MVP for using rust-lld as part of cc

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -5,7 +5,7 @@ use rustc_fs_util::fix_windows_verbatim_for_gcc;
 use rustc_hir::def_id::CrateNum;
 use rustc_middle::middle::cstore::{DllImport, LibSource};
 use rustc_middle::middle::dependency_format::Linkage;
-use rustc_session::config::{self, CFGuard, CrateType, DebugInfo, Strip};
+use rustc_session::config::{self, CFGuard, CrateType, DebugInfo, LdImpl, Strip};
 use rustc_session::config::{OutputFilenames, OutputType, PrintRequest};
 use rustc_session::output::{check_file_is_writeable, invalid_output_for_target, out_filename};
 use rustc_session::search_paths::PathKind;
@@ -1927,6 +1927,8 @@ fn add_order_independent_options(
     out_filename: &Path,
     tmpdir: &Path,
 ) {
+    add_gcc_ld_path(cmd, sess, flavor);
+
     add_apple_sdk(cmd, sess, flavor);
 
     add_link_script(cmd, sess, tmpdir, crate_type);
@@ -2528,3 +2530,30 @@ fn get_apple_sdk_root(sdk_name: &str) -> Result<String, String> {
         Err(e) => Err(format!("failed to get {} SDK path: {}", sdk_name, e)),
     }
 }
+
+fn add_gcc_ld_path(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
+    if let Some(ld_impl) = sess.opts.debugging_opts.gcc_ld {
+        if let LinkerFlavor::Gcc = flavor {
+            match ld_impl {
+                LdImpl::Lld => {
+                    let tools_path =
+                        sess.host_filesearch(PathKind::All).get_tools_search_paths(false);
+                    let lld_path = tools_path
+                        .into_iter()
+                        .map(|p| p.join("gcc-ld"))
+                        .find(|p| {
+                            p.join(if sess.host.is_like_windows { "ld.exe" } else { "ld" }).exists()
+                        })
+                        .unwrap_or_else(|| sess.fatal("rust-lld (as ld) not found"));
+                    cmd.cmd().arg({
+                        let mut arg = OsString::from("-B");
+                        arg.push(lld_path);
+                        arg
+                    });
+                }
+            }
+        } else {
+            sess.fatal("option `-Z gcc-ld` is used even though linker flavor is not gcc");
+        }
+    }
+}

compiler/rustc_session/src/config.rs

@@ -2417,6 +2417,7 @@ impl PpMode {
 /// we have an opt-in scheme here, so one is hopefully forced to think about
 /// how the hash should be calculated when adding a new command-line argument.
 crate mod dep_tracking {
+    use super::LdImpl;
     use super::{
         CFGuard, CrateType, DebugInfo, ErrorOutputType, InstrumentCoverage, LinkerPluginLto,
         LtoCli, OptLevel, OutputTypes, Passes, SourceFileHashAlgorithm, SwitchWithOptPath,
@@ -2497,6 +2498,7 @@ crate mod dep_tracking {
         SymbolManglingVersion,
         SourceFileHashAlgorithm,
         TrimmedDefPaths,
+        Option<LdImpl>,
     );
 
     impl<T1, T2> DepTrackingHash for (T1, T2)

compiler/rustc_session/src/options.rs

@@ -370,6 +370,7 @@ mod desc {
     pub const parse_wasi_exec_model: &str = "either `command` or `reactor`";
     pub const parse_split_debuginfo: &str =
         "one of supported split-debuginfo modes (`off`, `packed`, or `unpacked`)";
+    pub const parse_gcc_ld: &str = "one of: no value, `lld`";
 }
 
 mod parse {
@@ -864,6 +865,15 @@ mod parse {
         }
         true
     }
+
+    crate fn parse_gcc_ld(slot: &mut Option<LdImpl>, v: Option<&str>) -> bool {
+        match v {
+            None => *slot = None,
+            Some("lld") => *slot = Some(LdImpl::Lld),
+            _ => return false,
+        }
+        true
+    }
 }
 
