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To: sef@freebsd.org
cc: hackers@freebsd.org
Subject: Something fishy with our PT_ATTACH code!
Date: Fri, 26 Apr 1996 02:57:31 -0700
Message-ID: <29493.830512651@time.cdrom.com>
From: "Jordan K. Hubbard" <jkh@time.cdrom.com>
Sender: owner-hackers@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

Just got back from Kirk's usual Thursday-night OS class and while we
were going through exit1(), I noticed something that looked a little
odd in the ptrace "reattach" code.  In following it (and it later
turned out to be correct), I happened to notice the following weird
behavior with attach and detach:

Sequence:

[d0] jkh-ttyp4@time-> cat
<leave cat hanging around reading from stdin>

[d1] jkh-ttyp5@time-> ps ax | grep cat
<get cat's pid>

[d2] jkh-ttyp5@time-> gdb
     (gdb) attach <catpid>

[d3] <cat process is now in TX+ state, no wait channel>

[d4] (gdb) detach

[d5] [1]+  Suspended (signal)      cat


This is probably a bit hard to read, so I'll give you
a synopsis:  Start cat, attach cat from another tty with
gdb, watch cat go to sleep, detach cat in gdb and watch
cat erroneously suspend itself.

It would seem to me that the far more correct behavior would
be something like:

Start cat, attach cat from another tty with gdb, watch cat go to
sleep, detach cat in gdb and watch it return to its previous
un-stopped state.

Or am I off-base on this one somehow?

					Jordan