native.rs

//! Compilation of native dependencies like LLVM.
//!
//! Native projects like LLVM unfortunately aren't suited just yet for
//! compilation in build scripts that Cargo has. This is because the
//! compilation takes a *very* long time but also because we don't want to
//! compile LLVM 3 times as part of a normal bootstrap (we want it cached).
//!
//! LLVM and compiler-rt are essentially just wired up to everything else to
//! ensure that they're always in place if needed.

use std::env;
use std::env::consts::EXE_EXTENSION;
use std::ffi::{OsStr, OsString};
use std::fs::{self, File};
use std::io;
use std::path::{Path, PathBuf};
use std::process::Command;

use crate::builder::{Builder, RunConfig, ShouldRun, Step};
use crate::config::TargetSelection;
use crate::util::get_clang_cl_resource_dir;
use crate::util::{self, exe, output, program_out_of_date, t, up_to_date};
use crate::{CLang, GitRepo};

pub struct Meta {
    stamp: HashStamp,
    build_llvm_config: PathBuf,
    out_dir: PathBuf,
    root: String,
}

// Linker flags to pass to LLVM's CMake invocation.
#[derive(Debug, Clone, Default)]
struct LdFlags {
    // CMAKE_EXE_LINKER_FLAGS
    exe: OsString,
    // CMAKE_SHARED_LINKER_FLAGS
    shared: OsString,
    // CMAKE_MODULE_LINKER_FLAGS
    module: OsString,
}

impl LdFlags {
    fn push_all(&mut self, s: impl AsRef<OsStr>) {
        let s = s.as_ref();
        self.exe.push(" ");
        self.exe.push(s);
        self.shared.push(" ");
        self.shared.push(s);
        self.module.push(" ");
        self.module.push(s);
    }
}

// This returns whether we've already previously built LLVM.
//
// It's used to avoid busting caches during x.py check -- if we've already built
// LLVM, it's fine for us to not try to avoid doing so.
//
// This will return the llvm-config if it can get it (but it will not build it
// if not).
pub fn prebuilt_llvm_config(
    builder: &Builder<'_>,
    target: TargetSelection,
) -> Result<PathBuf, Meta> {
    maybe_download_ci_llvm(builder);

    // If we're using a custom LLVM bail out here, but we can only use a
    // custom LLVM for the build triple.
    if let Some(config) = builder.config.target_config.get(&target) {
        if let Some(ref s) = config.llvm_config {
            check_llvm_version(builder, s);
            return Ok(s.to_path_buf());
        }
    }

    let root = "src/llvm-project/llvm";
    let out_dir = builder.llvm_out(target);

    let mut llvm_config_ret_dir = builder.llvm_out(builder.config.build);
    if !builder.config.build.contains("msvc") || builder.ninja() {
        llvm_config_ret_dir.push("build");
    }
    llvm_config_ret_dir.push("bin");

    let build_llvm_config = llvm_config_ret_dir.join(exe("llvm-config", builder.config.build));

    let stamp = out_dir.join("llvm-finished-building");
    let stamp = HashStamp::new(stamp, builder.in_tree_llvm_info.sha());

    if builder.config.llvm_skip_rebuild && stamp.path.exists() {
        builder.info(
            "Warning: \
                Using a potentially stale build of LLVM; \
                This may not behave well.",
        );
        return Ok(build_llvm_config);
    }

    if stamp.is_done() {
        if stamp.hash.is_none() {
            builder.info(
                "Could not determine the LLVM submodule commit hash. \
                     Assuming that an LLVM rebuild is not necessary.",
            );
            builder.info(&format!(
                "To force LLVM to rebuild, remove the file `{}`",
                stamp.path.display()
            ));
        }
        return Ok(build_llvm_config);
    }

    Err(Meta { stamp, build_llvm_config, out_dir, root: root.into() })
}

/// This retrieves the LLVM sha we *want* to use, according to git history.
pub(crate) fn detect_llvm_sha(config: &crate::config::Config) -> String {
    let mut rev_list = config.git();
    rev_list.args(&[
        PathBuf::from("rev-list"),
        format!("--author={}", config.stage0_metadata.config.git_merge_commit_email).into(),
        "-n1".into(),
        "--first-parent".into(),
        "HEAD".into(),
        "--".into(),
        config.src.join("src/llvm-project"),
        config.src.join("src/bootstrap/download-ci-llvm-stamp"),
        // the LLVM shared object file is named `LLVM-12-rust-{version}-nightly`
        config.src.join("src/version"),
    ]);
    let llvm_sha = output(&mut rev_list);
    let llvm_sha = llvm_sha.trim();

