linux-kernel - RE: [PATCH] x86: Fix early boot crash on gcc-10, next try

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Message-ID: <0ce42f2537124ee3829a307eefd12db4@AcuMS.aculab.com>
Date:   Mon, 27 Apr 2020 17:07:53 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Borislav Petkov' <bp@...en8.de>,
        Arvind Sankar <nivedita@...m.mit.edu>
CC:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Michael Matz <matz@...e.de>, Jakub Jelinek <jakub@...hat.com>,
        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>,
        Peter Zijlstra <peterz@...radead.org>,
        "x86@...nel.org" <x86@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kees Cook <keescook@...omium.org>,
        Martin Liška <mliska@...e.cz>,
        Frédéric Pierret (fepitre) 
        <frederic.pierret@...es-os.org>,
        "boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
        "jgross@...e.com" <jgross@...e.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Subject: RE: [PATCH] x86: Fix early boot crash on gcc-10, next try

From: Borislav Petkov
> Sent: 25 April 2020 18:53
...
> IOW, something like this (ontop) which takes care of the xen case too.
> If it needs to be used by all arches, then I'll split the patch:
.
> -	asm ("");
> +	prevent_tail_call_optimization();
>  }

One obvious implementation would be a real function call.
Which the compiler would convert into a tail call.
Just to confuse matters :-)

	David

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