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

[Andrew Cagney <cagney at gnu dot 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