the input prompt above). If an input
+ prompt is visible the default value is presented to the user and can
+ be overridden by him.
+ Optionally, dependencies only for this default value can be added with
+ "if".
+
+ The default value deliberately defaults to 'n' in order to avoid bloating the
+ build. With few exceptions, new config options should not change this. The
+ intent is for "make oldconfig" to add as little as possible to the config from
+ release to release.
+
+ Note:
+ Things that merit "default y/m" include:
+
+ a) A new Kconfig option for something that used to always be built
+ should be "default y".
+
+ b) A new gatekeeping Kconfig option that hides/shows other Kconfig
+ options (but does not generate any code of its own), should be
+ "default y" so people will see those other options.
+
+ c) Sub-driver behavior or similar options for a driver that is
+ "default n". This allows you to provide sane defaults.
+
+ d) Hardware or infrastructure that everybody expects, such as CONFIG_NET
+ or CONFIG_BLOCK. These are rare exceptions.
+
+- type definition + default value::
+
+ "def_bool"/"def_tristate" <expr> ["if" <expr>]
+
+ This is a shorthand notation for a type definition plus a value.
+ Optionally dependencies for this default value can be added with "if".
+
+- dependencies: "depends on" <expr>
+ This defines a dependency for this menu entry. If multiple
+ dependencies are defined, they are connected with '&&'. Dependencies
+ are applied to all other options within this menu entry (which also
+ accept an "if" expression), so these two examples are equivalent::
+
+ bool "foo" if BAR
+ default y if BAR
+
+ and::
+
+ depends on BAR
+ bool "foo"
+ default y
+
+- reverse dependencies: "select" <symbol> ["if" <expr>]
+ While normal dependencies reduce the upper limit of a symbol (see
+ below), reverse dependencies can be used to force a lower limit of
+ another symbol. The value of the current menu symbol is used as the
+ minimal value <symbol> can be set to. If <symbol> is selected multiple
+ times, the limit is set to the largest selection.
+ Reverse dependencies can only be used with boolean or tristate
+ symbols.
+
+ Note:
+ select should be used with care. select will force
+ a symbol to a value without visiting the dependencies.
+ By abusing select you are able to select a symbol FOO even
+ if FOO depends on BAR that is not set.
+ In general use select only for non-visible symbols
+ (no prompts anywhere) and for symbols with no dependencies.
+ That will limit the usefulness but on the other hand avoid
+ the illegal configurations all over.
+
+- weak reverse dependencies: "imply" <symbol> ["if" <expr>]
+ This is similar to "select" as it enforces a lower limit on another
+ symbol except that the "implied" symbol's value may still be set to n
+ from a direct dependency or with a visible prompt.
+
+ Given the following example::
+
+ config FOO
+ tristate
+ imply BAZ
+
+ config BAZ
+ tristate
+ depends on BAR
+
+ The following values are possible:
+
+ === === ============= ==============
+ FOO BAR BAZ's default choice for BAZ
+ === === ============= ==============
+ n y n N/m/y
+ m y m M/y/n
+ y y y Y/n
+ y n * N
+ === === ============= ==============
+
+ This is useful e.g. with multiple drivers that want to indicate their
+ ability to hook into a secondary subsystem while allowing the user to
+ configure that subsystem out without also having to unset these drivers.
+
+- limiting menu display: "visible if" <expr>
+ This attribute is only applicable to menu blocks, if the condition is
+ false, the menu block is not displayed to the user (the symbols
+ contained there can still be selected by other symbols, though). It is
+ similar to a conditional "prompt" attribute for individual menu
+ entries. Default value of "visible" is true.
+
+- numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
+ This allows to limit the range of possible input values for int
+ and hex symbols. The user can only input a value which is larger than
+ or equal to the first symbol and smaller than or equal to the second
+ symbol.
+
+- help text: "help" or "---help---"
+ This defines a help text. The end of the help text is determined by
+ the indentation level, this means it ends at the first line which has
+ a smaller indentation than the first line of the help text.
+ "---help---" and "help" do not differ in behaviour, "---help---" is
+ used to help visually separate configuration logic from help within
+ the file as an aid to developers.
+
+- misc options: "option" <symbol>[=<value>]
+ Various less common options can be defined via this option syntax,
+ which can modify the behaviour of the menu entry and its config
+ symbol. These options are currently possible:
+
+ - "defconfig_list"
+ This declares a list of default entries which can be used when
+ looking for the default configuration (which is used when the main
+ .config doesn't exists yet.)
+
+ - "modules"
+ This declares the symbol to be used as the MODULES symbol, which
+ enables the third modular state for all config symbols.
+ At most one symbol may have the "modules" option set.
+
+ - "allnoconfig_y"
+ This declares the symbol as one that should have the value y when
+ using "allnoconfig". Used for symbols that hide other symbols.
+
+Menu dependencies
+-----------------
+
+Dependencies define the visibility of a menu entry and can also reduce
+the input range of tristate symbols. The tristate logic used in the
+expressions uses one more state than normal boolean logic to express the
+module state. Dependency expressions have the following syntax::
+
+ <expr> ::= <symbol> (1)
+ <symbol> '=' <symbol> (2)
+ <symbol> '!=' <symbol> (3)
+ <symbol1> '<' <symbol2> (4)
+ <symbol1> '>' <symbol2> (4)
+ <symbol1> '<=' <symbol2> (4)
+ <symbol1> '>=' <symbol2> (4)
+ '(' <expr> ')' (5)
+ '!' <expr> (6)
+ <expr> '&&' <expr> (7)
+ <expr> '||' <expr> (8)
+
+Expressions are listed in decreasing order of precedence.
+
+(1) Convert the symbol into an expression. Boolean and tristate symbols
+ are simply converted into the respective expression values. All
+ other symbol types result in 'n'.
+(2) If the values of both symbols are equal, it returns 'y',
+ otherwise 'n'.
+(3) If the values of both symbols are equal, it returns 'n',
+ otherwise 'y'.
+(4) If value of <symbol1> is respectively lower, greater, lower-or-equal,
+ or greater-or-equal than value of <symbol2>, it returns 'y',
+ otherwise 'n'.
+(5) Returns the value of the expression. Used to override precedence.
+(6) Returns the result of (2-/expr/).
+(7) Returns the result of min(/expr/, /expr/).
+(8) Returns the result of max(/expr/, /expr/).
+
+An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
+respectively for calculations). A menu entry becomes visible when its
+expression evaluates to 'm' or 'y'.
+
+There are two types of symbols: constant and non-constant symbols.
+Non-constant symbols are the most common ones and are defined with the
+'config' statement. Non-constant symbols consist entirely of alphanumeric
+characters or underscores.
+Constant symbols are only part of expressions. Constant symbols are
+always surrounded by single or double quotes. Within the quote, any
+other character is allowed and the quotes can be escaped using '\'.
+
+Menu structure
+--------------
+
+The position of a menu entry in the tree is determined in two ways. First
+it can be specified explicitly::
+
+ menu "Network device support"
+ depends on NET
+
+ config NETDEVICES
+ ...
+
+ endmenu
+
+All entries within the "menu" ... "endmenu" block become a submenu of
+"Network device support". All subentries inherit the dependencies from
+the menu entry, e.g. this means the dependency "NET" is added to the
+dependency list of the config option NETDEVICES.
+
+The other way to generate the menu structure is done by analyzing the
+dependencies. If a menu entry somehow depends on the previous entry, it
+can be made a submenu of it. First, the previous (parent) symbol must
+be part of the dependency list and then one of these two conditions
+must be true:
+
+- the child entry must become invisible, if the parent is set to 'n'
+- the child entry must only be visible, if the parent is visible::
+
+ config MODULES
+ bool "Enable loadable module support"
+
+ config MODVERSIONS
+ bool "Set version information on all module symbols"
+ depends on MODULES
+
+ comment "module support disabled"
+ depends on !MODULES
+
+MODVERSIONS directly depends on MODULES, this means it's only visible if
+MODULES is different from 'n'. The comment on the other hand is only
+visible when MODULES is set to 'n'.
+
+
+Kconfig syntax
+--------------
+
+The configuration file describes a series of menu entries, where every
+line starts with a keyword (except help texts). The following keywords
+end a menu entry:
+
+- config
+- menuconfig
+- choice/endchoice
+- comment
+- menu/endmenu
+- if/endif
+- source
+
+The first five also start the definition of a menu entry.
+
+config::
+ "config" <symbol>
+ <config options>
+
+This defines a config symbol <symbol> and accepts any of above
+attributes as options.
+
+menuconfig::
+ "menuconfig" <symbol>
+ <config options>
+
+This is similar to the simple config entry above, but it also gives a
+hint to front ends, that all suboptions should be displayed as a
+separate list of options. To make sure all the suboptions will really
+show up under the menuconfig entry and not outside of it, every item
+from the <config options> list must depend on the menuconfig symbol.
+In practice, this is achieved by using one of the next two constructs::
+
+ (1):
+ menuconfig M
+ if M
+ config C1
+ config C2
+ endif
+
+ (2):
+ menuconfig M
+ config C1
+ depends on M
+ config C2
+ depends on M
+
+In the following examples (3) and (4), C1 and C2 still have the M
+dependency, but will not appear under menuconfig M anymore, because
+of C0, which doesn't depend on M::
+
+ (3):
+ menuconfig M
+ config C0
+ if M
+ config C1
+ config C2
+ endif
+
+ (4):
+ menuconfig M
+ config C0
+ config C1
+ depends on M
+ config C2
+ depends on M
+
+choices::
+
+ "choice" [symbol]
+ <choice options>
+ <choice block>
+ "endchoice"
+
+This defines a choice group and accepts any of the above attributes as
+options. A choice can only be of type bool or tristate. If no type is
+specified for a choice, its type will be determined by the type of
+the first choice element in the group or remain unknown if none of the
+choice elements have a type specified, as well.
+
+While a boolean choice only allows a single config entry to be
+selected, a tristate choice also allows any number of config entries
+to be set to 'm'. This can be used if multiple drivers for a single
+hardware exists and only a single driver can be compiled/loaded into
+the kernel, but all drivers can be compiled as modules.
+
+A choice accepts another option "optional", which allows to set the
+choice to 'n' and no entry needs to be selected.
+If no [symbol] is associated with a choice, then you can not have multiple
+definitions of that choice. If a [symbol] is associated to the choice,
+then you may define the same choice (i.e. with the same entries) in another
+place.
+
+comment::
+
+ "comment" <prompt>
+ <comment options>
+
+This defines a comment which is displayed to the user during the
+configuration process and is also echoed to the output files. The only
+possible options are dependencies.
+
+menu::
+
+ "menu" <prompt>
+ <menu options>
+ <menu block>
+ "endmenu"
+
+This defines a menu block, see "Menu structure" above for more
+information. The only possible options are dependencies and "visible"
+attributes.
+
+if::
+
+ "if" <expr>
+ <if block>
+ "endif"
+
+This defines an if block. The dependency expression <expr> is appended
+to all enclosed menu entries.
+
+source::
+
+ "source" <prompt>
+
+This reads the specified configuration file. This file is always parsed.
+
+mainmenu::
+
+ "mainmenu" <prompt>
+
+This sets the config program's title bar if the config program chooses
+to use it. It should be placed at the top of the configuration, before any
+other statement.
+
+'#' Kconfig source file comment:
+
+An unquoted '#' character anywhere in a source file line indicates
+the beginning of a source file comment. The remainder of that line
+is a comment.
+
+
+Kconfig hints
+-------------
+This is a collection of Kconfig tips, most of which aren't obvious at
+first glance and most of which have become idioms in several Kconfig
+files.
+
+Adding common features and make the usage configurable
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It is a common idiom to implement a feature/functionality that are
+relevant for some architectures but not all.
+The recommended way to do so is to use a config variable named HAVE_*
+that is defined in a common Kconfig file and selected by the relevant
+architectures.
+An example is the generic IOMAP functionality.
+
+We would in lib/Kconfig see::
+
+ # Generic IOMAP is used to ...
+ config HAVE_GENERIC_IOMAP
+
+ config GENERIC_IOMAP
+ depends on HAVE_GENERIC_IOMAP && FOO
+
+And in lib/Makefile we would see::
+
+ obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
+
+For each architecture using the generic IOMAP functionality we would see::
+
+ config X86
+ select ...
+ select HAVE_GENERIC_IOMAP
+ select ...
+
+Note: we use the existing config option and avoid creating a new
+config variable to select HAVE_GENERIC_IOMAP.
+
+Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is
+introduced to overcome the limitation of select which will force a
+config option to 'y' no matter the dependencies.
+The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the
+situation where select forces a symbol equals to 'y'.
+
+Adding features that need compiler support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are several features that need compiler support. The recommended way
+to describe the dependency on the compiler feature is to use "depends on"
+followed by a test macro::
+
+ config STACKPROTECTOR
+ bool "Stack Protector buffer overflow detection"
+ depends on $(cc-option,-fstack-protector)
+ ...
+
+If you need to expose a compiler capability to makefiles and/or C source files,
+`CC_HAS_` is the recommended prefix for the config option::
+
+ config CC_HAS_STACKPROTECTOR_NONE
+ def_bool $(cc-option,-fno-stack-protector)
+
+Build as module only
+~~~~~~~~~~~~~~~~~~~~
+To restrict a component build to module-only, qualify its config symbol
+with "depends on m". E.g.::
+
+ config FOO
+ depends on BAR && m
+
+limits FOO to module (=m) or disabled (=n).
+
+Kconfig recursive dependency limitations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you've hit the Kconfig error: "recursive dependency detected" you've run
+into a recursive dependency issue with Kconfig, a recursive dependency can be
+summarized as a circular dependency. The kconfig tools need to ensure that
+Kconfig files comply with specified configuration requirements. In order to do
+that kconfig must determine the values that are possible for all Kconfig
+symbols, this is currently not possible if there is a circular relation
+between two or more Kconfig symbols. For more details refer to the "Simple
+Kconfig recursive issue" subsection below. Kconfig does not do recursive
+dependency resolution; this has a few implications for Kconfig file writers.
+We'll first explain why this issues exists and then provide an example
+technical limitation which this brings upon Kconfig developers. Eager
+developers wishing to try to address this limitation should read the next
+subsections.
+
+Simple Kconfig recursive issue
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Read: Documentation/kbuild/Kconfig.recursion-issue-01
+
+Test with::
+
+ make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig
+
+Cumulative Kconfig recursive issue
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Read: Documentation/kbuild/Kconfig.recursion-issue-02
+
+Test with::
+
+ make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-02 allnoconfig
+
+Practical solutions to kconfig recursive issue
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Developers who run into the recursive Kconfig issue have two options
+at their disposal. We document them below and also provide a list of
+historical issues resolved through these different solutions.
+
+ a) Remove any superfluous "select FOO" or "depends on FOO"
+ b) Match dependency semantics:
+
+ b1) Swap all "select FOO" to "depends on FOO" or,
+
+ b2) Swap all "depends on FOO" to "select FOO"
+
+The resolution to a) can be tested with the sample Kconfig file
+Documentation/kbuild/Kconfig.recursion-issue-01 through the removal
+of the "select CORE" from CORE_BELL_A_ADVANCED as that is implicit already
+since CORE_BELL_A depends on CORE. At times it may not be possible to remove
+some dependency criteria, for such cases you can work with solution b).
+
+The two different resolutions for b) can be tested in the sample Kconfig file
+Documentation/kbuild/Kconfig.recursion-issue-02.
+
+Below is a list of examples of prior fixes for these types of recursive issues;
+all errors appear to involve one or more select's and one or more "depends on".
+
+============ ===================================
+commit fix
+============ ===================================
+06b718c01208 select A -> depends on A
+c22eacfe82f9 depends on A -> depends on B
+6a91e854442c select A -> depends on A
+118c565a8f2e select A -> select B
+f004e5594705 select A -> depends on A
+c7861f37b4c6 depends on A -> (null)
+80c69915e5fb select A -> (null) (1)
+c2218e26c0d0 select A -> depends on A (1)
+d6ae99d04e1c select A -> depends on A
+95ca19cf8cbf select A -> depends on A
+8f057d7bca54 depends on A -> (null)
+8f057d7bca54 depends on A -> select A
+a0701f04846e select A -> depends on A
+0c8b92f7f259 depends on A -> (null)
+e4e9e0540928 select A -> depends on A (2)
+7453ea886e87 depends on A > (null) (1)
+7b1fff7e4fdf select A -> depends on A
+86c747d2a4f0 select A -> depends on A
+d9f9ab51e55e select A -> depends on A
+0c51a4d8abd6 depends on A -> select A (3)
+e98062ed6dc4 select A -> depends on A (3)
+91e5d284a7f1 select A -> (null)
+============ ===================================
+
+(1) Partial (or no) quote of error.
+(2) That seems to be the gist of that fix.
+(3) Same error.
+
+Future kconfig work
+~~~~~~~~~~~~~~~~~~~
+
+Work on kconfig is welcomed on both areas of clarifying semantics and on
+evaluating the use of a full SAT solver for it. A full SAT solver can be
+desirable to enable more complex dependency mappings and / or queries,
+for instance on possible use case for a SAT solver could be that of handling
+the current known recursive dependency issues. It is not known if this would
+address such issues but such evaluation is desirable. If support for a full SAT
+solver proves too complex or that it cannot address recursive dependency issues
+Kconfig should have at least clear and well defined semantics which also
+addresses and documents limitations or requirements such as the ones dealing
+with recursive dependencies.
+
+Further work on both of these areas is welcomed on Kconfig. We elaborate
+on both of these in the next two subsections.
+
+Semantics of Kconfig
+~~~~~~~~~~~~~~~~~~~~
+
+The use of Kconfig is broad, Linux is now only one of Kconfig's users:
+one study has completed a broad analysis of Kconfig use in 12 projects [0]_.
+Despite its widespread use, and although this document does a reasonable job
+in documenting basic Kconfig syntax a more precise definition of Kconfig
+semantics is welcomed. One project deduced Kconfig semantics through
+the use of the xconfig configurator [1]_. Work should be done to confirm if
+the deduced semantics matches our intended Kconfig design goals.
+
+Having well defined semantics can be useful for tools for practical
+evaluation of depenencies, for instance one such use known case was work to
+express in boolean abstraction of the inferred semantics of Kconfig to
+translate Kconfig logic into boolean formulas and run a SAT solver on this to
+find dead code / features (always inactive), 114 dead features were found in
+Linux using this methodology [1]_ (Section 8: Threats to validity).
+
+Confirming this could prove useful as Kconfig stands as one of the the leading
+industrial variability modeling languages [1]_ [2]_. Its study would help
+evaluate practical uses of such languages, their use was only theoretical
+and real world requirements were not well understood. As it stands though
+only reverse engineering techniques have been used to deduce semantics from
+variability modeling languages such as Kconfig [3]_.
+
+.. [0] http://www.eng.uwaterloo.ca/~shshe/kconfig_semantics.pdf
+.. [1] http://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf
+.. [2] http://gsd.uwaterloo.ca/sites/default/files/ase241-berger_0.pdf
+.. [3] http://gsd.uwaterloo.ca/sites/default/files/icse2011.pdf
+
+Full SAT solver for Kconfig
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Although SAT solvers [4]_ haven't yet been used by Kconfig directly, as noted
+in the previous subsection, work has been done however to express in boolean
+abstraction the inferred semantics of Kconfig to translate Kconfig logic into
+boolean formulas and run a SAT solver on it [5]_. Another known related project
+is CADOS [6]_ (former VAMOS [7]_) and the tools, mainly undertaker [8]_, which
+has been introduced first with [9]_. The basic concept of undertaker is to
+exract variability models from Kconfig, and put them together with a
+propositional formula extracted from CPP #ifdefs and build-rules into a SAT
+solver in order to find dead code, dead files, and dead symbols. If using a SAT
+solver is desirable on Kconfig one approach would be to evaluate repurposing
+such efforts somehow on Kconfig. There is enough interest from mentors of
+existing projects to not only help advise how to integrate this work upstream
+but also help maintain it long term. Interested developers should visit:
+
+http://kernelnewbies.org/KernelProjects/kconfig-sat
+
+.. [4] http://www.cs.cornell.edu/~sabhar/chapters/SATSolvers-KR-Handbook.pdf
+.. [5] http://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf
+.. [6] https://cados.cs.fau.de
+.. [7] https://vamos.cs.fau.de
+.. [8] https://undertaker.cs.fau.de
+.. [9] https://www4.cs.fau.de/Publications/2011/tartler_11_eurosys.pdf
+++ /dev/null
-Introduction
-------------
-
-The configuration database is a collection of configuration options
-organized in a tree structure:
-
- +- Code maturity level options
- | +- Prompt for development and/or incomplete code/drivers
- +- General setup
- | +- Networking support
- | +- System V IPC
- | +- BSD Process Accounting
- | +- Sysctl support
- +- Loadable module support
- | +- Enable loadable module support
- | +- Set version information on all module symbols
- | +- Kernel module loader
- +- ...
-
-Every entry has its own dependencies. These dependencies are used
-to determine the visibility of an entry. Any child entry is only
-visible if its parent entry is also visible.
-
-Menu entries
-------------
-
-Most entries define a config option; all other entries help to organize
-them. A single configuration option is defined like this:
-
-config MODVERSIONS
- bool "Set version information on all module symbols"
- depends on MODULES
- help
- Usually, modules have to be recompiled whenever you switch to a new
- kernel. ...
-
-Every line starts with a key word and can be followed by multiple
-arguments. "config" starts a new config entry. The following lines
-define attributes for this config option. Attributes can be the type of
-the config option, input prompt, dependencies, help text and default
-values. A config option can be defined multiple times with the same
-name, but every definition can have only a single input prompt and the
-type must not conflict.
-
-Menu attributes
----------------
-
-A menu entry can have a number of attributes. Not all of them are
-applicable everywhere (see syntax).
-
-- type definition: "bool"/"tristate"/"string"/"hex"/"int"
- Every config option must have a type. There are only two basic types:
- tristate and string; the other types are based on these two. The type
- definition optionally accepts an input prompt, so these two examples
- are equivalent:
-
- bool "Networking support"
- and
- bool
- prompt "Networking support"
-
-- input prompt: "prompt" <prompt> ["if" <expr>]
- Every menu entry can have at most one prompt, which is used to display
- to the user. Optionally dependencies only for this prompt can be added
- with "if".
-
-- default value: "default" <expr> ["if" <expr>]
- A config option can have any number of default values. If multiple
- default values are visible, only the first defined one is active.
- Default values are not limited to the menu entry where they are
- defined. This means the default can be defined somewhere else or be
- overridden by an earlier definition.
- The default value is only assigned to the config symbol if no other
- value was set by the user (via the input prompt above). If an input
- prompt is visible the default value is presented to the user and can
- be overridden by him.
- Optionally, dependencies only for this default value can be added with
- "if".
-
- The default value deliberately defaults to 'n' in order to avoid bloating the
- build. With few exceptions, new config options should not change this. The
- intent is for "make oldconfig" to add as little as possible to the config from
- release to release.
-
- Note:
- Things that merit "default y/m" include:
-
- a) A new Kconfig option for something that used to always be built
- should be "default y".
-
- b) A new gatekeeping Kconfig option that hides/shows other Kconfig
- options (but does not generate any code of its own), should be
- "default y" so people will see those other options.
-
- c) Sub-driver behavior or similar options for a driver that is
- "default n". This allows you to provide sane defaults.
-
- d) Hardware or infrastructure that everybody expects, such as CONFIG_NET
- or CONFIG_BLOCK. These are rare exceptions.
-
-- type definition + default value:
- "def_bool"/"def_tristate" <expr> ["if" <expr>]
- This is a shorthand notation for a type definition plus a value.
- Optionally dependencies for this default value can be added with "if".
-
-- dependencies: "depends on" <expr>
- This defines a dependency for this menu entry. If multiple
- dependencies are defined, they are connected with '&&'. Dependencies
- are applied to all other options within this menu entry (which also
- accept an "if" expression), so these two examples are equivalent:
-
- bool "foo" if BAR
- default y if BAR
- and
- depends on BAR
- bool "foo"
- default y
-
-- reverse dependencies: "select" <symbol> ["if" <expr>]
- While normal dependencies reduce the upper limit of a symbol (see
- below), reverse dependencies can be used to force a lower limit of
- another symbol. The value of the current menu symbol is used as the
- minimal value <symbol> can be set to. If <symbol> is selected multiple
- times, the limit is set to the largest selection.
- Reverse dependencies can only be used with boolean or tristate
- symbols.
- Note:
- select should be used with care. select will force
- a symbol to a value without visiting the dependencies.
- By abusing select you are able to select a symbol FOO even
- if FOO depends on BAR that is not set.
- In general use select only for non-visible symbols
- (no prompts anywhere) and for symbols with no dependencies.
- That will limit the usefulness but on the other hand avoid
- the illegal configurations all over.
-
-- weak reverse dependencies: "imply" <symbol> ["if" <expr>]
- This is similar to "select" as it enforces a lower limit on another
- symbol except that the "implied" symbol's value may still be set to n
- from a direct dependency or with a visible prompt.
-
- Given the following example:
-
- config FOO
- tristate
- imply BAZ
-
- config BAZ
- tristate
- depends on BAR
-
- The following values are possible:
-
- FOO BAR BAZ's default choice for BAZ
- --- --- ------------- --------------
- n y n N/m/y
- m y m M/y/n
- y y y Y/n
- y n * N
-
- This is useful e.g. with multiple drivers that want to indicate their
- ability to hook into a secondary subsystem while allowing the user to
- configure that subsystem out without also having to unset these drivers.
-
-- limiting menu display: "visible if" <expr>
- This attribute is only applicable to menu blocks, if the condition is
- false, the menu block is not displayed to the user (the symbols
- contained there can still be selected by other symbols, though). It is
- similar to a conditional "prompt" attribute for individual menu
- entries. Default value of "visible" is true.
-
-- numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
- This allows to limit the range of possible input values for int
- and hex symbols. The user can only input a value which is larger than
- or equal to the first symbol and smaller than or equal to the second
- symbol.
-
-- help text: "help" or "---help---"
- This defines a help text. The end of the help text is determined by
- the indentation level, this means it ends at the first line which has
- a smaller indentation than the first line of the help text.
- "---help---" and "help" do not differ in behaviour, "---help---" is
- used to help visually separate configuration logic from help within
- the file as an aid to developers.
-
-- misc options: "option" <symbol>[=<value>]
- Various less common options can be defined via this option syntax,
- which can modify the behaviour of the menu entry and its config
- symbol. These options are currently possible:
-
- - "defconfig_list"
- This declares a list of default entries which can be used when
- looking for the default configuration (which is used when the main
- .config doesn't exists yet.)
-
- - "modules"
- This declares the symbol to be used as the MODULES symbol, which
- enables the third modular state for all config symbols.
- At most one symbol may have the "modules" option set.
-
- - "allnoconfig_y"
- This declares the symbol as one that should have the value y when
- using "allnoconfig". Used for symbols that hide other symbols.
