Messages in this thread | | | Subject | Re: What is ptrace flag PT_TRACESYSGOOD for? | From | "Charles P. Wright" <> | Date | Tue, 14 Mar 2006 09:01:54 -0500 |
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On Tue, 2006-03-14 at 05:26 -0500, Chuck Ebbert wrote: > I am trying to document PTRACE_SETOPTIONS and I can't figure out what > the option PTRACE_O_TRACESYSGOOD is used for. Google is no help; > I can't find an explanation for _why_ it's there. All I can see is that > it causes ptrace() to deliver syscall stops with SIGTRAP | 0x80 > instead of just SIGTRAP and it can be used with PTRACE_SYSEMU. Chuck,
The PTRACE_O_TRACESYSGOOD is useful, because it allows you to differentiate between a standard SIGTRAP and a system call entry or exit. For example, if you have a ptrace monitor and receive a SIGTRAP, without O_SYSGOOD, it isn't clear if the kernel returned from wait (1) because someone did kill -TRAP pid, or (2) the process was entering a system call.
Charles
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