linux-kernel - Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage

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Message-ID: <CAKwvOdns1WPE21F3zVO++ceTjwZ071rDKQ1hd4w==1DEWjdCrg@mail.gmail.com>
Date:   Tue, 9 Nov 2021 14:15:38 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Bill Wendling <morbo@...gle.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, mark.rutland@....com,
        dvyukov@...gle.com, seanjc@...gle.com, pbonzini@...hat.com,
        mbenes@...e.cz, llvm@...ts.linux.dev,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage

On Tue, Nov 9, 2021 at 2:11 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Nov 09, 2021 at 01:25:47PM -0800, Nick Desaulniers wrote:
> > On Tue, Nov 9, 2021 at 1:21 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > On Tue, Nov 09, 2021 at 12:59:12PM -0800, Bill Wendling wrote:
> > > >
> > > > Adding attributes to labels shouldn't be difficult, as you mention. In
> > > > the case of cold/hot, it's adjusting some of the metadata that already
> > > > exists on some basic blocks. It might be enough to allow the normal
> > > > block placement algorithms to move the hot and cold blocks around for
> > > > us. The question becomes how many attributes does GCC allow on labels?
> > >
> > > I'm aware of 3: unused, hot, cold. Also:
> > >
> > >   https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html
> >
> > Re: unused:
> > Being able to selectively disable -Wunused-label via
> > __attribute__((unused)); seems useful, too.
>
> kernel/sched/fair.c:done: __maybe_unused;
>
> Yes it is ;-)

Ah, that's already supported: https://godbolt.org/z/aa76aexnv, so it's
just hot/cold that could be implemented next.
-- 
Thanks,
~Nick Desaulniers