From patchwork Thu Nov 15 01:51:50 2012
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Subject: RFC: PATCH to add abi_tag attribute
Date: Wed, 14 Nov 2012 15:51:50 -0000
From: Jason Merrill <jason@redhat.com>
X-Patchwork-Id: 199102
Message-Id: <50A44AB6.9060904@redhat.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: gcc-patches List <gcc-patches@gcc.gnu.org>

On 11/11/2012 11:58 PM, Jason Merrill wrote:
> On 11/11/2012 08:01 AM, Florian Weimer wrote:
>> I'm not sure if this sufficiently far-reaching.  It seems that this
>> doesn't allow me to implement a virtual function which takes a
>> std::string parameter in new-ABI-mode when the base class is also used
>> in old-ABI-mode.
>
> Ah, yes; since virtual functions are called through the vtable the
> signatures of virtual functions are also part of the class ABI, so the
> base class also needs to be tagged.  I guess I should add that to
> -Wabi-tag.

Like so:

Tested x86_64-pc-linux-gnu, applying to trunk.


commit 0c1d53def870aef5f785278eb447fceb2974df09
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Nov 13 12:23:52 2012 -0500

    	* class.c (finish_struct_1): Check virtual functions
    	for missing ABI tags.

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index 0665e90..cdc02ae 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -6275,6 +6275,12 @@ finish_struct_1 (tree t)
 	/* Here we know enough to change the type of our virtual
 	   function table, but we will wait until later this function.  */
 	build_primary_vtable (CLASSTYPE_PRIMARY_BINFO (t), t);
+
+      /* If we're warning about ABI tags, check the types of the new
+	 virtual functions.  */
+      if (warn_abi_tag)
+	for (tree v = virtuals; v; v = TREE_CHAIN (v))
+	  check_abi_tags (t, TREE_VALUE (v));
     }
 
   if (TYPE_CONTAINS_VPTR_P (t))
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 25dd685..43b21c6 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -15622,7 +15622,7 @@ A redeclaration of a function or class must not add new ABI tags,
 since doing so would change the mangled name.
 
 The @option{-Wabi-tag} flag enables a warning about a class which does
-not have all the ABI tags used by its subobjects; for users with code
+not have all the ABI tags used by its subobjects and virtual functions; for users with code
 that needs to coexist with an earlier ABI, using this option can help
 to find all affected types that need to be tagged.
 
diff --git a/gcc/testsuite/g++.dg/abi/abi-tag4.C b/gcc/testsuite/g++.dg/abi/abi-tag4.C
new file mode 100644
index 0000000..3f8d7bf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/abi-tag4.C
@@ -0,0 +1,8 @@
+// { dg-options "-Wabi-tag" }
+
+struct __attribute ((abi_tag ("X"))) A { };
+
+struct B			// { dg-warning "abi tag" }
+{
+  virtual void f(A);		// { dg-message "declared here" }
+};