Add correction message to bad linkage error.

src/PNaClTranslator.cpp

 //===- subzero/src/PNaClTranslator.cpp - ICE from bitcode -----------------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 455 matching lines @@
                                 bool SuppressMangling, bool IsExternal) const {
     if (IsExternal) {
       return getTranslator().getContext()->getConstantExternSym(Name);
     } else {
       const Ice::RelocOffsetT Offset = 0;
       return getTranslator().getContext()->getConstantSym(Offset, Name,
                                                           SuppressMangling);
     }
   }
 
+  void reportLinkageError(const char *Kind,
+                          const Ice::GlobalDeclaration &Decl) {
+    std::string Buffer;
+    raw_string_ostream StrBuf(Buffer);
+    StrBuf << Kind << " " << Decl.getName()
+           << " has incorrect linkage: " << Decl.getLinkageName();
+    if (Decl.isExternal())
+      StrBuf << "\n  Use flag -allow-externally-defined-symbols to override";
+    Error(StrBuf.str());
+  }
+
   // Converts function declarations into constant value IDs.
   void createValueIDsForFunctions() {
     Ice::GlobalContext *Ctx = getTranslator().getContext();
     for (const Ice::FunctionDeclaration *Func : FunctionDeclarations) {
-      if (!Func->verifyLinkageCorrect(Ctx)) {
-        std::string Buffer;
-        raw_string_ostream StrBuf(Buffer);
-        StrBuf << "Function " << Func->getName()
-               << " has incorrect linkage: " << Func->getLinkageName();
-        Error(StrBuf.str());
-        continue;
-      }
+      if (!Func->verifyLinkageCorrect(Ctx))
+        reportLinkageError("Function", *Func);
       Ice::Constant *C = nullptr;
       if (!isIRGenerationDisabled()) {
         C = getConstantSym(Func->getName(), Func->getSuppressMangling(),
                            Func->isProto());
       }
       ValueIDConstants.push_back(C);
     }
   }
 
   // Converts global variable declarations into constant value IDs.
   void createValueIDsForGlobalVars() {
     Ice::GlobalContext *Ctx = getTranslator().getContext();
     for (const Ice::VariableDeclaration *Decl : *VariableDeclarations) {
-      if (!Decl->verifyLinkageCorrect(Ctx)) {
-        std::string Buffer;
-        raw_string_ostream StrBuf(Buffer);
-        StrBuf << "Global " << Decl->getName()
-               << " has incorrect linkage: " << Decl->getLinkageName();
-        Error(StrBuf.str());
-      }
+      if (!Decl->verifyLinkageCorrect(Ctx))
+        reportLinkageError("Global", *Decl);
       Ice::Constant *C = nullptr;
       if (!isIRGenerationDisabled()) {
         C = getConstantSym(Decl->getName(), Decl->getSuppressMangling(),
                            !Decl->hasInitializer());
       }
       ValueIDConstants.push_back(C);
     }
   }
 
   // Reports that type ID is undefined, or not of the WantedType.
@@ skipping 2779 matching lines @@
     raw_string_ostream StrBuf(Buffer);
     StrBuf << IRFilename << ": Does not contain a module!";
     llvm::report_fatal_error(StrBuf.str());
   }
   if (InputStreamFile.getBitcodeBytes().getExtent() % 4 != 0) {
     llvm::report_fatal_error("Bitcode stream should be a multiple of 4 bytes");
   }
 }
 
 } // end of namespace Ice