Problems in Subprocesses of Tracees

Robert O'Callahan robert at ocallahan.org
Wed Dec 6 05:04:01 UTC 2017


On Wed, Dec 6, 2017 at 5:45 PM, Jun Inoue <jun.lambda at gmail.com> wrote:

> Hi there!  I'm having trouble with rr barfing on a subprocess of a
> tracee, which is called rtcd.
> Recording seems to go fine, but during replay I get "Assertion
> `ticks_now == trace_ticks' failed to hold" (more details at the end of
> this email).  The snag is that rr then suggests me to attach gdb to
> /sbin/ifconfig, rather than rtcd - it's a subprocess of rtcd, and not
> rtcd itself that rr is barfing on.
>
> Now, /sbin/ifconfig seems to be one of those programs that use shared
> memories to communicate with the outside world, so I want to prevent
> rtcd from monitoring this subprocess at all.  AFAIK all communications
> between rtcd and ifconfig happen through pipes, so this shouldn't
> affect rr's ability to replay.  Is there a way to do this?
>

No, we don't support detaching a tracee subprocess from recording, although
I suppose it wouldn't be that hard in principle.

I don't know of anything in /sbin/ifconfig that should cause problems. It's
more likely it's a syscall-related issue than a shmem issue. Can you `rr
dump -b -m -p` the trace leading up to event 1816?

Rob
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