From 3a665576c16c353d8f524189d695e3c9140eefb8 Mon Sep 17 00:00:00 2001 From: David Majnemer Date: Sat, 2 Nov 2013 11:19:13 +0000 Subject: [PATCH] Sema: Disallow derived classes with virtual bases from having flexible array members Flexible array members only work out if they are the last field of a record, however virtual bases would give us many situations where the flexible array member would overlap with the virtual base fields. It is unlikely in the extreme that this behavior was intended by the user so raise a diagnostic instead of accepting. This is will not reject conforming code because flexible array members are an extension in C++ mode. git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193920 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/clang/Basic/DiagnosticSemaKinds.td | 3 +++ lib/Sema/SemaDecl.cpp | 9 +++++++++ test/SemaCXX/flexible-array-test.cpp | 4 ++++ 3 files changed, 16 insertions(+) diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td index ae2d9c9e77..86108be0b9 100644 --- a/include/clang/Basic/DiagnosticSemaKinds.td +++ b/include/clang/Basic/DiagnosticSemaKinds.td @@ -3937,6 +3937,9 @@ def ext_variable_sized_type_in_struct : ExtWarn< def ext_c99_flexible_array_member : Extension< "flexible array members are a C99 feature">, InGroup; +def err_flexible_array_virtual_base : Error< + "flexible array member %0 not allowed in " + "%select{struct|interface|union|class|enum}1 which has a virtual base class">; def err_flexible_array_empty_aggregate : Error< "flexible array member %0 not allowed in otherwise empty " "%select{struct|interface|union|class|enum}1 is not allowed">; diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp index 101f4ce898..d9dd4507de 100644 --- a/lib/Sema/SemaDecl.cpp +++ b/lib/Sema/SemaDecl.cpp @@ -11841,6 +11841,15 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl, if (DiagID) Diag(FD->getLocation(), DiagID) << FD->getDeclName() << Record->getTagKind(); + // While the layout of types that contain virtual bases is not specified + // by the C++ standard, both the Itanium and Microsoft C++ ABIs place + // virtual bases after the derived members. This would make a flexible + // array member declared at the end of an object not adjacent to the end + // of the type. + if (CXXRecordDecl *RD = dyn_cast(Record)) + if (RD->getNumVBases() != 0) + Diag(FD->getLocation(), diag::err_flexible_array_virtual_base) + << FD->getDeclName() << Record->getTagKind(); if (!getLangOpts().C99) Diag(FD->getLocation(), diag::ext_c99_flexible_array_member) << FD->getDeclName() << Record->getTagKind(); diff --git a/test/SemaCXX/flexible-array-test.cpp b/test/SemaCXX/flexible-array-test.cpp index e6c3132801..f287711eeb 100644 --- a/test/SemaCXX/flexible-array-test.cpp +++ b/test/SemaCXX/flexible-array-test.cpp @@ -66,4 +66,8 @@ struct Storage : StorageBase { int data[]; }; +struct VirtStorage : virtual StorageBase { + int data[]; // expected-error {{flexible array member 'data' not allowed in struct which has a virtual base class}} +}; + } -- 2.40.0