Re: [PATCH] 0001-Fix-multi-thread-debug-bug-in-AIX.patch

[Ulrich Weigand <Ulrich.Weigand@de.ibm.com>]

Aditya Kamath1 <Aditya.Kamath1@ibm.com> wrote:

>>You should find out why the "priv" field isn't
>>set up correctly, and fix whatever was going
>>wrong there.  (I believe this should have been
>>done in sync_threadlists.)
>
>You were right about this. What is happening is the main process 
>and the thread representing it are treated as two separate threads
>by the libpthread library. Main process had no private data set
>whereas the thread representing it had. Usually, both of them
>should have it and their private data must be the same. 

I see.  I agree this is the root cause of the issue, but the fix
doesn't look quite right to me.

You should not even *have* the duplicate GDB thread in the first place.

>(gdb) info threads
>  Id   Target Id                          Frame 
>* 1    process 12059046                   0xd0595fb0 in _p_nsleep () from /usr/lib/libpthread.a(shr_xpg5.o)
>  2    Thread 1 (tid 39125487, running)   0xd0595fb0 in _p_nsleep () from /usr/lib/libpthread.a(shr_xpg5.o)
>  3    Thread 258 (tid 23396809, running) thread_function (arg=0x0) at continue-pending-status.c:36
>  4    Thread 515 (tid 36503883, running) thread_function (arg=warning: (Internal error: pc 0x0 in read in psymtab, but not in symtab.)

This is not how GDB threads are handled on any other platform.  While
you do have a single dummy thread representing the process if it is
*non-threaded*, as soon as the process is recognized as multi-threaded,
you will only see a single GDB thread per target thread, and no
separate "thread" for the whole process.

So I think instead of adding a "priv" struct to that GDB thread
identifying the main process, the sync_threadlists routine should
actually just delete it (or replace it with the actual first thread,
whatever is easier).

Looking at the code, there already seems to be a place where
sync_threadlists deletes GDB threads that do not match onto
and of the threads reported by the AIX thread library - can
you verify why this doesn't trigger here?

Bye,
Ulrich