On Wed, Jul 17, 2019 at 5:02 PM Vaibhav Rustagi vaibhavrustagi@google.com wrote:
Compiling the purgatory code with clang results in using of mmx registers.
$ objdump -d arch/x86/purgatory/purgatory.ro | grep xmm
112: 0f 28 00 movaps (%rax),%xmm0 115: 0f 11 07 movups %xmm0,(%rdi) 122: 0f 28 00 movaps (%rax),%xmm0 125: 0f 11 47 10 movups %xmm0,0x10(%rdi)Add -mno-sse, -mno-mmx, -mno-sse2 to avoid generating SSE instructions.
Signed-off-by: Vaibhav Rustagi vaibhavrustagi@google.com
arch/x86/purgatory/Makefile | 1 + 1 file changed, 1 insertion(+)
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile index 3cf302b26332..3589ec4a28c7 100644 --- a/arch/x86/purgatory/Makefile +++ b/arch/x86/purgatory/Makefile @@ -20,6 +20,7 @@ KCOV_INSTRUMENT := n # sure how to relocate those. Like kexec-tools, use custom flags.
KBUILD_CFLAGS := -fno-strict-aliasing -Wall -Wstrict-prototypes -fno-zero-initialized-in-bss -fno-builtin -ffreestanding -c -Os -mcmodel=large +KBUILD_CFLAGS += -mno-mmx -mno-sse -mno-sse2
Yep, this is a commonly recurring bug in the kernel, observed again and again for Clang builds. The top level Makefile carefully sets KBUILD_CFLAGS, then lower subdirs in the kernel wipe them away with `:=` assignment. Invariably important flags don't always get re-added. In this case, these flags are used in arch/x86/Makefile, but not here and should be IMO. Thanks for the patch. Reviewed-by: Nick Desaulniers ndesaulniers@google.com
(Note that arch/x86/Makefile additionally sets -mno-3dnow and -mno-avx (if supported by the compiler). Not sure if the maintainers would like a v2 with those added, and we don't strictly need them yet, but we may someday).