From: Johannes Stezenbach <js@sig21.net>
To: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: crossgcc@sourceware.org, Bob Dunlop <bob.dunlop@xyzzy.org.uk>,
Richard Koch <n1gp@hotmail.com>,
Martin Guy <martinwguy@gmail.com>
Subject: Re: Compiler Memory Alignment Issue
Date: Fri, 03 Feb 2012 14:14:00 -0000 [thread overview]
Message-ID: <20120203141359.GA13360@sig21.net> (raw)
In-Reply-To: <201202031421.23553.yann.morin.1998@free.fr>
Hi Yann,
On Fri, Feb 03, 2012 at 02:21:23PM +0100, Yann E. MORIN wrote:
> On Friday 03 February 2012 11:16:27 Bob Dunlop wrote:
> > On Thu, Feb 02 at 01:15, Richard Koch wrote:
> > > I'm seeing an alignment issue when I'm incrementing a pointer.
>
> I Just tried your .config and your sample C code, and it seems to work here
> (with the buffer overflow fixed):
As Martin Guy pointed out the issue may be caused
by wrong alignment. In fact the behaviour of the code
is undefined according to C99 if buffer is not suitably aligned:
https://www.securecoding.cert.org/confluence/display/seccode/EXP36-C.+Do+not+convert+pointers+into+more+strictly+aligned+pointer+types
I'd suggest to add a printf for the buffer address.
For ARM, unaligned access is supported for ARMv6+, in ARMv5
unaligned write is UNPREDICTABLE (unaligned read is
defined as rotated read from aligned address).
Not sure what's the default CPU for qemu-arm but
Richard has ARMv5. I know Linux on ARM926EJ-S can
fix it up in sw like Martin described, but I'm not
sure every ARMv5 CPU supports alignment trap.
Johannes
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next prev parent reply other threads:[~2012-02-03 14:14 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-02 18:15 Richard Koch
2012-02-02 23:09 ` Martin Guy
2012-02-02 23:26 ` Rod Nussbaumer
2012-02-03 9:52 ` Martin Guy
2012-02-03 10:16 ` Bob Dunlop
2012-02-03 13:21 ` Yann E. MORIN
2012-02-03 14:14 ` Johannes Stezenbach [this message]
2012-02-03 14:23 ` Yann E. MORIN
2012-02-03 20:41 ` Johannes Stezenbach
2012-02-03 15:13 ` Richard Koch
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