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SubjectRe: [tip:x86/fpu] x86-64, asm: Use fxsaveq/fxrestorq in more places
On 10/22/2010 07:11 PM, Linus Torvalds wrote:
> On Fri, Oct 22, 2010 at 6:20 PM, tip-bot for H. Peter Anvin
> <hpa@zytor.com> wrote:
>>
>> Checkin d7acb92fea932ad2e7846480aeacddc2c03c8485 made use of fxsaveq
>> in fpu_fxsave() if the assembler supports it; this adds
>> fxsaveq/fxrstorq to fxrstor_checking() and fxsave_user() as well.
>
> Hmm. I really think you should be able to do something like this
>
> #ifdef CONFIG_AS_FXSAVEQ
> #define FXSAVEQ_INSN "fxsaveq %[fx]"
> #define FXRSTORQ_INSN "fxrstorq %[fx]"
> #define FX_EXTRA(ptr)
> #else
> #define FXSAVEQ_INSN "rex64/fxsave (%[fxr])"
> #define FXRSTORQ_INSN "rex64/fxrstor (%[fxr])"
> #define FX_EXTRA(ptr) [fxr] "R" (ptr)
> #endif
>
> and then you should be able to write the actual code something like
>
> asm volatile(FXSAVEQ_INSN
> :[fx] "=m" (memory)
> :FX_EXTRA(&memory))
>
> and
>
> #define __COMMA_CONCAT(x) ,##x
> #define COMMA_CONCAT(x) __COMMA_CONCAT(x)
> asm volatile(FXRSTRORQ_INSN
> : :[fx] "m" (memory) COMMA_CONCAT(FX_EXTRA(&memory)));
>
> or something like that (obviously you'll need the exception stuff too there).
>
> With no #ifdef's in the actual code. Hmm?
>

Well sure, but it is already encapsulated in 3 inlines. To me, the
above is quite frankly quite a bit harder to read than the broken-out form.

-hpa

--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.



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