    if llvm_sha == "" {
        eprintln!("error: could not find commit hash for downloading LLVM");
        eprintln!("help: maybe your repository history is too shallow?");
        eprintln!("help: consider disabling `download-ci-llvm`");
        eprintln!("help: or fetch enough history to include one upstream commit");
        panic!();
    }

    llvm_sha.to_owned()
}

/// Returns whether the CI-found LLVM is currently usable.
///
/// This checks both the build triple platform to confirm we're usable at all,
/// and then verifies if the current HEAD matches the detected LLVM SHA head,
/// in which case LLVM is indicated as not available.
pub(crate) fn is_ci_llvm_available(config: &crate::config::Config, asserts: bool) -> bool {
    // This is currently all tier 1 targets and tier 2 targets with host tools
    // (since others may not have CI artifacts)
    // https://doc.rust-lang.org/rustc/platform-support.html#tier-1
    let supported_platforms = [
        // tier 1
        "aarch64-unknown-linux-gnu",
        "i686-pc-windows-gnu",
        "i686-pc-windows-msvc",
        "i686-unknown-linux-gnu",
        "x86_64-unknown-linux-gnu",
        "x86_64-apple-darwin",
        "x86_64-pc-windows-gnu",
        "x86_64-pc-windows-msvc",
        // tier 2 with host tools
        "aarch64-apple-darwin",
        "aarch64-pc-windows-msvc",
        "aarch64-unknown-linux-musl",
        "arm-unknown-linux-gnueabi",
        "arm-unknown-linux-gnueabihf",
        "armv7-unknown-linux-gnueabihf",
        "mips-unknown-linux-gnu",
        "mips64-unknown-linux-gnuabi64",
        "mips64el-unknown-linux-gnuabi64",
        "mipsel-unknown-linux-gnu",
        "powerpc-unknown-linux-gnu",
        "powerpc64-unknown-linux-gnu",
        "powerpc64le-unknown-linux-gnu",
        "riscv64gc-unknown-linux-gnu",
        "s390x-unknown-linux-gnu",
        "x86_64-unknown-freebsd",
        "x86_64-unknown-illumos",
        "x86_64-unknown-linux-musl",
        "x86_64-unknown-netbsd",
    ];
    if !supported_platforms.contains(&&*config.build.triple) {
        return false;
    }

    let triple = &*config.build.triple;
    if (triple == "aarch64-unknown-linux-gnu" || triple.contains("i686")) && asserts {
        // No alt builder for aarch64-unknown-linux-gnu today.
        return false;
    }

    if crate::util::CiEnv::is_ci() {
        let llvm_sha = detect_llvm_sha(config);
        let head_sha = output(config.git().arg("rev-parse").arg("HEAD"));
        let head_sha = head_sha.trim();
        if llvm_sha == head_sha {
            eprintln!(
                "Detected LLVM as non-available: running in CI and modified LLVM in this change"
            );
            return false;
        }
    }

    true
}

pub(crate) fn maybe_download_ci_llvm(builder: &Builder<'_>) {
    let config = &builder.config;
    if !config.llvm_from_ci {
        return;
    }
    let llvm_root = config.ci_llvm_root();
    let llvm_stamp = llvm_root.join(".llvm-stamp");
    let llvm_sha = detect_llvm_sha(&config);
    let key = format!("{}{}", llvm_sha, config.llvm_assertions);
    if program_out_of_date(&llvm_stamp, &key) && !config.dry_run {
        download_ci_llvm(builder, &llvm_sha);
        for entry in t!(fs::read_dir(llvm_root.join("bin"))) {
            builder.fix_bin_or_dylib(&t!(entry).path());
        }

