2 files changed, 13 insertions, 0 deletions
diff --git a/ChangeLog b/ChangeLog
index 0f6ef823..5dec2d8a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2015-02-06  Kaz Kylheku  <kaz@kylheku.com>
 
+	* unwind.c (uw_throw): Detect invalid re-entry and bail.
+	Cautiously, we use fprintf rather than our streams system, in case some
+	problem with the streams is involved in this mess.
+
+2015-02-06  Kaz Kylheku  <kaz@kylheku.com>
+
 	* unwind.c (uw_throw): Put a txr: prefix on the unhandled
 	exception in early initialization message.
 
diff --git a/unwind.c b/unwind.c
index 7e35c937..5d358e42 100644
--- a/unwind.c
+++ b/unwind.c
@@ -260,6 +260,12 @@ val uw_exception_subtype_p(val sub, val sup)
 val uw_throw(val sym, val args)
 {
   uw_frame_t *ex;
+  static int reentry_count = 0;
+
+  if (++reentry_count > 1) {
+    fprintf(stderr, "txr: invalid re-entry of exception handling logic\n");
+    abort();
+  }
 
   if (!listp(args))
     args = cons(args, nil);
@@ -334,6 +340,7 @@ val uw_throw(val sym, val args)
   ex->ca.sym = sym;
   ex->ca.args = args;
   uw_exit_point = ex;
+  reentry_count--;
   uw_unwind_to_exit_point();
   abort();
 }