[Bug tapsets/12471] Support wait4 *status printing

[dsmith at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12471

--- Comment #3 from David Smith <dsmith at redhat dot com> 2011-02-09 17:45:12 UTC ---
(In reply to comment #2)
> (In reply to comment #1)
> > Perhaps adding a new variable called 'statusstr' or 'status_str' that just gets
> > the value of _wait_status_str() is a better idea.
> 
> I used it before but such variable needs to be thread/SMP protected.  There
> should be some primitives to have per_cpu() accessible from .stp.

Here's what I was suggesting:

probe syscall.wait4.return = kernel.function("sys_wait4").return
{
  name = "wait4"
  status_str = ($stat_addr == 0) ? "NULL"
     : _wait_status_str(user_int($stat_addr))
  retstr = return_str(1, $return)
}

> > We could also provide the user with WIFEXITED/WEXITSTATUS/etc. functions if
> > anyone thinks that would be a good idea.
> 
> That decoding is provided by this patch, isn't it?

This patch provides the WIFEXITED/WEXITSTATUS data as a string.  My thought
above was that we could provide functions like this:

function WTERMSIG:long(status:long) {
 return (status & 0x7f)
}

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