add a dist-thumb builder to build rust-std for the THUMB targets

the rust-std component only contains the core and compiler-builtins (+c +mem) crates

cc #49382

src/bootstrap/compile.rs

@@ -140,12 +140,18 @@ pub fn std_cargo(build: &Builder,
                  compiler: &Compiler,
                  target: Interned<String>,
                  cargo: &mut Command) {
-    let mut features = build.std_features();
-
     if let Some(target) = env::var_os("MACOSX_STD_DEPLOYMENT_TARGET") {
         cargo.env("MACOSX_DEPLOYMENT_TARGET", target);
     }
 
+    if build.no_std(target) == Some(true) {
+        // for no-std targets we only compile core and compiler-builtins
+        cargo.arg("--features").arg("c mem")
+            .arg("--manifest-path")
+            .arg(build.src.join("src/rustc/compiler_builtins_shim/Cargo.toml"));
+    } else {
+        let mut features = build.std_features();
+
         // When doing a local rebuild we tell cargo that we're stage1 rather than
         // stage0. This works fine if the local rust and being-built rust have the
         // same view of what the default allocator is, but fails otherwise. Since
@@ -185,6 +191,7 @@ pub fn std_cargo(build: &Builder,
             }
         }
     }
+}
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 struct StdLink {

src/bootstrap/config.rs

@@ -159,6 +159,7 @@ pub struct Target {
     pub crt_static: Option<bool>,
     pub musl_root: Option<PathBuf>,
     pub qemu_rootfs: Option<PathBuf>,
+    pub no_std: bool,
 }
 
 /// Structure of the `config.toml` file that configuration is read from.

src/bootstrap/dist.rs

@@ -648,9 +648,14 @@ impl Step for Std {
         // depend on librustc and otherwise we just depend on libtest.
         if build.hosts.iter().any(|t| t == target) {
             builder.ensure(compile::Rustc { compiler, target });
+        } else {
+            if build.no_std(target) == Some(true) {
+                // the `test` doesn't compile for no-std targets
+                builder.ensure(compile::Std { compiler, target });
             } else {
                 builder.ensure(compile::Test { compiler, target });
             }
+        }
 
         let image = tmpdir(build).join(format!("{}-{}-image", name, target));
         let _ = fs::remove_dir_all(&image);

src/bootstrap/lib.rs

@@ -709,6 +709,12 @@ impl Build {
             .map(|p| &**p)
     }
 
+    /// Returns true if this is a no-std `target`, if defined
+    fn no_std(&self, target: Interned<String>) -> Option<bool> {
+        self.config.target_config.get(&target)
+            .map(|t| t.no_std)
+    }
+
     /// Returns whether the target will be tested using the `remote-test-client`
     /// and `remote-test-server` binaries.
     fn remote_tested(&self, target: Interned<String>) -> bool {

src/bootstrap/sanity.rs

@@ -169,6 +169,19 @@ pub fn check(build: &mut Build) {
             panic!("the iOS target is only supported on macOS");
         }
 
+        if target.starts_with("thumbv") {
+            if build.no_std(*target).is_none() {
+                let target = build.config.target_config.entry(target.clone())
+                    .or_insert(Default::default());
+
+                target.no_std = true;
+            }
+
+            if build.no_std(*target) == Some(false) {
+                panic!("All the THUMB targets are no-std targets")
+            }
+        }
+
         // 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,

src/ci/docker/dist-various-3/Dockerfile

@@ -0,0 +1,19 @@
+FROM ubuntu:17.10
+
+COPY scripts/cross-apt-packages.sh /scripts/
+RUN sh /scripts/cross-apt-packages.sh
+
+RUN apt-get build-dep -y clang llvm && apt-get install -y --no-install-recommends \
+  gcc-arm-none-eabi \
+  libnewlib-arm-none-eabi
+
+COPY scripts/sccache.sh /scripts/
+RUN sh /scripts/sccache.sh
+
+ENV TARGETS=thumbv6m-none-eabi
+ENV TARGETS=$TARGETS,thumbv7m-none-eabi
+ENV TARGETS=$TARGETS,thumbv7em-none-eabi
+ENV TARGETS=$TARGETS,thumbv7em-none-eabihf
+
+ENV RUST_CONFIGURE_ARGS --disable-docs
+ENV SCRIPT python2.7 ../x.py dist --target $TARGETS

src/rustc/compiler_builtins_shim/Cargo.toml

@@ -35,5 +35,6 @@ cc = "1.0.1"
 [features]
 c = []
 default = ["c", "rustbuild", "compiler-builtins"]
+mem = []
 rustbuild = []
 compiler-builtins = []