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kbuild: Add build salt to the kernel and modules

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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>
This commit is contained in:
Laura Abbott 2018-07-05 17:49:37 -07:00 committed by Masahiro Yamada
parent 934193a654
commit 9afb719e70
4 changed files with 35 additions and 0 deletions
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20
include/linux/build-salt.h Normal file
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@ -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 */

9
init/Kconfig
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@ -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

3
init/version.c
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@ -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;

3
scripts/mod/modpost.c
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@ -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");