[PATCH] libdw_visit_scopes: Don't recurse into imported unit children.

[Mark Wielaard <mjw at redhat dot com>]

There were two issues with __libdw_visit_scopes. First it returned an
error whenever called with a root DIE that didn't have any children.
However a DIE abbrev can have DW_CHILDREN_yes set and still have an
empty child list. It is inefficient and should be fixed in the DWARF
producer, but it is legal DWARF. Secondly __libdw_visit_scopes would
recurse into an imported unit and then forget about the rest of the
children of the root DIE. For an imported unit the children of that
unit DIE should be treated as if they were logical children of the
root DIE and not increase the recursion depth. Both issues were shown
by a systemtap bug using dwarf_getscopes () on a CU that had various
partial units imported through dwz.

See http://sourceware.org/bugzilla/show_bug.cgi?id=15671

Signed-off-by: Mark Wielaard <mjw@redhat.com>
---
 libdw/ChangeLog            |    7 +++
 libdw/libdw_visit_scopes.c |   95 ++++++++++++++++++++++++--------------------
 2 files changed, 59 insertions(+), 43 deletions(-)

diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index 59b6c63..31f1f48 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,10 @@
+2013-06-26  Mark Wielaard  <mjw@redhat.com>
+
+	* libdw_visit_scopes.c (__libdw_visit_scopes): Don't reject root
+	DIEs without children. Don't call recurse and increase the depth
+	for an imported unit. Walk the children of an imported unit as
+	if they are logical children of the parent root DIE.
+
 2013-05-03  Mark Wielaard  <mjw@redhat.com>
 
 	* dwarf_getsrclines.c (dwarf_getsrclines): Only set end_sequence
diff --git a/libdw/libdw_visit_scopes.c b/libdw/libdw_visit_scopes.c
index ea0c6b4..7d27851 100644
--- a/libdw/libdw_visit_scopes.c
+++ b/libdw/libdw_visit_scopes.c
@@ -87,7 +87,7 @@ __libdw_visit_scopes (depth, root, previsit, postvisit, arg)
 
   child.parent = root;
   if (INTUSE(dwarf_child) (&root->die, &child.die) != 0)
-    return -1;
+    return 0; // Having zero children is legal.
 
   inline int recurse (void)
     {
@@ -95,63 +95,72 @@ __libdw_visit_scopes (depth, root, previsit, postvisit, arg)
 				   previsit, postvisit, arg);
     }
 
-  do
-    {
-      child.prune = false;
-
-      if (previsit != NULL)
-	{
-	  int result = (*previsit) (depth + 1, &child, arg);
-	  if (result != DWARF_CB_OK)
-	    return result;
-	}
-
-      if (!child.prune)
-	switch (classify_die (&child.die))
+  inline int walk_children ()
+  {
+    do
+      {
+	/* For an imported unit, it is logically as if the children of
+	   that unit are siblings of the other children.  So don't do
+	   a full recursion into the imported unit, but just walk the
+	   children in place before moving to the next real child.  */
+	while (classify_die (&child.die) == imported)
 	  {
-	  case match:
-	  case match_inline:
-	  case walk:
-	    if (INTUSE(dwarf_haschildren) (&child.die))
+	    Dwarf_Die orig_child_die = child.die;
+	    Dwarf_Attribute attr_mem;
+	    Dwarf_Attribute *attr = INTUSE(dwarf_attr) (&child.die,
+							DW_AT_import,
+							&attr_mem);
+	    if (INTUSE(dwarf_formref_die) (attr, &child.die) != NULL
+                && INTUSE(dwarf_child) (&child.die, &child.die) == 0)
 	      {
-		int result = recurse ();
+		int result = walk_children ();
 		if (result != DWARF_CB_OK)
 		  return result;
 	      }
-	    break;
 
-	  case imported:
+	    /* Any "real" children left?  */
+	    if (INTUSE(dwarf_siblingof) (&orig_child_die, &child.die) != 0)
+	      return 0;
+	  };
+
+	child.prune = false;
+
+	if (previsit != NULL)
+	  {
+	    int result = (*previsit) (depth + 1, &child, arg);
+	    if (result != DWARF_CB_OK)
+	      return result;
+	  }
+
+	if (!child.prune)
+	  switch (classify_die (&child.die))
 	    {
-	      /* This imports another compilation unit to appear
-		 as part of this one, inside the current scope.
-		 Recurse to search the referenced unit, but without
-		 recording it as an inner scoping level.  */
-
-	      Dwarf_Attribute attr_mem;
-	      Dwarf_Attribute *attr = INTUSE(dwarf_attr) (&child.die,
-							  DW_AT_import,
-							  &attr_mem);
-	      if (INTUSE(dwarf_formref_die) (attr, &child.die) != NULL)
+	    case match:
+	    case match_inline:
+	    case walk:
+	      if (INTUSE(dwarf_haschildren) (&child.die))
 		{
 		  int result = recurse ();
 		  if (result != DWARF_CB_OK)
 		    return result;
 		}
+	      break;
+
+	    default:
+	      break;
 	    }
-	    break;
 
-	  default:
-	    break;
+	if (postvisit != NULL)
+	  {
+	    int result = (*postvisit) (depth + 1, &child, arg);
+	    if (result != DWARF_CB_OK)
+	      return result;
 	  }
+      }
+    while (INTUSE(dwarf_siblingof) (&child.die, &child.die) == 0);
 
-      if (postvisit != NULL)
-	{
-	  int result = (*postvisit) (depth + 1, &child, arg);
-	  if (result != DWARF_CB_OK)
-	    return result;
-	}
-    }
-  while (INTUSE(dwarf_siblingof) (&child.die, &child.die) == 0);
+    return 0;
+  }
 
-  return 0;
+  return walk_children ();
 }
-- 
1.7.1