From ff715e2d5ec91e971daa70fdcfc153903030cd15 Mon Sep 17 00:00:00 2001
From: Eli Bendersky <eliben@google.com>
Date: Fri, 12 Jun 2015 23:26:42 +0000
Subject: [PATCH] Fix returning error message in LLVMLinkModules

On error, the temporary output stream wouldn't be flushed and therefore the
caller would see an empty error message.

Patch by Antoine Pitrou

Differential Revision: http://reviews.llvm.org/D10241

llvm-svn: 239646
---
 llvm/lib/Linker/LinkModules.cpp           |  4 +++-
 llvm/unittests/Linker/LinkModulesTest.cpp | 40 +++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Linker/LinkModules.cpp b/llvm/lib/Linker/LinkModules.cpp
index 1b7a331..b47d268 100644
--- a/llvm/lib/Linker/LinkModules.cpp
+++ b/llvm/lib/Linker/LinkModules.cpp
@@ -1802,7 +1802,9 @@ LLVMBool LLVMLinkModules(LLVMModuleRef Dest, LLVMModuleRef Src,
   LLVMBool Result = Linker::LinkModules(
       D, unwrap(Src), [&](const DiagnosticInfo &DI) { DI.print(DP); });
 
-  if (OutMessages && Result)
+  if (OutMessages && Result) {
+    Stream.flush();
     *OutMessages = strdup(Message.c_str());
+  }
   return Result;
 }
diff --git a/llvm/unittests/Linker/LinkModulesTest.cpp b/llvm/unittests/Linker/LinkModulesTest.cpp
index b4689cb..58a3e72 100644
--- a/llvm/unittests/Linker/LinkModulesTest.cpp
+++ b/llvm/unittests/Linker/LinkModulesTest.cpp
@@ -15,6 +15,7 @@
 #include "llvm/IR/Module.h"
 #include "llvm/Linker/Linker.h"
 #include "llvm/Support/SourceMgr.h"
+#include "llvm-c/Linker.h"
 #include "gtest/gtest.h"
 
 using namespace llvm;
@@ -125,6 +126,22 @@ TEST_F(LinkModuleTest, BlockAddress) {
   delete LinkedModule;
 }
 
+static Module *getExternal(LLVMContext &Ctx, StringRef FuncName) {
+  // Create a module with an empty externally-linked function
+  Module *M = new Module("ExternalModule", Ctx);
+  FunctionType *FTy = FunctionType::get(
+      Type::getVoidTy(Ctx), Type::getInt8PtrTy(Ctx), false /*=isVarArgs*/);
+
+  Function *F =
+      Function::Create(FTy, Function::ExternalLinkage, FuncName, M);
+  F->setCallingConv(CallingConv::C);
+
+  BasicBlock *BB = BasicBlock::Create(Ctx, "", F);
+  IRBuilder<> Builder(BB);
+  Builder.CreateRetVoid();
+  return M;
+}
+
 static Module *getInternal(LLVMContext &Ctx) {
   Module *InternalM = new Module("InternalModule", Ctx);
   FunctionType *FTy = FunctionType::get(
@@ -178,4 +195,27 @@ TEST_F(LinkModuleTest, TypeMerge) {
             M1->getNamedGlobal("t2")->getType());
 }
 
+TEST_F(LinkModuleTest, CAPISuccess) {
+  std::unique_ptr<Module> DestM(getExternal(Ctx, "foo"));
+  std::unique_ptr<Module> SourceM(getExternal(Ctx, "bar"));
+  char *errout = nullptr;
+  LLVMBool result = LLVMLinkModules(wrap(DestM.get()), wrap(SourceM.get()),
+                                    LLVMLinkerDestroySource, &errout);
+  EXPECT_EQ(0, result);
+  EXPECT_EQ(nullptr, errout);
+  // "bar" is present in destination module
+  EXPECT_NE(nullptr, DestM->getFunction("bar"));
+}
+
+TEST_F(LinkModuleTest, CAPIFailure) {
+  // Symbol clash between two modules
+  std::unique_ptr<Module> DestM(getExternal(Ctx, "foo"));
+  std::unique_ptr<Module> SourceM(getExternal(Ctx, "foo"));
+  char *errout = nullptr;
+  LLVMBool result = LLVMLinkModules(wrap(DestM.get()), wrap(SourceM.get()),
+                                    LLVMLinkerDestroySource, &errout);
+  EXPECT_EQ(1, result);
+  EXPECT_STREQ("Linking globals named 'foo': symbol multiply defined!", errout);
+}
+
 } // end anonymous namespace
-- 
2.7.4