RE: ARM register pages

["Thomas Rauscher" <trauscher@loytec.com>]

  

> -----Original Message-----
> From: Richard Earnshaw [mailto:rearnsha@gcc.gnu.org] 
> Sent: Friday, June 10, 2005 10:14 AM
> To: Shaun Jackman
> Cc: gdb@sources.redhat.com
> Subject: Re: ARM register pages
> 
> On Thu, 2005-06-09 at 22:14, Shaun Jackman wrote:
> > On 6/9/05, Daniel Jacobowitz <drow@false.org> wrote:
> > > The easiest solution will be to do this instead:
> > > abt:    [copy the banked address to lr, which is not 
> useful at this
> > >          point]
> > > 1:      b 1b
> > 
> > If it's possible, I'd prefer to accomplish a backtrace without
> > altering the target's code. I was hoping that "set $cpsr=0x1f" would
> > make $lr_usr visible in $lr to gdb, but the value of $lr 
> displayed by
> > "i reg" remains the same. Does gdb cache the value of the 
> register? Is
> > there a way to force gdb to reload the value of the 
> register from the
> > remote target?
> 
> Be careful.  If you set the CPSR to user mode in this way, 
> the only way
> back out again will be to take another trap, thus destroying 
> any machine
> state you might have.  That is, reading the user mode 
> registers in this
> way will be destructive to your debugging session.
> 
> R.
> 
> 

A quite simple way to do this is to find the exception handler
and use

set $pc = ...

to set the PC to the 'movs' instruction at the end of the
exception handler. Then issue a single instruction step

si

to return to user mode. 

This however skips the exception handler entirely so that
the program would crash most likely when continuing.

Regards,
Thomas Rauscher

--
Thomas Rauscher
LOYTEC electronics GmbH
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