[OpenBIOS] ppc(64) debugging (was: Q: How to "squeeze" C functions in between two symbols?)

[Artyom Tarasenko]

On Mon, Nov 1, 2010 at 12:33 AM, Andreas Färber <andreas.faerber at web.de> wrote:
> Am 08.10.2010 um 15:30 schrieb Alexander Graf:
>
>> You can use the apple gdb without an object file, so you don't get
>> symbols. But if you have an instruction pointer, just
>>
>>  $ qemu-system-ppc -s -S ...
>>  (gdb) target remote localhost:1234
>>  (gdb) b *0x1234 <- address of rtas_something
>>  (gdb) c
>>
>> It should break on that IP and then you can evaluate the register contents
>> at least. Either by
>>
>>  (gdb) info registers
>>
>> or
>>
>>  (qemu) info registers
>
> I'm trying to find out how far we get with the ppc64 OpenBIOS, so I've tried
> the following:
>
> $ .../ppc64-softmmu/qemu-system-ppc64 ... -nographic -prom-env
> 'auto-boot?=false' -s -S
>
> $ gdb --arch=ppc64
> GNU gdb 6.3.50-20050815 (Apple version gdb-967) (Tue Jul 14 02:15:14 UTC
> 2009)
> Copyright 2004 Free Software Foundation, Inc.
> GDB is free software, covered by the GNU General Public License, and you are
> welcome to change it and/or distribute copies of it under certain
> conditions.
> Type "show copying" to see the conditions.
> There is absolutely no warranty for GDB.  Type "show warranty" for details.
> This GDB was configured as "powerpc-apple-darwin".
> (gdb) target remote localhost:1234
> Remote debugging using localhost:1234
> [New thread 1]
> 0x0000000000000000 in ?? ()
> (gdb) b *0xfffffffc
> Breakpoint 1 at 0xfffffffc
> (gdb) c
> Continuing.
>
> It doesn't break though and executes to the OpenBIOS prompt.
> 0xfffffffc is supposed to be the hard reset vector, i.e. the very first
> instruction it must execute to branch to _entry.
>
> Any suggestions?

Maybe try to do "stepi" instead of "c" to prove execution starts from
0xfffffffc?
Breakpoints are unreliable in qemu. Particularly traps are really hard
to debug (at least in the sparc port).

-- 
Regards,
Artyom Tarasenko

solaris/sparc under qemu blog: http://tyom.blogspot.com/