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Date: Fri, 13 Jun 2025 14:25:17 -0700 (PDT)
X-X-Sender: jeremyd AT resin DOT csoft DOT net
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Subject: Re: posix_spawn difference from Linux
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From: Jeremy Drake via Cygwin <cygwin AT cygwin DOT com>
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On Fri, 13 Jun 2025, Jeremy Drake wrote:

> I am working on some posix_spawn tests for the new stc repository [1], and
> making sure they behave the same between Cygwin and Linux.  I found one
> case (so far) which does not: passing NULL for argument "envp" to
> posix_spawn.
>
> In Cygwin, this results in the child inheriting the environment from the
> caller (same as passing "environ"), but on Linux this results in the child
> getting an empty environment (same as passing a char *envp[] = {NULL}).
>
> The Open Group doc on posix_spawn[2] doesn't seem to say anything about
> the potential for envp being NULL, but does mention
>
> > For the Ada language binding for Start_Process to be implemented with
> > posix_spawn(), that binding would need to explicitly pass an empty
> > signal mask and the parent's environment to posix_spawn() whenever the
> > caller of Start_Process allowed these arguments to default, since
> > posix_spawn() does not provide such defaults.
>
> That at least implies that passing NULL does not default to using the
> parent's environment.
>
> Thoughts?  Is this a bug in Cygwin, or "undefined behavior" that it's
> perfectly within its rights to do whatever it feels like in response
> (empty environment or inherited environment, or crash every second
> Tuesday)?

Oops, I forgot my footnote links:

[1]: https://cygwin.com/cgit/cygwin-apps/stc/
[2]: https://pubs.opengroup.org/onlinepubs/007904975/functions/posix_spawn.html

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