[TUHS] MacOS X is Unix (tm)

Joerg Schilling schily at schily.net
Wed Jan 4 03:51:36 AEST 2017


Random832 <random832 at fastmail.com> wrote:

> On Tue, Jan 3, 2017, at 10:08, Joerg Schilling wrote:
> > Random832 <random832 at fastmail.com> wrote:
> > > However, OSX only claims compliance to Issue 6 (unistd.h _XOPEN_VERSION
> > > 600), and the text requiring that the full 32-bit value be preserved is
> > > new to Issue 7.
> > 
> > The text requiring the full 32-bit value is not new....
>
> Is there some other text you have in mind other than "The exit value in
> si_status shall be equal to the full exit value (that is, the value
> passed to _exit(), _Exit(), or exit(), or returned from main()); it
> shall not be limited to the least significant eight bits of the value."
> in the description of signal.h (not present in Issue 6 or SUSv2)? Or
> maybe something from "2.13. Status Information" (whole section is new in
> Issue 7).

This has now been worded to make it obvious that masking off bits is not 
permitted - except for the historic UNIX wait()/waitpid() interfaces.

> In SUSv2, the text of exit() states "If the parent process of the
> calling process is executing a wait(), wait3(), waitid() or waitpid(),
> [...] it is notified of the calling process' termination and the
> low-order eight bits (that is, bits 0377) of status are made available
> to it." with no indication of any of these functions allowing the parent
> process to get more bits of status. More or less the same text appears
> in Issue 6, with some rearrangement due to waitid being part of the XSI
> option.

SUSv2 is the standard with the correct text:

Here is a part of it's wait() description:

WEXITSTATUS(stat_val)
    If the value of WIFEXITED(stat_val) is non-zero, this macro evaluates to 
the low-order 8 bits of the status argument that the child process passed to 
_exit() or exit(), or the value the child process returned from main(). 

from the signal.h description:

int           si_status exit value or signal

So masking is only mentioned for wait() and waitpid()

> > It was required in 1996 already, but then somebody introduced a bug into
> > the text and that was not aligned with the expected behavior.
>
> Oh, so there was a bug in *the text*. That would be the text of the
> standard that OSX conforms to?

In SUSv2, it did just describes the waitid() interface without mentioning that
there is a mask. People at that time seem to believe that everybody knows that
si_status is a full int.

Note that the WEXITSTATUS() macro does not apply to waitid().

Later, the wrong masking text has been added.

POSIX never introduced own inventions, but rather standardizes existing 
features. The siginfo/waitid() interface has been introduced by SVr4 in 1989 
and platforms that correctly implement SVr4 compliance of course all return the 
full int.

Apple seem to have known that the compliance test did only check for

	"more than 8 bits"

by using a 16 bit exit() value in the tests...

Jörg

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