Re: thread ptids when debugging from core file (x86-linux)

[Andrew Cagney <cagney@gnu.org>]

>>Joel, this observation of yours is the key:
>>> 
>>
>>>> >Unfortunately, that doesn't work when debugging from a core file,
>>>> >because the PTID of the threads are not the same as when debugging
>>>> >live. 
>>
>>> 
>>> The best way to appreciate this is to consider:
>>> 
>>> (gdb) attach program
>>> (gdb) info threads
>>> thread output #1
>>> (gdb) info lwp -- yes ok, that cmd doesn't exist :-)
>>> lwp output #1 (different to the thread output)
>>> (gdb) gcore program.gcore
>>> (gdb) detach
>>> Segmentation fault core dumped to program.core
>>> (gdb) corefile program.core
>>> (gdb) info threads
>>> identical thread output #2
>>> (gdb) info lwp
>>> identical lwp output #2
>>> (gdb) corefile program.gcore
>>> (gdb) info threads
>>> also identical output #3
>>> (gdb) info lwp
>>> also identical lwp output #3
> 
> 
> I am sorry, I don't understand what you are saying. What do you
> mean by "identical output #n"? What is it identical to? to output
> #1? (right now, it is not).

Yes.  ``thread output'' #1, #2, an #3 should be identical.  Similarly 
``lwp output'' 1-3 should also be identical.

The're not, its a bug (and one everyone has been trying to sweep under 
the carpet).  The corefile code should be loading libthread_db so that 
GDB can use the .reg/<LWPID> along with memory information to re-create 
the thread list.  At one stage it even did that but it was then disabled 
because it caused a core dump and ...

Andrew