Support lto on mingw

CMakeLists.txt

@@ -58,7 +58,11 @@ endif()
 
 add_executable(mold)
 target_compile_features(mold PRIVATE cxx_std_20)
-target_link_libraries(mold PRIVATE ${CMAKE_DL_LIBS})
+if(MINGW)
+  target_link_libraries(mold PRIVATE dl)
+else()
+  target_link_libraries(mold PRIVATE ${CMAKE_DL_LIBS})
+endif()
 
 if(NOT "${CMAKE_CXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "MSVC")
   target_compile_options(mold PRIVATE
@@ -328,7 +332,7 @@ list(APPEND MOLD_ELF_TEMPLATE_FILES
   elf/tls.cc
   )
 
-if(WIN32)
+if(WIN32 AND NOT(MINGW))
   list(APPEND MOLD_ELF_TEMPLATE_FILES elf/lto-win32.cc)
 else()
   list(APPEND MOLD_ELF_TEMPLATE_FILES elf/lto-unix.cc)

common/common.h

@@ -1001,6 +1001,32 @@ class MappedFile {
     return name;
   }
 
+  void close_fd() {
+#ifdef WIN32
+    if (fd != INVALID_HANDLE_VALUE) {
+      CloseHandle(fd);
+      fd = INVALID_HANDLE_VALUE;
+    }
+#else
+    if (fd != -1) {
+      close(fd);
+      fd = -1;
+    }
+#endif
+  }
+
+  void reopen_fd(const char *path) {
+#ifdef WIN32
+    if (fd != INVALID_HANDLE_VALUE)
+      fd = CreateFileA(path, GENERIC_READ,
+                       FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
+                       nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
+#else
+    if (fd == -1)
+      fd = open(path, O_RDONLY);
+#endif
+  }
+
   std::string name;
   u8 *data = nullptr;
   i64 size = 0;

elf/lto-unix.cc

@@ -200,10 +200,7 @@ static PluginStatus release_input_file(const void *handle) {
   LOG << "release_input_file\n";
 
   ObjectFile<E> &file = *(ObjectFile<E> *)handle;
-  if (file.mf->fd != -1) {
-    close(file.mf->fd);
-    file.mf->fd = -1;
-  }
+  file.mf->close_fd();
   return LDPS_OK;
 }
 
@@ -570,7 +567,11 @@ static ElfSym<E> to_elf_sym(PluginSymbol &psym) {
 // Returns false if it's GCC.
 template <typename E>
 static bool is_llvm(Context<E> &ctx) {
+#ifdef __MINGW32__
+  return ctx.arg.plugin.ends_with("LLVMgold.dll");
+#else
   return ctx.arg.plugin.ends_with("LLVMgold.so");
+#endif
 }
 
 // Returns true if a given linker plugin supports the get_symbols_v3 API.
@@ -590,11 +591,11 @@ create_plugin_input_file(Context<E> &ctx, MappedFile *mf) {
   file.offset = mf->get_offset();
   file.filesize = mf->size;
 
-  if (mf2->fd == -1)
-    mf2->fd = open(file.name, O_RDONLY);
+  mf2->reopen_fd(file.name);
+
   file.fd = mf2->fd;
 
-  if (file.fd == -1)
+  if (!file.fd)
     Fatal(ctx) << "cannot open " << file.name << ": " << errno_string();
   return file;
 }
@@ -645,8 +646,7 @@ ObjectFile<E> *read_lto_object(Context<E> &ctx, MappedFile *mf) {
   // open files" issue, we close fd only for GCC. This is ugly, though.
   if (!is_llvm(ctx)) {
     MappedFile *mf2 = mf->parent ? mf->parent : mf;
-    close(mf2->fd);
-    mf2->fd = -1;
+    mf2->close_fd();
   }
 
   // Create a symbol strtab

elf/lto.h

@@ -73,7 +73,11 @@ enum PluginOutputFileType {
 
 struct PluginInputFile {
   const char *name;
-  i32 fd;
+#if __MINGW32__
+  HANDLE fd;
+#else
+  int fd;
+#endif
   u64 offset;
   u64 filesize;
   void *handle;