Re: What is ptrace flag PT_TRACESYSGOOD for?

["Charles P. Wright" <cwright@cs.sunysb.edu>]

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