how to see DAR (data access register) on ppc using gdb 7.0.1 on Linux?

[Luis Gustavo]

On 09/07/2012 10:26 AM, Stefan Puiu wrote:
> Hi,
>
> I'm trying to debug a crash on our embedded Linux platform using:
>
> # gdb --version
>
> warning: Can not parse XML syscalls information; XML support was
> disabled at compile time.
> GNU gdb (GDB) 7.0.1
> Copyright (C) 2009 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later<http://gnu.org/licenses/gpl.html>
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
> and "show warranty" for details.
> This GDB was configured as "powerpc-750-linux-gnu".
>
> I was trying to see the PPC registers after a crash:
>
>      (gdb) info registers
>       r0             0x1034875e       271877982
>       r1             0x7fffed30       2147478832
>       r2             0xfd7f7a0        265811872
>       [...]
>       pc             0xf18d718        0xf18d718
>       msr            0xd032   53298
>       cr             0x80000848       2147485768
>       lr             0xf18d6f8        0xf18d6f8
>       ctr            0xf235d90        253975952
>       xer            0x20000000       536870912
>       orig_r3        0x26     38
>       trap           0x300    768
>
> I noticed that the DAR (data access register) is not present here -
> I'm trying to see the memory address whose access caused the crash. I
> only see the trap register, which confirms that there was an invalid
> memory access, but that's it as far as I can tell.
>
> I know the contents of the DAR are printed in case of kernel crashes
> (in oops dumps), is there a way to view the register from gdb? 'info
> register dar' doesn't work...
>
> Thanks in advance,
> Stefan.
>

Such a register is not made visible to GDB by the kernel, so you won't 
be able to see it through GDB.

Luis