        // Update the timestamp of llvm-config to force rustc_llvm to be
        // rebuilt. This is a hacky workaround for a deficiency in Cargo where
        // the rerun-if-changed directive doesn't handle changes very well.
        // https://github.com/rust-lang/cargo/issues/10791
        // Cargo only compares the timestamp of the file relative to the last
        // time `rustc_llvm` build script ran. However, the timestamps of the
        // files in the tarball are in the past, so it doesn't trigger a
        // rebuild.
        let now = filetime::FileTime::from_system_time(std::time::SystemTime::now());
        let llvm_config = llvm_root.join("bin").join(exe("llvm-config", builder.config.build));
        t!(filetime::set_file_times(&llvm_config, now, now));

        let llvm_lib = llvm_root.join("lib");
        for entry in t!(fs::read_dir(&llvm_lib)) {
            let lib = t!(entry).path();
            if lib.extension().map_or(false, |ext| ext == "so") {
                builder.fix_bin_or_dylib(&lib);
            }
        }
        t!(fs::write(llvm_stamp, key));
    }
}

fn download_ci_llvm(builder: &Builder<'_>, llvm_sha: &str) {
    let llvm_assertions = builder.config.llvm_assertions;

    let cache_prefix = format!("llvm-{}-{}", llvm_sha, llvm_assertions);
    let cache_dst = builder.out.join("cache");
    let rustc_cache = cache_dst.join(cache_prefix);
    if !rustc_cache.exists() {
        t!(fs::create_dir_all(&rustc_cache));
    }
    let base = if llvm_assertions {
        &builder.config.stage0_metadata.config.artifacts_with_llvm_assertions_server
    } else {
        &builder.config.stage0_metadata.config.artifacts_server
    };
    let channel = builder.config.artifact_channel(llvm_sha);
    let filename = format!("rust-dev-{}-{}.tar.xz", channel, builder.build.build.triple);
    let tarball = rustc_cache.join(&filename);
    if !tarball.exists() {
        let help_on_error = "error: failed to download llvm from ci

help: old builds get deleted after a certain time
help: if trying to compile an old commit of rustc, disable `download-ci-llvm` in config.toml:

[llvm]
download-ci-llvm = false
";
        builder.download_component(
            &format!("{base}/{llvm_sha}/{filename}"),
            &tarball,
            help_on_error,
        );
    }
    let llvm_root = builder.config.ci_llvm_root();
    builder.unpack(&tarball, &llvm_root, "rust-dev");
}

#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
pub struct Llvm {
    pub target: TargetSelection,
}

impl Step for Llvm {
    type Output = PathBuf; // path to llvm-config

    const ONLY_HOSTS: bool = true;

    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
        run.path("src/llvm-project").path("src/llvm-project/llvm")
    }

    fn make_run(run: RunConfig<'_>) {
        run.builder.ensure(Llvm { target: run.target });
    }

    /// Compile LLVM for `target`.
    fn run(self, builder: &Builder<'_>) -> PathBuf {
        let target = self.target;
        let target_native = if self.target.starts_with("riscv") {
            // RISC-V target triples in Rust is not named the same as C compiler target triples.
            // This converts Rust RISC-V target triples to C compiler triples.
            let idx = target.triple.find('-').unwrap();

            format!("riscv{}{}", &target.triple[5..7], &target.triple[idx..])
        } else if self.target.starts_with("powerpc") && self.target.ends_with("freebsd") {
            // FreeBSD 13 had incompatible ABI changes on all PowerPC platforms.
            // Set the version suffix to 13.0 so the correct target details are used.
            format!("{}{}", self.target, "13.0")
        } else {
            target.to_string()
        };

        let Meta { stamp, build_llvm_config, out_dir, root } =
            match prebuilt_llvm_config(builder, target) {
                Ok(p) => return p,
                Err(m) => m,
            };

        builder.update_submodule(&Path::new("src").join("llvm-project"));
        if builder.llvm_link_shared() && target.contains("windows") {
            panic!("shared linking to LLVM is not currently supported on {}", target.triple);
        }

        builder.info(&format!("Building LLVM for {}", target));
        t!(stamp.remove());
        let _time = util::timeit(&builder);
        t!(fs::create_dir_all(&out_dir));

        // https://llvm.org/docs/CMake.html
        let mut cfg = cmake::Config::new(builder.src.join(root));
        let mut ldflags = LdFlags::default();

        let profile = match (builder.config.llvm_optimize, builder.config.llvm_release_debuginfo) {
            (false, _) => "Debug",
            (true, false) => "Release",
            (true, true) => "RelWithDebInfo",
        };

