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cd238eff | 1 | ====================== |
1da177e4 | 2 | Linux Kernel Makefiles |
cd238eff | 3 | ====================== |
1da177e4 LT |
4 | |
5 | This document describes the Linux kernel Makefiles. | |
6 | ||
cd238eff | 7 | .. Table of Contents |
1da177e4 LT |
8 | |
9 | === 1 Overview | |
10 | === 2 Who does what | |
11 | === 3 The kbuild files | |
12 | --- 3.1 Goal definitions | |
13 | --- 3.2 Built-in object goals - obj-y | |
14 | --- 3.3 Loadable module goals - obj-m | |
15 | --- 3.4 Objects which export symbols | |
16 | --- 3.5 Library file goals - lib-y | |
17 | --- 3.6 Descending down in directories | |
18 | --- 3.7 Compilation flags | |
19 | --- 3.8 Command line dependency | |
20 | --- 3.9 Dependency tracking | |
21 | --- 3.10 Special Rules | |
20a468b5 | 22 | --- 3.11 $(CC) support functions |
691ef3e7 | 23 | --- 3.12 $(LD) support functions |
1da177e4 LT |
24 | |
25 | === 4 Host Program support | |
26 | --- 4.1 Simple Host Program | |
27 | --- 4.2 Composite Host Programs | |
62e22107 MY |
28 | --- 4.3 Using C++ for host programs |
29 | --- 4.4 Controlling compiler options for host programs | |
30 | --- 4.5 When host programs are actually built | |
1da177e4 | 31 | |
e079a08c MY |
32 | === 5 Userspace Program support |
33 | --- 5.1 Simple Userspace Program | |
34 | --- 5.2 Composite Userspace Programs | |
35 | --- 5.3 Controlling compiler options for userspace programs | |
36 | --- 5.4 When userspace programs are actually built | |
37 | ||
38 | === 6 Kbuild clean infrastructure | |
39 | ||
40 | === 7 Architecture Makefiles | |
41 | --- 7.1 Set variables to tweak the build to the architecture | |
42 | --- 7.2 Add prerequisites to archheaders: | |
43 | --- 7.3 Add prerequisites to archprepare: | |
44 | --- 7.4 List directories to visit when descending | |
45 | --- 7.5 Architecture-specific boot images | |
46 | --- 7.6 Building non-kbuild targets | |
47 | --- 7.7 Commands useful for building a boot image | |
48 | --- 7.8 Custom kbuild commands | |
49 | --- 7.9 Preprocessing linker scripts | |
50 | --- 7.10 Generic header files | |
51 | --- 7.11 Post-link pass | |
52 | ||
53 | === 8 Kbuild syntax for exported headers | |
54 | --- 8.1 no-export-headers | |
55 | --- 8.2 generic-y | |
56 | --- 8.3 generated-y | |
57 | --- 8.4 mandatory-y | |
58 | ||
59 | === 9 Kbuild Variables | |
60 | === 10 Makefile language | |
61 | === 11 Credits | |
62 | === 12 TODO | |
1da177e4 | 63 | |
cd238eff MCC |
64 | 1 Overview |
65 | ========== | |
1da177e4 | 66 | |
cd238eff | 67 | The Makefiles have five parts:: |
1da177e4 LT |
68 | |
69 | Makefile the top Makefile. | |
70 | .config the kernel configuration file. | |
71 | arch/$(ARCH)/Makefile the arch Makefile. | |
72 | scripts/Makefile.* common rules etc. for all kbuild Makefiles. | |
73 | kbuild Makefiles there are about 500 of these. | |
74 | ||
75 | The top Makefile reads the .config file, which comes from the kernel | |
76 | configuration process. | |
77 | ||
78 | The top Makefile is responsible for building two major products: vmlinux | |
79 | (the resident kernel image) and modules (any module files). | |
80 | It builds these goals by recursively descending into the subdirectories of | |
81 | the kernel source tree. | |
82 | The list of subdirectories which are visited depends upon the kernel | |
83 | configuration. The top Makefile textually includes an arch Makefile | |
84 | with the name arch/$(ARCH)/Makefile. The arch Makefile supplies | |
85 | architecture-specific information to the top Makefile. | |
86 | ||
87 | Each subdirectory has a kbuild Makefile which carries out the commands | |
88 | passed down from above. The kbuild Makefile uses information from the | |
39e6e9cf | 89 | .config file to construct various file lists used by kbuild to build |
1da177e4 LT |
90 | any built-in or modular targets. |
91 | ||
92 | scripts/Makefile.* contains all the definitions/rules etc. that | |
93 | are used to build the kernel based on the kbuild makefiles. | |
94 | ||
95 | ||
cd238eff MCC |
96 | 2 Who does what |
97 | =============== | |
1da177e4 LT |
98 | |
99 | People have four different relationships with the kernel Makefiles. | |
100 | ||
101 | *Users* are people who build kernels. These people type commands such as | |
102 | "make menuconfig" or "make". They usually do not read or edit | |
103 | any kernel Makefiles (or any other source files). | |
104 | ||
105 | *Normal developers* are people who work on features such as device | |
106 | drivers, file systems, and network protocols. These people need to | |
a07f6033 | 107 | maintain the kbuild Makefiles for the subsystem they are |
1da177e4 LT |
108 | working on. In order to do this effectively, they need some overall |
109 | knowledge about the kernel Makefiles, plus detailed knowledge about the | |
110 | public interface for kbuild. | |
111 | ||
112 | *Arch developers* are people who work on an entire architecture, such | |
113 | as sparc or ia64. Arch developers need to know about the arch Makefile | |
114 | as well as kbuild Makefiles. | |
115 | ||
116 | *Kbuild developers* are people who work on the kernel build system itself. | |
117 | These people need to know about all aspects of the kernel Makefiles. | |
118 | ||
119 | This document is aimed towards normal developers and arch developers. | |
120 | ||
121 | ||
cd238eff MCC |
122 | 3 The kbuild files |
123 | ================== | |
1da177e4 LT |
124 | |
125 | Most Makefiles within the kernel are kbuild Makefiles that use the | |
a07f6033 | 126 | kbuild infrastructure. This chapter introduces the syntax used in the |
1da177e4 | 127 | kbuild makefiles. |
172c3ae3 | 128 | The preferred name for the kbuild files are 'Makefile' but 'Kbuild' can |
a07f6033 | 129 | be used and if both a 'Makefile' and a 'Kbuild' file exists, then the 'Kbuild' |
172c3ae3 | 130 | file will be used. |
1da177e4 LT |
131 | |
132 | Section 3.1 "Goal definitions" is a quick intro, further chapters provide | |
133 | more details, with real examples. | |
134 | ||
cd238eff MCC |
135 | 3.1 Goal definitions |
136 | -------------------- | |
1da177e4 LT |
137 | |
138 | Goal definitions are the main part (heart) of the kbuild Makefile. | |
139 | These lines define the files to be built, any special compilation | |
140 | options, and any subdirectories to be entered recursively. | |
141 | ||
142 | The most simple kbuild makefile contains one line: | |
143 | ||
cd238eff MCC |
144 | Example:: |
145 | ||
1da177e4 LT |
146 | obj-y += foo.o |
147 | ||
5c811e59 | 148 | This tells kbuild that there is one object in that directory, named |
1da177e4 LT |
149 | foo.o. foo.o will be built from foo.c or foo.S. |
150 | ||
151 | If foo.o shall be built as a module, the variable obj-m is used. | |
152 | Therefore the following pattern is often used: | |
153 | ||
cd238eff MCC |
154 | Example:: |
155 | ||
1da177e4 LT |
156 | obj-$(CONFIG_FOO) += foo.o |
157 | ||
158 | $(CONFIG_FOO) evaluates to either y (for built-in) or m (for module). | |
159 | If CONFIG_FOO is neither y nor m, then the file will not be compiled | |
160 | nor linked. | |
161 | ||
cd238eff MCC |
162 | 3.2 Built-in object goals - obj-y |
163 | --------------------------------- | |
1da177e4 LT |
164 | |
165 | The kbuild Makefile specifies object files for vmlinux | |
a07f6033 | 166 | in the $(obj-y) lists. These lists depend on the kernel |
1da177e4 LT |
167 | configuration. |
168 | ||
169 | Kbuild compiles all the $(obj-y) files. It then calls | |
f49821ee | 170 | "$(AR) rcSTP" to merge these files into one built-in.a file. |
dee94953 MY |
171 | This is a thin archive without a symbol table. It will be later |
172 | linked into vmlinux by scripts/link-vmlinux.sh | |
1da177e4 LT |
173 | |
174 | The order of files in $(obj-y) is significant. Duplicates in | |
175 | the lists are allowed: the first instance will be linked into | |
f49821ee | 176 | built-in.a and succeeding instances will be ignored. |
1da177e4 LT |
177 | |
178 | Link order is significant, because certain functions | |
179 | (module_init() / __initcall) will be called during boot in the | |
180 | order they appear. So keep in mind that changing the link | |
a07f6033 JE |
181 | order may e.g. change the order in which your SCSI |
182 | controllers are detected, and thus your disks are renumbered. | |
1da177e4 | 183 | |
cd238eff MCC |
184 | Example:: |
185 | ||
1da177e4 LT |
186 | #drivers/isdn/i4l/Makefile |
187 | # Makefile for the kernel ISDN subsystem and device drivers. | |
188 | # Each configuration option enables a list of files. | |
2f5a2f81 | 189 | obj-$(CONFIG_ISDN_I4L) += isdn.o |
1da177e4 LT |
190 | obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o |
191 | ||
cd238eff MCC |
192 | 3.3 Loadable module goals - obj-m |
193 | --------------------------------- | |
1da177e4 | 194 | |
