Re: Debugging gdb under gdb

[Michael Eager <eager at eagercon dot com>]

Michael Snyder wrote:
> Michael Eager wrote:
> > Hi --
> >
> > When I try to run a test gdb under gdb, the host gdb hangs.
> >
> > The hang occurs when the test gdb is executing pex_unix_exec_child().
> > As soon as the test gdb executes fork(), the host gdb hangs.
> > I've tried all of the permutations of follow-fork-mode
> > and detach-on-fork, with no luck.  The host neither follows
> > the parent nor the child processes.
> >
> > The host gdb is "GNU gdb Fedora (6.8-32.fc10)".
> >
> > Suggestions?
>
> Are you stepping or continuing when this occurs?
>
> There is a point, somewhere around where gdb is forking the child,
> where stepping always hangs for me.  I don't remember exactly where.
> I work around it by setting a breakpoint somewhere just after, and
> continuing.

I've tried both stepping and continuing.  I set breakpoints in
the code shared between parent & child (where it checks the pid)
and also on both paths.  None of the breakpoints are hit.

The host gdb also hangs when there are no breakpoints set and
I just run the test gdb.

> It's been a while since I've done this... but see if that helps.

The call to pex_unix_exec_child() is in find_charset_names().
My workaround is to have the host gdb force a return from
find_charset_names() in the test gdb, so it never tries to
do a fork().

--
Michael Eager	 eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077