Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1571 insertions, 0 deletions

diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
new file mode 100644
index 000000000..dd2b9d593
--- /dev/null
+++ b/src/bootstrap/compile.rs
@@ -0,0 +1,1571 @@
+//! Implementation of compiling various phases of the compiler and standard
+//! library.
+//!
+//! This module contains some of the real meat in the rustbuild build system
+//! which is where Cargo is used to compile the standard library, libtest, and
+//! the compiler. This module is also responsible for assembling the sysroot as it
+//! goes along from the output of the previous stage.
+
+use std::borrow::Cow;
+use std::collections::HashSet;
+use std::env;
+use std::fs;
+use std::io::prelude::*;
+use std::io::BufReader;
+use std::path::{Path, PathBuf};
+use std::process::{Command, Stdio};
+use std::str;
+
+use serde::Deserialize;
+
+use crate::builder::Cargo;
+use crate::builder::{Builder, Kind, RunConfig, ShouldRun, Step};
+use crate::cache::{Interned, INTERNER};
+use crate::config::{LlvmLibunwind, TargetSelection};
+use crate::dist;
+use crate::native;
+use crate::tool::SourceType;
+use crate::util::get_clang_cl_resource_dir;
+use crate::util::{exe, is_debug_info, is_dylib, output, symlink_dir, t, up_to_date};
+use crate::LLVM_TOOLS;
+use crate::{CLang, Compiler, DependencyType, GitRepo, Mode};
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct Std {
+    pub target: TargetSelection,
+    pub compiler: Compiler,
+    /// Whether to build only a subset of crates in the standard library.
+    ///
+    /// This shouldn't be used from other steps; see the comment on [`Rustc`].
+    crates: Interned<Vec<String>>,
+}
+
+impl Std {
+    pub fn new(compiler: Compiler, target: TargetSelection) -> Self {
+        Self { target, compiler, crates: Default::default() }
+    }
+}
+
+/// Return a `-p=x -p=y` string suitable for passing to a cargo invocation.
+fn build_crates_in_set(run: &RunConfig<'_>) -> Interned<Vec<String>> {
+    let mut crates = Vec::new();
+    for krate in &run.paths {
+        let path = krate.assert_single_path();
+        let crate_name = run.builder.crate_paths[&path.path];
+        crates.push(format!("-p={crate_name}"));
+    }
+    INTERNER.intern_list(crates)
+}
+
+impl Step for Std {
+    type Output = ();
+    const DEFAULT: bool = true;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        // When downloading stage1, the standard library has already been copied to the sysroot, so
+        // there's no need to rebuild it.
+        let builder = run.builder;
+        run.crate_or_deps("test")
+            .path("library")
+            .lazy_default_condition(Box::new(|| !builder.download_rustc()))
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        // Normally, people will pass *just* library if they pass it.
+        // But it's possible (although strange) to pass something like `library std core`.
+        // Build all crates anyway, as if they hadn't passed the other args.
+        let has_library =
+            run.paths.iter().any(|set| set.assert_single_path().path.ends_with("library"));
+        let crates = if has_library { Default::default() } else { build_crates_in_set(&run) };
+        run.builder.ensure(Std {
+            compiler: run.builder.compiler(run.builder.top_stage, run.build_triple()),
+            target: run.target,
+            crates,
+        });
+    }
+
+    /// Builds the standard library.
+    ///
+    /// This will build the standard library for a particular stage of the build
+    /// using the `compiler` targeting the `target` architecture. The artifacts
+    /// created will also be linked into the sysroot directory.
+    fn run(self, builder: &Builder<'_>) {
+        let target = self.target;
+        let compiler = self.compiler;
+
+        // These artifacts were already copied (in `impl Step for Sysroot`).
+        // Don't recompile them.
+        // NOTE: the ABI of the beta compiler is different from the ABI of the downloaded compiler,
+        // so its artifacts can't be reused.
+        if builder.download_rustc() && compiler.stage != 0 {
+            return;
+        }
+
+        if builder.config.keep_stage.contains(&compiler.stage)
+            || builder.config.keep_stage_std.contains(&compiler.stage)
+        {
+            builder.info("Warning: Using a potentially old libstd. This may not behave well.");
+            builder.ensure(StdLink::from_std(self, compiler));
+            return;
+        }
+
+        builder.update_submodule(&Path::new("library").join("stdarch"));
+
+        // Profiler information requires LLVM's compiler-rt
+        if builder.config.profiler {
+            builder.update_submodule(&Path::new("src/llvm-project"));
+        }
+
+        let mut target_deps = builder.ensure(StartupObjects { compiler, target });
+
+        let compiler_to_use = builder.compiler_for(compiler.stage, compiler.host, target);
+        if compiler_to_use != compiler {
+            builder.ensure(Std::new(compiler_to_use, target));
+            builder.info(&format!("Uplifting stage1 std ({} -> {})", compiler_to_use.host, target));
+
+            // Even if we're not building std this stage, the new sysroot must
+            // still contain the third party objects needed by various targets.
+            copy_third_party_objects(builder, &compiler, target);
+            copy_self_contained_objects(builder, &compiler, target);
+
+            builder.ensure(StdLink::from_std(self, compiler_to_use));
+            return;
+        }
+
+        target_deps.extend(copy_third_party_objects(builder, &compiler, target));
+        target_deps.extend(copy_self_contained_objects(builder, &compiler, target));
+
+        let mut cargo = builder.cargo(compiler, Mode::Std, SourceType::InTree, target, "build");
+        std_cargo(builder, target, compiler.stage, &mut cargo);
+
+        builder.info(&format!(
+            "Building stage{} std artifacts ({} -> {})",
+            compiler.stage, &compiler.host, target
+        ));
+        run_cargo(
+            builder,
+            cargo,
+            self.crates.to_vec(),
+            &libstd_stamp(builder, compiler, target),
+            target_deps,
+            false,
+        );
+
+        builder.ensure(StdLink::from_std(
+            self,
+            builder.compiler(compiler.stage, builder.config.build),
+        ));
+    }
+}
+
+fn copy_and_stamp(
+    builder: &Builder<'_>,
+    libdir: &Path,
+    sourcedir: &Path,
+    name: &str,
+    target_deps: &mut Vec<(PathBuf, DependencyType)>,
+    dependency_type: DependencyType,
+) {
+    let target = libdir.join(name);
+    builder.copy(&sourcedir.join(name), &target);
+
+    target_deps.push((target, dependency_type));
+}
+
+fn copy_llvm_libunwind(builder: &Builder<'_>, target: TargetSelection, libdir: &Path) -> PathBuf {
+    let libunwind_path = builder.ensure(native::Libunwind { target });
+    let libunwind_source = libunwind_path.join("libunwind.a");
+    let libunwind_target = libdir.join("libunwind.a");
+    builder.copy(&libunwind_source, &libunwind_target);
+    libunwind_target
+}
+
+/// Copies third party objects needed by various targets.
+fn copy_third_party_objects(
+    builder: &Builder<'_>,
+    compiler: &Compiler,
+    target: TargetSelection,
+) -> Vec<(PathBuf, DependencyType)> {
+    let mut target_deps = vec![];
+
+    // FIXME: remove this in 2021
+    if target == "x86_64-fortanix-unknown-sgx" {
+        if env::var_os("X86_FORTANIX_SGX_LIBS").is_some() {
+            builder.info("Warning: X86_FORTANIX_SGX_LIBS environment variable is ignored, libunwind is now compiled as part of rustbuild");
+        }
+    }
+
+    if builder.config.sanitizers_enabled(target) && compiler.stage != 0 {
+        // The sanitizers are only copied in stage1 or above,
+        // to avoid creating dependency on LLVM.
