linux-kernel - Re: [PATCH v2] x86: fix early boot crash on gcc-10

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Message-ID: <20200422135531.GM2424@tucnak>
Date:   Wed, 22 Apr 2020 15:55:31 +0200
From:   Jakub Jelinek <jakub@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Michael Matz <matz@...e.de>,
        Sergei Trofimovich <slyfox@...too.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v2] x86: fix early boot crash on gcc-10

On Wed, Apr 22, 2020 at 03:49:24PM +0200, Borislav Petkov wrote:
> On Wed, Apr 22, 2020 at 01:40:07PM +0200, Peter Zijlstra wrote:
> > You haz a whitespace issue there.
> 
> Fixed.
> 
> > Also, can we get this in writing, signed in blood, from the various
> > compiler teams ;-)
> 
> Yah, I wouldn't want to go fix this again in gcc11 or so. That's why I
> wanted the explicit marking but let's try this first - it is too simple
> to pass over without having tested it.

If virtual blood is enough, AFAIK GCC has never tried to accept volatile
inline asm (asm ("") is such; non-volatile asm such as int x; asm ("" : "=r" (x));
could be e.g. dead code eliminated) in the statements between function call and
return when deciding about what function can be tail-called or can use
tail-recursion and there are no plans to change that.

	Jakub