Warn about virtual table mismatches

Jan Hubicka hubicka@ucw.cz
Wed Feb 12 06:27:00 GMT 2014


> On 02/11/2014 07:54 PM, Jan Hubicka wrote:
> >+	  /* Allow combining RTTI and non-RTTI is OK.  */
> 
> You mean combining -frtti and -fno-rtti compiles?  Yes, that's fine,
> though you need to prefer the -frtti version in case code from that
> translation unit uses the RTTI info.

Is there some mechanism that linker will do so? At the moment we just chose variant
that would be selected by linker.  I can make the choice, but what happens with non-LTO?
> 
> >/aux/hubicka/firefox/accessible/src/generic/DocAccessible.cpp:1232:0: note: the first different method is �HandleAccEvent�
> 
> I don't see where this note would come from in the patch.
> 
Sorry, diffed old tree

Index: ipa-devirt.c
===================================================================
--- ipa-devirt.c	(revision 207702)
+++ ipa-devirt.c	(working copy)
@@ -1675,6 +1675,132 @@
 }
 
 
+/* Compare two virtual tables, PREVAILING and VTABLE and output ODR
+   violation warings.  */
+
+void
+compare_virtual_tables (tree prevailing, tree vtable)
+{
+  tree init1 = DECL_INITIAL (prevailing), init2 = DECL_INITIAL (vtable);
+  tree val1 = NULL, val2 = NULL;
+  if (!DECL_VIRTUAL_P (prevailing))
+    {
+      odr_violation_reported = true;
+      if (warning_at (DECL_SOURCE_LOCATION (prevailing), 0,
+			 "declaration %D conflict with a virtual table",
+			 prevailing))
+	inform (DECL_SOURCE_LOCATION (TYPE_NAME (DECL_CONTEXT (vtable))),
+		"a type defining the virtual table in another translation unit");
+      return;
+    }
+  if (init1 == init2 || init2 == error_mark_node)
+    return;
+  /* Be sure to keep virtual table contents even for external
+     vtables when they are available.  */
+  gcc_assert (init1 && init1 != error_mark_node);
+  if (!init2 && DECL_EXTERNAL (vtable))
+    return;
+  if (init1 && init2
+      && CONSTRUCTOR_NELTS (init1) == CONSTRUCTOR_NELTS (init2))
+    {
+      unsigned i;
+      tree field1, field2;
+      bool matched = true;
+
+      FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (init1),
+				 i, field1, val1)
+	{
+	  gcc_assert (!field1);
+	  field2 = CONSTRUCTOR_ELT (init2, i)->index;
+	  val2 = CONSTRUCTOR_ELT (init2, i)->value;
+	  gcc_assert (!field2);
+	  if (val2 == val1)
+	    continue;
+	  if (TREE_CODE (val1) == NOP_EXPR)
+	    val1 = TREE_OPERAND (val1, 0);
+	  if (TREE_CODE (val2) == NOP_EXPR)
+	    val2 = TREE_OPERAND (val2, 0);
+	  /* Unwind
+	      val <addr_expr type <pointer_type>
+	       readonly constant
+	       arg 0 <mem_ref type <pointer_type __vtbl_ptr_type>
+		   readonly
+		   arg 0 <addr_expr type <pointer_type>
+		       arg 0 <var_decl _ZTCSd0_Si>> arg 1 <integer_cst 24>>> */
+
+	  while (TREE_CODE (val1) == TREE_CODE (val2)
+		 && (((TREE_CODE (val1) == MEM_REF
+	               || TREE_CODE (val1) == POINTER_PLUS_EXPR)
+		      && (TREE_OPERAND (val1, 1))
+		        == TREE_OPERAND (val2, 1))
+		     || TREE_CODE (val1) == ADDR_EXPR))
+	    {
+	      val1 = TREE_OPERAND (val1, 0);
+	      val2 = TREE_OPERAND (val2, 0);
+	      if (TREE_CODE (val1) == NOP_EXPR)
+		val1 = TREE_OPERAND (val1, 0);
+	      if (TREE_CODE (val2) == NOP_EXPR)
+		val2 = TREE_OPERAND (val2, 0);
+	    }
+	  if (val1 == val2)
+	    continue;
+	  if (TREE_CODE (val2) == ADDR_EXPR)
