[uml-devel] Re: Debian bug 271069, gdb startup fails

[Daniel Jacobowitz <dan@debian.org>]

On Sat, Nov 13, 2004 at 04:14:43PM -0500, Daniel Jacobowitz wrote:
> History:
>   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=271069
> 
> I've been looking at this bug.  I've already fixed the EINTR problem;
> I didn't see your patch (not sure why the BTS didn't forward it to me).
> But 2.6.10-rc1 does the same thing outside of UML, so I needed to fix
> it anyway.
> 
> However, GDB startup still fails in UML using './linux debug'.  Here's
> what happens:
> 
> - GDB forks
> - the child issues TRACEME
> - GDB waits for it, successfully now that EINTR is handled
> - GDB issues PTRACE_SETOPTIONS (returns -EINVAL because the proxy
>   does not support it)
> - GDB decides that the feature isn't available (good so far; it isn't)
> - GDB tries to clean up.  It sends PTRACE_KILL to the child it forked.
> - GDB waits for the child to exit.  Which it never does.
> 
> I imagine the proxy is just not able to cope with this.  It certainly
> doesn't look as if it can.  For instance, arg2 is completely ignored
> except for PTRACE_ATTACH; I think what has happened is that the
> PTRACE_KILL was sent to the wrong process.  And the waitpids are
> probably waiting for the wrong process too.
> 
> I think the only way to fix this is to teach the UML proxy to get out
> of the way if the pid is not the expected one, for at least PTRACE_KILL
> and waitpid; but it should probably continue to return failure for
> PTRACE_SETOPTIONS.

Actually, while the proxy probably should be fixed anyway, I've worked
around this in GDB.  It will be in the Debian 6.3-2 packages, which I'm
working on right now.

Should "kill" work from the GDB prompt?  If so, that does need some
work in the proxy.

-- 
Daniel Jacobowitz


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