4 files changed, 101 insertions, 0 deletions

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 92180e60514..8d8602d41cc 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2015,6 +2015,10 @@ def err_attribute_weakref_without_alias : Error<
   "weakref declaration of '%0' must also have an alias attribute">;
 def err_alias_not_supported_on_darwin : Error <
   "only weak aliases are supported on darwin">;
+def err_alias_to_undefined : Error<
+  "alias must point to a defined variable or function">;
+def err_cyclic_alias : Error<
+  "alias definition is part of a cycle">;
 def warn_attribute_wrong_decl_type : Warning<
   "%0 attribute only applies to %select{functions|unions|"
   "variables and functions|functions and methods|parameters|"
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 96ae437ff46..d0f34dddca3 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -37,6 +37,7 @@
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/Version.h"
 #include "clang/Frontend/CodeGenOptions.h"
+#include "clang/Sema/SemaDiagnostic.h"
 #include "llvm/ADT/APSInt.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/IR/CallingConv.h"
@@ -171,8 +172,42 @@ void CodeGenModule::createCUDARuntime() {
   CUDARuntime = CreateNVCUDARuntime(*this);
 }
 
+void CodeGenModule::checkAliases() {
+  bool Error = false;
+  for (std::vector<GlobalDecl>::iterator I = Aliases.begin(),
+         E = Aliases.end(); I != E; ++I) {
+    const GlobalDecl &GD = *I;
+    const ValueDecl *D = cast<ValueDecl>(GD.getDecl());
+    const AliasAttr *AA = D->getAttr<AliasAttr>();
+    StringRef MangledName = getMangledName(GD);
+    llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
+    llvm::GlobalAlias *Alias = cast<llvm::GlobalAlias>(Entry);
+    llvm::GlobalValue *GV = Alias->getAliasedGlobal();
+    if (GV->isDeclaration()) {
+      Error = true;
+      getDiags().Report(AA->getLocation(), diag::err_alias_to_undefined);
+    } else if (!Alias->resolveAliasedGlobal(/*stopOnWeak*/ false)) {
+      Error = true;
+      getDiags().Report(AA->getLocation(), diag::err_cyclic_alias);
+    }
+  }
+  if (!Error)
+    return;
+
+  for (std::vector<GlobalDecl>::iterator I = Aliases.begin(),
+         E = Aliases.end(); I != E; ++I) {
+    const GlobalDecl &GD = *I;
+    StringRef MangledName = getMangledName(GD);
+    llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
+    llvm::GlobalAlias *Alias = cast<llvm::GlobalAlias>(Entry);
+    Alias->replaceAllUsesWith(llvm::UndefValue::get(Alias->getType()));
+    Alias->eraseFromParent();
+  }
+}
+
 void CodeGenModule::Release() {
   EmitDeferred();
+  checkAliases();
   EmitCXXGlobalInitFunc();
   EmitCXXGlobalDtorFunc();
   EmitCXXThreadLocalInitFunc();
@@ -2088,6 +2123,8 @@ void CodeGenModule::EmitAliasDefinition(GlobalDecl GD) {
   if (Entry && !Entry->isDeclaration())
     return;
 
+  Aliases.push_back(GD);
+
   llvm::Type *DeclTy = getTypes().ConvertTypeForMem(D->getType());
 
   // Create a reference to the named value.  This ensures that it is emitted
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 066009ca7df..25aaae61e48 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -275,6 +275,10 @@ class CodeGenModule : public CodeGenTypeCache {
   /// is done.
   std::vector<GlobalDecl> DeferredDeclsToEmit;
 
+  /// List of alias we have emitted. Used to make sure that what they point to
+  /// is defined once we get to the end of the of the translation unit.
+  std::vector<GlobalDecl> Aliases;
+
   /// DeferredVTables - A queue of (optional) vtables to consider emitting.
   std::vector<const CXXRecordDecl*> DeferredVTables;
 
@@ -1077,6 +1081,8 @@ private:
   /// was deferred.
   void EmitDeferred();
 
+  void checkAliases();
+
   /// EmitDeferredVTables - Emit any vtables which we deferred and
   /// still have a use for.
   void EmitDeferredVTables();
diff --git a/clang/test/Sema/attr-alias-elf.c b/clang/test/Sema/attr-alias-elf.c
new file mode 100644
index 00000000000..88bd7b70958
--- /dev/null
+++ b/clang/test/Sema/attr-alias-elf.c
@@ -0,0 +1,54 @@
+// RUN: %clang_cc1 -triple x86_64-pc-linux  -fsyntax-only -verify -emit-llvm-only %s
+
+void f1(void) __attribute__((alias("g1")));
+void g1(void) {
+}
+
+void f2(void) __attribute__((alias("g2"))); // expected-error {{alias must point to a defined variable or function}}
+
+
+void f3(void) __attribute__((alias("g3"))); // expected-error {{alias must point to a defined variable or function}}
+void g3(void);
+
+
+void f4() __attribute__((alias("g4")));
+void g4() {}
+void h4() __attribute__((alias("f4")));
+
+void f5() __attribute__((alias("g5")));
+void h5() __attribute__((alias("f5")));
+void g5() {}
+
+void g6() {}
+void f6() __attribute__((alias("g6")));
+void h6() __attribute__((alias("f6")));
+
+void g7() {}
+void h7() __attribute__((alias("f7")));
+void f7() __attribute__((alias("g7")));
+
+void h8() __attribute__((alias("f8")));
+void g8() {}
+void f8() __attribute__((alias("g8")));
+
+void h9() __attribute__((alias("f9")));
+void f9() __attribute__((alias("g9")));
+void g9() {}
+
+void f10() __attribute__((alias("g10"))); // expected-error {{alias definition is part of a cycle}}
+void g10() __attribute__((alias("f10"))); // expected-error {{alias definition is part of a cycle}}
+
+// FIXME: This could be a bit better, h10 is not part of the cycle, it points
+// to it.
+void h10() __attribute__((alias("g10"))); // expected-error {{alias definition is part of a cycle}}
+
+extern int a1 __attribute__((alias("b1")));
+int b1 = 42;
+
+extern int a2 __attribute__((alias("b2"))); // expected-error {{alias must point to a defined variable or function}}
+
+extern int a3 __attribute__((alias("b3"))); // expected-error {{alias must point to a defined variable or function}}
+extern int b3;
+
+extern int a4 __attribute__((alias("b4"))); // expected-error {{alias must point to a defined variable or function}}
+typedef int b4;