Patchwork Fix problems with -fdebug-types-section and local types

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Submitter Cary Coutant
Date Aug. 8, 2012, 1:21 a.m.
Message ID <20120808012132.58C6AE0822@ccoutant.mtv.corp.google.com>
Download mbox | patch
Permalink /patch/175825/
State New
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Comments

Cary Coutant - Aug. 8, 2012, 1:21 a.m.
With --std=c++11, a template parameter can refer to a local type defined
within a function.  Because that local type doesn't qualify for its own
type unit, we copy it as an "unworthy" type into the type unit that refers
to it, but we copy too much, leading to a comdat type unit that contains a
DIE with subprogram definitions rather than declarations.  These DIEs may
have DW_AT_low_pc/high_pc or DW_AT_ranges attributes, and consequently can
refer to range list entries that don't get emitted because they're not
marked when the compile unit is scanned, eventually causing an undefined
symbol at link time.

In addition, while debugging this problem, I found that the
DW_AT_object_pointer attribute, when left in the skeletons that are left
behind in the compile unit, causes duplicate copies of the types to be
copied back into the compile unit.

This patch fixes these problems by removing the DW_AT_object_pointer
attribute from the skeleton left behind in the compile unit, and by
copying DW_TAG_subprogram DIEs as declarations when copying "unworthy"
types into a type unit.  In order to preserve information in the DIE
structure, I also added DW_AT_abstract_origin as an attribute that
should be copied when cloning a DIE as a declaration.

I also fixed the dwarf4-typedef.C test, which should be turning on
the -fdebug-types-section flag.

Bootstrapped and tested on x86. OK for trunk?

-cary


2012-08-07   Cary Coutant  <ccoutant@google.com>

gcc/
	* dwarf2out.c (clone_as_declaration): Copy DW_AT_abstract_origin
	attribute.
	(generate_skeleton_bottom_up): Remove DW_AT_object_pointer attribute
	from original DIE.
	(clone_tree_hash): Rename to ...
	(clone_tree_partial): ... this; change callers.  Copy
	DW_TAG_subprogram DIEs as declarations.

gcc/testsuite/
	* testsuite/g++.dg/debug/dwarf2/dwarf4-nested.C: New test case.
	* testsuite/g++.dg/debug/dwarf2/dwarf4-typedef.C: Add
	-fdebug-types-section flag.
Cary Coutant - Aug. 8, 2012, 6:30 p.m.
> Index: gcc/testsuite/g++.dg/debug/dwarf2/dwarf4-nested.C
> ===================================================================
> --- gcc/testsuite/g++.dg/debug/dwarf2/dwarf4-nested.C   (revision 0)
> +++ gcc/testsuite/g++.dg/debug/dwarf2/dwarf4-nested.C   (revision 0)
> @@ -0,0 +1,55 @@
> +// { dg-do compile }
> +// { dg-options "--std=c++11 -dA -gdwarf-4 -fdebug-types-section -fno-merge-debug-strings" }
> +
> +// Check that -fdebug-types-sections does not copy a full referenced type
> +// into a type unit.
> +
> +// Checks that at least one type unit is generated.
> +//
> +// { dg-final { scan-assembler "DIE \\(.*\\) DW_TAG_type_unit" } }
> +//
> +// Check that func is declared exactly twice in the debug info:
> +// once in the type unit for struct D, and once in the compile unit.
> +//
> +// { dg-final { scan-assembler-times "\\.ascii \"func\\\\0\"\[^\n\]*DW_AT_name" 2 } }
> +//
> +// Check to make sure that no type unit contains a DIE with DW_AT_low_pc
> +// or DW_AT_ranges.  These patterns assume that the compile unit is always
> +// emitted after all type units.
> +//
> +// { dg-final { scan-assembler-not "\\.quad.*DW_AT_low_pc.*DIE \\(.*\\) DW_TAG_compile_unit" } }
> +// { dg-final { scan-assembler-not "\\.quad.*DW_AT_ranges.*DIE \\(.*\\) DW_TAG_compile_unit" } }

I found a minor problem with the regexps above -- I was using ".*" in
a few places where I should have been using "\[^\n\]*". Fixed as
follows:

+// { dg-final { scan-assembler "DIE \\(\[^\n\]*\\) DW_TAG_type_unit" } }

+// { dg-final { scan-assembler-times "\\.ascii
\"func\\\\0\"\[^\n\]*DW_AT_name" 2 } }

+// { dg-final { scan-assembler-not "\\.quad\[^\n\]*DW_AT_low_pc.*DIE
\\(\[^\n\]*\\) DW_TAG_compile_unit" } }
+// { dg-final { scan-assembler-not "\\.quad\[^\n\]*DW_AT_ranges.*DIE
\\(\[^\n\]*\\) DW_TAG_compile_unit" } }

(Sorry, these will probably get split into two lines by gmail, but
they're each a single line in the actual patch.)