+        target_deps.extend(
+            copy_sanitizers(builder, &compiler, target)
+                .into_iter()
+                .map(|d| (d, DependencyType::Target)),
+        );
+    }
+
+    if target == "x86_64-fortanix-unknown-sgx"
+        || target.contains("pc-windows-gnullvm")
+        || builder.config.llvm_libunwind(target) == LlvmLibunwind::InTree
+            && (target.contains("linux") || target.contains("fuchsia"))
+    {
+        let libunwind_path =
+            copy_llvm_libunwind(builder, target, &builder.sysroot_libdir(*compiler, target));
+        target_deps.push((libunwind_path, DependencyType::Target));
+    }
+
+    target_deps
+}
+
+/// Copies third party objects needed by various targets for self-contained linkage.
+fn copy_self_contained_objects(
+    builder: &Builder<'_>,
+    compiler: &Compiler,
+    target: TargetSelection,
+) -> Vec<(PathBuf, DependencyType)> {
+    let libdir_self_contained = builder.sysroot_libdir(*compiler, target).join("self-contained");
+    t!(fs::create_dir_all(&libdir_self_contained));
+    let mut target_deps = vec![];
+
+    // Copies the libc and CRT objects.
+    //
+    // rustc historically provides a more self-contained installation for musl targets
+    // not requiring the presence of a native musl toolchain. For example, it can fall back
+    // to using gcc from a glibc-targeting toolchain for linking.
+    // 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_libdir(target).unwrap_or_else(|| {
+            panic!("Target {:?} does not have a \"musl-libdir\" key", target.triple)
+        });
+        for &obj in &["libc.a", "crt1.o", "Scrt1.o", "rcrt1.o", "crti.o", "crtn.o"] {
+            copy_and_stamp(
+                builder,
+                &libdir_self_contained,
+                &srcdir,
+                obj,
+                &mut target_deps,
+                DependencyType::TargetSelfContained,
+            );
+        }
+        let crt_path = builder.ensure(native::CrtBeginEnd { target });
+        for &obj in &["crtbegin.o", "crtbeginS.o", "crtend.o", "crtendS.o"] {
+            let src = crt_path.join(obj);
+            let target = libdir_self_contained.join(obj);
+            builder.copy(&src, &target);
+            target_deps.push((target, DependencyType::TargetSelfContained));
+        }
+
+        if !target.starts_with("s390x") {
+            let libunwind_path = copy_llvm_libunwind(builder, target, &libdir_self_contained);
+            target_deps.push((libunwind_path, DependencyType::TargetSelfContained));
+        }
+    } else if target.ends_with("-wasi") {
+        let srcdir = builder
+            .wasi_root(target)
+            .unwrap_or_else(|| {
+                panic!("Target {:?} does not have a \"wasi-root\" key", target.triple)
+            })
+            .join("lib/wasm32-wasi");
+        for &obj in &["libc.a", "crt1-command.o", "crt1-reactor.o"] {
+            copy_and_stamp(
+                builder,
+                &libdir_self_contained,
+                &srcdir,
+                obj,
+                &mut target_deps,
+                DependencyType::TargetSelfContained,
+            );
+        }
+    } else if target.ends_with("windows-gnu") {
+        for obj in ["crt2.o", "dllcrt2.o"].iter() {
+            let src = compiler_file(builder, builder.cc(target), target, CLang::C, obj);
+            let target = libdir_self_contained.join(obj);
+            builder.copy(&src, &target);
+            target_deps.push((target, DependencyType::TargetSelfContained));
+        }
+    }
+
+    target_deps
+}
+
+/// Configure cargo to compile the standard library, adding appropriate env vars
+/// and such.
+pub fn std_cargo(builder: &Builder<'_>, target: TargetSelection, stage: u32, cargo: &mut Cargo) {
+    if let Some(target) = env::var_os("MACOSX_STD_DEPLOYMENT_TARGET") {
+        cargo.env("MACOSX_DEPLOYMENT_TARGET", target);
+    }
+
+    // Determine if we're going to compile in optimized C intrinsics to
+    // the `compiler-builtins` crate. These intrinsics live in LLVM's
+    // `compiler-rt` repository, but our `src/llvm-project` submodule isn't
+    // always checked out, so we need to conditionally look for this. (e.g. if
+    // an external LLVM is used we skip the LLVM submodule checkout).
+    //
+    // Note that this shouldn't affect the correctness of `compiler-builtins`,
+    // but only its speed. Some intrinsics in C haven't been translated to Rust
+    // yet but that's pretty rare. Other intrinsics have optimized
+    // implementations in C which have only had slower versions ported to Rust,
+    // so we favor the C version where we can, but it's not critical.
+    //
+    // If `compiler-rt` is available ensure that the `c` feature of the
+    // `compiler-builtins` crate is enabled and it's configured to learn where
+    // `compiler-rt` is located.
+    let compiler_builtins_root = builder.src.join("src/llvm-project/compiler-rt");
+    let compiler_builtins_c_feature = if compiler_builtins_root.exists() {
+        // Note that `libprofiler_builtins/build.rs` also computes this so if
+        // you're changing something here please also change that.
+        cargo.env("RUST_COMPILER_RT_ROOT", &compiler_builtins_root);
+        " compiler-builtins-c"
+    } else {
+        ""
+    };
+
+    if builder.no_std(target) == Some(true) {
+        let mut features = "compiler-builtins-mem".to_string();
+        if !target.starts_with("bpf") {
+            features.push_str(compiler_builtins_c_feature);
+        }
+
+        // for no-std targets we only compile a few no_std crates
+        cargo
+            .args(&["-p", "alloc"])
+            .arg("--manifest-path")
+            .arg(builder.src.join("library/alloc/Cargo.toml"))
+            .arg("--features")
+            .arg(features);
+    } else {
+        let mut features = builder.std_features(target);
+        features.push_str(compiler_builtins_c_feature);
+
+        cargo
+            .arg("--features")
+            .arg(features)
+            .arg("--manifest-path")
+            .arg(builder.src.join("library/test/Cargo.toml"));
+
+        // Help the libc crate compile by assisting it in finding various
+        // sysroot native libraries.
+        if target.contains("musl") {
+            if let Some(p) = builder.musl_libdir(target) {
+                let root = format!("native={}", p.to_str().unwrap());
+                cargo.rustflag("-L").rustflag(&root);
+            }
+        }
+
+        if target.ends_with("-wasi") {
+            if let Some(p) = builder.wasi_root(target) {
+                let root = format!("native={}/lib/wasm32-wasi", p.to_str().unwrap());
+                cargo.rustflag("-L").rustflag(&root);
+            }
+        }
+    }
+
+    // By default, rustc uses `-Cembed-bitcode=yes`, and Cargo overrides that
+    // with `-Cembed-bitcode=no` for non-LTO builds. However, libstd must be
+    // built with bitcode so that the produced rlibs can be used for both LTO
+    // builds (which use bitcode) and non-LTO builds (which use object code).
+    // So we override the override here!
+    //
+    // But we don't bother for the stage 0 compiler because it's never used
+    // with LTO.
