[COFF] Make the weak aliases optional

[mstorsjo]

Summary

When creating an import library from lld, the cases with Name != ExtName shouldn't end up as a weak alias, but as a real export of the new name, which is what actually is exported from the DLL.

This restores the behaviour of renamed exports to what it was in 4.0 - this is a regression since the introduction of llvm-dlltool.

The other half of this commit, including a test, goes into lld.

[rnk]

lgtm

include/llvm/Object/COFFImportFile.h

struct COFFShortExport {
   friend bool operator!=(const COFFShortExport &L, const COFFShortExport &R) {
     return !(L == R);
   }
 };
 
 std::error_code writeImportLibrary(StringRef ImportName,
                                    StringRef Path,
                                    ArrayRef<COFFShortExport> Exports,
-                                   COFF::MachineTypes Machine);
+                                   COFF::MachineTypes Machine,
+                                   bool MakeWeakAliases);
 
 } // namespace object
 } // namespace llvm
 
 #endif

lib/Object/COFFImportFile.cpp

NewArchiveMember ObjectFactory::createWeakExternal(StringRef Sym,
   // Copied here so we can still use writeStringTable
   char *Buf = Alloc.Allocate<char>(Buffer.size());
   memcpy(Buf, Buffer.data(), Buffer.size());
   return {MemoryBufferRef(StringRef(Buf, Buffer.size()), ImportName)};
 }
 
 std::error_code writeImportLibrary(StringRef ImportName, StringRef Path,
                                    ArrayRef<COFFShortExport> Exports,
-                                   MachineTypes Machine) {
+                                   MachineTypes Machine, bool MakeWeakAliases) {
 
   std::vector<NewArchiveMember> Members;
   ObjectFactory OF(llvm::sys::path::filename(ImportName), Machine);
 
   std::vector<uint8_t> ImportDescriptor;
   Members.push_back(OF.createImportDescriptor(ImportDescriptor));
 
   std::vector<uint8_t> NullImportDescriptor;
   Members.push_back(OF.createNullImportDescriptor(NullImportDescriptor));
 
   std::vector<uint8_t> NullThunk;
   Members.push_back(OF.createNullThunk(NullThunk));
 
   for (COFFShortExport E : Exports) {
     if (E.Private)
       continue;
 
-    if (E.isWeak()) {
+    if (E.isWeak() && MakeWeakAliases) {
       Members.push_back(OF.createWeakExternal(E.Name, E.ExtName, false));
       Members.push_back(OF.createWeakExternal(E.Name, E.ExtName, true));
       continue;
     }
 
     ImportType ImportType = IMPORT_CODE;
     if (E.Data)
       ImportType = IMPORT_DATA;

lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp

for (COFFShortExport& E : Def->Exports) {
       // a prefix here, even if they shouldn't.)
       E.Name = E.Name.substr(0, E.Name.find('@', 1));
       // By making sure E.SymbolName != E.Name for decorated symbols,
       // writeImportLibrary writes these symbols with the type
       // IMPORT_NAME_UNDECORATE.
     }
   }
 
-  if (writeImportLibrary(Def->OutputFile, Path, Def->Exports, Machine))
+  if (writeImportLibrary(Def->OutputFile, Path, Def->Exports, Machine, true))
     return 1;
   return 0;
 }