-
-Menu dependencies
------------------
-
-Dependencies define the visibility of a menu entry and can also reduce
-the input range of tristate symbols. The tristate logic used in the
-expressions uses one more state than normal boolean logic to express the
-module state. Dependency expressions have the following syntax:
-
-<expr> ::= <symbol> (1)
- <symbol> '=' <symbol> (2)
- <symbol> '!=' <symbol> (3)
- <symbol1> '<' <symbol2> (4)
- <symbol1> '>' <symbol2> (4)
- <symbol1> '<=' <symbol2> (4)
- <symbol1> '>=' <symbol2> (4)
- '(' <expr> ')' (5)
- '!' <expr> (6)
- <expr> '&&' <expr> (7)
- <expr> '||' <expr> (8)
-
-Expressions are listed in decreasing order of precedence.
-
-(1) Convert the symbol into an expression. Boolean and tristate symbols
- are simply converted into the respective expression values. All
- other symbol types result in 'n'.
-(2) If the values of both symbols are equal, it returns 'y',
- otherwise 'n'.
-(3) If the values of both symbols are equal, it returns 'n',
- otherwise 'y'.
-(4) If value of <symbol1> is respectively lower, greater, lower-or-equal,
- or greater-or-equal than value of <symbol2>, it returns 'y',
- otherwise 'n'.
-(5) Returns the value of the expression. Used to override precedence.
-(6) Returns the result of (2-/expr/).
-(7) Returns the result of min(/expr/, /expr/).
-(8) Returns the result of max(/expr/, /expr/).
-
-An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
-respectively for calculations). A menu entry becomes visible when its
-expression evaluates to 'm' or 'y'.
-
-There are two types of symbols: constant and non-constant symbols.
-Non-constant symbols are the most common ones and are defined with the
-'config' statement. Non-constant symbols consist entirely of alphanumeric
-characters or underscores.
-Constant symbols are only part of expressions. Constant symbols are
-always surrounded by single or double quotes. Within the quote, any
-other character is allowed and the quotes can be escaped using '\'.
-
-Menu structure
---------------
-
-The position of a menu entry in the tree is determined in two ways. First
-it can be specified explicitly:
-
-menu "Network device support"
- depends on NET
-
-config NETDEVICES
- ...
-
-endmenu
-
-All entries within the "menu" ... "endmenu" block become a submenu of
-"Network device support". All subentries inherit the dependencies from
-the menu entry, e.g. this means the dependency "NET" is added to the
-dependency list of the config option NETDEVICES.
-
-The other way to generate the menu structure is done by analyzing the
-dependencies. If a menu entry somehow depends on the previous entry, it
-can be made a submenu of it. First, the previous (parent) symbol must
-be part of the dependency list and then one of these two conditions
-must be true:
-- the child entry must become invisible, if the parent is set to 'n'
-- the child entry must only be visible, if the parent is visible
-
-config MODULES
- bool "Enable loadable module support"
-
-config MODVERSIONS
- bool "Set version information on all module symbols"
- depends on MODULES
-
-comment "module support disabled"
- depends on !MODULES
-
-MODVERSIONS directly depends on MODULES, this means it's only visible if
-MODULES is different from 'n'. The comment on the other hand is only
-visible when MODULES is set to 'n'.
-
-
-Kconfig syntax
---------------
-
-The configuration file describes a series of menu entries, where every
-line starts with a keyword (except help texts). The following keywords
-end a menu entry:
-- config
-- menuconfig
-- choice/endchoice
-- comment
-- menu/endmenu
-- if/endif
-- source
-The first five also start the definition of a menu entry.
-
-config:
-
- "config" <symbol>
- <config options>
-
-This defines a config symbol <symbol> and accepts any of above
-attributes as options.
-
-menuconfig:
- "menuconfig" <symbol>
- <config options>
-
-This is similar to the simple config entry above, but it also gives a
-hint to front ends, that all suboptions should be displayed as a
-separate list of options. To make sure all the suboptions will really
-show up under the menuconfig entry and not outside of it, every item
-from the <config options> list must depend on the menuconfig symbol.
-In practice, this is achieved by using one of the next two constructs:
-
-(1):
-menuconfig M
-if M
- config C1
- config C2
-endif
-
-(2):
-menuconfig M
-config C1
- depends on M
-config C2
- depends on M
-
-In the following examples (3) and (4), C1 and C2 still have the M
-dependency, but will not appear under menuconfig M anymore, because
-of C0, which doesn't depend on M:
-
-(3):
-menuconfig M
- config C0
-if M
- config C1
- config C2
-endif
-
-(4):
-menuconfig M
-config C0
-config C1
- depends on M
-config C2
- depends on M
-
-choices:
-
- "choice" [symbol]
- <choice options>
- <choice block>
- "endchoice"
-
-This defines a choice group and accepts any of the above attributes as
-options. A choice can only be of type bool or tristate. If no type is
-specified for a choice, its type will be determined by the type of
-the first choice element in the group or remain unknown if none of the
-choice elements have a type specified, as well.
-
-While a boolean choice only allows a single config entry to be
-selected, a tristate choice also allows any number of config entries
-to be set to 'm'. This can be used if multiple drivers for a single
-hardware exists and only a single driver can be compiled/loaded into
-the kernel, but all drivers can be compiled as modules.
-
-A choice accepts another option "optional", which allows to set the
-choice to 'n' and no entry needs to be selected.
-If no [symbol] is associated with a choice, then you can not have multiple
-definitions of that choice. If a [symbol] is associated to the choice,
-then you may define the same choice (i.e. with the same entries) in another
-place.
-
-comment:
-
- "comment" <prompt>
- <comment options>
-
-This defines a comment which is displayed to the user during the
-configuration process and is also echoed to the output files. The only
-possible options are dependencies.
-
-menu:
-
- "menu" <prompt>
- <menu options>
- <menu block>
- "endmenu"
-
-This defines a menu block, see "Menu structure" above for more
-information. The only possible options are dependencies and "visible"
-attributes.
-
-if:
-
- "if" <expr>
- <if block>
- "endif"
-
-This defines an if block. The dependency expression <expr> is appended
-to all enclosed menu entries.
-
-source:
-
- "source" <prompt>
-
-This reads the specified configuration file. This file is always parsed.
-
-mainmenu:
-
- "mainmenu" <prompt>
-
-This sets the config program's title bar if the config program chooses
-to use it. It should be placed at the top of the configuration, before any
-other statement.
-
-'#' Kconfig source file comment:
-
-An unquoted '#' character anywhere in a source file line indicates
-the beginning of a source file comment. The remainder of that line
-is a comment.
-
-
-Kconfig hints
--------------
-This is a collection of Kconfig tips, most of which aren't obvious at
-first glance and most of which have become idioms in several Kconfig
-files.
-
-Adding common features and make the usage configurable
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-It is a common idiom to implement a feature/functionality that are
-relevant for some architectures but not all.
-The recommended way to do so is to use a config variable named HAVE_*
-that is defined in a common Kconfig file and selected by the relevant
-architectures.
-An example is the generic IOMAP functionality.
-
-We would in lib/Kconfig see:
-
-# Generic IOMAP is used to ...
-config HAVE_GENERIC_IOMAP
-
-config GENERIC_IOMAP
- depends on HAVE_GENERIC_IOMAP && FOO
-
-And in lib/Makefile we would see:
-obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
-
-For each architecture using the generic IOMAP functionality we would see:
-
-config X86
- select ...
- select HAVE_GENERIC_IOMAP
- select ...
-
-Note: we use the existing config option and avoid creating a new
-config variable to select HAVE_GENERIC_IOMAP.
-
-Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is
-introduced to overcome the limitation of select which will force a
-config option to 'y' no matter the dependencies.
-The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the
-situation where select forces a symbol equals to 'y'.
-
-Adding features that need compiler support
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-There are several features that need compiler support. The recommended way
-to describe the dependency on the compiler feature is to use "depends on"
-followed by a test macro.
-
-config STACKPROTECTOR
- bool "Stack Protector buffer overflow detection"
- depends on $(cc-option,-fstack-protector)
- ...
-
-If you need to expose a compiler capability to makefiles and/or C source files,
-CC_HAS_ is the recommended prefix for the config option.
-
-config CC_HAS_STACKPROTECTOR_NONE
- def_bool $(cc-option,-fno-stack-protector)
-
-Build as module only
-~~~~~~~~~~~~~~~~~~~~
-To restrict a component build to module-only, qualify its config symbol
-with "depends on m". E.g.:
-
-config FOO
- depends on BAR && m
-
-limits FOO to module (=m) or disabled (=n).
-
-Kconfig recursive dependency limitations
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-If you've hit the Kconfig error: "recursive dependency detected" you've run
-into a recursive dependency issue with Kconfig, a recursive dependency can be
-summarized as a circular dependency. The kconfig tools need to ensure that
-Kconfig files comply with specified configuration requirements. In order to do
-that kconfig must determine the values that are possible for all Kconfig
-symbols, this is currently not possible if there is a circular relation
-between two or more Kconfig symbols. For more details refer to the "Simple
-Kconfig recursive issue" subsection below. Kconfig does not do recursive
-dependency resolution; this has a few implications for Kconfig file writers.
-We'll first explain why this issues exists and then provide an example
-technical limitation which this brings upon Kconfig developers. Eager
-developers wishing to try to address this limitation should read the next
-subsections.
-
-Simple Kconfig recursive issue
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Read: Documentation/kbuild/Kconfig.recursion-issue-01
-
-Test with:
-
-make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig
-
-Cumulative Kconfig recursive issue
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Read: Documentation/kbuild/Kconfig.recursion-issue-02
-
-Test with:
-
-make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-02 allnoconfig
-
-Practical solutions to kconfig recursive issue
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Developers who run into the recursive Kconfig issue have two options
-at their disposal. We document them below and also provide a list of
-historical issues resolved through these different solutions.
-
- a) Remove any superfluous "select FOO" or "depends on FOO"
- b) Match dependency semantics:
- b1) Swap all "select FOO" to "depends on FOO" or,
- b2) Swap all "depends on FOO" to "select FOO"
-
-The resolution to a) can be tested with the sample Kconfig file
-Documentation/kbuild/Kconfig.recursion-issue-01 through the removal
-of the "select CORE" from CORE_BELL_A_ADVANCED as that is implicit already
-since CORE_BELL_A depends on CORE. At times it may not be possible to remove
-some dependency criteria, for such cases you can work with solution b).
-
-The two different resolutions for b) can be tested in the sample Kconfig file
-Documentation/kbuild/Kconfig.recursion-issue-02.
-
-Below is a list of examples of prior fixes for these types of recursive issues;
-all errors appear to involve one or more select's and one or more "depends on".
-
-commit fix
-====== ===
-06b718c01208 select A -> depends on A
-c22eacfe82f9 depends on A -> depends on B
-6a91e854442c select A -> depends on A
-118c565a8f2e select A -> select B
-f004e5594705 select A -> depends on A
-c7861f37b4c6 depends on A -> (null)
-80c69915e5fb select A -> (null) (1)
-c2218e26c0d0 select A -> depends on A (1)
-d6ae99d04e1c select A -> depends on A
-95ca19cf8cbf select A -> depends on A
-8f057d7bca54 depends on A -> (null)
-8f057d7bca54 depends on A -> select A
-a0701f04846e select A -> depends on A
-0c8b92f7f259 depends on A -> (null)
-e4e9e0540928 select A -> depends on A (2)
-7453ea886e87 depends on A > (null) (1)
-7b1fff7e4fdf select A -> depends on A
-86c747d2a4f0 select A -> depends on A
-d9f9ab51e55e select A -> depends on A
-0c51a4d8abd6 depends on A -> select A (3)
-e98062ed6dc4 select A -> depends on A (3)
-91e5d284a7f1 select A -> (null)
-
-(1) Partial (or no) quote of error.
-(2) That seems to be the gist of that fix.
-(3) Same error.
-
-Future kconfig work
-~~~~~~~~~~~~~~~~~~~
-
-Work on kconfig is welcomed on both areas of clarifying semantics and on
-evaluating the use of a full SAT solver for it. A full SAT solver can be
-desirable to enable more complex dependency mappings and / or queries,
-for instance on possible use case for a SAT solver could be that of handling
-the current known recursive dependency issues. It is not known if this would
-address such issues but such evaluation is desirable. If support for a full SAT
-solver proves too complex or that it cannot address recursive dependency issues
-Kconfig should have at least clear and well defined semantics which also
-addresses and documents limitations or requirements such as the ones dealing
-with recursive dependencies.
-
-Further work on both of these areas is welcomed on Kconfig. We elaborate
-on both of these in the next two subsections.
-
-Semantics of Kconfig
-~~~~~~~~~~~~~~~~~~~~
-
-The use of Kconfig is broad, Linux is now only one of Kconfig's users:
-one study has completed a broad analysis of Kconfig use in 12 projects [0].
-Despite its widespread use, and although this document does a reasonable job
-in documenting basic Kconfig syntax a more precise definition of Kconfig
-semantics is welcomed. One project deduced Kconfig semantics through
-the use of the xconfig configurator [1]. Work should be done to confirm if
-the deduced semantics matches our intended Kconfig design goals.
-
-Having well defined semantics can be useful for tools for practical
-evaluation of depenencies, for instance one such use known case was work to
-express in boolean abstraction of the inferred semantics of Kconfig to
-translate Kconfig logic into boolean formulas and run a SAT solver on this to
-find dead code / features (always inactive), 114 dead features were found in
-Linux using this methodology [1] (Section 8: Threats to validity).
-
-Confirming this could prove useful as Kconfig stands as one of the the leading
-industrial variability modeling languages [1] [2]. Its study would help
-evaluate practical uses of such languages, their use was only theoretical
-and real world requirements were not well understood. As it stands though
-only reverse engineering techniques have been used to deduce semantics from
-variability modeling languages such as Kconfig [3].
-
-[0] http://www.eng.uwaterloo.ca/~shshe/kconfig_semantics.pdf
-[1] http://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf
-[2] http://gsd.uwaterloo.ca/sites/default/files/ase241-berger_0.pdf
-[3] http://gsd.uwaterloo.ca/sites/default/files/icse2011.pdf
-
-Full SAT solver for Kconfig
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Although SAT solvers [0] haven't yet been used by Kconfig directly, as noted in
-the previous subsection, work has been done however to express in boolean
-abstraction the inferred semantics of Kconfig to translate Kconfig logic into
-boolean formulas and run a SAT solver on it [1]. Another known related project
-is CADOS [2] (former VAMOS [3]) and the tools, mainly undertaker [4], which has
-been introduced first with [5]. The basic concept of undertaker is to exract
-variability models from Kconfig, and put them together with a propositional
-formula extracted from CPP #ifdefs and build-rules into a SAT solver in order
-to find dead code, dead files, and dead symbols. If using a SAT solver is
-desirable on Kconfig one approach would be to evaluate repurposing such efforts
-somehow on Kconfig. There is enough interest from mentors of existing projects
-to not only help advise how to integrate this work upstream but also help
-maintain it long term. Interested developers should visit:
-
-http://kernelnewbies.org/KernelProjects/kconfig-sat
-
-[0] http://www.cs.cornell.edu/~sabhar/chapters/SATSolvers-KR-Handbook.pdf
-[1] http://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf
-[2] https://cados.cs.fau.de
-[3] https://vamos.cs.fau.de
-[4] https://undertaker.cs.fau.de
-[5] https://www4.cs.fau.de/Publications/2011/tartler_11_eurosys.pdf
--- /dev/null
+======================
+Kconfig macro language
+======================
+
+Concept
+-------
+
+The basic idea was inspired by Make. When we look at Make, we notice sort of
+two languages in one. One language describes dependency graphs consisting of
+targets and prerequisites. The other is a macro language for performing textual
+substitution.
+
+There is clear distinction between the two language stages. For example, you
+can write a makefile like follows::
+
+ APP := foo
+ SRC := foo.c
+ CC := gcc
+
+ $(APP): $(SRC)
+ $(CC) -o $(APP) $(SRC)
+
+The macro language replaces the variable references with their expanded form,
+and handles as if the source file were input like follows::
+
+ foo: foo.c
+ gcc -o foo foo.c
+
+Then, Make analyzes the dependency graph and determines the targets to be
+updated.
+
+The idea is quite similar in Kconfig - it is possible to describe a Kconfig
+file like this::
+
+ CC := gcc
+
+ config CC_HAS_FOO
+ def_bool $(shell, $(srctree)/scripts/gcc-check-foo.sh $(CC))
+
+The macro language in Kconfig processes the source file into the following
+intermediate::
+
+ config CC_HAS_FOO
+ def_bool y
+
+Then, Kconfig moves onto the evaluation stage to resolve inter-symbol
+dependency as explained in kconfig-language.txt.
+
+
+Variables
+---------
+
+Like in Make, a variable in Kconfig works as a macro variable. A macro
+variable is expanded "in place" to yield a text string that may then be
+expanded further. To get the value of a variable, enclose the variable name in
+$( ). The parentheses are required even for single-letter variable names; $X is
+a syntax error. The curly brace form as in ${CC} is not supported either.
+
+There are two types of variables: simply expanded variables and recursively
+expanded variables.
+
+A simply expanded variable is defined using the := assignment operator. Its
+righthand side is expanded immediately upon reading the line from the Kconfig
+file.
+
+A recursively expanded variable is defined using the = assignment operator.
+Its righthand side is simply stored as the value of the variable without
+expanding it in any way. Instead, the expansion is performed when the variable
+is used.
+
+There is another type of assignment operator; += is used to append text to a
+variable. The righthand side of += is expanded immediately if the lefthand
+side was originally defined as a simple variable. Otherwise, its evaluation is
+deferred.
+
+The variable reference can take parameters, in the following form::
+
+ $(name,arg1,arg2,arg3)
+
+You can consider the parameterized reference as a function. (more precisely,
+"user-defined function" in contrast to "built-in function" listed below).
+
+Useful functions must be expanded when they are used since the same function is
+expanded differently if different parameters are passed. Hence, a user-defined
+function is defined using the = assignment operator. The parameters are
+referenced within the body definition with $(1), $(2), etc.
+
+In fact, recursively expanded variables and user-defined functions are the same
+internally. (In other words, "variable" is "function with zero argument".)
+When we say "variable" in a broad sense, it includes "user-defined function".
+
+
+Built-in functions
+------------------
+
+Like Make, Kconfig provides several built-in functions. Every function takes a
+particular number of arguments.
+
+In Make, every built-in function takes at least one argument. Kconfig allows
+zero argument for built-in functions, such as $(fileno), $(lineno). You could
+consider those as "built-in variable", but it is just a matter of how we call
+it after all. Let's say "built-in function" here to refer to natively supported
+functionality.
+
+Kconfig currently supports the following built-in functions.
+
+ - $(shell,command)
+
+ The "shell" function accepts a single argument that is expanded and passed
+ to a subshell for execution. The standard output of the command is then read
+ and returned as the value of the function. Every newline in the output is
+ replaced with a space. Any trailing newlines are deleted. The standard error
+ is not returned, nor is any program exit status.
+
+ - $(info,text)
+
+ The "info" function takes a single argument and prints it to stdout.
+ It evaluates to an empty string.
+
+ - $(warning-if,condition,text)
+
+ The "warning-if" function takes two arguments. If the condition part is "y",
+ the text part is sent to stderr. The text is prefixed with the name of the
+ current Kconfig file and the current line number.
+
+ - $(error-if,condition,text)
+
+ The "error-if" function is similar to "warning-if", but it terminates the
+ parsing immediately if the condition part is "y".
+
+ - $(filename)
+
+ The 'filename' takes no argument, and $(filename) is expanded to the file
+ name being parsed.
+
+ - $(lineno)
+
+ The 'lineno' takes no argument, and $(lineno) is expanded to the line number
+ being parsed.
+
+
+Make vs Kconfig
+---------------
+
+Kconfig adopts Make-like macro language, but the function call syntax is
+slightly different.
+
+A function call in Make looks like this::
+
+ $(func-name arg1,arg2,arg3)
+
+The function name and the first argument are separated by at least one
+whitespace. Then, leading whitespaces are trimmed from the first argument,
+while whitespaces in the other arguments are kept. You need to use a kind of
+trick to start the first parameter with spaces. For example, if you want
+to make "info" function print " hello", you can write like follows::
+
+ empty :=
+ space := $(empty) $(empty)
+ $(info $(space)$(space)hello)
+
+Kconfig uses only commas for delimiters, and keeps all whitespaces in the
+function call. Some people prefer putting a space after each comma delimiter::
+
+ $(func-name, arg1, arg2, arg3)
+
+In this case, "func-name" will receive " arg1", " arg2", " arg3". The presence
+of leading spaces may matter depending on the function. The same applies to
+Make - for example, $(subst .c, .o, $(sources)) is a typical mistake; it
+replaces ".c" with " .o".
+
+In Make, a user-defined function is referenced by using a built-in function,
+'call', like this::
+
+ $(call my-func,arg1,arg2,arg3)
+
+Kconfig invokes user-defined functions and built-in functions in the same way.
+The omission of 'call' makes the syntax shorter.
+
+In Make, some functions treat commas verbatim instead of argument separators.
+For example, $(shell echo hello, world) runs the command "echo hello, world".
+Likewise, $(info hello, world) prints "hello, world" to stdout. You could say
+this is _useful_ inconsistency.
+
+In Kconfig, for simpler implementation and grammatical consistency, commas that
+appear in the $( ) context are always delimiters. It means::
+
+ $(shell, echo hello, world)
+
+is an error because it is passing two parameters where the 'shell' function
+accepts only one. To pass commas in arguments, you can use the following trick::
+
+ comma := ,
+ $(shell, echo hello$(comma) world)
+
+
+Caveats
+-------
+
+A variable (or function) cannot be expanded across tokens. So, you cannot use
+a variable as a shorthand for an expression that consists of multiple tokens.
+The following works::
+
+ RANGE_MIN := 1
+ RANGE_MAX := 3
+
+ config FOO
+ int "foo"
+ range $(RANGE_MIN) $(RANGE_MAX)
+
+But, the following does not work::
+
+ RANGES := 1 3
+
+ config FOO
+ int "foo"
+ range $(RANGES)
+
+A variable cannot be expanded to any keyword in Kconfig. The following does
+not work::
+
+ MY_TYPE := tristate
+
+ config FOO
+ $(MY_TYPE) "foo"
+ default y
+
+Obviously from the design, $(shell command) is expanded in the textual
+substitution phase. You cannot pass symbols to the 'shell' function.
+
+The following does not work as expected::
+
+ config ENDIAN_FLAG
+ string
+ default "-mbig-endian" if CPU_BIG_ENDIAN
+ default "-mlittle-endian" if CPU_LITTLE_ENDIAN
+
+ config CC_HAS_ENDIAN_FLAG
+ def_bool $(shell $(srctree)/scripts/gcc-check-flag ENDIAN_FLAG)
+
+Instead, you can do like follows so that any function call is statically
+expanded::
+
+ config CC_HAS_ENDIAN_FLAG
+ bool
+ default $(shell $(srctree)/scripts/gcc-check-flag -mbig-endian) if CPU_BIG_ENDIAN
+ default $(shell $(srctree)/scripts/gcc-check-flag -mlittle-endian) if CPU_LITTLE_ENDIAN
+++ /dev/null
-Concept
--------
-
-The basic idea was inspired by Make. When we look at Make, we notice sort of
-two languages in one. One language describes dependency graphs consisting of
-targets and prerequisites. The other is a macro language for performing textual
-substitution.
-
-There is clear distinction between the two language stages. For example, you
-can write a makefile like follows:
-
- APP := foo
- SRC := foo.c
- CC := gcc
-
- $(APP): $(SRC)
- $(CC) -o $(APP) $(SRC)
-
-The macro language replaces the variable references with their expanded form,
-and handles as if the source file were input like follows:
-
- foo: foo.c
- gcc -o foo foo.c
-
-Then, Make analyzes the dependency graph and determines the targets to be
-updated.
-
-The idea is quite similar in Kconfig - it is possible to describe a Kconfig
-file like this:
-
- CC := gcc
-
- config CC_HAS_FOO
- def_bool $(shell, $(srctree)/scripts/gcc-check-foo.sh $(CC))
-
-The macro language in Kconfig processes the source file into the following
-intermediate:
-
- config CC_HAS_FOO
- def_bool y
-
-Then, Kconfig moves onto the evaluation stage to resolve inter-symbol
-dependency as explained in kconfig-language.txt.
-
-
-Variables
----------
-
-Like in Make, a variable in Kconfig works as a macro variable. A macro
-variable is expanded "in place" to yield a text string that may then be
-expanded further. To get the value of a variable, enclose the variable name in
-$( ). The parentheses are required even for single-letter variable names; $X is
-a syntax error. The curly brace form as in ${CC} is not supported either.
-
-There are two types of variables: simply expanded variables and recursively
-expanded variables.
-
-A simply expanded variable is defined using the := assignment operator. Its
-righthand side is expanded immediately upon reading the line from the Kconfig
-file.
-
-A recursively expanded variable is defined using the = assignment operator.
-Its righthand side is simply stored as the value of the variable without
-expanding it in any way. Instead, the expansion is performed when the variable
-is used.
-
-There is another type of assignment operator; += is used to append text to a
-variable. The righthand side of += is expanded immediately if the lefthand
-side was originally defined as a simple variable. Otherwise, its evaluation is
-deferred.
-
-The variable reference can take parameters, in the following form:
-
- $(name,arg1,arg2,arg3)
-
-You can consider the parameterized reference as a function. (more precisely,
-"user-defined function" in contrast to "built-in function" listed below).
-
-Useful functions must be expanded when they are used since the same function is
-expanded differently if different parameters are passed. Hence, a user-defined
-function is defined using the = assignment operator. The parameters are
-referenced within the body definition with $(1), $(2), etc.
-
-In fact, recursively expanded variables and user-defined functions are the same
-internally. (In other words, "variable" is "function with zero argument".)
-When we say "variable" in a broad sense, it includes "user-defined function".
-
-
-Built-in functions
-------------------
-
-Like Make, Kconfig provides several built-in functions. Every function takes a
-particular number of arguments.
-
-In Make, every built-in function takes at least one argument. Kconfig allows
-zero argument for built-in functions, such as $(fileno), $(lineno). You could
-consider those as "built-in variable", but it is just a matter of how we call
-it after all. Let's say "built-in function" here to refer to natively supported
-functionality.
-
-Kconfig currently supports the following built-in functions.
-
- - $(shell,command)
-
- The "shell" function accepts a single argument that is expanded and passed
- to a subshell for execution. The standard output of the command is then read
- and returned as the value of the function. Every newline in the output is
- replaced with a space. Any trailing newlines are deleted. The standard error
- is not returned, nor is any program exit status.
-
- - $(info,text)
-
- The "info" function takes a single argument and prints it to stdout.
- It evaluates to an empty string.
-
- - $(warning-if,condition,text)
-
- The "warning-if" function takes two arguments. If the condition part is "y",
- the text part is sent to stderr. The text is prefixed with the name of the
- current Kconfig file and the current line number.
-
- - $(error-if,condition,text)
-
- The "error-if" function is similar to "warning-if", but it terminates the
- parsing immediately if the condition part is "y".
