Avoid recursion in resolve_unit_addrs_overlap

This patch replaces recursion with explicit stack of enclosing ranges.
This fixes stack overflow on certain binaries when initialization
happens inside a fiber.

See #155 for original discussion.

Author: MikailBag

dwarf.c

@@ -1615,8 +1615,7 @@ unit_addrs_search (const void *vkey, const void *ventry)
 
 static int
 resolve_unit_addrs_overlap_walk (struct backtrace_state *state,
-				 size_t *pfrom, size_t *pto,
-				 struct unit_addrs *enclosing,
+				 struct backtrace_vector *enclosing,
 				 struct unit_addrs_vector *old_vec,
 				 backtrace_error_callback error_callback,
 				 void *data,
@@ -1627,91 +1626,100 @@ resolve_unit_addrs_overlap_walk (struct backtrace_state *state,
   struct unit_addrs *new_addrs;
   size_t from;
   size_t to;
+  size_t enclosing_count;
 
   old_addrs = (struct unit_addrs *) old_vec->vec.base;
   old_count = old_vec->count;
   new_addrs = (struct unit_addrs *) new_vec->vec.base;
 
-  for (from = *pfrom, to = *pto; from < old_count; from++, to++)
+  enclosing_count = 0;
+
+  to = 0;
+  for (from = 0; from < old_count; from++)
     {
-      /* If we are in the scope of a larger range that can no longer
-	 cover any further ranges, return back to the caller.  */
+      struct unit_addrs *current_enclosing;
+      new_addrs[to] = old_addrs[from];
+      to++;
+
+      /* While we are in the scope of a larger range that can no longer
+      	 cover any further ranges, pop it from the enclosing stack.  */
+      while (enclosing_count > 0
+        && ((struct unit_addrs**)enclosing->base)[enclosing_count-1]->high <= old_addrs[from].low)
+        {
+          enclosing_count--;
+          enclosing->alc += sizeof (struct unit_addrs*);
+        }
+      if (enclosing_count > 0) {
+        current_enclosing = ((struct unit_addrs**)enclosing->base)[enclosing_count-1];
+      } else {
+        current_enclosing = NULL;
+      }
 
-      if (enclosing != NULL
-	  && enclosing->high <= old_addrs[from].low)
-	{
-	  *pfrom = from;
-	  *pto = to;
-	  return 1;
-	}
 
-      new_addrs[to] = old_addrs[from];
 
       /* If we are in scope of a larger range, fill in any gaps
 	 between this entry and the next one.
 
 	 There is an extra entry at the end of the vector, so it's
 	 always OK to refer to from + 1.  */
 
-      if (enclosing != NULL
-	  && enclosing->high > old_addrs[from].high
-	  && old_addrs[from].high < old_addrs[from + 1].low)
-	{
-	  void *grew;
-	  size_t new_high;
+      if (current_enclosing != NULL
+	      && current_enclosing->high > old_addrs[from].high
+	      && old_addrs[from].high < old_addrs[from + 1].low)
+	      {
+	        void *grew;
+	        size_t new_high;
 
-	  grew = backtrace_vector_grow (state, sizeof (struct unit_addrs),
+	        grew = backtrace_vector_grow (state, sizeof (struct unit_addrs),
 					error_callback, data, &new_vec->vec);
-	  if (grew == NULL)
-	    return 0;
-	  new_addrs = (struct unit_addrs *) new_vec->vec.base;
-	  to++;
-	  new_addrs[to].low = old_addrs[from].high;
-	  new_high = old_addrs[from + 1].low;
-	  if (enclosing->high < new_high)
-	    new_high = enclosing->high;
-	  new_addrs[to].high = new_high;
-	  new_addrs[to].u = enclosing->u;
-	}
+	        if (grew == NULL)
+	          return 0;
+	        new_addrs = (struct unit_addrs *) new_vec->vec.base;
+	        new_addrs[to].low = old_addrs[from].high;
+	        new_high = old_addrs[from + 1].low;
+	        if (current_enclosing->high < new_high)
+	          new_high = current_enclosing->high;
+	        new_addrs[to].high = new_high;
+	        new_addrs[to].u = current_enclosing->u;
+          to++;
+	      }
 
       /* If this range has a larger scope than the next one, use it to
-	 fill in any gaps.  */
+	     fill in any gaps.  */
 
       if (old_addrs[from].high > old_addrs[from + 1].high)
-	{
-	  *pfrom = from + 1;
-	  *pto = to + 1;
-	  if (!resolve_unit_addrs_overlap_walk (state, pfrom, pto,
-						&old_addrs[from], old_vec,
-						error_callback, data, new_vec))
-	    return 0;
-	  from = *pfrom;
-	  to = *pto;
-
-	  /* Undo the increment the loop is about to do.  */
-	  from--;
-	  to--;
-	}
+	      {
+	        void* grew;
+          struct unit_addrs **enclosing_top;
+
+          grew = backtrace_vector_grow (state, sizeof (struct unit_addrs *),
+                error_callback, data, enclosing);
+          if (grew == NULL)
+            return 0;
+          enclosing_top = ((struct unit_addrs **) (enclosing->base)) + enclosing_count;
+    
+          *enclosing_top = &old_addrs[from];
+	      }
     }
 
-  if (enclosing == NULL)
-    {
-      struct unit_addrs *pa;
+  
+  
+  struct unit_addrs *pa;
 
-      /* Add trailing entry.  */
+  /* Add trailing entry.  */
 
-      pa = ((struct unit_addrs *)
-	    backtrace_vector_grow (state, sizeof (struct unit_addrs),
-				   error_callback, data, &new_vec->vec));
-      if (pa == NULL)
-	return 0;
-      pa->low = 0;
-      --pa->low;
-      pa->high = pa->low;
-      pa->u = NULL;
+  pa = ((struct unit_addrs *)
+	backtrace_vector_grow (state, sizeof (struct unit_addrs),
+				error_callback, data, &new_vec->vec));
+  if (pa == NULL)
+	  return 0;
+  pa->low = 0;
+  --pa->low;
+  pa->high = pa->low;
+  pa->u = NULL;
 
-      new_vec->count = to;
-    }
+  new_vec->count = to;
+  
 
   return 1;
 }
@@ -1756,8 +1764,8 @@ resolve_unit_addrs_overlap (struct backtrace_state *state,
   size_t i;
   struct unit_addrs_vector new_vec;
   void *grew;
-  size_t from;
-  size_t to;
+  int walk_ok;
+  struct backtrace_vector enclosing;
 
   addrs = (struct unit_addrs *) addrs_vec->vec.base;
   count = addrs_vec->count;
@@ -1787,15 +1795,16 @@ resolve_unit_addrs_overlap (struct backtrace_state *state,
 				error_callback, data, &new_vec.vec);
   if (grew == NULL)
     return 0;
+  memset (&enclosing, 0, sizeof enclosing);
 
-  from = 0;
-  to = 0;
-  resolve_unit_addrs_overlap_walk (state, &from, &to, NULL, addrs_vec,
+  walk_ok = resolve_unit_addrs_overlap_walk (state, &enclosing, addrs_vec,
 				   error_callback, data, &new_vec);
   backtrace_vector_free (state, &addrs_vec->vec, error_callback, data);
-  *addrs_vec = new_vec;
+  backtrace_vector_free (state, &enclosing, error_callback, data);
+  if (walk_ok)
+    *addrs_vec = new_vec;
 
-  return 1;
+  return walk_ok;
 }
 
 /* Sort the line vector by PC.  We want a stable sort here to maintain