39fed701 | 195 | $(obj-m) specifies object files which are built as loadable |
1da177e4 LT |
196 | kernel modules. |
197 | ||
198 | A module may be built from one source file or several source | |
199 | files. In the case of one source file, the kbuild makefile | |
200 | simply adds the file to $(obj-m). | |
201 | ||
cd238eff MCC |
202 | Example:: |
203 | ||
1da177e4 LT |
204 | #drivers/isdn/i4l/Makefile |
205 | obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o | |
206 | ||
207 | Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm' | |
208 | ||
209 | If a kernel module is built from several source files, you specify | |
4f827280 MM |
210 | that you want to build a module in the same way as above; however, |
211 | kbuild needs to know which object files you want to build your | |
212 | module from, so you have to tell it by setting a $(<module_name>-y) | |
213 | variable. | |
1da177e4 | 214 | |
cd238eff MCC |
215 | Example:: |
216 | ||
1da177e4 | 217 | #drivers/isdn/i4l/Makefile |
4f827280 MM |
218 | obj-$(CONFIG_ISDN_I4L) += isdn.o |
219 | isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o | |
1da177e4 LT |
220 | |
221 | In this example, the module name will be isdn.o. Kbuild will | |
4f827280 | 222 | compile the objects listed in $(isdn-y) and then run |
1da177e4 LT |
223 | "$(LD) -r" on the list of these files to generate isdn.o. |
224 | ||
4f827280 | 225 | Due to kbuild recognizing $(<module_name>-y) for composite objects, |
cd238eff | 226 | you can use the value of a `CONFIG_` symbol to optionally include an |
4f827280 | 227 | object file as part of a composite object. |
1da177e4 | 228 | |
cd238eff MCC |
229 | Example:: |
230 | ||
1da177e4 | 231 | #fs/ext2/Makefile |
4f827280 MM |
232 | obj-$(CONFIG_EXT2_FS) += ext2.o |
233 | ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \ | |
234 | namei.o super.o symlink.o | |
235 | ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \ | |
236 | xattr_trusted.o | |
237 | ||
238 | In this example, xattr.o, xattr_user.o and xattr_trusted.o are only | |
239 | part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR) | |
240 | evaluates to 'y'. | |
1da177e4 LT |
241 | |
242 | Note: Of course, when you are building objects into the kernel, | |
243 | the syntax above will also work. So, if you have CONFIG_EXT2_FS=y, | |
244 | kbuild will build an ext2.o file for you out of the individual | |
f49821ee | 245 | parts and then link this into built-in.a, as you would expect. |
1da177e4 | 246 | |
cd238eff MCC |
247 | 3.4 Objects which export symbols |
248 | -------------------------------- | |
1da177e4 LT |
249 | |
250 | No special notation is required in the makefiles for | |
251 | modules exporting symbols. | |
252 | ||
cd238eff MCC |
253 | 3.5 Library file goals - lib-y |
254 | ------------------------------ | |
1da177e4 | 255 | |
a07f6033 | 256 | Objects listed with obj-* are used for modules, or |
f49821ee | 257 | combined in a built-in.a for that specific directory. |
1da177e4 LT |
258 | There is also the possibility to list objects that will |
259 | be included in a library, lib.a. | |
260 | All objects listed with lib-y are combined in a single | |
261 | library for that directory. | |
5d3f083d ML |
262 | Objects that are listed in obj-y and additionally listed in |
263 | lib-y will not be included in the library, since they will | |
264 | be accessible anyway. | |
a07f6033 | 265 | For consistency, objects listed in lib-m will be included in lib.a. |
1da177e4 LT |
266 | |
267 | Note that the same kbuild makefile may list files to be built-in | |
268 | and to be part of a library. Therefore the same directory | |
f49821ee | 269 | may contain both a built-in.a and a lib.a file. |
1da177e4 | 270 | |
cd238eff MCC |
271 | Example:: |
272 | ||
2f5a2f81 MM |
273 | #arch/x86/lib/Makefile |
274 | lib-y := delay.o | |
1da177e4 | 275 | |
2f5a2f81 MM |
276 | This will create a library lib.a based on delay.o. For kbuild to |
277 | actually recognize that there is a lib.a being built, the directory | |
278 | shall be listed in libs-y. | |
cd238eff | 279 | |
052ad274 | 280 | See also "6.4 List directories to visit when descending". |
39e6e9cf | 281 | |
cd238eff | 282 | Use of lib-y is normally restricted to `lib/` and `arch/*/lib`. |
1da177e4 | 283 | |
cd238eff MCC |
284 | 3.6 Descending down in directories |
285 | ---------------------------------- | |
1da177e4 LT |
286 | |
287 | A Makefile is only responsible for building objects in its own | |
288 | directory. Files in subdirectories should be taken care of by | |
289 | Makefiles in these subdirs. The build system will automatically | |
290 | invoke make recursively in subdirectories, provided you let it know of | |
291 | them. | |
292 | ||
a07f6033 | 293 | To do so, obj-y and obj-m are used. |
1da177e4 LT |
294 | ext2 lives in a separate directory, and the Makefile present in fs/ |
295 | tells kbuild to descend down using the following assignment. | |
296 | ||
cd238eff MCC |
297 | Example:: |
298 | ||
1da177e4 LT |
299 | #fs/Makefile |
300 | obj-$(CONFIG_EXT2_FS) += ext2/ | |
301 | ||
302 | If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular) | |
303 | the corresponding obj- variable will be set, and kbuild will descend | |
304 | down in the ext2 directory. | |
28f94a44 MY |
305 | |
306 | Kbuild uses this information not only to decide that it needs to visit | |
307 | the directory, but also to decide whether or not to link objects from | |
308 | the directory into vmlinux. | |
309 | ||
310 | When Kbuild descends into the directory with 'y', all built-in objects | |
311 | from that directory are combined into the built-in.a, which will be | |
312 | eventually linked into vmlinux. | |
313 | ||
314 | When Kbuild descends into the directory with 'm', in contrast, nothing | |
315 | from that directory will be linked into vmlinux. If the Makefile in | |
316 | that directory specifies obj-y, those objects will be left orphan. | |
317 | It is very likely a bug of the Makefile or of dependencies in Kconfig. | |
1da177e4 | 318 | |
cd238eff | 319 | It is good practice to use a `CONFIG_` variable when assigning directory |
1da177e4 | 320 | names. This allows kbuild to totally skip the directory if the |
cd238eff | 321 | corresponding `CONFIG_` option is neither 'y' nor 'm'. |
1da177e4 | 322 | |
cd238eff MCC |
323 | 3.7 Compilation flags |
324 | --------------------- | |
1da177e4 | 325 | |
f77bf014 | 326 | ccflags-y, asflags-y and ldflags-y |
c95940f2 NK |
327 | These three flags apply only to the kbuild makefile in which they |
328 | are assigned. They are used for all the normal cc, as and ld | |
329 | invocations happening during a recursive build. | |
f77bf014 | 330 | Note: Flags with the same behaviour were previously named: |
c95940f2 NK |
331 | EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS. |
332 | They are still supported but their usage is deprecated. | |
1da177e4 | 333 | |
eb07e1b4 | 334 | ccflags-y specifies options for compiling with $(CC). |
1da177e4 | 335 | |
cd238eff MCC |
336 | Example:: |
337 | ||
3d91a353 SD |
338 | # drivers/acpi/acpica/Makefile |
339 | ccflags-y := -Os -D_LINUX -DBUILDING_ACPICA | |
340 | ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT | |
1da177e4 LT |
341 | |
342 | This variable is necessary because the top Makefile owns the | |
a0f97e06 | 343 | variable $(KBUILD_CFLAGS) and uses it for compilation flags for the |
1da177e4 LT |
344 | entire tree. |
345 | ||
5ef87263 | 346 | asflags-y specifies assembler options. |
1da177e4 | 347 | |
cd238eff MCC |
348 | Example:: |
349 | ||
eb07e1b4 MM |
350 | #arch/sparc/kernel/Makefile |
351 | asflags-y := -ansi | |
1da177e4 | 352 | |
eb07e1b4 | 353 | ldflags-y specifies options for linking with $(LD). |
1da177e4 | 354 | |
cd238eff MCC |
355 | Example:: |
356 | ||
eb07e1b4 MM |
357 | #arch/cris/boot/compressed/Makefile |
358 | ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds | |
1da177e4 | 359 | |
720097d8 | 360 | subdir-ccflags-y, subdir-asflags-y |
eb07e1b4 | 361 | The two flags listed above are similar to ccflags-y and asflags-y. |
c95940f2 NK |
362 | The difference is that the subdir- variants have effect for the kbuild |
363 | file where they are present and all subdirectories. | |
364 | Options specified using subdir-* are added to the commandline before | |
365 | the options specified using the non-subdir variants. | |
720097d8 | 366 | |
cd238eff MCC |
367 | Example:: |
368 | ||
720097d8 SR |
369 | subdir-ccflags-y := -Werror |
370 | ||
1da177e4 | 371 | CFLAGS_$@, AFLAGS_$@ |
1da177e4 LT |
372 | CFLAGS_$@ and AFLAGS_$@ only apply to commands in current |
373 | kbuild makefile. | |
374 | ||
375 | $(CFLAGS_$@) specifies per-file options for $(CC). The $@ | |
376 | part has a literal value which specifies the file that it is for. | |
377 | ||
cd238eff MCC |
378 | Example:: |
379 | ||