-cary
Cary Coutant - Aug. 13, 2012, 8:13 p.m.
> 2012-08-07   Cary Coutant  <ccoutant@google.com>
>
> gcc/
>         * dwarf2out.c (clone_as_declaration): Copy DW_AT_abstract_origin
>         attribute.
>         (generate_skeleton_bottom_up): Remove DW_AT_object_pointer attribute
>         from original DIE.
>         (clone_tree_hash): Rename to ...
>         (clone_tree_partial): ... this; change callers.  Copy
>         DW_TAG_subprogram DIEs as declarations.
>
> gcc/testsuite/
>         * testsuite/g++.dg/debug/dwarf2/dwarf4-nested.C: New test case.
>         * testsuite/g++.dg/debug/dwarf2/dwarf4-typedef.C: Add
>         -fdebug-types-section flag.

Ping?

-cary
Cary Coutant - Aug. 20, 2012, 8:31 p.m.
Ping.

http://gcc.gnu.org/ml/gcc-patches/2012-08/msg00398.html

-cary

On Mon, Aug 13, 2012 at 1:13 PM, Cary Coutant <ccoutant@google.com> wrote:
>> 2012-08-07   Cary Coutant  <ccoutant@google.com>
>>
>> gcc/
>>         * dwarf2out.c (clone_as_declaration): Copy DW_AT_abstract_origin
>>         attribute.
>>         (generate_skeleton_bottom_up): Remove DW_AT_object_pointer attribute
>>         from original DIE.
>>         (clone_tree_hash): Rename to ...
>>         (clone_tree_partial): ... this; change callers.  Copy
>>         DW_TAG_subprogram DIEs as declarations.
>>
>> gcc/testsuite/
>>         * testsuite/g++.dg/debug/dwarf2/dwarf4-nested.C: New test case.
>>         * testsuite/g++.dg/debug/dwarf2/dwarf4-typedef.C: Add
>>         -fdebug-types-section flag.
>
> Ping?
>
> -cary
Cary Coutant - Aug. 29, 2012, 6:55 p.m.
> Ping.
>
> http://gcc.gnu.org/ml/gcc-patches/2012-08/msg00398.html

Because much of this patch was superceded by this recent patch:

   http://gcc.gnu.org/ml/gcc-patches/2012-08/msg01968.html

I'll combine the two and submit a new patch.

-cary

Patch

Index: gcc/testsuite/g++.dg/debug/dwarf2/dwarf4-nested.C
===================================================================
--- gcc/testsuite/g++.dg/debug/dwarf2/dwarf4-nested.C	(revision 0)
+++ gcc/testsuite/g++.dg/debug/dwarf2/dwarf4-nested.C	(revision 0)
@@ -0,0 +1,55 @@ 
+// { dg-do compile }
+// { dg-options "--std=c++11 -dA -gdwarf-4 -fdebug-types-section -fno-merge-debug-strings" }
+
+// Check that -fdebug-types-sections does not copy a full referenced type
+// into a type unit.
+
+// Checks that at least one type unit is generated.
+//
+// { dg-final { scan-assembler "DIE \\(.*\\) DW_TAG_type_unit" } }
+//
+// Check that func is declared exactly twice in the debug info:
+// once in the type unit for struct D, and once in the compile unit.
+//
+// { dg-final { scan-assembler-times "\\.ascii \"func\\\\0\"\[^\n\]*DW_AT_name" 2 } }
+//
+// Check to make sure that no type unit contains a DIE with DW_AT_low_pc
+// or DW_AT_ranges.  These patterns assume that the compile unit is always
+// emitted after all type units.
+//
+// { dg-final { scan-assembler-not "\\.quad.*DW_AT_low_pc.*DIE \\(.*\\) DW_TAG_compile_unit" } }
+// { dg-final { scan-assembler-not "\\.quad.*DW_AT_ranges.*DIE \\(.*\\) DW_TAG_compile_unit" } }
+
+struct A {
+  A();
+  virtual ~A();
+  virtual void foo();
+ private:
+  int data;
+};
+
+struct B {
+  B();
+  virtual ~B();
+};
+
+extern B* table[];
+
+struct D {
+  template <typename T>
+  T* get(int i)
+  {
+    B*& cell = table[i];
+    if (cell == 0)
+      cell = new T();
+    return static_cast<T*>(cell);
+  }
+};
+
+void func(D* d)
+{
+  struct C : B {
+    A a;
+  };
+  d->get<C>(0)->a.foo();
+}
Index: gcc/testsuite/g++.dg/debug/dwarf2/dwarf4-typedef.C
===================================================================
--- gcc/testsuite/g++.dg/debug/dwarf2/dwarf4-typedef.C	(revision 190189)
+++ gcc/testsuite/g++.dg/debug/dwarf2/dwarf4-typedef.C	(working copy)
@@ -1,5 +1,5 @@ 
 /* { dg-do compile } */
-/* { dg-options "-gdwarf-4" } */
+/* { dg-options "-gdwarf-4 -fdebug-types-section" } */
 
