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>

1 files changed, 9 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 041f3a022122..d39b31484c52 100644
--- 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