linux-kernel - Re: [GIT PULL] io_uring updates for 5.10-rc1

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Message-ID: <20201013210602.GA1466033@rani.riverdale.lan>
Date:   Tue, 13 Oct 2020 17:06:02 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        io-uring <io-uring@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] io_uring updates for 5.10-rc1

On Tue, Oct 13, 2020 at 01:49:01PM -0600, Jens Axboe wrote:
> On 10/13/20 1:46 PM, Linus Torvalds wrote:
> > On Mon, Oct 12, 2020 at 6:46 AM Jens Axboe <axboe@...nel.dk> wrote:
> >>
> >> Here are the io_uring updates for 5.10.
> > 
> > Very strange. My clang build gives a warning I've never seen before:
> > 
> >    /tmp/io_uring-dd40c4.s:26476: Warning: ignoring changed section
> > attributes for .data..read_mostly
> > 
> > and looking at what clang generates for the *.s file, it seems to be
> > the "section" line in:
> > 
> >         .type   io_op_defs,@object      # @io_op_defs
> >         .section        .data..read_mostly,"a",@progbits
> >         .p2align        4
> > 
> > I think it's the combination of "const" and "__read_mostly".
> > 
> > I think the warning is sensible: how can a piece of data be both
> > "const" and "__read_mostly"? If it's "const", then it's not "mostly"
> > read - it had better be _always_ read.
> > 
> > I'm letting it go, and I've pulled this (gcc doesn't complain), but
> > please have a look.
> 
> Huh weird, I'll take a look. FWIW, the construct isn't unique across
> the kernel.
> 
> What clang are you using?
> 
> -- 
> Jens Axboe
> 

If const and non-const __read_mostly appeared in the same file, both gcc
and clang would give errors.