COFF: Add /noentry flag.

This option is sometimes used to create a resource-only DLL that
doesn't need any initialization.

llvm-svn: 240915

3 files changed, 17 insertions, 5 deletions

diff --git a/lld/COFF/Config.h b/lld/COFF/Config.h
index 801478149697..67f6034b0fa4 100644
--- a/lld/COFF/Config.h
+++ b/lld/COFF/Config.h
@@ -43,6 +43,7 @@ struct Configuration {
   bool Verbose = false;
   WindowsSubsystem Subsystem = llvm::COFF::IMAGE_SUBSYSTEM_UNKNOWN;
   StringRef EntryName;
+  bool NoEntry = false;
   std::string OutputFile;
   bool DoGC = true;
   bool Relocatable = true;
diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index d2dbd96a8fe2..c643f517024e 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -275,11 +275,20 @@ bool LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
     addUndefined(Config->EntryName);
   }
 
+  // Handle /noentry
+  if (Args.hasArg(OPT_noentry)) {
+    if (!Args.hasArg(OPT_dll)) {
+      llvm::errs() << "/noentry must be specified with /dll\n";
+      return false;
+    }
+    Config->NoEntry = true;
+  }
+
   // Handle /dll
   if (Args.hasArg(OPT_dll)) {
     Config->DLL = true;
     Config->ManifestID = 2;
-    if (Config->EntryName.empty()) {
+    if (Config->EntryName.empty() && !Config->NoEntry) {
       Config->EntryName = "_DllMainCRTStartup";
       addUndefined("_DllMainCRTStartup");
     }
@@ -539,15 +548,15 @@ bool LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
     // Windows specific -- If entry point name is not given, we need to
     // infer that from user-defined entry name. The symbol table takes
     // care of details.
-    if (Config->EntryName.empty()) {
+    if (Config->EntryName.empty() && !Config->NoEntry) {
       auto EntryOrErr = Symtab.findDefaultEntry();
       if (auto EC = EntryOrErr.getError()) {
         llvm::errs() << EC.message() << "\n";
         return false;
       }
       Config->EntryName = EntryOrErr.get();
+      addUndefined(Config->EntryName);
     }
-    addUndefined(Config->EntryName);
 
     if (auto EC = Symtab.run()) {
       llvm::errs() << EC.message() << "\n";
diff --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index 81a9b2425527..c0a7f4565e2a 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -316,8 +316,10 @@ void Writer::writeHeader() {
   PE->Subsystem = Config->Subsystem;
   PE->SizeOfImage = SizeOfImage;
   PE->SizeOfHeaders = SizeOfHeaders;
-  Defined *Entry = cast<Defined>(Symtab->find(Config->EntryName));
-  PE->AddressOfEntryPoint = Entry->getRVA();
+  if (!Config->NoEntry) {
+    Defined *Entry = cast<Defined>(Symtab->find(Config->EntryName));
+    PE->AddressOfEntryPoint = Entry->getRVA();
+  }
   PE->SizeOfStackReserve = Config->StackReserve;
   PE->SizeOfStackCommit = Config->StackCommit;
   PE->SizeOfHeapReserve = Config->HeapReserve;