linux-kernel - Re: [PATCH v3 03/11] riscv: Implement cmpxchg8/16() using Zabha

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Message-ID: <CAHVXubjQo9WaHu1FwEaJ496xpYtshrOkkw_HP9cP_3rWjnMxzw@mail.gmail.com>
Date: Thu, 18 Jul 2024 18:20:15 +0200
From: Alexandre Ghiti <alexghiti@...osinc.com>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: Alexandre Ghiti <alex@...ti.fr>, Jonathan Corbet <corbet@....net>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Conor Dooley <conor@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Andrea Parri <parri.andrea@...il.com>, 
	Nathan Chancellor <nathan@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>, 
	Arnd Bergmann <arnd@...db.de>, Leonardo Bras <leobras@...hat.com>, Guo Ren <guoren@...nel.org>, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH v3 03/11] riscv: Implement cmpxchg8/16() using Zabha

On Thu, Jul 18, 2024 at 6:06 PM Andrew Jones <ajones@...tanamicro.com> wrote:
>
> On Thu, Jul 18, 2024 at 02:50:28PM GMT, Alexandre Ghiti wrote:
> ...
> > > > +                                                                 \
> > > > +         __asm__ __volatile__ (                                  \
> > > > +                 prepend                                         \
> > > > +                 "       amocas" cas_sfx " %0, %z2, %1\n"        \
> > > > +                 append                                          \
> > > > +                 : "+&r" (r), "+A" (*(p))                        \
> > > > +                 : "rJ" (n)                                      \
> > > > +                 : "memory");                                    \
> > > > +         goto end;                                               \
> > > > + }                                                               \
> > > > +                                                                 \
> > > > +no_zabha_zacas:;                                                 \
> > > unnecessary ;
> >
> >
> > Actually it is, it fixes a warning encountered on llvm:
> > https://lore.kernel.org/linux-riscv/20240528193110.GA2196855@thelio-3990X/
>
> I'm not complaining about the 'end:' label. That one we need ';' because
> there's no following statement and labels must be followed by a statement.
> But no_zabha_zacas always has following statements.

My bad, that's another warning that is emitted by llvm and requires the ';':

../include/linux/atomic/atomic-arch-fallback.h:2026:9: warning: label
followed by a declaration is a C23 extension [-Wc23-extensions]
 2026 |         return raw_cmpxchg(&v->counter, old, new);
      |                ^
../include/linux/atomic/atomic-arch-fallback.h:55:21: note: expanded
from macro 'raw_cmpxchg'
   55 | #define raw_cmpxchg arch_cmpxchg
      |                     ^
../arch/riscv/include/asm/cmpxchg.h:310:2: note: expanded from macro
'arch_cmpxchg'
  310 |         _arch_cmpxchg((ptr), (o), (n), ".rl", ".aqrl",
         \
      |         ^
../arch/riscv/include/asm/cmpxchg.h:269:3: note: expanded from macro
'_arch_cmpxchg'
  269 |                 __arch_cmpxchg_masked(sc_sfx, ".b" cas_sfx,
         \
      |                 ^
../arch/riscv/include/asm/cmpxchg.h:178:2: note: expanded from macro
'__arch_cmpxchg_masked'
  178 |         u32 *__ptr32b = (u32 *)((ulong)(p) & ~0x3);
         \
      |         ^


>
> Thanks,
> drew