Let guard frames optionally pass through unwinding.

We have a bug in that when an exception occurs in a context
called from obj_print, the guard for stopping continuation
captures across obj_print also unintentially blocks the
unwinding. Let's make the unwinding blockage optional

* unwind.c (uw_unwind_to_exit_point): If a UW_GUARD is
encountered, do not abort if the uw_ok flag is set;
keep unwinding.
(uw_push_guard): New uw_ok argument, initializes the
uw_ok member of a guard frame.

* unwind.h (struct uw_guard): New struct type.
(union uw_frame): New member gu of type struct uw_guard.
(uw_push_guard): Declaration updated.

* ftw.c (ftw_callback): Pass zero as new uw_push_guard
argument: no unwinding across the POSIX library function ftw.

* glob.c (errfunc_thunk): Likewise, no unwinding across
the library function glob.

* lib.c (obj_print): Pass 1 as new uw_push_guard argument:
continuations can't be captured, but unwinding is okay.

1 files changed, 8 insertions, 1 deletions

diff --git a/unwind.h b/unwind.h
index 7177f0b1..20e3c987 100644
--- a/unwind.h
+++ b/unwind.h
@@ -79,6 +79,12 @@ struct uw_cont_copy {
   void (*copy)(mem_t *ptr, int parent);
 };
 
+struct uw_guard {
+  uw_frame_t *up;
+  uw_frtype_t type;
+  int uw_ok;
+};
+
 struct uw_debug {
   uw_frame_t *up;
   uw_frtype_t type;
@@ -98,6 +104,7 @@ union uw_frame {
   struct uw_catch ca;
   struct uw_handler ha;
   struct uw_cont_copy cp;
+  struct uw_guard gu;
   struct uw_debug db;
 };
 
@@ -124,7 +131,7 @@ noreturn val uw_errorfv(val fmt, struct args *args);
 val uw_register_subtype(val sub, val super);
 val uw_exception_subtype_p(val sub, val sup);
 void uw_continue(uw_frame_t *target);
-void uw_push_guard(uw_frame_t *);
+void uw_push_guard(uw_frame_t *, int uw_ok);
 void uw_push_debug(uw_frame_t *, val func, struct args *,
                    val ub_p_a_pairs, val env, val data,
                    val line, val chr);