{"id":2223532,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2223532/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/20260415140617.2347118-1-jason@redhat.com/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/1.1/projects/17/?format=json","name":"GNU Compiler Collection","link_name":"gcc","list_id":"gcc-patches.gcc.gnu.org","list_email":"gcc-patches@gcc.gnu.org","web_url":null,"scm_url":null,"webscm_url":null},"msgid":"<20260415140617.2347118-1-jason@redhat.com>","date":"2026-04-15T14:05:11","name":"[pushed] c++: mangling of extern \"C\" in anon ns [PR117133]","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"34cc344ab0e51a501e553a219be8e1c3f6c2fb58","submitter":{"id":4337,"url":"http://patchwork.ozlabs.org/api/1.1/people/4337/?format=json","name":"Jason Merrill","email":"jason@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/20260415140617.2347118-1-jason@redhat.com/mbox/","series":[{"id":499993,"url":"http://patchwork.ozlabs.org/api/1.1/series/499993/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=499993","date":"2026-04-15T14:05:11","name":"[pushed] c++: mangling of extern \"C\" in anon ns [PR117133]","version":1,"mbox":"http://patchwork.ozlabs.org/series/499993/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2223532/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2223532/checks/","tags":{},"headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=el56Tg30;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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charset=\"US-ASCII\"; x-default=true","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"},"content":"Tested x86_64-pc-linux-gnu, applying to trunk.\n\n-- 8< --\n\nr15-3910 updated decl_linkage to return 'internal' for extern \"C\"\ndeclarations in an anonymous namespace, as specified by C++11. This\nunintentionally changed the result of unmangled_name_p for such variables,\nthough functions were unaffected.\n\nThe standard says that only variables with external linkage have language\nlinkage, but it doesn't say anything about name mangling for declarations\nwith internal linkage, so I think we might as well retain the old mangling\nbehavior. And then we don't need to document the mangling change.\n\nI also notice that such variables still get global symbols, as\nconstrain_visibility still thinks that extern \"C\" takes priority, but let's\nsave fixing (and documenting) that for GCC 17.\n\n\tPR c++/117133\n\tPR c++/124768\n\tPR c++/124773\n\ngcc/cp/ChangeLog:\n\n\t* mangle.cc (unmangled_name_p): Don't mangle internal extern \"C\"\n\tvariables.\n\ngcc/ChangeLog:\n\n\t* doc/trouble.texi (Linkage in Anonymous Namespaces): Remove.\n\ngcc/testsuite/ChangeLog:\n\n\t* g++.dg/abi/mangle84.C: New test.\n---\n gcc/doc/trouble.texi | 16 ----------------\n gcc/cp/mangle.cc | 8 ++++----\n gcc/testsuite/g++.dg/abi/mangle84.C | 5 +++++\n 3 files changed, 9 insertions(+), 20 deletions(-)\n create mode 100644 gcc/testsuite/g++.dg/abi/mangle84.C\n\n\nbase-commit: 3bf1ba4c723b8fd6274fb134890c83031d00d408","diff":"diff --git a/gcc/doc/trouble.texi b/gcc/doc/trouble.texi\nindex 4882e2fabab..ad13357c30a 100644\n--- a/gcc/doc/trouble.texi\n+++ b/gcc/doc/trouble.texi\n@@ -638,7 +638,6 @@ give rise to questions of this sort.\n * Name lookup:: Name lookup, templates, and accessing members of base classes\n * Temporaries:: Temporaries may vanish before you expect\n * Copy Assignment:: Copy Assignment operators copy virtual bases twice\n-* Linkage in Anonymous Namespaces:: Names have internal linkage\n @end menu\n \n @node Static Definitions\n@@ -913,21 +912,6 @@ copy-assignment operator removes any uncertainties. With such an\n operator, the application can define whether and how the virtual base\n subobject is assigned.\n \n-@node Linkage in Anonymous Namespaces\n-@subsection Linkage in Anonymous Namespaces\n-\n-The C++11 standard changed the linkage of anonymous namespaces from\n-external (using a unique generated name) to internal. That means that\n-names declared in such a namespace now also have internal linkage, and\n-@code{extern \"C\"} has no effect. GCC implemented this change in\n-behavior starting with the GCC 15 release; code using this idiom that\n-worked in earlier versions of GCC, or with @option{-std=} options\n-prior to C++11, may encounter unexpected linker issues due to changes\n-in name mangling.\n-\n-For more information about the change to the C++ standard, see\n-@uref{https://cplusplus.github.io/CWG/issues/2772.html}.\n-\n @node Non-bugs\n @section Certain Changes We Don't Want to Make\n \ndiff --git a/gcc/cp/mangle.cc b/gcc/cp/mangle.cc\nindex a577e4e2a1c..6e6b16d389d 100644\n--- a/gcc/cp/mangle.cc\n+++ b/gcc/cp/mangle.cc\n@@ -768,14 +768,14 @@ unmangled_name_p (const tree decl)\n }\n else if (VAR_P (decl))\n {\n+ /* extern \"C\" declarations aren't mangled. */\n+ if (DECL_NAMESPACE_SCOPE_P (decl) && DECL_EXTERN_C_P (decl))\n+\treturn true;\n+\n /* static variables are mangled. */\n if (!DECL_EXTERNAL_LINKAGE_P (decl))\n \treturn false;\n \n- /* extern \"C\" declarations aren't mangled. */\n- if (DECL_EXTERN_C_P (decl))\n-\treturn true;\n-\n /* Other variables at non-global scope are mangled. */\n if (CP_DECL_CONTEXT (decl) != global_namespace)\n \treturn false;\ndiff --git a/gcc/testsuite/g++.dg/abi/mangle84.C b/gcc/testsuite/g++.dg/abi/mangle84.C\nnew file mode 100644\nindex 00000000000..2116f1ab2cb\n--- /dev/null\n+++ b/gcc/testsuite/g++.dg/abi/mangle84.C\n@@ -0,0 +1,5 @@\n+// PR c++/124768\n+// { dg-final { scan-assembler \"two:\" } }\n+// { dg-final { scan-assembler-not \"_ZN12_GLOBAL__N_13twoE:\" } }\n+namespace { extern \"C\" { int two = 2; } }\n+int main() { return two; }\n","prefixes":["pushed"]}