[U-Boot] [PATCH] disk: add -mno-unaligned-access to CFLAGS

[Marc Dietrich]

Hi Albert,

On Thursday 28 March 2013 21:42:13 Albert ARIBAUD wrote:
> On Thu, 28 Mar 2013 19:57:31 +0100, Marc Dietrich <marvin24 at gmx.de>
> wrote:
> > Many on-disk structures used in the directory are accessed in a
> > non aligned manner. gcc => 4.7 (and gcc-4.6 from Linaro) switched
> > to -munaligned-access on default causing exceptions on ARM. The
> > easiest way to fix this is to force no-unaligned-access in this
> > (non speed critical) directory.
> > 
> > Signed-off-by: Marc Dietrich <marvin24 at gmx.de>
> > ---
> > 
> >  disk/Makefile |    1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/disk/Makefile b/disk/Makefile
> > index 5affe34..01134a3 100644
> > --- a/disk/Makefile
> > +++ b/disk/Makefile
> > @@ -24,6 +24,7 @@
> > 
> >  include $(TOPDIR)/config.mk
> >  
> >  #CFLAGS += -DET_DEBUG -DDEBUG
> > 
> > +CFLAGS += -mno-unaligned-access
> > 
> >  LIB	= $(obj)libdisk.o
> 
> Which fields, which structures, which files are affected by the
> unalignment issue?

in my test case, it is the start sector of a partition (check 
include/part_efi.h). disk/part_efi.c reads the legacy mbr (to an aligned 
buffer) which has a partition structure on offset 440+4+2 (<- not aligned to 4 
byte boundary) and inside this a 32 bit field start_sect (aligned to 4 byte 
boundary). Reading this field (and also the next, nr_sects) will cause an 
exception. Same is for part_dos, but there we still use le32_to_int which 
reads byte by byte. I didn't checked others.

Marc