-
- - $(filename)
-
- The 'filename' takes no argument, and $(filename) is expanded to the file
- name being parsed.
-
- - $(lineno)
-
- The 'lineno' takes no argument, and $(lineno) is expanded to the line number
- being parsed.
-
-
-Make vs Kconfig
----------------
-
-Kconfig adopts Make-like macro language, but the function call syntax is
-slightly different.
-
-A function call in Make looks like this:
-
- $(func-name arg1,arg2,arg3)
-
-The function name and the first argument are separated by at least one
-whitespace. Then, leading whitespaces are trimmed from the first argument,
-while whitespaces in the other arguments are kept. You need to use a kind of
-trick to start the first parameter with spaces. For example, if you want
-to make "info" function print " hello", you can write like follows:
-
- empty :=
- space := $(empty) $(empty)
- $(info $(space)$(space)hello)
-
-Kconfig uses only commas for delimiters, and keeps all whitespaces in the
-function call. Some people prefer putting a space after each comma delimiter:
-
- $(func-name, arg1, arg2, arg3)
-
-In this case, "func-name" will receive " arg1", " arg2", " arg3". The presence
-of leading spaces may matter depending on the function. The same applies to
-Make - for example, $(subst .c, .o, $(sources)) is a typical mistake; it
-replaces ".c" with " .o".
-
-In Make, a user-defined function is referenced by using a built-in function,
-'call', like this:
-
- $(call my-func,arg1,arg2,arg3)
-
-Kconfig invokes user-defined functions and built-in functions in the same way.
-The omission of 'call' makes the syntax shorter.
-
-In Make, some functions treat commas verbatim instead of argument separators.
-For example, $(shell echo hello, world) runs the command "echo hello, world".
-Likewise, $(info hello, world) prints "hello, world" to stdout. You could say
-this is _useful_ inconsistency.
-
-In Kconfig, for simpler implementation and grammatical consistency, commas that
-appear in the $( ) context are always delimiters. It means
-
- $(shell, echo hello, world)
-
-is an error because it is passing two parameters where the 'shell' function
-accepts only one. To pass commas in arguments, you can use the following trick:
-
- comma := ,
- $(shell, echo hello$(comma) world)
-
-
-Caveats
--------
-
-A variable (or function) cannot be expanded across tokens. So, you cannot use
-a variable as a shorthand for an expression that consists of multiple tokens.
-The following works:
-
- RANGE_MIN := 1
- RANGE_MAX := 3
-
- config FOO
- int "foo"
- range $(RANGE_MIN) $(RANGE_MAX)
-
-But, the following does not work:
-
- RANGES := 1 3
-
- config FOO
- int "foo"
- range $(RANGES)
-
-A variable cannot be expanded to any keyword in Kconfig. The following does
-not work:
-
- MY_TYPE := tristate
-
- config FOO
- $(MY_TYPE) "foo"
- default y
-
-Obviously from the design, $(shell command) is expanded in the textual
-substitution phase. You cannot pass symbols to the 'shell' function.
-The following does not work as expected.
-
- config ENDIAN_FLAG
- string
- default "-mbig-endian" if CPU_BIG_ENDIAN
- default "-mlittle-endian" if CPU_LITTLE_ENDIAN
-
- config CC_HAS_ENDIAN_FLAG
- def_bool $(shell $(srctree)/scripts/gcc-check-flag ENDIAN_FLAG)
-
-Instead, you can do like follows so that any function call is statically
-expanded.
-
- config CC_HAS_ENDIAN_FLAG
- bool
- default $(shell $(srctree)/scripts/gcc-check-flag -mbig-endian) if CPU_BIG_ENDIAN
- default $(shell $(srctree)/scripts/gcc-check-flag -mlittle-endian) if CPU_LITTLE_ENDIAN
--- /dev/null
+===================
+Kconfig make config
+===================
+
+This file contains some assistance for using `make *config`.
+
+Use "make help" to list all of the possible configuration targets.
+
+The xconfig ('qconf'), menuconfig ('mconf'), and nconfig ('nconf')
+programs also have embedded help text. Be sure to check that for
+navigation, search, and other general help text.
+
+General
+-------
+
+New kernel releases often introduce new config symbols. Often more
+important, new kernel releases may rename config symbols. When
+this happens, using a previously working .config file and running
+"make oldconfig" won't necessarily produce a working new kernel
+for you, so you may find that you need to see what NEW kernel
+symbols have been introduced.
+
+To see a list of new config symbols, use::
+
+ cp user/some/old.config .config
+ make listnewconfig
+
+and the config program will list any new symbols, one per line.
+
+Alternatively, you can use the brute force method::
+
+ make oldconfig
+ scripts/diffconfig .config.old .config | less
+
+----------------------------------------------------------------------
+
+Environment variables for `*config`
+
+KCONFIG_CONFIG
+--------------
+This environment variable can be used to specify a default kernel config
+file name to override the default name of ".config".
+
+KCONFIG_OVERWRITECONFIG
+-----------------------
+If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not
+break symlinks when .config is a symlink to somewhere else.
+
+`CONFIG_`
+---------
+If you set `CONFIG_` in the environment, Kconfig will prefix all symbols
+with its value when saving the configuration, instead of using the default,
+`CONFIG_`.
+
+----------------------------------------------------------------------
+
+Environment variables for '{allyes/allmod/allno/rand}config'
+
+KCONFIG_ALLCONFIG
+-----------------
+(partially based on lkml email from/by Rob Landley, re: miniconfig)
+
+--------------------------------------------------
+
+The allyesconfig/allmodconfig/allnoconfig/randconfig variants can also
+use the environment variable KCONFIG_ALLCONFIG as a flag or a filename
+that contains config symbols that the user requires to be set to a
+specific value. If KCONFIG_ALLCONFIG is used without a filename where
+KCONFIG_ALLCONFIG == "" or KCONFIG_ALLCONFIG == "1", `make *config`
+checks for a file named "all{yes/mod/no/def/random}.config"
+(corresponding to the `*config` command that was used) for symbol values
+that are to be forced. If this file is not found, it checks for a
+file named "all.config" to contain forced values.
+
+This enables you to create "miniature" config (miniconfig) or custom
+config files containing just the config symbols that you are interested
+in. Then the kernel config system generates the full .config file,
+including symbols of your miniconfig file.
+
+This 'KCONFIG_ALLCONFIG' file is a config file which contains
+(usually a subset of all) preset config symbols. These variable
+settings are still subject to normal dependency checks.
+
+Examples::
+
+ KCONFIG_ALLCONFIG=custom-notebook.config make allnoconfig
+
+or::
+
+ KCONFIG_ALLCONFIG=mini.config make allnoconfig
+
+or::
+
+ make KCONFIG_ALLCONFIG=mini.config allnoconfig
+
+These examples will disable most options (allnoconfig) but enable or
+disable the options that are explicitly listed in the specified
+mini-config files.
+
+----------------------------------------------------------------------
+
+Environment variables for 'randconfig'
+
+KCONFIG_SEED
+------------
+You can set this to the integer value used to seed the RNG, if you want
+to somehow debug the behaviour of the kconfig parser/frontends.
+If not set, the current time will be used.
+
+KCONFIG_PROBABILITY
+-------------------
+This variable can be used to skew the probabilities. This variable can
+be unset or empty, or set to three different formats:
+
+ ======================= ================== =====================
+ KCONFIG_PROBABILITY y:n split y:m:n split
+ ======================= ================== =====================
+ unset or empty 50 : 50 33 : 33 : 34
+ N N : 100-N N/2 : N/2 : 100-N
+ [1] N:M N+M : 100-(N+M) N : M : 100-(N+M)
+ [2] N:M:L N : 100-N M : L : 100-(M+L)
+ ======================= ================== =====================
+
+where N, M and L are integers (in base 10) in the range [0,100], and so
+that:
+
+ [1] N+M is in the range [0,100]
+
+ [2] M+L is in the range [0,100]
+
+Examples::
+
+ KCONFIG_PROBABILITY=10
+ 10% of booleans will be set to 'y', 90% to 'n'
+ 5% of tristates will be set to 'y', 5% to 'm', 90% to 'n'
+ KCONFIG_PROBABILITY=15:25
+ 40% of booleans will be set to 'y', 60% to 'n'
+ 15% of tristates will be set to 'y', 25% to 'm', 60% to 'n'
+ KCONFIG_PROBABILITY=10:15:15
+ 10% of booleans will be set to 'y', 90% to 'n'
+ 15% of tristates will be set to 'y', 15% to 'm', 70% to 'n'
+
+----------------------------------------------------------------------
+
+Environment variables for 'syncconfig'
+
+KCONFIG_NOSILENTUPDATE
+----------------------
+If this variable has a non-blank value, it prevents silent kernel
+config updates (requires explicit updates).
+
+KCONFIG_AUTOCONFIG
+------------------
+This environment variable can be set to specify the path & name of the
+"auto.conf" file. Its default value is "include/config/auto.conf".
+
+KCONFIG_TRISTATE
+----------------
+This environment variable can be set to specify the path & name of the
+"tristate.conf" file. Its default value is "include/config/tristate.conf".
+
+KCONFIG_AUTOHEADER
+------------------
+This environment variable can be set to specify the path & name of the
+"autoconf.h" (header) file.
+Its default value is "include/generated/autoconf.h".
+
+
+----------------------------------------------------------------------
+
+menuconfig
+----------
+
+SEARCHING for CONFIG symbols
+
+Searching in menuconfig:
+
+ The Search function searches for kernel configuration symbol
+ names, so you have to know something close to what you are
+ looking for.
+
+ Example::
+
+ /hotplug
+ This lists all config symbols that contain "hotplug",
+ e.g., HOTPLUG_CPU, MEMORY_HOTPLUG.
+
+ For search help, enter / followed by TAB-TAB (to highlight
+ <Help>) and Enter. This will tell you that you can also use
+ regular expressions (regexes) in the search string, so if you
+ are not interested in MEMORY_HOTPLUG, you could try::
+
+ /^hotplug
+
+ When searching, symbols are sorted thus:
+
+ - first, exact matches, sorted alphabetically (an exact match
+ is when the search matches the complete symbol name);
+ - then, other matches, sorted alphabetically.
+
+ For example: ^ATH.K matches:
+
+ ATH5K ATH9K ATH5K_AHB ATH5K_DEBUG [...] ATH6KL ATH6KL_DEBUG
+ [...] ATH9K_AHB ATH9K_BTCOEX_SUPPORT ATH9K_COMMON [...]
+
+ of which only ATH5K and ATH9K match exactly and so are sorted
+ first (and in alphabetical order), then come all other symbols,
+ sorted in alphabetical order.
+
+----------------------------------------------------------------------
+
+User interface options for 'menuconfig'
+
+MENUCONFIG_COLOR
+----------------
+It is possible to select different color themes using the variable
+MENUCONFIG_COLOR. To select a theme use::
+
+ make MENUCONFIG_COLOR=<theme> menuconfig
+
+Available themes are::
+
+ - mono => selects colors suitable for monochrome displays
+ - blackbg => selects a color scheme with black background
+ - classic => theme with blue background. The classic look
+ - bluetitle => a LCD friendly version of classic. (default)
+
+MENUCONFIG_MODE
+---------------
+This mode shows all sub-menus in one large tree.
+
+Example::
+
+ make MENUCONFIG_MODE=single_menu menuconfig
+
+----------------------------------------------------------------------
+
+nconfig
+-------
+
+nconfig is an alternate text-based configurator. It lists function
+keys across the bottom of the terminal (window) that execute commands.
+You can also just use the corresponding numeric key to execute the
+commands unless you are in a data entry window. E.g., instead of F6
+for Save, you can just press 6.
+
+Use F1 for Global help or F3 for the Short help menu.
+
+Searching in nconfig:
+
+ You can search either in the menu entry "prompt" strings
+ or in the configuration symbols.
+
+ Use / to begin a search through the menu entries. This does
+ not support regular expressions. Use <Down> or <Up> for
+ Next hit and Previous hit, respectively. Use <Esc> to
+ terminate the search mode.
+
+ F8 (SymSearch) searches the configuration symbols for the
+ given string or regular expression (regex).
+
+NCONFIG_MODE
+------------
+This mode shows all sub-menus in one large tree.
+
+Example::
+ make NCONFIG_MODE=single_menu nconfig
+
+----------------------------------------------------------------------
+
+xconfig
+-------
+
+Searching in xconfig:
+
+ The Search function searches for kernel configuration symbol
+ names, so you have to know something close to what you are
+ looking for.
+
+ Example:
+ Ctrl-F hotplug
+ or
+ Menu: File, Search, hotplug
+
+ lists all config symbol entries that contain "hotplug" in
+ the symbol name. In this Search dialog, you may change the
+ config setting for any of the entries that are not grayed out.
+ You can also enter a different search string without having
+ to return to the main menu.
+
+
+----------------------------------------------------------------------
+
+gconfig
+-------
+
+Searching in gconfig:
+
+ There is no search command in gconfig. However, gconfig does
+ have several different viewing choices, modes, and options.
+++ /dev/null
-This file contains some assistance for using "make *config".
-
-Use "make help" to list all of the possible configuration targets.
-
-The xconfig ('qconf'), menuconfig ('mconf'), and nconfig ('nconf')
-programs also have embedded help text. Be sure to check that for
-navigation, search, and other general help text.
-
-======================================================================
-General
---------------------------------------------------
-
-New kernel releases often introduce new config symbols. Often more
-important, new kernel releases may rename config symbols. When
-this happens, using a previously working .config file and running
-"make oldconfig" won't necessarily produce a working new kernel
-for you, so you may find that you need to see what NEW kernel
-symbols have been introduced.
-
-To see a list of new config symbols, use
-
- cp user/some/old.config .config
- make listnewconfig
-
-and the config program will list any new symbols, one per line.
-
-Alternatively, you can use the brute force method:
-
- make oldconfig
- scripts/diffconfig .config.old .config | less
-
-______________________________________________________________________
-Environment variables for '*config'
-
-KCONFIG_CONFIG
---------------------------------------------------
-This environment variable can be used to specify a default kernel config
-file name to override the default name of ".config".
-
-KCONFIG_OVERWRITECONFIG
---------------------------------------------------
-If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not
-break symlinks when .config is a symlink to somewhere else.
-
-CONFIG_
---------------------------------------------------
-If you set CONFIG_ in the environment, Kconfig will prefix all symbols
-with its value when saving the configuration, instead of using the default,
-"CONFIG_".
-
-______________________________________________________________________
-Environment variables for '{allyes/allmod/allno/rand}config'
-
-KCONFIG_ALLCONFIG
---------------------------------------------------
-(partially based on lkml email from/by Rob Landley, re: miniconfig)
---------------------------------------------------
-The allyesconfig/allmodconfig/allnoconfig/randconfig variants can also
-use the environment variable KCONFIG_ALLCONFIG as a flag or a filename
-that contains config symbols that the user requires to be set to a
-specific value. If KCONFIG_ALLCONFIG is used without a filename where
-KCONFIG_ALLCONFIG == "" or KCONFIG_ALLCONFIG == "1", "make *config"
-checks for a file named "all{yes/mod/no/def/random}.config"
-(corresponding to the *config command that was used) for symbol values
-that are to be forced. If this file is not found, it checks for a
-file named "all.config" to contain forced values.
-
-This enables you to create "miniature" config (miniconfig) or custom
-config files containing just the config symbols that you are interested
-in. Then the kernel config system generates the full .config file,
-including symbols of your miniconfig file.
-
-This 'KCONFIG_ALLCONFIG' file is a config file which contains
-(usually a subset of all) preset config symbols. These variable
-settings are still subject to normal dependency checks.
-
-Examples:
- KCONFIG_ALLCONFIG=custom-notebook.config make allnoconfig
-or
- KCONFIG_ALLCONFIG=mini.config make allnoconfig
-or
- make KCONFIG_ALLCONFIG=mini.config allnoconfig
-
-These examples will disable most options (allnoconfig) but enable or
-disable the options that are explicitly listed in the specified
-mini-config files.
-
-______________________________________________________________________
-Environment variables for 'randconfig'
-
-KCONFIG_SEED
---------------------------------------------------
-You can set this to the integer value used to seed the RNG, if you want
-to somehow debug the behaviour of the kconfig parser/frontends.
-If not set, the current time will be used.
-
-KCONFIG_PROBABILITY
---------------------------------------------------
-This variable can be used to skew the probabilities. This variable can
-be unset or empty, or set to three different formats:
- KCONFIG_PROBABILITY y:n split y:m:n split
- -----------------------------------------------------------------
- unset or empty 50 : 50 33 : 33 : 34
- N N : 100-N N/2 : N/2 : 100-N
- [1] N:M N+M : 100-(N+M) N : M : 100-(N+M)
- [2] N:M:L N : 100-N M : L : 100-(M+L)
-
-where N, M and L are integers (in base 10) in the range [0,100], and so
-that:
- [1] N+M is in the range [0,100]
- [2] M+L is in the range [0,100]
-
-Examples:
- KCONFIG_PROBABILITY=10
- 10% of booleans will be set to 'y', 90% to 'n'
- 5% of tristates will be set to 'y', 5% to 'm', 90% to 'n'
- KCONFIG_PROBABILITY=15:25
- 40% of booleans will be set to 'y', 60% to 'n'
- 15% of tristates will be set to 'y', 25% to 'm', 60% to 'n'
- KCONFIG_PROBABILITY=10:15:15
- 10% of booleans will be set to 'y', 90% to 'n'
- 15% of tristates will be set to 'y', 15% to 'm', 70% to 'n'
-
-______________________________________________________________________
-Environment variables for 'syncconfig'
-
-KCONFIG_NOSILENTUPDATE
---------------------------------------------------
-If this variable has a non-blank value, it prevents silent kernel
-config updates (requires explicit updates).
-
-KCONFIG_AUTOCONFIG
---------------------------------------------------
-This environment variable can be set to specify the path & name of the
-"auto.conf" file. Its default value is "include/config/auto.conf".
-
-KCONFIG_TRISTATE
---------------------------------------------------
-This environment variable can be set to specify the path & name of the
-"tristate.conf" file. Its default value is "include/config/tristate.conf".
-
-KCONFIG_AUTOHEADER
---------------------------------------------------
-This environment variable can be set to specify the path & name of the
-"autoconf.h" (header) file.
-Its default value is "include/generated/autoconf.h".
-
-
-======================================================================
-menuconfig
---------------------------------------------------
-
-SEARCHING for CONFIG symbols
-
-Searching in menuconfig:
-
- The Search function searches for kernel configuration symbol
- names, so you have to know something close to what you are
- looking for.
-
- Example:
- /hotplug
- This lists all config symbols that contain "hotplug",
- e.g., HOTPLUG_CPU, MEMORY_HOTPLUG.
-
- For search help, enter / followed by TAB-TAB (to highlight
- <Help>) and Enter. This will tell you that you can also use
- regular expressions (regexes) in the search string, so if you
- are not interested in MEMORY_HOTPLUG, you could try
-
- /^hotplug
-
- When searching, symbols are sorted thus:
- - first, exact matches, sorted alphabetically (an exact match
- is when the search matches the complete symbol name);
- - then, other matches, sorted alphabetically.
- For example: ^ATH.K matches:
- ATH5K ATH9K ATH5K_AHB ATH5K_DEBUG [...] ATH6KL ATH6KL_DEBUG
- [...] ATH9K_AHB ATH9K_BTCOEX_SUPPORT ATH9K_COMMON [...]
- of which only ATH5K and ATH9K match exactly and so are sorted
- first (and in alphabetical order), then come all other symbols,
- sorted in alphabetical order.
-
-______________________________________________________________________
-User interface options for 'menuconfig'
-
-MENUCONFIG_COLOR
---------------------------------------------------
-It is possible to select different color themes using the variable
-MENUCONFIG_COLOR. To select a theme use:
-
- make MENUCONFIG_COLOR=<theme> menuconfig
-
-Available themes are:
- mono => selects colors suitable for monochrome displays
- blackbg => selects a color scheme with black background
- classic => theme with blue background. The classic look
- bluetitle => a LCD friendly version of classic. (default)
-
-MENUCONFIG_MODE
---------------------------------------------------
-This mode shows all sub-menus in one large tree.
-
-Example:
- make MENUCONFIG_MODE=single_menu menuconfig
-
-
-======================================================================
-nconfig
---------------------------------------------------
-
-nconfig is an alternate text-based configurator. It lists function
-keys across the bottom of the terminal (window) that execute commands.
-You can also just use the corresponding numeric key to execute the
-commands unless you are in a data entry window. E.g., instead of F6
-for Save, you can just press 6.
-
-Use F1 for Global help or F3 for the Short help menu.
-
-Searching in nconfig:
-
- You can search either in the menu entry "prompt" strings
- or in the configuration symbols.
-
- Use / to begin a search through the menu entries. This does
- not support regular expressions. Use <Down> or <Up> for
- Next hit and Previous hit, respectively. Use <Esc> to
- terminate the search mode.
-
- F8 (SymSearch) searches the configuration symbols for the
- given string or regular expression (regex).
-
-NCONFIG_MODE
---------------------------------------------------
-This mode shows all sub-menus in one large tree.
-
-Example:
- make NCONFIG_MODE=single_menu nconfig
-
-
-======================================================================
-xconfig
---------------------------------------------------
-
-Searching in xconfig:
-
- The Search function searches for kernel configuration symbol
- names, so you have to know something close to what you are
- looking for.
-
- Example:
- Ctrl-F hotplug
- or
- Menu: File, Search, hotplug
-
- lists all config symbol entries that contain "hotplug" in
- the symbol name. In this Search dialog, you may change the
- config setting for any of the entries that are not grayed out.
- You can also enter a different search string without having
- to return to the main menu.
-
-
-======================================================================
-gconfig
---------------------------------------------------
-
-Searching in gconfig:
-
- There is no search command in gconfig. However, gconfig does
- have several different viewing choices, modes, and options.
-
-###
--- /dev/null
+======================
+Linux Kernel Makefiles
+======================
+
+This document describes the Linux kernel Makefiles.
+
+.. Table of Contents
+
+ === 1 Overview
+ === 2 Who does what
+ === 3 The kbuild files
+ --- 3.1 Goal definitions
+ --- 3.2 Built-in object goals - obj-y
+ --- 3.3 Loadable module goals - obj-m
+ --- 3.4 Objects which export symbols
+ --- 3.5 Library file goals - lib-y
+ --- 3.6 Descending down in directories
+ --- 3.7 Compilation flags
+ --- 3.8 Command line dependency
+ --- 3.9 Dependency tracking
+ --- 3.10 Special Rules
+ --- 3.11 $(CC) support functions
+ --- 3.12 $(LD) support functions
+
+ === 4 Host Program support
+ --- 4.1 Simple Host Program
+ --- 4.2 Composite Host Programs
+ --- 4.3 Using C++ for host programs
+ --- 4.4 Controlling compiler options for host programs
+ --- 4.5 When host programs are actually built
+ --- 4.6 Using hostprogs-$(CONFIG_FOO)
+
+ === 5 Kbuild clean infrastructure
+
+ === 6 Architecture Makefiles
+ --- 6.1 Set variables to tweak the build to the architecture
+ --- 6.2 Add prerequisites to archheaders:
+ --- 6.3 Add prerequisites to archprepare:
+ --- 6.4 List directories to visit when descending
+ --- 6.5 Architecture-specific boot images
+ --- 6.6 Building non-kbuild targets
+ --- 6.7 Commands useful for building a boot image
+ --- 6.8 Custom kbuild commands
+ --- 6.9 Preprocessing linker scripts
+ --- 6.10 Generic header files
+ --- 6.11 Post-link pass
+
+ === 7 Kbuild syntax for exported headers
+ --- 7.1 no-export-headers
+ --- 7.2 generic-y
+ --- 7.3 generated-y
+ --- 7.4 mandatory-y
+
+ === 8 Kbuild Variables
+ === 9 Makefile language
+ === 10 Credits
+ === 11 TODO
+
+1 Overview
+==========
+
+The Makefiles have five parts::
+
+ Makefile the top Makefile.
+ .config the kernel configuration file.
+ arch/$(ARCH)/Makefile the arch Makefile.
+ scripts/Makefile.* common rules etc. for all kbuild Makefiles.
+ kbuild Makefiles there are about 500 of these.
+
+The top Makefile reads the .config file, which comes from the kernel
+configuration process.
+
+The top Makefile is responsible for building two major products: vmlinux
+(the resident kernel image) and modules (any module files).
+It builds these goals by recursively descending into the subdirectories of
+the kernel source tree.
+The list of subdirectories which are visited depends upon the kernel
+configuration. The top Makefile textually includes an arch Makefile
+with the name arch/$(ARCH)/Makefile. The arch Makefile supplies
+architecture-specific information to the top Makefile.
+
+Each subdirectory has a kbuild Makefile which carries out the commands
+passed down from above. The kbuild Makefile uses information from the
+.config file to construct various file lists used by kbuild to build
+any built-in or modular targets.
+
+scripts/Makefile.* contains all the definitions/rules etc. that
+are used to build the kernel based on the kbuild makefiles.
+
+
+2 Who does what
+===============
+
+People have four different relationships with the kernel Makefiles.
+
+*Users* are people who build kernels. These people type commands such as
+"make menuconfig" or "make". They usually do not read or edit
+any kernel Makefiles (or any other source files).
+
+*Normal developers* are people who work on features such as device
+drivers, file systems, and network protocols. These people need to
+maintain the kbuild Makefiles for the subsystem they are
+working on. In order to do this effectively, they need some overall
+knowledge about the kernel Makefiles, plus detailed knowledge about the
+public interface for kbuild.
+
+*Arch developers* are people who work on an entire architecture, such
+as sparc or ia64. Arch developers need to know about the arch Makefile
+as well as kbuild Makefiles.
+
+*Kbuild developers* are people who work on the kernel build system itself.
+These people need to know about all aspects of the kernel Makefiles.
+
+This document is aimed towards normal developers and arch developers.
+
+
+3 The kbuild files
+==================
+
+Most Makefiles within the kernel are kbuild Makefiles that use the
+kbuild infrastructure. This chapter introduces the syntax used in the
+kbuild makefiles.
+The preferred name for the kbuild files are 'Makefile' but 'Kbuild' can
+be used and if both a 'Makefile' and a 'Kbuild' file exists, then the 'Kbuild'
+file will be used.
+
+Section 3.1 "Goal definitions" is a quick intro, further chapters provide
+more details, with real examples.
+
+3.1 Goal definitions
+--------------------
+
+ Goal definitions are the main part (heart) of the kbuild Makefile.
+ These lines define the files to be built, any special compilation
+ options, and any subdirectories to be entered recursively.
+
+ The most simple kbuild makefile contains one line:
+
+ Example::
+
+ obj-y += foo.o
+
+ This tells kbuild that there is one object in that directory, named
+ foo.o. foo.o will be built from foo.c or foo.S.
+
+ If foo.o shall be built as a module, the variable obj-m is used.
+ Therefore the following pattern is often used:
+
+ Example::
+
+ obj-$(CONFIG_FOO) += foo.o
+
+ $(CONFIG_FOO) evaluates to either y (for built-in) or m (for module).
