On Thu, 27 Nov 2014 12:17:39 +0100, Mark Wielaard wrote:
> On Wed, 2014-11-26 at 15:44 +0100, Jan Kratochvil wrote:
> > I was trying to figure out some more generic functionality than --core-pattern
> > but given that for core_pattern one needs to:
> > 	PTRACE_SEIZE
> > 	close(0)
> > 	waitpid()
> > I do not find any part of this sequence separable, do you?
> 
> The close (0) is somewhat odd. I assume it signals the process is done
> with handling the core file data and waitpid () never returns without
> that?

Yes.


> But it does seem somewhat harmless. Are there any bad side effects from
> closing stdin? We don't handle stdin at the moment. Although we could
> maybe add --core=- to be explicit about the core data coming from stdin.

I have discussed reading core file for --core-pattern in my other mail.


> The waitpid () really is just waiting for PTRACE_EVENT_EXIT. So if you
> wrap that in a while loop wouldn't it just work fine too in case the
> user uses it with -p <tid> on a thread that they want to get the
> backtrace of when it exits instead of in a core file pattern handler
> pipe?

Which way?
#1
	PTRACE_SEIZE
	waitpid()
	 = lock-up on waitpid()
#2
	close(0); (in a process exec-ing eu-readelf)
	PTRACE_SEIZE
	 = ESRCH; not tested but I find it obvious, the process has disappeared
	waitpid()
	 = ECHILD; not tested but obviously there is no ptraced process

I do not see where a while loop could be applied.


Thanks,
Jan