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Bug #47566 PCNTL Waitpid exit status incorrect
Submitted: 2009-03-04 21:59 UTC Modified: 2009-05-26 14:03 UTC
From: james at jamesreno dot com Assigned:
Status: Closed Package: PCNTL related
PHP Version: 5.2.9 OS: linux-2.6
Private report: No CVE-ID:
 [2009-03-04 21:59 UTC] james at jamesreno dot com
Description:
------------
The $status exitcode returned by pcntl_waitpid() is incorrectly casted resulting in an invalid number being returned.

I believe the int is converted to a long in ext/pcntl/pcntl.c, resulting in an invalid integer being returned to the parent.

        zval *z_status = NULL;
        int status;
        convert_to_long_ex(&z_status);
        status = Z_LVAL_P(z_status);
        child_id = waitpid((pid_t) pid, &status, options);
        Z_LVAL_P(z_status) = status;

z_status is a long, but status is an int...


Reproduce code:
---------------
<?
$pid = pcntl_fork();
if ($pid == -1) {
 echo "Unable to fork";
 exit;
} elseif ($pid) {
 $epid = pcntl_waitpid(-1,$status);
 echo "PARENT: {$pid}/{$epid} exited {$status}\n";
 exit(128);
} else {
 echo "CHILD: Exiting with exit code 128\n";
 exit(128);
}
?>

Expected result:
----------------
[james@localhost ~]$ php test.php
CHILD: Exiting with exit code 128
PARENT: 7598/7598 exited 128
[james@localhost ~]$ echo $?
128
[james@localhost ~]$


Actual result:
--------------
[james@localhost ~]$ php test.php
CHILD: Exiting with exit code 128
PARENT: 7598/7598 exited 32768
[james@localhost ~]$ echo $?
128
[james@localhost ~]$

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 [2009-03-05 20:54 UTC] james at jamesreno dot com
exit(254);

$pid = pcntl_waitpid(-1,$status);

if (pcntl_wifexited($status)) {
 $status = pcntl_wexitstatus($status);
 echo $status;
}

Then why is $status, -2 rather than '254'?

This method does not seem work *properly* either...
 [2009-05-26 04:47 UTC] james at jamesreno dot com
Not bogus.... see below:

Its obviously not returning properly:
   1.      while (($pid=pcntl_waitpid(-1,$status,WNOHANG))>0) {
   2.       echo "RAW: {$status}\n";
   3.       var_dump(pcntl_wifexited($status));
   4.        var_dump(pcntl_wexitstatus($status));
   5.       var_dump(pcntl_wifsignaled($status));
   6.        var_dump(pcntl_wtermsig($status));
   7.       var_dump(pcntl_wifstopped($status));
   8.        var_dump(pcntl_wstopsig($status));
   9.       echo "END RAW: {$status}\n";
  10.      }
  11.       
  12.      RAW: 65280
  13.      pcntl_wifexited   == bool(true)  => pcntl_wexitstatus == int(-1)
  14.      pcntl_wifsignaled == bool(false) => pcntl_wtermsig    == int(0)
  15.      pcntl_wifstopped  == bool(false) => pcntl_wstopsig    == int(255)
  16.      END RAW: 65280
  17.
  18.  
  19.      RAW: 65280
  20.      bool(true)
  21.      int(-1)
  22.      bool(false)
  23.      int(0)
  24.      bool(false)
  25.      int(255)
  26.      END RAW: 65280

Guess ill be hax0ring the code to make it work properly.

seems the same on PHP 5.3.0-RC2
 [2009-05-26 05:27 UTC] james at jamesreno dot com
/* {{{ proto int pcntl_wexitstatus(int status)
   Returns the status code of a child's exit */
PHP_FUNCTION(pcntl_wexitstatus)

The function definition says it returns an INT, as it SHOULD -- exit codes can not be negative! and are in the range of 0-255 (8 bits) on posix systems. (iirc).


-- HOWEVER --

Php actually returns:
        status_word = (int) Z_LVAL_PP(status);
        /* WEXITSTATUS only returns 8 bits so we *MUST* cast this to signed char
           if you want to have valid negative exit codes */

        RETURN_LONG((signed char) WEXITSTATUS(status_word));

It should NOT, it should not cast it to a (signed char)


So if you actually want the right result in your code :(
In php-5.2.9/ext/pcntl/pcntl.c line 379

Change:
        RETURN_LONG((signed char) WEXITSTATUS(status_word));
to:
        RETURN_LONG(WEXITSTATUS(status_word));
 [2009-05-26 14:03 UTC] lbarnaud@php.net
This bug has been fixed in CVS.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.


 
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