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Re: single-stepping and internal breakpoints on a multi-threaded program
- From: Jim Blandy <jimb at codesourcery dot com>
- To: Emi SUZUKI <emi-suzuki at tjsys dot co dot jp>
- Cc: gdb at sourceware dot org
- Date: Fri, 06 Apr 2007 15:12:05 -0700
- Subject: Re: single-stepping and internal breakpoints on a multi-threaded program
- References: <email@example.com>
Emi SUZUKI <firstname.lastname@example.org> writes:
> The attached program makes two sub threads, and we do single-stepping
> on one of them.
> When the target get stopped by a internal breakpoint hit (ex. thread
> creation, thread death, shared library loading) during singe-stepping,
> GDB unconditionally resume all the thread and it result in running
> over the range of single-stepping.
I'm able to reproduce this problem on my FC6 x86 dual core system.
Thanks very much for the clear reproduction instructions.
> I saw that the context of single-stepping thread is preserved by
> context_switch called in handle_inferior_event, but GDB doesn't go
> back to that context till the thread is trapped in another reason
> (in the above case, the death of the thread).
> I think it should either stop immediately and prompt the user that the
> single-stepping has been cancelled, or goes back to the preserved
> context somehow and continue single-stepping.
> How do you think of it?
So, if I'm understanding correctly, we single-step the 'counter'
thread, which proceeds normally until the 'no_counter' thread hits its
TD_CREATE event, to tell GDB about its existence. Then, GDB fails to
resume single-stepping the 'counter' thread, letting it run until it
exits and reports its TD_DEATH event.
The fact that the inferior uses breakpoints to report thread creation
and thread death is supposed to be an internal detail of the thread
library --- or, more properly, of the thread debugging interface. One
thread stepping shouldn't be affected by other threads being created
(although GDB should still print the 'new thread' messages).
So I think the right behavior would be for GDB to continue
single-stepping after processing creation and death events for other
I have forgetten exactly how GDB handles multi-threaded single
stepping; I'm afraid I can't suggest how to do this. If you're unable
to fix it yourself, please file a bug report, and include your test