MS ABI: Disallow dllimported/exported variables from having TLS

Windows TLS relies on indexing through a tls_index in order to get at
the DLL's thread local variables.  However, this index is not exported
along with the variable: it is assumed that all accesses to thread local
variables are inside the same module which created the variable in the
first place.

While there are several implementation techniques we could adopt to fix
this (notably, the Itanium ABI gets this for free), it is not worth the
heroics.

Instead, let's just ban this combination.  We could revisit this in the
future if we need to.

This fixes PR21111.

llvm-svn: 219049

6 files changed, 26 insertions, 1 deletions

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 5fb3af61908..7db98d59923 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2161,6 +2161,8 @@ def err_declspec_thread_on_thread_variable : Error<
   "thread-local storage specifier">;
 def err_attribute_dll_not_extern : Error<
   "%q0 must have external linkage when declared %q1">;
+def err_attribute_dll_thread_local : Error<
+  "%q0 cannot be thread local when declared %q1">;
 def warn_attribute_invalid_on_definition : Warning<
   "'%0' attribute cannot be specified on a definition">,
   InGroup<IgnoredAttributes>;
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 03dd2a7093c..c3c436d8e31 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -9534,8 +9534,11 @@ Sema::FinalizeDeclaration(Decl *ThisDecl) {
     }
   }
 
+  // Grab the dllimport or dllexport attribute off of the VarDecl.
+  const InheritableAttr *DLLAttr = getDLLAttr(VD);
+
   // Imported static data members cannot be defined out-of-line.
-  if (const DLLImportAttr *IA = VD->getAttr<DLLImportAttr>()) {
+  if (const auto *IA = dyn_cast_or_null<DLLImportAttr>(DLLAttr)) {
     if (VD->isStaticDataMember() && VD->isOutOfLine() &&
         VD->isThisDeclarationADefinition()) {
       // We allow definitions of dllimport class template static data members
@@ -9556,6 +9559,14 @@ Sema::FinalizeDeclaration(Decl *ThisDecl) {
     }
   }
 
+  // dllimport/dllexport variables cannot be thread local, their TLS index
+  // isn't exported with the variable.
+  if (DLLAttr && VD->getTLSKind()) {
+    Diag(VD->getLocation(), diag::err_attribute_dll_thread_local) << VD
+                                                                  << DLLAttr;
+    VD->setInvalidDecl();
+  }
+
   if (UsedAttr *Attr = VD->getAttr<UsedAttr>()) {
     if (!Attr->isInherited() && !VD->isThisDeclarationADefinition()) {
       Diag(Attr->getLocation(), diag::warn_attribute_ignored) << Attr;
diff --git a/clang/test/Sema/dllexport.c b/clang/test/Sema/dllexport.c
index 6c71ad82987..76b6f6dc5a0 100644
--- a/clang/test/Sema/dllexport.c
+++ b/clang/test/Sema/dllexport.c
@@ -49,6 +49,9 @@ __declspec(dllexport) extern int GlobalRedecl4; // expected-warning{{redeclarati
 // External linkage is required.
 __declspec(dllexport) static int StaticGlobal; // expected-error{{'StaticGlobal' must have external linkage when declared 'dllexport'}}
 
+// Thread local variables are invalid.
+__declspec(dllexport) __thread int ThreadLocalGlobal; // expected-error{{'ThreadLocalGlobal' cannot be thread local when declared 'dllexport'}}
+
 // Export in local scope.
 void functionScope() {
   __declspec(dllexport)        int LocalVarDecl; // expected-error{{'LocalVarDecl' must have external linkage when declared 'dllexport'}}
diff --git a/clang/test/Sema/dllimport.c b/clang/test/Sema/dllimport.c
index d64c85953d0..1b111077b62 100644
--- a/clang/test/Sema/dllimport.c
+++ b/clang/test/Sema/dllimport.c
@@ -77,6 +77,9 @@ __declspec(dllimport) extern int GlobalRedecl5; // expected-warning{{redeclarati
 // External linkage is required.
 __declspec(dllimport) static int StaticGlobal; // expected-error{{'StaticGlobal' must have external linkage when declared 'dllimport'}}
 
+// Thread local variables are invalid.
+__declspec(dllimport) __thread int ThreadLocalGlobal; // expected-error{{'ThreadLocalGlobal' cannot be thread local when declared 'dllimport'}}
+
 // Import in local scope.
 __declspec(dllimport) float LocalRedecl1; // expected-note{{previous definition is here}}
 __declspec(dllimport) float LocalRedecl2; // expected-note{{previous definition is here}}
diff --git a/clang/test/SemaCXX/dllexport.cpp b/clang/test/SemaCXX/dllexport.cpp
index df87c737865..5d688944095 100644
--- a/clang/test/SemaCXX/dllexport.cpp
+++ b/clang/test/SemaCXX/dllexport.cpp
@@ -64,6 +64,9 @@ namespace ns { __declspec(dllexport) int ExternalGlobal; }
 __declspec(dllexport) auto InternalAutoTypeGlobal = Internal(); // expected-error{{'InternalAutoTypeGlobal' must have external linkage when declared 'dllexport'}}
 __declspec(dllexport) auto ExternalAutoTypeGlobal = External();
 
+// Thread local variables are invalid.
+__declspec(dllexport) __thread int ThreadLocalGlobal; // expected-error{{'ThreadLocalGlobal' cannot be thread local when declared 'dllexport'}}
+
 // Export in local scope.
 void functionScope() {
   __declspec(dllexport)        int LocalVarDecl; // expected-error{{'LocalVarDecl' must have external linkage when declared 'dllexport'}}
diff --git a/clang/test/SemaCXX/dllimport.cpp b/clang/test/SemaCXX/dllimport.cpp
index d0e88368fc3..1ba25dbbc5c 100644
--- a/clang/test/SemaCXX/dllimport.cpp
+++ b/clang/test/SemaCXX/dllimport.cpp
@@ -86,6 +86,9 @@ namespace ns { __declspec(dllimport) int ExternalGlobal; }
 __declspec(dllimport) auto InternalAutoTypeGlobal = Internal(); // expected-error{{'InternalAutoTypeGlobal' must have external linkage when declared 'dllimport'}}
                                                                 // expected-error@-1{{definition of dllimport data}}
 
+// Thread local variables are invalid.
+__declspec(dllimport) __thread int ThreadLocalGlobal; // expected-error{{'ThreadLocalGlobal' cannot be thread local when declared 'dllimport'}}
+
 // Import in local scope.
 __declspec(dllimport) float LocalRedecl1; // expected-note{{previous definition is here}}
 __declspec(dllimport) float LocalRedecl2; // expected-note{{previous definition is here}}