linux-kernel - Re: [PATCH] futex: send SIGBUS if argument is not aligned on a four-byte boundary

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Message-ID: <CAEMqeSqr9D6uj2OB0_5uT03c_au3906z_oyhX3zfg4OempTJVw@mail.gmail.com>
Date:   Tue, 19 May 2020 13:22:48 -0400
From:   "Carlos O'Donell" <carlos@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Darren Hart <dvhart@...radead.org>,
        Maxim Samoylov <max7255@...dex-team.ru>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] futex: send SIGBUS if argument is not aligned on a
 four-byte boundary

On Fri, May 15, 2020 at 1:50 PM Carlos O'Donell <carlos@...hat.com> wrote:
> This isn't fixed because this is the older code in pthread_mutex_lock
> which we haven't ported to futex-internal.h yet, otherwise we would abort
> the process.

I filed this upstream as a QoI issue so I don't forget to port the existing code
to the newer internal interfaces for futex handling.

"Bug 25997 - pthread_mutex_lock QoI issue for unaligned futex."
https://sourceware.org/bugzilla/show_bug.cgi?id=25997

I checked that -Wcast-align=strict does warn about this case, but it's
rarely used
in production code that I've worked with. I'm following up with the
compiler people
to see if we can consistently warn in these cases and so avoid this kind of code
existing in the first place.

Cheers,
Carlos.