Nonblocking GDB stub

Nonblocking GDB stub

[Mattias Wildeman]

Hello!

I've been using GDB for a while, running it with a ARM based board and a

serial connection (remote debugging).

To activate GDB, i'll install a breakpoint on the target and connect GDB
throught that.
Standard behavior.

Now, what i would like to do is to have GDB interact with the target
without the target being stopped.
Yes, this breaks some of the purpose of the debugger, but i would like
to use GDB to analyze memory and datastructures without freezing the
program. The OS i am running do support task-switching, so i was
thinking about making the stub exception_handler non-blocking (e.g.
remove the while(1==1) statement that makes it accept commands until i
kill it), and instead have a call scheduled for it regularly.

Has anyone had experience with doing this? Or know of any place were i
could get more information on this? Is it even feasible?

I looked through Google, but was unable to find anything on this level.

Thank you for your time!

Regards,
Mattias Wildeman

Re: Nonblocking GDB stub

[Andrew Cagney]

> Hello!
> 
> I've been using GDB for a while, running it with a ARM based board and a
> 
> serial connection (remote debugging).
> 
> To activate GDB, i'll install a breakpoint on the target and connect GDB
> throught that.
> Standard behavior.
> 
> Now, what i would like to do is to have GDB interact with the target
> without the target being stopped.
> Yes, this breaks some of the purpose of the debugger, but i would like
> to use GDB to analyze memory and datastructures without freezing the
> program. The OS i am running do support task-switching, so i was
> thinking about making the stub exception_handler non-blocking (e.g.
> remove the while(1==1) statement that makes it accept commands until i
> kill it), and instead have a call scheduled for it regularly.
> 
> Has anyone had experience with doing this? Or know of any place were i
> could get more information on this? Is it even feasible?
> 
> I looked through Google, but was unable to find anything on this level.
> 
> Thank you for your time!

Perhaphs have a look through the tracepoints section of the documentation:
http://sources.redhat.com/gdb/onlinedocs/gdb_10.html#SEC68

Another option is to look at modifying GDB so that it doesn't stop all 
threads - instead only specified threads.  This is a little bit more 
ambitious though.

Andrew

Re: Nonblocking GDB stub

[Michael Snyder]

Mattias Wildeman wrote:
> 
> Hello!
> 
> I've been using GDB for a while, running it with a ARM based board and a
> 
> serial connection (remote debugging).
> 
> To activate GDB, i'll install a breakpoint on the target and connect GDB
> throught that.
> Standard behavior.
> 
> Now, what i would like to do is to have GDB interact with the target
> without the target being stopped.
> Yes, this breaks some of the purpose of the debugger, but i would like
> to use GDB to analyze memory and datastructures without freezing the
> program. The OS i am running do support task-switching, so i was
> thinking about making the stub exception_handler non-blocking (e.g.
> remove the while(1==1) statement that makes it accept commands until i
> kill it), and instead have a call scheduled for it regularly.
> 
> Has anyone had experience with doing this? Or know of any place were i
> could get more information on this? Is it even feasible?
> 
> I looked through Google, but was unable to find anything on this level.
> 
> Thank you for your time!
> 
> Regards,
> Mattias Wildeman

I did do this once, a number of years ago, so I know it's possible.
You have to watch out for a few things, of course.  It makes no sense
to talk about register values, for instance, nor to say run, step, or
continue.