+ If CONFIG_FOO is neither y nor m, then the file will not be compiled
+ nor linked.
+
+3.2 Built-in object goals - obj-y
+---------------------------------
+
+ The kbuild Makefile specifies object files for vmlinux
+ in the $(obj-y) lists. These lists depend on the kernel
+ configuration.
+
+ Kbuild compiles all the $(obj-y) files. It then calls
+ "$(AR) rcSTP" to merge these files into one built-in.a file.
+ This is a thin archive without a symbol table. It will be later
+ linked into vmlinux by scripts/link-vmlinux.sh
+
+ The order of files in $(obj-y) is significant. Duplicates in
+ the lists are allowed: the first instance will be linked into
+ built-in.a and succeeding instances will be ignored.
+
+ Link order is significant, because certain functions
+ (module_init() / __initcall) will be called during boot in the
+ order they appear. So keep in mind that changing the link
+ order may e.g. change the order in which your SCSI
+ controllers are detected, and thus your disks are renumbered.
+
+ Example::
+
+ #drivers/isdn/i4l/Makefile
+ # Makefile for the kernel ISDN subsystem and device drivers.
+ # Each configuration option enables a list of files.
+ obj-$(CONFIG_ISDN_I4L) += isdn.o
+ obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
+
+3.3 Loadable module goals - obj-m
+---------------------------------
+
+ $(obj-m) specifies object files which are built as loadable
+ kernel modules.
+
+ A module may be built from one source file or several source
+ files. In the case of one source file, the kbuild makefile
+ simply adds the file to $(obj-m).
+
+ Example::
+
+ #drivers/isdn/i4l/Makefile
+ obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
+
+ Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm'
+
+ If a kernel module is built from several source files, you specify
+ that you want to build a module in the same way as above; however,
+ kbuild needs to know which object files you want to build your
+ module from, so you have to tell it by setting a $(<module_name>-y)
+ variable.
+
+ Example::
+
+ #drivers/isdn/i4l/Makefile
+ obj-$(CONFIG_ISDN_I4L) += isdn.o
+ isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o
+
+ In this example, the module name will be isdn.o. Kbuild will
+ compile the objects listed in $(isdn-y) and then run
+ "$(LD) -r" on the list of these files to generate isdn.o.
+
+ Due to kbuild recognizing $(<module_name>-y) for composite objects,
+ you can use the value of a `CONFIG_` symbol to optionally include an
+ object file as part of a composite object.
+
+ Example::
+
+ #fs/ext2/Makefile
+ obj-$(CONFIG_EXT2_FS) += ext2.o
+ ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \
+ namei.o super.o symlink.o
+ ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \
+ xattr_trusted.o
+
+ In this example, xattr.o, xattr_user.o and xattr_trusted.o are only
+ part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR)
+ evaluates to 'y'.
+
+ Note: Of course, when you are building objects into the kernel,
+ the syntax above will also work. So, if you have CONFIG_EXT2_FS=y,
+ kbuild will build an ext2.o file for you out of the individual
+ parts and then link this into built-in.a, as you would expect.
+
+3.4 Objects which export symbols
+--------------------------------
+
+ No special notation is required in the makefiles for
+ modules exporting symbols.
+
+3.5 Library file goals - lib-y
+------------------------------
+
+ Objects listed with obj-* are used for modules, or
+ combined in a built-in.a for that specific directory.
+ There is also the possibility to list objects that will
+ be included in a library, lib.a.
+ All objects listed with lib-y are combined in a single
+ library for that directory.
+ Objects that are listed in obj-y and additionally listed in
+ lib-y will not be included in the library, since they will
+ be accessible anyway.
+ For consistency, objects listed in lib-m will be included in lib.a.
+
+ Note that the same kbuild makefile may list files to be built-in
+ and to be part of a library. Therefore the same directory
+ may contain both a built-in.a and a lib.a file.
+
+ Example::
+
+ #arch/x86/lib/Makefile
+ lib-y := delay.o
+
+ This will create a library lib.a based on delay.o. For kbuild to
+ actually recognize that there is a lib.a being built, the directory
+ shall be listed in libs-y.
+
+ See also "6.4 List directories to visit when descending".
+
+ Use of lib-y is normally restricted to `lib/` and `arch/*/lib`.
+
+3.6 Descending down in directories
+----------------------------------
+
+ A Makefile is only responsible for building objects in its own
+ directory. Files in subdirectories should be taken care of by
+ Makefiles in these subdirs. The build system will automatically
+ invoke make recursively in subdirectories, provided you let it know of
+ them.
+
+ To do so, obj-y and obj-m are used.
+ ext2 lives in a separate directory, and the Makefile present in fs/
+ tells kbuild to descend down using the following assignment.
+
+ Example::
+
+ #fs/Makefile
+ obj-$(CONFIG_EXT2_FS) += ext2/
+
+ If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular)
+ the corresponding obj- variable will be set, and kbuild will descend
+ down in the ext2 directory.
+ Kbuild only uses this information to decide that it needs to visit
+ the directory, it is the Makefile in the subdirectory that
+ specifies what is modular and what is built-in.
+
+ It is good practice to use a `CONFIG_` variable when assigning directory
+ names. This allows kbuild to totally skip the directory if the
+ corresponding `CONFIG_` option is neither 'y' nor 'm'.
+
+3.7 Compilation flags
+---------------------
+
+ ccflags-y, asflags-y and ldflags-y
+ These three flags apply only to the kbuild makefile in which they
+ are assigned. They are used for all the normal cc, as and ld
+ invocations happening during a recursive build.
+ Note: Flags with the same behaviour were previously named:
+ EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS.
+ They are still supported but their usage is deprecated.
+
+ ccflags-y specifies options for compiling with $(CC).
+
+ Example::
+
+ # drivers/acpi/acpica/Makefile
+ ccflags-y := -Os -D_LINUX -DBUILDING_ACPICA
+ ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT
+
+ This variable is necessary because the top Makefile owns the
+ variable $(KBUILD_CFLAGS) and uses it for compilation flags for the
+ entire tree.
+
+ asflags-y specifies options for assembling with $(AS).
+
+ Example::
+
+ #arch/sparc/kernel/Makefile
+ asflags-y := -ansi
+
+ ldflags-y specifies options for linking with $(LD).
+
+ Example::
+
+ #arch/cris/boot/compressed/Makefile
+ ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds
+
+ subdir-ccflags-y, subdir-asflags-y
+ The two flags listed above are similar to ccflags-y and asflags-y.
+ The difference is that the subdir- variants have effect for the kbuild
+ file where they are present and all subdirectories.
+ Options specified using subdir-* are added to the commandline before
+ the options specified using the non-subdir variants.
+
+ Example::
+
+ subdir-ccflags-y := -Werror
+
+ CFLAGS_$@, AFLAGS_$@
+ CFLAGS_$@ and AFLAGS_$@ only apply to commands in current
+ kbuild makefile.
+
+ $(CFLAGS_$@) specifies per-file options for $(CC). The $@
+ part has a literal value which specifies the file that it is for.
+
+ Example::
+
+ # drivers/scsi/Makefile
+ CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF
+ CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \
+ -DGDTH_STATISTICS
+
+ These two lines specify compilation flags for aha152x.o and gdth.o.
+
+ $(AFLAGS_$@) is a similar feature for source files in assembly
+ languages.
+
+ Example::
+
+ # arch/arm/kernel/Makefile
+ AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
+ AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312
+ AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt
+
+
+3.9 Dependency tracking
+-----------------------
+
+ Kbuild tracks dependencies on the following:
+ 1) All prerequisite files (both `*.c` and `*.h`)
+ 2) `CONFIG_` options used in all prerequisite files
+ 3) Command-line used to compile target
+
+ Thus, if you change an option to $(CC) all affected files will
+ be re-compiled.
+
+3.10 Special Rules
+------------------
+
+ Special rules are used when the kbuild infrastructure does
+ not provide the required support. A typical example is
+ header files generated during the build process.
+ Another example are the architecture-specific Makefiles which
+ need special rules to prepare boot images etc.
+
+ Special rules are written as normal Make rules.
+ Kbuild is not executing in the directory where the Makefile is
+ located, so all special rules shall provide a relative
+ path to prerequisite files and target files.
+
+ Two variables are used when defining special rules:
+
+ $(src)
+ $(src) is a relative path which points to the directory
+ where the Makefile is located. Always use $(src) when
+ referring to files located in the src tree.
+
+ $(obj)
+ $(obj) is a relative path which points to the directory
+ where the target is saved. Always use $(obj) when
+ referring to generated files.
+
+ Example::
+
+ #drivers/scsi/Makefile
+ $(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl
+ $(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl
+
+ This is a special rule, following the normal syntax
+ required by make.
+
+ The target file depends on two prerequisite files. References
+ to the target file are prefixed with $(obj), references
+ to prerequisites are referenced with $(src) (because they are not
+ generated files).
+
+ $(kecho)
+ echoing information to user in a rule is often a good practice
+ but when execution "make -s" one does not expect to see any output
+ except for warnings/errors.
+ To support this kbuild defines $(kecho) which will echo out the
+ text following $(kecho) to stdout except if "make -s" is used.
+
+ Example::
+
+ #arch/blackfin/boot/Makefile
+ $(obj)/vmImage: $(obj)/vmlinux.gz
+ $(call if_changed,uimage)
+ @$(kecho) 'Kernel: $@ is ready'
+
+
+3.11 $(CC) support functions
+----------------------------
+
+ The kernel may be built with several different versions of
+ $(CC), each supporting a unique set of features and options.
+ kbuild provides basic support to check for valid options for $(CC).
+ $(CC) is usually the gcc compiler, but other alternatives are
+ available.
+
+ as-option
+ as-option is used to check if $(CC) -- when used to compile
+ assembler (`*.S`) files -- supports the given option. An optional
+ second option may be specified if the first option is not supported.
+
+ Example::
+
+ #arch/sh/Makefile
+ cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),)
+
+ In the above example, cflags-y will be assigned the option
+ -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC).
+ The second argument is optional, and if supplied will be used
+ if first argument is not supported.
+
+ cc-ldoption
+ cc-ldoption is used to check if $(CC) when used to link object files
+ supports the given option. An optional second option may be
+ specified if first option are not supported.
+
+ Example::
+
+ #arch/x86/kernel/Makefile
+ vsyscall-flags += $(call cc-ldoption, -Wl$(comma)--hash-style=sysv)
+
+ In the above example, vsyscall-flags will be assigned the option
+ -Wl$(comma)--hash-style=sysv if it is supported by $(CC).
+ The second argument is optional, and if supplied will be used
+ if first argument is not supported.
+
+ as-instr
+ as-instr checks if the assembler reports a specific instruction
+ and then outputs either option1 or option2
+ C escapes are supported in the test instruction
+ Note: as-instr-option uses KBUILD_AFLAGS for $(AS) options
+
+ cc-option
+ cc-option is used to check if $(CC) supports a given option, and if
+ not supported to use an optional second option.
+
+ Example::
+
+ #arch/x86/Makefile
+ cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586)
+
+ In the above example, cflags-y will be assigned the option
+ -march=pentium-mmx if supported by $(CC), otherwise -march=i586.
+ The second argument to cc-option is optional, and if omitted,
+ cflags-y will be assigned no value if first option is not supported.
+ Note: cc-option uses KBUILD_CFLAGS for $(CC) options
+
+ cc-option-yn
+ cc-option-yn is used to check if gcc supports a given option
+ and return 'y' if supported, otherwise 'n'.
+
+ Example::
+
+ #arch/ppc/Makefile
+ biarch := $(call cc-option-yn, -m32)
+ aflags-$(biarch) += -a32
+ cflags-$(biarch) += -m32
+
+ In the above example, $(biarch) is set to y if $(CC) supports the -m32
+ option. When $(biarch) equals 'y', the expanded variables $(aflags-y)
+ and $(cflags-y) will be assigned the values -a32 and -m32,
+ respectively.
+ Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options
+
+ cc-disable-warning
+ cc-disable-warning checks if gcc supports a given warning and returns
+ the commandline switch to disable it. This special function is needed,
+ because gcc 4.4 and later accept any unknown -Wno-* option and only
+ warn about it if there is another warning in the source file.
+
+ Example::
+
+ KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
+
+ In the above example, -Wno-unused-but-set-variable will be added to
+ KBUILD_CFLAGS only if gcc really accepts it.
+
+ cc-ifversion
+ cc-ifversion tests the version of $(CC) and equals the fourth parameter
+ if version expression is true, or the fifth (if given) if the version
+ expression is false.
+
+ Example::
+
+ #fs/reiserfs/Makefile
+ ccflags-y := $(call cc-ifversion, -lt, 0402, -O1)
+
+ In this example, ccflags-y will be assigned the value -O1 if the
+ $(CC) version is less than 4.2.
+ cc-ifversion takes all the shell operators:
+ -eq, -ne, -lt, -le, -gt, and -ge
+ The third parameter may be a text as in this example, but it may also
+ be an expanded variable or a macro.
+
+ cc-cross-prefix
+ cc-cross-prefix is used to check if there exists a $(CC) in path with
+ one of the listed prefixes. The first prefix where there exist a
+ prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found
+ then nothing is returned.
+ Additional prefixes are separated by a single space in the
+ call of cc-cross-prefix.
+ This functionality is useful for architecture Makefiles that try
+ to set CROSS_COMPILE to well-known values but may have several
+ values to select between.
+ It is recommended only to try to set CROSS_COMPILE if it is a cross
+ build (host arch is different from target arch). And if CROSS_COMPILE
+ is already set then leave it with the old value.
+
+ Example::
+
+ #arch/m68k/Makefile
+ ifneq ($(SUBARCH),$(ARCH))
+ ifeq ($(CROSS_COMPILE),)
+ CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-)
+ endif
+ endif
+
+3.12 $(LD) support functions
+----------------------------
+
+ ld-option
+ ld-option is used to check if $(LD) supports the supplied option.
+ ld-option takes two options as arguments.
+ The second argument is an optional option that can be used if the
+ first option is not supported by $(LD).
+
+ Example::
+
+ #Makefile
+ LDFLAGS_vmlinux += $(call ld-option, -X)
+
+
+4 Host Program support
+======================
+
+Kbuild supports building executables on the host for use during the
+compilation stage.
+Two steps are required in order to use a host executable.
+
+The first step is to tell kbuild that a host program exists. This is
+done utilising the variable hostprogs-y.
+
+The second step is to add an explicit dependency to the executable.
+This can be done in two ways. Either add the dependency in a rule,
+or utilise the variable $(always).
+Both possibilities are described in the following.
+
+4.1 Simple Host Program
+-----------------------
+
+ In some cases there is a need to compile and run a program on the
+ computer where the build is running.
+ The following line tells kbuild that the program bin2hex shall be
+ built on the build host.
+
+ Example::
+
+ hostprogs-y := bin2hex
+
+ Kbuild assumes in the above example that bin2hex is made from a single
+ c-source file named bin2hex.c located in the same directory as
+ the Makefile.
+
+4.2 Composite Host Programs
+---------------------------
+
+ Host programs can be made up based on composite objects.
+ The syntax used to define composite objects for host programs is
+ similar to the syntax used for kernel objects.
+ $(<executable>-objs) lists all objects used to link the final
+ executable.
+
+ Example::
+
+ #scripts/lxdialog/Makefile
+ hostprogs-y := lxdialog
+ lxdialog-objs := checklist.o lxdialog.o
+
+ Objects with extension .o are compiled from the corresponding .c
+ files. In the above example, checklist.c is compiled to checklist.o
+ and lxdialog.c is compiled to lxdialog.o.
+
+ Finally, the two .o files are linked to the executable, lxdialog.
+ Note: The syntax <executable>-y is not permitted for host-programs.
+
+4.3 Using C++ for host programs
+-------------------------------
+
+ kbuild offers support for host programs written in C++. This was
+ introduced solely to support kconfig, and is not recommended
+ for general use.
+
+ Example::
+
+ #scripts/kconfig/Makefile
+ hostprogs-y := qconf
+ qconf-cxxobjs := qconf.o
+
+ In the example above the executable is composed of the C++ file
+ qconf.cc - identified by $(qconf-cxxobjs).
+
+ If qconf is composed of a mixture of .c and .cc files, then an
+ additional line can be used to identify this.
+
+ Example::
+
+ #scripts/kconfig/Makefile
+ hostprogs-y := qconf
+ qconf-cxxobjs := qconf.o
+ qconf-objs := check.o
+
+4.4 Controlling compiler options for host programs
+--------------------------------------------------
+
+ When compiling host programs, it is possible to set specific flags.
+ The programs will always be compiled utilising $(HOSTCC) passed
+ the options specified in $(KBUILD_HOSTCFLAGS).
+ To set flags that will take effect for all host programs created
+ in that Makefile, use the variable HOST_EXTRACFLAGS.
+
+ Example::
+
+ #scripts/lxdialog/Makefile
+ HOST_EXTRACFLAGS += -I/usr/include/ncurses
+
+ To set specific flags for a single file the following construction
+ is used:
+
+ Example::
+
+ #arch/ppc64/boot/Makefile
+ HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE)
+
+ It is also possible to specify additional options to the linker.
+
+ Example::
+
+ #scripts/kconfig/Makefile
+ HOSTLDLIBS_qconf := -L$(QTDIR)/lib
+
+ When linking qconf, it will be passed the extra option
+ "-L$(QTDIR)/lib".
+
+4.5 When host programs are actually built
+-----------------------------------------
+
+ Kbuild will only build host-programs when they are referenced
+ as a prerequisite.
+ This is possible in two ways:
+
+ (1) List the prerequisite explicitly in a special rule.
+
+ Example::
+
+ #drivers/pci/Makefile
+ hostprogs-y := gen-devlist
+ $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist
+ ( cd $(obj); ./gen-devlist ) < $<
+
+ The target $(obj)/devlist.h will not be built before
+ $(obj)/gen-devlist is updated. Note that references to
+ the host programs in special rules must be prefixed with $(obj).
+
+ (2) Use $(always)
+
+ When there is no suitable special rule, and the host program
+ shall be built when a makefile is entered, the $(always)
+ variable shall be used.
+
+ Example::
+
+ #scripts/lxdialog/Makefile
+ hostprogs-y := lxdialog
+ always := $(hostprogs-y)
+
+ This will tell kbuild to build lxdialog even if not referenced in
+ any rule.
+
+4.6 Using hostprogs-$(CONFIG_FOO)
+---------------------------------
+
+ A typical pattern in a Kbuild file looks like this:
+
+ Example::
+
+ #scripts/Makefile
+ hostprogs-$(CONFIG_KALLSYMS) += kallsyms
+
+ Kbuild knows about both 'y' for built-in and 'm' for module.
+ So if a config symbol evaluates to 'm', kbuild will still build
+ the binary. In other words, Kbuild handles hostprogs-m exactly
+ like hostprogs-y. But only hostprogs-y is recommended to be used
+ when no CONFIG symbols are involved.
+
+5 Kbuild clean infrastructure
+=============================
+
+"make clean" deletes most generated files in the obj tree where the kernel
+is compiled. This includes generated files such as host programs.
+Kbuild knows targets listed in $(hostprogs-y), $(hostprogs-m), $(always),
+$(extra-y) and $(targets). They are all deleted during "make clean".
+Files matching the patterns "*.[oas]", "*.ko", plus some additional files
+generated by kbuild are deleted all over the kernel src tree when
+"make clean" is executed.
+
+Additional files can be specified in kbuild makefiles by use of $(clean-files).
+
+ Example::
+
+ #lib/Makefile
+ clean-files := crc32table.h
+
+When executing "make clean", the file "crc32table.h" will be deleted.
+Kbuild will assume files to be in the same relative directory as the
+Makefile, except if prefixed with $(objtree).
+
+To delete a directory hierarchy use:
+
+ Example::
+
+ #scripts/package/Makefile
+ clean-dirs := $(objtree)/debian/
+
+This will delete the directory debian in the toplevel directory, including all
+subdirectories.
+
+To exclude certain files from make clean, use the $(no-clean-files) variable.
+This is only a special case used in the top level Kbuild file:
+
+ Example::
+
+ #Kbuild
+ no-clean-files := $(bounds-file) $(offsets-file)
+
+Usually kbuild descends down in subdirectories due to "obj-* := dir/",
+but in the architecture makefiles where the kbuild infrastructure
+is not sufficient this sometimes needs to be explicit.
+
+ Example::
+
+ #arch/x86/boot/Makefile
+ subdir- := compressed/
+
+The above assignment instructs kbuild to descend down in the
+directory compressed/ when "make clean" is executed.
+
+To support the clean infrastructure in the Makefiles that build the
+final bootimage there is an optional target named archclean:
+
+ Example::
+
+ #arch/x86/Makefile
+ archclean:
+ $(Q)$(MAKE) $(clean)=arch/x86/boot
+
+When "make clean" is executed, make will descend down in arch/x86/boot,
+and clean as usual. The Makefile located in arch/x86/boot/ may use
+the subdir- trick to descend further down.
+
+Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is
+included in the top level makefile, and the kbuild infrastructure
+is not operational at that point.
+
+Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will
+be visited during "make clean".
+
+6 Architecture Makefiles
+========================
+
+The top level Makefile sets up the environment and does the preparation,
+before starting to descend down in the individual directories.
+The top level makefile contains the generic part, whereas
+arch/$(ARCH)/Makefile contains what is required to set up kbuild
+for said architecture.
+To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines
+a few targets.
+
+When kbuild executes, the following steps are followed (roughly):
+
+1) Configuration of the kernel => produce .config
+2) Store kernel version in include/linux/version.h
+3) Updating all other prerequisites to the target prepare:
+ - Additional prerequisites are specified in arch/$(ARCH)/Makefile
+4) Recursively descend down in all directories listed in
+ init-* core* drivers-* net-* libs-* and build all targets.
+ - The values of the above variables are expanded in arch/$(ARCH)/Makefile.
+5) All object files are then linked and the resulting file vmlinux is
+ located at the root of the obj tree.
+ The very first objects linked are listed in head-y, assigned by
+ arch/$(ARCH)/Makefile.
+6) Finally, the architecture-specific part does any required post processing
+ and builds the final bootimage.
+ - This includes building boot records
+ - Preparing initrd images and the like
+
+
+6.1 Set variables to tweak the build to the architecture
+--------------------------------------------------------
+
+ LDFLAGS
+ Generic $(LD) options
+
+ Flags used for all invocations of the linker.
+ Often specifying the emulation is sufficient.
+
+ Example::
+
+ #arch/s390/Makefile
+ LDFLAGS := -m elf_s390
+
+ Note: ldflags-y can be used to further customise
+ the flags used. See chapter 3.7.
+
+ LDFLAGS_vmlinux
+ Options for $(LD) when linking vmlinux
+
+ LDFLAGS_vmlinux is used to specify additional flags to pass to
+ the linker when linking the final vmlinux image.
+ LDFLAGS_vmlinux uses the LDFLAGS_$@ support.
+
+ Example::
+
+ #arch/x86/Makefile
+ LDFLAGS_vmlinux := -e stext
+
+ OBJCOPYFLAGS
+ objcopy flags
+
+ When $(call if_changed,objcopy) is used to translate a .o file,
+ the flags specified in OBJCOPYFLAGS will be used.
+ $(call if_changed,objcopy) is often used to generate raw binaries on
+ vmlinux.
+
+ Example::
+
+ #arch/s390/Makefile
+ OBJCOPYFLAGS := -O binary
+
+ #arch/s390/boot/Makefile
+ $(obj)/image: vmlinux FORCE
+ $(call if_changed,objcopy)
+
+ In this example, the binary $(obj)/image is a binary version of
+ vmlinux. The usage of $(call if_changed,xxx) will be described later.
+
+ KBUILD_AFLAGS
+ $(AS) assembler flags
+
+ Default value - see top level Makefile
+ Append or modify as required per architecture.
+
+ Example::
+
+ #arch/sparc64/Makefile
+ KBUILD_AFLAGS += -m64 -mcpu=ultrasparc
+
+ KBUILD_CFLAGS
+ $(CC) compiler flags
+
+ Default value - see top level Makefile
+ Append or modify as required per architecture.
+
+ Often, the KBUILD_CFLAGS variable depends on the configuration.
+
+ Example::
+
+ #arch/x86/boot/compressed/Makefile
+ cflags-$(CONFIG_X86_32) := -march=i386
+ cflags-$(CONFIG_X86_64) := -mcmodel=small
+ KBUILD_CFLAGS += $(cflags-y)
+
+ Many arch Makefiles dynamically run the target C compiler to
+ probe supported options::
+
+ #arch/x86/Makefile
+
+ ...
+ cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\
+ -march=pentium2,-march=i686)
+ ...
+ # Disable unit-at-a-time mode ...
+ KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time)
+ ...
+
+
+ The first example utilises the trick that a config option expands
+ to 'y' when selected.
+
+ KBUILD_AFLAGS_KERNEL
+ $(AS) options specific for built-in
+
+ $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile
+ resident kernel code.
+
+ KBUILD_AFLAGS_MODULE
+ Options for $(AS) when building modules
+
+ $(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that
+ are used for $(AS).
+
+ From commandline AFLAGS_MODULE shall be used (see kbuild.txt).
+
+ KBUILD_CFLAGS_KERNEL
+ $(CC) options specific for built-in
+
+ $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile
+ resident kernel code.
+
+ KBUILD_CFLAGS_MODULE
+ Options for $(CC) when building modules
+
+ $(KBUILD_CFLAGS_MODULE) is used to add arch-specific options that
+ are used for $(CC).
+ From commandline CFLAGS_MODULE shall be used (see kbuild.txt).
+
+ KBUILD_LDFLAGS_MODULE
+ Options for $(LD) when linking modules
+
+ $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options
+ used when linking modules. This is often a linker script.
+
+ From commandline LDFLAGS_MODULE shall be used (see kbuild.txt).
+
+ KBUILD_ARFLAGS Options for $(AR) when creating archives
+
+ $(KBUILD_ARFLAGS) set by the top level Makefile to "D" (deterministic
+ mode) if this option is supported by $(AR).
+
+ ARCH_CPPFLAGS, ARCH_AFLAGS, ARCH_CFLAGS Overrides the kbuild defaults
+
+ These variables are appended to the KBUILD_CPPFLAGS,
+ KBUILD_AFLAGS, and KBUILD_CFLAGS, respectively, after the
+ top-level Makefile has set any other flags. This provides a
+ means for an architecture to override the defaults.
+
+
+6.2 Add prerequisites to archheaders
+------------------------------------
+
+ The archheaders: rule is used to generate header files that
+ may be installed into user space by "make header_install" or
+ "make headers_install_all". In order to support
+ "make headers_install_all", this target has to be able to run
+ on an unconfigured tree, or a tree configured for another
+ architecture.
+
+ It is run before "make archprepare" when run on the
+ architecture itself.
+
+
+6.3 Add prerequisites to archprepare
+------------------------------------
+
+ The archprepare: rule is used to list prerequisites that need to be
+ built before starting to descend down in the subdirectories.
+ This is usually used for header files containing assembler constants.
