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Re: [patch] Fix attaching to Linux stopped processes
On Mon, 18 Sep 2006 00:26:22 +0200, Daniel Jacobowitz wrote:
> On Mon, Sep 18, 2006 at 12:12:28AM +0200, Jan Kratochvil wrote:
> > Hi,
> >
> > sleep 1h& pid=$!; kill -STOP $pid; gdb sleep $pid
> > ->
> > Attaching to program: /bin/sleep, process 20768
> > ../../gdb/linux-nat.c:1057: internal-error: linux_nat_attach: Assertion `pid == GET_PID (inferior_ptid) && WIFSTOPPED (status) && WSTOPSIG (status) == SIGSTOP' failed.
>
> > + /* Do not check `WSTOPSIG (status) == SIGSTOP' as the status may be
> > + arbitrary - depending on the signal that stopped the processes.
> > + If the process was running we get SIGSTOP, if it was already stopped
> > + by SIGSTOP we get 0. The value gets used for `PTRACE_CONT'. */
>
> So I checked. Sure enough, on my 2.6.18-rc4
> installation, this is _not_ what happens. Instead, the traditional
> thing happens: wait hangs and no new event is returned.
>
> Is this new in kernel.org? Or is it a Red Hat kernel patch? Where
> did it come from?
Thanks for checking it.
OK, the patch was originally for GDB on Red Hat "kernel-2.6.17-1.2647.fc6".
Still it is reproducible even on both linux-2.6.17.13 and linux-2.6.18-rc4, you
just need to "kill -CONT $pid" the inferior as gdb(1) will hang during
attaching to it. Screenshot (sorry for graphics):
http://www.jankratochvil.net/priv/gdb.png
gdb is built from the current clean CVS snapshot.
Also the patch looks right to me - after `PT_ATTACH' it is appropriate that
`WSTOPSIG (status)' will report the original signal that stopped process,
(WSTOPSIG (status) == SIGSTOP) <=> (process was in running/sleeping mode).
Regards,
Jan