+    if stage >= 1 {
+        cargo.rustflag("-Cembed-bitcode=yes");
+    }
+
+    // By default, rustc does not include unwind tables unless they are required
+    // for a particular target. They are not required by RISC-V targets, but
+    // compiling the standard library with them means that users can get
+    // backtraces without having to recompile the standard library themselves.
+    //
+    // This choice was discussed in https://github.com/rust-lang/rust/pull/69890
+    if target.contains("riscv") {
+        cargo.rustflag("-Cforce-unwind-tables=yes");
+    }
+
+    let html_root =
+        format!("-Zcrate-attr=doc(html_root_url=\"{}/\")", builder.doc_rust_lang_org_channel(),);
+    cargo.rustflag(&html_root);
+    cargo.rustdocflag(&html_root);
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+struct StdLink {
+    pub compiler: Compiler,
+    pub target_compiler: Compiler,
+    pub target: TargetSelection,
+    /// Not actually used; only present to make sure the cache invalidation is correct.
+    crates: Interned<Vec<String>>,
+}
+
+impl StdLink {
+    fn from_std(std: Std, host_compiler: Compiler) -> Self {
+        Self {
+            compiler: host_compiler,
+            target_compiler: std.compiler,
+            target: std.target,
+            crates: std.crates,
+        }
+    }
+}
+
+impl Step for StdLink {
+    type Output = ();
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.never()
+    }
+
+    /// Link all libstd rlibs/dylibs into the sysroot location.
+    ///
+    /// Links those artifacts generated by `compiler` to the `stage` compiler's
+    /// sysroot for the specified `host` and `target`.
+    ///
+    /// Note that this assumes that `compiler` has already generated the libstd
+    /// libraries for `target`, and this method will find them in the relevant
+    /// output directory.
+    fn run(self, builder: &Builder<'_>) {
+        let compiler = self.compiler;
+        let target_compiler = self.target_compiler;
+        let target = self.target;
+        builder.info(&format!(
+            "Copying stage{} std from stage{} ({} -> {} / {})",
+            target_compiler.stage, compiler.stage, &compiler.host, target_compiler.host, target
+        ));
+        let libdir = builder.sysroot_libdir(target_compiler, target);
+        let hostdir = builder.sysroot_libdir(target_compiler, compiler.host);
+        add_to_sysroot(builder, &libdir, &hostdir, &libstd_stamp(builder, compiler, target));
+    }
+}
+
+/// Copies sanitizer runtime libraries into target libdir.
+fn copy_sanitizers(
+    builder: &Builder<'_>,
+    compiler: &Compiler,
+    target: TargetSelection,
+) -> Vec<PathBuf> {
+    let runtimes: Vec<native::SanitizerRuntime> = builder.ensure(native::Sanitizers { target });
+
+    if builder.config.dry_run {
+        return Vec::new();
+    }
+
+    let mut target_deps = Vec::new();
+    let libdir = builder.sysroot_libdir(*compiler, target);
+
+    for runtime in &runtimes {
+        let dst = libdir.join(&runtime.name);
+        builder.copy(&runtime.path, &dst);
+
+        if target == "x86_64-apple-darwin" || target == "aarch64-apple-darwin" {
+            // Update the library’s install name to reflect that it has has been renamed.
+            apple_darwin_update_library_name(&dst, &format!("@rpath/{}", &runtime.name));
+            // Upon renaming the install name, the code signature of the file will invalidate,
+            // so we will sign it again.
+            apple_darwin_sign_file(&dst);
+        }
+
+        target_deps.push(dst);
+    }
+
+    target_deps
+}
+
+fn apple_darwin_update_library_name(library_path: &Path, new_name: &str) {
+    let status = Command::new("install_name_tool")
+        .arg("-id")
+        .arg(new_name)
+        .arg(library_path)
+        .status()
+        .expect("failed to execute `install_name_tool`");
+    assert!(status.success());
+}
+
+fn apple_darwin_sign_file(file_path: &Path) {
+    let status = Command::new("codesign")
+        .arg("-f") // Force to rewrite the existing signature
+        .arg("-s")
+        .arg("-")
+        .arg(file_path)
+        .status()
+        .expect("failed to execute `codesign`");
+    assert!(status.success());
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct StartupObjects {
+    pub compiler: Compiler,
+    pub target: TargetSelection,
+}
+
+impl Step for StartupObjects {
+    type Output = Vec<(PathBuf, DependencyType)>;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.path("library/rtstartup")
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(StartupObjects {
+            compiler: run.builder.compiler(run.builder.top_stage, run.build_triple()),
+            target: run.target,
+        });
+    }
+
+    /// Builds and prepare startup objects like rsbegin.o and rsend.o
+    ///
+    /// These are primarily used on Windows right now for linking executables/dlls.
+    /// They don't require any library support as they're just plain old object
+    /// files, so we just use the nightly snapshot compiler to always build them (as
+    /// no other compilers are guaranteed to be available).
+    fn run(self, builder: &Builder<'_>) -> Vec<(PathBuf, DependencyType)> {
+        let for_compiler = self.compiler;
+        let target = self.target;
+        if !target.ends_with("windows-gnu") {
+            return vec![];
+        }
+
+        let mut target_deps = vec![];
+
+        let src_dir = &builder.src.join("library").join("rtstartup");
+        let dst_dir = &builder.native_dir(target).join("rtstartup");
+        let sysroot_dir = &builder.sysroot_libdir(for_compiler, target);
+        t!(fs::create_dir_all(dst_dir));
+
+        for file in &["rsbegin", "rsend"] {
+            let src_file = &src_dir.join(file.to_string() + ".rs");
+            let dst_file = &dst_dir.join(file.to_string() + ".o");
+            if !up_to_date(src_file, dst_file) {
+                let mut cmd = Command::new(&builder.initial_rustc);
+                cmd.env("RUSTC_BOOTSTRAP", "1");
+                if !builder.local_rebuild {
+                    // a local_rebuild compiler already has stage1 features
+                    cmd.arg("--cfg").arg("bootstrap");
+                }
+                builder.run(
+                    cmd.arg("--target")
+                        .arg(target.rustc_target_arg())
+                        .arg("--emit=obj")
+                        .arg("-o")
+                        .arg(dst_file)
+                        .arg(src_file),
+                );
+            }
+
+            let target = sysroot_dir.join((*file).to_string() + ".o");
+            builder.copy(dst_file, &target);
+            target_deps.push((target, DependencyType::Target));
+        }
+
+        target_deps
+    }
+}
+
+#[derive(Debug, PartialOrd, Ord, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct Rustc {
+    pub target: TargetSelection,
+    pub compiler: Compiler,
+    /// Whether to build a subset of crates, rather than the whole compiler.
+    ///
+    /// This should only be requested by the user, not used within rustbuild itself.
+    /// Using it within rustbuild can lead to confusing situation where lints are replayed
+    /// in two different steps.
+    crates: Interned<Vec<String>>,
+}
+
+impl Rustc {
+    pub fn new(compiler: Compiler, target: TargetSelection) -> Self {
+        Self { target, compiler, crates: Default::default() }
+    }
+}
+
+impl Step for Rustc {
+    type Output = ();
+    const ONLY_HOSTS: bool = true;
+    const DEFAULT: bool = false;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        let mut crates = run.builder.in_tree_crates("rustc-main", None);
+        for (i, krate) in crates.iter().enumerate() {
+            if krate.name == "rustc-main" {
+                crates.swap_remove(i);
+                break;
+            }
+        }
+        run.crates(crates)
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        let crates = build_crates_in_set(&run);
+        run.builder.ensure(Rustc {
+            compiler: run.builder.compiler(run.builder.top_stage, run.build_triple()),
+            target: run.target,
+            crates,
+        });
+    }
+
+    /// Builds the compiler.
