Re: [FYI 1/2] {test-protocols} tap/awk: handle exit statuses > 256 (seen on few korn shells)

[Eric Blake]

On 09/28/2011 08:34 AM, Stefano Lattarini wrote:
> Some Korn shells, when a child process die due to signal number
> n, can leave in $? an exit status of 256+n instead of the more
> standard 128+n.  Apparently, both behaviours are allowed by
> POSIX,

Indeed.  Here's some further reading:

http://austingroupbugs.net/view.php?id=51
http://austingroupbugs.net/view.php?id=347

which includes:


    "Implementations are encouraged to choose exit values greater than
    256 to indicate programs that terminate by a signal so that the
    exit status cannot be confused with an exit status generated by a
    normal termination."

add

    "However, the use of exit values greater than 256 poses a problem
    for the shell's own exit status. Historically this was the exit
    status of the last command invoked by the shell, but if the last
    command was terminated by a signal and was assigned an exit status
    greater than 256 by the shell, this value would be truncated to
    eight bits in the shell's exit status. Likewise truncation would
    occur with use of

        exit $?

    or

        ret=$?
        ....
        exit $ret

    in shell scripts. To avoid this truncation, shells which assign
    exit statuses greater than 256 are required to propagate the wait
    status of the last command to the shell's own wait status (by
    sending itself the same signal), and to handle exit values greater
    than 256 passed to the exit builtin by mimicking the wait status
    that would give rise to assignment of that exit status in the shell.
    Note that this requirement does not apply to signals that do not
    cause termination, such as SIGCHLD, since the shell can never
    actually assign a corresponding exit status greater than 256, and
    the requirement is worded in terms of this assignment."

> so be prepared to handle them both.

Yes, portability does demand we handle both.  Also, would you mind 
preparing an autoconf patch to mention this?

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org