[Mach-O] Add -object_path_lto

macho/cmdline.cc

@@ -55,6 +55,7 @@ Options:
   -no_deduplicate             Ignored
   -no_uuid                    Do not generate an LC_UUID load command
   -o <FILE>                   Set output filename
+  -object_path_lto <FILE>     Write a LTO temporary file to a given path
   -pagezero_size <SIZE>       Specify the size of the __PAGEZERO segment
   -platform_version <PLATFORM> <MIN_VERSION> <SDK_VERSION>
                               Set platform, platform version and SDK version
@@ -293,6 +294,8 @@ std::vector<std::string> parse_nonpositional_args(Context<E> &ctx) {
       ctx.arg.uuid = UUID_NONE;
     } else if (read_arg("-o")) {
       ctx.arg.output = arg;
+    } else if (read_arg("-object_path_lto")) {
+      ctx.arg.object_path_lto = arg;
     } else if (read_hex("-pagezero_size")) {
       pagezero_size = hex_arg;
     } else if (read_flag("-perf")) {

macho/lto.cc

@@ -2,6 +2,7 @@
 #include "mold.h"
 
 #include <algorithm>
+#include <cstdio>
 #include <dlfcn.h>
 
 namespace mold::macho {
@@ -118,6 +119,17 @@ void do_lto(Context<E> &ctx) {
   // Run the compiler backend to do LTO.
   size_t size;
   u8 *data = (u8 *)ctx.lto.codegen_compile(cg, &size);
+  if (!data)
+    Fatal(ctx) << "lto_codegen_compile failed: " << ctx.lto.get_error_message();
+
+  if (!ctx.arg.object_path_lto.empty()) {
+    FILE *out = fopen(ctx.arg.object_path_lto.c_str(), "w");
+    if (!out)
+      Fatal(ctx) << "-object_path_lto: cannot open " << ctx.arg.object_path_lto
+                 << ": " << errno_string();
+    fwrite(data, size, 1, out);
+    fclose(out);
+  }
 
   // Remove bitcode object files from ctx.objs.
   for (ObjectFile<E> *file : ctx.objs) {

macho/mold.h

@@ -874,6 +874,7 @@ struct Context {
     std::string install_name;
     std::string lto_library;
     std::string map;
+    std::string object_path_lto;
     std::string output = "a.out";
     std::vector<SectCreateOption> sectcreate;
     std::vector<std::string> U;

test/macho/object-path-lto.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+export LC_ALL=C
+set -e
+CC="${TEST_CC:-cc}"
+CXX="${TEST_CXX:-c++}"
+GCC="${TEST_GCC:-gcc}"
+GXX="${TEST_GXX:-g++}"
+OBJDUMP="${OBJDUMP:-objdump}"
+MACHINE="${MACHINE:-$(uname -m)}"
+testname=$(basename "$0" .sh)
+echo -n "Testing $testname ... "
+cd "$(dirname "$0")"/../..
+t=out/test/macho/$testname
+mkdir -p $t
+
+cat <<EOF | $CC -o $t/a.o -c -xc - -flto
+#include <stdio.h>
+int main() {
+  printf("Hello world\n");
+}
+EOF
+
+clang --ld-path=./ld64 -o $t/exe $t/a.o -flto -Wl,-object_path_lto,$t/obj
+$t/exe | grep -q 'Hello world'
+otool -l $t/obj > /dev/null
+
+echo OK