[U-Boot] [PATCH] 8313erdb: Set guarded bit on BAT that covers the end of the address space.

[Anton Vorontsov]

On Tue, Mar 17, 2009 at 12:09:31PM -0500, Scott Wood wrote:
> This board currently sets DBAT6 to cover all of the final 256MiB of
> address space; however, not all of this space is covered by a device.  In
> particular, flash sits at 0xfe000000-0xfe7fffff, and nothing is mapped
> at the far end of the address space.
> 
> In zlib, there is a loop that references p[-1] if p is non-NULL.  Under
> some circumstances, this leads to the CPU speculatively loading from
> 0xfffffff8 if p is NULL.  This leads to a machine check.
> 
> Signed-off-by: Scott Wood <scottwood at freescale.com>
> ---
> Note that there are likely other board with the same issue.

Wow, I was actually chasing this (I think) bug for some time.

The effect of this bug was quite weird: some kernels didn't
boot, and the only difference in the kernel image was.. the build
date (i.e. data in linux_banner and init_uts_ns symbols).

I suspected the decompression code (what else could it be?), but I
didn't manage to track it down to a failing instruction, as the
failing kernel was booting *OK* with BDI-2000 attached. Heh.

I wonder how you tracked it down to zlib code and a particular
loop, please share the technique. ;-)

Thanks!

-- 
Anton Vorontsov
email: cbouatmailru at gmail.com
irc://irc.freenode.net/bd2