Re: [Emacs-diffs] trunk r117912: Minor improvements to new stack-allocated Lisp objects.

[Eli Zaretskii]

> Date: Mon, 22 Sep 2014 10:42:35 +0400
> From: Dmitry Antipov <address@hidden>
> Cc: address@hidden
> 
> > We should also audit uses of make_local_vector, make_local_string, and 
> > build_local_string to make sure
> > that none of them are in loops that could blow the stack.  I think most 
> > uses of these are OK but
> > some are questionable.
> 
> SAFE_ALLOCA and friends has exactly the same problems, and I don't see the 
> way to make it
> absolutely safe with an existing implementations of alloca.  This applies to 
> VLAs as well.

We indeed have a few calls to SAFE_ALLOCA and SAFE_NALLOCA inside loops.

> Someday we will be able to utilize -fsplit-stack; it may be reasonable to 
> define
> USE_LOCAL_LISP_OBJECTS only if -fsplit-stack is also supported.

AFAIU, -fsplit-stack is a mixed blessing at best when calling code
that was not compiled with that switch (a.k.a. "external libraries").