+    ///
+    /// This will build the compiler for a particular stage of the build using
+    /// the `compiler` targeting the `target` architecture. The artifacts
+    /// created will also be linked into the sysroot directory.
+    fn run(self, builder: &Builder<'_>) {
+        let compiler = self.compiler;
+        let target = self.target;
+
+        // NOTE: the ABI of the beta compiler is different from the ABI of the downloaded compiler,
+        // so its artifacts can't be reused.
+        if builder.download_rustc() && compiler.stage != 0 {
+            // Copy the existing artifacts instead of rebuilding them.
+            // NOTE: this path is only taken for tools linking to rustc-dev.
+            builder.ensure(Sysroot { compiler });
+            return;
+        }
+
+        builder.ensure(Std::new(compiler, target));
+
+        if builder.config.keep_stage.contains(&compiler.stage) {
+            builder.info("Warning: Using a potentially old librustc. This may not behave well.");
+            builder.info("Warning: Use `--keep-stage-std` if you want to rebuild the compiler when it changes");
+            builder.ensure(RustcLink::from_rustc(self, compiler));
+            return;
+        }
+
+        let compiler_to_use = builder.compiler_for(compiler.stage, compiler.host, target);
+        if compiler_to_use != compiler {
+            builder.ensure(Rustc::new(compiler_to_use, target));
+            builder
+                .info(&format!("Uplifting stage1 rustc ({} -> {})", builder.config.build, target));
+            builder.ensure(RustcLink::from_rustc(self, compiler_to_use));
+            return;
+        }
+
+        // Ensure that build scripts and proc macros have a std / libproc_macro to link against.
+        builder.ensure(Std::new(
+            builder.compiler(self.compiler.stage, builder.config.build),
+            builder.config.build,
+        ));
+
+        let mut cargo = builder.cargo(compiler, Mode::Rustc, SourceType::InTree, target, "build");
+        rustc_cargo(builder, &mut cargo, target);
+
+        if builder.config.rust_profile_use.is_some()
+            && builder.config.rust_profile_generate.is_some()
+        {
+            panic!("Cannot use and generate PGO profiles at the same time");
+        }
+
+        // With LLD, we can use ICF (identical code folding) to reduce the executable size
+        // of librustc_driver/rustc and to improve i-cache utilization.
+        if builder.config.use_lld {
+            cargo.rustflag("-Clink-args=-Wl,--icf=all");
+        }
+
+        let is_collecting = if let Some(path) = &builder.config.rust_profile_generate {
+            if compiler.stage == 1 {
+                cargo.rustflag(&format!("-Cprofile-generate={}", path));
+                // Apparently necessary to avoid overflowing the counters during
+                // a Cargo build profile
+                cargo.rustflag("-Cllvm-args=-vp-counters-per-site=4");
+                true
+            } else {
+                false
+            }
+        } else if let Some(path) = &builder.config.rust_profile_use {
+            if compiler.stage == 1 {
+                cargo.rustflag(&format!("-Cprofile-use={}", path));
+                cargo.rustflag("-Cllvm-args=-pgo-warn-missing-function");
+                true
+            } else {
+                false
+            }
+        } else {
+            false
+        };
+        if is_collecting {
+            // Ensure paths to Rust sources are relative, not absolute.
+            cargo.rustflag(&format!(
+                "-Cllvm-args=-static-func-strip-dirname-prefix={}",
+                builder.config.src.components().count()
+            ));
+        }
+
+        builder.info(&format!(
+            "Building stage{} compiler artifacts ({} -> {})",
+            compiler.stage, &compiler.host, target
+        ));
+        run_cargo(
+            builder,
+            cargo,
+            self.crates.to_vec(),
+            &librustc_stamp(builder, compiler, target),
+            vec![],
+            false,
+        );
+
+        builder.ensure(RustcLink::from_rustc(
+            self,
+            builder.compiler(compiler.stage, builder.config.build),
+        ));
+    }
+}
+
+pub fn rustc_cargo(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelection) {
+    cargo
+        .arg("--features")
+        .arg(builder.rustc_features(builder.kind))
+        .arg("--manifest-path")
+        .arg(builder.src.join("compiler/rustc/Cargo.toml"));
+    rustc_cargo_env(builder, cargo, target);
+}
+
+pub fn rustc_cargo_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelection) {
+    // Set some configuration variables picked up by build scripts and
+    // the compiler alike
+    cargo
+        .env("CFG_RELEASE", builder.rust_release())
+        .env("CFG_RELEASE_CHANNEL", &builder.config.channel)
+        .env("CFG_VERSION", builder.rust_version());
+
+    if let Some(backend) = builder.config.rust_codegen_backends.get(0) {
+        cargo.env("CFG_DEFAULT_CODEGEN_BACKEND", backend);
+    }
+
+    let libdir_relative = builder.config.libdir_relative().unwrap_or_else(|| Path::new("lib"));
+    let target_config = builder.config.target_config.get(&target);
+
+    cargo.env("CFG_LIBDIR_RELATIVE", libdir_relative);
+
+    if let Some(ref ver_date) = builder.rust_info.commit_date() {
+        cargo.env("CFG_VER_DATE", ver_date);
+    }
+    if let Some(ref ver_hash) = builder.rust_info.sha() {
+        cargo.env("CFG_VER_HASH", ver_hash);
+    }
+    if !builder.unstable_features() {
+        cargo.env("CFG_DISABLE_UNSTABLE_FEATURES", "1");
+    }
+
+    // Prefer the current target's own default_linker, else a globally
+    // specified one.
+    if let Some(s) = target_config.and_then(|c| c.default_linker.as_ref()) {
+        cargo.env("CFG_DEFAULT_LINKER", s);
+    } else if let Some(ref s) = builder.config.rustc_default_linker {
+        cargo.env("CFG_DEFAULT_LINKER", s);
+    }
+
+    if builder.config.rustc_parallel {
+        // keep in sync with `bootstrap/lib.rs:Build::rustc_features`
+        // `cfg` option for rustc, `features` option for cargo, for conditional compilation
+        cargo.rustflag("--cfg=parallel_compiler");
+        cargo.rustdocflag("--cfg=parallel_compiler");
+    }
+    if builder.config.rust_verify_llvm_ir {
+        cargo.env("RUSTC_VERIFY_LLVM_IR", "1");
+    }
+
+    // Pass down configuration from the LLVM build into the build of
+    // rustc_llvm and rustc_codegen_llvm.
+    //
+    // Note that this is disabled if LLVM itself is disabled or we're in a check
+    // build. If we are in a check build we still go ahead here presuming we've
+    // detected that LLVM is already built and good to go which helps prevent
+    // busting caches (e.g. like #71152).
+    if builder.config.llvm_enabled()
+        && (builder.kind != Kind::Check
+            || crate::native::prebuilt_llvm_config(builder, target).is_ok())
+    {
+        if builder.is_rust_llvm(target) {
+            cargo.env("LLVM_RUSTLLVM", "1");
+        }
+        let llvm_config = builder.ensure(native::Llvm { target });
+        cargo.env("LLVM_CONFIG", &llvm_config);
+        if let Some(s) = target_config.and_then(|c| c.llvm_config.as_ref()) {
+            cargo.env("CFG_LLVM_ROOT", s);
+        }
+
+        // Some LLVM linker flags (-L and -l) may be needed to link `rustc_llvm`. Its build script
+        // expects these to be passed via the `LLVM_LINKER_FLAGS` env variable, separated by
+        // whitespace.
