linux-kernel - RE: [PATCH v3] devres: Explicitly align datai[] to 64-bit

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Date:   Mon, 9 Jul 2018 16:10:19 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Mark Rutland' <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>
CC:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "greg@...ah.com" <greg@...ah.com>,
        "will.deacon@....com" <will.deacon@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "geert@...ux-m68k.org" <geert@...ux-m68k.org>
Subject: RE: [PATCH v3] devres: Explicitly align datai[] to 64-bit

From: Mark Rutland
> Sent: 09 July 2018 16:49
> 
> On Mon, Jul 09, 2018 at 05:45:21PM +0200, Peter Zijlstra wrote:
> > On Mon, Jul 09, 2018 at 05:34:27PM +0200, Peter Zijlstra wrote:
> > > On Mon, Jul 09, 2018 at 04:29:58PM +0100, Mark Rutland wrote:
> > > > Shouldn't that be 8? AFAICT, __alignof__(unsigned long long) is 8 on
> > > > x86_32:
> > >
> > > Curious, I wonder why we put that align in atomic64_32 then.
> >
> > Shiny, look at this: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54188
> >
> 
> Ouch.

Indeed.

changing the definition to:
struct ull {
        unsigned long long v __attribute__((aligned(__alignof__(long long))));
};

prints 8 for the structure alignment.

Time to audit uses of __alignof__().

#define actual_alignof(type) __alignof__(struct { type jsdjdhjdjh; })

	David