[rfa] set processing_current_prefix properly (PR gdb/1520)

[David Carlton <carlton@kealia.com>]

This is a fix for PR gdb/1520, a namespace problem with GCC 3.4.  The
problem was that, if we have this situation:

  namespace N {
    void foo() { }
  }

then the compiler I had been using generated dies as following in its
DWARF 2 output:

1: DW_TAG_namespace:

  2: DW_TAG_subprogram:

     // Definition of N::foo

whereas GCC head does:

1: DW_TAG_namespace:

  2: DW_TAG_subprogram:

     // Declaration for N::foo

3: DW_TAG_subprogram:

  DW_AT_specification: reference to die #2

  // Definition of N::foo.


So I've added code to notice if a die representing a function's
definition has a specification located elsewhere; if so, it looks at
that specification to discover the current enclosing class/namespace.

(Probably there are other places where we need to do this; hopefully,
after a bit more experience, we'll find a less ad-hoc way of handling
this issue.)

It also fixes an inconsistency in my last patch - I had tried to
maintain the invariant that processing_current_prefix was always
non-NULL (i.e. was an actual string, albeit possibly an empty one),
but I was using determine_prefix in ways that violated that invariant.

Tested on i686-pc-linux-gnu, DWARF 2, with GCC 3.2, GCC 3.2 +
DW_TAG_namespace patch, GCC 2.95.3, and GCC head.  No regressions;
fixes lots of FAILs in gdb.cp/namespace.exp with GCC head.  (From now
on, I'll probably stop testing with my patched GCC 3.2 and switch to
using a GCC snapshot generating DW_TAG_namespace, so I don't miss
problems like this.)

Okay to commit?

David Carlton
carlton@kealia.com

2004-01-19  David Carlton  <carlton@kealia.com>

	Patch for PR c++/1520:
	* dwarf2read.c (read_func_scope): Set processing_current_prefix
	properly if we have a specification die.
	(possibly_determine_prefix): Rename from determine_prefix.
	(determine_prefix): Like the old determine_prefix, but never
	returns NULL.

Index: dwarf2read.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2read.c,v
retrieving revision 1.122
diff -u -p -r1.122 dwarf2read.c
--- dwarf2read.c	17 Jan 2004 05:35:47 -0000	1.122
+++ dwarf2read.c	19 Jan 2004 20:20:13 -0000
@@ -774,6 +774,8 @@ static void read_type_die (struct die_in
 
 static char *determine_prefix (struct die_info *die);
 
+static char *possibly_determine_prefix (struct die_info *die);
+
 static char *typename_concat (const char *prefix, const char *suffix);
 
 static char *class_name (struct die_info *die);
@@ -2180,6 +2182,8 @@ read_func_scope (struct die_info *die, s
   struct die_info *child_die;
   struct attribute *attr;
   char *name;
+  const char *previous_prefix = processing_current_prefix;
+  struct cleanup *back_to = NULL;
 
   name = dwarf2_linkage_name (die);
 
@@ -2188,6 +2192,18 @@ read_func_scope (struct die_info *die, s
   if (name == NULL || !dwarf2_get_pc_bounds (die, &lowpc, &highpc, cu))
     return;
 
+  if (cu_language == language_cplus)
+    {
+      struct die_info *spec_die = die_specification (die);
+
+      if (spec_die != NULL)
+	{
+	  char *specification_prefix = determine_prefix (spec_die);
+	  processing_current_prefix = specification_prefix;
+	  back_to = make_cleanup (xfree, specification_prefix);
+	}
+    }
+
   lowpc += baseaddr;
   highpc += baseaddr;
 
@@ -2238,6 +2254,10 @@ read_func_scope (struct die_info *die, s
      symbols go in the file symbol list.  */
   if (outermost_context_p ())
     list_in_scope = &file_symbols;
+
+  processing_current_prefix = previous_prefix;
+  if (back_to != NULL)
+    do_cleanups (back_to);
 }
 
 /* Process all the DIES contained within a lexical block scope.  Start
@@ -5942,12 +5962,23 @@ read_type_die (struct die_info *die, str
   do_cleanups (back_to);
 }
 
+/* Return the name of the namespace/class that DIE is defined within,
+   or "" if we can't tell.  The caller should xfree the result.  */
+
+static char *
+determine_prefix (struct die_info *die)
+{
+  char *prefix = possibly_determine_prefix (die);
+
+  return prefix ? prefix : xstrdup ("");
+}
+
 /* Return the name of the namespace/class that DIE is defined
    within, or NULL if we can't tell.  The caller should xfree the
    result.  */
 
 static char *
-determine_prefix (struct die_info *die)
+possibly_determine_prefix (struct die_info *die)
 {
   struct die_info *parent;
 
@@ -5962,7 +5993,7 @@ determine_prefix (struct die_info *die)
     }
   else
     {
-      char *parent_prefix = determine_prefix (parent);
+      char *parent_prefix = possibly_determine_prefix (parent);
       char *retval;
 
       switch (parent->tag) {