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Date: Fri, 13 Jun 2025 14:23:11 -0700 (PDT)
To: cygwin AT cygwin DOT com
Subject: posix_spawn difference from Linux
Message-ID: <35d5a3b2-e060-cb17-7e2a-75f6b6e8d0a5@jdrake.com>
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From: Jeremy Drake via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Jeremy Drake <cygwin AT jdrake DOT com>
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Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>

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 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)?

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