+
+ Example::
+
+ #arch/arm/Makefile
+ archprepare: maketools
+
+ In this example, the file target maketools will be processed
+ before descending down in the subdirectories.
+ See also chapter XXX-TODO that describe how kbuild supports
+ generating offset header files.
+
+
+6.4 List directories to visit when descending
+---------------------------------------------
+
+ An arch Makefile cooperates with the top Makefile to define variables
+ which specify how to build the vmlinux file. Note that there is no
+ corresponding arch-specific section for modules; the module-building
+ machinery is all architecture-independent.
+
+
+ head-y, init-y, core-y, libs-y, drivers-y, net-y
+ $(head-y) lists objects to be linked first in vmlinux.
+
+ $(libs-y) lists directories where a lib.a archive can be located.
+
+ The rest list directories where a built-in.a object file can be
+ located.
+
+ $(init-y) objects will be located after $(head-y).
+
+ Then the rest follows in this order:
+
+ $(core-y), $(libs-y), $(drivers-y) and $(net-y).
+
+ The top level Makefile defines values for all generic directories,
+ and arch/$(ARCH)/Makefile only adds architecture-specific
+ directories.
+
+ Example::
+
+ #arch/sparc64/Makefile
+ core-y += arch/sparc64/kernel/
+ libs-y += arch/sparc64/prom/ arch/sparc64/lib/
+ drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/
+
+
+6.5 Architecture-specific boot images
+-------------------------------------
+
+ An arch Makefile specifies goals that take the vmlinux file, compress
+ it, wrap it in bootstrapping code, and copy the resulting files
+ somewhere. This includes various kinds of installation commands.
+ The actual goals are not standardized across architectures.
+
+ It is common to locate any additional processing in a boot/
+ directory below arch/$(ARCH)/.
+
+ Kbuild does not provide any smart way to support building a
+ target specified in boot/. Therefore arch/$(ARCH)/Makefile shall
+ call make manually to build a target in boot/.
+
+ The recommended approach is to include shortcuts in
+ arch/$(ARCH)/Makefile, and use the full path when calling down
+ into the arch/$(ARCH)/boot/Makefile.
+
+ Example::
+
+ #arch/x86/Makefile
+ boot := arch/x86/boot
+ bzImage: vmlinux
+ $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
+
+ "$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke
+ make in a subdirectory.
+
+ There are no rules for naming architecture-specific targets,
+ but executing "make help" will list all relevant targets.
+ To support this, $(archhelp) must be defined.
+
+ Example::
+
+ #arch/x86/Makefile
+ define archhelp
+ echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)'
+ endif
+
+ When make is executed without arguments, the first goal encountered
+ will be built. In the top level Makefile the first goal present
+ is all:.
+ An architecture shall always, per default, build a bootable image.
+ In "make help", the default goal is highlighted with a '*'.
+ Add a new prerequisite to all: to select a default goal different
+ from vmlinux.
+
+ Example::
+
+ #arch/x86/Makefile
+ all: bzImage
+
+ When "make" is executed without arguments, bzImage will be built.
+
+6.6 Building non-kbuild targets
+-------------------------------
+
+ extra-y
+ extra-y specifies additional targets created in the current
+ directory, in addition to any targets specified by `obj-*`.
+
+ Listing all targets in extra-y is required for two purposes:
+
+ 1) Enable kbuild to check changes in command lines
+
+ - When $(call if_changed,xxx) is used
+
+ 2) kbuild knows what files to delete during "make clean"
+
+ Example::
+
+ #arch/x86/kernel/Makefile
+ extra-y := head.o init_task.o
+
+ In this example, extra-y is used to list object files that
+ shall be built, but shall not be linked as part of built-in.a.
+
+
+6.7 Commands useful for building a boot image
+---------------------------------------------
+
+ Kbuild provides a few macros that are useful when building a
+ boot image.
+
+ if_changed
+ if_changed is the infrastructure used for the following commands.
+
+ Usage::
+
+ target: source(s) FORCE
+ $(call if_changed,ld/objcopy/gzip/...)
+
+ When the rule is evaluated, it is checked to see if any files
+ need an update, or the command line has changed since the last
+ invocation. The latter will force a rebuild if any options
+ to the executable have changed.
+ Any target that utilises if_changed must be listed in $(targets),
+ otherwise the command line check will fail, and the target will
+ always be built.
+ Assignments to $(targets) are without $(obj)/ prefix.
+ if_changed may be used in conjunction with custom commands as
+ defined in 6.8 "Custom kbuild commands".
+
+ Note: It is a typical mistake to forget the FORCE prerequisite.
+ Another common pitfall is that whitespace is sometimes
+ significant; for instance, the below will fail (note the extra space
+ after the comma)::
+
+ target: source(s) FORCE
+
+ **WRONG!** $(call if_changed, ld/objcopy/gzip/...)
+
+ Note:
+ if_changed should not be used more than once per target.
+ It stores the executed command in a corresponding .cmd
+
+ file and multiple calls would result in overwrites and
+ unwanted results when the target is up to date and only the
+ tests on changed commands trigger execution of commands.
+
+ ld
+ Link target. Often, LDFLAGS_$@ is used to set specific options to ld.
+
+ Example::
+
+ #arch/x86/boot/Makefile
+ LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary
+ LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext
+
+ targets += setup setup.o bootsect bootsect.o
+ $(obj)/setup $(obj)/bootsect: %: %.o FORCE
+ $(call if_changed,ld)
+
+ In this example, there are two possible targets, requiring different
+ options to the linker. The linker options are specified using the
+ LDFLAGS_$@ syntax - one for each potential target.
+ $(targets) are assigned all potential targets, by which kbuild knows
+ the targets and will:
+
+ 1) check for commandline changes
+ 2) delete target during make clean
+
+ The ": %: %.o" part of the prerequisite is a shorthand that
+ frees us from listing the setup.o and bootsect.o files.
+
+ Note:
+ It is a common mistake to forget the "targets :=" assignment,
+ resulting in the target file being recompiled for no
+ obvious reason.
+
+ objcopy
+ Copy binary. Uses OBJCOPYFLAGS usually specified in
+ arch/$(ARCH)/Makefile.
+ OBJCOPYFLAGS_$@ may be used to set additional options.
+
+ gzip
+ Compress target. Use maximum compression to compress target.
+
+ Example::
+
+ #arch/x86/boot/compressed/Makefile
+ $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE
+ $(call if_changed,gzip)
+
+ dtc
+ Create flattened device tree blob object suitable for linking
+ into vmlinux. Device tree blobs linked into vmlinux are placed
+ in an init section in the image. Platform code *must* copy the
+ blob to non-init memory prior to calling unflatten_device_tree().
+
+ To use this command, simply add `*.dtb` into obj-y or targets, or make
+ some other target depend on `%.dtb`
+
+ A central rule exists to create `$(obj)/%.dtb` from `$(src)/%.dts`;
+ architecture Makefiles do no need to explicitly write out that rule.
+
+ Example::
+
+ targets += $(dtb-y)
+ DTC_FLAGS ?= -p 1024
+
+6.8 Custom kbuild commands
+--------------------------
+
+ When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand
+ of a command is normally displayed.
+ To enable this behaviour for custom commands kbuild requires
+ two variables to be set::
+
+ quiet_cmd_<command> - what shall be echoed
+ cmd_<command> - the command to execute
+
+ Example::
+
+ #
+ quiet_cmd_image = BUILD $@
+ cmd_image = $(obj)/tools/build $(BUILDFLAGS) \
+ $(obj)/vmlinux.bin > $@
+
+ targets += bzImage
+ $(obj)/bzImage: $(obj)/vmlinux.bin $(obj)/tools/build FORCE
+ $(call if_changed,image)
+ @echo 'Kernel: $@ is ready'
+
+ When updating the $(obj)/bzImage target, the line:
+
+ BUILD arch/x86/boot/bzImage
+
+ will be displayed with "make KBUILD_VERBOSE=0".
+
+
+--- 6.9 Preprocessing linker scripts
+
+ When the vmlinux image is built, the linker script
+ arch/$(ARCH)/kernel/vmlinux.lds is used.
+ The script is a preprocessed variant of the file vmlinux.lds.S
+ located in the same directory.
+ kbuild knows .lds files and includes a rule `*lds.S` -> `*lds`.
+
+ Example::
+
+ #arch/x86/kernel/Makefile
+ always := vmlinux.lds
+
+ #Makefile
+ export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)
+
+ The assignment to $(always) is used to tell kbuild to build the
+ target vmlinux.lds.
+ The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the
+ specified options when building the target vmlinux.lds.
+
+ When building the `*.lds` target, kbuild uses the variables::
+
+ KBUILD_CPPFLAGS : Set in top-level Makefile
+ cppflags-y : May be set in the kbuild makefile
+ CPPFLAGS_$(@F) : Target-specific flags.
+ Note that the full filename is used in this
+ assignment.
+
+ The kbuild infrastructure for `*lds` files is used in several
+ architecture-specific files.
+
+6.10 Generic header files
+-------------------------
+
+ The directory include/asm-generic contains the header files
+ that may be shared between individual architectures.
+ The recommended approach how to use a generic header file is
+ to list the file in the Kbuild file.
+ See "7.2 generic-y" for further info on syntax etc.
+
+6.11 Post-link pass
+-------------------
+
+ If the file arch/xxx/Makefile.postlink exists, this makefile
+ will be invoked for post-link objects (vmlinux and modules.ko)
+ for architectures to run post-link passes on. Must also handle
+ the clean target.
+
+ This pass runs after kallsyms generation. If the architecture
+ needs to modify symbol locations, rather than manipulate the
+ kallsyms, it may be easier to add another postlink target for
+ .tmp_vmlinux? targets to be called from link-vmlinux.sh.
+
+ For example, powerpc uses this to check relocation sanity of
+ the linked vmlinux file.
+
+7 Kbuild syntax for exported headers
+------------------------------------
+
+The kernel includes a set of headers that is exported to userspace.
+Many headers can be exported as-is but other headers require a
+minimal pre-processing before they are ready for user-space.
+The pre-processing does:
+
+- drop kernel-specific annotations
+- drop include of compiler.h
+- drop all sections that are kernel internal (guarded by `ifdef __KERNEL__`)
+
+All headers under include/uapi/, include/generated/uapi/,
+arch/<arch>/include/uapi/ and arch/<arch>/include/generated/uapi/
+are exported.
+
+A Kbuild file may be defined under arch/<arch>/include/uapi/asm/ and
+arch/<arch>/include/asm/ to list asm files coming from asm-generic.
+See subsequent chapter for the syntax of the Kbuild file.
+
+7.1 no-export-headers
+---------------------
+
+ no-export-headers is essentially used by include/uapi/linux/Kbuild to
+ avoid exporting specific headers (e.g. kvm.h) on architectures that do
+ not support it. It should be avoided as much as possible.
+
+7.2 generic-y
+-------------
+
+ If an architecture uses a verbatim copy of a header from
+ include/asm-generic then this is listed in the file
+ arch/$(ARCH)/include/asm/Kbuild like this:
+
+ Example::
+
+ #arch/x86/include/asm/Kbuild
+ generic-y += termios.h
+ generic-y += rtc.h
+
+ During the prepare phase of the build a wrapper include
+ file is generated in the directory::
+
+ arch/$(ARCH)/include/generated/asm
+
+ When a header is exported where the architecture uses
+ the generic header a similar wrapper is generated as part
+ of the set of exported headers in the directory::
+
+ usr/include/asm
+
+ The generated wrapper will in both cases look like the following:
+
+ Example: termios.h::
+
+ #include <asm-generic/termios.h>
+
+7.3 generated-y
+---------------
+
+ If an architecture generates other header files alongside generic-y
+ wrappers, generated-y specifies them.
+
+ This prevents them being treated as stale asm-generic wrappers and
+ removed.
+
+ Example::
+
+ #arch/x86/include/asm/Kbuild
+ generated-y += syscalls_32.h
+
+7.4 mandatory-y
+---------------
+
+ mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild
+ to define the minimum set of ASM headers that all architectures must have.
+
+ This works like optional generic-y. If a mandatory header is missing
+ in arch/$(ARCH)/include/(uapi/)/asm, Kbuild will automatically generate
+ a wrapper of the asm-generic one.
+
+ The convention is to list one subdir per line and
+ preferably in alphabetic order.
+
+8 Kbuild Variables
+==================
+
+The top Makefile exports the following variables:
+
+ VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION
+ These variables define the current kernel version. A few arch
+ Makefiles actually use these values directly; they should use
+ $(KERNELRELEASE) instead.
+
+ $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic
+ three-part version number, such as "2", "4", and "0". These three
+ values are always numeric.
+
+ $(EXTRAVERSION) defines an even tinier sublevel for pre-patches
+ or additional patches. It is usually some non-numeric string
+ such as "-pre4", and is often blank.
+
+ KERNELRELEASE
+ $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable
+ for constructing installation directory names or showing in
+ version strings. Some arch Makefiles use it for this purpose.
+
+ ARCH
+ This variable defines the target architecture, such as "i386",
+ "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to
+ determine which files to compile.
+
+ By default, the top Makefile sets $(ARCH) to be the same as the
+ host system architecture. For a cross build, a user may
+ override the value of $(ARCH) on the command line::
+
+ make ARCH=m68k ...
+
+
+ INSTALL_PATH
+ This variable defines a place for the arch Makefiles to install
+ the resident kernel image and System.map file.
+ Use this for architecture-specific install targets.
+
+ INSTALL_MOD_PATH, MODLIB
+ $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module
+ installation. This variable is not defined in the Makefile but
+ may be passed in by the user if desired.
+
+ $(MODLIB) specifies the directory for module installation.
+ The top Makefile defines $(MODLIB) to
+ $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may
+ override this value on the command line if desired.
+
+ INSTALL_MOD_STRIP
+ If this variable is specified, it will cause modules to be stripped
+ after they are installed. If INSTALL_MOD_STRIP is '1', then the
+ default option --strip-debug will be used. Otherwise, the
+ INSTALL_MOD_STRIP value will be used as the option(s) to the strip
+ command.
+
+
+9 Makefile language
+===================
+
+The kernel Makefiles are designed to be run with GNU Make. The Makefiles
+use only the documented features of GNU Make, but they do use many
+GNU extensions.
+
+GNU Make supports elementary list-processing functions. The kernel
+Makefiles use a novel style of list building and manipulation with few
+"if" statements.
+
+GNU Make has two assignment operators, ":=" and "=". ":=" performs
+immediate evaluation of the right-hand side and stores an actual string
+into the left-hand side. "=" is like a formula definition; it stores the
+right-hand side in an unevaluated form and then evaluates this form each
+time the left-hand side is used.
+
+There are some cases where "=" is appropriate. Usually, though, ":="
+is the right choice.
+
+10 Credits
+==========
+
+- Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net>
+- Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>
+- Updates by Sam Ravnborg <sam@ravnborg.org>
+- Language QA by Jan Engelhardt <jengelh@gmx.de>
+
+11 TODO
+=======
+
+- Describe how kbuild supports shipped files with _shipped.
+- Generating offset header files.
+- Add more variables to section 7?
+++ /dev/null
-Linux Kernel Makefiles
-
-This document describes the Linux kernel Makefiles.
-
-=== Table of Contents
-
- === 1 Overview
- === 2 Who does what
- === 3 The kbuild files
- --- 3.1 Goal definitions
- --- 3.2 Built-in object goals - obj-y
- --- 3.3 Loadable module goals - obj-m
- --- 3.4 Objects which export symbols
- --- 3.5 Library file goals - lib-y
- --- 3.6 Descending down in directories
- --- 3.7 Compilation flags
- --- 3.8 Command line dependency
- --- 3.9 Dependency tracking
- --- 3.10 Special Rules
- --- 3.11 $(CC) support functions
- --- 3.12 $(LD) support functions
-
- === 4 Host Program support
- --- 4.1 Simple Host Program
- --- 4.2 Composite Host Programs
- --- 4.3 Using C++ for host programs
- --- 4.4 Controlling compiler options for host programs
- --- 4.5 When host programs are actually built
- --- 4.6 Using hostprogs-$(CONFIG_FOO)
-
- === 5 Kbuild clean infrastructure
-
- === 6 Architecture Makefiles
- --- 6.1 Set variables to tweak the build to the architecture
- --- 6.2 Add prerequisites to archheaders:
- --- 6.3 Add prerequisites to archprepare:
- --- 6.4 List directories to visit when descending
- --- 6.5 Architecture-specific boot images
- --- 6.6 Building non-kbuild targets
- --- 6.7 Commands useful for building a boot image
- --- 6.8 Custom kbuild commands
- --- 6.9 Preprocessing linker scripts
- --- 6.10 Generic header files
- --- 6.11 Post-link pass
-
- === 7 Kbuild syntax for exported headers
- --- 7.1 no-export-headers
- --- 7.2 generic-y
- --- 7.3 generated-y
- --- 7.4 mandatory-y
-
- === 8 Kbuild Variables
- === 9 Makefile language
- === 10 Credits
- === 11 TODO
-
-=== 1 Overview
-
-The Makefiles have five parts:
-
- Makefile the top Makefile.
- .config the kernel configuration file.
- arch/$(ARCH)/Makefile the arch Makefile.
- scripts/Makefile.* common rules etc. for all kbuild Makefiles.
- kbuild Makefiles there are about 500 of these.
-
-The top Makefile reads the .config file, which comes from the kernel
-configuration process.
-
-The top Makefile is responsible for building two major products: vmlinux
-(the resident kernel image) and modules (any module files).
-It builds these goals by recursively descending into the subdirectories of
-the kernel source tree.
-The list of subdirectories which are visited depends upon the kernel
-configuration. The top Makefile textually includes an arch Makefile
-with the name arch/$(ARCH)/Makefile. The arch Makefile supplies
-architecture-specific information to the top Makefile.
-
-Each subdirectory has a kbuild Makefile which carries out the commands
-passed down from above. The kbuild Makefile uses information from the
-.config file to construct various file lists used by kbuild to build
-any built-in or modular targets.
-
-scripts/Makefile.* contains all the definitions/rules etc. that
-are used to build the kernel based on the kbuild makefiles.
-
-
-=== 2 Who does what
-
-People have four different relationships with the kernel Makefiles.
-
-*Users* are people who build kernels. These people type commands such as
-"make menuconfig" or "make". They usually do not read or edit
-any kernel Makefiles (or any other source files).
-
-*Normal developers* are people who work on features such as device
-drivers, file systems, and network protocols. These people need to
-maintain the kbuild Makefiles for the subsystem they are
-working on. In order to do this effectively, they need some overall
-knowledge about the kernel Makefiles, plus detailed knowledge about the
-public interface for kbuild.
-
-*Arch developers* are people who work on an entire architecture, such
-as sparc or ia64. Arch developers need to know about the arch Makefile
-as well as kbuild Makefiles.
-
-*Kbuild developers* are people who work on the kernel build system itself.
-These people need to know about all aspects of the kernel Makefiles.
-
-This document is aimed towards normal developers and arch developers.
-
-
-=== 3 The kbuild files
-
-Most Makefiles within the kernel are kbuild Makefiles that use the
-kbuild infrastructure. This chapter introduces the syntax used in the
-kbuild makefiles.
-The preferred name for the kbuild files are 'Makefile' but 'Kbuild' can
-be used and if both a 'Makefile' and a 'Kbuild' file exists, then the 'Kbuild'
-file will be used.
-
-Section 3.1 "Goal definitions" is a quick intro, further chapters provide
-more details, with real examples.
-
---- 3.1 Goal definitions
-
- Goal definitions are the main part (heart) of the kbuild Makefile.
- These lines define the files to be built, any special compilation
- options, and any subdirectories to be entered recursively.
-
- The most simple kbuild makefile contains one line:
-
- Example:
- obj-y += foo.o
-
- This tells kbuild that there is one object in that directory, named
- foo.o. foo.o will be built from foo.c or foo.S.
-
- If foo.o shall be built as a module, the variable obj-m is used.
- Therefore the following pattern is often used:
-
- Example:
- obj-$(CONFIG_FOO) += foo.o
-
- $(CONFIG_FOO) evaluates to either y (for built-in) or m (for module).
- If CONFIG_FOO is neither y nor m, then the file will not be compiled
- nor linked.
-
---- 3.2 Built-in object goals - obj-y
-
- The kbuild Makefile specifies object files for vmlinux
- in the $(obj-y) lists. These lists depend on the kernel
- configuration.
-
- Kbuild compiles all the $(obj-y) files. It then calls
- "$(AR) rcSTP" to merge these files into one built-in.a file.
- This is a thin archive without a symbol table. It will be later
- linked into vmlinux by scripts/link-vmlinux.sh
-
- The order of files in $(obj-y) is significant. Duplicates in
- the lists are allowed: the first instance will be linked into
- built-in.a and succeeding instances will be ignored.
-
- Link order is significant, because certain functions
- (module_init() / __initcall) will be called during boot in the
- order they appear. So keep in mind that changing the link
- order may e.g. change the order in which your SCSI
- controllers are detected, and thus your disks are renumbered.
-
- Example:
- #drivers/isdn/i4l/Makefile
- # Makefile for the kernel ISDN subsystem and device drivers.
- # Each configuration option enables a list of files.
- obj-$(CONFIG_ISDN_I4L) += isdn.o
- obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
-
---- 3.3 Loadable module goals - obj-m
-
- $(obj-m) specifies object files which are built as loadable
- kernel modules.
-
- A module may be built from one source file or several source
- files. In the case of one source file, the kbuild makefile
- simply adds the file to $(obj-m).
-
- Example:
- #drivers/isdn/i4l/Makefile
- obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
-
- Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm'
-
- If a kernel module is built from several source files, you specify
- that you want to build a module in the same way as above; however,
- kbuild needs to know which object files you want to build your
- module from, so you have to tell it by setting a $(<module_name>-y)
- variable.
-
- Example:
- #drivers/isdn/i4l/Makefile
- obj-$(CONFIG_ISDN_I4L) += isdn.o
- isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o
-
- In this example, the module name will be isdn.o. Kbuild will
- compile the objects listed in $(isdn-y) and then run
- "$(LD) -r" on the list of these files to generate isdn.o.
-
- Due to kbuild recognizing $(<module_name>-y) for composite objects,
- you can use the value of a CONFIG_ symbol to optionally include an
- object file as part of a composite object.
-
- Example:
- #fs/ext2/Makefile
- obj-$(CONFIG_EXT2_FS) += ext2.o
- ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \
- namei.o super.o symlink.o
- ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \
- xattr_trusted.o
-
- In this example, xattr.o, xattr_user.o and xattr_trusted.o are only
- part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR)
- evaluates to 'y'.
-
- Note: Of course, when you are building objects into the kernel,
- the syntax above will also work. So, if you have CONFIG_EXT2_FS=y,
- kbuild will build an ext2.o file for you out of the individual
- parts and then link this into built-in.a, as you would expect.
-
---- 3.4 Objects which export symbols
-
- No special notation is required in the makefiles for
- modules exporting symbols.
-
---- 3.5 Library file goals - lib-y
-
- Objects listed with obj-* are used for modules, or
- combined in a built-in.a for that specific directory.
- There is also the possibility to list objects that will
- be included in a library, lib.a.
- All objects listed with lib-y are combined in a single
- library for that directory.
- Objects that are listed in obj-y and additionally listed in
- lib-y will not be included in the library, since they will
- be accessible anyway.
- For consistency, objects listed in lib-m will be included in lib.a.
-
- Note that the same kbuild makefile may list files to be built-in
- and to be part of a library. Therefore the same directory
- may contain both a built-in.a and a lib.a file.
-
- Example:
- #arch/x86/lib/Makefile
- lib-y := delay.o
-
- This will create a library lib.a based on delay.o. For kbuild to
- actually recognize that there is a lib.a being built, the directory
- shall be listed in libs-y.
- See also "6.4 List directories to visit when descending".
-
- Use of lib-y is normally restricted to lib/ and arch/*/lib.
-
---- 3.6 Descending down in directories
-
- A Makefile is only responsible for building objects in its own
- directory. Files in subdirectories should be taken care of by
- Makefiles in these subdirs. The build system will automatically
- invoke make recursively in subdirectories, provided you let it know of
- them.
-
- To do so, obj-y and obj-m are used.
- ext2 lives in a separate directory, and the Makefile present in fs/
- tells kbuild to descend down using the following assignment.
-
- Example:
- #fs/Makefile
- obj-$(CONFIG_EXT2_FS) += ext2/
-
- If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular)
- the corresponding obj- variable will be set, and kbuild will descend
- down in the ext2 directory.
- Kbuild only uses this information to decide that it needs to visit
- the directory, it is the Makefile in the subdirectory that
- specifies what is modular and what is built-in.
-
- It is good practice to use a CONFIG_ variable when assigning directory
- names. This allows kbuild to totally skip the directory if the
- corresponding CONFIG_ option is neither 'y' nor 'm'.
-
---- 3.7 Compilation flags
-
- ccflags-y, asflags-y and ldflags-y
- These three flags apply only to the kbuild makefile in which they
- are assigned. They are used for all the normal cc, as and ld
- invocations happening during a recursive build.
- Note: Flags with the same behaviour were previously named:
- EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS.
- They are still supported but their usage is deprecated.
-
- ccflags-y specifies options for compiling with $(CC).
-
- Example:
- # drivers/acpi/acpica/Makefile
- ccflags-y := -Os -D_LINUX -DBUILDING_ACPICA
- ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT
-
- This variable is necessary because the top Makefile owns the
- variable $(KBUILD_CFLAGS) and uses it for compilation flags for the
- entire tree.
-
- asflags-y specifies options for assembling with $(AS).
-
- Example:
- #arch/sparc/kernel/Makefile
- asflags-y := -ansi
-
- ldflags-y specifies options for linking with $(LD).
-
- Example:
- #arch/cris/boot/compressed/Makefile
- ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds
-
- subdir-ccflags-y, subdir-asflags-y
- The two flags listed above are similar to ccflags-y and asflags-y.
- The difference is that the subdir- variants have effect for the kbuild
- file where they are present and all subdirectories.
- Options specified using subdir-* are added to the commandline before
- the options specified using the non-subdir variants.
-
- Example:
- subdir-ccflags-y := -Werror
-
- CFLAGS_$@, AFLAGS_$@
-
- CFLAGS_$@ and AFLAGS_$@ only apply to commands in current
- kbuild makefile.
-
- $(CFLAGS_$@) specifies per-file options for $(CC). The $@
- part has a literal value which specifies the file that it is for.
-
- Example:
- # drivers/scsi/Makefile
- CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF
- CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \
- -DGDTH_STATISTICS
-
- These two lines specify compilation flags for aha152x.o and gdth.o.
-
- $(AFLAGS_$@) is a similar feature for source files in assembly
- languages.
-
- Example:
- # arch/arm/kernel/Makefile
- AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
- AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312
- AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt
-
-
---- 3.9 Dependency tracking
-
- Kbuild tracks dependencies on the following:
- 1) All prerequisite files (both *.c and *.h)
- 2) CONFIG_ options used in all prerequisite files
- 3) Command-line used to compile target
-
- Thus, if you change an option to $(CC) all affected files will
- be re-compiled.
