Re: [PATCH 0/5]

[Nathan Froyd <froydnj@codesourcery.com>]

On Tue, Jul 28, 2009 at 04:11:57PM +0800, Liu Yu-B13201 wrote:
> > On Sat, Jul 25, 2009 at 04:40:12PM +0800, Liu Yu wrote:
> > > For example booke has a code template for
> > > jumping to and returning from interrupt handlers:
> > >
> > > 	bl transfer
> > > 	.long handler_addr
> > > 	.long ret_addr
> > >
> > > when call transfer, it never return but
> > > in transfer assembly code it will read the handler_addr
> > > and ultimately call the handler.
> > > Gdb doesn't know that and treat it as a normal function call.
> > > so gdb put a software breakpoint instruction at handler_addr,
> > > in order to get trap there when return from transfer.
> > >
> > > Then guest will read software breakpoint as handler_addr 
> > and jump to there..
> > >
> > > I'm not sure if x86 suffer this kind of issue.
> > > Is there any way to avoid this?
> > 
> > You would need to modify GDB to recognize this sort of case with the
> > skip_trampoline_code gdbarch method.
> 
> Hmm.. I am not a gdb expert.
> But even gdb can recognize this pattern, is it safe to skip it?

The code doesn't get skipped.  skip_trampoline_code is a hook for
telling GDB "this function doesn't return in the normal way: here's
where execution will resume once this function finishes."  That way GDB
can place the software breakpoint in the correct location: in this case,
at the address handler_addr.

-Nathan