Re: PR debug/47510

[Dodji Seketeli <dodji at redhat dot com>]

Tom Tromey <tromey@redhat.com> writes:

> After a lot of discussion on irc, we came up with another idea: extend
> this patch to add DW_AT_linkage_name == 't' to the anonymous
> structure.  This makes the DWARF remain a faithful representation of
> the C++, but also makes it simple for debuginfo readers to understand
> what is going on.  In particular I think it will make the gdb side of
> this tractable.

I have updated the patch to make add the DW_AT_linkage_name to the
anonymous type.

Tested on x86_64-unknown-linux-gnus against trunk and 4.6.  I think this
is material for 4.7 that we can backport to 4.6 after its release.

-- 
		Dodji

>From 5cc08083834604525a11e4e4b6de830734520f6e Mon Sep 17 00:00:00 2001
From: Dodji Seketeli <dodji@redhat.com>
Date: Fri, 28 Jan 2011 11:53:49 +0100
Subject: [PATCH] PR debug/47510

	PR debug/47510
	* gcc/dwarf2out.c (strip_naming_typedef): Factorize out of ...
	(lookup_type_die_strip_naming_typedef): ... here.
	(get_context_die): Use it.
	(gen_typedef_die): Add a DW_AT_{MIPS}_linkage_name attribute to
	the anonymous struct named by the naming typedef.
	* gcc/testsuite/g++.dg/debug/dwarf2/typedef6.C: New test.
---
 gcc/dwarf2out.c                              |   36 +++++++++++++++++++++----
 gcc/testsuite/g++.dg/debug/dwarf2/typedef6.C |   30 +++++++++++++++++++++
 2 files changed, 60 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/debug/dwarf2/typedef6.C

diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index dfe1086..cf935d0 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -6346,6 +6346,7 @@ static void remove_child_TAG (dw_die_ref, enum dwarf_tag);
 static void add_child_die (dw_die_ref, dw_die_ref);
 static dw_die_ref new_die (enum dwarf_tag, dw_die_ref, tree);
 static dw_die_ref lookup_type_die (tree);
+static dw_die_ref strip_naming_typedef (tree, dw_die_ref);
 static dw_die_ref lookup_type_die_strip_naming_typedef (tree);
 static void equate_type_number_to_die (tree, dw_die_ref);
 static hashval_t decl_die_table_hash (const void *);
@@ -8120,6 +8121,22 @@ lookup_type_die (tree type)
   return TYPE_SYMTAB_DIE (type);
 }
 
+/* Given a TYPE_DIE representing the type TYPE, if TYPE is an
+   anonymous type named by the typedef TYPE_DIE, return the DIE of the
+   anonymous type instead the one of the naming typedef.  */
+
+static inline dw_die_ref
+strip_naming_typedef (tree type, dw_die_ref type_die)
+{
+  if (type
+      && TREE_CODE (type) == RECORD_TYPE
+      && type_die
+      && type_die->die_tag == DW_TAG_typedef
+      && is_naming_typedef_decl (TYPE_NAME (type)))
+    type_die = get_AT_ref (type_die, DW_AT_type);
+  return type_die;
+}
+
 /* Like lookup_type_die, but if type is an anonymous type named by a
    typedef[1], return the DIE of the anonymous type instead the one of
    the naming typedef.  This is because in gen_typedef_die, we did
@@ -8134,11 +8151,7 @@ static inline dw_die_ref
 lookup_type_die_strip_naming_typedef (tree type)
 {
   dw_die_ref die = lookup_type_die (type);
-  if (TREE_CODE (type) == RECORD_TYPE
-      && die->die_tag == DW_TAG_typedef
-      && is_naming_typedef_decl (TYPE_NAME (type)))
-    die = get_AT_ref (die, DW_AT_type);
-  return die;
+  return strip_naming_typedef (type, die);
 }
 
 /* Equate a DIE to a given type specifier.  */
@@ -20350,6 +20363,14 @@ gen_typedef_die (tree decl, dw_die_ref context_die)
 	         anonymous struct DIE.  */
 	      if (!TREE_ASM_WRITTEN (type))
 	        gen_tagged_type_die (type, context_die, DINFO_USAGE_DIR_USE);
+
+	      /* This is a GNU Extension.  We are adding a
+		 DW_AT_linkage_name attribute to the DIE of the
+		 anonymous struct TYPE.  The value of that attribute
+		 is the name of the typedef decl naming the anonymous
+		 struct.  This greatly eases the work of consumers of
+		 this debug info.  */
+	      add_linkage_attr (lookup_type_die (type), decl);
 	    }
 	}
 
@@ -20830,7 +20851,10 @@ get_context_die (tree context)
     {
       /* Find die that represents this context.  */
       if (TYPE_P (context))
-	return force_type_die (TYPE_MAIN_VARIANT (context));
+	{
+	  context = TYPE_MAIN_VARIANT (context);
+	  return strip_naming_typedef (context, force_type_die (context));
+	}
       else
 	return force_decl_die (context);
     }
diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/typedef6.C b/gcc/testsuite/g++.dg/debug/dwarf2/typedef6.C
new file mode 100644
index 0000000..8896446
--- /dev/null
+++ b/gcc/testsuite/g++.dg/debug/dwarf2/typedef6.C
@@ -0,0 +1,30 @@
+// Origin PR debug/
+// { dg-options "-g -dA" }
+
+class C {
+public:
+  C() {}
+  ~C() {}
+};
+typedef struct {
+  C m;
+} t;
+typedef t s;
+s v;
+
+/*
+  We want to check that we have a DIE describing the typedef t like this:
+
+	.uleb128 0xc	# (DIE (0xb8) DW_TAG_typedef)
+	.ascii "t\0"	# DW_AT_name
+	.byte	0x1	# DW_AT_decl_file (../../prtests/test.cc)
+	.byte	0xb	# DW_AT_decl_line
+	.long	0x78	# DW_AT_type
+
+  e.g, it should not haven any child DIE -- the bug here was that this
+  DIE had children DIEs. So we check that the last line is immediately
+  followed by a line containing the pattern "(DIE (", instead of a
+  line containing a DW_AT_sibling attribute.
+ */
+
+// { dg-final { scan-assembler-times "\[^\n\r\]*\\(DIE \[^\n\r\]* DW_TAG_typedef\\)\[\n\r\]{1,2}\[^\n\r\].*\"t\\\\0\"\[^\n\r\]*DW_AT_name\[\n\r\]{1,2}\[^\n\r\]*\[\n\r\]{1,2}\[^\n\r\]*\[\n\r\]{1,2}\[^\n\r\]*DW_AT_type\[\n\r\]{1,2}\[^\n\r\]*\\(DIE" 1 } }
-- 
1.7.3.4