-
---- 3.10 Special Rules
-
- Special rules are used when the kbuild infrastructure does
- not provide the required support. A typical example is
- header files generated during the build process.
- Another example are the architecture-specific Makefiles which
- need special rules to prepare boot images etc.
-
- Special rules are written as normal Make rules.
- Kbuild is not executing in the directory where the Makefile is
- located, so all special rules shall provide a relative
- path to prerequisite files and target files.
-
- Two variables are used when defining special rules:
-
- $(src)
- $(src) is a relative path which points to the directory
- where the Makefile is located. Always use $(src) when
- referring to files located in the src tree.
-
- $(obj)
- $(obj) is a relative path which points to the directory
- where the target is saved. Always use $(obj) when
- referring to generated files.
-
- Example:
- #drivers/scsi/Makefile
- $(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl
- $(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl
-
- This is a special rule, following the normal syntax
- required by make.
- The target file depends on two prerequisite files. References
- to the target file are prefixed with $(obj), references
- to prerequisites are referenced with $(src) (because they are not
- generated files).
-
- $(kecho)
- echoing information to user in a rule is often a good practice
- but when execution "make -s" one does not expect to see any output
- except for warnings/errors.
- To support this kbuild defines $(kecho) which will echo out the
- text following $(kecho) to stdout except if "make -s" is used.
-
- Example:
- #arch/blackfin/boot/Makefile
- $(obj)/vmImage: $(obj)/vmlinux.gz
- $(call if_changed,uimage)
- @$(kecho) 'Kernel: $@ is ready'
-
-
---- 3.11 $(CC) support functions
-
- The kernel may be built with several different versions of
- $(CC), each supporting a unique set of features and options.
- kbuild provides basic support to check for valid options for $(CC).
- $(CC) is usually the gcc compiler, but other alternatives are
- available.
-
- as-option
- as-option is used to check if $(CC) -- when used to compile
- assembler (*.S) files -- supports the given option. An optional
- second option may be specified if the first option is not supported.
-
- Example:
- #arch/sh/Makefile
- cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),)
-
- In the above example, cflags-y will be assigned the option
- -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC).
- The second argument is optional, and if supplied will be used
- if first argument is not supported.
-
- as-instr
- as-instr checks if the assembler reports a specific instruction
- and then outputs either option1 or option2
- C escapes are supported in the test instruction
- Note: as-instr-option uses KBUILD_AFLAGS for $(AS) options
-
- cc-option
- cc-option is used to check if $(CC) supports a given option, and if
- not supported to use an optional second option.
-
- Example:
- #arch/x86/Makefile
- cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586)
-
- In the above example, cflags-y will be assigned the option
- -march=pentium-mmx if supported by $(CC), otherwise -march=i586.
- The second argument to cc-option is optional, and if omitted,
- cflags-y will be assigned no value if first option is not supported.
- Note: cc-option uses KBUILD_CFLAGS for $(CC) options
-
- cc-option-yn
- cc-option-yn is used to check if gcc supports a given option
- and return 'y' if supported, otherwise 'n'.
-
- Example:
- #arch/ppc/Makefile
- biarch := $(call cc-option-yn, -m32)
- aflags-$(biarch) += -a32
- cflags-$(biarch) += -m32
-
- In the above example, $(biarch) is set to y if $(CC) supports the -m32
- option. When $(biarch) equals 'y', the expanded variables $(aflags-y)
- and $(cflags-y) will be assigned the values -a32 and -m32,
- respectively.
- Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options
-
- cc-disable-warning
- cc-disable-warning checks if gcc supports a given warning and returns
- the commandline switch to disable it. This special function is needed,
- because gcc 4.4 and later accept any unknown -Wno-* option and only
- warn about it if there is another warning in the source file.
-
- Example:
- KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
-
- In the above example, -Wno-unused-but-set-variable will be added to
- KBUILD_CFLAGS only if gcc really accepts it.
-
- cc-ifversion
- cc-ifversion tests the version of $(CC) and equals the fourth parameter
- if version expression is true, or the fifth (if given) if the version
- expression is false.
-
- Example:
- #fs/reiserfs/Makefile
- ccflags-y := $(call cc-ifversion, -lt, 0402, -O1)
-
- In this example, ccflags-y will be assigned the value -O1 if the
- $(CC) version is less than 4.2.
- cc-ifversion takes all the shell operators:
- -eq, -ne, -lt, -le, -gt, and -ge
- The third parameter may be a text as in this example, but it may also
- be an expanded variable or a macro.
-
- cc-cross-prefix
- cc-cross-prefix is used to check if there exists a $(CC) in path with
- one of the listed prefixes. The first prefix where there exist a
- prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found
- then nothing is returned.
- Additional prefixes are separated by a single space in the
- call of cc-cross-prefix.
- This functionality is useful for architecture Makefiles that try
- to set CROSS_COMPILE to well-known values but may have several
- values to select between.
- It is recommended only to try to set CROSS_COMPILE if it is a cross
- build (host arch is different from target arch). And if CROSS_COMPILE
- is already set then leave it with the old value.
-
- Example:
- #arch/m68k/Makefile
- ifneq ($(SUBARCH),$(ARCH))
- ifeq ($(CROSS_COMPILE),)
- CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-)
- endif
- endif
-
---- 3.12 $(LD) support functions
-
- ld-option
- ld-option is used to check if $(LD) supports the supplied option.
- ld-option takes two options as arguments.
- The second argument is an optional option that can be used if the
- first option is not supported by $(LD).
-
- Example:
- #Makefile
- LDFLAGS_vmlinux += $(call ld-option, -X)
-
-
-=== 4 Host Program support
-
-Kbuild supports building executables on the host for use during the
-compilation stage.
-Two steps are required in order to use a host executable.
-
-The first step is to tell kbuild that a host program exists. This is
-done utilising the variable hostprogs-y.
-
-The second step is to add an explicit dependency to the executable.
-This can be done in two ways. Either add the dependency in a rule,
-or utilise the variable $(always).
-Both possibilities are described in the following.
-
---- 4.1 Simple Host Program
-
- In some cases there is a need to compile and run a program on the
- computer where the build is running.
- The following line tells kbuild that the program bin2hex shall be
- built on the build host.
-
- Example:
- hostprogs-y := bin2hex
-
- Kbuild assumes in the above example that bin2hex is made from a single
- c-source file named bin2hex.c located in the same directory as
- the Makefile.
-
---- 4.2 Composite Host Programs
-
- Host programs can be made up based on composite objects.
- The syntax used to define composite objects for host programs is
- similar to the syntax used for kernel objects.
- $(<executable>-objs) lists all objects used to link the final
- executable.
-
- Example:
- #scripts/lxdialog/Makefile
- hostprogs-y := lxdialog
- lxdialog-objs := checklist.o lxdialog.o
-
- Objects with extension .o are compiled from the corresponding .c
- files. In the above example, checklist.c is compiled to checklist.o
- and lxdialog.c is compiled to lxdialog.o.
- Finally, the two .o files are linked to the executable, lxdialog.
- Note: The syntax <executable>-y is not permitted for host-programs.
-
---- 4.3 Using C++ for host programs
-
- kbuild offers support for host programs written in C++. This was
- introduced solely to support kconfig, and is not recommended
- for general use.
-
- Example:
- #scripts/kconfig/Makefile
- hostprogs-y := qconf
- qconf-cxxobjs := qconf.o
-
- In the example above the executable is composed of the C++ file
- qconf.cc - identified by $(qconf-cxxobjs).
-
- If qconf is composed of a mixture of .c and .cc files, then an
- additional line can be used to identify this.
-
- Example:
- #scripts/kconfig/Makefile
- hostprogs-y := qconf
- qconf-cxxobjs := qconf.o
- qconf-objs := check.o
-
---- 4.4 Controlling compiler options for host programs
-
- When compiling host programs, it is possible to set specific flags.
- The programs will always be compiled utilising $(HOSTCC) passed
- the options specified in $(KBUILD_HOSTCFLAGS).
- To set flags that will take effect for all host programs created
- in that Makefile, use the variable HOST_EXTRACFLAGS.
-
- Example:
- #scripts/lxdialog/Makefile
- HOST_EXTRACFLAGS += -I/usr/include/ncurses
-
- To set specific flags for a single file the following construction
- is used:
-
- Example:
- #arch/ppc64/boot/Makefile
- HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE)
-
- It is also possible to specify additional options to the linker.
-
- Example:
- #scripts/kconfig/Makefile
- HOSTLDLIBS_qconf := -L$(QTDIR)/lib
-
- When linking qconf, it will be passed the extra option
- "-L$(QTDIR)/lib".
-
---- 4.5 When host programs are actually built
-
- Kbuild will only build host-programs when they are referenced
- as a prerequisite.
- This is possible in two ways:
-
- (1) List the prerequisite explicitly in a special rule.
-
- Example:
- #drivers/pci/Makefile
- hostprogs-y := gen-devlist
- $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist
- ( cd $(obj); ./gen-devlist ) < $<
-
- The target $(obj)/devlist.h will not be built before
- $(obj)/gen-devlist is updated. Note that references to
- the host programs in special rules must be prefixed with $(obj).
-
- (2) Use $(always)
- When there is no suitable special rule, and the host program
- shall be built when a makefile is entered, the $(always)
- variable shall be used.
-
- Example:
- #scripts/lxdialog/Makefile
- hostprogs-y := lxdialog
- always := $(hostprogs-y)
-
- This will tell kbuild to build lxdialog even if not referenced in
- any rule.
-
---- 4.6 Using hostprogs-$(CONFIG_FOO)
-
- A typical pattern in a Kbuild file looks like this:
-
- Example:
- #scripts/Makefile
- hostprogs-$(CONFIG_KALLSYMS) += kallsyms
-
- Kbuild knows about both 'y' for built-in and 'm' for module.
- So if a config symbol evaluates to 'm', kbuild will still build
- the binary. In other words, Kbuild handles hostprogs-m exactly
- like hostprogs-y. But only hostprogs-y is recommended to be used
- when no CONFIG symbols are involved.
-
-=== 5 Kbuild clean infrastructure
-
-"make clean" deletes most generated files in the obj tree where the kernel
-is compiled. This includes generated files such as host programs.
-Kbuild knows targets listed in $(hostprogs-y), $(hostprogs-m), $(always),
-$(extra-y) and $(targets). They are all deleted during "make clean".
-Files matching the patterns "*.[oas]", "*.ko", plus some additional files
-generated by kbuild are deleted all over the kernel src tree when
-"make clean" is executed.
-
-Additional files can be specified in kbuild makefiles by use of $(clean-files).
-
- Example:
- #lib/Makefile
- clean-files := crc32table.h
-
-When executing "make clean", the file "crc32table.h" will be deleted.
-Kbuild will assume files to be in the same relative directory as the
-Makefile, except if prefixed with $(objtree).
-
-To delete a directory hierarchy use:
-
- Example:
- #scripts/package/Makefile
- clean-dirs := $(objtree)/debian/
-
-This will delete the directory debian in the toplevel directory, including all
-subdirectories.
-
-To exclude certain files from make clean, use the $(no-clean-files) variable.
-This is only a special case used in the top level Kbuild file:
-
- Example:
- #Kbuild
- no-clean-files := $(bounds-file) $(offsets-file)
-
-Usually kbuild descends down in subdirectories due to "obj-* := dir/",
-but in the architecture makefiles where the kbuild infrastructure
-is not sufficient this sometimes needs to be explicit.
-
- Example:
- #arch/x86/boot/Makefile
- subdir- := compressed/
-
-The above assignment instructs kbuild to descend down in the
-directory compressed/ when "make clean" is executed.
-
-To support the clean infrastructure in the Makefiles that build the
-final bootimage there is an optional target named archclean:
-
- Example:
- #arch/x86/Makefile
- archclean:
- $(Q)$(MAKE) $(clean)=arch/x86/boot
-
-When "make clean" is executed, make will descend down in arch/x86/boot,
-and clean as usual. The Makefile located in arch/x86/boot/ may use
-the subdir- trick to descend further down.
-
-Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is
-included in the top level makefile, and the kbuild infrastructure
-is not operational at that point.
-
-Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will
-be visited during "make clean".
-
-=== 6 Architecture Makefiles
-
-The top level Makefile sets up the environment and does the preparation,
-before starting to descend down in the individual directories.
-The top level makefile contains the generic part, whereas
-arch/$(ARCH)/Makefile contains what is required to set up kbuild
-for said architecture.
-To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines
-a few targets.
-
-When kbuild executes, the following steps are followed (roughly):
-1) Configuration of the kernel => produce .config
-2) Store kernel version in include/linux/version.h
-3) Updating all other prerequisites to the target prepare:
- - Additional prerequisites are specified in arch/$(ARCH)/Makefile
-4) Recursively descend down in all directories listed in
- init-* core* drivers-* net-* libs-* and build all targets.
- - The values of the above variables are expanded in arch/$(ARCH)/Makefile.
-5) All object files are then linked and the resulting file vmlinux is
- located at the root of the obj tree.
- The very first objects linked are listed in head-y, assigned by
- arch/$(ARCH)/Makefile.
-6) Finally, the architecture-specific part does any required post processing
- and builds the final bootimage.
- - This includes building boot records
- - Preparing initrd images and the like
-
-
---- 6.1 Set variables to tweak the build to the architecture
-
- LDFLAGS Generic $(LD) options
-
- Flags used for all invocations of the linker.
- Often specifying the emulation is sufficient.
-
- Example:
- #arch/s390/Makefile
- LDFLAGS := -m elf_s390
- Note: ldflags-y can be used to further customise
- the flags used. See chapter 3.7.
-
- LDFLAGS_vmlinux Options for $(LD) when linking vmlinux
-
- LDFLAGS_vmlinux is used to specify additional flags to pass to
- the linker when linking the final vmlinux image.
- LDFLAGS_vmlinux uses the LDFLAGS_$@ support.
-
- Example:
- #arch/x86/Makefile
- LDFLAGS_vmlinux := -e stext
-
- OBJCOPYFLAGS objcopy flags
-
- When $(call if_changed,objcopy) is used to translate a .o file,
- the flags specified in OBJCOPYFLAGS will be used.
- $(call if_changed,objcopy) is often used to generate raw binaries on
- vmlinux.
-
- Example:
- #arch/s390/Makefile
- OBJCOPYFLAGS := -O binary
-
- #arch/s390/boot/Makefile
- $(obj)/image: vmlinux FORCE
- $(call if_changed,objcopy)
-
- In this example, the binary $(obj)/image is a binary version of
- vmlinux. The usage of $(call if_changed,xxx) will be described later.
-
- KBUILD_AFLAGS $(AS) assembler flags
-
- Default value - see top level Makefile
- Append or modify as required per architecture.
-
- Example:
- #arch/sparc64/Makefile
- KBUILD_AFLAGS += -m64 -mcpu=ultrasparc
-
- KBUILD_CFLAGS $(CC) compiler flags
-
- Default value - see top level Makefile
- Append or modify as required per architecture.
-
- Often, the KBUILD_CFLAGS variable depends on the configuration.
-
- Example:
- #arch/x86/boot/compressed/Makefile
- cflags-$(CONFIG_X86_32) := -march=i386
- cflags-$(CONFIG_X86_64) := -mcmodel=small
- KBUILD_CFLAGS += $(cflags-y)
-
- Many arch Makefiles dynamically run the target C compiler to
- probe supported options:
-
- #arch/x86/Makefile
-
- ...
- cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\
- -march=pentium2,-march=i686)
- ...
- # Disable unit-at-a-time mode ...
- KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time)
- ...
-
-
- The first example utilises the trick that a config option expands
- to 'y' when selected.
-
- KBUILD_AFLAGS_KERNEL $(AS) options specific for built-in
-
- $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile
- resident kernel code.
-
- KBUILD_AFLAGS_MODULE Options for $(AS) when building modules
-
- $(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that
- are used for $(AS).
- From commandline AFLAGS_MODULE shall be used (see kbuild.txt).
-
- KBUILD_CFLAGS_KERNEL $(CC) options specific for built-in
-
- $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile
- resident kernel code.
-
- KBUILD_CFLAGS_MODULE Options for $(CC) when building modules
-
- $(KBUILD_CFLAGS_MODULE) is used to add arch-specific options that
- are used for $(CC).
- From commandline CFLAGS_MODULE shall be used (see kbuild.txt).
-
- KBUILD_LDFLAGS_MODULE Options for $(LD) when linking modules
-
- $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options
- used when linking modules. This is often a linker script.
- From commandline LDFLAGS_MODULE shall be used (see kbuild.txt).
-
- KBUILD_ARFLAGS Options for $(AR) when creating archives
-
- $(KBUILD_ARFLAGS) set by the top level Makefile to "D" (deterministic
- mode) if this option is supported by $(AR).
-
- ARCH_CPPFLAGS, ARCH_AFLAGS, ARCH_CFLAGS Overrides the kbuild defaults
-
- These variables are appended to the KBUILD_CPPFLAGS,
- KBUILD_AFLAGS, and KBUILD_CFLAGS, respectively, after the
- top-level Makefile has set any other flags. This provides a
- means for an architecture to override the defaults.
-
-
---- 6.2 Add prerequisites to archheaders:
-
- The archheaders: rule is used to generate header files that
- may be installed into user space by "make header_install" or
- "make headers_install_all". In order to support
- "make headers_install_all", this target has to be able to run
- on an unconfigured tree, or a tree configured for another
- architecture.
-
- It is run before "make archprepare" when run on the
- architecture itself.
-
-
---- 6.3 Add prerequisites to archprepare:
-
- The archprepare: rule is used to list prerequisites that need to be
- built before starting to descend down in the subdirectories.
- This is usually used for header files containing assembler constants.
-
- Example:
- #arch/arm/Makefile
- archprepare: maketools
-
- In this example, the file target maketools will be processed
- before descending down in the subdirectories.
- See also chapter XXX-TODO that describe how kbuild supports
- generating offset header files.
-
-
---- 6.4 List directories to visit when descending
-
- An arch Makefile cooperates with the top Makefile to define variables
- which specify how to build the vmlinux file. Note that there is no
- corresponding arch-specific section for modules; the module-building
- machinery is all architecture-independent.
-
-
- head-y, init-y, core-y, libs-y, drivers-y, net-y
-
- $(head-y) lists objects to be linked first in vmlinux.
- $(libs-y) lists directories where a lib.a archive can be located.
- The rest list directories where a built-in.a object file can be
- located.
-
- $(init-y) objects will be located after $(head-y).
- Then the rest follows in this order:
- $(core-y), $(libs-y), $(drivers-y) and $(net-y).
-
- The top level Makefile defines values for all generic directories,
- and arch/$(ARCH)/Makefile only adds architecture-specific directories.
-
- Example:
- #arch/sparc64/Makefile
- core-y += arch/sparc64/kernel/
- libs-y += arch/sparc64/prom/ arch/sparc64/lib/
- drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/
-
-
---- 6.5 Architecture-specific boot images
-
- An arch Makefile specifies goals that take the vmlinux file, compress
- it, wrap it in bootstrapping code, and copy the resulting files
- somewhere. This includes various kinds of installation commands.
- The actual goals are not standardized across architectures.
-
- It is common to locate any additional processing in a boot/
- directory below arch/$(ARCH)/.
-
- Kbuild does not provide any smart way to support building a
- target specified in boot/. Therefore arch/$(ARCH)/Makefile shall
- call make manually to build a target in boot/.
-
- The recommended approach is to include shortcuts in
- arch/$(ARCH)/Makefile, and use the full path when calling down
- into the arch/$(ARCH)/boot/Makefile.
-
- Example:
- #arch/x86/Makefile
- boot := arch/x86/boot
- bzImage: vmlinux
- $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
-
- "$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke
- make in a subdirectory.
-
- There are no rules for naming architecture-specific targets,
- but executing "make help" will list all relevant targets.
- To support this, $(archhelp) must be defined.
-
- Example:
- #arch/x86/Makefile
- define archhelp
- echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)'
- endif
-
- When make is executed without arguments, the first goal encountered
- will be built. In the top level Makefile the first goal present
- is all:.
- An architecture shall always, per default, build a bootable image.
- In "make help", the default goal is highlighted with a '*'.
- Add a new prerequisite to all: to select a default goal different
- from vmlinux.
-
- Example:
- #arch/x86/Makefile
- all: bzImage
-
- When "make" is executed without arguments, bzImage will be built.
-
---- 6.6 Building non-kbuild targets
-
- extra-y
-
- extra-y specifies additional targets created in the current
- directory, in addition to any targets specified by obj-*.
-
- Listing all targets in extra-y is required for two purposes:
- 1) Enable kbuild to check changes in command lines
- - When $(call if_changed,xxx) is used
- 2) kbuild knows what files to delete during "make clean"
-
- Example:
- #arch/x86/kernel/Makefile
- extra-y := head.o init_task.o
-
- In this example, extra-y is used to list object files that
- shall be built, but shall not be linked as part of built-in.a.
-
-
---- 6.7 Commands useful for building a boot image
-
- Kbuild provides a few macros that are useful when building a
- boot image.
-
- if_changed
-
- if_changed is the infrastructure used for the following commands.
-
- Usage:
- target: source(s) FORCE
- $(call if_changed,ld/objcopy/gzip/...)
-
- When the rule is evaluated, it is checked to see if any files
- need an update, or the command line has changed since the last
- invocation. The latter will force a rebuild if any options
- to the executable have changed.
- Any target that utilises if_changed must be listed in $(targets),
- otherwise the command line check will fail, and the target will
- always be built.
- Assignments to $(targets) are without $(obj)/ prefix.
- if_changed may be used in conjunction with custom commands as
- defined in 6.8 "Custom kbuild commands".
-
- Note: It is a typical mistake to forget the FORCE prerequisite.
- Another common pitfall is that whitespace is sometimes
- significant; for instance, the below will fail (note the extra space
- after the comma):
- target: source(s) FORCE
- #WRONG!# $(call if_changed, ld/objcopy/gzip/...)
-
- Note: if_changed should not be used more than once per target.
- It stores the executed command in a corresponding .cmd
- file and multiple calls would result in overwrites and
- unwanted results when the target is up to date and only the
- tests on changed commands trigger execution of commands.
-
- ld
- Link target. Often, LDFLAGS_$@ is used to set specific options to ld.
-
- Example:
- #arch/x86/boot/Makefile
- LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary
- LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext
-
- targets += setup setup.o bootsect bootsect.o
- $(obj)/setup $(obj)/bootsect: %: %.o FORCE
- $(call if_changed,ld)
-
- In this example, there are two possible targets, requiring different
- options to the linker. The linker options are specified using the
- LDFLAGS_$@ syntax - one for each potential target.
- $(targets) are assigned all potential targets, by which kbuild knows
- the targets and will:
- 1) check for commandline changes
- 2) delete target during make clean
-
- The ": %: %.o" part of the prerequisite is a shorthand that
- frees us from listing the setup.o and bootsect.o files.
- Note: It is a common mistake to forget the "targets :=" assignment,
- resulting in the target file being recompiled for no
- obvious reason.
-
- objcopy
- Copy binary. Uses OBJCOPYFLAGS usually specified in
- arch/$(ARCH)/Makefile.
- OBJCOPYFLAGS_$@ may be used to set additional options.
-
- gzip
- Compress target. Use maximum compression to compress target.
-
- Example:
- #arch/x86/boot/compressed/Makefile
- $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE
- $(call if_changed,gzip)
-
- dtc
- Create flattened device tree blob object suitable for linking
- into vmlinux. Device tree blobs linked into vmlinux are placed
- in an init section in the image. Platform code *must* copy the
- blob to non-init memory prior to calling unflatten_device_tree().
-
- To use this command, simply add *.dtb into obj-y or targets, or make
- some other target depend on %.dtb
-
- A central rule exists to create $(obj)/%.dtb from $(src)/%.dts;
- architecture Makefiles do no need to explicitly write out that rule.
-
- Example:
- targets += $(dtb-y)
- DTC_FLAGS ?= -p 1024
-
---- 6.8 Custom kbuild commands
-
- When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand
- of a command is normally displayed.
- To enable this behaviour for custom commands kbuild requires
- two variables to be set:
- quiet_cmd_<command> - what shall be echoed
- cmd_<command> - the command to execute
-
- Example:
- #
- quiet_cmd_image = BUILD $@
- cmd_image = $(obj)/tools/build $(BUILDFLAGS) \
- $(obj)/vmlinux.bin > $@
-
- targets += bzImage
- $(obj)/bzImage: $(obj)/vmlinux.bin $(obj)/tools/build FORCE
- $(call if_changed,image)
- @echo 'Kernel: $@ is ready'
-
- When updating the $(obj)/bzImage target, the line
-
- BUILD arch/x86/boot/bzImage
-
- will be displayed with "make KBUILD_VERBOSE=0".
-
-
---- 6.9 Preprocessing linker scripts
-
- When the vmlinux image is built, the linker script
- arch/$(ARCH)/kernel/vmlinux.lds is used.
- The script is a preprocessed variant of the file vmlinux.lds.S
- located in the same directory.
- kbuild knows .lds files and includes a rule *lds.S -> *lds.
-
- Example:
- #arch/x86/kernel/Makefile
- always := vmlinux.lds
-
- #Makefile
- export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)
-
- The assignment to $(always) is used to tell kbuild to build the
- target vmlinux.lds.
- The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the
- specified options when building the target vmlinux.lds.
-
- When building the *.lds target, kbuild uses the variables:
- KBUILD_CPPFLAGS : Set in top-level Makefile
- cppflags-y : May be set in the kbuild makefile
- CPPFLAGS_$(@F) : Target-specific flags.
- Note that the full filename is used in this
- assignment.
-
- The kbuild infrastructure for *lds files is used in several
- architecture-specific files.
-
---- 6.10 Generic header files
-
- The directory include/asm-generic contains the header files
- that may be shared between individual architectures.
- The recommended approach how to use a generic header file is
- to list the file in the Kbuild file.
- See "7.2 generic-y" for further info on syntax etc.
-
---- 6.11 Post-link pass
-
- If the file arch/xxx/Makefile.postlink exists, this makefile
- will be invoked for post-link objects (vmlinux and modules.ko)
- for architectures to run post-link passes on. Must also handle
- the clean target.
-
- This pass runs after kallsyms generation. If the architecture
- needs to modify symbol locations, rather than manipulate the
- kallsyms, it may be easier to add another postlink target for
- .tmp_vmlinux? targets to be called from link-vmlinux.sh.
-
- For example, powerpc uses this to check relocation sanity of
- the linked vmlinux file.
-
-=== 7 Kbuild syntax for exported headers
-
-The kernel includes a set of headers that is exported to userspace.
-Many headers can be exported as-is but other headers require a
-minimal pre-processing before they are ready for user-space.
-The pre-processing does:
-- drop kernel-specific annotations
-- drop include of compiler.h
-- drop all sections that are kernel internal (guarded by ifdef __KERNEL__)
-
-All headers under include/uapi/, include/generated/uapi/,
-arch/<arch>/include/uapi/ and arch/<arch>/include/generated/uapi/
-are exported.