+        //
+        // For example:
+        // - on windows, when `clang-cl` is used with instrumentation, we need to manually add
+        // clang's runtime library resource directory so that the profiler runtime library can be
+        // found. This is to avoid the linker errors about undefined references to
+        // `__llvm_profile_instrument_memop` when linking `rustc_driver`.
+        let mut llvm_linker_flags = String::new();
+        if builder.config.llvm_profile_generate && target.contains("msvc") {
+            if let Some(ref clang_cl_path) = builder.config.llvm_clang_cl {
+                // Add clang's runtime library directory to the search path
+                let clang_rt_dir = get_clang_cl_resource_dir(clang_cl_path);
+                llvm_linker_flags.push_str(&format!("-L{}", clang_rt_dir.display()));
+            }
+        }
+
+        // The config can also specify its own llvm linker flags.
+        if let Some(ref s) = builder.config.llvm_ldflags {
+            if !llvm_linker_flags.is_empty() {
+                llvm_linker_flags.push_str(" ");
+            }
+            llvm_linker_flags.push_str(s);
+        }
+
+        // Set the linker flags via the env var that `rustc_llvm`'s build script will read.
+        if !llvm_linker_flags.is_empty() {
+            cargo.env("LLVM_LINKER_FLAGS", llvm_linker_flags);
+        }
+
+        // Building with a static libstdc++ is only supported on linux right now,
+        // not for MSVC or macOS
+        if builder.config.llvm_static_stdcpp
+            && !target.contains("freebsd")
+            && !target.contains("msvc")
+            && !target.contains("apple")
+            && !target.contains("solaris")
+        {
+            let file = compiler_file(
+                builder,
+                builder.cxx(target).unwrap(),
+                target,
+                CLang::Cxx,
+                "libstdc++.a",
+            );
+            cargo.env("LLVM_STATIC_STDCPP", file);
+        }
+        if builder.llvm_link_shared() {
+            cargo.env("LLVM_LINK_SHARED", "1");
+        }
+        if builder.config.llvm_use_libcxx {
+            cargo.env("LLVM_USE_LIBCXX", "1");
+        }
+        if builder.config.llvm_optimize && !builder.config.llvm_release_debuginfo {
+            cargo.env("LLVM_NDEBUG", "1");
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+struct RustcLink {
+    pub compiler: Compiler,
+    pub target_compiler: Compiler,
+    pub target: TargetSelection,
+    /// Not actually used; only present to make sure the cache invalidation is correct.
+    crates: Interned<Vec<String>>,
+}
+
+impl RustcLink {
+    fn from_rustc(rustc: Rustc, host_compiler: Compiler) -> Self {
+        Self {
+            compiler: host_compiler,
+            target_compiler: rustc.compiler,
+            target: rustc.target,
+            crates: rustc.crates,
+        }
+    }
+}
+
+impl Step for RustcLink {
+    type Output = ();
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.never()
+    }
+
+    /// Same as `std_link`, only for librustc
+    fn run(self, builder: &Builder<'_>) {
+        let compiler = self.compiler;
+        let target_compiler = self.target_compiler;
+        let target = self.target;
+        builder.info(&format!(
+            "Copying stage{} rustc from stage{} ({} -> {} / {})",
+            target_compiler.stage, compiler.stage, &compiler.host, target_compiler.host, target
+        ));
+        add_to_sysroot(
+            builder,
+            &builder.sysroot_libdir(target_compiler, target),
+            &builder.sysroot_libdir(target_compiler, compiler.host),
+            &librustc_stamp(builder, compiler, target),
+        );
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct CodegenBackend {
+    pub target: TargetSelection,
+    pub compiler: Compiler,
+    pub backend: Interned<String>,
+}
+
+impl Step for CodegenBackend {
+    type Output = ();
+    const ONLY_HOSTS: bool = true;
+    // Only the backends specified in the `codegen-backends` entry of `config.toml` are built.
+    const DEFAULT: bool = true;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.paths(&["compiler/rustc_codegen_cranelift", "compiler/rustc_codegen_gcc"])
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        for &backend in &run.builder.config.rust_codegen_backends {
+            if backend == "llvm" {
+                continue; // Already built as part of rustc
+            }
+
+            run.builder.ensure(CodegenBackend {
+                target: run.target,
+                compiler: run.builder.compiler(run.builder.top_stage, run.build_triple()),
+                backend,
+            });
+        }
+    }
+
+    fn run(self, builder: &Builder<'_>) {
+        let compiler = self.compiler;
+        let target = self.target;
+        let backend = self.backend;
+
+        builder.ensure(Rustc::new(compiler, target));
+
+        if builder.config.keep_stage.contains(&compiler.stage) {
+            builder.info(
+                "Warning: Using a potentially old codegen backend. \
+                This may not behave well.",
+            );
+            // Codegen backends are linked separately from this step today, so we don't do
+            // anything here.
+            return;
+        }
+
+        let compiler_to_use = builder.compiler_for(compiler.stage, compiler.host, target);
+        if compiler_to_use != compiler {
+            builder.ensure(CodegenBackend { compiler: compiler_to_use, target, backend });
+            return;
+        }
+
+        let out_dir = builder.cargo_out(compiler, Mode::Codegen, target);
+
+        let mut cargo = builder.cargo(compiler, Mode::Codegen, SourceType::InTree, target, "build");
+        cargo
+            .arg("--manifest-path")
+            .arg(builder.src.join(format!("compiler/rustc_codegen_{}/Cargo.toml", backend)));
+        rustc_cargo_env(builder, &mut cargo, target);
+
+        let tmp_stamp = out_dir.join(".tmp.stamp");
+
+        builder.info(&format!(
+            "Building stage{} codegen backend {} ({} -> {})",
+            compiler.stage, backend, &compiler.host, target
+        ));
+        let files = run_cargo(builder, cargo, vec![], &tmp_stamp, vec![], false);
+        if builder.config.dry_run {
+            return;
+        }
+        let mut files = files.into_iter().filter(|f| {
+            let filename = f.file_name().unwrap().to_str().unwrap();
+            is_dylib(filename) && filename.contains("rustc_codegen_")
+        });
+        let codegen_backend = match files.next() {
+            Some(f) => f,
+            None => panic!("no dylibs built for codegen backend?"),
+        };
+        if let Some(f) = files.next() {
+            panic!(
+                "codegen backend built two dylibs:\n{}\n{}",
+                codegen_backend.display(),
+                f.display()
+            );
+        }
+        let stamp = codegen_backend_stamp(builder, compiler, target, backend);
+        let codegen_backend = codegen_backend.to_str().unwrap();
+        t!(fs::write(&stamp, &codegen_backend));
+    }
+}
+
+/// Creates the `codegen-backends` folder for a compiler that's about to be
+/// assembled as a complete compiler.
+///
+/// This will take the codegen artifacts produced by `compiler` and link them
+/// into an appropriate location for `target_compiler` to be a functional
+/// compiler.
