Automated GDB

Instead of tracing program manually, we can automate the trace procedure in GDB. The magic is the commands...end construct:

break somePoint

commands
[gdb commands here]
end

The commands construct will attach a piece of GDB commands to the last-defined break point. Whenever the break point is reached, the piece of command is executed as if it is typed by us. For example, we can do the following to show how many outstanding objects are there whenever we reached FunctionX:

set pagination off

set $count=0

break CreatorFunction

commands
silent
set $count = $count + 1
continue
end

break DestroyFunction

commands
silent
set $count = $count - 1
continue
end

break FunctionX

commands
silent
print $count
continue
end

run

The line set pagination off is to turn off manual intervention when the screen is full. And the key point in the above is the continue command right before the end construct to let the break point continue.

Sometimes, we may not just want the things automate, but to stop when some condition is met. This can also be done. The way to do is:

break FunctionY if FunctionZ()==0

Then, the break point will really break only if the condition is met. The condition can also be written using out-of-band variables, for example:

break FunctionY if $count==0

Which the $count is a variable defined inside GDB. In case it is an address, just call *$addr to dereference it, as in C. If we wrote everything in a file, we can do the automation in command line by:

gdb -x script program_to_debug