From a6a0ae608be83c9c286fc9f11d0a380301922535 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers@google.com>
Date: Thu, 22 Aug 2019 20:47:12 +0000
Subject: [PATCH] [Clang][CodeGen] set alias linkage on QualType

Summary:
It seems that CodeGen was always using ExternalLinkage when emitting a
GlobalDecl with __attribute__((alias)). This leads to symbol
redefinitions (ODR) that cause failures at link time for static aliases.
This is readily attempting to link an ARM (32b) allyesconfig Linux
kernel built with Clang.

Reported-by: nathanchance
Suggested-by: ihalip
Link: https://bugs.llvm.org/show_bug.cgi?id=42377
Link: https://github.com/ClangBuiltLinux/linux/issues/631

Reviewers: rsmith, aaron.ballman, erichkeane

Reviewed By: aaron.ballman

Subscribers: javed.absar, kristof.beyls, cfe-commits, srhines, ihalip, nathanchance

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66492

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@369705 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/CodeGenModule.cpp | 13 +++++++++----
 test/CodeGen/alias.c          | 11 +++++++++++
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 0f7ac2a202..3dc40a8486 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -4363,17 +4363,22 @@ void CodeGenModule::EmitAliasDefinition(GlobalDecl GD) {
   // Create a reference to the named value.  This ensures that it is emitted
   // if a deferred decl.
   llvm::Constant *Aliasee;
-  if (isa<llvm::FunctionType>(DeclTy))
+  llvm::GlobalValue::LinkageTypes LT;
+  if (isa<llvm::FunctionType>(DeclTy)) {
     Aliasee = GetOrCreateLLVMFunction(AA->getAliasee(), DeclTy, GD,
                                       /*ForVTable=*/false);
-  else
+    LT = getFunctionLinkage(GD);
+  } else {
     Aliasee = GetOrCreateLLVMGlobal(AA->getAliasee(),
                                     llvm::PointerType::getUnqual(DeclTy),
                                     /*D=*/nullptr);
+    LT = getLLVMLinkageVarDefinition(cast<VarDecl>(GD.getDecl()),
+                                     D->getType().isConstQualified());
+  }
 
   // Create the new alias itself, but don't set a name yet.
-  auto *GA = llvm::GlobalAlias::create(
-      DeclTy, 0, llvm::Function::ExternalLinkage, "", Aliasee, &getModule());
+  auto *GA =
+      llvm::GlobalAlias::create(DeclTy, 0, LT, "", Aliasee, &getModule());
 
   if (Entry) {
     if (GA->getAliasee() == Entry) {
diff --git a/test/CodeGen/alias.c b/test/CodeGen/alias.c
index 78b020454a..296a707c44 100644
--- a/test/CodeGen/alias.c
+++ b/test/CodeGen/alias.c
@@ -2,6 +2,7 @@
 // RUN: %clang_cc1 -triple i386-pc-linux-gnu -emit-llvm -o - %s | FileCheck -check-prefix=CHECKBASIC %s
 // RUN: %clang_cc1 -triple armv7a-eabi -mfloat-abi hard -emit-llvm -o - %s | FileCheck -check-prefix=CHECKCC %s
 // RUN: %clang_cc1 -triple armv7a-eabi -mfloat-abi hard -S -o - %s | FileCheck -check-prefix=CHECKASM %s
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck -check-prefix=CHECKGLOBALS %s
 
 int g0;
 // CHECKBASIC-DAG: @g0 = common global i32 0
@@ -88,3 +89,13 @@ 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")));
+
+// Test that the alias gets its linkage from its declared qual type.
+// CHECKGLOBALS: @test10_foo = internal
+// CHECKGLOBALS-NOT: @test10_foo = dso_local
+int test10;
+static int test10_foo __attribute__((alias("test10")));
+// CHECKGLOBALS: @test11_foo = internal
+// CHECKGLOBALS-NOT: @test11_foo = dso_local
+void test11(void) {}
+static void test11_foo(void) __attribute__((alias("test11")));
-- 
2.50.1