Rollup merge of rust-lang#40113 - smaeul:native-musl, r=alexcrichton

Support dynamically-linked and/or native musl targets

These changes allow native compilation on musl-based distributions and the use of dynamic libraries on linux-musl targets. This is intended to remove limitations based on past assumptions about musl targets, while maintaining existing behavior by default.

A minor related bugfix is included.

Author: frewsxcv

src/bootstrap/bin/rustc.rs

@@ -207,9 +207,15 @@ fn main() {
             }
         }
 
-        if target.contains("pc-windows-msvc") {
-            cmd.arg("-Z").arg("unstable-options");
-            cmd.arg("-C").arg("target-feature=+crt-static");
+        if let Ok(s) = env::var("RUST_CRT_STATIC") {
+            if s == "true" {
+                cmd.arg("-Z").arg("unstable-options");
+                cmd.arg("-C").arg("target-feature=+crt-static");
+            }
+            if s == "false" {
+                cmd.arg("-Z").arg("unstable-options");
+                cmd.arg("-C").arg("target-feature=-crt-static");
+            }
         }
     }
 

src/bootstrap/compile.rs

@@ -106,14 +106,17 @@ pub fn std_link(build: &Build,
     t!(fs::create_dir_all(&libdir));
     add_to_sysroot(&out_dir, &libdir);
 
-    if target.contains("musl") && !target.contains("mips") {
+    if target.contains("musl") {
         copy_musl_third_party_objects(build, target, &libdir);
     }
 }
 
 /// Copies the crt(1,i,n).o startup objects
 ///
-/// Only required for musl targets that statically link to libc
+/// Since musl supports fully static linking, we can cross link for it even
+/// with a glibc-targeting toolchain, given we have the appropriate startup
+/// files. As those shipped with glibc won't work, copy the ones provided by
+/// musl so we have them on linux-gnu hosts.
 fn copy_musl_third_party_objects(build: &Build, target: &str, into: &Path) {
     for &obj in &["crt1.o", "crti.o", "crtn.o"] {
         copy(&build.musl_root(target).unwrap().join("lib").join(obj), &into.join(obj));

src/bootstrap/config.rs

@@ -117,6 +117,7 @@ pub struct Target {
     pub cc: Option<PathBuf>,
     pub cxx: Option<PathBuf>,
     pub ndk: Option<PathBuf>,
+    pub crt_static: Option<bool>,
     pub musl_root: Option<PathBuf>,
     pub qemu_rootfs: Option<PathBuf>,
 }
@@ -231,6 +232,7 @@ struct TomlTarget {
     cc: Option<String>,
     cxx: Option<String>,
     android_ndk: Option<String>,
+    crt_static: Option<bool>,
     musl_root: Option<String>,
     qemu_rootfs: Option<String>,
 }
@@ -375,6 +377,7 @@ impl Config {
                 }
                 target.cxx = cfg.cxx.clone().map(PathBuf::from);
                 target.cc = cfg.cc.clone().map(PathBuf::from);
+                target.crt_static = cfg.crt_static.clone();
                 target.musl_root = cfg.musl_root.clone().map(PathBuf::from);
                 target.qemu_rootfs = cfg.qemu_rootfs.clone().map(PathBuf::from);
 

src/bootstrap/lib.rs

@@ -473,6 +473,10 @@ impl Build {
              .env("RUSTDOC_REAL", self.rustdoc(compiler))
              .env("RUSTC_FLAGS", self.rustc_flags(target).join(" "));
 
+        if let Some(x) = self.crt_static(target) {
+             cargo.env("RUST_CRT_STATIC", x.to_string());
+        }
+
         // Enable usage of unstable features
         cargo.env("RUSTC_BOOTSTRAP", "1");
         self.add_rust_test_threads(&mut cargo);
@@ -880,6 +884,16 @@ impl Build {
         return base
     }
 
+    /// Returns if this target should statically link the C runtime, if specified
+    fn crt_static(&self, target: &str) -> Option<bool> {
+        if target.contains("pc-windows-msvc") {
+            Some(true)
+        } else {
+            self.config.target_config.get(target)
+                .and_then(|t| t.crt_static)
+        }
+    }
+
     /// Returns the "musl root" for this `target`, if defined
     fn musl_root(&self, target: &str) -> Option<&Path> {
         self.config.target_config.get(target)

src/bootstrap/sanity.rs

@@ -157,8 +157,15 @@ pub fn check(build: &mut Build) {
             panic!("the iOS target is only supported on OSX");
         }
 
