[musl] AT_MINSIGSTKSZ mismatched interpretation kernel vs libc

[Florian Weimer]

* Rich Felker:

> This is ambiguously worded (does "operating system" mean kernel?) and
> does not agree with POSIX, which defines it as:
>
>     Minimum stack size for a signal handler.
>
> And otherwise just specifies that sigaltstack shall fail if given a
> smaller size.
>
> The POSIX definition is also underspecified but it's clear that it
> should be possible to execute at least a do-nothing signal handler
> (like one which immediately returns and whose sole purpose is to
> induce EINTR when intalled without SA_RESTART), or even a minimal one
> that does something like storing to a global variable, with such a
> small stack. Allowing a size where even a do-nothing signal handler
> results in a memory-clobbering overflow or access fault seems
> non-conforming to me.

POSIX does not specify what happens on a stack overflow (or more
generally, if most resource limits are exceeded), so I think the
behavior is conforming on a technicality.

Thanks,
Florian