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kbuild: lto: add a default list of used symbols

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With CONFIG_LTO_CLANG, LLVM bitcode has not yet been compiled into a
binary when the .mod files are generated, which means they don't yet
contain references to certain symbols that will be present in the final
binaries. This includes intrinsic functions, such as memcpy, memmove,
and memset [1], and stack protector symbols [2]. This change adds a
default symbol list to use with CONFIG_TRIM_UNUSED_KSYMS when Clang's
LTO is used.

[1] https://llvm.org/docs/LangRef.html#standard-c-c-library-intrinsics
[2] https://llvm.org/docs/LangRef.html#llvm-stackprotector-intrinsic

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201211184633.3213045-7-samitolvanen@google.com
This commit is contained in:
Sami Tolvanen 2020-12-11 10:46:23 -08:00 committed by Kees Cook
parent dd2776222a
commit fbe078d397
2 changed files with 6 additions and 0 deletions
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1
init/Kconfig
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@ -2297,6 +2297,7 @@ config TRIM_UNUSED_KSYMS
config UNUSED_KSYMS_WHITELIST config UNUSED_KSYMS_WHITELIST
string "Whitelist of symbols to keep in ksymtab" string "Whitelist of symbols to keep in ksymtab"
depends on TRIM_UNUSED_KSYMS depends on TRIM_UNUSED_KSYMS
default "scripts/lto-used-symbollist.txt" if LTO_CLANG
help help
By default, all unused exported symbols will be un-exported from the By default, all unused exported symbols will be un-exported from the
build when TRIM_UNUSED_KSYMS is selected. build when TRIM_UNUSED_KSYMS is selected.

5
scripts/lto-used-symbollist.txt Normal file
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@ -0,0 +1,5 @@
memcpy
memmove
memset
__stack_chk_fail
__stack_chk_guard