1da177e4 LT |
380 | # drivers/scsi/Makefile |
381 | CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF | |
382 | CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \ | |
383 | -DGDTH_STATISTICS | |
1da177e4 | 384 | |
eb07e1b4 | 385 | These two lines specify compilation flags for aha152x.o and gdth.o. |
1da177e4 LT |
386 | |
387 | $(AFLAGS_$@) is a similar feature for source files in assembly | |
388 | languages. | |
389 | ||
cd238eff MCC |
390 | Example:: |
391 | ||
1da177e4 | 392 | # arch/arm/kernel/Makefile |
eb07e1b4 MM |
393 | AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) |
394 | AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312 | |
395 | AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt | |
396 | ||
1da177e4 | 397 | |
cd238eff MCC |
398 | 3.9 Dependency tracking |
399 | ----------------------- | |
1da177e4 LT |
400 | |
401 | Kbuild tracks dependencies on the following: | |
16886949 | 402 | |
cd238eff MCC |
403 | 1) All prerequisite files (both `*.c` and `*.h`) |
404 | 2) `CONFIG_` options used in all prerequisite files | |
1da177e4 LT |
405 | 3) Command-line used to compile target |
406 | ||
407 | Thus, if you change an option to $(CC) all affected files will | |
408 | be re-compiled. | |
409 | ||
cd238eff MCC |
410 | 3.10 Special Rules |
411 | ------------------ | |
1da177e4 LT |
412 | |
413 | Special rules are used when the kbuild infrastructure does | |
414 | not provide the required support. A typical example is | |
415 | header files generated during the build process. | |
5c811e59 | 416 | Another example are the architecture-specific Makefiles which |
a07f6033 | 417 | need special rules to prepare boot images etc. |
1da177e4 LT |
418 | |
419 | Special rules are written as normal Make rules. | |
420 | Kbuild is not executing in the directory where the Makefile is | |
421 | located, so all special rules shall provide a relative | |
422 | path to prerequisite files and target files. | |
423 | ||
424 | Two variables are used when defining special rules: | |
425 | ||
cd238eff MCC |
426 | $(src) |
427 | $(src) is a relative path which points to the directory | |
428 | where the Makefile is located. Always use $(src) when | |
429 | referring to files located in the src tree. | |
430 | ||
431 | $(obj) | |
432 | $(obj) is a relative path which points to the directory | |
433 | where the target is saved. Always use $(obj) when | |
434 | referring to generated files. | |
1da177e4 | 435 | |
cd238eff | 436 | Example:: |
1da177e4 | 437 | |
1da177e4 LT |
438 | #drivers/scsi/Makefile |
439 | $(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl | |
440 | $(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl | |
441 | ||
cd238eff MCC |
442 | This is a special rule, following the normal syntax |
443 | required by make. | |
444 | ||
445 | The target file depends on two prerequisite files. References | |
446 | to the target file are prefixed with $(obj), references | |
447 | to prerequisites are referenced with $(src) (because they are not | |
448 | generated files). | |
449 | ||
450 | $(kecho) | |
451 | echoing information to user in a rule is often a good practice | |
452 | but when execution "make -s" one does not expect to see any output | |
453 | except for warnings/errors. | |
454 | To support this kbuild defines $(kecho) which will echo out the | |
455 | text following $(kecho) to stdout except if "make -s" is used. | |
456 | ||
457 | Example:: | |
458 | ||
5410ecc0 MF |
459 | #arch/blackfin/boot/Makefile |
460 | $(obj)/vmImage: $(obj)/vmlinux.gz | |
461 | $(call if_changed,uimage) | |
462 | @$(kecho) 'Kernel: $@ is ready' | |
463 | ||
464 | ||
cd238eff MCC |
465 | 3.11 $(CC) support functions |
466 | ---------------------------- | |
20a468b5 | 467 | |
a07f6033 | 468 | The kernel may be built with several different versions of |
20a468b5 | 469 | $(CC), each supporting a unique set of features and options. |
39fed701 | 470 | kbuild provides basic support to check for valid options for $(CC). |
e95be9a5 | 471 | $(CC) is usually the gcc compiler, but other alternatives are |
20a468b5 SR |
472 | available. |
473 | ||
474 | as-option | |
a07f6033 | 475 | as-option is used to check if $(CC) -- when used to compile |
cd238eff | 476 | assembler (`*.S`) files -- supports the given option. An optional |
a07f6033 | 477 | second option may be specified if the first option is not supported. |
20a468b5 | 478 | |
cd238eff MCC |
479 | Example:: |
480 | ||
20a468b5 SR |
481 | #arch/sh/Makefile |
482 | cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),) | |
483 | ||
a07f6033 | 484 | In the above example, cflags-y will be assigned the option |
20a468b5 SR |
485 | -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC). |
486 | The second argument is optional, and if supplied will be used | |
cd238eff MCC |
487 | if first argument is not supported. |
488 | ||
e2414910 AK |
489 | as-instr |
490 | as-instr checks if the assembler reports a specific instruction | |
491 | and then outputs either option1 or option2 | |
492 | C escapes are supported in the test instruction | |
5ef87263 | 493 | Note: as-instr-option uses KBUILD_AFLAGS for assembler options |
e2414910 | 494 | |
20a468b5 | 495 | cc-option |
39fed701 GU |
496 | cc-option is used to check if $(CC) supports a given option, and if |
497 | not supported to use an optional second option. | |
20a468b5 | 498 | |
cd238eff MCC |
499 | Example:: |
500 | ||
25eb650a | 501 | #arch/x86/Makefile |
20a468b5 SR |
502 | cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) |
503 | ||
5c811e59 | 504 | In the above example, cflags-y will be assigned the option |
a07f6033 JE |
505 | -march=pentium-mmx if supported by $(CC), otherwise -march=i586. |
506 | The second argument to cc-option is optional, and if omitted, | |
20a468b5 | 507 | cflags-y will be assigned no value if first option is not supported. |
a0f97e06 | 508 | Note: cc-option uses KBUILD_CFLAGS for $(CC) options |
20a468b5 SR |
509 | |
510 | cc-option-yn | |
39e6e9cf | 511 | cc-option-yn is used to check if gcc supports a given option |
20a468b5 SR |
512 | and return 'y' if supported, otherwise 'n'. |
513 | ||
cd238eff MCC |
514 | Example:: |
515 | ||
20a468b5 SR |
516 | #arch/ppc/Makefile |
517 | biarch := $(call cc-option-yn, -m32) | |
518 | aflags-$(biarch) += -a32 | |
519 | cflags-$(biarch) += -m32 | |
39e6e9cf | 520 | |
a07f6033 JE |
521 | In the above example, $(biarch) is set to y if $(CC) supports the -m32 |
522 | option. When $(biarch) equals 'y', the expanded variables $(aflags-y) | |
523 | and $(cflags-y) will be assigned the values -a32 and -m32, | |
524 | respectively. | |
a0f97e06 | 525 | Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options |
20a468b5 | 526 | |
8417da6f MM |
527 | cc-disable-warning |
528 | cc-disable-warning checks if gcc supports a given warning and returns | |
529 | the commandline switch to disable it. This special function is needed, | |
530 | because gcc 4.4 and later accept any unknown -Wno-* option and only | |
531 | warn about it if there is another warning in the source file. | |
532 | ||
cd238eff MCC |
533 | Example:: |
534 | ||
8417da6f MM |
535 | KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) |
536 | ||
537 | In the above example, -Wno-unused-but-set-variable will be added to | |
538 | KBUILD_CFLAGS only if gcc really accepts it. | |
539 | ||
20a468b5 | 540 | cc-ifversion |
6dcb4e5e MY |
541 | cc-ifversion tests the version of $(CC) and equals the fourth parameter |
542 | if version expression is true, or the fifth (if given) if the version | |
543 | expression is false. | |
20a468b5 | 544 | |
cd238eff MCC |
545 | Example:: |
546 | ||
20a468b5 | 547 | #fs/reiserfs/Makefile |
f77bf014 | 548 | ccflags-y := $(call cc-ifversion, -lt, 0402, -O1) |
20a468b5 | 549 | |
f77bf014 | 550 | In this example, ccflags-y will be assigned the value -O1 if the |
20a468b5 | 551 | $(CC) version is less than 4.2. |
39e6e9cf | 552 | cc-ifversion takes all the shell operators: |
20a468b5 SR |
553 | -eq, -ne, -lt, -le, -gt, and -ge |
554 | The third parameter may be a text as in this example, but it may also | |
555 | be an expanded variable or a macro. | |
556 | ||
910b4046 | 557 | cc-cross-prefix |
631bcfbb | 558 | cc-cross-prefix is used to check if there exists a $(CC) in path with |
910b4046 SR |
559 | one of the listed prefixes. The first prefix where there exist a |
560 | prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found | |
561 | then nothing is returned. | |
562 | Additional prefixes are separated by a single space in the | |
563 | call of cc-cross-prefix. | |
631bcfbb GU |
564 | This functionality is useful for architecture Makefiles that try |
565 | to set CROSS_COMPILE to well-known values but may have several | |
910b4046 | 566 | values to select between. |
631bcfbb GU |
