bootstrap: Configurable musl libdir

Make it possible to customize the location of musl libdir using
musl-libdir in config.toml, e.g., to use lib64 instead of lib.

config.toml.example

@@ -359,7 +359,7 @@
 # nightly features
 #channel = "dev"
 
-# The root location of the MUSL installation directory.
+# The root location of the musl installation directory.
 #musl-root = "..."
 
 # By default the `rustc` executable is built with `-Wl,-rpath` flags on Unix
@@ -502,12 +502,15 @@
 # only use static libraries. If unset, the target's default linkage is used.
 #crt-static = false
 
-# The root location of the MUSL installation directory. The library directory
+# The root location of the musl installation directory. The library directory
 # will also need to contain libunwind.a for an unwinding implementation. Note
-# that this option only makes sense for MUSL targets that produce statically
+# that this option only makes sense for musl targets that produce statically
 # linked binaries
 #musl-root = "..."
 
+# The full path to the musl libdir.
+#musl-libdir = musl-root/lib
+
 # The root location of the `wasm32-wasi` sysroot.
 #wasi-root = "..."
 

src/bootstrap/compile.rs

@@ -133,7 +133,7 @@ fn copy_third_party_objects(
     // To do that we have to distribute musl startup objects as a part of Rust toolchain
     // and link with them manually in the self-contained mode.
     if target.contains("musl") {
-        let srcdir = builder.musl_root(target).unwrap().join("lib");
+        let srcdir = builder.musl_libdir(target).unwrap();
         for &obj in &["crt1.o", "Scrt1.o", "rcrt1.o", "crti.o", "crtn.o"] {
             copy_and_stamp(&srcdir, obj);
         }
@@ -219,8 +219,8 @@ pub fn std_cargo(builder: &Builder<'_>, target: Interned<String>, stage: u32, ca
         // Help the libc crate compile by assisting it in finding various
         // sysroot native libraries.
         if target.contains("musl") {
-            if let Some(p) = builder.musl_root(target) {
-                let root = format!("native={}/lib", p.to_str().unwrap());
+            if let Some(p) = builder.musl_libdir(target) {
+                let root = format!("native={}", p.to_str().unwrap());
                 cargo.rustflag("-L").rustflag(&root);
             }
         }

src/bootstrap/config.rs

@@ -173,6 +173,7 @@ pub struct Target {
     pub ndk: Option<PathBuf>,
     pub crt_static: Option<bool>,
     pub musl_root: Option<PathBuf>,
+    pub musl_libdir: Option<PathBuf>,
     pub wasi_root: Option<PathBuf>,
     pub qemu_rootfs: Option<PathBuf>,
     pub no_std: bool,
@@ -363,6 +364,7 @@ struct TomlTarget {
     android_ndk: Option<String>,
     crt_static: Option<bool>,
     musl_root: Option<String>,
+    musl_libdir: Option<String>,
     wasi_root: Option<String>,
     qemu_rootfs: Option<String>,
     no_std: Option<bool>,
@@ -631,6 +633,7 @@ pub fn parse(args: &[String]) -> Config {
                 target.linker = cfg.linker.clone().map(PathBuf::from);
                 target.crt_static = cfg.crt_static;
                 target.musl_root = cfg.musl_root.clone().map(PathBuf::from);
+                target.musl_libdir = cfg.musl_libdir.clone().map(PathBuf::from);
                 target.wasi_root = cfg.wasi_root.clone().map(PathBuf::from);
                 target.qemu_rootfs = cfg.qemu_rootfs.clone().map(PathBuf::from);
 

src/bootstrap/lib.rs

@@ -877,6 +877,15 @@ fn musl_root(&self, target: Interned<String>) -> Option<&Path> {
             .map(|p| &**p)
     }
 
+    /// Returns the "musl libdir" for this `target`.
+    fn musl_libdir(&self, target: Interned<String>) -> Option<PathBuf> {
+        let t = self.config.target_config.get(&target)?;
+        if let libdir @ Some(_) = &t.musl_libdir {
+            return libdir.clone();
+        }
+        self.musl_root(target).map(|root| root.join("lib"))
+    }
+
     /// Returns the sysroot for the wasi target, if defined
     fn wasi_root(&self, target: Interned<String>) -> Option<&Path> {
         self.config.target_config.get(&target).and_then(|t| t.wasi_root.as_ref()).map(|p| &**p)

src/bootstrap/sanity.rs

@@ -199,10 +199,10 @@ pub fn check(build: &mut Build) {
                 let target = build.config.target_config.entry(target.clone()).or_default();
                 target.musl_root = Some("/usr".into());
             }
-            match build.musl_root(*target) {
-                Some(root) => {
-                    if fs::metadata(root.join("lib/libc.a")).is_err() {
-                        panic!("couldn't find libc.a in musl dir: {}", root.join("lib").display());
+            match build.musl_libdir(*target) {
+                Some(libdir) => {
+                    if fs::metadata(libdir.join("libc.a")).is_err() {
+                        panic!("couldn't find libc.a in musl libdir: {}", libdir.display());
                     }
                 }
                 None => panic!(