Re: windows exit codes truncated to 1 Byte

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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On Mar 31 09:24, Eric Blake wrote:
> On 03/31/2016 07:30 AM, Björn Stabel wrote:
> > Am 31.03.2016 um 15:01 schrieb Cristian:
> >> I noted that exit codes returned by CMD and other apps (msiexec) are truncated to 1 byte (0 .. 255).
> 
> This matches Linux, but not POSIX.

Why?  Does bash use waitid?

> >> Windows exit codes are represented using 32 bits, so is this limitation intentional?
> 
> Part intentional (we do what Linux does), and part accidental (Cygwin
> handles the return status slightly different than Windows, and that
> handling makes it impossible to easily preserve all 32-bits, even if
> Linux were to be patched to obey POSIX).

I don't quite understand this.  Right now the exitcode value is
truncated to 8 bits to fit into the 32 bit status value as defined
for wait/waitpid, but this is not set in stone.  We could change
the communication between parent and child to allow preserving the
full 32 bit value for waitid.

But...

> > POSIX specifies that the lower 8 bits of the exit status be made
> > available to the caller of wait/waitpid:
> > http://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html
> 
> Correct: wait() and waitpid() can only return 8 bits; but POSIX states
> that waitid() MUST be able to access all 32-bits untruncated; this is
> where Linux gets it wrong (Linux truncates during exit(), so waitid()
> can only return 8 bits; other operating systems do NOT truncate during
> exit, but preserve all 32 bits; if you use wait() or waitpid() you only
> get 8 bits, but if you use waitid() you can see the full 32 bits).

...that only makes sense if we implement waitid at all.  SHTDI and all
that...


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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