Automating 'stop', 'print' and 'continue' in GDB

nayankk · 06-01-2009, 10:10 AM

Hey Guys,

I am debugging an real-time problem, where I cannot stop the execution for longer time. In this real-time use case, I get an even X at regular intervals and corresponding event handler function handle_x() gets called. I want to print the data within this event X, without stopping execution of program for longer time. Basically, I want to automate 'stop' (Ctrl-C), 'print' and 'cont' gdb commands such that this sequence of commands gets executed everytime when event X occurs in the system.

Is there any way to do so in GDB? I really appreciate any help.

Thank you,

Regards,
-Nayan

KenJackson · 06-02-2009, 05:00 AM

I don't know the direct answer to your question, but when I get in situations like that, I often add temporary debug code to gather data. Declare a large text buffer and sprintf() debug information to the end of it and then later print it. Or even print it from a different thread or process. If memory or time is more critical you store only binary data.

Hko · 06-02-2009, 05:58 AM

Never this feature myself, but to me it sounds like GDB's "tracepoints" is what you're looking for.

ntubski · 06-02-2009, 09:43 AM

Hmm

Quote:

The tracepoint facility is currently available only for remote targets. See section 17. Specifying a Debugging Target. In addition, your remote target must know how to collect trace data. This functionality is implemented in the remote stub; however, none of the stubs distributed with GDB support tracepoints as of this writing. The format of the remote packets used to implement tracepoints are described in D.6 Tracepoint Packets.

I think you could use Breakpoint Command Lists .

Quote:

For example, here is how you could use breakpoint commands to print the value of x at entry to foo whenever x is positive.

break foo if x>0
commands
silent
printf "x is %d\n",x
cont
end

Just replace "break foo if x>0" with "break handle_x".

nayankk · 06-03-2009, 04:06 AM

Thanks for all in helping me. My target did not support tracepoint. Tried out 'command list' and it worked.