Watching memory adress given by an expression

Yves Jaradin
2009-01-12T12:57:04Z

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