567 | It is recommended only to try to set CROSS_COMPILE if it is a cross |
568 | build (host arch is different from target arch). And if CROSS_COMPILE | |
910b4046 SR |
569 | is already set then leave it with the old value. |
570 | ||
cd238eff MCC |
571 | Example:: |
572 | ||
910b4046 SR |
573 | #arch/m68k/Makefile |
574 | ifneq ($(SUBARCH),$(ARCH)) | |
575 | ifeq ($(CROSS_COMPILE),) | |
576 | CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-) | |
577 | endif | |
578 | endif | |
579 | ||
cd238eff MCC |
580 | 3.12 $(LD) support functions |
581 | ---------------------------- | |
691ef3e7 SR |
582 | |
583 | ld-option | |
584 | ld-option is used to check if $(LD) supports the supplied option. | |
585 | ld-option takes two options as arguments. | |
586 | The second argument is an optional option that can be used if the | |
587 | first option is not supported by $(LD). | |
588 | ||
cd238eff MCC |
589 | Example:: |
590 | ||
691ef3e7 | 591 | #Makefile |
5b83df2b | 592 | LDFLAGS_vmlinux += $(call ld-option, -X) |
691ef3e7 SR |
593 | |
594 | ||
cd238eff MCC |
595 | 4 Host Program support |
596 | ====================== | |
1da177e4 LT |
597 | |
598 | Kbuild supports building executables on the host for use during the | |
599 | compilation stage. | |
600 | Two steps are required in order to use a host executable. | |
601 | ||
602 | The first step is to tell kbuild that a host program exists. This is | |
5f2fb52f | 603 | done utilising the variable "hostprogs". |
1da177e4 LT |
604 | |
605 | The second step is to add an explicit dependency to the executable. | |
39e6e9cf | 606 | This can be done in two ways. Either add the dependency in a rule, |
5f2fb52f | 607 | or utilise the variable "always-y". |
1da177e4 LT |
608 | Both possibilities are described in the following. |
609 | ||
cd238eff MCC |
610 | 4.1 Simple Host Program |
611 | ----------------------- | |
1da177e4 LT |
612 | |
613 | In some cases there is a need to compile and run a program on the | |
614 | computer where the build is running. | |
615 | The following line tells kbuild that the program bin2hex shall be | |
616 | built on the build host. | |
617 | ||
cd238eff MCC |
618 | Example:: |
619 | ||
5f2fb52f | 620 | hostprogs := bin2hex |
1da177e4 LT |
621 | |
622 | Kbuild assumes in the above example that bin2hex is made from a single | |
623 | c-source file named bin2hex.c located in the same directory as | |
624 | the Makefile. | |
39e6e9cf | 625 | |
cd238eff MCC |
626 | 4.2 Composite Host Programs |
627 | --------------------------- | |
1da177e4 LT |
628 | |
629 | Host programs can be made up based on composite objects. | |
630 | The syntax used to define composite objects for host programs is | |
631 | similar to the syntax used for kernel objects. | |
5d3f083d | 632 | $(<executable>-objs) lists all objects used to link the final |
1da177e4 LT |
633 | executable. |
634 | ||
cd238eff MCC |
635 | Example:: |
636 | ||
1da177e4 | 637 | #scripts/lxdialog/Makefile |
5f2fb52f | 638 | hostprogs := lxdialog |
1da177e4 LT |
639 | lxdialog-objs := checklist.o lxdialog.o |
640 | ||
641 | Objects with extension .o are compiled from the corresponding .c | |
a07f6033 | 642 | files. In the above example, checklist.c is compiled to checklist.o |
1da177e4 | 643 | and lxdialog.c is compiled to lxdialog.o. |
cd238eff | 644 | |
a07f6033 | 645 | Finally, the two .o files are linked to the executable, lxdialog. |
1da177e4 LT |
646 | Note: The syntax <executable>-y is not permitted for host-programs. |
647 | ||
cd238eff MCC |
648 | 4.3 Using C++ for host programs |
649 | ------------------------------- | |
1da177e4 LT |
650 | |
651 | kbuild offers support for host programs written in C++. This was | |
652 | introduced solely to support kconfig, and is not recommended | |
653 | for general use. | |
654 | ||
cd238eff MCC |
655 | Example:: |
656 | ||
1da177e4 | 657 | #scripts/kconfig/Makefile |
5f2fb52f | 658 | hostprogs := qconf |
1da177e4 LT |
659 | qconf-cxxobjs := qconf.o |
660 | ||
661 | In the example above the executable is composed of the C++ file | |
662 | qconf.cc - identified by $(qconf-cxxobjs). | |
39e6e9cf | 663 | |
39fed701 | 664 | If qconf is composed of a mixture of .c and .cc files, then an |
1da177e4 LT |
665 | additional line can be used to identify this. |
666 | ||
cd238eff MCC |
667 | Example:: |
668 | ||
1da177e4 | 669 | #scripts/kconfig/Makefile |
5f2fb52f | 670 | hostprogs := qconf |
1da177e4 LT |
671 | qconf-cxxobjs := qconf.o |
672 | qconf-objs := check.o | |
39e6e9cf | 673 | |
cd238eff MCC |
674 | 4.4 Controlling compiler options for host programs |
675 | -------------------------------------------------- | |
1da177e4 LT |
676 | |
677 | When compiling host programs, it is possible to set specific flags. | |
678 | The programs will always be compiled utilising $(HOSTCC) passed | |
96f14fe7 | 679 | the options specified in $(KBUILD_HOSTCFLAGS). |
1da177e4 | 680 | To set flags that will take effect for all host programs created |
a07f6033 | 681 | in that Makefile, use the variable HOST_EXTRACFLAGS. |
1da177e4 | 682 | |
cd238eff MCC |
683 | Example:: |
684 | ||
1da177e4 LT |
685 | #scripts/lxdialog/Makefile |
686 | HOST_EXTRACFLAGS += -I/usr/include/ncurses | |
39e6e9cf | 687 | |
1da177e4 LT |
688 | To set specific flags for a single file the following construction |
689 | is used: | |
690 | ||
cd238eff MCC |
691 | Example:: |
692 | ||
1da177e4 LT |
693 | #arch/ppc64/boot/Makefile |
694 | HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE) | |
39e6e9cf | 695 | |
1da177e4 | 696 | It is also possible to specify additional options to the linker. |
39e6e9cf | 697 | |
cd238eff MCC |
698 | Example:: |
699 | ||
1da177e4 | 700 | #scripts/kconfig/Makefile |
c86b1f93 | 701 | HOSTLDLIBS_qconf := -L$(QTDIR)/lib |
1da177e4 | 702 | |
a07f6033 JE |
703 | When linking qconf, it will be passed the extra option |
704 | "-L$(QTDIR)/lib". | |
39e6e9cf | 705 | |
cd238eff MCC |
706 | 4.5 When host programs are actually built |
707 | ----------------------------------------- | |
1da177e4 LT |
708 | |
709 | Kbuild will only build host-programs when they are referenced | |
710 | as a prerequisite. | |
711 | This is possible in two ways: | |
712 | ||
713 | (1) List the prerequisite explicitly in a special rule. | |
714 | ||
cd238eff MCC |
715 | Example:: |
716 | ||
1da177e4 | 717 | #drivers/pci/Makefile |
5f2fb52f | 718 | hostprogs := gen-devlist |
1da177e4 LT |
719 | $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist |
720 | ( cd $(obj); ./gen-devlist ) < $< | |
721 | ||
39e6e9cf | 722 | The target $(obj)/devlist.h will not be built before |
1da177e4 LT |
723 | $(obj)/gen-devlist is updated. Note that references to |
724 | the host programs in special rules must be prefixed with $(obj). | |
725 | ||
5f2fb52f | 726 | (2) Use always-y |
cd238eff | 727 | |
1da177e4 | 728 | When there is no suitable special rule, and the host program |
5f2fb52f | 729 | shall be built when a makefile is entered, the always-y |
1da177e4 LT |
730 | variable shall be used. |
731 | ||
cd238eff MCC |
732 | Example:: |
733 | ||
1da177e4 | 734 | #scripts/lxdialog/Makefile |
5f2fb52f MY |
735 | hostprogs := lxdialog |
736 | always-y := $(hostprogs) | |
1da177e4 LT |
737 | |
738 | This will tell kbuild to build lxdialog even if not referenced in | |
739 | any rule. | |
740 | ||
e079a08c MY |
741 | 5 Userspace Program support |
742 | =========================== | |
743 | ||
744 | Just like host programs, Kbuild also supports building userspace executables | |
745 | for the target architecture (i.e. the same architecture as you are building | |
746 | the kernel for). | |
747 | ||
748 | The syntax is quite similar. The difference is to use "userprogs" instead of | |
749 | "hostprogs". | |
750 | ||
751 | 5.1 Simple Userspace Program | |
752 | ---------------------------- | |
753 | ||
754 | The following line tells kbuild that the program bpf-direct shall be | |
755 | built for the target architecture. | |
756 | ||
757 | Example:: | |
758 | ||
759 | userprogs := bpf-direct | |
760 | ||
761 | Kbuild assumes in the above example that bpf-direct is made from a | |
762 | single C source file named bpf-direct.c located in the same directory | |
763 | as the Makefile. | |
764 | ||
765 | 5.2 Composite Userspace Programs | |
766 | -------------------------------- | |
767 | ||
768 | Userspace programs can be made up based on composite objects. | |
769 | The syntax used to define composite objects for userspace programs is | |
770 | similar to the syntax used for kernel objects. | |
771 | $(<executable>-objs) lists all objects used to link the final | |
772 | executable. | |
773 | ||
774 | Example:: | |
775 | ||
776 | #samples/seccomp/Makefile | |
777 | userprogs := bpf-fancy | |
778 | bpf-fancy-objs := bpf-fancy.o bpf-helper.o | |
779 | ||
780 | Objects with extension .o are compiled from the corresponding .c | |