        // NOTE: remember to also update `config.toml.example` when changing the
        // defaults!
        let llvm_targets = match &builder.config.llvm_targets {
            Some(s) => s,
            None => {
                "AArch64;ARM;BPF;Hexagon;MSP430;Mips;NVPTX;PowerPC;RISCV;\
                     Sparc;SystemZ;WebAssembly;X86"
            }
        };

        let llvm_exp_targets = match builder.config.llvm_experimental_targets {
            Some(ref s) => s,
            None => "AVR;M68k",
        };

        let assertions = if builder.config.llvm_assertions { "ON" } else { "OFF" };
        let plugins = if builder.config.llvm_plugins { "ON" } else { "OFF" };
        let enable_tests = if builder.config.llvm_tests { "ON" } else { "OFF" };

        cfg.out_dir(&out_dir)
            .profile(profile)
            .define("LLVM_ENABLE_ASSERTIONS", assertions)
            .define("LLVM_ENABLE_PLUGINS", plugins)
            .define("LLVM_TARGETS_TO_BUILD", llvm_targets)
            .define("LLVM_EXPERIMENTAL_TARGETS_TO_BUILD", llvm_exp_targets)
            .define("LLVM_INCLUDE_EXAMPLES", "OFF")
            .define("LLVM_INCLUDE_DOCS", "OFF")
            .define("LLVM_INCLUDE_BENCHMARKS", "OFF")
            .define("LLVM_INCLUDE_TESTS", enable_tests)
            .define("LLVM_ENABLE_TERMINFO", "OFF")
            .define("LLVM_ENABLE_LIBEDIT", "OFF")
            .define("LLVM_ENABLE_BINDINGS", "OFF")
            .define("LLVM_ENABLE_Z3_SOLVER", "OFF")
            .define("LLVM_PARALLEL_COMPILE_JOBS", builder.jobs().to_string())
            .define("LLVM_TARGET_ARCH", target_native.split('-').next().unwrap())
            .define("LLVM_DEFAULT_TARGET_TRIPLE", target_native);

        // Parts of our test suite rely on the `FileCheck` tool, which is built by default in
        // `build/$TARGET/llvm/build/bin` is but *not* then installed to `build/$TARGET/llvm/bin`.
        // This flag makes sure `FileCheck` is copied in the final binaries directory.
        cfg.define("LLVM_INSTALL_UTILS", "ON");

        if builder.config.llvm_profile_generate {
            cfg.define("LLVM_BUILD_INSTRUMENTED", "IR");
            if let Ok(llvm_profile_dir) = std::env::var("LLVM_PROFILE_DIR") {
                cfg.define("LLVM_PROFILE_DATA_DIR", llvm_profile_dir);
            }
            cfg.define("LLVM_BUILD_RUNTIME", "No");
        }
        if let Some(path) = builder.config.llvm_profile_use.as_ref() {
            cfg.define("LLVM_PROFDATA_FILE", &path);
        }

        // Disable zstd to avoid a dependency on libzstd.so.
        cfg.define("LLVM_ENABLE_ZSTD", "OFF");

        if target != "aarch64-apple-darwin" && !target.contains("windows") {
            cfg.define("LLVM_ENABLE_ZLIB", "ON");
        } else {
            cfg.define("LLVM_ENABLE_ZLIB", "OFF");
        }

        // Are we compiling for iOS/tvOS/watchOS?
        if target.contains("apple-ios")
            || target.contains("apple-tvos")
            || target.contains("apple-watchos")
        {
            // These two defines prevent CMake from automatically trying to add a MacOSX sysroot, which leads to a compiler error.
            cfg.define("CMAKE_OSX_SYSROOT", "/");
            cfg.define("CMAKE_OSX_DEPLOYMENT_TARGET", "");
            // Prevent cmake from adding -bundle to CFLAGS automatically, which leads to a compiler error because "-bitcode_bundle" also gets added.
            cfg.define("LLVM_ENABLE_PLUGINS", "OFF");
            // Zlib fails to link properly, leading to a compiler error.
            cfg.define("LLVM_ENABLE_ZLIB", "OFF");
        }

        // This setting makes the LLVM tools link to the dynamic LLVM library,
        // which saves both memory during parallel links and overall disk space
        // for the tools. We don't do this on every platform as it doesn't work
        // equally well everywhere.
        //
        // If we're not linking rustc to a dynamic LLVM, though, then don't link
        // tools to it.
        let llvm_link_shared =
            builder.llvm_link_tools_dynamically(target) && builder.llvm_link_shared();
        if llvm_link_shared {
            cfg.define("LLVM_LINK_LLVM_DYLIB", "ON");
        }

