diff options
| author | H.J. Lu <[email protected]> | 2014-12-17 18:05:29 -0800 |
|---|---|---|
| committer | Ingo Molnar <[email protected]> | 2015-05-06 11:11:01 +0200 |
| commit | d9ee948d82203811a545ba26b0172fce4970d1dc (patch) | |
| tree | f0c8e0b81f2f475f89b7d332fe4811847a8861e8 | |
| parent | 3f5159a9221f19b08275b0a6388ab14392ae4eec (diff) | |
x86/asm: Use -mskip-rax-setup if supported
GCC 5 added a compiler option, -mskip-rax-setup, for x86-64. It skips
setting up the RAX register when SSE is disabled and there are no
variable arguments passed in vector registers. (According to the x86_64
ABI, %al is used as a hidden register containing the number of vector
registers used).
Since the kernel doesn't pass vector registers to functions with
variable arguments, this option can be used to optimize the x86-64
kernel.
This GCC feature was suggested by Rasmus Villemoes <[email protected]>.
This is the corresponding kernel change using it.
For kernel v3.17:
text data bss dec filename
11455921 2204048 5853184 19513153 vmlinux #with -mskip-rax-setup
11480079 2204048 5853184 19537311 vmlinux
For Kernel v4.0+ - custom config:
text data bss dec filename
10231778 3479800 16617472 30329050 vmlinux-gcc5+-mskip-rax-setup
10268797 3547448 16621568 30437813 vmlinux
Signed-off-by: H.J. Lu <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
| -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 5ba2d9ce82dc..40af1bac2b7d 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -84,6 +84,9 @@ else # Use -mpreferred-stack-boundary=3 if supported. KBUILD_CFLAGS += $(call cc-option,-mpreferred-stack-boundary=3) + # Use -mskip-rax-setup if supported. + KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup) + # FIXME - should be integrated in Makefile.cpu (Makefile_32.cpu) cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8) cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona) |