[lld-macho] Switch to new tool ID

[keith]

Summary

As of Xcode 15 there is now a tool ID for LLD, likely driven by Apple's
tests with using LLD for their CAS work in clang. This updates LLD to
use the correct ID, and updates the object library so that llvm-objdump
prints it correctly.

[smeenai]

Neat.

[davide]

As of Xcode 15 there is now a tool ID for LLD, likely driven by Apple's tests with using LLD for their CAS work in clang.

The tool ID is something Apple introduced to stamp in the load command what linker is used to produce the executable, and it's unrelated to the CAS.
That's useful to distinguish between ld(1) -- as provided by Apple and 3rd party linkers. dyld can also parse this field potentially to make the behavior more strict on Apple produced binaries, as other linkers could produce slightly broken (for some definition of broken) binaries that can create binary compatibility problems (e.g. some load commands aren't emitted).

Thanks for adopting. HTH.

lld/MachO/Writer.cpp

void writeTo(uint8_t *buf) const override {
     c->cmdsize = getSize();
 
     c->platform = static_cast<uint32_t>(platformInfo.target.Platform);
     c->minos = encodeVersion(platformInfo.target.MinDeployment);
     c->sdk = encodeVersion(platformInfo.sdk);
 
     c->ntools = ntools;
     auto *t = reinterpret_cast<build_tool_version *>(&c[1]);
-    t->tool = TOOL_LD;
+    t->tool = TOOL_LLD;
     t->version = encodeVersion(VersionTuple(
         LLVM_VERSION_MAJOR, LLVM_VERSION_MINOR, LLVM_VERSION_PATCH));
   }
 
 private:
   const PlatformInfo &platformInfo;
 };
 

lld/test/MachO/lc-build-version.s

 # REQUIRES: x86
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 
 # RUN: %lld -platform_version macos 10.14 10.15 -o %t.macos-10-14 %t.o
 # RUN: llvm-objdump --macho --all-headers %t.macos-10-14 | FileCheck %s --check-prefix=MACOS-10-14
 
 # MACOS-10-14: cmd LC_BUILD_VERSION
 # MACOS-10-14-NEXT: cmdsize 32
 # MACOS-10-14-NEXT: platform macos
 # MACOS-10-14-NEXT: sdk 10.15
 # MACOS-10-14-NEXT: minos 10.14
 # MACOS-10-14-NEXT: ntools 1
-# MACOS-10-14-NEXT: tool ld
+# MACOS-10-14-NEXT: tool lld
 # MACOS-10-14-NEXT: version {{[0-9\.]+}}
 
 # RUN: %lld -platform_version macos 10.13 10.15 -o %t.macos-10-13 %t.o
 # RUN: llvm-objdump --macho --all-headers %t.macos-10-13 | FileCheck %s --check-prefix=MACOS-10-13
 
 # MACOS-10-13: cmd LC_VERSION_MIN_MACOSX
 # MACOS-10-13-NEXT: cmdsize 16
 # MACOS-10-13-NEXT: version 10.13

llvm/include/llvm/BinaryFormat/MachO.h

enum PlatformType {
   PLATFORM_MACCATALYST = 6,
   PLATFORM_IOSSIMULATOR = 7,
   PLATFORM_TVOSSIMULATOR = 8,
   PLATFORM_WATCHOSSIMULATOR = 9,
   PLATFORM_DRIVERKIT = 10,
 };
 
 // Values for tools enum in build_tool_version.
-enum { TOOL_CLANG = 1, TOOL_SWIFT = 2, TOOL_LD = 3 };
+enum { TOOL_CLANG = 1, TOOL_SWIFT = 2, TOOL_LD = 3, TOOL_LLD = 4 };
 
 // Structs from <mach-o/loader.h>
 
 struct mach_header {
   uint32_t magic;
   uint32_t cputype;
   uint32_t cpusubtype;
   uint32_t filetype;

llvm/include/llvm/Object/MachO.h

static std::string getBuildPlatform(uint32_t platform) {
     }
   }
 
   static std::string getBuildTool(uint32_t tools) {
     switch (tools) {
     case MachO::TOOL_CLANG: return "clang";
     case MachO::TOOL_SWIFT: return "swift";
     case MachO::TOOL_LD: return "ld";
+    case MachO::TOOL_LLD:
+      return "lld";
     default:
       std::string ret;
       raw_string_ostream ss(ret);
       ss << format_hex(tools, 8, true);
       return ss.str();
     }
   }