        if target.starts_with("riscv") && !target.contains("freebsd") && !target.contains("openbsd")
        {
            // RISC-V GCC erroneously requires linking against
            // `libatomic` when using 1-byte and 2-byte C++
            // atomics but the LLVM build system check cannot
            // detect this. Therefore it is set manually here.
            // Some BSD uses Clang as its system compiler and
            // provides no libatomic in its base system so does
            // not want this.
            ldflags.exe.push(" -latomic");
            ldflags.shared.push(" -latomic");
        }

        if target.contains("msvc") {
            cfg.define("LLVM_USE_CRT_DEBUG", "MT");
            cfg.define("LLVM_USE_CRT_RELEASE", "MT");
            cfg.define("LLVM_USE_CRT_RELWITHDEBINFO", "MT");
            cfg.static_crt(true);
        }

        if target.starts_with("i686") {
            cfg.define("LLVM_BUILD_32_BITS", "ON");
        }

        let mut enabled_llvm_projects = Vec::new();

        if util::forcing_clang_based_tests() {
            enabled_llvm_projects.push("clang");
            enabled_llvm_projects.push("compiler-rt");
        }

        if builder.config.llvm_polly {
            enabled_llvm_projects.push("polly");
        }

        if builder.config.llvm_clang {
            enabled_llvm_projects.push("clang");
        }

        // We want libxml to be disabled.
        // See https://github.com/rust-lang/rust/pull/50104
        cfg.define("LLVM_ENABLE_LIBXML2", "OFF");

        if !enabled_llvm_projects.is_empty() {
            enabled_llvm_projects.sort();
            enabled_llvm_projects.dedup();
            cfg.define("LLVM_ENABLE_PROJECTS", enabled_llvm_projects.join(";"));
        }

        if let Some(num_linkers) = builder.config.llvm_link_jobs {
            if num_linkers > 0 {
                cfg.define("LLVM_PARALLEL_LINK_JOBS", num_linkers.to_string());
            }
        }

        // Workaround for ppc32 lld limitation
        if target == "powerpc-unknown-freebsd" {
            ldflags.exe.push(" -fuse-ld=bfd");
        }

        // https://llvm.org/docs/HowToCrossCompileLLVM.html
        if target != builder.config.build {
            builder.ensure(Llvm { target: builder.config.build });
            // FIXME: if the llvm root for the build triple is overridden then we
            //        should use llvm-tblgen from there, also should verify that it
            //        actually exists most of the time in normal installs of LLVM.
            let host_bin = builder.llvm_out(builder.config.build).join("bin");
            cfg.define("LLVM_TABLEGEN", host_bin.join("llvm-tblgen").with_extension(EXE_EXTENSION));
            // LLVM_NM is required for cross compiling using MSVC
            cfg.define("LLVM_NM", host_bin.join("llvm-nm").with_extension(EXE_EXTENSION));
            cfg.define(
                "LLVM_CONFIG_PATH",
                host_bin.join("llvm-config").with_extension(EXE_EXTENSION),
            );
            if builder.config.llvm_clang {
                let build_bin = builder.llvm_out(builder.config.build).join("build").join("bin");
                let clang_tblgen = build_bin.join("clang-tblgen").with_extension(EXE_EXTENSION);
                if !builder.config.dry_run && !clang_tblgen.exists() {
                    panic!("unable to find {}", clang_tblgen.display());
                }
                cfg.define("CLANG_TABLEGEN", clang_tblgen);
            }
        }

        let llvm_version_suffix = if let Some(ref suffix) = builder.config.llvm_version_suffix {
            // Allow version-suffix="" to not define a version suffix at all.
            if !suffix.is_empty() { Some(suffix.to_string()) } else { None }
        } else if builder.config.channel == "dev" {
            // Changes to a version suffix require a complete rebuild of the LLVM.
            // To avoid rebuilds during a time of version bump, don't include rustc
            // release number on the dev channel.
            Some("-rust-dev".to_string())
        } else {
            Some(format!("-rust-{}-{}", builder.version, builder.config.channel))
        };
        if let Some(ref suffix) = llvm_version_suffix {
            cfg.define("LLVM_VERSION_SUFFIX", suffix);
        }

        configure_cmake(builder, target, &mut cfg, true, ldflags);
        configure_llvm(builder, target, &mut cfg);

        for (key, val) in &builder.config.llvm_build_config {
            cfg.define(key, val);
        }

        // FIXME: we don't actually need to build all LLVM tools and all LLVM
        //        libraries here, e.g., we just want a few components and a few
        //        tools. Figure out how to filter them down and only build the right
        //        tools and libs on all platforms.

