Re: Does GDB 6.7.1 for PowerPC require the framepointer register for backtracing?

[Daniel Jacobowitz <drow at false dot org>]

On Mon, Feb 11, 2008 at 12:03:25PM +0100, Stefan Bylund wrote:
> Hi,
>
> We recently upgraded from GDB 6.3 to GDB 6.7.1 and noticed that for  
> PowerPC we can longer get a backtrace in certain cases. The problem is  
> that when we initially attach to an existing process on a remote target,  
> only the PC and SP registers are available. This worked fine with GDB 6.3 
> when doing a backtrace. However, GDB 6.7.1 fails when doing a backtrace in 
> this case, and it seems that it tries to use the framepointer register 
> (R31) for doing the backtrace and since this register is not available 
> (i.e. it has value 0 in GDB's perspective), the backtrace fails.
>
> Does GDB 6.7.1 requires the framepoint register (R31) for doing a backtrace?

It depends on your program and the available symbols and unwind
information.  For instance, it will use DWARF unwind tables if
they are provided.

> I have also noticed that if I don't install the dwarf2_frame_sniffer()  
> and rs6000_adjust_frame_regnum() functions in rs6000_gdbarch_init() in  
> rs6000-tdep.c, the backtrace works again even if the framepointer  
> register is not available. However, I'm not sure exactly why... Is it  
> safe to omit these two functions?

It sounds to me like you have DWARF information that says to use the
frame pointer.  Do you know if that's true?

-- 
Daniel Jacobowitz
CodeSourcery