[fedora-arm] Broken sha512sum in coreutils

[Chris Tyler]

On Fri, 2011-01-07 at 20:23 +0000, Andy Green wrote:
> On 01/07/11 19:46, Somebody in the thread at some point said:
> > ..snip..
> >
> >>>
> >>> This must be a bug in sha512sum -- it shouldn't be affected by alignment.
> >>
> >> I am inclined to think it might be compiler related. Andy's package is
> >> the same version as mine, his works, mine does not. The only thing that
> >> is likely to be different is the build environment.
> >
> > That and the development board. You are using a sheevaplug.
> > It is also likely that Andy's hardware does fixups for misaligned accesses.
> 
> It's an NXP LPC3250, ARM926EJ-S.  I have no idea if the hardware is 
> handling the alignment issue but that would explain why everything is 
> exactly zero on that box's alignment error stats.  Searching the 
> datasheet for 'alignment' doesn't tell anything relevant.

As I understant it, the 'A' profile for armv7 includes mandatory
alignment fixup. Thus, if your CPU is armv7 it should do fixups in
hardware -- with cost, but transparent. Most armv5 does not appear to do
this.

(Did the PHP 2.5*5 bug come up in this discussion? On a machine without
hardware fixup, PHP prints 5.3114652946464E-315 as the answer for 2.5*5
with 0 in /proc/cpu/alignment, but prints 5 when fixups are enabled.
This seems to be a useful quick test).

Related proposal: I think we should have the startup scripts
set /proc/cpu/alignment to 3 (warn+fixup) by default in Fedora-ARM (we
do this on the Koji builder image). I don't see a downside, and there's
a definite upside on armv5 systems.

-Chris