Re: MI: event notification

[Daniel Jacobowitz <drow at false dot org>]

On Wed, Jun 21, 2006 at 01:16:09PM +1200, Nick Roberts wrote:
> In the past there have been discussions about the performance of certain
> MI commands.  To reduce the overhead, I would like to add some event
> notification where GDB informs that front end when something has changed
> 
> I think this has always been the intention but that nothing has so far
> been implemented.  As a start, and by way of an example, I attach a patch
> that tries to say when the stack has changed so that MI command(s)
> -stack-list-frames, -stack-list-arguments need not be issued while stepping
> within the same frame, for example.  
> 
> From the manual:
> 
> `NOTIFY-ASYNC-OUTPUT ==>'
>      `[ TOKEN ] "=" ASYNC-OUTPUT'
> 
> 
> Using the patch, "=stack-changed\n" gets printed every time the stack changes
> e.g

Good idea in general, bad choice of example.  This is not a valid
optimization, at least not where you put it.

- Stepping within a frame can change the values displayed by
  -stack-list-arguments.  On most targets + compilers they
  are sometimes corrupt at the beginning of a function.  On
  many targets the "incoming" value of the argument changes
  when that variable is assigned to.

- You can encounter the same frame ID for two consecutive stops
  but have a different backtrace, e.g. if you continued and then
  hit a breakpoint near the same function.

A good place to start might be asking the Xcode folks where they put
events.  I know they put a bunch of them, e.g. shlib related.  I don't
know if they're all suitable for GDB/MI, but I bet most of them are.
(And I think I talked with Jim about this particular one at some point,
and they either didn't have one, or didn't use it for much).

-- 
Daniel Jacobowitz
CodeSourcery