linux-kernel - Re: [tip: x86/fpu] x86/fpu: Use XSAVE{,OPT,C,S} and XRSTOR{,S} mnemonics in xstate.h

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Message-ID: <CAFULd4b_a=3xs2b_88WaDR9hLuhMqNZiMu+kNAbrgJf2MoVNnQ@mail.gmail.com>
Date: Mon, 17 Mar 2025 12:06:11 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org, 
	Ingo Molnar <mingo@...nel.org>, Andy Lutomirski <luto@...nel.org>, Brian Gerst <brgerst@...il.com>, 
	"H. Peter Anvin" <hpa@...or.com>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org
Subject: Re: [tip: x86/fpu] x86/fpu: Use XSAVE{,OPT,C,S} and XRSTOR{,S}
 mnemonics in xstate.h

On Mon, Mar 17, 2025 at 11:46 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Mon, Mar 17, 2025 at 11:28:58AM +0100, Uros Bizjak wrote:
> > > > @@ -114,10 +113,10 @@ static inline int update_pkru_in_sigframe(struct xregs_state __user *buf, u64 ma
> > > >  #define XSTATE_OP(op, st, lmask, hmask, err)                         \
> > > >       asm volatile("1:" op "\n\t"                                     \
> > > >                    "xor %[err], %[err]\n"                             \
> > > > -                  "2:\n\t"                                           \
> > > > +                  "2:\n"                                             \
> > > >                    _ASM_EXTABLE_TYPE(1b, 2b, EX_TYPE_FAULT_MCE_SAFE)  \
> > > >                    : [err] "=a" (err)                                 \
> > > > -                  : "D" (st), "m" (*st), "a" (lmask), "d" (hmask)    \
> > > > +                  : [xa] "m" (*(st)), "a" (lmask), "d" (hmask)       \
> > >
> > > This [xa] needs documenting in the comment above this.
> > >
> > > What does "xa" even mean?
> >
> > xsave area.
>
> That's struct xregs_state in kernel nomenclature.
>
> And the macro's argument is called "st".
>
> And when it says [xa] there, one wonders where that "xa" comes from. So please
> add a comment above the macro explaining that.

This is an internal label for a named argument. The name shouldn't
bother anybody, it could be anything, [xa], [ptr], [arg] or whatnot,
so I see no reason why a comment should explain the choice. It's like
arguing about the name of a variable.

Uros.