Pass GCC offload data to the LTO backend

Fixes #1190

elf/input-files.cc

@@ -240,6 +240,12 @@ void ObjectFile<E>::initialize_sections(Context<E> &ctx) {
     const ElfShdr<E> &shdr = this->elf_sections[i];
     std::string_view name = this->shstrtab.data() + shdr.sh_name;
 
+    if ((shdr.sh_flags & SHF_EXCLUDE) &&
+        name.starts_with(".gnu.offload_lto_.symtab.")) {
+      this->is_gcc_offload_obj = true;
+      continue;
+    }
+
     if ((shdr.sh_flags & SHF_EXCLUDE) && !(shdr.sh_flags & SHF_ALLOC) &&
         shdr.sh_type != SHT_LLVM_ADDRSIG && !ctx.arg.relocatable)
       continue;

elf/lto-unix.cc

@@ -717,6 +717,18 @@ std::vector<ObjectFile<E> *> do_lto(Context<E> &ctx) {
   for (Symbol<E> *sym : ctx.arg.undefined)
     sym->referenced_by_regular_obj = true;
 
+  // Object files containing .gnu.offload_lto_.* sections need to be
+  // given to the LTO backend. Such sections contains code and data for
+  // peripherails (typically GPUs).
+  for (ObjectFile<E> *file : ctx.objs) {
+    if (!file->is_lto_obj && file->is_gcc_offload_obj) {
+      PluginInputFile pfile = create_plugin_input_file(ctx, file->mf);
+      int claimed = false;
+      claim_file_hook(&pfile, &claimed);
+      assert(!claimed);
+    }
+  }
+
   // all_symbols_read_hook() calls add_input_file() and add_input_library()
   LOG << "all symbols read\n";
   if (PluginStatus st = all_symbols_read_hook(); st != LDPS_OK)

elf/mold.h

@@ -1189,6 +1189,7 @@ class ObjectFile : public InputFile<E> {
   std::map<u32, u32> gnu_properties;
   bool needs_executable_stack = false;
   bool is_lto_obj = false;
+  bool is_gcc_offload_obj = false;
   bool is_rust_obj = false;
 
   u64 num_dynrel = 0;

elf/passes.cc

@@ -302,7 +302,7 @@ void resolve_symbols(Context<E> &ctx) {
 
   bool has_lto_obj = false;
   for (ObjectFile<E> *file : objs)
-    if (file->is_lto_obj)
+    if (file->is_lto_obj || file->is_gcc_offload_obj)
       has_lto_obj = true;
 
   if (has_lto_obj) {