Watching memory adress given by an expression

Watching memory adress given by an expression

[Yves Jaradin]

Hi,

Recently, I stumbled upon a dangling pointer in some code I'm maintaining.
The best reproducible crash was still very time sensitive (order of a 
few seconds at most),
so I couldn't really debug interactively.
Some structure on the heap was corrupted, so I set up a breakpoint when 
the structure was correctly initialized with commands to set up a 
watchpoint on the memory that would be corrupted.
Unfortunately, the expression I had for the to-be-corrupted memory was 
going out of scope before the corruption.
I resorted to this:

break emulate.cc:316
ignore $bpnum 9
commands
print entry
x &(entry.pc)
set $targetpc=$_
watch *($targetpc)
continue
end
continue


Which is ugly because:
I works only for a single triggering of the breakpoint.
It prints an extra value.
The $_ business I'm doing is really a hack.

I could remove the first problem using shell, source, etc. but this 
isn't cleaner.

Is there a cleaner way to do this kind of debugging?

I would have liked to have a command like:
watchmem &(entry.pc)
which would immediately evaluate it's expression to a pointer and set a 
watcher to the pointed space.

Regards,
Yves

Re: Watching memory adress given by an expression

[Andreas Schwab]

Yves Jaradin <yves.jaradin@uclouvain.be> writes:

> break emulate.cc:316
> ignore $bpnum 9
> commands
> print entry
> x &(entry.pc)
> set $targetpc=$_
> watch *($targetpc)
> continue
> end
> continue
>
>
> Which is ugly because:
> I works only for a single triggering of the breakpoint.
> It prints an extra value.
> The $_ business I'm doing is really a hack.

What do you need it for?  You can set $targetpc directly to &entry.pc.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
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