 options! {
@@ -1067,6 +1077,7 @@ options! {
         "set the optimization fuel quota for a crate"),
     function_sections: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "whether each function should go in its own section"),
+    gcc_ld: Option<LdImpl> = (None, parse_gcc_ld, [TRACKED], "implementation of ld used by cc"),
     graphviz_dark_mode: bool = (false, parse_bool, [UNTRACKED],
         "use dark-themed colors in graphviz output (default: no)"),
     graphviz_font: String = ("Courier, monospace".to_string(), parse_string, [UNTRACKED],
@@ -1321,3 +1332,8 @@ pub enum WasiExecModel {
     Command,
     Reactor,
 }
+
+#[derive(Clone, Copy, Hash)]
+pub enum LdImpl {
+    Lld,
+}

src/bootstrap/compile.rs

@@ -1108,6 +1108,13 @@ impl Step for Assemble {
             let src_exe = exe("lld", target_compiler.host);
             let dst_exe = exe("rust-lld", target_compiler.host);
             builder.copy(&lld_install.join("bin").join(&src_exe), &libdir_bin.join(&dst_exe));
+            // for `-Z gcc-ld=lld`
+            let gcc_ld_dir = libdir_bin.join("gcc-ld");
+            t!(fs::create_dir(&gcc_ld_dir));
+            builder.copy(
+                &lld_install.join("bin").join(&src_exe),
+                &gcc_ld_dir.join(exe("ld", target_compiler.host)),
+            );
         }
 
         // Similarly, copy `llvm-dwp` into libdir for Split DWARF. Only copy it when the LLVM

src/bootstrap/dist.rs

@@ -402,6 +402,10 @@ impl Step for Rustc {
             if builder.config.lld_enabled {
                 let exe = exe("rust-lld", compiler.host);
                 builder.copy(&src_dir.join(&exe), &dst_dir.join(&exe));
+                // for `-Z gcc-ld=lld`
+                let gcc_lld_dir = dst_dir.join("gcc-ld");
+                t!(fs::create_dir(&gcc_lld_dir));
+                builder.copy(&src_dir.join(&exe), &gcc_lld_dir.join(&exe));
             }
 
             // Copy over llvm-dwp if it's there

src/test/run-make/issue-71519/Makefile

@@ -0,0 +1,6 @@
+-include ../../run-make-fulldeps/tools.mk
+
+# needs-rust-lld
+all:
+	RUSTC_LOG=rustc_codegen_ssa::back::link=info $(RUSTC) -Z gcc-ld=lld -C link-args=-Wl,-v main.rs 2> $(TMPDIR)/output.txt
+	$(CGREP) -e "^LLD [0-9]+\.[0-9]+\.[0-9]+" < $(TMPDIR)/output.txt

src/test/run-make/issue-71519/main.rs

@@ -0,0 +1,4 @@
+// test linking using cc with rust-lld injected into search path as ld
+// see rust-lang/rust#71519 for more info
+
+fn main() {}

src/tools/compiletest/src/header.rs

@@ -50,6 +50,15 @@ impl EarlyProps {
         let has_msan = util::MSAN_SUPPORTED_TARGETS.contains(&&*config.target);
         let has_tsan = util::TSAN_SUPPORTED_TARGETS.contains(&&*config.target);
         let has_hwasan = util::HWASAN_SUPPORTED_TARGETS.contains(&&*config.target);
+        // for `-Z gcc-ld=lld`
+        let has_rust_lld = config
+            .compile_lib_path
+            .join("rustlib")
+            .join(&config.target)
+            .join("bin")
+            .join("gcc-ld")
+            .join(if config.host.contains("windows") { "ld.exe" } else { "ld" })
+            .exists();
 
         iter_header(testfile, None, rdr, &mut |ln| {
             // we should check if any only-<platform> exists and if it exists
@@ -136,6 +145,10 @@ impl EarlyProps {
                 if config.debugger == Some(Debugger::Lldb) && ignore_lldb(config, ln) {
                     props.ignore = true;
                 }
+
+                if !has_rust_lld && config.parse_name_directive(ln, "needs-rust-lld") {
+                    props.ignore = true;
+                }
             }
 
             if let Some(s) = config.parse_aux_build(ln) {