Re: unaligned access in part_efi.c

[Marc Dietrich <marvin24-Mmb7MZpHnFY@public.gmane.org>]

On Wednesday 27 March 2013 12:23:22 Stephen Warren wrote:
> On 03/26/2013 02:42 PM, Marc Dietrich wrote:
> > Hi,
> > 
> > access to part->start_sect in pmbr_part_valid() (form disk/part_efi.c) and
> > propably other positions/fields causes an unaligned access on ARM (tegra
> > in my case) and a uboot crash. This was introduced by commit fae2bf22 [1]
> > which changed le32_to_int (which is a byte access) to le32_to_cpu (which
> > is a 32bit access).
> 
> I can't reproduce this with latest u-boot-arm/master, which includes
> that commit. Both "mmc dev N; mmc rescan ; mmcinfo" and "part list mmc
> N" work fine for me with both DOS PT and GPT.
> 
> I did test this on a Tegra Seaboard which isn't identical to the AC100,
> but the only practical difference is 512M vs 1G RAM, which seems
> unlikely to cause this.
> 
> It'd help if you pointed out exactly which access causes the issue;
> which piece of code is failing. The most likely issue is that some
> memory buffer is assumed to be aligned to 4-bytes, but actually isn't.
> To track that down, we'd need to know which code and which buffer. Also,
> a disassembly of the problematic function would be useful.

As discussed on IRC, this only happens with gcc 4.7 or patched gcc 4.6 (e.g. 
from linaro) which has -maligned-access as default enabled. I added -mno-
aligned-access to the disk/Makefile and now it boots, but I doubt that this is 
the best solution.

Marc