+fn copy_codegen_backends_to_sysroot(
+    builder: &Builder<'_>,
+    compiler: Compiler,
+    target_compiler: Compiler,
+) {
+    let target = target_compiler.host;
+
+    // Note that this step is different than all the other `*Link` steps in
+    // that it's not assembling a bunch of libraries but rather is primarily
+    // moving the codegen backend into place. The codegen backend of rustc is
+    // not linked into the main compiler by default but is rather dynamically
+    // selected at runtime for inclusion.
+    //
+    // Here we're looking for the output dylib of the `CodegenBackend` step and
+    // we're copying that into the `codegen-backends` folder.
+    let dst = builder.sysroot_codegen_backends(target_compiler);
+    t!(fs::create_dir_all(&dst), dst);
+
+    if builder.config.dry_run {
+        return;
+    }
+
+    for backend in builder.config.rust_codegen_backends.iter() {
+        if backend == "llvm" {
+            continue; // Already built as part of rustc
+        }
+
+        let stamp = codegen_backend_stamp(builder, compiler, target, *backend);
+        let dylib = t!(fs::read_to_string(&stamp));
+        let file = Path::new(&dylib);
+        let filename = file.file_name().unwrap().to_str().unwrap();
+        // change `librustc_codegen_cranelift-xxxxxx.so` to
+        // `librustc_codegen_cranelift-release.so`
+        let target_filename = {
+            let dash = filename.find('-').unwrap();
+            let dot = filename.find('.').unwrap();
+            format!("{}-{}{}", &filename[..dash], builder.rust_release(), &filename[dot..])
+        };
+        builder.copy(&file, &dst.join(target_filename));
+    }
+}
+
+/// Cargo's output path for the standard library in a given stage, compiled
+/// by a particular compiler for the specified target.
+pub fn libstd_stamp(builder: &Builder<'_>, compiler: Compiler, target: TargetSelection) -> PathBuf {
+    builder.cargo_out(compiler, Mode::Std, target).join(".libstd.stamp")
+}
+
+/// Cargo's output path for librustc in a given stage, compiled by a particular
+/// compiler for the specified target.
+pub fn librustc_stamp(
+    builder: &Builder<'_>,
+    compiler: Compiler,
+    target: TargetSelection,
+) -> PathBuf {
+    builder.cargo_out(compiler, Mode::Rustc, target).join(".librustc.stamp")
+}
+
+/// Cargo's output path for librustc_codegen_llvm in a given stage, compiled by a particular
+/// compiler for the specified target and backend.
+fn codegen_backend_stamp(
+    builder: &Builder<'_>,
+    compiler: Compiler,
+    target: TargetSelection,
+    backend: Interned<String>,
+) -> PathBuf {
+    builder
+        .cargo_out(compiler, Mode::Codegen, target)
+        .join(format!(".librustc_codegen_{}.stamp", backend))
+}
+
+pub fn compiler_file(
+    builder: &Builder<'_>,
+    compiler: &Path,
+    target: TargetSelection,
+    c: CLang,
+    file: &str,
+) -> PathBuf {
+    let mut cmd = Command::new(compiler);
+    cmd.args(builder.cflags(target, GitRepo::Rustc, c));
+    cmd.arg(format!("-print-file-name={}", file));
+    let out = output(&mut cmd);
+    PathBuf::from(out.trim())
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct Sysroot {
+    pub compiler: Compiler,
+}
+
+impl Step for Sysroot {
+    type Output = Interned<PathBuf>;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.never()
+    }
+
+    /// Returns the sysroot for the `compiler` specified that *this build system
+    /// generates*.
+    ///
+    /// That is, the sysroot for the stage0 compiler is not what the compiler
+    /// thinks it is by default, but it's the same as the default for stages
+    /// 1-3.
+    fn run(self, builder: &Builder<'_>) -> Interned<PathBuf> {
+        let compiler = self.compiler;
+        let sysroot = if compiler.stage == 0 {
+            builder.out.join(&compiler.host.triple).join("stage0-sysroot")
+        } else {
+            builder.out.join(&compiler.host.triple).join(format!("stage{}", compiler.stage))
+        };
+        let _ = fs::remove_dir_all(&sysroot);
+        t!(fs::create_dir_all(&sysroot));
+
+        // If we're downloading a compiler from CI, we can use the same compiler for all stages other than 0.
+        if builder.download_rustc() && compiler.stage != 0 {
+            assert_eq!(
+                builder.config.build, compiler.host,
+                "Cross-compiling is not yet supported with `download-rustc`",
+            );
+            // Copy the compiler into the correct sysroot.
+            let ci_rustc_dir =
+                builder.config.out.join(&*builder.config.build.triple).join("ci-rustc");
+            builder.cp_r(&ci_rustc_dir, &sysroot);
+            return INTERNER.intern_path(sysroot);
+        }
+
+        // Symlink the source root into the same location inside the sysroot,
+        // where `rust-src` component would go (`$sysroot/lib/rustlib/src/rust`),
+        // so that any tools relying on `rust-src` also work for local builds,
+        // and also for translating the virtual `/rustc/$hash` back to the real
+        // directory (for running tests with `rust.remap-debuginfo = true`).
+        let sysroot_lib_rustlib_src = sysroot.join("lib/rustlib/src");
+        t!(fs::create_dir_all(&sysroot_lib_rustlib_src));
+        let sysroot_lib_rustlib_src_rust = sysroot_lib_rustlib_src.join("rust");
+        if let Err(e) = symlink_dir(&builder.config, &builder.src, &sysroot_lib_rustlib_src_rust) {
+            eprintln!(
+                "warning: creating symbolic link `{}` to `{}` failed with {}",
+                sysroot_lib_rustlib_src_rust.display(),
+                builder.src.display(),
+                e,
+            );
+            if builder.config.rust_remap_debuginfo {
+                eprintln!(
+                    "warning: some `src/test/ui` tests will fail when lacking `{}`",
+                    sysroot_lib_rustlib_src_rust.display(),
+                );
+            }
+        }
+
+        INTERNER.intern_path(sysroot)
+    }
+}
+
+#[derive(Debug, Copy, PartialOrd, Ord, Clone, PartialEq, Eq, Hash)]
+pub struct Assemble {
+    /// The compiler which we will produce in this step. Assemble itself will
+    /// take care of ensuring that the necessary prerequisites to do so exist,
+    /// that is, this target can be a stage2 compiler and Assemble will build
+    /// previous stages for you.
+    pub target_compiler: Compiler,
+}
+
+impl Step for Assemble {
+    type Output = Compiler;
+    const ONLY_HOSTS: bool = true;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.path("compiler/rustc").path("compiler")
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(Assemble {
+            target_compiler: run.builder.compiler(run.builder.top_stage + 1, run.target),
+        });
+    }
+
+    /// Prepare a new compiler from the artifacts in `stage`
+    ///
+    /// This will assemble a compiler in `build/$host/stage$stage`. The compiler
+    /// must have been previously produced by the `stage - 1` builder.build
+    /// compiler.
+    fn run(self, builder: &Builder<'_>) -> Compiler {
+        let target_compiler = self.target_compiler;
+
+        if target_compiler.stage == 0 {
+            assert_eq!(
+                builder.config.build, target_compiler.host,
+                "Cannot obtain compiler for non-native build triple at stage 0"
+            );
+            // The stage 0 compiler for the build triple is always pre-built.
+            return target_compiler;
+        }
+
+        // Get the compiler that we'll use to bootstrap ourselves.
+        //
+        // Note that this is where the recursive nature of the bootstrap
+        // happens, as this will request the previous stage's compiler on
+        // downwards to stage 0.
