netdev - RE: alignment faults in 3.6

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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B703B@saturn3.aculab.com>
Date:	Thu, 11 Oct 2012 11:16:16 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	Måns Rullgård <mans@...sr.com>
Cc:	"Jon Masters" <jonathan@...masters.org>,
	<linux-arm-kernel@...ts.infradead.org>, <netdev@...r.kernel.org>
Subject: RE: alignment faults in 3.6

> > It might be enough to use __attribute__((aligned(2))) on some structure
> > members (actually does 'ldm' need 8 byte alignment?? - in which case
> > aligned(4) is enough).
> 
> The aligned attribute can only increase alignment.

Not true.
If you have:

struct foo {
    short   a;
    int     b __attribute__((aligned(2)));
    short   c;
};

You'll find sizeof (struct foo) is 8, and that, on arm/sparc etc,
gcc will generate 2 16bit accesses (and shifts) for foo.b;

	David



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