Add import libraries to list of modules in PDB

[aganea]

Summary

This patch adds import libraries such as kernel32.dll to the list of modules stored in the PDB, similar to MSVC's link.exe.
Import libraries are first collected into a set and then output as "Import:AModuleNameHere.dll" into the list of modules in order to mimic MSVC's behaviour.

Fixes bug 36275:
https://bugs.llvm.org/show_bug.cgi?id=36275

[stefan_reinalter]

Updated diff to only contain formatted changes for new code.

[aganea]

This will also require a test to illustrate the change.

You could probably start from /lld/trunk/test/COFF/pdb-linker-module.test and bake something along the lines, which links some .objs, then checks the result with llvm-pdbutil and FileCheck to ensure the .pdb contains indeed the expected imports.

[aganea]

Will be closed by D54802.

[aganea]

Commited as part of rL357308. Many thanks again @stefan_reinalter !

COFF/Driver.cpp

else
       Driver->addBuffer(std::move(MBOrErr.first), WholeArchive);
   });
 }
 
 void LinkerDriver::addArchiveBuffer(MemoryBufferRef MB, StringRef SymName,
                                     StringRef ParentName) {
   file_magic Magic = identify_magic(MB.getBuffer());
   if (Magic == file_magic::coff_import_library) {
-    Symtab->addFile(make<ImportFile>(MB));
+    InputFile *Imp = make<ImportFile>(MB);
+    Imp->ParentName = ParentName;
+    Symtab->addFile(Imp);
     return;
   }
 
   InputFile *Obj;
   if (Magic == file_magic::coff_object) {
     Obj = make<ObjFile>(MB);
   } else if (Magic == file_magic::bitcode) {
     Obj = make<BitcodeFile>(MB);

COFF/PDB.cpp

public:
   void initialize(const llvm::codeview::DebugInfo &BuildId);
 
   /// Add natvis files specified on the command line.
   void addNatvisFiles();
 
   /// Link CodeView from each object file in the symbol table into the PDB.
   void addObjectsToPDB();
 
+  /// Link info for each import file in the symbol table into the PDB.
+  void addImportFilesToPDB();
+
   /// Link CodeView from a single object file into the PDB.
   void addObjFile(ObjFile *File);
 
   /// Produce a mapping from the type and item indices used in the object
   /// file to those in the destination PDB.
   ///
   /// If the object file uses a type server PDB (compiled with /Zi), merge TPI
   /// and IPI from the type server PDB and return a map for it. Each unique type
std::sort(Publics.begin(), Publics.end(),
               [](const PublicSym32 &L, const PublicSym32 &R) {
                 return L.Name < R.Name;
               });
     for (const PublicSym32 &Pub : Publics)
       GsiBuilder.addPublicSymbol(Pub);
   }
 }
 
+// Add all import files as modules to the PDB.
+void PDBLinker::addImportFilesToPDB() {
+  // Gather unique import files first.
+  std::vector<ImportFile *> ImpFiles;
+  ImpFiles.reserve(ImportFile::Instances.size());
+
+  std::unordered_set<std::string> UniqueImpFiles;
+  for (ImportFile *File : ImportFile::Instances) {
+    const auto &InsertIt = UniqueImpFiles.insert(File->DLLName);
+    if (InsertIt.second) {
+      // Found a new unique import file.
+      ImpFiles.push_back(File);
+    }
+  }
+
+  // Now walk all import files and add them as modules to the PDB.
+  for (ImportFile *File : ImpFiles) {
+    SmallString<128> LibPath = File->ParentName;
+    sys::fs::make_absolute(LibPath);
+    sys::path::native(LibPath, sys::path::Style::windows);
+
+    // Name modules similar to MSVC's link.exe.
+    SmallString<128> Name = "Import:" + File->DLLName;
+    llvm::pdb::DbiModuleDescriptorBuilder *ModuleDBI =
+        &ExitOnErr(Builder.getDbiBuilder().addModuleInfo(Name));
+    ModuleDBI->setObjFileName(LibPath);
+    ExitOnErr(Builder.getDbiBuilder().addModuleSourceFile(*ModuleDBI, Name));
+
+    ObjNameSym ONS(SymbolRecordKind::ObjNameSym);
+    ONS.Name = File->DLLName;
+    ONS.Signature = 0;
+
+    ModuleDBI->addSymbol(codeview::SymbolSerializer::writeOneSymbol(
+        ONS, Alloc, CodeViewContainer::Pdb));
+  }
+}
+
 void PDBLinker::addNatvisFiles() {
   for (StringRef File : Config->NatvisFiles) {
     ErrorOr<std::unique_ptr<MemoryBuffer>> DataOrErr =
         MemoryBuffer::getFile(File);
     if (!DataOrErr) {
       warn("Cannot open input file: " + File);
       continue;
     }
void coff::createPDB(SymbolTable *Symtab,
                      ArrayRef<OutputSection *> OutputSections,
                      ArrayRef<uint8_t> SectionTable,
                      const llvm::codeview::DebugInfo &BuildId) {
   ScopedTimer T1(TotalPdbLinkTimer);
   PDBLinker PDB(Symtab);
 
   PDB.initialize(BuildId);
   PDB.addObjectsToPDB();
+  PDB.addImportFilesToPDB();
   PDB.addSections(OutputSections, SectionTable);
   PDB.addNatvisFiles();
 
   ScopedTimer T2(DiskCommitTimer);
   PDB.commit();
 }
 
 void PDBLinker::initialize(const llvm::codeview::DebugInfo &BuildId) {