Re: problem debugging assembler functions

[Vladimir Prus <ghost@cs.msu.su>]

On Tuesday 14 June 2005 18:58, Daniel Jacobowitz wrote:
> On Tue, Jun 14, 2005 at 06:54:03PM +0400, Vladimir Prus wrote:
> > > > 2. In my case, no function names for assembler modules are present in
> > > > debug info, but line information is there, so the function is
> > > > debuggable. Is there a way to check of line info in condition, not
> > > > for function name?
> > >
> > > You have line numbers, but not even minimal symbols?  That is, ELF
> > > symbols, not DWARF2 symbols.
> >
> > Exactly. ELF symbol table is absolutely empty.
> >
> > > That's really bizarre.
> >
> > Well, for a binary for embedded system with no dynamic linking this is
> > not so unreasonable. Anyway, that's not something I can easily change.
>
> Not having dynamic symbols, sure, that's perfectly reasonable.  Those
> go into target memory.  But this is far from the only thing in GDB that
> is not going to work without a static symbol table!  For instance, you
> can't use prologue analysis.  You'll never find the start of any
> function.

Do you mean prologue analysis for assembler modules? For C++ modules DWARF2 
info contains everything. 

Well, I don't need to analyse prologue for assembler modules at all, because
if I understand correctly it's only needed to proper unwind stack, and I have 
a much better way for stack unwinding. My target is actually a simulator, so 
I just store register values on each call instruction and can fetch them via
extended version of "get registers" remote protocol command.

> > > We don't have a
> > > good interface for handling functions with line numbers but no sym or
> > > minsym, but perhaps we need one.  I agree that the presence of line
> > > number information seems more relevant right here.
> >
> > FWIW, I've just modified that code to be:
> >
> >   ecs->sal = find_pc_line (stop_pc, 0);
> >   .......
> >   if (step_over_calls == STEP_OVER_UNDEBUGGABLE
> >       && ecs->sal.line == 0)
> >
> > and it works as expected. Does the change seem reasonable?
>
> I'm not thrilled with adding another lookup here; this code executes
> quite a few times when stepping.  

The current code looks like:
 
  if (step_over_calls == STEP_OVER_UNDEBUGGABLE
      &&  ecs->stop_func_name == NULL
  {
  }

  if (step_range_end == 1)
  {
      /* It is stepi or nexti.
	  ...
      return;
  }

  ecs->sal = find_pc_line(stop_pc, 0)


So, moving 'find_pc_line' above will reasult in extra lookup only if 
- the command is stepi/nexti, or
- the first condition evaluates to true (which means we've entered   
  undebuggable code)

I have no idea is that's bad or not performance-wise, just clarifying what's
going on.
   
> It does seem plausible, but it would 
> need wider testing.

Ok.

- Volodya