-        // Make sure musl-root is valid if specified
-        if target.contains("musl") && !target.contains("mips") {
+        // Make sure musl-root is valid
+        if target.contains("musl") {
+            // If this is a native target (host is also musl) and no musl-root is given,
+            // fall back to the system toolchain in /usr before giving up
+            if build.musl_root(target).is_none() && build.config.build == *target {
+                let target = build.config.target_config.entry(target.clone())
+                                 .or_insert(Default::default());
+                target.musl_root = Some("/usr".into());
+            }
             match build.musl_root(target) {
                 Some(root) => {
                     if fs::metadata(root.join("lib/libc.a")).is_err() {

src/librustc/session/mod.rs

@@ -34,6 +34,7 @@ use syntax::parse::ParseSess;
 use syntax::symbol::Symbol;
 use syntax::{ast, codemap};
 use syntax::feature_gate::AttributeType;
+use syntax::feature_gate::UnstableFeatures;
 use syntax_pos::{Span, MultiSpan};
 
 use rustc_back::PanicStrategy;
@@ -378,6 +379,34 @@ impl Session {
             .unwrap_or(self.opts.debug_assertions)
     }
 
+    pub fn crt_static(&self) -> bool {
+        let requested_features = self.opts.cg.target_feature.split(',');
+        let unstable_options = self.opts.debugging_opts.unstable_options;
+        let is_nightly = UnstableFeatures::from_environment().is_nightly_build();
+        let found_negative = requested_features.clone().any(|r| r == "-crt-static");
+        let found_positive = requested_features.clone().any(|r| r == "+crt-static");
+
+        // If the target we're compiling for requests a static crt by default,
+        // then see if the `-crt-static` feature was passed to disable that.
+        // Otherwise if we don't have a static crt by default then see if the
+        // `+crt-static` feature was passed.
+        let crt_static = if self.target.target.options.crt_static_default {
+            !found_negative
+        } else {
+            found_positive
+        };
+
+        // If we switched from the default then that's only allowed on nightly, so
+        // gate that here.
+        if (found_positive || found_negative) && (!is_nightly || !unstable_options) {
+            self.fatal("specifying the `crt-static` target feature is only allowed \
+                on the nightly channel with `-Z unstable-options` passed \
+                as well");
+        }
+
+        return crt_static;
+    }
+
     pub fn must_not_eliminate_frame_pointers(&self) -> bool {
         self.opts.debuginfo != DebugInfoLevel::NoDebugInfo ||
         !self.target.target.options.eliminate_frame_pointer

src/librustc_back/target/linux_musl_base.rs

@@ -59,14 +59,7 @@ pub fn opts() -> TargetOptions {
     base.pre_link_objects_exe.push("crti.o".to_string());
     base.post_link_objects.push("crtn.o".to_string());
 
-    // MUSL support doesn't currently include dynamic linking, so there's no
-    // need for dylibs or rpath business. Additionally `-pie` is incompatible
-    // with `-static`, so we can't pass `-pie`.
-    base.dynamic_linking = false;
-    base.has_rpath = false;
-    base.position_independent_executables = false;
-
-    // These targets statically link libc by default
+    // Except for on MIPS, these targets statically link libc by default.
     base.crt_static_default = true;
 
     base

src/librustc_back/target/mips_unknown_linux_musl.rs

@@ -25,6 +25,7 @@ pub fn target() -> TargetResult {
             features: "+mips32r2,+soft-float".to_string(),
             max_atomic_width: Some(32),
 
+            crt_static_default: false,
             // see #36994
             exe_allocation_crate: "alloc_system".to_string(),
 

src/librustc_back/target/mipsel_unknown_linux_musl.rs

@@ -25,6 +25,7 @@ pub fn target() -> TargetResult {
             features: "+mips32,+soft-float".to_string(),
             max_atomic_width: Some(32),
 
+            crt_static_default: false,
             // see #36994
             exe_allocation_crate: "alloc_system".to_string(),
 

src/librustc_driver/target_features.rs

@@ -12,7 +12,6 @@ use syntax::ast;
 use llvm::LLVMRustHasFeature;
 use rustc::session::Session;
 use rustc_trans::back::write::create_target_machine;
-use syntax::feature_gate::UnstableFeatures;
 use syntax::symbol::Symbol;
 use libc::c_char;
 
