Messages in this thread | | | Date | Thu, 21 Jul 2011 18:51:37 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] man ptrace: add extended description of various ptrace quirks |
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On 07/21, Denys Vlasenko wrote: > > Deleted several outright false statements: > - pid 1 can be traced > - tracer is not shown as parent in ps output > - PTRACE_ATTACH is not "the same behavior as if tracee had done > a PTRACE_TRACEME": PTRACE_ATTACH delivers a SIGSTOP. > - SIGSTOP _can_ be injected.
Yes, this is correct, thanks.
> +Tracer can not assume that tracee ALWAYS ends its life by reporting > +WIFEXITED(status) or WIFSIGNALED(status). > +.LP > +.\" or can it? Do we include such a promise into ptrace API?
IIRC, we already discussed this... The traced group leader can disappear during mt-exec, otherwise the tracee can never go away silently.
> +Tracer can kill a tracee with ptrace(PTRACE_KILL, pid, 0, 0). This > +operation is deprecated, use kill(SIGKILL) or tgkill(SIGKILL) instead. > +The problem with this operation is that it requires tracee to be in > +signal-delivery-stop, otherwise it may not work (may complete > +successfully but won't kill the tracee),
In short, ptrace(PTRACE_KILL) is more or less ptrace(PTRACE_CONT, SIGKILL), but it always returns 0. IOW, it never worked as decribed in the man page. And I guess today nobody can explain why PTRACE_KILL exists.
Oleg.
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