RE: debug of multithreaded program turns to be impossible during execution

[Avi Gozlan <avi at checkpoint dot com>]

GDB 7.8 yields a similar behavior:

(gdb) c
Continuing.
...
[New Thread 0x43c05940 (LWP 3311)]
[New Thread 0x44606940 (LWP 3312)]
...
[Thread 0x44606940 (LWP 3312) exited]
[Switching to Thread 0x43c05940 (LWP 3311)]
Cannot remove breakpoints because program is no longer writable.
Further execution is probably impossible.
0x00002aaaab98348f in start_thread () from /lib64/libpthread.so.0
ptrace: No such process.
(gdb) [Thread 0x46409940 (LWP 3315) exited]
[Thread 0x45a08940 (LWP 3314) exited]
[Thread 0x43c05940 (LWP 3311) exited]
[Inferior 1 (process 3268) exited normally]

The only difference is that in 7.8 case, GDB continues automatically after giving the ptrace message.

Avi

-----Original Message-----
From: Pedro Alves [mailto:palves@redhat.com] 
Sent: Thursday, July 31, 2014 1:17 PM
To: Avi Gozlan; gdb@sourceware.org
Subject: Re: debug of multithreaded program turns to be impossible during execution

On 07/31/2014 10:27 AM, Avi Gozlan wrote:
> Hello,
> 
> I'm debugging a multithreaded program using GDB. Various threads are created and exit during execution. GDB copes successfully with the multiple threads (e.g. 'thread apply 3 bt' reports successfully backtrace of thread 3), but then at one point loses control of the program:
> 
> (gdb) c
> Continuing.
> [New Thread 0x41401940 (LWP 13370)]
>  [Thread 0x40a00940 (LWP 13333) exited] [New Thread 0x41e02940 (LWP 
> 13371)] ...
> [New Thread 0x45a08940 (LWP 13377)]
> [New Thread 0x46409940 (LWP 13378)]
>  [Thread 0x41e02940 (LWP 13371) exited]  [Switching to Thread 
> 0x45a08940 (LWP 13377)] Cannot remove breakpoints because program is 
> no longer writable.
> Further execution is probably impossible.
> 0x00002aaaab98348f in start_thread () from /lib64/libpthread.so.0
> ptrace: No such process.
> 
> Surprisingly, although debugging is no more possible, the program is not dead:

I have a vague recollection that this was fixed a while ago.  Like, GDB was picking the wrong thread to access memory, and it ended up picking a running or exited thread, and that fails (in either case ptrace complains the same say).

> GDB version: 7.6

Is there a chance you could try a more recent GDB version?  Ideally 7.8, which we just released.

Thanks,
Pedro Alves


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