5.4-stable review patch. If anyone has any objections, please let me know.
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From: Nathan Chancellor natechancellor@gmail.com
commit 8dcd71b45df34d9b903450fab147ee8c1e6c16b5 upstream.
LLVM revision 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.
Reviewed-by: Nick Desaulneris ndesaulniers@google.com Signed-off-by: Nathan Chancellor natechancellor@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20191119045712.39633-4-natechancellor@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/kernel/Makefile | 1 + 1 file changed, 1 insertion(+)
--- a/arch/powerpc/kernel/Makefile +++ b/arch/powerpc/kernel/Makefile @@ -21,6 +21,7 @@ CFLAGS_prom.o += $(DISABLE_LATENT_ENTROP
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