Re: process attaching gdb to itself

Andrew Cagney
2003-09-29T13:21:55Z

>> works on BSD but fails on GNU/Linux. When doing an attach, BSD always
>> generates something for wait4 to consume. GNU/Linux does not, leaving
>> GDB stuck in wait4 :-(
>
>
> Yes, I've known about this problem for a long time. We've [I, Roland,

This explains something.

> a couple of other people I can't recall] talked about changing it and
> decided that, really, the current behavior makes more sense.

Not to me.

GDB sends a message to the kernel asking for the process to stop. The
kernel sends a message back indicating that the request has completed.

> It's not at all hard to make GDB work in the current system anyway.
> Just have to do it. It goes something like:
> - attach
> - wait4 WNOHANG, break if succeeds (optimistic, not necessary)
> - check in /proc to make sure the process is in a stopped state
> - If it was:
> - wait4 WNOHANG
> - If we get a status, then the process was running when we attached
> - If no status is available then the process was stopped when
> we attached
> - If it wasn't:
> - The process was running when we attached and hasn't stopped yet
> - wait4 without WNOHANG

I feel ill. What happens, for instance, if /proc isn't there?

Andrew