diff options
| author | H.J. Lu | 2012-05-29 14:31:23 -0700 |
|---|---|---|
| committer | H. Peter Anvin | 2012-06-23 19:25:22 -0700 |
| commit | d9b0cde91c60da0ed5f92cdc3ac878142e6b5f27 (patch) | |
| tree | 4b90bee8a829aa5ec07118626247c12138c0c434 /arch/x86/Makefile | |
| parent | 485802a6c524e62b5924849dd727ddbb1497cc71 (diff) | |
x86-64, gcc: Use -mpreferred-stack-boundary=3 if supported
On x86-64, the standard ABI requires alignment to 16 bytes. However,
this is not actually necessary in the kernel (we don't do SSE except
in very controlled ways); and furthermore, the standard kernel entry
on x86-64 actually leaves the stack on an odd 8-byte boundary, which
means that gcc will generate extra instructions to keep the stack
*mis*aligned!
gcc 4.8 adds an -mpreferred-stack-boundary=3 option to override this
and lets us save some stack space and a handful of instructions.
Note that this causes us to pass -mno-sse twice; this is redundant,
but necessary since the cc-option test will fail unless -mno-sse is
passed on the same command line.
[ hpa: rewrote the patch description ]
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Link: http://lkml.kernel.org/r/CAMe9rOqPfy3JcZRLaUeCjBe9BVY-P6e0uaSbMi5hvS-6WwQueg@mail.gmail.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/Makefile')
| -rw-r--r-- | arch/x86/Makefile | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 1f2521434554..b0c5276861ec 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -49,6 +49,9 @@ else KBUILD_AFLAGS += -m64 KBUILD_CFLAGS += -m64 + # Use -mpreferred-stack-boundary=3 if supported. + KBUILD_CFLAGS += $(call cc-option,-mno-sse -mpreferred-stack-boundary=3) + # FIXME - should be integrated in Makefile.cpu (Makefile_32.cpu) cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8) cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona) |