ARM unaligned MMIO access with attribute((packed))
davem at davemloft.net
Wed Feb 2 16:59:54 EST 2011
From: Russell King - ARM Linux <linux at arm.linux.org.uk>
Date: Wed, 2 Feb 2011 21:45:22 +0000
> On Wed, Feb 02, 2011 at 01:38:31PM -0800, David Miller wrote:
>> From: Russell King - ARM Linux <linux at arm.linux.org.uk>
>> Date: Wed, 2 Feb 2011 16:37:02 +0000
>> > 1. there's no way to tell GCC that the inline assembly is a load
>> > instruction and therefore it needs to schedule the following
>> > instructions appropriately.
>> Just add a dummy '"m" (pointer)' asm input argument to the inline asm
>> statement. Just make sure "typeof(pointer)" has a size matching the
>> size of the load your are performing.
> That involves this problematical cast from a packed struct pointer to
> an unsigned long pointer, which according to the C standard and GCC
> folk is undefined.
It's alignment may be undefined, but it's size definitely is well
defined and that's what matters here.
> Practice over the last 15 years on ARM has also shown that this is not
Sorry oh big super man, little ole' me is only a kernel newbie.
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