On January 5, 2026 1:39:07 AM PST, Uros Bizjak <[email protected]> wrote: >x86_64 zero extends 32bit operations, so for 64bit operands, >XOR r32,r32 is functionally equal to XOR r64,r64, but avoids >a REX prefix byte when legacy registers are used. > >Signed-off-by: Uros Bizjak <[email protected]> >Reviewed-by: Juergen Gross <[email protected]> >Cc: Ajay Kaher <[email protected]> >Cc: Alexey Makhalov <[email protected]> >Cc: Thomas Gleixner <[email protected]> >Cc: Ingo Molnar <[email protected]> >Cc: Borislav Petkov <[email protected]> >Cc: Dave Hansen <[email protected]> >Cc: "H. Peter Anvin" <[email protected]> >--- > arch/x86/include/asm/paravirt.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > >diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h >index 4f6ec60b4cb3..59aec695ae5f 100644 >--- a/arch/x86/include/asm/paravirt.h >+++ b/arch/x86/include/asm/paravirt.h >@@ -577,7 +577,7 @@ static __always_inline void pv_kick(int cpu) > static __always_inline bool pv_vcpu_is_preempted(long cpu) > { > return PVOP_ALT_CALLEE1(bool, lock.vcpu_is_preempted, cpu, >- "xor %%" _ASM_AX ", %%" _ASM_AX, >+ "xor %%eax, %%eax", > ALT_NOT(X86_FEATURE_VCPUPREEMPT)); > } >
Acked-by: H. Peter Anvin (Intel) <[email protected]>