-
-A Kbuild file may be defined under arch/<arch>/include/uapi/asm/ and
-arch/<arch>/include/asm/ to list asm files coming from asm-generic.
-See subsequent chapter for the syntax of the Kbuild file.
-
---- 7.1 no-export-headers
-
- no-export-headers is essentially used by include/uapi/linux/Kbuild to
- avoid exporting specific headers (e.g. kvm.h) on architectures that do
- not support it. It should be avoided as much as possible.
-
---- 7.2 generic-y
-
- If an architecture uses a verbatim copy of a header from
- include/asm-generic then this is listed in the file
- arch/$(ARCH)/include/asm/Kbuild like this:
-
- Example:
- #arch/x86/include/asm/Kbuild
- generic-y += termios.h
- generic-y += rtc.h
-
- During the prepare phase of the build a wrapper include
- file is generated in the directory:
-
- arch/$(ARCH)/include/generated/asm
-
- When a header is exported where the architecture uses
- the generic header a similar wrapper is generated as part
- of the set of exported headers in the directory:
-
- usr/include/asm
-
- The generated wrapper will in both cases look like the following:
-
- Example: termios.h
- #include <asm-generic/termios.h>
-
---- 7.3 generated-y
-
- If an architecture generates other header files alongside generic-y
- wrappers, generated-y specifies them.
-
- This prevents them being treated as stale asm-generic wrappers and
- removed.
-
- Example:
- #arch/x86/include/asm/Kbuild
- generated-y += syscalls_32.h
-
---- 7.4 mandatory-y
-
- mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild
- to define the minimum set of ASM headers that all architectures must have.
-
- This works like optional generic-y. If a mandatory header is missing
- in arch/$(ARCH)/include/(uapi/)/asm, Kbuild will automatically generate
- a wrapper of the asm-generic one.
-
- The convention is to list one subdir per line and
- preferably in alphabetic order.
-
-=== 8 Kbuild Variables
-
-The top Makefile exports the following variables:
-
- VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION
-
- These variables define the current kernel version. A few arch
- Makefiles actually use these values directly; they should use
- $(KERNELRELEASE) instead.
-
- $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic
- three-part version number, such as "2", "4", and "0". These three
- values are always numeric.
-
- $(EXTRAVERSION) defines an even tinier sublevel for pre-patches
- or additional patches. It is usually some non-numeric string
- such as "-pre4", and is often blank.
-
- KERNELRELEASE
-
- $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable
- for constructing installation directory names or showing in
- version strings. Some arch Makefiles use it for this purpose.
-
- ARCH
-
- This variable defines the target architecture, such as "i386",
- "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to
- determine which files to compile.
-
- By default, the top Makefile sets $(ARCH) to be the same as the
- host system architecture. For a cross build, a user may
- override the value of $(ARCH) on the command line:
-
- make ARCH=m68k ...
-
-
- INSTALL_PATH
-
- This variable defines a place for the arch Makefiles to install
- the resident kernel image and System.map file.
- Use this for architecture-specific install targets.
-
- INSTALL_MOD_PATH, MODLIB
-
- $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module
- installation. This variable is not defined in the Makefile but
- may be passed in by the user if desired.
-
- $(MODLIB) specifies the directory for module installation.
- The top Makefile defines $(MODLIB) to
- $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may
- override this value on the command line if desired.
-
- INSTALL_MOD_STRIP
-
- If this variable is specified, it will cause modules to be stripped
- after they are installed. If INSTALL_MOD_STRIP is '1', then the
- default option --strip-debug will be used. Otherwise, the
- INSTALL_MOD_STRIP value will be used as the option(s) to the strip
- command.
-
-
-=== 9 Makefile language
-
-The kernel Makefiles are designed to be run with GNU Make. The Makefiles
-use only the documented features of GNU Make, but they do use many
-GNU extensions.
-
-GNU Make supports elementary list-processing functions. The kernel
-Makefiles use a novel style of list building and manipulation with few
-"if" statements.
-
-GNU Make has two assignment operators, ":=" and "=". ":=" performs
-immediate evaluation of the right-hand side and stores an actual string
-into the left-hand side. "=" is like a formula definition; it stores the
-right-hand side in an unevaluated form and then evaluates this form each
-time the left-hand side is used.
-
-There are some cases where "=" is appropriate. Usually, though, ":="
-is the right choice.
-
-=== 10 Credits
-
-Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net>
-Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>
-Updates by Sam Ravnborg <sam@ravnborg.org>
-Language QA by Jan Engelhardt <jengelh@gmx.de>
-
-=== 11 TODO
-
-- Describe how kbuild supports shipped files with _shipped.
-- Generating offset header files.
-- Add more variables to section 7?
-
-
-
--- /dev/null
+=========================
+Building External Modules
+=========================
+
+This document describes how to build an out-of-tree kernel module.
+
+.. Table of Contents
+
+ === 1 Introduction
+ === 2 How to Build External Modules
+ --- 2.1 Command Syntax
+ --- 2.2 Options
+ --- 2.3 Targets
+ --- 2.4 Building Separate Files
+ === 3. Creating a Kbuild File for an External Module
+ --- 3.1 Shared Makefile
+ --- 3.2 Separate Kbuild file and Makefile
+ --- 3.3 Binary Blobs
+ --- 3.4 Building Multiple Modules
+ === 4. Include Files
+ --- 4.1 Kernel Includes
+ --- 4.2 Single Subdirectory
+ --- 4.3 Several Subdirectories
+ === 5. Module Installation
+ --- 5.1 INSTALL_MOD_PATH
+ --- 5.2 INSTALL_MOD_DIR
+ === 6. Module Versioning
+ --- 6.1 Symbols From the Kernel (vmlinux + modules)
+ --- 6.2 Symbols and External Modules
+ --- 6.3 Symbols From Another External Module
+ === 7. Tips & Tricks
+ --- 7.1 Testing for CONFIG_FOO_BAR
+
+
+
+1. Introduction
+===============
+
+"kbuild" is the build system used by the Linux kernel. Modules must use
+kbuild to stay compatible with changes in the build infrastructure and
+to pick up the right flags to "gcc." Functionality for building modules
+both in-tree and out-of-tree is provided. The method for building
+either is similar, and all modules are initially developed and built
+out-of-tree.
+
+Covered in this document is information aimed at developers interested
+in building out-of-tree (or "external") modules. The author of an
+external module should supply a makefile that hides most of the
+complexity, so one only has to type "make" to build the module. This is
+easily accomplished, and a complete example will be presented in
+section 3.
+
+
+2. How to Build External Modules
+================================
+
+To build external modules, you must have a prebuilt kernel available
+that contains the configuration and header files used in the build.
+Also, the kernel must have been built with modules enabled. If you are
+using a distribution kernel, there will be a package for the kernel you
+are running provided by your distribution.
+
+An alternative is to use the "make" target "modules_prepare." This will
+make sure the kernel contains the information required. The target
+exists solely as a simple way to prepare a kernel source tree for
+building external modules.
+
+NOTE: "modules_prepare" will not build Module.symvers even if
+CONFIG_MODVERSIONS is set; therefore, a full kernel build needs to be
+executed to make module versioning work.
+
+2.1 Command Syntax
+==================
+
+ The command to build an external module is::
+
+ $ make -C <path_to_kernel_src> M=$PWD
+
+ The kbuild system knows that an external module is being built
+ due to the "M=<dir>" option given in the command.
+
+ To build against the running kernel use::
+
+ $ make -C /lib/modules/`uname -r`/build M=$PWD
+
+ Then to install the module(s) just built, add the target
+ "modules_install" to the command::
+
+ $ make -C /lib/modules/`uname -r`/build M=$PWD modules_install
+
+2.2 Options
+===========
+
+ ($KDIR refers to the path of the kernel source directory.)
+
+ make -C $KDIR M=$PWD
+
+ -C $KDIR
+ The directory where the kernel source is located.
+ "make" will actually change to the specified directory
+ when executing and will change back when finished.
+
+ M=$PWD
+ Informs kbuild that an external module is being built.
+ The value given to "M" is the absolute path of the
+ directory where the external module (kbuild file) is
+ located.
+
+2.3 Targets
+===========
+
+ When building an external module, only a subset of the "make"
+ targets are available.
+
+ make -C $KDIR M=$PWD [target]
+
+ The default will build the module(s) located in the current
+ directory, so a target does not need to be specified. All
+ output files will also be generated in this directory. No
+ attempts are made to update the kernel source, and it is a
+ precondition that a successful "make" has been executed for the
+ kernel.
+
+ modules
+ The default target for external modules. It has the
+ same functionality as if no target was specified. See
+ description above.
+
+ modules_install
+ Install the external module(s). The default location is
+ /lib/modules/<kernel_release>/extra/, but a prefix may
+ be added with INSTALL_MOD_PATH (discussed in section 5).
+
+ clean
+ Remove all generated files in the module directory only.
+
+ help
+ List the available targets for external modules.
+
+2.4 Building Separate Files
+===========================
+
+ It is possible to build single files that are part of a module.
+ This works equally well for the kernel, a module, and even for
+ external modules.
+
+ Example (The module foo.ko, consist of bar.o and baz.o)::
+
+ make -C $KDIR M=$PWD bar.lst
+ make -C $KDIR M=$PWD baz.o
+ make -C $KDIR M=$PWD foo.ko
+ make -C $KDIR M=$PWD ./
+
+
+3. Creating a Kbuild File for an External Module
+================================================
+
+In the last section we saw the command to build a module for the
+running kernel. The module is not actually built, however, because a
+build file is required. Contained in this file will be the name of
+the module(s) being built, along with the list of requisite source
+files. The file may be as simple as a single line::
+
+ obj-m := <module_name>.o
+
+The kbuild system will build <module_name>.o from <module_name>.c,
+and, after linking, will result in the kernel module <module_name>.ko.
+The above line can be put in either a "Kbuild" file or a "Makefile."
+When the module is built from multiple sources, an additional line is
+needed listing the files::
+
+ <module_name>-y := <src1>.o <src2>.o ...
+
+NOTE: Further documentation describing the syntax used by kbuild is
+located in Documentation/kbuild/makefiles.rst.
+
+The examples below demonstrate how to create a build file for the
+module 8123.ko, which is built from the following files::
+
+ 8123_if.c
+ 8123_if.h
+ 8123_pci.c
+ 8123_bin.o_shipped <= Binary blob
+
+--- 3.1 Shared Makefile
+
+ An external module always includes a wrapper makefile that
+ supports building the module using "make" with no arguments.
+ This target is not used by kbuild; it is only for convenience.
+ Additional functionality, such as test targets, can be included
+ but should be filtered out from kbuild due to possible name
+ clashes.
+
+ Example 1::
+
+ --> filename: Makefile
+ ifneq ($(KERNELRELEASE),)
+ # kbuild part of makefile
+ obj-m := 8123.o
+ 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
+
+ else
+ # normal makefile
+ KDIR ?= /lib/modules/`uname -r`/build
+
+ default:
+ $(MAKE) -C $(KDIR) M=$$PWD
+
+ # Module specific targets
+ genbin:
+ echo "X" > 8123_bin.o_shipped
+
+ endif
+
+ The check for KERNELRELEASE is used to separate the two parts
+ of the makefile. In the example, kbuild will only see the two
+ assignments, whereas "make" will see everything except these
+ two assignments. This is due to two passes made on the file:
+ the first pass is by the "make" instance run on the command
+ line; the second pass is by the kbuild system, which is
+ initiated by the parameterized "make" in the default target.
+
+3.2 Separate Kbuild File and Makefile
+-------------------------------------
+
+ In newer versions of the kernel, kbuild will first look for a
+ file named "Kbuild," and only if that is not found, will it
+ then look for a makefile. Utilizing a "Kbuild" file allows us
+ to split up the makefile from example 1 into two files:
+
+ Example 2::
+
+ --> filename: Kbuild
+ obj-m := 8123.o
+ 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
+
+ --> filename: Makefile
+ KDIR ?= /lib/modules/`uname -r`/build
+
+ default:
+ $(MAKE) -C $(KDIR) M=$$PWD
+
+ # Module specific targets
+ genbin:
+ echo "X" > 8123_bin.o_shipped
+
+ The split in example 2 is questionable due to the simplicity of
+ each file; however, some external modules use makefiles
+ consisting of several hundred lines, and here it really pays
+ off to separate the kbuild part from the rest.
+
+ The next example shows a backward compatible version.
+
+ Example 3::
+
+ --> filename: Kbuild
+ obj-m := 8123.o
+ 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
+
+ --> filename: Makefile
+ ifneq ($(KERNELRELEASE),)
+ # kbuild part of makefile
+ include Kbuild
+
+ else
+ # normal makefile
+ KDIR ?= /lib/modules/`uname -r`/build
+
+ default:
+ $(MAKE) -C $(KDIR) M=$$PWD
+
+ # Module specific targets
+ genbin:
+ echo "X" > 8123_bin.o_shipped
+
+ endif
+
+ Here the "Kbuild" file is included from the makefile. This
+ allows an older version of kbuild, which only knows of
+ makefiles, to be used when the "make" and kbuild parts are
+ split into separate files.
+
+3.3 Binary Blobs
+----------------
+
+ Some external modules need to include an object file as a blob.
+ kbuild has support for this, but requires the blob file to be
+ named <filename>_shipped. When the kbuild rules kick in, a copy
+ of <filename>_shipped is created with _shipped stripped off,
+ giving us <filename>. This shortened filename can be used in
+ the assignment to the module.
+
+ Throughout this section, 8123_bin.o_shipped has been used to
+ build the kernel module 8123.ko; it has been included as
+ 8123_bin.o::
+
+ 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
+
+ Although there is no distinction between the ordinary source
+ files and the binary file, kbuild will pick up different rules
+ when creating the object file for the module.
+
+3.4 Building Multiple Modules
+=============================
+
+ kbuild supports building multiple modules with a single build
+ file. For example, if you wanted to build two modules, foo.ko
+ and bar.ko, the kbuild lines would be::
+
+ obj-m := foo.o bar.o
+ foo-y := <foo_srcs>
+ bar-y := <bar_srcs>
+
+ It is that simple!
+
+
+4. Include Files
+================
+
+Within the kernel, header files are kept in standard locations
+according to the following rule:
+
+ * If the header file only describes the internal interface of a
+ module, then the file is placed in the same directory as the
+ source files.
+ * If the header file describes an interface used by other parts
+ of the kernel that are located in different directories, then
+ the file is placed in include/linux/.
+
+ NOTE:
+ There are two notable exceptions to this rule: larger
+ subsystems have their own directory under include/, such as
+ include/scsi; and architecture specific headers are located
+ under arch/$(ARCH)/include/.
+
+4.1 Kernel Includes
+-------------------
+
+ To include a header file located under include/linux/, simply
+ use::
+
+ #include <linux/module.h>
+
+ kbuild will add options to "gcc" so the relevant directories
+ are searched.
+
+4.2 Single Subdirectory
+-----------------------
+
+ External modules tend to place header files in a separate
+ include/ directory where their source is located, although this
+ is not the usual kernel style. To inform kbuild of the
+ directory, use either ccflags-y or CFLAGS_<filename>.o.
+
+ Using the example from section 3, if we moved 8123_if.h to a
+ subdirectory named include, the resulting kbuild file would
+ look like::
+
+ --> filename: Kbuild
+ obj-m := 8123.o
+
+ ccflags-y := -Iinclude
+ 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
+
+ Note that in the assignment there is no space between -I and
+ the path. This is a limitation of kbuild: there must be no
+ space present.
+
+4.3 Several Subdirectories
+--------------------------
+
+ kbuild can handle files that are spread over several directories.
+ Consider the following example::
+
+ .
+ |__ src
+ | |__ complex_main.c
+ | |__ hal
+ | |__ hardwareif.c
+ | |__ include
+ | |__ hardwareif.h
+ |__ include
+ |__ complex.h
+
+ To build the module complex.ko, we then need the following
+ kbuild file::
+
+ --> filename: Kbuild
+ obj-m := complex.o
+ complex-y := src/complex_main.o
+ complex-y += src/hal/hardwareif.o
+
+ ccflags-y := -I$(src)/include
+ ccflags-y += -I$(src)/src/hal/include
+
+ As you can see, kbuild knows how to handle object files located
+ in other directories. The trick is to specify the directory
+ relative to the kbuild file's location. That being said, this
+ is NOT recommended practice.
+
+ For the header files, kbuild must be explicitly told where to
+ look. When kbuild executes, the current directory is always the
+ root of the kernel tree (the argument to "-C") and therefore an
+ absolute path is needed. $(src) provides the absolute path by
+ pointing to the directory where the currently executing kbuild
+ file is located.
+
+
+5. Module Installation
+======================
+
+Modules which are included in the kernel are installed in the
+directory:
+
+ /lib/modules/$(KERNELRELEASE)/kernel/
+
+And external modules are installed in:
+
+ /lib/modules/$(KERNELRELEASE)/extra/
+
+5.1 INSTALL_MOD_PATH
+--------------------
+
+ Above are the default directories but as always some level of
+ customization is possible. A prefix can be added to the
+ installation path using the variable INSTALL_MOD_PATH::
+
+ $ make INSTALL_MOD_PATH=/frodo modules_install
+ => Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel/
+
+ INSTALL_MOD_PATH may be set as an ordinary shell variable or,
+ as shown above, can be specified on the command line when
+ calling "make." This has effect when installing both in-tree
+ and out-of-tree modules.
+
+5.2 INSTALL_MOD_DIR
+-------------------
+
+ External modules are by default installed to a directory under
+ /lib/modules/$(KERNELRELEASE)/extra/, but you may wish to
+ locate modules for a specific functionality in a separate
+ directory. For this purpose, use INSTALL_MOD_DIR to specify an
+ alternative name to "extra."::
+
+ $ make INSTALL_MOD_DIR=gandalf -C $KDIR \
+ M=$PWD modules_install
+ => Install dir: /lib/modules/$(KERNELRELEASE)/gandalf/
+
+
+6. Module Versioning
+====================
+
+Module versioning is enabled by the CONFIG_MODVERSIONS tag, and is used
+as a simple ABI consistency check. A CRC value of the full prototype
+for an exported symbol is created. When a module is loaded/used, the
+CRC values contained in the kernel are compared with similar values in
+the module; if they are not equal, the kernel refuses to load the
+module.
+
+Module.symvers contains a list of all exported symbols from a kernel
+build.
+
+6.1 Symbols From the Kernel (vmlinux + modules)
+-----------------------------------------------
+
+ During a kernel build, a file named Module.symvers will be
+ generated. Module.symvers contains all exported symbols from
+ the kernel and compiled modules. For each symbol, the
+ corresponding CRC value is also stored.
+
+ The syntax of the Module.symvers file is::
+
+ <CRC> <Symbol> <module>
+
+ 0x2d036834 scsi_remove_host drivers/scsi/scsi_mod
+
+ For a kernel build without CONFIG_MODVERSIONS enabled, the CRC
+ would read 0x00000000.
+
+ Module.symvers serves two purposes:
+
+ 1) It lists all exported symbols from vmlinux and all modules.
+ 2) It lists the CRC if CONFIG_MODVERSIONS is enabled.
+
+6.2 Symbols and External Modules
+--------------------------------
+
+ When building an external module, the build system needs access
+ to the symbols from the kernel to check if all external symbols
+ are defined. This is done in the MODPOST step. modpost obtains
+ the symbols by reading Module.symvers from the kernel source
+ tree. If a Module.symvers file is present in the directory
+ where the external module is being built, this file will be
+ read too. During the MODPOST step, a new Module.symvers file
+ will be written containing all exported symbols that were not
+ defined in the kernel.
+
+--- 6.3 Symbols From Another External Module
+
+ Sometimes, an external module uses exported symbols from
+ another external module. kbuild needs to have full knowledge of
+ all symbols to avoid spitting out warnings about undefined
+ symbols. Three solutions exist for this situation.
+
+ NOTE: The method with a top-level kbuild file is recommended
+ but may be impractical in certain situations.
+
+ Use a top-level kbuild file
+ If you have two modules, foo.ko and bar.ko, where
+ foo.ko needs symbols from bar.ko, you can use a
+ common top-level kbuild file so both modules are
+ compiled in the same build. Consider the following
+ directory layout::
+
+ ./foo/ <= contains foo.ko
+ ./bar/ <= contains bar.ko
+
+ The top-level kbuild file would then look like::
+
+ #./Kbuild (or ./Makefile):
+ obj-y := foo/ bar/
+
+ And executing::
+
+ $ make -C $KDIR M=$PWD
+
+ will then do the expected and compile both modules with
+ full knowledge of symbols from either module.
+
+ Use an extra Module.symvers file
+ When an external module is built, a Module.symvers file
+ is generated containing all exported symbols which are
+ not defined in the kernel. To get access to symbols
+ from bar.ko, copy the Module.symvers file from the
+ compilation of bar.ko to the directory where foo.ko is
+ built. During the module build, kbuild will read the
+ Module.symvers file in the directory of the external
+ module, and when the build is finished, a new
+ Module.symvers file is created containing the sum of
+ all symbols defined and not part of the kernel.
+
+ Use "make" variable KBUILD_EXTRA_SYMBOLS
+ If it is impractical to copy Module.symvers from
+ another module, you can assign a space separated list
+ of files to KBUILD_EXTRA_SYMBOLS in your build file.
+ These files will be loaded by modpost during the
+ initialization of its symbol tables.
+
+
+7. Tips & Tricks
+================
+
+7.1 Testing for CONFIG_FOO_BAR
+------------------------------
+
+ Modules often need to check for certain `CONFIG_` options to
+ decide if a specific feature is included in the module. In
+ kbuild this is done by referencing the `CONFIG_` variable
+ directly::
+
+ #fs/ext2/Makefile
+ obj-$(CONFIG_EXT2_FS) += ext2.o
+
+ ext2-y := balloc.o bitmap.o dir.o
+ ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o
+
+ External modules have traditionally used "grep" to check for
+ specific `CONFIG_` settings directly in .config. This usage is
+ broken. As introduced before, external modules should use
+ kbuild for building and can therefore use the same methods as
+ in-tree modules when testing for `CONFIG_` definitions.
+++ /dev/null
-Building External Modules
-
-This document describes how to build an out-of-tree kernel module.
-
-=== Table of Contents
-
- === 1 Introduction
- === 2 How to Build External Modules
- --- 2.1 Command Syntax
- --- 2.2 Options
- --- 2.3 Targets
- --- 2.4 Building Separate Files
- === 3. Creating a Kbuild File for an External Module
- --- 3.1 Shared Makefile
- --- 3.2 Separate Kbuild file and Makefile
- --- 3.3 Binary Blobs
- --- 3.4 Building Multiple Modules
- === 4. Include Files
- --- 4.1 Kernel Includes
- --- 4.2 Single Subdirectory
- --- 4.3 Several Subdirectories
- === 5. Module Installation
- --- 5.1 INSTALL_MOD_PATH
- --- 5.2 INSTALL_MOD_DIR
- === 6. Module Versioning
- --- 6.1 Symbols From the Kernel (vmlinux + modules)
- --- 6.2 Symbols and External Modules
- --- 6.3 Symbols From Another External Module
- === 7. Tips & Tricks
- --- 7.1 Testing for CONFIG_FOO_BAR
-
-
-
-=== 1. Introduction
-
-"kbuild" is the build system used by the Linux kernel. Modules must use
-kbuild to stay compatible with changes in the build infrastructure and
-to pick up the right flags to "gcc." Functionality for building modules
-both in-tree and out-of-tree is provided. The method for building
-either is similar, and all modules are initially developed and built
-out-of-tree.
-
-Covered in this document is information aimed at developers interested
-in building out-of-tree (or "external") modules. The author of an
-external module should supply a makefile that hides most of the
-complexity, so one only has to type "make" to build the module. This is
-easily accomplished, and a complete example will be presented in
-section 3.
-
-
-=== 2. How to Build External Modules
-
-To build external modules, you must have a prebuilt kernel available
-that contains the configuration and header files used in the build.
-Also, the kernel must have been built with modules enabled. If you are
-using a distribution kernel, there will be a package for the kernel you
-are running provided by your distribution.
-
-An alternative is to use the "make" target "modules_prepare." This will
-make sure the kernel contains the information required. The target
-exists solely as a simple way to prepare a kernel source tree for
-building external modules.
-
-NOTE: "modules_prepare" will not build Module.symvers even if
-CONFIG_MODVERSIONS is set; therefore, a full kernel build needs to be
-executed to make module versioning work.
-
---- 2.1 Command Syntax
-
- The command to build an external module is:
-
- $ make -C <path_to_kernel_src> M=$PWD
-
- The kbuild system knows that an external module is being built
- due to the "M=<dir>" option given in the command.
-
- To build against the running kernel use:
-
- $ make -C /lib/modules/`uname -r`/build M=$PWD
-
- Then to install the module(s) just built, add the target
- "modules_install" to the command:
-
- $ make -C /lib/modules/`uname -r`/build M=$PWD modules_install
-
---- 2.2 Options
-
- ($KDIR refers to the path of the kernel source directory.)
-
- make -C $KDIR M=$PWD
-
- -C $KDIR
- The directory where the kernel source is located.
- "make" will actually change to the specified directory
- when executing and will change back when finished.
-
- M=$PWD
- Informs kbuild that an external module is being built.
- The value given to "M" is the absolute path of the
- directory where the external module (kbuild file) is
- located.
-
---- 2.3 Targets
-
- When building an external module, only a subset of the "make"
- targets are available.
-
- make -C $KDIR M=$PWD [target]
-
- The default will build the module(s) located in the current
- directory, so a target does not need to be specified. All
- output files will also be generated in this directory. No
- attempts are made to update the kernel source, and it is a
- precondition that a successful "make" has been executed for the
- kernel.
-
- modules
- The default target for external modules. It has the
- same functionality as if no target was specified. See
- description above.
-
- modules_install
- Install the external module(s). The default location is
- /lib/modules/<kernel_release>/extra/, but a prefix may
- be added with INSTALL_MOD_PATH (discussed in section 5).
-
- clean
- Remove all generated files in the module directory only.
-
- help
- List the available targets for external modules.
-
---- 2.4 Building Separate Files
-
- It is possible to build single files that are part of a module.
- This works equally well for the kernel, a module, and even for
- external modules.
-
- Example (The module foo.ko, consist of bar.o and baz.o):
- make -C $KDIR M=$PWD bar.lst
- make -C $KDIR M=$PWD baz.o
- make -C $KDIR M=$PWD foo.ko
- make -C $KDIR M=$PWD ./
-
-
-=== 3. Creating a Kbuild File for an External Module
-
-In the last section we saw the command to build a module for the
-running kernel. The module is not actually built, however, because a
-build file is required. Contained in this file will be the name of
-the module(s) being built, along with the list of requisite source
-files. The file may be as simple as a single line:
-
- obj-m := <module_name>.o
-
-The kbuild system will build <module_name>.o from <module_name>.c,
-and, after linking, will result in the kernel module <module_name>.ko.
-The above line can be put in either a "Kbuild" file or a "Makefile."
-When the module is built from multiple sources, an additional line is
-needed listing the files:
-
- <module_name>-y := <src1>.o <src2>.o ...
