On 05/01/2026 3:16 pm, Jan Beulich wrote:
> On 02.01.2026 17:01, Andrew Cooper wrote:
>> On 30/12/2025 1:54 pm, Andrew Cooper wrote:
>>> --- a/xen/arch/x86/xstate.c
>>> +++ b/xen/arch/x86/xstate.c
>>> @@ -310,21 +310,21 @@ void xsave(struct vcpu *v, uint64_t mask)
>>> uint32_t hmask = mask >> 32;
>>> uint32_t lmask = mask;
>>> unsigned int fip_width = v->domain->arch.x87_fip_width;
>>> -#define XSAVE(pfx) \
>>> - if ( v->arch.xcr0_accum & XSTATE_XSAVES_ONLY ) \
>>> - asm volatile ( ".byte " pfx "0x0f,0xc7,0x2f\n" /* xsaves */ \
>>> - : "=m" (*ptr) \
>>> - : "a" (lmask), "d" (hmask), "D" (ptr) ); \
>>> - else \
>>> - alternative_io(".byte " pfx "0x0f,0xae,0x27\n", /* xsave */ \
>>> - ".byte " pfx "0x0f,0xae,0x37\n", /* xsaveopt */
>>> \
>>> - X86_FEATURE_XSAVEOPT, \
>>> - "=m" (*ptr), \
>>> - "a" (lmask), "d" (hmask), "D" (ptr))
>>> +
>>> +#define XSAVE(pfx) \
>>> + if ( v->arch.xcr0_accum & XSTATE_XSAVES_ONLY ) \
>>> + asm volatile ( "xsaves %0" \
>>> + : "=m" (*ptr) \
>>> + : "a" (lmask), "d" (hmask) ); \
>>> + else \
>>> + alternative_io("xsave %0", \
>>> + "xsaveopt %0", X86_FEATURE_XSAVEOPT, \
>>> + "=m" (*ptr), \
>>> + "a" (lmask), "d" (hmask))
>> This loses the pfx. I've fixed up locally and double checked the
>> disassembly.
> Question being: Do we want to stick to using the prefix form, when gas
> specifically has been offering a kind-of-suffix form instead from the
> very beginning (xsaves and xsaves64)?
>
> If we wanted to stick to the prefixes, I'd favor a form where the use
> sites don't need to supply the separating blank (i.e. the macro itself
> would insert it, as doing do with an empty prefix results in merely
> an indentation "issue" in the generated assembly). Thoughts?
I don't expect this macro to survive the fixes to use the compressed
format. From that point of view, "closest to the original" is least churn.
One problem with using a suffix form is that you could feed in "opt"
instead of "64" and break things in rather more subtle ways.
I'll adjust the position of the space, but I think this can keep on
using prefixes in the short term.
~Andrew