+        //
+        // Also note that we're building a compiler for the host platform. We
+        // only assume that we can run `build` artifacts, which means that to
+        // produce some other architecture compiler we need to start from
+        // `build` to get there.
+        //
+        // FIXME: It may be faster if we build just a stage 1 compiler and then
+        //        use that to bootstrap this compiler forward.
+        let build_compiler = builder.compiler(target_compiler.stage - 1, builder.config.build);
+
+        // If we're downloading a compiler from CI, we can use the same compiler for all stages other than 0.
+        if builder.download_rustc() {
+            builder.ensure(Sysroot { compiler: target_compiler });
+            return target_compiler;
+        }
+
+        // Build the libraries for this compiler to link to (i.e., the libraries
+        // it uses at runtime). NOTE: Crates the target compiler compiles don't
+        // link to these. (FIXME: Is that correct? It seems to be correct most
+        // of the time but I think we do link to these for stage2/bin compilers
+        // when not performing a full bootstrap).
+        builder.ensure(Rustc::new(build_compiler, target_compiler.host));
+
+        for &backend in builder.config.rust_codegen_backends.iter() {
+            if backend == "llvm" {
+                continue; // Already built as part of rustc
+            }
+
+            builder.ensure(CodegenBackend {
+                compiler: build_compiler,
+                target: target_compiler.host,
+                backend,
+            });
+        }
+
+        let lld_install = if builder.config.lld_enabled {
+            Some(builder.ensure(native::Lld { target: target_compiler.host }))
+        } else {
+            None
+        };
+
+        let stage = target_compiler.stage;
+        let host = target_compiler.host;
+        builder.info(&format!("Assembling stage{} compiler ({})", stage, host));
+
+        // Link in all dylibs to the libdir
+        let stamp = librustc_stamp(builder, build_compiler, target_compiler.host);
+        let proc_macros = builder
+            .read_stamp_file(&stamp)
+            .into_iter()
+            .filter_map(|(path, dependency_type)| {
+                if dependency_type == DependencyType::Host {
+                    Some(path.file_name().unwrap().to_owned().into_string().unwrap())
+                } else {
+                    None
+                }
+            })
+            .collect::<HashSet<_>>();
+
+        let sysroot = builder.sysroot(target_compiler);
+        let rustc_libdir = builder.rustc_libdir(target_compiler);
+        t!(fs::create_dir_all(&rustc_libdir));
+        let src_libdir = builder.sysroot_libdir(build_compiler, host);
+        for f in builder.read_dir(&src_libdir) {
+            let filename = f.file_name().into_string().unwrap();
+            if (is_dylib(&filename) || is_debug_info(&filename)) && !proc_macros.contains(&filename)
+            {
+                builder.copy(&f.path(), &rustc_libdir.join(&filename));
+            }
+        }
+
+        copy_codegen_backends_to_sysroot(builder, build_compiler, target_compiler);
+
+        // We prepend this bin directory to the user PATH when linking Rust binaries. To
+        // avoid shadowing the system LLD we rename the LLD we provide to `rust-lld`.
+        let libdir = builder.sysroot_libdir(target_compiler, target_compiler.host);
+        let libdir_bin = libdir.parent().unwrap().join("bin");
+        t!(fs::create_dir_all(&libdir_bin));
+        if let Some(lld_install) = lld_install {
+            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));
+            let lld_wrapper_exe = builder.ensure(crate::tool::LldWrapper {
+                compiler: build_compiler,
+                target: target_compiler.host,
+            });
+            builder.copy(&lld_wrapper_exe, &gcc_ld_dir.join(exe("ld", target_compiler.host)));
+        }
+
+        if builder.config.rust_codegen_backends.contains(&INTERNER.intern_str("llvm")) {
+            let llvm_config_bin = builder.ensure(native::Llvm { target: target_compiler.host });
+            if !builder.config.dry_run {
+                let llvm_bin_dir = output(Command::new(llvm_config_bin).arg("--bindir"));
+                let llvm_bin_dir = Path::new(llvm_bin_dir.trim());
+
+                // Since we've already built the LLVM tools, install them to the sysroot.
+                // This is the equivalent of installing the `llvm-tools-preview` component via
+                // rustup, and lets developers use a locally built toolchain to
+                // build projects that expect llvm tools to be present in the sysroot
+                // (e.g. the `bootimage` crate).
+                for tool in LLVM_TOOLS {
+                    let tool_exe = exe(tool, target_compiler.host);
+                    let src_path = llvm_bin_dir.join(&tool_exe);
+                    // When using `download-ci-llvm`, some of the tools
+                    // may not exist, so skip trying to copy them.
+                    if src_path.exists() {
+                        builder.copy(&src_path, &libdir_bin.join(&tool_exe));
+                    }
+                }
+            }
+        }
+
+        // Ensure that `libLLVM.so` ends up in the newly build compiler directory,
+        // so that it can be found when the newly built `rustc` is run.
+        dist::maybe_install_llvm_runtime(builder, target_compiler.host, &sysroot);
+        dist::maybe_install_llvm_target(builder, target_compiler.host, &sysroot);
+
+        // Link the compiler binary itself into place
+        let out_dir = builder.cargo_out(build_compiler, Mode::Rustc, host);
+        let rustc = out_dir.join(exe("rustc-main", host));
+        let bindir = sysroot.join("bin");
+        t!(fs::create_dir_all(&bindir));
+        let compiler = builder.rustc(target_compiler);
+        builder.copy(&rustc, &compiler);
+
+        target_compiler
+    }
+}
+
+/// Link some files into a rustc sysroot.
+///
+/// For a particular stage this will link the file listed in `stamp` into the
+/// `sysroot_dst` provided.
+pub fn add_to_sysroot(
+    builder: &Builder<'_>,
+    sysroot_dst: &Path,
+    sysroot_host_dst: &Path,
+    stamp: &Path,
+) {
+    let self_contained_dst = &sysroot_dst.join("self-contained");
+    t!(fs::create_dir_all(&sysroot_dst));
+    t!(fs::create_dir_all(&sysroot_host_dst));
+    t!(fs::create_dir_all(&self_contained_dst));
+    for (path, dependency_type) in builder.read_stamp_file(stamp) {
+        let dst = match dependency_type {
+            DependencyType::Host => sysroot_host_dst,
+            DependencyType::Target => sysroot_dst,
+            DependencyType::TargetSelfContained => self_contained_dst,
+        };
+        builder.copy(&path, &dst.join(path.file_name().unwrap()));
+    }
+}
+
+pub fn run_cargo(
+    builder: &Builder<'_>,
+    cargo: Cargo,
+    tail_args: Vec<String>,
+    stamp: &Path,
+    additional_target_deps: Vec<(PathBuf, DependencyType)>,
+    is_check: bool,
+) -> Vec<PathBuf> {
+    if builder.config.dry_run {
+        return Vec::new();
+    }
+
+    // `target_root_dir` looks like $dir/$target/release
+    let target_root_dir = stamp.parent().unwrap();
+    // `target_deps_dir` looks like $dir/$target/release/deps
+    let target_deps_dir = target_root_dir.join("deps");
+    // `host_root_dir` looks like $dir/release
+    let host_root_dir = target_root_dir
+        .parent()
+        .unwrap() // chop off `release`
+        .parent()
+        .unwrap() // chop off `$target`
+        .join(target_root_dir.file_name().unwrap());
+
+    // Spawn Cargo slurping up its JSON output. We'll start building up the
+    // `deps` array of all files it generated along with a `toplevel` array of
+    // files we need to probe for later.
