From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Subject: Revert "kbuild: disable clang's default use of -fmerge-all-constants" This reverts commit 87e0d4f0f37fb0c8c4aeeac46fff5e957738df79. -fno-merge-all-constants has been the default since clang-6; the minimum supported version of clang in the kernel is clang-10 (10.0.1). Link: https://lkml.kernel.org/r/20200902225911.209899-3-ndesaulniers@xxxxxxxxxx Link: https://reviews.llvm.org/rL329300. Link: https://github.com/ClangBuiltLinux/linux/issues/9 Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Suggested-by: Nathan Chancellor <natechancellor@xxxxxxxxx> Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> Reviewed-by: Fangrui Song <maskray@xxxxxxxxxx> Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx> Reviewed-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Cc: Marco Elver <elver@xxxxxxxxxx> Cc: Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx> Cc: Alexei Starovoitov <ast@xxxxxxxxxx> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Makefile | 9 --------- 1 file changed, 9 deletions(-) --- a/Makefile~revert-kbuild-disable-clangs-default-use-of-fmerge-all-constants +++ a/Makefile @@ -921,15 +921,6 @@ KBUILD_CFLAGS += $(call cc-disable-warni # disable invalid "can't wrap" optimizations for signed / pointers KBUILD_CFLAGS += $(call cc-option,-fno-strict-overflow) -# clang sets -fmerge-all-constants by default as optimization, but this -# is non-conforming behavior for C and in fact breaks the kernel, so we -# need to disable it here generally. -KBUILD_CFLAGS += $(call cc-option,-fno-merge-all-constants) - -# for gcc -fno-merge-all-constants disables everything, but it is fine -# to have actual conforming behavior enabled. -KBUILD_CFLAGS += $(call cc-option,-fmerge-constants) - # Make sure -fstack-check isn't enabled (like gentoo apparently did) KBUILD_CFLAGS += $(call cc-option,-fno-stack-check,) _
