Improve linker detection for ld64.lld for Apple devices #86064

tschuett · 2021-06-06T15:19:23Z

Other Apple devices will need a similar solution, but I have no hardware.

I can now build a large workspace with 300+ crates.

rust-highfive · 2021-06-06T15:19:25Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @davidtwco (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

bors · 2021-06-06T19:48:34Z

☔ The latest upstream changes (presumably #85086) made this pull request unmergeable. Please resolve the merge conflicts.

tschuett · 2021-06-07T03:34:12Z

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -2504,3 +2512,59 @@ fn get_apple_sdk_root(sdk_name: &str) -> Result<String, String> {
        Err(e) => Err(format!("failed to get {} SDK path: {}", sdk_name, e)),
    }
 }
+


The LLVM linker requires the platform_version option. The Apple linker also supports it.

tschuett · 2021-06-07T03:34:37Z

compiler/rustc_target/src/spec/x86_64_apple_darwin.rs

@@ -9,6 +9,10 @@ pub fn target() -> Target {
        LinkerFlavor::Gcc,
        vec!["-m64".to_string(), "-arch".to_string(), "x86_64".to_string()],
    );
+    base.pre_link_args.insert(


This will be needed for other Apple devices, but I have no hardware.

tschuett · 2021-06-07T03:35:40Z

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -2183,7 +2187,11 @@ fn add_upstream_rust_crates<'a, B: ArchiveBuilder<'a>>(

    // Converts a library file-stem into a cc -l argument
    fn unlib<'a>(target: &Target, stem: &'a str) -> &'a str {
-        if stem.starts_with("lib") && !target.is_like_windows { &stem[3..] } else { stem }
+        if stem.starts_with("lib") && !target.is_like_windows {


This change was by rustfmt.

tschuett · 2021-06-07T07:22:44Z

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -231,7 +231,9 @@ impl<'a> GccLinker<'a> {
    fn build_dylib(&mut self, out_filename: &Path) {
        // On mac we need to tell the linker to let this library be rpathed
        if self.sess.target.is_like_osx {
-            self.cmd.arg("-dynamiclib");
+            if self.sess.target.lld_flavor != LldFlavor::Ld64 {
+                self.cmd.arg("-dynamiclib");


This seems be only needed for gcc. -dynamiclib is an gcc option.

tschuett · 2021-06-07T07:26:08Z

compiler/rustc_codegen_ssa/src/back/link.rs

+    };
+
+    let path = format!("{}/usr/lib", &sdk_path);
+    cmd.args(&["-syslibroot", &sdk_path]);


This is an implementation of -isysroot for ld64.

petrochenkov · 2021-06-07T10:23:58Z

@tschuett
From #85938:

First issue, rust appends -Wl, which makes the linker unhappy.

rustc doesn't generally support linking with a "naked" linker (with exception of bare-metal platforms, cc #11937), and lld is supposed to be used indirectly through the -fuse-ld=lld option to C compiler.

This PR attempts to add support for linking directly with ld64 for Apple targets, which I'm not sure is something desirable.

tschuett · 2021-06-07T10:26:25Z

How do I get cargo to use ld64.lld?

petrochenkov · 2021-06-07T10:27:05Z

In other words, -Clinker ld64.lld may be an intuitive way to switch linker to LLD, but it's not correct, the working way is -Clink-arg -fuse-ld=lld (although I didn't personally try it on Apple).

rust-log-analyzer · 2021-06-07T10:29:49Z

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

configure: rust.channel         := nightly
configure: rust.debug-assertions := True
configure: llvm.assertions      := True
configure: dist.missing-tools   := True
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
configure: 
configure: run `python /checkout/x.py --help`
configure: 
---
skip untracked path cpu-usage.csv during rustfmt invocations
skip untracked path src/doc/book/ during rustfmt invocations
skip untracked path src/doc/rust-by-example/ during rustfmt invocations
skip untracked path src/llvm-project/ during rustfmt invocations
Diff in /checkout/compiler/rustc_codegen_ssa/src/back/link.rs at line 2187:
 
     // Converts a library file-stem into a cc -l argument
     fn unlib<'a>(target: &Target, stem: &'a str) -> &'a str {
-        if stem.starts_with("lib") && !target.is_like_windows {
-            &stem[3..]
-            stem
-        }
-        }
+        if stem.starts_with("lib") && !target.is_like_windows { &stem[3..] } else { stem }
 
 
     // Adds the static "rlib" versions of all crates to the command line.
Running `"/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt" "--config-path" "/checkout" "--edition" "2018" "--unstable-features" "--skip-children" "--check" "/checkout/compiler/rustc_codegen_ssa/src/back/rpath/tests.rs" "/checkout/compiler/rustc_codegen_ssa/src/back/metadata.rs" "/checkout/compiler/rustc_codegen_ssa/src/back/link.rs" "/checkout/compiler/rustc_codegen_ssa/src/common.rs" "/checkout/compiler/rustc_lint/src/methods.rs" "/checkout/compiler/rustc_codegen_ssa/src/back/archive.rs" "/checkout/compiler/rustc_lint/src/early.rs" "/checkout/compiler/rustc_codegen_ssa/src/back/command.rs"` failed.
If you're running `tidy`, try again with `--bless`. Or, if you just want to format code, run `./x.py fmt` instead.
Build completed unsuccessfully in 0:00:18

tschuett · 2021-06-07T10:36:02Z

Indeed

RUSTFLAGS="-C link-arg=-fuse-ld=/..../ld64.lld" cargo build

succeeds.

rust-highfive assigned davidtwco Jun 6, 2021

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 6, 2021

tschuett changed the title ~~Improve linker detection for ld64 for Apple devices~~ Improve linker detection for ld64.lld for Apple devices Jun 6, 2021

tschuett added 3 commits June 7, 2021 05:30

remove obsolete -m64 option

1357ec4

improve linker detection for ld64 for Apple devices

820e8d2

add support for -platform_version option

4caeb6a

tschuett commented Jun 7, 2021

View reviewed changes

tschuett added 3 commits June 7, 2021 08:18

add path to sysroot + /usr/lib

88d7494

add -syslibroot

31f4ec7

fix gcc call

dae13ae

tschuett commented Jun 7, 2021

View reviewed changes

petrochenkov self-assigned this Jun 7, 2021

tschuett closed this Jun 7, 2021

petrochenkov mentioned this pull request Nov 10, 2021

Fix ld64 flags #90717

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Improve linker detection for ld64.lld for Apple devices #86064

Improve linker detection for ld64.lld for Apple devices #86064

tschuett commented Jun 6, 2021 •

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bors commented Jun 6, 2021

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petrochenkov commented Jun 7, 2021

tschuett commented Jun 7, 2021

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tschuett commented Jun 7, 2021

Improve linker detection for ld64.lld for Apple devices #86064

Improve linker detection for ld64.lld for Apple devices #86064

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