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SubjectRe: Compat 32-bit syscall entry from 64-bit task!?
Denys Vlasenko wrote:
> On Thu, Jan 26, 2012 at 11:31 AM, Jamie Lokier <jamie@shareable.org> wrote:
> > Indan Zupancic wrote:
> >> On Thu, January 26, 2012 02:08, Jamie Lokier wrote:
> >> > Is it disambiguated by PTRACE_EVENT_EXEC happening before the execve
> >> > returns, and you knowing the TID always changes to the PID?  I haven't
> >> > yet checked which TID gets the PTRACE_EVENT_EXEC event, but if it's
> >> > not the old one, perhaps that could be changed.
> >>
> >> Please don't ever change the behaviour of PTRACE_EVENT_EXEC, it's
> >> barely documented already, but if if ever changes it will be also
> >> unreliable.
> >>
> >> It's still unclear if the PTRACE_EVENT_EXEC comes before or after
> >> or instead of the post-execve ptrace event.
>
> Denis <- confused.
> Was ist das "post-execve ptrace event"? I know no such thing.
> I know about PTRACE_EVENT_EXEC, and "post-execve SIGTRAP".

Sorry, I meant to write execve-syscall-exit event.

> >> I guess before, but
> >> can I count on that? If it is after then I get a stray weird
> >> execve event that messes up the system call cadence.
> >
> > It should be *sent* before because the exec steps must finish before
> > the execve() syscall "returns".
> >
> > I'm not sure if the events are guaranteed to be received in the same
> > order as they are sent.
>
> All ptrace stops (events and other stops) are synchronous.
> Tracee stops, tracer notices it, tracer restarts tracee,
> and only after this tracee can generate next event.
> Therefore ptrace stops can't get reordered.

That's good to know, thanks.

-- Jamie
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