r374662 gives LLVM the ability to convert certain loops into a reference to bcmp as an optimization; this breaks prom_init_check.sh:
CALL arch/powerpc/kernel/prom_init_check.sh Error: External symbol 'bcmp' referenced from prom_init.c make[2]: *** [arch/powerpc/kernel/Makefile:196: prom_init_check] Error 1 bcmp is defined in lib/string.c as a wrapper for memcmp so this could be added to the whitelist. However, commit 450e7dd4001f ("powerpc/prom_init: don't use string functions from lib/") copied memcmp as prom_memcmp to avoid KASAN instrumentation so having bcmp be resolved to regular memcmp would break that assumption. Furthermore, because the compiler is the one that inserted bcmp, we cannot provide something like prom_bcmp. To prevent LLVM from being clever with optimizations like this, use -ffreestanding to tell LLVM we are not hosted so it is not free to make transformations like this. Link: https://github.com/ClangBuiltLinux/linux/issues/647 Link: https://github.com/llvm/llvm-project/commit/76cdcf25b883751d83402baea6316772aa73865c Reviewed-by: Nick Desaulneris <ndesaulni...@google.com> Signed-off-by: Nathan Chancellor <natechancel...@gmail.com> --- v1 -> v3: * New patch in the series v3 -> v4: * Rebase on v5.4-rc3. * Add Nick's reviewed-by tag. * Update the LLVM commit reference to the latest applied version (r374662) as it was originally committed as r370454, reverted in r370788, and reapplied as r374662. v4 -> v5: * Rebase on next-20191118 to avoid a conflict with commit 6266a4dadb1d ("powerpc/64s: Always disable branch profiling for prom_init.o") arch/powerpc/kernel/Makefile | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile index 3c113ae0de2b..82170c155cb6 100644 --- a/arch/powerpc/kernel/Makefile +++ b/arch/powerpc/kernel/Makefile @@ -23,6 +23,7 @@ CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector) CFLAGS_prom_init.o += -DDISABLE_BRANCH_PROFILING +CFLAGS_prom_init.o += -ffreestanding ifdef CONFIG_FUNCTION_TRACER # Do not trace early boot code -- 2.24.0