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

["Cédric Le Goater" <clg@kaod.org>]

On 12/8/21 14:07, Thomas Huth wrote:
> 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...


a fix restoring address 0, something like :

@@ -60,6 +60,9 @@ long get_ram_size(long *base, long maxsi
  		return (0);
  	}
  
+	addr = base;
+	*addr = save[i];
+
  	for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
  		addr = base + cnt;	/* pointer arith! */
  		val = *addr;

is not enough. trap_init() will also overwrite the kernel image.
And u-boot will complain about a wrong CRC.

The 405 series I sent improves support and latest kernel 5.16-rc4
can be loaded without uboot. It's a start to debug user space.

Thanks,

C.