Breakpoints and multi-process using the same binary

Breakpoints and multi-process using the same binary

[Marc Khouzam]

Hi,

the next release of Eclipse CDT will make use of GDB's great
multi-process (multi-exec) support.  Nice work!

Quick question about breakpoints in that case (with non-stop).
I'm trying to set a breakpoint in a process that has one 
thread stopped.  The problem is that there is another
process fully running, which uses the same binary
(parent/child of a fork()).

From what I can see, I cannot set such a breakpoint without
interrupting a thread for each and every process sharing the 
binary.

I just wanted to confirm that this was the right behavior
for GDB.  

Of course, when I run the same binary on two
different GDBs, things are completely independent.
I guess that is not possible under the same GDB?

Thanks

Marc

Re: Breakpoints and multi-process using the same binary

[Pedro Alves]

On Monday 11 April 2011 15:52:45, Marc Khouzam wrote:
> Hi,
> 
> the next release of Eclipse CDT will make use of GDB's great
> multi-process (multi-exec) support.  Nice work!
> 
> Quick question about breakpoints in that case (with non-stop).
> I'm trying to set a breakpoint in a process that has one 
> thread stopped.  The problem is that there is another
> process fully running, which uses the same binary
> (parent/child of a fork()).
> 
> From what I can see, I cannot set such a breakpoint without
> interrupting a thread for each and every process sharing the 
> binary.
> 
> I just wanted to confirm that this was the right behavior
> for GDB.  

Yeah, it's a current limitation.  I've looked at this a
bit after Tom reporting some other multi-process breakage, and
it  didn't look like a quick fix.  You may not need that
against linux gdbserver since it allows reading/writing
memory even when threads are running, while native linux gdb
doesn't.  We're likely to get to fix all of this for
proper ptsets/itsets support (which we'll be starting
on real soon).

-- 
Pedro Alves

RE: Breakpoints and multi-process using the same binary

[Marc Khouzam]

> -----Original Message-----
> From: Pedro Alves [mailto:pedro@codesourcery.com] 
> Sent: Monday, April 11, 2011 1:16 PM
> To: gdb@sourceware.org
> Cc: Marc Khouzam
> Subject: Re: Breakpoints and multi-process using the same binary
> 
> On Monday 11 April 2011 15:52:45, Marc Khouzam wrote:
> > Hi,
> > 
> > the next release of Eclipse CDT will make use of GDB's great
> > multi-process (multi-exec) support.  Nice work!
> > 
> > Quick question about breakpoints in that case (with non-stop).
> > I'm trying to set a breakpoint in a process that has one 
> > thread stopped.  The problem is that there is another
> > process fully running, which uses the same binary
> > (parent/child of a fork()).
> > 
> > From what I can see, I cannot set such a breakpoint without
> > interrupting a thread for each and every process sharing the 
> > binary.
> > 
> > I just wanted to confirm that this was the right behavior
> > for GDB.  
> 
> Yeah, it's a current limitation.  I've looked at this a
> bit after Tom reporting some other multi-process breakage, and
> it  didn't look like a quick fix.  You may not need that
> against linux gdbserver since it allows reading/writing
> memory even when threads are running, while native linux gdb
> doesn't.  

Thanks for mentioning that, I was not aware of it, but did
confirm it just now.  I was able to set a breakpoint while
the inferior was completely running using gdbserver, but 
only with GDB 7.3 (even 7.2.1 didn't support it).

For native gdb (or pre-7.3), I'll have to interrupt a thread
for every process before dealing with breakpoints.
(I could be more efficient and look for processes that have
the same executable, but I won't break my head over that
small optimization).

> We're likely to get to fix all of this for
> proper ptsets/itsets support (which we'll be starting
> on real soon).

Looking forward to it.

Thanks for the quick answer.

Marc