lkml.org 
[lkml]   [2011]   [May]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH 03/10] ptrace: implement PTRACE_SEIZE
Date
On Tuesday 24 May 2011 13:00:13, Tejun Heo wrote:
> Hello,
>
> On Tue, May 24, 2011 at 10:49:58AM +0100, Pedro Alves wrote:
> > A couple interface questions that just crossed my mind:
> >
> > - on a fork/vfork/clone, if PTRACE_EVENT_FORK|VFORK|CLONE have been
> > enabled, will the tracer still see the new child stop with a
> > SIGSTOP, or will it see a PTRACE_EVENT_INTERRUPT?
>
> This won't change, so SIGSTOP although we probably want to improve it
> such that this can be distinguished from SIGTRAP from userland.

(I assume you meant SIGSTOP from userland.) So that if a SIGSTOPs
from userland is sent before the tracer waits for the child, the
tracer sees a siginfo corresponding to the userland SIGSTOP? Sounds
like it might work.

> > - is PTRACE_INTERRUPT on PTRACE_TRACEME-traced-child planed to
> > be allowed (for convenience)?
> > A PTRACE_O_TRACEINTERRUPT, or some such PTRACE_SETOPTIONS
> > option might be necessary to get PTRACE_EVENT_INTERRUPT instead
> > of SIGSTOP in the point above.
>
> I'm currently leaning toward deprecating PTRACE_TRACEME. If a task
> can PTRACE_TRACEME, it may as well just do pause(2) and let the parent
> SEIZE it.

Debuggers will want to nurse the child through a couple of
execs (shell, then real debuggee), so that scheme requires a bit
more synchronization, because SEIZE hides the magic exec SIGTRAP,
and so the tracer needs to set the O_TRACEXEC option before the first
exec, and make sure external signals don't break the synchronization.
Reading/writing to/from blocking pipes for that initial synchronization
is what GDB uses instead for e.g., hpux/ttrace support, which looks
similar to using PTRACE_SEIZE for PTRACE_TRACEME. A bit more
cumbersome, though doable, I suppose.

Thanks.

--
Pedro Alves


\
 
 \ /
  Last update: 2011-05-24 14:39    [W:0.101 / U:0.548 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site