kbuild: Add build salt to the kernel and modules

In Fedora, the debug information is packaged separately (foo-debuginfo) and
can be installed separately. There's been a long standing issue where only
one version of a debuginfo info package can be installed at a time. There's
been an effort for Fedora for parallel debuginfo to rectify this problem.

Part of the requirement to allow parallel debuginfo to work is that build ids
are unique between builds. The existing upstream rpm implementation ensures
this by re-calculating the build-id using the version and release as a
seed. This doesn't work 100% for the kernel because of the vDSO which is
its own binary and doesn't get updated when embedded.

Fix this by adding some data in an ELF note for both the kernel and modules.
The data is controlled via a Kconfig option so distributions can set it
to an appropriate value to ensure uniqueness between builds.

Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

diff --git a/include/linux/build-salt.h b/include/linux/build-salt.h
new file mode 100644 (file)
index 0000000..bb007bd
--- /dev/null
+++ b/include/linux/build-salt.h
@@ -0,0 +1,20 @@
+#ifndef __BUILD_SALT_H
+#define __BUILD_SALT_H
+
+#include <linux/elfnote.h>
+
+#define LINUX_ELFNOTE_BUILD_SALT       0x100
+
+#ifdef __ASSEMBLER__
+
+#define BUILD_SALT \
+       ELFNOTE(Linux, LINUX_ELFNOTE_BUILD_SALT, .asciz CONFIG_BUILD_SALT)
+
+#else
+
+#define BUILD_SALT \
+       ELFNOTE32("Linux", LINUX_ELFNOTE_BUILD_SALT, CONFIG_BUILD_SALT)
+
+#endif
+
+#endif /* __BUILD_SALT_H */

diff --git a/init/Kconfig b/init/Kconfig
index 041f3a022122d559b8588c8c24c8db37756464de..d39b31484c52d2229734019dc7659e7e1466d583 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -107,6 +107,15 @@ config LOCALVERSION_AUTO
 
          which is done within the script "scripts/setlocalversion".)
 
+config BUILD_SALT
+       string "Build ID Salt"
+       default ""
+       help
+          The build ID is used to link binaries and their debug info. Setting
+          this option will use the value in the calculation of the build id.
+          This is mostly useful for distributions which want to ensure the
+          build is unique between builds. It's safe to leave the default.
+
 config HAVE_KERNEL_GZIP
        bool
 

diff --git a/init/version.c b/init/version.c
index bfb4e3f4955e0caed1ae3d5b404f55ccdacf35a0..ef4012ec43751122eea2e55e86f9b5ec8faad3c9 100644 (file)
--- a/init/version.c
+++ b/init/version.c
@@ -7,6 +7,7 @@
  */
 
 #include <generated/compile.h>
+#include <linux/build-salt.h>
 #include <linux/export.h>
 #include <linux/uts.h>
 #include <linux/utsname.h>
@@ -49,3 +50,5 @@ const char linux_proc_banner[] =
        "%s version %s"
        " (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ")"
        " (" LINUX_COMPILER ") %s\n";
+
+BUILD_SALT;

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 1663fb19343a46fff9f4c23b6fda2a56ebce3190..dc6d714e4dcb310817de378ec88e136263ab8030 100644 (file)
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2125,10 +2125,13 @@ static int check_modname_len(struct module *mod)
  **/
 static void add_header(struct buffer *b, struct module *mod)
 {
+       buf_printf(b, "#include <linux/build-salt.h>\n");
        buf_printf(b, "#include <linux/module.h>\n");
        buf_printf(b, "#include <linux/vermagic.h>\n");
        buf_printf(b, "#include <linux/compiler.h>\n");
        buf_printf(b, "\n");
+       buf_printf(b, "BUILD_SALT;\n");
+       buf_printf(b, "\n");
        buf_printf(b, "MODULE_INFO(vermagic, VERMAGIC_STRING);\n");
        buf_printf(b, "MODULE_INFO(name, KBUILD_MODNAME);\n");
        buf_printf(b, "\n");