On Wed, Aug 19, 2020 at 12:16:53PM -0700, Nick Desaulniers wrote:
> We're reverting
> commit 5f074f3e192f ("lib/string.c: implement a basic bcmp")
> in favor of -fno-builtin-bcmp. Remove the additional definition here,
> too.
>
> arch/x86/purgatory/Makefile uses -ffreestanding, so there's no risk of
> this libcall optimization occurring for arch/x86/boot/purgatory.ro.
>
> arch/x86/boot/Makefile resets KBUILD_CFLAGS, so make sure to reset this
> flag that was set for the top level Makefile.
>
> Fixes: 4ce97317f41d ("x86/purgatory: Do not use __builtin_memcpy and __builtin_memset")
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> ---
> arch/x86/boot/Makefile | 1 +
> arch/x86/boot/string.c | 8 --------
> 2 files changed, 1 insertion(+), 8 deletions(-)
>
> diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
> index fe605205b4ce..ef7f15bfceab 100644
> --- a/arch/x86/boot/Makefile
> +++ b/arch/x86/boot/Makefile
> @@ -70,6 +70,7 @@ KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP
> KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
> KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
> +KBUILD_CFLAGS += -fno-builtin-bcmp
> GCOV_PROFILE := n
> UBSAN_SANITIZE := n
>
This should be unnecessary: KBUILD_CFLAGS in arch/x86/boot/Makefile is
set to REALMODE_CFLAGS (defined in arch/x86/Makefile), which includes
-ffreestanding.
