linux-kernel - Re: [tip:x86/x32] x32: Fix alignment fail in struct compat

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Date:	Wed, 14 Mar 2012 17:33:51 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/x32] x32: Fix alignment fail in struct compat_siginfo

On Wed, Mar 14, 2012 at 4:19 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 03/14/2012 04:17 PM, H.J. Lu wrote:
>>
>> Just for the record, although the offsets of _utime and _stime are
>> multiple of 8 bytes, struct siginfo is only aligned at 4 bytes.  So
>> the addresses of  _utime and _stime may not be 8byte aligned.
>> But misaligned int64 load/store are OK for x86-64.
>>
>
> Yes; the real question I guess is where struct siginfo appears and if it
> is misaligned by construction.  It obviously appears in the signal stack
> frame but also in a couple of system calls.  It might be possible to put
> an __attribute__((aligned(8))) on the whole structure in the x32 case?

It is possible to add  __attribute__((aligned(8))) on struct siginfo
in the x32 case.  But it only affects system calls with struct siginfo.
The signal stack frame may still be misaligned.

-- 
H.J.
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