[PECOFF] Add /dllexport option.

/DLLEXPORT is a command line option to export a symbol. __declspec(dllexport)
uses that to make the linker to export DLLExport'ed functions, by adding the
option to .drectve section.

This patch implements the parser of the command line option.

llvm-svn: 197122

lld/include/lld/ReaderWriter/PECOFFLinkingContext.h

@@ -219,6 +219,9 @@ public:
   void setDosStub(ArrayRef<uint8_t> data) { _dosStub = data; }
   ArrayRef<uint8_t> getDosStub() const { return _dosStub; }
 
+  void addDllExport(StringRef sym) { _dllExports.insert(sym); }
+  const std::set<std::string> &getDllExports() const { return _dllExports; }
+
   StringRef allocate(StringRef ref) const {
     char *x = _allocator.Allocate<char>(ref.size() + 1);
     memcpy(x, ref.data(), ref.size());
@@ -297,6 +300,9 @@ private:
   std::map<std::string, uint32_t> _sectionSetMask;
   std::map<std::string, uint32_t> _sectionClearMask;
 
+  // DLLExport'ed symbols.
+  std::set<std::string> _dllExports;
+
   // List of files that will be removed on destruction.
   std::vector<std::unique_ptr<llvm::FileRemover> > _tempFiles;
 

lld/lib/Driver/WinLinkDriver.cpp

@@ -832,6 +832,10 @@ WinLinkDriver::parse(int argc, const char *argv[], PECOFFLinkingContext &ctx,
       ctx.setEntrySymbolName(ctx.allocate(inputArg->getValue()));
       break;
 
+    case OPT_export:
+      ctx.addDllExport(inputArg->getValue());
+      break;
+
     case OPT_libpath:
       ctx.appendInputSearchPath(ctx.allocate(inputArg->getValue()));
       break;

lld/lib/Driver/WinLinkOptions.td

@@ -22,6 +22,7 @@ def nodefaultlib : P<"nodefaultlib", "Remove a default library">;
 def disallowlib : Joined<["/", "-", "-?"], "disallowlib:">, Alias<nodefaultlib>;
 def entry   : P<"entry", "Name of entry point symbol">;
 // No help text because /failifmismatch is not intended to be used by the user.
+def export  : P<"export", "Export a function">;
 def failifmismatch : P<"failifmismatch", "">;
 def heap    : P<"heap", "Size of the heap">;
 def align   : P<"align", "Section alignment">;

lld/unittests/DriverTests/WinLinkDriverTest.cpp

@@ -155,6 +155,13 @@ TEST_F(WinLinkParserTest, AlternateName) {
   EXPECT_EQ("", _context.getAlternateName("foo"));
 }
 
+TEST_F(WinLinkParserTest, Export) {
+  EXPECT_TRUE(parse("link.exe", "/export:_foo", "a.out", nullptr));
+  const std::set<std::string> &exports = _context.getDllExports();
+  EXPECT_TRUE(exports.count("_foo") == 1);
+  EXPECT_TRUE(exports.count("nosuchsym") == 0);
+}
+
 TEST_F(WinLinkParserTest, MachineX86) {
   EXPECT_TRUE(parse("link.exe", "/machine:x86", "a.obj", nullptr));
   EXPECT_EQ(llvm::COFF::IMAGE_FILE_MACHINE_I386, _context.getMachineType());