Commit d7acb92f authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

x86-64, asm: If the assembler supports fxsave64, use it 



Kbuild allows for us to probe for the existence of specific constructs
in the assembler, use them to find out if we can use fxsave64 and
permit the compiler to generate better code.

Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 7fe977da

arch/x86/Makefile

+6 −2
Original line number Diff line number Diff line
@@ -96,8 +96,12 @@ cfi := $(call as-instr,.cfi_startproc\n.cfi_rel_offset $(sp-y)$(comma)0\n.cfi_en 
# is .cfi_signal_frame supported too?

cfi-sigframe := $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONFIG_AS_CFI_SIGNAL_FRAME=1)

cfi-sections := $(call as-instr,.cfi_sections .debug_frame,-DCONFIG_AS_CFI_SECTIONS=1)

KBUILD_AFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections)

KBUILD_CFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections)



# does binutils support specific instructions?

asinstr := $(call as-instr,fxsaveq (%rax),-DCONFIG_AS_FXSAVEQ=1)



KBUILD_AFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr)

KBUILD_CFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr)



LDFLAGS := -m elf_$(UTS_MACHINE)

arch/x86/include/asm/i387.h

+1 −1
Original line number Diff line number Diff line
@@ -175,7 +175,7 @@ static inline void fpu_fxsave(struct fpu *fpu) 
	   uses any extended registers for addressing, a second REX prefix

	   will be generated (to the assembler, rex64 followed by semicolon

	   is a separate instruction), and hence the 64-bitness is lost. */

#if 0

#ifdef CONFIG_AS_FXSAVEQ

	/* Using "fxsaveq %0" would be the ideal choice, but is only supported

	   starting with gas 2.16. */

	__asm__ __volatile__("fxsaveq %0"

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