2 files changed, 111 insertions, 0 deletions
diff --git a/src/tools/lld-wrapper/Cargo.toml b/src/tools/lld-wrapper/Cargo.toml
new file mode 100644
index 000000000..bf5138b16
--- /dev/null
+++ b/src/tools/lld-wrapper/Cargo.toml
@@ -0,0 +1,5 @@
+[package]
+name = "lld-wrapper"
+version = "0.1.0"
+edition = "2021"
+license = "MIT OR Apache-2.0"
diff --git a/src/tools/lld-wrapper/src/main.rs b/src/tools/lld-wrapper/src/main.rs
new file mode 100644
index 000000000..90bd24a75
--- /dev/null
+++ b/src/tools/lld-wrapper/src/main.rs
@@ -0,0 +1,106 @@
+//! Script to invoke the bundled rust-lld with the correct flavor.
+//!
+//! lld supports multiple command line interfaces. If `-flavor <flavor>` are passed as the first
+//! two arguments the `<flavor>` command line interface is used to process the remaining arguments.
+//! If no `-flavor` argument is present the flavor is determined by the executable name.
+//!
+//! In Rust with `-Z gcc-ld=lld` we have gcc or clang invoke rust-lld. Since there is no way to
+//! make gcc/clang pass `-flavor <flavor>` as the first two arguments in the linker invocation
+//! and since Windows does not support symbolic links for files this wrapper is used in place of a
+//! symbolic link. It execs `../rust-lld -flavor <flavor>` by propagating the flavor argument
+//! passed to the wrapper as the first two arguments. On Windows it spawns a `..\rust-lld.exe`
+//! child process.
+
+use std::fmt::Display;
+use std::path::{Path, PathBuf};
+use std::{env, process};
+
+trait UnwrapOrExitWith<T> {
+    fn unwrap_or_exit_with(self, context: &str) -> T;
+}
+
+impl<T> UnwrapOrExitWith<T> for Option<T> {
+    fn unwrap_or_exit_with(self, context: &str) -> T {
+        self.unwrap_or_else(|| {
+            eprintln!("lld-wrapper: {}", context);
+            process::exit(1);
+        })
+    }
+}
+
+impl<T, E: Display> UnwrapOrExitWith<T> for Result<T, E> {
+    fn unwrap_or_exit_with(self, context: &str) -> T {
+        self.unwrap_or_else(|err| {
+            eprintln!("lld-wrapper: {}: {}", context, err);
+            process::exit(1);
+        })
+    }
+}
+
+/// Returns the path to rust-lld in the parent directory.
+///
+/// Exits if the parent directory cannot be determined.
+fn get_rust_lld_path(current_exe_path: &Path) -> PathBuf {
+    let mut rust_lld_exe_name = "rust-lld".to_owned();
+    rust_lld_exe_name.push_str(env::consts::EXE_SUFFIX);
+    let mut rust_lld_path = current_exe_path
+        .parent()
+        .unwrap_or_exit_with("directory containing current executable could not be determined")
+        .parent()
+        .unwrap_or_exit_with("parent directory could not be determined")
+        .to_owned();
+    rust_lld_path.push(rust_lld_exe_name);
+    rust_lld_path
+}
+
+/// Returns the command for invoking rust-lld with the correct flavor.
+/// LLD only accepts the flavor argument at the first two arguments, so move it there.
+///
+/// Exits on error.
+fn get_rust_lld_command(current_exe_path: &Path) -> process::Command {
+    let rust_lld_path = get_rust_lld_path(current_exe_path);
+    let mut command = process::Command::new(rust_lld_path);
+
+    let mut flavor = None;
+    let args = env::args_os()
+        .skip(1)
+        .filter(|arg| match arg.to_str().and_then(|s| s.strip_prefix("-rustc-lld-flavor=")) {
+            Some(suffix) => {
+                flavor = Some(suffix.to_string());
+                false
+            }
+            None => true,
+        })
+        .collect::<Vec<_>>();
+
+    command.arg("-flavor");
+    command.arg(flavor.unwrap_or_exit_with("-rustc-lld-flavor=<flavor> is not passed"));
+    command.args(args);
+    command
+}
+
+#[cfg(unix)]
+fn exec_lld(mut command: process::Command) {
+    use std::os::unix::prelude::CommandExt;
+    Result::<(), _>::Err(command.exec()).unwrap_or_exit_with("could not exec rust-lld");
+    unreachable!("lld-wrapper: after exec without error");
+}
+
+#[cfg(not(unix))]
+fn exec_lld(mut command: process::Command) {
+    // Windows has no exec(), spawn a child process and wait for it.
+    let exit_status = command.status().unwrap_or_exit_with("error running rust-lld child process");
+    let code = exit_status
+        .code()
+        .ok_or(exit_status)
+        .unwrap_or_exit_with("rust-lld child process exited with error");
+    // Return the original lld exit code.
+    process::exit(code);
+}
+
+fn main() {
+    let current_exe_path =
+        env::current_exe().unwrap_or_exit_with("could not get the path of the current executable");
+
+    exec_lld(get_rust_lld_command(current_exe_path.as_ref()));
+}