Fix pr19653.

Warn if an alias requests a section other than the aliasee section.

llvm-svn: 207997

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -2106,6 +2106,9 @@ def err_alias_to_undefined : Error<
 def warn_alias_to_weak_alias : Warning<
   "alias will always resolve to %0 even if weak definition of alias %1 is overridden">,
   InGroup<IgnoredAttributes>;
+def warn_alias_with_section : Warning<
+  "alias will not be in section '%0' but in the same section as the aliasee">,
+  InGroup<IgnoredAttributes>;
 def err_duplicate_mangled_name : Error<
   "definition with same mangled name as another definition">;
 def err_cyclic_alias : Error<

clang/lib/CodeGen/CodeGenModule.cpp

@@ -238,11 +238,6 @@ void CodeGenModule::checkAliases() {
       Diags.Report(AA->getLocation(), diag::err_alias_to_undefined);
     }
 
-    // We have to handle alias to weak aliases in here. LLVM itself disallows
-    // this since the object semantics would not match the IL one. For
-    // compatibility with gcc we implement it by just pointing the alias
-    // to its aliasee's aliasee. We also warn, since the user is probably
-    // expecting the link to be weak.
     llvm::Constant *Aliasee = Alias->getAliasee();
     llvm::GlobalValue *AliaseeGV;
     if (auto CE = dyn_cast<llvm::ConstantExpr>(Aliasee)) {
@@ -253,6 +248,19 @@ void CodeGenModule::checkAliases() {
     } else {
       AliaseeGV = cast<llvm::GlobalValue>(Aliasee);
     }
+
+    if (const SectionAttr *SA = D->getAttr<SectionAttr>()) {
+      StringRef AliasSection = SA->getName();
+      if (AliasSection != AliaseeGV->getSection())
+        Diags.Report(SA->getLocation(), diag::warn_alias_with_section)
+            << AliasSection;
+    }
+
+    // We have to handle alias to weak aliases in here. LLVM itself disallows
+    // this since the object semantics would not match the IL one. For
+    // compatibility with gcc we implement it by just pointing the alias
+    // to its aliasee's aliasee. We also warn, since the user is probably
+    // expecting the link to be weak.
     if (auto GA = dyn_cast<llvm::GlobalAlias>(AliaseeGV)) {
       if (GA->mayBeOverridden()) {
         Diags.Report(AA->getLocation(), diag::warn_alias_to_weak_alias)
@@ -585,7 +593,7 @@ CodeGenModule::getFunctionLinkage(GlobalDecl GD) {
 /// variables (these details are set in EmitGlobalVarDefinition for variables).
 void CodeGenModule::SetFunctionDefinitionAttributes(const FunctionDecl *D,
                                                     llvm::GlobalValue *GV) {
-  SetCommonAttributes(D, GV);
+  setNonAliasAttributes(D, GV);
 }
 
 void CodeGenModule::SetLLVMFunctionAttributes(const Decl *D,
@@ -711,13 +719,17 @@ void CodeGenModule::SetCommonAttributes(const Decl *D,
 
   if (D->hasAttr<UsedAttr>())
     addUsedGlobal(GV);
+}
+
+void CodeGenModule::setNonAliasAttributes(const Decl *D,
+                                          llvm::GlobalValue *GV) {
+  assert(!isa<llvm::GlobalAlias>(GV));
+  SetCommonAttributes(D, GV);
 
   if (const SectionAttr *SA = D->getAttr<SectionAttr>())
     GV->setSection(SA->getName());
 
-  // Alias cannot have attributes. Filter them here.
-  if (!isa<llvm::GlobalAlias>(GV))
-    getTargetCodeGenInfo().SetTargetAttributes(D, GV, *this);
+  getTargetCodeGenInfo().SetTargetAttributes(D, GV, *this);
 }
 
 void CodeGenModule::SetInternalFunctionAttributes(const Decl *D,
@@ -728,7 +740,7 @@ void CodeGenModule::SetInternalFunctionAttributes(const Decl *D,
 
   F->setLinkage(llvm::Function::InternalLinkage);
 
-  SetCommonAttributes(D, F);
+  setNonAliasAttributes(D, F);
 }
 
 static void setLinkageAndVisibilityForGV(llvm::GlobalValue *GV,
@@ -1879,7 +1891,7 @@ void CodeGenModule::EmitGlobalVarDefinition(const VarDecl *D) {
     // common vars aren't constant even if declared const.
     GV->setConstant(false);
 
-  SetCommonAttributes(D, GV);
+  setNonAliasAttributes(D, GV);
 
   // Emit the initializer function if necessary.
   if (NeedsGlobalCtor || NeedsGlobalDtor)

clang/lib/CodeGen/CodeGenModule.h

@@ -1050,6 +1050,8 @@ private:
   /// NOTE: This should only be called for definitions.
   void SetCommonAttributes(const Decl *D, llvm::GlobalValue *GV);
 
+  void setNonAliasAttributes(const Decl *D, llvm::GlobalValue *GV);
+
   /// SetFunctionDefinitionAttributes - Set attributes for a global definition.
   void SetFunctionDefinitionAttributes(const FunctionDecl *D,
                                        llvm::GlobalValue *GV);

clang/test/CodeGen/alias.c

@@ -16,6 +16,7 @@ extern void f1(void) __attribute((alias("f0")));
 // CHECKBASIC-DAG: @f1 = alias void ()* @f0
 // CHECKBASIC-DAG: @test8_foo = alias weak bitcast (void ()* @test8_bar to void (...)*)
 // CHECKBASIC-DAG: @test8_zed = alias bitcast (void ()* @test8_bar to void (...)*)
+// CHECKBASIC-DAG: @test9_zed = alias void ()* @test9_bar
 // CHECKBASIC: define void @f0() [[NUW:#[0-9]+]] {
 
 // Make sure that aliases cause referenced values to be emitted.
@@ -54,3 +55,7 @@ int outer_weak(int a) { return inner_weak_a(a); }
 void test8_bar() {}
 void test8_foo() __attribute__((weak, alias("test8_bar")));
 void test8_zed() __attribute__((alias("test8_foo")));
+
+void test9_bar(void) { }
+void test9_zed(void) __attribute__((section("test")));
+void test9_zed(void) __attribute__((alias("test9_bar")));

clang/test/Sema/attr-alias-elf.c

@@ -56,3 +56,11 @@ typedef int b4;
 void test2_bar() {}
 void test2_foo() __attribute__((weak, alias("test2_bar")));
 void test2_zed() __attribute__((alias("test2_foo"))); // expected-warning {{alias will always resolve to test2_bar even if weak definition of alias test2_foo is overridden}}
+
+void test3_bar() { }
+void test3_foo() __attribute__((section("test"))); // expected-warning {{alias will not be in section 'test' but in the same section as the aliasee}}
+void test3_foo() __attribute__((alias("test3_bar")));
+
+__attribute__((section("test"))) void test4_bar() { }
+void test4_foo() __attribute__((section("test")));
+void test4_foo() __attribute__((alias("test4_bar")));