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Re: [RFA:] Caveat for ARM in gcc-4.7/changes.html: unaligned accesses
- From: Hans-Peter Nilsson <hans-peter dot nilsson at axis dot com>
- To: michael dot hope at linaro dot org
- Cc: gcc-patches at gcc dot gnu dot org, richard dot earnshaw at arm dot com
- Date: Mon, 11 Jun 2012 00:59:57 +0200
- Subject: Re: [RFA:] Caveat for ARM in gcc-4.7/changes.html: unaligned accesses
> From: Michael Hope <michael.hope@linaro.org>
> Date: Mon, 11 Jun 2012 00:04:19 +0200
> On 8 June 2012 16:53, Hans-Peter Nilsson <hans-peter.nilsson@axis.com> wrote:
> >> From: Hans-Peter Nilsson <hp@axis.com>
> >> Date: Fri, 8 Jun 2012 06:29:04 +0200
> >
> >> > From: Michael Hope <michael.hope@linaro.org>
> >> > Date: Fri, 8 Jun 2012 05:50:52 +0200
> >> > ?The combination of
> >> > older Linux ARM kernels and GCC 4.7 gives a faulty kernel.
> >>
> >> We're in agreement!
> >
> > Oh wait sorry, my bad, I misread. ?Instead of "gives a faulty
> > kernel", I'd say "for ARMv6 and later (not -M), gives faulty
> > user-space code". ?Maybe the kernel too, I can't say; there was
> > IIRC no sign of it.
>
> Is there a bugzilla ticket logged for this? I'd like to try to reproduce it.
No, I think it was clear that it was a deliberate change. I'm
waiting for an ARM maintainer to review the gcc-4.7/changes.html
patch or reconsider the mentioned change.
> It's interesting as we backported the patch into the Linaro GCC that
> was used to build Ubuntu Precise and didn't find any faults.
You don't think unaligned accesses are generated or what's your
point? Did you use -marmv6 when compiling the user code?
As already mentioned, for example anything that executes
busybox/libbb/procps.c:365 (procps_scan), but that's just one
random location. I think you'd have seen it assuming your
kernel was configured as mentioned and your usercode was
configured for armv6 or higher (or gcc configured to default
generate for armv6 or higher).
brgds, H-P