781 | files. In the above example, bpf-fancy.c is compiled to bpf-fancy.o | |
782 | and bpf-helper.c is compiled to bpf-helper.o. | |
783 | ||
784 | Finally, the two .o files are linked to the executable, bpf-fancy. | |
785 | Note: The syntax <executable>-y is not permitted for userspace programs. | |
786 | ||
787 | 5.3 Controlling compiler options for userspace programs | |
788 | ------------------------------------------------------- | |
789 | ||
790 | When compiling userspace programs, it is possible to set specific flags. | |
791 | The programs will always be compiled utilising $(CC) passed | |
792 | the options specified in $(KBUILD_USERCFLAGS). | |
793 | To set flags that will take effect for all userspace programs created | |
794 | in that Makefile, use the variable userccflags. | |
795 | ||
796 | Example:: | |
797 | ||
798 | # samples/seccomp/Makefile | |
799 | userccflags += -I usr/include | |
800 | ||
801 | To set specific flags for a single file the following construction | |
802 | is used: | |
803 | ||
804 | Example:: | |
805 | ||
806 | bpf-helper-userccflags += -I user/include | |
807 | ||
808 | It is also possible to specify additional options to the linker. | |
809 | ||
810 | Example:: | |
811 | ||
812 | # net/bpfilter/Makefile | |
813 | bpfilter_umh-userldflags += -static | |
814 | ||
815 | When linking bpfilter_umh, it will be passed the extra option -static. | |
816 | ||
817 | 5.4 When userspace programs are actually built | |
818 | ---------------------------------------------- | |
819 | ||
820 | Same as "When host programs are actually built". | |
821 | ||
822 | 6 Kbuild clean infrastructure | |
cd238eff | 823 | ============================= |
1da177e4 | 824 | |
a07f6033 | 825 | "make clean" deletes most generated files in the obj tree where the kernel |
1da177e4 | 826 | is compiled. This includes generated files such as host programs. |
5f2fb52f MY |
827 | Kbuild knows targets listed in $(hostprogs), $(always-y), $(always-m), |
828 | $(always-), $(extra-y), $(extra-) and $(targets). They are all deleted | |
829 | during "make clean". Files matching the patterns "*.[oas]", "*.ko", plus | |
830 | some additional files generated by kbuild are deleted all over the kernel | |
831 | source tree when "make clean" is executed. | |
1da177e4 | 832 | |
1634f2bf MY |
833 | Additional files or directories can be specified in kbuild makefiles by use of |
834 | $(clean-files). | |
1da177e4 | 835 | |
cd238eff MCC |
836 | Example:: |
837 | ||
97659181 MM |
838 | #lib/Makefile |
839 | clean-files := crc32table.h | |
1da177e4 | 840 | |
bd55daf4 JR |
841 | When executing "make clean", the file "crc32table.h" will be deleted. |
842 | Kbuild will assume files to be in the same relative directory as the | |
97659181 | 843 | Makefile, except if prefixed with $(objtree). |
1da177e4 | 844 | |
1634f2bf MY |
845 | To exclude certain files or directories from make clean, use the |
846 | $(no-clean-files) variable. | |
ef8ff89b | 847 | |
1da177e4 LT |
848 | Usually kbuild descends down in subdirectories due to "obj-* := dir/", |
849 | but in the architecture makefiles where the kbuild infrastructure | |
850 | is not sufficient this sometimes needs to be explicit. | |
851 | ||
cd238eff MCC |
852 | Example:: |
853 | ||
25eb650a | 854 | #arch/x86/boot/Makefile |
eabc8bcb | 855 | subdir- := compressed |
1da177e4 LT |
856 | |
857 | The above assignment instructs kbuild to descend down in the | |
858 | directory compressed/ when "make clean" is executed. | |
859 | ||
39fed701 | 860 | To support the clean infrastructure in the Makefiles that build the |
1da177e4 LT |
861 | final bootimage there is an optional target named archclean: |
862 | ||
cd238eff MCC |
863 | Example:: |
864 | ||
25eb650a | 865 | #arch/x86/Makefile |
1da177e4 | 866 | archclean: |
25eb650a | 867 | $(Q)$(MAKE) $(clean)=arch/x86/boot |
1da177e4 | 868 | |
25eb650a WG |
869 | When "make clean" is executed, make will descend down in arch/x86/boot, |
870 | and clean as usual. The Makefile located in arch/x86/boot/ may use | |
1da177e4 LT |
871 | the subdir- trick to descend further down. |
872 | ||
873 | Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is | |
874 | included in the top level makefile, and the kbuild infrastructure | |
875 | is not operational at that point. | |
876 | ||
877 | Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will | |
878 | be visited during "make clean". | |
879 | ||
e079a08c | 880 | 7 Architecture Makefiles |
cd238eff | 881 | ======================== |
1da177e4 LT |
882 | |
883 | The top level Makefile sets up the environment and does the preparation, | |
884 | before starting to descend down in the individual directories. | |
a07f6033 JE |
885 | The top level makefile contains the generic part, whereas |
886 | arch/$(ARCH)/Makefile contains what is required to set up kbuild | |
887 | for said architecture. | |
888 | To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines | |
1da177e4 LT |
889 | a few targets. |
890 | ||
a07f6033 | 891 | When kbuild executes, the following steps are followed (roughly): |
cd238eff | 892 | |
a07f6033 | 893 | 1) Configuration of the kernel => produce .config |
1da177e4 | 894 | 2) Store kernel version in include/linux/version.h |
b22ae40e | 895 | 3) Updating all other prerequisites to the target prepare: |
1da177e4 | 896 | - Additional prerequisites are specified in arch/$(ARCH)/Makefile |
b22ae40e | 897 | 4) Recursively descend down in all directories listed in |
1da177e4 | 898 | init-* core* drivers-* net-* libs-* and build all targets. |
a07f6033 | 899 | - The values of the above variables are expanded in arch/$(ARCH)/Makefile. |
b22ae40e | 900 | 5) All object files are then linked and the resulting file vmlinux is |
a07f6033 | 901 | located at the root of the obj tree. |
1da177e4 LT |
902 | The very first objects linked are listed in head-y, assigned by |
903 | arch/$(ARCH)/Makefile. | |
b22ae40e | 904 | 6) Finally, the architecture-specific part does any required post processing |
1da177e4 LT |
905 | and builds the final bootimage. |
906 | - This includes building boot records | |
5c811e59 | 907 | - Preparing initrd images and the like |
1da177e4 LT |
908 | |
909 | ||
e079a08c | 910 | 7.1 Set variables to tweak the build to the architecture |
cd238eff | 911 | -------------------------------------------------------- |
1da177e4 | 912 | |
cd238eff MCC |
913 | LDFLAGS |
914 | Generic $(LD) options | |
1da177e4 LT |
915 | |
916 | Flags used for all invocations of the linker. | |
917 | Often specifying the emulation is sufficient. | |
918 | ||
cd238eff MCC |
919 | Example:: |
920 | ||
1da177e4 LT |
921 | #arch/s390/Makefile |
922 | LDFLAGS := -m elf_s390 | |
cd238eff | 923 | |
f77bf014 | 924 | Note: ldflags-y can be used to further customise |
a9af3305 | 925 | the flags used. See chapter 3.7. |
39e6e9cf | 926 | |
cd238eff MCC |
927 | LDFLAGS_vmlinux |
928 | Options for $(LD) when linking vmlinux | |
1da177e4 LT |
929 | |
930 | LDFLAGS_vmlinux is used to specify additional flags to pass to | |
a07f6033 | 931 | the linker when linking the final vmlinux image. |
1da177e4 LT |
932 | LDFLAGS_vmlinux uses the LDFLAGS_$@ support. |
933 | ||
cd238eff MCC |
934 | Example:: |
935 | ||
25eb650a | 936 | #arch/x86/Makefile |
1da177e4 LT |
937 | LDFLAGS_vmlinux := -e stext |
938 | ||
cd238eff MCC |
939 | OBJCOPYFLAGS |
940 | objcopy flags | |
1da177e4 LT |
941 | |
942 | When $(call if_changed,objcopy) is used to translate a .o file, | |
a07f6033 | 943 | the flags specified in OBJCOPYFLAGS will be used. |
1da177e4 LT |
944 | $(call if_changed,objcopy) is often used to generate raw binaries on |
945 | vmlinux. | |
946 | ||
cd238eff MCC |
947 | Example:: |
948 | ||
1da177e4 LT |
949 | #arch/s390/Makefile |
950 | OBJCOPYFLAGS := -O binary | |
951 | ||
952 | #arch/s390/boot/Makefile | |
953 | $(obj)/image: vmlinux FORCE | |
954 | $(call if_changed,objcopy) | |
955 | ||
a07f6033 | 956 | In this example, the binary $(obj)/image is a binary version of |
1da177e4 LT |
957 | vmlinux. The usage of $(call if_changed,xxx) will be described later. |
958 | ||
cd238eff | 959 | KBUILD_AFLAGS |
5ef87263 | 960 | Assembler flags |
1da177e4 LT |
961 | |
962 | Default value - see top level Makefile | |
963 | Append or modify as required per architecture. | |
964 | ||
cd238eff MCC |
965 | Example:: |
966 | ||
1da177e4 | 967 | #arch/sparc64/Makefile |
222d394d | 968 | KBUILD_AFLAGS += -m64 -mcpu=ultrasparc |
1da177e4 | 969 | |
cd238eff MCC |
970 | KBUILD_CFLAGS |
971 | $(CC) compiler flags | |
1da177e4 LT |
972 | |
973 | Default value - see top level Makefile | |
974 | Append or modify as required per architecture. | |
975 | ||
a0f97e06 | 976 | Often, the KBUILD_CFLAGS variable depends on the configuration. |
1da177e4 | 977 | |
cd238eff MCC |
978 | Example:: |
979 | ||