+    let mut deps = Vec::new();
+    let mut toplevel = Vec::new();
+    let ok = stream_cargo(builder, cargo, tail_args, &mut |msg| {
+        let (filenames, crate_types) = match msg {
+            CargoMessage::CompilerArtifact {
+                filenames,
+                target: CargoTarget { crate_types },
+                ..
+            } => (filenames, crate_types),
+            _ => return,
+        };
+        for filename in filenames {
+            // Skip files like executables
+            if !(filename.ends_with(".rlib")
+                || filename.ends_with(".lib")
+                || filename.ends_with(".a")
+                || is_debug_info(&filename)
+                || is_dylib(&filename)
+                || (is_check && filename.ends_with(".rmeta")))
+            {
+                continue;
+            }
+
+            let filename = Path::new(&*filename);
+
+            // If this was an output file in the "host dir" we don't actually
+            // worry about it, it's not relevant for us
+            if filename.starts_with(&host_root_dir) {
+                // Unless it's a proc macro used in the compiler
+                if crate_types.iter().any(|t| t == "proc-macro") {
+                    deps.push((filename.to_path_buf(), DependencyType::Host));
+                }
+                continue;
+            }
+
+            // If this was output in the `deps` dir then this is a precise file
+            // name (hash included) so we start tracking it.
+            if filename.starts_with(&target_deps_dir) {
+                deps.push((filename.to_path_buf(), DependencyType::Target));
+                continue;
+            }
+
+            // Otherwise this was a "top level artifact" which right now doesn't
+            // have a hash in the name, but there's a version of this file in
+            // the `deps` folder which *does* have a hash in the name. That's
+            // the one we'll want to we'll probe for it later.
+            //
+            // We do not use `Path::file_stem` or `Path::extension` here,
+            // because some generated files may have multiple extensions e.g.
+            // `std-<hash>.dll.lib` on Windows. The aforementioned methods only
+            // split the file name by the last extension (`.lib`) while we need
+            // to split by all extensions (`.dll.lib`).
+            let expected_len = t!(filename.metadata()).len();
+            let filename = filename.file_name().unwrap().to_str().unwrap();
+            let mut parts = filename.splitn(2, '.');
+            let file_stem = parts.next().unwrap().to_owned();
+            let extension = parts.next().unwrap().to_owned();
+
+            toplevel.push((file_stem, extension, expected_len));
+        }
+    });
+
+    if !ok {
+        crate::detail_exit(1);
+    }
+
+    // Ok now we need to actually find all the files listed in `toplevel`. We've
+    // got a list of prefix/extensions and we basically just need to find the
+    // most recent file in the `deps` folder corresponding to each one.
+    let contents = t!(target_deps_dir.read_dir())
+        .map(|e| t!(e))
+        .map(|e| (e.path(), e.file_name().into_string().unwrap(), t!(e.metadata())))
+        .collect::<Vec<_>>();
+    for (prefix, extension, expected_len) in toplevel {
+        let candidates = contents.iter().filter(|&&(_, ref filename, ref meta)| {
+            meta.len() == expected_len
+                && filename
+                    .strip_prefix(&prefix[..])
+                    .map(|s| s.starts_with('-') && s.ends_with(&extension[..]))
+                    .unwrap_or(false)
+        });
+        let max = candidates.max_by_key(|&&(_, _, ref metadata)| {
+            metadata.modified().expect("mtime should be available on all relevant OSes")
+        });
+        let path_to_add = match max {
+            Some(triple) => triple.0.to_str().unwrap(),
+            None => panic!("no output generated for {:?} {:?}", prefix, extension),
+        };
+        if is_dylib(path_to_add) {
+            let candidate = format!("{}.lib", path_to_add);
+            let candidate = PathBuf::from(candidate);
+            if candidate.exists() {
+                deps.push((candidate, DependencyType::Target));
+            }
+        }
+        deps.push((path_to_add.into(), DependencyType::Target));
+    }
+
+    deps.extend(additional_target_deps);
+    deps.sort();
+    let mut new_contents = Vec::new();
+    for (dep, dependency_type) in deps.iter() {
+        new_contents.extend(match *dependency_type {
+            DependencyType::Host => b"h",
+            DependencyType::Target => b"t",
+            DependencyType::TargetSelfContained => b"s",
+        });
+        new_contents.extend(dep.to_str().unwrap().as_bytes());
+        new_contents.extend(b"\0");
+    }
+    t!(fs::write(&stamp, &new_contents));
+    deps.into_iter().map(|(d, _)| d).collect()
+}
+
+pub fn stream_cargo(
+    builder: &Builder<'_>,
+    cargo: Cargo,
+    tail_args: Vec<String>,
+    cb: &mut dyn FnMut(CargoMessage<'_>),
+) -> bool {
+    let mut cargo = Command::from(cargo);
+    if builder.config.dry_run {
+        return true;
+    }
+    // Instruct Cargo to give us json messages on stdout, critically leaving
+    // stderr as piped so we can get those pretty colors.
+    let mut message_format = if builder.config.json_output {
+        String::from("json")
+    } else {
+        String::from("json-render-diagnostics")
+    };
+    if let Some(s) = &builder.config.rustc_error_format {
+        message_format.push_str(",json-diagnostic-");
+        message_format.push_str(s);
+    }
+    cargo.arg("--message-format").arg(message_format).stdout(Stdio::piped());
+
+    for arg in tail_args {
+        cargo.arg(arg);
+    }
+
+    builder.verbose(&format!("running: {:?}", cargo));
+    let mut child = match cargo.spawn() {
+        Ok(child) => child,
+        Err(e) => panic!("failed to execute command: {:?}\nerror: {}", cargo, e),
+    };
+
+    // Spawn Cargo slurping up its JSON output. We'll start building up the
+    // `deps` array of all files it generated along with a `toplevel` array of
+    // files we need to probe for later.
+    let stdout = BufReader::new(child.stdout.take().unwrap());
+    for line in stdout.lines() {
+        let line = t!(line);
+        match serde_json::from_str::<CargoMessage<'_>>(&line) {
+            Ok(msg) => {
+                if builder.config.json_output {
+                    // Forward JSON to stdout.
+                    println!("{}", line);
+                }
+                cb(msg)
+            }
+            // If this was informational, just print it out and continue
+            Err(_) => println!("{}", line),
+        }
+    }
+
+    // Make sure Cargo actually succeeded after we read all of its stdout.
+    let status = t!(child.wait());
+    if builder.is_verbose() && !status.success() {
+        eprintln!(
+            "command did not execute successfully: {:?}\n\
+                  expected success, got: {}",
+            cargo, status
+        );
+    }
+    status.success()
+}
+
+#[derive(Deserialize)]
+pub struct CargoTarget<'a> {
+    crate_types: Vec<Cow<'a, str>>,
+}
+
+#[derive(Deserialize)]
+#[serde(tag = "reason", rename_all = "kebab-case")]
+pub enum CargoMessage<'a> {
+    CompilerArtifact {
+        package_id: Cow<'a, str>,
+        features: Vec<Cow<'a, str>>,
+        filenames: Vec<Cow<'a, str>>,
+        target: CargoTarget<'a>,
+    },
+    BuildScriptExecuted {
+        package_id: Cow<'a, str>,
+    },
+    BuildFinished {
+        success: bool,
+    },
+}