From 174c2620c82a47d067ec7b5062a4f513155a0b1f Mon Sep 17 00:00:00 2001
From: M Joonas Pihlaja <jpihlaja@cc.helsinki.fi>
Date: Fri, 24 Jul 2009 07:42:57 +0300
Subject: [trace] Check for object stack underflow.

If the tracer's object stack underflows we want to
know about is as soon as possible. This patch adds
checks against the stack overflowing and aborts the
program with an object stack dump if it does.
---
 util/cairo-trace/trace.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/util/cairo-trace/trace.c b/util/cairo-trace/trace.c
index 3c47aafc..beeec204 100644
--- a/util/cairo-trace/trace.c
+++ b/util/cairo-trace/trace.c
@@ -828,11 +828,31 @@ _get_object (enum operand_type op_type, const void *ptr)
 static Object *current_object[2048]; /* XXX limit operand stack */
 static int current_stack_depth;
 
+static void
+ensure_operands (int num_operands)
+{
+    if (current_stack_depth < num_operands)
+    {
+	int n;
+
+	fprintf (stderr, "Operand stack underflow!\n");
+	for (n = 0; n < current_stack_depth; n++) {
+	    Object *obj = current_object[n];
+
+	    fprintf (stderr, "  [%3d] = %s%ld\n",
+		     n, obj->type->op_code, obj->token);
+	}
+
+	abort ();
+    }
+}
+
 static void
 _consume_operand (void)
 {
     Object *obj;
 
+    ensure_operands (1);
     obj = current_object[--current_stack_depth];
     if (! obj->defined) {
 	_trace_printf ("dup /%s%ld exch def\n",
@@ -848,6 +868,7 @@ _exch_operands (void)
 {
     Object *tmp;
 
+    ensure_operands (2);
     tmp = current_object[current_stack_depth-1];
     tmp->operand--;
     current_object[current_stack_depth-1] = current_object[current_stack_depth-2];
@@ -871,6 +892,7 @@ _pop_operands_to_object (Object *obj)
     while (current_stack_depth > obj->operand + 1) {
 	Object *c_obj;
 
+	ensure_operands (1);
 	c_obj = current_object[--current_stack_depth];
 	c_obj->operand = -1;
 	if (! c_obj->defined) {
@@ -912,8 +934,7 @@ _push_operand (enum operand_type t, const void *ptr)
 {
     Object *obj = _get_object (t, ptr);
 
-    if (current_stack_depth ==
-	sizeof (current_object) / sizeof (current_object[0]))
+    if (current_stack_depth == ARRAY_LENGTH (current_object))
     {
 	int n;
 
@@ -936,6 +957,7 @@ static void
 _object_remove (Object *obj)
 {
     if (obj->operand != -1) {
+	ensure_operands (1);
 	if (obj->operand == current_stack_depth - 1) {
 	    _trace_printf ("pop %% %s%ld destroyed\n",
 			   obj->type->op_code, obj->token);
-- 
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