Messages in this thread | | | From | Nick Desaulniers <> | Date | Wed, 11 Sep 2019 14:01:59 -0700 | Subject | Re: [PATCH v3 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp |
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On Wed, Sep 11, 2019 at 11:21 AM Nathan Chancellor <natechancellor@gmail.com> wrote: > > r370454 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/5c9f3cfec78f9e9ae013de9a0d092a68e3e79e002
The above link doesn't work for me (HTTP 404). PEBKAC? https://github.com/llvm/llvm-project/commit/5c9f3cfec78f9e9ae013de9a0d092a68e3e79e002
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > --- > > New patch in the series so no previous version. > > arch/powerpc/kernel/Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile > index 19f19c8c874b..aa78b3f6271e 100644 > --- a/arch/powerpc/kernel/Makefile > +++ b/arch/powerpc/kernel/Makefile > @@ -21,7 +21,7 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > > -CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector) > +CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector) -ffreestanding > > ifdef CONFIG_FUNCTION_TRACER > # Do not trace early boot code > -- > 2.23.0 >
-- Thanks, ~Nick Desaulniers
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