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

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Message-ID: <20120314233351.GA17669@banjo.employees.org>
Date:	Wed, 14 Mar 2012 16:33:51 -0700
From:	Derek Fawcus <dfawcus+lists-linux-kernel@...loyees.org>
To:	"H.J. Lu" <hjl.tools@...il.com>
Cc:	mingo@...hat.com, hpa@...or.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 04:17:29PM -0700, 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.

So whereas on i386 and x86_64 we can set eflags.AC (or rflags.AC) to test the
code for aligment safeness,  we'll not be able to do so with x32?

(Simply 'cause this could get false positive on syscalls).

Granted this is not a common use,  but I've done it for checking that code
will easily port to ppc/mips.

.pdf
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