Re: Timer

[Pedro Alves <palves@redhat.com>]

On 05/07/2013 07:42 AM, Marc Brünink wrote:
> 
> On May 7, 2013, at 12:43 PM, Doug Evans wrote:
> 
>> On Mon, May 6, 2013 at 2:52 AM, Marc Brünink <marc@nus.edu.sg> wrote:
>>> I want to execute a piece of code at regular intervals. Actually I'm sampling $pc.
>>> (let's not go into detail why I use gdb)
>>>
>>> My current solution just starts another process that sends a SIGTRAP to the debugged application. Using a simple script I can print the $pc.
>>>
>>> However, I just realised that this approach does not work too well. If gdb is stopped due to a breakpoint it will interpret the received SIGTRAP as another hit of the very same breakpoint.
>>>
>>> Reproduce:
>>> 1. Attach to any program
>>> 2. Create any breakpoint
>>> 3. Wait until breakpoint is hit
>>> 4. Send SIGTRAP to debugged application
>>> 5. continue
>>>
>>> Actually, now that I think about it, I should have anticipated this behaviour.
>>> Is there a better way to execute a piece of code at regular intervals?

You could also use another signal instead of SIGTRAP.

>> bash$ man setitimer
> 
> I suppose you are suggesting to modify either GDB or the application. This is exactly what I don't want. Any other way to accomplish this (using gdb)?

You could use LD_PRELOAD to inject a library that uses setitimer into your program.

I guess you could do it with gdb python scripting too.

-- 
Pedro Alves