ffi: a measure of safety for callbacks.

We don't want, by default, for callbacks to capture delimited
continuations across foreign code, or perpetrate non-local
transfers across foreign code. Here, we take an approach
similar for what was done in ftw_wrap.

* ffi.c (s_exit_point): New global variable with internal
linkage.
(ffi_call_wrap): If s_exit_point isn't nil, then it means that
the callback intercepted a nonlocal transfer and stored its
exit point. We resume the transfer to that exit point instead
of returning normally.
(ffi_closure_dispatch_safe): New static function.
(ffi_make_closure): Support a new argument which indicates
whether to make a closure which uses
ffi_closure_dispatch_safe, or ffi_closure_dispatch.
(ffi_init): Update registration of ffi-make-closure intrinsic.

* ffi.h (ffi_make_closure): Declaration updated.

* share/txr/stdlib/ffi.tl (sys:deffi-cb-expander): New
function.
(deffi-cb): Macro internals replaced by call to new
function.
(deffi-cb-safe): New macro.

* txr.1: Documentation of ffi-make-closure updated.
New deffi-cb-unsafe macro documented.

1 files changed, 1 insertions, 1 deletions

diff --git a/ffi.h b/ffi.h
index e11d8b51..8eb54a78 100644
--- a/ffi.h
+++ b/ffi.h
@@ -53,7 +53,7 @@ extern val ffi_type_s, ffi_call_desc_s, ffi_closure_s;
 
 val ffi_type_compile(val syntax);
 val ffi_make_call_desc(val ntotal, val nfixed, val rettype, val argtypes);
-val ffi_make_closure(val fun, val call_desc);
+val ffi_make_closure(val fun, val call_desc, val safe_p_in);
 mem_t *ffi_closure_get_fptr(val closure);
 val ffi_call_wrap(val ffi_call_desc, val fptr, val args);
 val ffi_typedef(val name, val type);