 /* Regression test for an ICE in output_die when using -gdwarf-4.  */
 
Index: gcc/dwarf2out.c
===================================================================
--- gcc/dwarf2out.c	(revision 190189)
+++ gcc/dwarf2out.c	(working copy)
@@ -6357,6 +6357,7 @@  clone_as_declaration (dw_die_ref die)
 
       switch (a->dw_attr)
         {
+        case DW_AT_abstract_origin:
         case DW_AT_artificial:
         case DW_AT_containing_type:
         case DW_AT_external:
@@ -6489,6 +6490,12 @@  generate_skeleton_bottom_up (skeleton_ch
         dw_die_ref clone = clone_die (c);
         move_all_children (c, clone);
 
+        /* If the original has a DW_AT_object_pointer attribute,
+           it would now point to a child DIE just moved to the
+           cloned tree, so we need to remove that attribute from
+           the original.  */
+        remove_AT (c, DW_AT_object_pointer);
+
         replace_child (c, clone, prev);
         generate_skeleton_ancestor_tree (parent);
         add_child_die (parent->new_die, c);
@@ -6716,28 +6723,36 @@  copy_ancestor_tree (dw_die_ref unit, dw_
   return copy;
 }
 
-/* Like clone_tree, but additionally enter all the children into
-   the hash table decl_table.  */
+/* Like clone_tree, but copy DW_TAG_subprogram DIEs as declarations.
+   Enter all the cloned children into the hash table decl_table.  */
 
 static dw_die_ref
-clone_tree_hash (dw_die_ref die, htab_t decl_table)
+clone_tree_partial (dw_die_ref die, htab_t decl_table)
 {
   dw_die_ref c;
-  dw_die_ref clone = clone_die (die);
+  dw_die_ref clone;
   struct decl_table_entry *entry;
-  void **slot = htab_find_slot_with_hash (decl_table, die,
-					  htab_hash_pointer (die), INSERT);
+  void **slot;
+
+  if (die->die_tag == DW_TAG_subprogram)
+    clone = clone_as_declaration (die);
+  else
+    clone = clone_die (die);
+
+  slot = htab_find_slot_with_hash (decl_table, die,
+				   htab_hash_pointer (die), INSERT);
   /* Assert that DIE isn't in the hash table yet.  If it would be there
      before, the ancestors would be necessarily there as well, therefore
-     clone_tree_hash wouldn't be called.  */
+     clone_tree_partial wouldn't be called.  */
   gcc_assert (*slot == HTAB_EMPTY_ENTRY);
   entry = XCNEW (struct decl_table_entry);
   entry->orig = die;
   entry->copy = clone;
   *slot = entry;
 
-  FOR_EACH_CHILD (die, c,
-		  add_child_die (clone, clone_tree_hash (c, decl_table)));
+  if (die->die_tag != DW_TAG_subprogram)
+    FOR_EACH_CHILD (die, c,
+		    add_child_die (clone, clone_tree_partial (c, decl_table)));
 
   return clone;
 }
@@ -6790,7 +6805,8 @@  copy_decls_walk (dw_die_ref unit, dw_die
 
 	      FOR_EACH_CHILD (targ, c,
 			      add_child_die (copy,
-					     clone_tree_hash (c, decl_table)));
+					     clone_tree_partial (c,
+								 decl_table)));
 
               /* Make sure the cloned tree is marked as part of the
                  type unit.  */