LLVM ld64.lld

[tschuett]

I tried to use the new MachO linker from LLVM:

RUSTFLAGS="-C linker=/Users/tschuett/modules/clang/git/bin/ld64.lld" cargo build

  = note: ld64.lld:
          ld64.lld: error: unknown argument '-Wl,-dead_strip'
          ld64.lld: error: must specify -platform_version

First issue, rust appends -Wl, which makes the linker unhappy. Dead stripping is supported since today (https://reviews.llvm.org/D103324).

Second issue the linker requires a platform version:
https://github.com/llvm/llvm-project/blob/06e047227d71b2c1c477e280172abed0f1eed2c8/lld/MachO/Driver.cpp#L598

platform_version was introduced into clang:
https://reviews.llvm.org/D71579

Did the LinkerFlavor detection fail?

#39915

[tschuett]

The full error message:

  = note: ld64.lld: error: unknown argument '-m64'
          ld64.lld: error: unknown argument '-Wl,-dead_strip'
          ld64.lld: error: unknown argument '-nodefaultlibs'
          ld64.lld: error: must specify -platform_version

[tschuett]

The -m64 issue is:
https://github.com/llvm/llvm-project/blob/70804f2a2f7b87227a873cd6d8852ad295068e79/lld/MachO/Options.td#L1040

[tschuett]

I couldn't find -nodefaultlibs neither in the ld man page nor in Options.td file. It seems to be a GNU thing.

[tschuett]

ld64.lld is missing here:

rust/compiler/rustc_codegen_ssa/src/back/link.rs

Line 957 in 016e9b5

fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {

[tschuett]

Add platform_version:

rust/compiler/rustc_codegen_ssa/src/back/link.rs

Line 2209 in 2577825

fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {

xcrun --show-sdk-platform-version -sdk macosx

[petrochenkov]

Closing as a duplicate of #11937 since this issue is about using ld64 directly rather than through a C compiler.