[LLD] COFF: /include'd symbols must be preserved

[ruiu]

Summary

Not only entry point symbol but also symbols specified by /include
option must be preserved, as they will never be dead-stripped.

[pcc]

LGTM with a test case.

Peter

COFF/Config.h

   llvm::COFF::MachineTypes MachineType = llvm::COFF::IMAGE_FILE_MACHINE_AMD64;
   bool Verbose = false;
   WindowsSubsystem Subsystem = llvm::COFF::IMAGE_SUBSYSTEM_UNKNOWN;
-  std::string EntryName;
+  StringRef EntryName;
+
+  // Symbols in this set are considered as live by the garbage collector.
+  std::set<StringRef> GCRoots;
 
   std::set<StringRef> NoDefaultLibs;
   bool NoDefaultLibAll = false;

COFF/Driver.cpp

 
   // Add undefined symbols given via the command line.
   // (/include is equivalent to Unix linker's -u option.)
-  for (auto *Arg : Args->filtered(OPT_incl))
-    Symtab.addUndefined(Arg->getValue());
+  for (auto *Arg : Args->filtered(OPT_incl)) {
+    StringRef Sym = Arg->getValue();
+    Symtab.addUndefined(Sym);
+    Config->GCRoots.insert(Sym);
+  }
 
   // Parse all input files and put all symbols to the symbol table.
   // The symbol table will take care of name resolution.

     }
     Config->EntryName = EntryOrErr.get();
   }
+  Config->GCRoots.insert(Config->EntryName);
 
   // Make sure we have resolved all symbols.
   if (Symtab.reportRemainingUndefines())
     return false;
 
+  // Do LTO by compiling bitcode input files to a native COFF file
+  // then link that file.
   if (auto EC = Symtab.addCombinedLTOObject()) {
     llvm::errs() << EC.message() << "\n";
     return false;

COFF/SymbolTable.cpp

     return std::error_code();
 
   llvm::LTOCodeGenerator CG;
-  std::set<DefinedBitcode *> PreservedBitcodeSymbols;
 
   // All symbols referenced by non-bitcode objects must be preserved.
   for (std::unique_ptr<ObjectFile> &File : ObjectFiles)
     for (SymbolBody *Body : File->getSymbols())
       if (auto *S = dyn_cast<DefinedBitcode>(Body->getReplacement()))
-        PreservedBitcodeSymbols.insert(S);
+        CG.addMustPreserveSymbol(S->getName());
 
-  // Likewise for the linker-generated reference to the entry point.
-  if (auto *S = dyn_cast<DefinedBitcode>(Symtab[Config->EntryName]->Body))
-    PreservedBitcodeSymbols.insert(S);
-
-  for (DefinedBitcode *S : PreservedBitcodeSymbols)
-    CG.addMustPreserveSymbol(S->getName());
+  // Likewise for other symbols that must be preserved.
+  for (StringRef Name : Config->GCRoots)
+    if (isa<DefinedBitcode>(Symtab[Name]->Body))
+      CG.addMustPreserveSymbol(Name);
 
   CG.setModule(BitcodeFiles[0]->releaseModule());
   for (unsigned I = 1, E = BitcodeFiles.size(); I != E; ++I)

COFF/Writer.h

   uint32_t ImportDirectoryTableSize = 0;
   uint32_t ImportAddressTableSize = 0;
 
-  Defined *Entry;
   uint64_t FileSize;
   uint64_t SizeOfImage;
   uint64_t SizeOfHeaders;

COFF/Writer.cpp

 }
 
 void Writer::markLive() {
-  Entry = cast<Defined>(Symtab->find(Config->EntryName));
-  Entry->markLive();
+  for (StringRef Name : Config->GCRoots)
+    cast<Defined>(Symtab->find(Name))->markLive();
   for (Chunk *C : Symtab->getChunks())
     if (C->isRoot())
       C->markLive();

   PE->Subsystem = Config->Subsystem;
   PE->SizeOfImage = SizeOfImage;
   PE->SizeOfHeaders = SizeOfHeaders;
+  Defined *Entry = cast<Defined>(Symtab->find(Config->EntryName));
   PE->AddressOfEntryPoint = Entry->getRVA();
   PE->SizeOfStackReserve = Config->StackReserve;
   PE->SizeOfStackCommit = Config->StackCommit;