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Re: [PATCH] hw/ppc/ppc405_boards: Change kernel load address


From: Thomas Huth
Subject: Re: [PATCH] hw/ppc/ppc405_boards: Change kernel load address
Date: Wed, 8 Dec 2021 14:07:09 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0

On 03/12/2021 13.25, Cédric Le Goater wrote:
On 12/3/21 11:40, Peter Maydell wrote:
On Fri, 3 Dec 2021 at 10:32, Thomas Huth <thuth@redhat.com> wrote:
I guess it's an accidential NULL pointer dereference somewhere in the u-boot
code ... which will be quite hard to track down when the first page of
memory is marked as writable... :-/

Attach a target-arch gdb to the QEMU gdbstub and put a watchpoint on
address zero ? (Or if you suspect something inside QEMU is doing it
then run QEMU under gdb and watchpoint the host memory location
corresponding to guest address 0, but that's more painful.) Nothing
in the pre-kernel part of the boot process will have set up paging,
so the watchpointing should be pretty reliable.

That's the guy:

https://gitlab.com/huth/u-boot/-/blob/taihu/arch/powerpc/cpu/ppc4xx/sdram.c#L199

There must be an error in how get_ram_size() restores the RAM values :

   https://gitlab.com/huth/u-boot/-/blob/taihu/common/memsize.c

There is definitely something wrong in that function. Seems like they tried to fix it once here:

 https://source.denx.de/u-boot/u-boot/-/commit/b8496cced856ff411f

but that patch got later reverted without a replacement later...

 Thomas





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