ff4eb04c PB |
980 | #arch/x86/boot/compressed/Makefile |
981 | cflags-$(CONFIG_X86_32) := -march=i386 | |
982 | cflags-$(CONFIG_X86_64) := -mcmodel=small | |
a0f97e06 | 983 | KBUILD_CFLAGS += $(cflags-y) |
1da177e4 LT |
984 | |
985 | Many arch Makefiles dynamically run the target C compiler to | |
cd238eff | 986 | probe supported options:: |
1da177e4 | 987 | |
25eb650a | 988 | #arch/x86/Makefile |
1da177e4 LT |
989 | |
990 | ... | |
991 | cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\ | |
992 | -march=pentium2,-march=i686) | |
993 | ... | |
994 | # Disable unit-at-a-time mode ... | |
a0f97e06 | 995 | KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time) |
1da177e4 LT |
996 | ... |
997 | ||
998 | ||
a07f6033 | 999 | The first example utilises the trick that a config option expands |
1da177e4 LT |
1000 | to 'y' when selected. |
1001 | ||
cd238eff | 1002 | KBUILD_AFLAGS_KERNEL |
5ef87263 | 1003 | Assembler options specific for built-in |
1da177e4 | 1004 | |
80c00ba9 | 1005 | $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile |
1da177e4 LT |
1006 | resident kernel code. |
1007 | ||
cd238eff | 1008 | KBUILD_AFLAGS_MODULE |
5ef87263 | 1009 | Assembler options specific for modules |
1da177e4 | 1010 | |
39fed701 | 1011 | $(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that |
5ef87263 | 1012 | are used for assembler. |
cd238eff | 1013 | |
2eebb7ab | 1014 | From commandline AFLAGS_MODULE shall be used (see kbuild.rst). |
1da177e4 | 1015 | |
cd238eff MCC |
1016 | KBUILD_CFLAGS_KERNEL |
1017 | $(CC) options specific for built-in | |
80c00ba9 SR |
1018 | |
1019 | $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile | |
1020 | resident kernel code. | |
1021 | ||
cd238eff MCC |
1022 | KBUILD_CFLAGS_MODULE |
1023 | Options for $(CC) when building modules | |
6588169d | 1024 | |
39fed701 | 1025 | $(KBUILD_CFLAGS_MODULE) is used to add arch-specific options that |
6588169d | 1026 | are used for $(CC). |
2eebb7ab | 1027 | From commandline CFLAGS_MODULE shall be used (see kbuild.rst). |
6588169d | 1028 | |
cd238eff MCC |
1029 | KBUILD_LDFLAGS_MODULE |
1030 | Options for $(LD) when linking modules | |
6588169d | 1031 | |
39fed701 | 1032 | $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options |
6588169d | 1033 | used when linking modules. This is often a linker script. |
cd238eff | 1034 | |
2eebb7ab | 1035 | From commandline LDFLAGS_MODULE shall be used (see kbuild.rst). |
39e6e9cf | 1036 | |
888f0c34 MY |
1037 | KBUILD_LDS |
1038 | ||
1039 | The linker script with full path. Assigned by the top-level Makefile. | |
1040 | ||
10df0638 MY |
1041 | KBUILD_LDS_MODULE |
1042 | ||
1043 | The module linker script with full path. Assigned by the top-level | |
1044 | Makefile and additionally by the arch Makefile. | |
1045 | ||
888f0c34 MY |
1046 | KBUILD_VMLINUX_OBJS |
1047 | ||
1048 | All object files for vmlinux. They are linked to vmlinux in the same | |
1049 | order as listed in KBUILD_VMLINUX_OBJS. | |
1050 | ||
1051 | KBUILD_VMLINUX_LIBS | |
1052 | ||
1053 | All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and | |
1054 | KBUILD_VMLINUX_LIBS together specify all the object files used to | |
1055 | link vmlinux. | |
61754c18 | 1056 | |
e079a08c | 1057 | 7.2 Add prerequisites to archheaders |
cd238eff | 1058 | ------------------------------------ |
052ad274 PA |
1059 | |
1060 | The archheaders: rule is used to generate header files that | |
f3c8d4c7 | 1061 | may be installed into user space by "make header_install". |
052ad274 PA |
1062 | |
1063 | It is run before "make archprepare" when run on the | |
1064 | architecture itself. | |
1065 | ||
1066 | ||
e079a08c | 1067 | 7.3 Add prerequisites to archprepare |
cd238eff | 1068 | ------------------------------------ |
1da177e4 | 1069 | |
a07f6033 | 1070 | The archprepare: rule is used to list prerequisites that need to be |
1da177e4 | 1071 | built before starting to descend down in the subdirectories. |
a07f6033 | 1072 | This is usually used for header files containing assembler constants. |
1da177e4 | 1073 | |
cd238eff MCC |
1074 | Example:: |
1075 | ||
5bb78269 SR |
1076 | #arch/arm/Makefile |
1077 | archprepare: maketools | |
1da177e4 | 1078 | |
a07f6033 | 1079 | In this example, the file target maketools will be processed |
5bb78269 | 1080 | before descending down in the subdirectories. |
1da177e4 LT |
1081 | See also chapter XXX-TODO that describe how kbuild supports |
1082 | generating offset header files. | |
1083 | ||
1084 | ||
e079a08c | 1085 | 7.4 List directories to visit when descending |
cd238eff | 1086 | --------------------------------------------- |
1da177e4 LT |
1087 | |
1088 | An arch Makefile cooperates with the top Makefile to define variables | |
1089 | which specify how to build the vmlinux file. Note that there is no | |
1090 | corresponding arch-specific section for modules; the module-building | |
1091 | machinery is all architecture-independent. | |
1092 | ||
39e6e9cf | 1093 | |
cd238eff MCC |
1094 | head-y, init-y, core-y, libs-y, drivers-y, net-y |
1095 | $(head-y) lists objects to be linked first in vmlinux. | |
1096 | ||
1097 | $(libs-y) lists directories where a lib.a archive can be located. | |
1098 | ||
1099 | The rest list directories where a built-in.a object file can be | |
1100 | located. | |
1da177e4 | 1101 | |
cd238eff | 1102 | $(init-y) objects will be located after $(head-y). |
1da177e4 | 1103 | |
cd238eff | 1104 | Then the rest follows in this order: |
1da177e4 | 1105 | |
cd238eff MCC |
1106 | $(core-y), $(libs-y), $(drivers-y) and $(net-y). |
1107 | ||
1108 | The top level Makefile defines values for all generic directories, | |
1109 | and arch/$(ARCH)/Makefile only adds architecture-specific | |
1110 | directories. | |
1111 | ||
1112 | Example:: | |
1da177e4 | 1113 | |
1da177e4 LT |
1114 | #arch/sparc64/Makefile |
1115 | core-y += arch/sparc64/kernel/ | |
1116 | libs-y += arch/sparc64/prom/ arch/sparc64/lib/ | |
1117 | drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/ | |
1118 | ||
1119 | ||
e079a08c | 1120 | 7.5 Architecture-specific boot images |
cd238eff | 1121 | ------------------------------------- |
1da177e4 LT |
1122 | |
1123 | An arch Makefile specifies goals that take the vmlinux file, compress | |
1124 | it, wrap it in bootstrapping code, and copy the resulting files | |
1125 | somewhere. This includes various kinds of installation commands. | |
1126 | The actual goals are not standardized across architectures. | |
1127 | ||
1128 | It is common to locate any additional processing in a boot/ | |
1129 | directory below arch/$(ARCH)/. | |
1130 | ||
1131 | Kbuild does not provide any smart way to support building a | |
1132 | target specified in boot/. Therefore arch/$(ARCH)/Makefile shall | |
1133 | call make manually to build a target in boot/. | |
1134 | ||
1135 | The recommended approach is to include shortcuts in | |
1136 | arch/$(ARCH)/Makefile, and use the full path when calling down | |
1137 | into the arch/$(ARCH)/boot/Makefile. | |
1138 | ||
cd238eff MCC |
1139 | Example:: |
1140 | ||
25eb650a WG |
1141 | #arch/x86/Makefile |
1142 | boot := arch/x86/boot | |
1da177e4 LT |
1143 | bzImage: vmlinux |
1144 | $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@ | |
1145 | ||
1146 | "$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke | |
1147 | make in a subdirectory. | |
1148 | ||
5c811e59 | 1149 | There are no rules for naming architecture-specific targets, |
1da177e4 | 1150 | but executing "make help" will list all relevant targets. |
a07f6033 | 1151 | To support this, $(archhelp) must be defined. |
1da177e4 | 1152 | |
cd238eff MCC |
1153 | Example:: |
1154 | ||
25eb650a | 1155 | #arch/x86/Makefile |
1da177e4 LT |
1156 | define archhelp |
1157 | echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)' | |
39e6e9cf | 1158 | endif |
1da177e4 LT |
1159 | |
1160 | When make is executed without arguments, the first goal encountered | |
1161 | will be built. In the top level Makefile the first goal present | |
1162 | is all:. | |
a07f6033 JE |
1163 | An architecture shall always, per default, build a bootable image. |
1164 | In "make help", the default goal is highlighted with a '*'. | |
1da177e4 LT |
1165 | Add a new prerequisite to all: to select a default goal different |
1166 | from vmlinux. | |
1167 | ||
cd238eff MCC |
1168 | Example:: |
1169 | ||
25eb650a | 1170 | #arch/x86/Makefile |
39e6e9cf | 1171 | all: bzImage |
1da177e4 LT |
1172 | |
1173 | When "make" is executed without arguments, bzImage will be built. | |
1174 | ||
e079a08c | 1175 | 7.6 Building non-kbuild targets |
cd238eff | 1176 | ------------------------------- |
1da177e4 LT |
1177 | |
1178 | extra-y | |
39fed701 | 1179 | extra-y specifies additional targets created in the current |
cd238eff | 1180 | directory, in addition to any targets specified by `obj-*`. |
