[Bug 215769] man 2 vfork() does not document corner case when PID == 1

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=215769

Florian Weimer (fweimer@redhat.com) changed:

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--- Comment #11 from Florian Weimer (fweimer@redhat.com) ---
(In reply to brauner from comment #10)
> glibc does vfork() via inline assembly massaging. There's probably
> atfork handlers and a bunch of other stuff involved so it's difficult to
> do a remote diagnosis.

glibc does not run fork handlers for vfork.

> (And note that calling anything other than execve() or _exit() after
> vfork() is basically undefined behavior.)

Historically, glibc supports calling malloc after vfork, so that applications
can implement their own form of close_range by reading /proc/self/fd.

I wonder if we need to handle CLONE_NEWTIME in posix_spawn in some way. Surely
that clone(CLONE_VM | CLONE_VFORK | SIGCHLD) call should fail as well if vfork
is blocked after CLONE_NEWTIME, so CLONE_NEWTIME probably breaks posix_spawn.

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