@@ -49,31 +48,7 @@ pub fn add_configuration(cfg: &mut ast::CrateConfig, sess: &Session) {
         }
     }
 
-    let requested_features = sess.opts.cg.target_feature.split(',');
-    let unstable_options = sess.opts.debugging_opts.unstable_options;
-    let is_nightly = UnstableFeatures::from_environment().is_nightly_build();
-    let found_negative = requested_features.clone().any(|r| r == "-crt-static");
-    let found_positive = requested_features.clone().any(|r| r == "+crt-static");
-
-    // If the target we're compiling for requests a static crt by default,
-    // then see if the `-crt-static` feature was passed to disable that.
-    // Otherwise if we don't have a static crt by default then see if the
-    // `+crt-static` feature was passed.
-    let crt_static = if sess.target.target.options.crt_static_default {
-        !found_negative
-    } else {
-        found_positive
-    };
-
-    // If we switched from the default then that's only allowed on nightly, so
-    // gate that here.
-    if (found_positive || found_negative) && (!is_nightly || !unstable_options) {
-        sess.fatal("specifying the `crt-static` target feature is only allowed \
-                    on the nightly channel with `-Z unstable-options` passed \
-                    as well");
-    }
-
-    if crt_static {
+    if sess.crt_static() {
         cfg.insert((tf, Some(Symbol::intern("crt-static"))));
     }
 }

src/librustc_trans/back/link.rs

@@ -715,13 +715,15 @@ fn link_natively(sess: &Session,
     let root = sess.target_filesearch(PathKind::Native).get_lib_path();
     cmd.args(&sess.target.target.options.pre_link_args);
 
-    let pre_link_objects = if crate_type == config::CrateTypeExecutable {
-        &sess.target.target.options.pre_link_objects_exe
-    } else {
-        &sess.target.target.options.pre_link_objects_dll
-    };
-    for obj in pre_link_objects {
-        cmd.arg(root.join(obj));
+    if sess.crt_static() {
+        let pre_link_objects = if crate_type == config::CrateTypeExecutable {
+            &sess.target.target.options.pre_link_objects_exe
+        } else {
+            &sess.target.target.options.pre_link_objects_dll
+        };
+        for obj in pre_link_objects {
+            cmd.arg(root.join(obj));
+        }
     }
 
     if sess.target.target.options.is_like_emscripten {
@@ -739,8 +741,10 @@ fn link_natively(sess: &Session,
                   objects, out_filename, outputs, trans);
     }
     cmd.args(&sess.target.target.options.late_link_args);
-    for obj in &sess.target.target.options.post_link_objects {
-        cmd.arg(root.join(obj));
+    if sess.crt_static() {
+        for obj in &sess.target.target.options.post_link_objects {
+            cmd.arg(root.join(obj));
+        }
     }
     cmd.args(&sess.target.target.options.post_link_args);
 

src/libstd/build.rs

@@ -30,7 +30,7 @@ fn main() {
             println!("cargo:rustc-link-lib=dl");
             println!("cargo:rustc-link-lib=log");
             println!("cargo:rustc-link-lib=gcc");
-        } else if !target.contains("musl") || target.contains("mips") {
+        } else if !target.contains("musl") {
             println!("cargo:rustc-link-lib=dl");
             println!("cargo:rustc-link-lib=rt");
             println!("cargo:rustc-link-lib=pthread");

src/libunwind/build.rs

@@ -15,8 +15,8 @@ fn main() {
     let target = env::var("TARGET").expect("TARGET was not set");
 
     if target.contains("linux") {
-        if target.contains("musl") && !target.contains("mips") {
-            println!("cargo:rustc-link-lib=static=unwind");
+        if target.contains("musl") {
+            // musl is handled in lib.rs
         } else if !target.contains("android") {
             println!("cargo:rustc-link-lib=gcc_s");
         }

src/libunwind/lib.rs

@@ -15,6 +15,7 @@
 #![deny(warnings)]
 
 #![feature(cfg_target_vendor)]
+#![feature(link_cfg)]
 #![feature(staged_api)]
 #![feature(unwind_attributes)]
 
@@ -27,3 +28,8 @@ extern crate libc;
 mod libunwind;
 #[cfg(not(target_env = "msvc"))]
 pub use libunwind::*;
+
+#[cfg(target_env = "musl")]
+#[link(name = "unwind", kind = "static", cfg(target_feature = "crt-static"))]
+#[link(name = "gcc_s", cfg(not(target_feature = "crt-static")))]
+extern {}