-
-NOTE: Further documentation describing the syntax used by kbuild is
-located in Documentation/kbuild/makefiles.txt.
-
-The examples below demonstrate how to create a build file for the
-module 8123.ko, which is built from the following files:
-
- 8123_if.c
- 8123_if.h
- 8123_pci.c
- 8123_bin.o_shipped <= Binary blob
-
---- 3.1 Shared Makefile
-
- An external module always includes a wrapper makefile that
- supports building the module using "make" with no arguments.
- This target is not used by kbuild; it is only for convenience.
- Additional functionality, such as test targets, can be included
- but should be filtered out from kbuild due to possible name
- clashes.
-
- Example 1:
- --> filename: Makefile
- ifneq ($(KERNELRELEASE),)
- # kbuild part of makefile
- obj-m := 8123.o
- 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
-
- else
- # normal makefile
- KDIR ?= /lib/modules/`uname -r`/build
-
- default:
- $(MAKE) -C $(KDIR) M=$$PWD
-
- # Module specific targets
- genbin:
- echo "X" > 8123_bin.o_shipped
-
- endif
-
- The check for KERNELRELEASE is used to separate the two parts
- of the makefile. In the example, kbuild will only see the two
- assignments, whereas "make" will see everything except these
- two assignments. This is due to two passes made on the file:
- the first pass is by the "make" instance run on the command
- line; the second pass is by the kbuild system, which is
- initiated by the parameterized "make" in the default target.
-
---- 3.2 Separate Kbuild File and Makefile
-
- In newer versions of the kernel, kbuild will first look for a
- file named "Kbuild," and only if that is not found, will it
- then look for a makefile. Utilizing a "Kbuild" file allows us
- to split up the makefile from example 1 into two files:
-
- Example 2:
- --> filename: Kbuild
- obj-m := 8123.o
- 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
-
- --> filename: Makefile
- KDIR ?= /lib/modules/`uname -r`/build
-
- default:
- $(MAKE) -C $(KDIR) M=$$PWD
-
- # Module specific targets
- genbin:
- echo "X" > 8123_bin.o_shipped
-
- The split in example 2 is questionable due to the simplicity of
- each file; however, some external modules use makefiles
- consisting of several hundred lines, and here it really pays
- off to separate the kbuild part from the rest.
-
- The next example shows a backward compatible version.
-
- Example 3:
- --> filename: Kbuild
- obj-m := 8123.o
- 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
-
- --> filename: Makefile
- ifneq ($(KERNELRELEASE),)
- # kbuild part of makefile
- include Kbuild
-
- else
- # normal makefile
- KDIR ?= /lib/modules/`uname -r`/build
-
- default:
- $(MAKE) -C $(KDIR) M=$$PWD
-
- # Module specific targets
- genbin:
- echo "X" > 8123_bin.o_shipped
-
- endif
-
- Here the "Kbuild" file is included from the makefile. This
- allows an older version of kbuild, which only knows of
- makefiles, to be used when the "make" and kbuild parts are
- split into separate files.
-
---- 3.3 Binary Blobs
-
- Some external modules need to include an object file as a blob.
- kbuild has support for this, but requires the blob file to be
- named <filename>_shipped. When the kbuild rules kick in, a copy
- of <filename>_shipped is created with _shipped stripped off,
- giving us <filename>. This shortened filename can be used in
- the assignment to the module.
-
- Throughout this section, 8123_bin.o_shipped has been used to
- build the kernel module 8123.ko; it has been included as
- 8123_bin.o.
-
- 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
-
- Although there is no distinction between the ordinary source
- files and the binary file, kbuild will pick up different rules
- when creating the object file for the module.
-
---- 3.4 Building Multiple Modules
-
- kbuild supports building multiple modules with a single build
- file. For example, if you wanted to build two modules, foo.ko
- and bar.ko, the kbuild lines would be:
-
- obj-m := foo.o bar.o
- foo-y := <foo_srcs>
- bar-y := <bar_srcs>
-
- It is that simple!
-
-
-=== 4. Include Files
-
-Within the kernel, header files are kept in standard locations
-according to the following rule:
-
- * If the header file only describes the internal interface of a
- module, then the file is placed in the same directory as the
- source files.
- * If the header file describes an interface used by other parts
- of the kernel that are located in different directories, then
- the file is placed in include/linux/.
-
- NOTE: There are two notable exceptions to this rule: larger
- subsystems have their own directory under include/, such as
- include/scsi; and architecture specific headers are located
- under arch/$(ARCH)/include/.
-
---- 4.1 Kernel Includes
-
- To include a header file located under include/linux/, simply
- use:
-
- #include <linux/module.h>
-
- kbuild will add options to "gcc" so the relevant directories
- are searched.
-
---- 4.2 Single Subdirectory
-
- External modules tend to place header files in a separate
- include/ directory where their source is located, although this
- is not the usual kernel style. To inform kbuild of the
- directory, use either ccflags-y or CFLAGS_<filename>.o.
-
- Using the example from section 3, if we moved 8123_if.h to a
- subdirectory named include, the resulting kbuild file would
- look like:
-
- --> filename: Kbuild
- obj-m := 8123.o
-
- ccflags-y := -Iinclude
- 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
-
- Note that in the assignment there is no space between -I and
- the path. This is a limitation of kbuild: there must be no
- space present.
-
---- 4.3 Several Subdirectories
-
- kbuild can handle files that are spread over several directories.
- Consider the following example:
-
- .
- |__ src
- | |__ complex_main.c
- | |__ hal
- | |__ hardwareif.c
- | |__ include
- | |__ hardwareif.h
- |__ include
- |__ complex.h
-
- To build the module complex.ko, we then need the following
- kbuild file:
-
- --> filename: Kbuild
- obj-m := complex.o
- complex-y := src/complex_main.o
- complex-y += src/hal/hardwareif.o
-
- ccflags-y := -I$(src)/include
- ccflags-y += -I$(src)/src/hal/include
-
- As you can see, kbuild knows how to handle object files located
- in other directories. The trick is to specify the directory
- relative to the kbuild file's location. That being said, this
- is NOT recommended practice.
-
- For the header files, kbuild must be explicitly told where to
- look. When kbuild executes, the current directory is always the
- root of the kernel tree (the argument to "-C") and therefore an
- absolute path is needed. $(src) provides the absolute path by
- pointing to the directory where the currently executing kbuild
- file is located.
-
-
-=== 5. Module Installation
-
-Modules which are included in the kernel are installed in the
-directory:
-
- /lib/modules/$(KERNELRELEASE)/kernel/
-
-And external modules are installed in:
-
- /lib/modules/$(KERNELRELEASE)/extra/
-
---- 5.1 INSTALL_MOD_PATH
-
- Above are the default directories but as always some level of
- customization is possible. A prefix can be added to the
- installation path using the variable INSTALL_MOD_PATH:
-
- $ make INSTALL_MOD_PATH=/frodo modules_install
- => Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel/
-
- INSTALL_MOD_PATH may be set as an ordinary shell variable or,
- as shown above, can be specified on the command line when
- calling "make." This has effect when installing both in-tree
- and out-of-tree modules.
-
---- 5.2 INSTALL_MOD_DIR
-
- External modules are by default installed to a directory under
- /lib/modules/$(KERNELRELEASE)/extra/, but you may wish to
- locate modules for a specific functionality in a separate
- directory. For this purpose, use INSTALL_MOD_DIR to specify an
- alternative name to "extra."
-
- $ make INSTALL_MOD_DIR=gandalf -C $KDIR \
- M=$PWD modules_install
- => Install dir: /lib/modules/$(KERNELRELEASE)/gandalf/
-
-
-=== 6. Module Versioning
-
-Module versioning is enabled by the CONFIG_MODVERSIONS tag, and is used
-as a simple ABI consistency check. A CRC value of the full prototype
-for an exported symbol is created. When a module is loaded/used, the
-CRC values contained in the kernel are compared with similar values in
-the module; if they are not equal, the kernel refuses to load the
-module.
-
-Module.symvers contains a list of all exported symbols from a kernel
-build.
-
---- 6.1 Symbols From the Kernel (vmlinux + modules)
-
- During a kernel build, a file named Module.symvers will be
- generated. Module.symvers contains all exported symbols from
- the kernel and compiled modules. For each symbol, the
- corresponding CRC value is also stored.
-
- The syntax of the Module.symvers file is:
- <CRC> <Symbol> <module>
-
- 0x2d036834 scsi_remove_host drivers/scsi/scsi_mod
-
- For a kernel build without CONFIG_MODVERSIONS enabled, the CRC
- would read 0x00000000.
-
- Module.symvers serves two purposes:
- 1) It lists all exported symbols from vmlinux and all modules.
- 2) It lists the CRC if CONFIG_MODVERSIONS is enabled.
-
---- 6.2 Symbols and External Modules
-
- When building an external module, the build system needs access
- to the symbols from the kernel to check if all external symbols
- are defined. This is done in the MODPOST step. modpost obtains
- the symbols by reading Module.symvers from the kernel source
- tree. If a Module.symvers file is present in the directory
- where the external module is being built, this file will be
- read too. During the MODPOST step, a new Module.symvers file
- will be written containing all exported symbols that were not
- defined in the kernel.
-
---- 6.3 Symbols From Another External Module
-
- Sometimes, an external module uses exported symbols from
- another external module. kbuild needs to have full knowledge of
- all symbols to avoid spitting out warnings about undefined
- symbols. Three solutions exist for this situation.
-
- NOTE: The method with a top-level kbuild file is recommended
- but may be impractical in certain situations.
-
- Use a top-level kbuild file
- If you have two modules, foo.ko and bar.ko, where
- foo.ko needs symbols from bar.ko, you can use a
- common top-level kbuild file so both modules are
- compiled in the same build. Consider the following
- directory layout:
-
- ./foo/ <= contains foo.ko
- ./bar/ <= contains bar.ko
-
- The top-level kbuild file would then look like:
-
- #./Kbuild (or ./Makefile):
- obj-y := foo/ bar/
-
- And executing
-
- $ make -C $KDIR M=$PWD
-
- will then do the expected and compile both modules with
- full knowledge of symbols from either module.
-
- Use an extra Module.symvers file
- When an external module is built, a Module.symvers file
- is generated containing all exported symbols which are
- not defined in the kernel. To get access to symbols
- from bar.ko, copy the Module.symvers file from the
- compilation of bar.ko to the directory where foo.ko is
- built. During the module build, kbuild will read the
- Module.symvers file in the directory of the external
- module, and when the build is finished, a new
- Module.symvers file is created containing the sum of
- all symbols defined and not part of the kernel.
-
- Use "make" variable KBUILD_EXTRA_SYMBOLS
- If it is impractical to copy Module.symvers from
- another module, you can assign a space separated list
- of files to KBUILD_EXTRA_SYMBOLS in your build file.
- These files will be loaded by modpost during the
- initialization of its symbol tables.
-
-
-=== 7. Tips & Tricks
-
---- 7.1 Testing for CONFIG_FOO_BAR
-
- Modules often need to check for certain CONFIG_ options to
- decide if a specific feature is included in the module. In
- kbuild this is done by referencing the CONFIG_ variable
- directly.
-
- #fs/ext2/Makefile
- obj-$(CONFIG_EXT2_FS) += ext2.o
-
- ext2-y := balloc.o bitmap.o dir.o
- ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o
-
- External modules have traditionally used "grep" to check for
- specific CONFIG_ settings directly in .config. This usage is
- broken. As introduced before, external modules should use
- kbuild for building and can therefore use the same methods as
- in-tree modules when testing for CONFIG_ definitions.
-
- Usually you want a configuration option for your kernel hack. Edit
``Kconfig`` in the appropriate directory. The Config language is
simple to use by cut and paste, and there's complete documentation in
- ``Documentation/kbuild/kconfig-language.txt``.
+ ``Documentation/kbuild/kconfig-language.rst``.
In your description of the option, make sure you address both the
expert user and the user who knows nothing about your feature.
- Edit the ``Makefile``: the CONFIG variables are exported here so you
can usually just add a "obj-$(CONFIG_xxx) += xxx.o" line. The syntax
- is documented in ``Documentation/kbuild/makefiles.txt``.
+ is documented in ``Documentation/kbuild/makefiles.rst``.
- Put yourself in ``CREDITS`` if you've done something noteworthy,
usually beyond a single file (your name should be at the top of the
...
For full documentation on the configuration files, see the file
-Documentation/kbuild/kconfig-language.txt.
+Documentation/kbuild/kconfig-language.rst.
11) Data structures
6) Any new or modified ``CONFIG`` options do not muck up the config menu and
default to off unless they meet the exception criteria documented in
- ``Documentation/kbuild/kconfig-language.txt`` Menu attributes: default value.
+ ``Documentation/kbuild/kconfig-language.rst`` Menu attributes: default value.
7) All new ``Kconfig`` options have help text.
- Solitamente vorrete un'opzione di configurazione per la vostra modifica
al kernel. Modificate ``Kconfig`` nella cartella giusta. Il linguaggio
Config è facile con copia ed incolla, e c'è una completa documentazione
- nel file ``Documentation/kbuild/kconfig-language.txt``.
+ nel file ``Documentation/kbuild/kconfig-language.rst``.
Nella descrizione della vostra opzione, assicuratevi di parlare sia agli
utenti esperti sia agli utente che non sanno nulla del vostro lavoro.
- Modificate il file ``Makefile``: le variabili CONFIG sono esportate qui,
quindi potete solitamente aggiungere una riga come la seguete
"obj-$(CONFIG_xxx) += xxx.o". La sintassi è documentata nel file
- ``Documentation/kbuild/makefiles.txt``.
+ ``Documentation/kbuild/makefiles.rst``.
- Aggiungete voi stessi in ``CREDITS`` se avete fatto qualcosa di notevole,
solitamente qualcosa che supera il singolo file (comunque il vostro nome
...
Per la documentazione completa sui file di configurazione, consultate
-il documento Documentation/kbuild/kconfig-language.txt
+il documento Documentation/kbuild/kconfig-language.rst
11) Strutture dati
6) Le opzioni ``CONFIG``, nuove o modificate, non scombussolano il menu
di configurazione e sono preimpostate come disabilitate a meno che non
- soddisfino i criteri descritti in ``Documentation/kbuild/kconfig-language.txt``
+ soddisfino i criteri descritti in ``Documentation/kbuild/kconfig-language.rst``
alla punto "Voci di menu: valori predefiniti".
7) Tutte le nuove opzioni ``Kconfig`` hanno un messaggio di aiuto.
depends on ADFS_FS
...
-要查看配置文件的完整文档，请看 Documentation/kbuild/kconfig-language.txt。
+要查看配置文件的完整文档，请看 Documentation/kbuild/kconfig-language.rst。
11) 数据结构
违规行为。
6) 任何新的或修改过的 ``CONFIG`` 选项都不会弄脏配置菜单，并默认为关闭，除非
- 它们符合 ``Documentation/kbuild/kconfig-language.txt`` 中记录的异常条件,
+ 它们符合 ``Documentation/kbuild/kconfig-language.rst`` 中记录的异常条件,
菜单属性：默认值.
7) 所有新的 ``kconfig`` 选项都有帮助文本。
# SPDX-License-Identifier: GPL-2.0
#
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
mainmenu "Linux/$(ARCH) $(KERNELVERSION) Kernel Configuration"
# SPDX-License-Identifier: GPL-2.0
#
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
menuconfig ARC_PLAT_EZNPS
# SPDX-License-Identifier: GPL-2.0
#
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
config C6X
# SPDX-License-Identifier: GPL-2.0-only
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
config TRACE_IRQFLAGS_SUPPORT
def_bool y
# SPDX-License-Identifier: GPL-2.0-only
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
# Platform selection Kconfig menu for MicroBlaze targets
#
# SPDX-License-Identifier: GPL-2.0-only
#
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
config NDS32
# SPDX-License-Identifier: GPL-2.0
#
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
config OPENRISC
# SPDX-License-Identifier: GPL-2.0
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
config PPC4xx_PCI_EXPRESS
# SPDX-License-Identifier: GPL-2.0-only
#
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
config 64BIT
# SPDX-License-Identifier: GPL-2.0
#
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
# Auxiliary display drivers configuration.
#
# SPDX-License-Identifier: GPL-2.0-only
#
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
menu "Firmware Drivers"
If you want to compile this driver as a module ( = code which can be
inserted in and removed from the running kernel whenever you want),
- say M here and read <file:Documentation/kbuild/modules.txt>.
+ say M here and read <file:Documentation/kbuild/modules.rst>.
The module will be called ms02-nv.
config MTD_DATAFLASH
This driver is also available as a module ( = code which can be
inserted in and removed from the running kernel whenever you want).
The module will be called smc91x. If you want to compile it as a
- module, say M here and read <file:Documentation/kbuild/modules.txt>.
+ module, say M here and read <file:Documentation/kbuild/modules.rst>.
config PCMCIA_SMC91C92
tristate "SMC 91Cxx PCMCIA support"
This driver is also available as a module. The module will be
called smc911x. If you want to compile it as a module, say M
- here and read <file:Documentation/kbuild/modules.txt>
+ here and read <file:Documentation/kbuild/modules.rst>
config SMSC911X
tristate "SMSC LAN911x/LAN921x families embedded ethernet support"
This driver is also available as a module. The module will be
called smsc9420. If you want to compile it as a module, say M
- here and read <file:Documentation/kbuild/modules.txt>
+ here and read <file:Documentation/kbuild/modules.rst>
endif # NET_VENDOR_SMSC
If you want to compile the driver as a module ( = code which can be
inserted in and removed from the running kernel whenever you want),
- say M here and read <file:Documentation/kbuild/modules.txt>. The
+ say M here and read <file:Documentation/kbuild/modules.rst>. The
module will be called iwl4965.
config IWL3945
If you want to compile the driver as a module ( = code which can be
inserted in and removed from the running kernel whenever you want),
- say M here and read <file:Documentation/kbuild/modules.txt>. The
+ say M here and read <file:Documentation/kbuild/modules.rst>. The
module will be called iwl3945.
menu "iwl3945 / iwl4965 Debugging Options"
If you want to compile the driver as a module ( = code which can be
inserted in and removed from the running kernel whenever you want),
- say M here and read <file:Documentation/kbuild/modules.txt>. The
+ say M here and read <file:Documentation/kbuild/modules.rst>. The
module will be called iwlwifi.
if IWLWIFI
# SPDX-License-Identifier: GPL-2.0-only
#
# For a description of the syntax of this configuration file,
-# see Documentation/kbuild/kconfig-language.txt.
+# see Documentation/kbuild/kconfig-language.rst.
#
# Parport configuration.
#
If you want to compile this as a module ( = code which can be
inserted in and removed from the running kernel whenever you want),
- say M here and read <file:Documentation/kbuild/modules.txt> and
+ say M here and read <file:Documentation/kbuild/modules.rst> and
<file:Documentation/scsi/scsi.txt>. The module will be called ch.o.
If unsure, say N.
This driver is also available as a module. This module will be
called zfcp. If you want to compile it as a module, say M here
- and read <file:Documentation/kbuild/modules.txt>.
+ and read <file:Documentation/kbuild/modules.rst>.
config SCSI_PMCRAID
tristate "PMC SIERRA Linux MaxRAID adapter support"
This driver is also available as a module. The module will be
called sm750fb. If you want to compile it as a module, say M
- here and read <file:Documentation/kbuild/modules.txt>.
+ here and read <file:Documentation/kbuild/modules.rst>.
This code is also available as a module ( = code which can be
inserted in and removed from the running kernel whenever you want).
The module will be called audio. If you want to compile it as a
- module, say M here and read <file:Documentation/kbuild/modules.txt>.
+ module, say M here and read <file:Documentation/kbuild/modules.rst>.
config USB_EMI26
tristate "EMI 2|6 USB Audio interface support"
inserted in and removed from the running kernel whenever you want).
The module will be called legousbtower. If you want to compile it as
a module, say M here and read
- <file:Documentation/kbuild/modules.txt>.
+ <file:Documentation/kbuild/modules.rst>.
config USB_LCD
tristate "USB LCD driver support"
If you want to compile this as a module (=code which can be
inserted into and removed from the running kernel), say M
- here and read <file:Documentation/kbuild/modules.txt>. The module
+ here and read <file:Documentation/kbuild/modules.rst>. The module
will be called amba-clcd.
config FB_ACORN
This driver is also available as a module ( = code which can be
inserted and removed from the running kernel whenever you want). The
module will be called pxafb. If you want to compile it as a module,
- say M here and read <file:Documentation/kbuild/modules.txt>.
+ say M here and read <file:Documentation/kbuild/modules.rst>.
If unsure, say N.
This driver is also available as a module ( = code which can be
inserted and removed from the running kernel whenever you want). The
module will be called w100fb. If you want to compile it as a module,
- say M here and read <file:Documentation/kbuild/modules.txt>.
+ say M here and read <file:Documentation/kbuild/modules.rst>.
If unsure, say N.
This driver is also available as a module ( = code which can be
inserted and removed from the running kernel whenever you want). The
module will be called tmiofb. If you want to compile it as a module,
- say M here and read <file:Documentation/kbuild/modules.txt>.
+ say M here and read <file:Documentation/kbuild/modules.rst>.
If unsure, say N.
This driver is also available as a module ( = code which can be
inserted and removed from the running kernel whenever you want). The
module will be called s3c2410fb. If you want to compile it as a module,
- say M here and read <file:Documentation/kbuild/modules.txt>.
+ say M here and read <file:Documentation/kbuild/modules.rst>.
If unsure, say N.
config FB_S3C2410_DEBUG
This driver is also available as a module ( = code which can be
inserted and removed from the running kernel whenever you want). The
module will be called sm501fb. If you want to compile it as a module,
- say M here and read <file:Documentation/kbuild/modules.txt>.
+ say M here and read <file:Documentation/kbuild/modules.rst>.
If unsure, say N.
This driver is also available as a module. The module will be
called sm712fb. If you want to compile it as a module, say M
- here and read <file:Documentation/kbuild/modules.txt>.
+ here and read <file:Documentation/kbuild/modules.rst>.
source "drivers/video/fbdev/omap/Kconfig"
source "drivers/video/fbdev/omap2/Kconfig"
equivalent of the iptables limit match.
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
config BRIDGE_EBT_MARK
tristate "ebt: mark filter support"
and OUTPUT chains.
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
# security table for MAC policy
config IP_NF_SECURITY
and OUTPUT chains.
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
# security table for MAC policy
config IP6_NF_SECURITY
the tables, chains, rules.
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
config NETFILTER_XT_TARGET_SECMARK
tristate '"SECMARK" target support'
eg. UNICAST, LOCAL, BROADCAST, ...
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
config NETFILTER_XT_MATCH_BPF
tristate '"bpf" match support'
comments in your iptables ruleset.
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
config NETFILTER_XT_MATCH_CONNBYTES
tristate '"connbytes" per-connection counter match support'
number of bytes and/or packets for each direction within a connection.
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
config NETFILTER_XT_MATCH_CONNLABEL
tristate '"connlabel" match support'
and DCCP flags.
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
config NETFILTER_XT_MATCH_DEVGROUP
tristate '"devgroup" match support'
byte counter.
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
config NETFILTER_XT_MATCH_RATEEST
tristate '"rateest" match support'
in tc world.
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
config NETFILTER_XT_MATCH_RECENT
tristate '"recent" match support'
and SCTP chunk types.
If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>. If unsure, say `N'.
+ <file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
config NETFILTER_XT_MATCH_SOCKET
tristate '"socket" match support'
This protocol support is also available as a module ( = code which
can be inserted in and removed from the running kernel whenever you
want). The module will be called tipc. If you want to compile it
- as a module, say M here and read <file:Documentation/kbuild/modules.txt>.
+ as a module, say M here and read <file:Documentation/kbuild/modules.rst>.
If in doubt, say N.
######
# gcc support functions
-# See documentation in Documentation/kbuild/makefiles.txt
+# See documentation in Documentation/kbuild/makefiles.rst
# cc-cross-prefix
# Usage: CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu- m68k-linux-)
# if_changed_dep - as if_changed, but uses fixdep to reveal dependencies
# including used config symbols
# if_changed_rule - as if_changed but execute rule instead
-# See Documentation/kbuild/makefiles.txt for more info
+# See Documentation/kbuild/makefiles.rst for more info
ifneq ($(KBUILD_NOCMDDEP),1)
# Check if both arguments are the same including their order. Result is empty
#
# Both C and C++ are supported, but preferred language is C for such utilities.
#
-# Sample syntax (see Documentation/kbuild/makefiles.txt for reference)
+# Sample syntax (see Documentation/kbuild/makefiles.rst for reference)
# hostprogs-y := bin2hex
# Will compile bin2hex.c and create an executable named bin2hex
#
}
fprintf(stderr,
- "For a resolution refer to Documentation/kbuild/kconfig-language.txt\n"
+ "For a resolution refer to Documentation/kbuild/kconfig-language.rst\n"
"subsection \"Kconfig recursive dependency limitations\"\n"
"\n");
Kconfig:11:error: recursive dependency detected!
Kconfig:11: symbol B is selected by B
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
subsection "Kconfig recursive dependency limitations"
Kconfig:5:error: recursive dependency detected!
Kconfig:5: symbol A depends on A
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
subsection "Kconfig recursive dependency limitations"
Kconfig:17:error: recursive dependency detected!
Kconfig:17: symbol C1 depends on C2
Kconfig:21: symbol C2 depends on C1
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
subsection "Kconfig recursive dependency limitations"
Kconfig:32:error: recursive dependency detected!
Kconfig:32: symbol D2 is selected by D1
Kconfig:27: symbol D1 depends on D2
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
subsection "Kconfig recursive dependency limitations"
Kconfig:37:error: recursive dependency detected!
Kconfig:37: symbol E1 depends on E2
Kconfig:42: symbol E2 is implied by E1
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
subsection "Kconfig recursive dependency limitations"
Kconfig:60:error: recursive dependency detected!
Kconfig:60: symbol G depends on G
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
subsection "Kconfig recursive dependency limitations"
Kconfig:51:error: recursive dependency detected!
Kconfig:51: symbol F2 depends on F1
Kconfig:49: symbol F1 default value contains F2
-For a resolution refer to Documentation/kbuild/kconfig-language.txt
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
subsection "Kconfig recursive dependency limitations"
This driver is also available as a module ( = code which can be
inserted in and removed from the running kernel whenever you
want). If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>.
+ <file:Documentation/kbuild/modules.rst>.
config DMASOUND_PAULA
tristate "Amiga DMA sound support"
This driver is also available as a module ( = code which can be
inserted in and removed from the running kernel whenever you
want). If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>.
+ <file:Documentation/kbuild/modules.rst>.
config DMASOUND_Q40
tristate "Q40 sound support"
This driver is also available as a module ( = code which can be
inserted in and removed from the running kernel whenever you
want). If you want to compile it as a module, say M here and read
- <file:Documentation/kbuild/modules.txt>.
+ <file:Documentation/kbuild/modules.rst>.
config DMASOUND
tristate
projects / mirror_ubuntu-focal-kernel.git / commitdiff