From 6b5fd105cefb333edfd2a39af1c6428bfb1c4e19 Mon Sep 17 00:00:00 2001
From: "Richard M. Stallman" <rms@gnu.org>
Date: Thu, 27 May 1993 23:48:18 +0000
Subject: [PATCH] (mark_object): Add debugging code to check for ptr clobbered.

---
 src/alloc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/alloc.c b/src/alloc.c
index 48117d4e356..a6f554ad086 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -1623,7 +1623,11 @@ mark_object (objptr)
 	    XUNMARK (obj);
 	    goto loop;
 	  }
+	if (ptr == 0)
+	  abort ();
 	mark_object (&ptr->car);
+	if (ptr == 0)
+	  abort ();
 	objptr = &ptr->cdr;
 	obj = ptr->cdr;
 	goto loop;