1da177e4 LT |
1181 | |
1182 | Listing all targets in extra-y is required for two purposes: | |
cd238eff | 1183 | |
1da177e4 | 1184 | 1) Enable kbuild to check changes in command lines |
cd238eff | 1185 | |
1da177e4 | 1186 | - When $(call if_changed,xxx) is used |
cd238eff | 1187 | |
1da177e4 LT |
1188 | 2) kbuild knows what files to delete during "make clean" |
1189 | ||
cd238eff MCC |
1190 | Example:: |
1191 | ||
25eb650a | 1192 | #arch/x86/kernel/Makefile |
1da177e4 LT |
1193 | extra-y := head.o init_task.o |
1194 | ||
a07f6033 | 1195 | In this example, extra-y is used to list object files that |
f49821ee | 1196 | shall be built, but shall not be linked as part of built-in.a. |
1da177e4 | 1197 | |
e079a08c | 1198 | 7.7 Commands useful for building a boot image |
cd238eff | 1199 | --------------------------------------------- |
1da177e4 | 1200 | |
cd238eff MCC |
1201 | Kbuild provides a few macros that are useful when building a |
1202 | boot image. | |
1da177e4 LT |
1203 | |
1204 | if_changed | |
1da177e4 LT |
1205 | if_changed is the infrastructure used for the following commands. |
1206 | ||
cd238eff MCC |
1207 | Usage:: |
1208 | ||
1da177e4 | 1209 | target: source(s) FORCE |
ef80f0a1 | 1210 | $(call if_changed,ld/objcopy/gzip/...) |
1da177e4 | 1211 | |
a07f6033 | 1212 | When the rule is evaluated, it is checked to see if any files |
5c811e59 | 1213 | need an update, or the command line has changed since the last |
1da177e4 LT |
1214 | invocation. The latter will force a rebuild if any options |
1215 | to the executable have changed. | |
1216 | Any target that utilises if_changed must be listed in $(targets), | |
1217 | otherwise the command line check will fail, and the target will | |
1218 | always be built. | |
1219 | Assignments to $(targets) are without $(obj)/ prefix. | |
1220 | if_changed may be used in conjunction with custom commands as | |
052ad274 | 1221 | defined in 6.8 "Custom kbuild commands". |
49490571 | 1222 | |
1da177e4 | 1223 | Note: It is a typical mistake to forget the FORCE prerequisite. |
49490571 PBG |
1224 | Another common pitfall is that whitespace is sometimes |
1225 | significant; for instance, the below will fail (note the extra space | |
cd238eff MCC |
1226 | after the comma):: |
1227 | ||
49490571 | 1228 | target: source(s) FORCE |
1da177e4 | 1229 | |
cd238eff MCC |
1230 | **WRONG!** $(call if_changed, ld/objcopy/gzip/...) |
1231 | ||
1232 | Note: | |
1233 | if_changed should not be used more than once per target. | |
bb81955f | 1234 | It stores the executed command in a corresponding .cmd |
cd238eff | 1235 | |
bb81955f DG |
1236 | file and multiple calls would result in overwrites and |
1237 | unwanted results when the target is up to date and only the | |
1238 | tests on changed commands trigger execution of commands. | |
1239 | ||
1da177e4 | 1240 | ld |
a07f6033 | 1241 | Link target. Often, LDFLAGS_$@ is used to set specific options to ld. |
39e6e9cf | 1242 | |
cd238eff MCC |
1243 | Example:: |
1244 | ||
25eb650a | 1245 | #arch/x86/boot/Makefile |
1da177e4 LT |
1246 | LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary |
1247 | LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext | |
1248 | ||
1249 | targets += setup setup.o bootsect bootsect.o | |
1250 | $(obj)/setup $(obj)/bootsect: %: %.o FORCE | |
1251 | $(call if_changed,ld) | |
1252 | ||
a07f6033 JE |
1253 | In this example, there are two possible targets, requiring different |
1254 | options to the linker. The linker options are specified using the | |
1da177e4 | 1255 | LDFLAGS_$@ syntax - one for each potential target. |
5d3f083d | 1256 | $(targets) are assigned all potential targets, by which kbuild knows |
1da177e4 | 1257 | the targets and will: |
cd238eff | 1258 | |
1da177e4 LT |
1259 | 1) check for commandline changes |
1260 | 2) delete target during make clean | |
1261 | ||
1262 | The ": %: %.o" part of the prerequisite is a shorthand that | |
39fed701 | 1263 | frees us from listing the setup.o and bootsect.o files. |
cd238eff MCC |
1264 | |
1265 | Note: | |
1266 | It is a common mistake to forget the "targets :=" assignment, | |
1da177e4 LT |
1267 | resulting in the target file being recompiled for no |
1268 | obvious reason. | |
1269 | ||
d87e47e1 C |
1270 | objcopy |
1271 | Copy binary. Uses OBJCOPYFLAGS usually specified in | |
1272 | arch/$(ARCH)/Makefile. | |
1273 | OBJCOPYFLAGS_$@ may be used to set additional options. | |
1274 | ||
1275 | gzip | |
1276 | Compress target. Use maximum compression to compress target. | |
1277 | ||
cd238eff MCC |
1278 | Example:: |
1279 | ||
d87e47e1 C |
1280 | #arch/x86/boot/compressed/Makefile |
1281 | $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE | |
1282 | $(call if_changed,gzip) | |
1283 | ||
aab94339 | 1284 | dtc |
c1410562 | 1285 | Create flattened device tree blob object suitable for linking |
aab94339 DB |
1286 | into vmlinux. Device tree blobs linked into vmlinux are placed |
1287 | in an init section in the image. Platform code *must* copy the | |
1288 | blob to non-init memory prior to calling unflatten_device_tree(). | |
1289 | ||
cd238eff MCC |
1290 | To use this command, simply add `*.dtb` into obj-y or targets, or make |
1291 | some other target depend on `%.dtb` | |
aab94339 | 1292 | |
cd238eff | 1293 | A central rule exists to create `$(obj)/%.dtb` from `$(src)/%.dts`; |
90b335fb | 1294 | architecture Makefiles do no need to explicitly write out that rule. |
aab94339 | 1295 | |
cd238eff MCC |
1296 | Example:: |
1297 | ||
90b335fb | 1298 | targets += $(dtb-y) |
90b335fb | 1299 | DTC_FLAGS ?= -p 1024 |
1da177e4 | 1300 | |
e079a08c | 1301 | 7.8 Custom kbuild commands |
cd238eff | 1302 | -------------------------- |
1da177e4 | 1303 | |
a07f6033 | 1304 | When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand |
1da177e4 LT |
1305 | of a command is normally displayed. |
1306 | To enable this behaviour for custom commands kbuild requires | |
cd238eff MCC |
1307 | two variables to be set:: |
1308 | ||
1309 | quiet_cmd_<command> - what shall be echoed | |
1310 | cmd_<command> - the command to execute | |
1311 | ||
1312 | Example:: | |
1da177e4 | 1313 | |
1da177e4 LT |
1314 | # |
1315 | quiet_cmd_image = BUILD $@ | |
1316 | cmd_image = $(obj)/tools/build $(BUILDFLAGS) \ | |
1317 | $(obj)/vmlinux.bin > $@ | |
1318 | ||
1319 | targets += bzImage | |
1320 | $(obj)/bzImage: $(obj)/vmlinux.bin $(obj)/tools/build FORCE | |
1321 | $(call if_changed,image) | |
1322 | @echo 'Kernel: $@ is ready' | |
1323 | ||
cd238eff | 1324 | When updating the $(obj)/bzImage target, the line: |
1da177e4 | 1325 | |
cd238eff | 1326 | BUILD arch/x86/boot/bzImage |
1da177e4 LT |
1327 | |
1328 | will be displayed with "make KBUILD_VERBOSE=0". | |
39e6e9cf | 1329 | |
1da177e4 | 1330 | |
e079a08c | 1331 | 7.9 Preprocessing linker scripts |
ff4634ee | 1332 | -------------------------------- |
1da177e4 | 1333 | |
a07f6033 | 1334 | When the vmlinux image is built, the linker script |
1da177e4 LT |
1335 | arch/$(ARCH)/kernel/vmlinux.lds is used. |
1336 | The script is a preprocessed variant of the file vmlinux.lds.S | |
1337 | located in the same directory. | |
cd238eff MCC |
1338 | kbuild knows .lds files and includes a rule `*lds.S` -> `*lds`. |
1339 | ||
1340 | Example:: | |
39e6e9cf | 1341 | |
25eb650a | 1342 | #arch/x86/kernel/Makefile |
faa7bdd7 | 1343 | extra-y := vmlinux.lds |
39e6e9cf | 1344 | |
1da177e4 LT |
1345 | #Makefile |
1346 | export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH) | |
39e6e9cf | 1347 | |
faa7bdd7 | 1348 | The assignment to extra-y is used to tell kbuild to build the |
a07f6033 JE |
1349 | target vmlinux.lds. |
1350 | The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the | |
1da177e4 | 1351 | specified options when building the target vmlinux.lds. |
39e6e9cf | 1352 | |
cd238eff MCC |
1353 | When building the `*.lds` target, kbuild uses the variables:: |
1354 | ||
1355 | KBUILD_CPPFLAGS : Set in top-level Makefile | |
1356 | cppflags-y : May be set in the kbuild makefile | |
1357 | CPPFLAGS_$(@F) : Target-specific flags. | |
1358 | Note that the full filename is used in this | |
1359 | assignment. | |
1da177e4 | 1360 | |
cd238eff | 1361 | The kbuild infrastructure for `*lds` files is used in several |
5c811e59 | 1362 | architecture-specific files. |
1da177e4 | 1363 | |
e079a08c | 1364 | 7.10 Generic header files |
cd238eff | 1365 | ------------------------- |
d8ecc5cd SR |
1366 | |
1367 | The directory include/asm-generic contains the header files | |
1368 | that may be shared between individual architectures. | |
1369 | The recommended approach how to use a generic header file is | |
1370 | to list the file in the Kbuild file. | |
d87e47e1 | 1371 | See "7.2 generic-y" for further info on syntax etc. |
d8ecc5cd | 1372 | |
e079a08c | 1373 | 7.11 Post-link pass |
cd238eff | 1374 | ------------------- |
