linux-kernel - Re: GCC 12 miscompilation of volatile asm (was: Re: [PATCH] arm64/io: Remind compiler that there is a memory side effect)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YlQBe5KbKogNU4vt@FVFF77S0Q05N>
Date:   Mon, 11 Apr 2022 11:22:51 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, gcc@....gnu.org,
        catalin.marinas@....com, will@...nel.org, marcan@...can.st,
        maz@...nel.org, szabolcs.nagy@....com, f.fainelli@...il.com,
        opendmb@...il.com, Andrew Pinski <pinskia@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>, x86@...nel.org,
        andrew.cooper3@...rix.com, Jeremy Linton <jeremy.linton@....com>
Subject: Re: GCC 12 miscompilation of volatile asm (was: Re: [PATCH]
 arm64/io: Remind compiler that there is a memory side effect)

On Tue, Apr 05, 2022 at 04:05:22PM +0200, Peter Zijlstra wrote:
> On Tue, Apr 05, 2022 at 01:51:30PM +0100, Mark Rutland wrote:
> > Hi all,
> > 
> > [adding kernel folk who work on asm stuff]
> > 
> > As a heads-up, GCC 12 (not yet released) appears to erroneously optimize away
> > calls to functions with volatile asm. Szabolcs has raised an issue on the GCC
> > bugzilla:  
> > 
> >   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105160
> > 
> > ... which is a P1 release blocker, and is currently being investigated.
> > 
> > Jemery originally reported this as an issue with {readl,writel}_relaxed(), but
> > the underlying problem doesn't have anything to do with those specifically.
> > 
> > I'm dumping a bunch of info here largely for posterity / archival, and to find
> > out who (from the kernel side) is willing and able to test proposed compiler
> > fixes, once those are available.
> > 
> > I'm happy to do so for aarch64; Peter, I assume you'd be happy to look at the
> > x86 side?
> 
> Sure..

FWIW, compiler explorer now have a trunk build with the fix, and my x86-64
example now gets compiled to something which looks correct:

  https://godbolt.org/z/cveff9hq5

Thanks,
Mark.