Messages in this thread Patch in this message | | | Date | Fri, 20 Apr 2001 12:13:12 +0200 | From | Éric Brunet <> | Subject | Re: Children first in fork |
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In ens.mailing-lists.linux-kernel, you wrote: >You're probably even better off just intercepting the fork, turning it >into a clone, and setting the CLONE_PTRACE option. Which (together with >tracing the parent, which you will obviously be doing already in order >to do all this in the first place) will nicely cause the child to get an >automatic SIGSTOP _and_ be already traced.
Well, I tried that, and it doesn't work. The problem is that the child starts ptraced, but it is its parent that will receive a signal for each syscall, and not the program that ptraces its parent. Of course, the parent will probably be a little bit confused by that (as it doesn't expect to receive those signals) and the monitoring programm won't see anything.
Maybe it would work if the function copy_flags in fork.c was modified into: ----------------------------------------------------------------- --- fork-old.c Fri Apr 20 12:01:09 2001 +++ fork.c Fri Apr 20 12:05:57 2001 @@ -552,8 +552,14 @@ new_flags &= ~(PF_SUPERPRIV | PF_USEDFPU | PF_VFORK); new_flags |= PF_FORKNOEXEC; - if (!(clone_flags & CLONE_PTRACE)) + if (!(clone_flags & CLONE_PTRACE)) { new_flags &= ~(PF_PTRACED|PF_TRACESYS); + if (p->p_pptr->flags &= PF_PTRACED) { + REMOVE_LINKS(p); + p->p_pptr = p->p_pptr->p_pptr; + SET_LINKS(child); + } + } if (clone_flags & CLONE_VFORK) new_flags |= PF_VFORK; p->flags = new_flags; ----------------------------------------------------------------- (sorry, it is a 2.2.19pre8 kernel, and I don't know what have changed since in that file) Ok, I haven't tried it (can't reboot a machine now), and I don't know what I am talking about, but the idea is simply ``if CLONE_PTRACE is set, and the parent is ptraced, then the child's effective parent should be its grandfather.'' Was it the way it was intended to work ? As it is now, I don't see any use of the CLONE_PTRACE flag.
Éric Brunet - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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