+	    {
+	      tree tmp = val1;
+	      val1 = val2;
+	      val2 = tmp;
+            }
+	  /* Combining RTTI and non-RTTI vtables is OK.
+	     ??? Perhaps we can alsa (optionally) warn here?  */
+	  if (TREE_CODE (val1) == ADDR_EXPR
+	      && TREE_CODE (TREE_OPERAND (val1, 0)) == VAR_DECL
+	      && !DECL_VIRTUAL_P (TREE_OPERAND (val1, 0))
+	      && integer_zerop (val2))
+	    continue;
+	  /* For some reason zeros gets NOP_EXPR wrappers.  */
+	  if (integer_zerop (val1)
+	      && integer_zerop (val2))
+	    continue;
+	  /* Compare assembler names; this function is run during
+	     declaration merging.  */
+	  if (DECL_P (val1) && DECL_P (val2)
+	      && DECL_ASSEMBLER_NAME (val1) == DECL_ASSEMBLER_NAME (val2))
+	    continue;
+	  matched = false;
+	  break;
+	}
+      if (!matched)
+	{
+	  odr_violation_reported = true;
+	  if (warning_at (DECL_SOURCE_LOCATION (TYPE_NAME (DECL_CONTEXT (vtable))), 0,
+			     "type %qD violates one definition rule",
+			     DECL_CONTEXT (vtable)))
+	    {
+	      inform (DECL_SOURCE_LOCATION (TYPE_NAME (DECL_CONTEXT (prevailing))),
+		      "a type with the same name but different virtual table is "
+		      "defined in another translation unit");
+	      /* See if we can be more informative.  */
+	      if (val1 && val2 && TREE_CODE (val1) == FUNCTION_DECL
+		  && TREE_CODE (val1) == FUNCTION_DECL
+		  && !DECL_ARTIFICIAL (val1) && !DECL_ARTIFICIAL (val2))
+		{
+		  inform (DECL_SOURCE_LOCATION (val1),
+			  "the first different method is %qD", val1);
+		  inform (DECL_SOURCE_LOCATION (val2),
+			  "a conflicting method is %qD", val2);
+		}
+	    }
+	}
+      return;
+    }
+  if (warning_at (DECL_SOURCE_LOCATION (TYPE_NAME (DECL_CONTEXT (vtable))), 0,
+		     "type %qD violates one definition rule",
+		     DECL_CONTEXT (vtable)))
+    inform (DECL_SOURCE_LOCATION (TYPE_NAME (DECL_CONTEXT (prevailing))),
+	    "a type with the same name but number of virtual methods is "
+	    "defined in another translation unit");
+}
+
 /* Return true if N looks like likely target of a polymorphic call.
    Rule out cxa_pure_virtual, noreturns, function declared cold and
    other obvious cases.  */
Index: lto/lto-symtab.c
===================================================================
--- lto/lto-symtab.c	(revision 207701)
+++ lto/lto-symtab.c	(working copy)
@@ -679,5 +679,14 @@
   if (!ret)
     return decl;
 
+  /* Check and report ODR violations on virtual tables.  */
+  if (decl != ret->decl
+      && TREE_CODE (decl) == VAR_DECL && DECL_VIRTUAL_P (decl))
+    {
+      compare_virtual_tables (ret->decl, decl);
+      /* We are done with checking and DECL will die after merigng.  */
+      DECL_VIRTUAL_P (decl) = 0;
+    }
+
   return ret->decl;
 }
Index: ipa-utils.h
===================================================================
--- ipa-utils.h	(revision 207702)
+++ ipa-utils.h	(working copy)
@@ -92,6 +92,7 @@
 					       tree, tree, HOST_WIDE_INT);
 tree vtable_pointer_value_to_binfo (tree t);
 bool vtable_pointer_value_to_vtable (tree, tree *, unsigned HOST_WIDE_INT *);
+void compare_virtual_tables (tree, tree);
 
 /* Return vector containing possible targets of polymorphic call E.
    If FINALP is non-NULL, store true if the list is complette. 



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