tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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: H. Peter Anvin <hpa@linux.intel.com>
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arch/x86/Makefile
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arch/x86/Makefile
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# is .cfi_signal_frame supported too?
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cfi-sigframe := $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONFIG_AS_CFI_SIGNAL_FRAME=1)
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cfi-sections := $(call as-instr,.cfi_sections .debug_frame,-DCONFIG_AS_CFI_SECTIONS=1)
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KBUILD_AFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections)
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KBUILD_CFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections)
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# does binutils support specific instructions?
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asinstr := $(call as-instr,fxsaveq (%rax),-DCONFIG_AS_FXSAVEQ=1)
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KBUILD_AFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr)
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KBUILD_CFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr)
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LDFLAGS := -m elf_$(UTS_MACHINE)
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arch/x86/include/asm/i387.h
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arch/x86/include/asm/i387.h
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uses any extended registers for addressing, a second REX prefix
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will be generated (to the assembler, rex64 followed by semicolon
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is a separate instruction), and hence the 64-bitness is lost. */
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#if 0
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#ifdef CONFIG_AS_FXSAVEQ
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/* Using "fxsaveq %0" would be the ideal choice, but is only supported
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starting with gas 2.16. */
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__asm__ __volatile__("fxsaveq %0"