fbe6e37d NP |
1375 | |
1376 | If the file arch/xxx/Makefile.postlink exists, this makefile | |
1377 | will be invoked for post-link objects (vmlinux and modules.ko) | |
1378 | for architectures to run post-link passes on. Must also handle | |
1379 | the clean target. | |
1380 | ||
1381 | This pass runs after kallsyms generation. If the architecture | |
1382 | needs to modify symbol locations, rather than manipulate the | |
1383 | kallsyms, it may be easier to add another postlink target for | |
1384 | .tmp_vmlinux? targets to be called from link-vmlinux.sh. | |
1385 | ||
1386 | For example, powerpc uses this to check relocation sanity of | |
1387 | the linked vmlinux file. | |
1388 | ||
e079a08c | 1389 | 8 Kbuild syntax for exported headers |
cd238eff | 1390 | ------------------------------------ |
c7bb349e | 1391 | |
39fed701 | 1392 | The kernel includes a set of headers that is exported to userspace. |
c95940f2 | 1393 | Many headers can be exported as-is but other headers require a |
c7bb349e SR |
1394 | minimal pre-processing before they are ready for user-space. |
1395 | The pre-processing does: | |
cd238eff | 1396 | |
39fed701 | 1397 | - drop kernel-specific annotations |
c7bb349e | 1398 | - drop include of compiler.h |
cd238eff | 1399 | - drop all sections that are kernel internal (guarded by `ifdef __KERNEL__`) |
c7bb349e | 1400 | |
fcc8487d | 1401 | All headers under include/uapi/, include/generated/uapi/, |
61562f98 | 1402 | arch/<arch>/include/uapi/ and arch/<arch>/include/generated/uapi/ |
fcc8487d | 1403 | are exported. |
c7bb349e | 1404 | |
fcc8487d ND |
1405 | A Kbuild file may be defined under arch/<arch>/include/uapi/asm/ and |
1406 | arch/<arch>/include/asm/ to list asm files coming from asm-generic. | |
1407 | See subsequent chapter for the syntax of the Kbuild file. | |
c7bb349e | 1408 | |
e079a08c | 1409 | 8.1 no-export-headers |
cd238eff | 1410 | --------------------- |
c7bb349e | 1411 | |
fcc8487d ND |
1412 | no-export-headers is essentially used by include/uapi/linux/Kbuild to |
1413 | avoid exporting specific headers (e.g. kvm.h) on architectures that do | |
1414 | not support it. It should be avoided as much as possible. | |
c7bb349e | 1415 | |
e079a08c | 1416 | 8.2 generic-y |
cd238eff | 1417 | ------------- |
d8ecc5cd SR |
1418 | |
1419 | If an architecture uses a verbatim copy of a header from | |
1420 | include/asm-generic then this is listed in the file | |
1421 | arch/$(ARCH)/include/asm/Kbuild like this: | |
1422 | ||
cd238eff MCC |
1423 | Example:: |
1424 | ||
d8ecc5cd SR |
1425 | #arch/x86/include/asm/Kbuild |
1426 | generic-y += termios.h | |
1427 | generic-y += rtc.h | |
1428 | ||
1429 | During the prepare phase of the build a wrapper include | |
cd238eff | 1430 | file is generated in the directory:: |
d8ecc5cd SR |
1431 | |
1432 | arch/$(ARCH)/include/generated/asm | |
1433 | ||
1434 | When a header is exported where the architecture uses | |
1435 | the generic header a similar wrapper is generated as part | |
cd238eff | 1436 | of the set of exported headers in the directory:: |
d8ecc5cd SR |
1437 | |
1438 | usr/include/asm | |
1439 | ||
1440 | The generated wrapper will in both cases look like the following: | |
1441 | ||
cd238eff MCC |
1442 | Example: termios.h:: |
1443 | ||
d8ecc5cd | 1444 | #include <asm-generic/termios.h> |
c7bb349e | 1445 | |
e079a08c | 1446 | 8.3 generated-y |
cd238eff | 1447 | --------------- |
54b880ca JH |
1448 | |
1449 | If an architecture generates other header files alongside generic-y | |
ae3f4151 | 1450 | wrappers, generated-y specifies them. |
54b880ca JH |
1451 | |
1452 | This prevents them being treated as stale asm-generic wrappers and | |
1453 | removed. | |
1454 | ||
cd238eff MCC |
1455 | Example:: |
1456 | ||
54b880ca JH |
1457 | #arch/x86/include/asm/Kbuild |
1458 | generated-y += syscalls_32.h | |
1459 | ||
e079a08c | 1460 | 8.4 mandatory-y |
cd238eff | 1461 | --------------- |
fcc8487d | 1462 | |
037fc336 | 1463 | mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild |
91998731 MY |
1464 | to define the minimum set of ASM headers that all architectures must have. |
1465 | ||
1466 | This works like optional generic-y. If a mandatory header is missing | |
1467 | in arch/$(ARCH)/include/(uapi/)/asm, Kbuild will automatically generate | |
1468 | a wrapper of the asm-generic one. | |
fcc8487d | 1469 | |
e079a08c | 1470 | 9 Kbuild Variables |
cd238eff | 1471 | ================== |
1da177e4 LT |
1472 | |
1473 | The top Makefile exports the following variables: | |
1474 | ||
1475 | VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION | |
1da177e4 LT |
1476 | These variables define the current kernel version. A few arch |
1477 | Makefiles actually use these values directly; they should use | |
1478 | $(KERNELRELEASE) instead. | |
1479 | ||
1480 | $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic | |
1481 | three-part version number, such as "2", "4", and "0". These three | |
1482 | values are always numeric. | |
1483 | ||
1484 | $(EXTRAVERSION) defines an even tinier sublevel for pre-patches | |
1485 | or additional patches. It is usually some non-numeric string | |
1486 | such as "-pre4", and is often blank. | |
1487 | ||
1488 | KERNELRELEASE | |
1da177e4 LT |
1489 | $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable |
1490 | for constructing installation directory names or showing in | |
1491 | version strings. Some arch Makefiles use it for this purpose. | |
1492 | ||
1493 | ARCH | |
1da177e4 LT |
1494 | This variable defines the target architecture, such as "i386", |
1495 | "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to | |
1496 | determine which files to compile. | |
1497 | ||
1498 | By default, the top Makefile sets $(ARCH) to be the same as the | |
1499 | host system architecture. For a cross build, a user may | |
cd238eff | 1500 | override the value of $(ARCH) on the command line:: |
1da177e4 LT |
1501 | |
1502 | make ARCH=m68k ... | |
1503 | ||
1504 | ||
1505 | INSTALL_PATH | |
1da177e4 LT |
1506 | This variable defines a place for the arch Makefiles to install |
1507 | the resident kernel image and System.map file. | |
5c811e59 | 1508 | Use this for architecture-specific install targets. |
1da177e4 LT |
1509 | |
1510 | INSTALL_MOD_PATH, MODLIB | |
1da177e4 LT |
1511 | $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module |
1512 | installation. This variable is not defined in the Makefile but | |
1513 | may be passed in by the user if desired. | |
1514 | ||
1515 | $(MODLIB) specifies the directory for module installation. | |
1516 | The top Makefile defines $(MODLIB) to | |
1517 | $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may | |
1518 | override this value on the command line if desired. | |
1519 | ||
ac031f26 | 1520 | INSTALL_MOD_STRIP |
39fed701 | 1521 | If this variable is specified, it will cause modules to be stripped |
ac031f26 | 1522 | after they are installed. If INSTALL_MOD_STRIP is '1', then the |
39fed701 | 1523 | default option --strip-debug will be used. Otherwise, the |
177b241d GE |
1524 | INSTALL_MOD_STRIP value will be used as the option(s) to the strip |
1525 | command. | |
ac031f26 TT |
1526 | |
1527 | ||
e079a08c MY |
1528 | 10 Makefile language |
1529 | ==================== | |
1da177e4 | 1530 | |
a07f6033 | 1531 | The kernel Makefiles are designed to be run with GNU Make. The Makefiles |
1da177e4 LT |
1532 | use only the documented features of GNU Make, but they do use many |
1533 | GNU extensions. | |
1534 | ||
1535 | GNU Make supports elementary list-processing functions. The kernel | |
1536 | Makefiles use a novel style of list building and manipulation with few | |
1537 | "if" statements. | |
1538 | ||
1539 | GNU Make has two assignment operators, ":=" and "=". ":=" performs | |
1540 | immediate evaluation of the right-hand side and stores an actual string | |
1541 | into the left-hand side. "=" is like a formula definition; it stores the | |
1542 | right-hand side in an unevaluated form and then evaluates this form each | |
1543 | time the left-hand side is used. | |
1544 | ||
1545 | There are some cases where "=" is appropriate. Usually, though, ":=" | |
1546 | is the right choice. | |
1547 | ||
e079a08c | 1548 | 11 Credits |
cd238eff | 1549 | ========== |
1da177e4 | 1550 | |
cd238eff MCC |
1551 | - Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net> |
1552 | - Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de> | |
1553 | - Updates by Sam Ravnborg <sam@ravnborg.org> | |
1554 | - Language QA by Jan Engelhardt <jengelh@gmx.de> | |
1da177e4 | 1555 | |
e079a08c | 1556 | 12 TODO |
cd238eff | 1557 | ======= |
1da177e4 | 1558 | |
a07f6033 | 1559 | - Describe how kbuild supports shipped files with _shipped. |
1da177e4 LT |
1560 | - Generating offset header files. |
1561 | - Add more variables to section 7? |