linux-kernel - Re: Surprising code generated for vdso_read

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Message-ID: <20200111113328.GX3191@gate.crashing.org>
Date:   Sat, 11 Jan 2020 05:33:28 -0600
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, arnd@...db.de,
        tglx@...utronix.de, vincenzo.frascino@....com, luto@...nel.org,
        x86@...nel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mips@...r.kernel.org
Subject: Re: Surprising code generated for vdso_read_begin()

On Fri, Jan 10, 2020 at 07:45:44AM +0100, Christophe Leroy wrote:
> Le 09/01/2020 à 21:07, Segher Boessenkool a écrit :
> >It looks like the compiler did loop peeling.  What GCC version is this?
> >Please try current trunk (to become GCC 10), or at least GCC 9?
> 
> It is with GCC 5.5
> 
> https://mirrors.edge.kernel.org/pub/tools/crosstool/ doesn't have more 
> recent than 8.1

Arnd, can you update the tools?  We are at 8.3 and 9.2 now :-)  Or is
this hard and/or painful to do?

> With 8.1, the problem doesn't show up.

Good to hear that.  Hrm, I wonder when it was fixed...


Segher