Re: [musl] AT_MINSIGSTKSZ mismatched interpretation kernel vs libc

[Rich Felker]

On Mon, Sep 02, 2024 at 02:07:36PM +0200, Florian Weimer wrote:
> * 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.

It doesn't specify what happens on overflow. It does specify what
happens on non-overflow: the program executes correctly. Failure to do
that is the problem here, not failure to trap on fault.

Rich