        if builder.config.dry_run {
            return build_llvm_config;
        }

        cfg.build();

        // When building LLVM with LLVM_LINK_LLVM_DYLIB for macOS, an unversioned
        // libLLVM.dylib will be built. However, llvm-config will still look
        // for a versioned path like libLLVM-14.dylib. Manually create a symbolic
        // link to make llvm-config happy.
        if llvm_link_shared && target.contains("apple-darwin") {
            let mut cmd = Command::new(&build_llvm_config);
            let version = output(cmd.arg("--version"));
            let major = version.split('.').next().unwrap();
            let lib_name = match llvm_version_suffix {
                Some(s) => format!("libLLVM-{}{}.dylib", major, s),
                None => format!("libLLVM-{}.dylib", major),
            };

            let lib_llvm = out_dir.join("build").join("lib").join(lib_name);
            if !lib_llvm.exists() {
                t!(builder.symlink_file("libLLVM.dylib", &lib_llvm));
            }
        }

        t!(stamp.write());

        build_llvm_config
    }
}

fn check_llvm_version(builder: &Builder<'_>, llvm_config: &Path) {
    if !builder.config.llvm_version_check {
        return;
    }

    if builder.config.dry_run {
        return;
    }

    let mut cmd = Command::new(llvm_config);
    let version = output(cmd.arg("--version"));
    let mut parts = version.split('.').take(2).filter_map(|s| s.parse::<u32>().ok());
    if let (Some(major), Some(_minor)) = (parts.next(), parts.next()) {
        if major >= 13 {
            return;
        }
    }
    panic!("\n\nbad LLVM version: {}, need >=13.0\n\n", version)
}

fn configure_cmake(
    builder: &Builder<'_>,
    target: TargetSelection,
    cfg: &mut cmake::Config,
    use_compiler_launcher: bool,
    mut ldflags: LdFlags,
) {
    // Do not print installation messages for up-to-date files.
    // LLVM and LLD builds can produce a lot of those and hit CI limits on log size.
    cfg.define("CMAKE_INSTALL_MESSAGE", "LAZY");

    // Do not allow the user's value of DESTDIR to influence where
    // LLVM will install itself. LLVM must always be installed in our
    // own build directories.
    cfg.env("DESTDIR", "");

    if builder.ninja() {
        cfg.generator("Ninja");
    }
    cfg.target(&target.triple).host(&builder.config.build.triple);

    if target != builder.config.build {
        cfg.define("CMAKE_CROSSCOMPILING", "True");

        if target.contains("netbsd") {
            cfg.define("CMAKE_SYSTEM_NAME", "NetBSD");
        } else if target.contains("freebsd") {
            cfg.define("CMAKE_SYSTEM_NAME", "FreeBSD");
        } else if target.contains("windows") {
            cfg.define("CMAKE_SYSTEM_NAME", "Windows");
        } else if target.contains("haiku") {
            cfg.define("CMAKE_SYSTEM_NAME", "Haiku");
        } else if target.contains("solaris") || target.contains("illumos") {
            cfg.define("CMAKE_SYSTEM_NAME", "SunOS");
        }
        // When cross-compiling we should also set CMAKE_SYSTEM_VERSION, but in
        // that case like CMake we cannot easily determine system version either.
        //
        // Since, the LLVM itself makes rather limited use of version checks in
        // CMakeFiles (and then only in tests), and so far no issues have been
        // reported, the system version is currently left unset.

        if target.contains("darwin") {
            // Make sure that CMake does not build universal binaries on macOS.
            // Explicitly specify the one single target architecture.
            if target.starts_with("aarch64") {
                // macOS uses a different name for building arm64
                cfg.define("CMAKE_OSX_ARCHITECTURES", "arm64");
            } else {
                cfg.define("CMAKE_OSX_ARCHITECTURES", target.triple.split('-').next().unwrap());
            }
        }
    }

    let sanitize_cc = |cc: &Path| {
        if target.contains("msvc") {
            OsString::from(cc.to_str().unwrap().replace("\\", "/"))
        } else {
            cc.as_os_str().to_owned()
        }
    };

    // MSVC with CMake uses msbuild by default which doesn't respect these
    // vars that we'd otherwise configure. In that case we just skip this
    // entirely.
    if target.contains("msvc") && !builder.ninja() {
        return;
    }

    let (cc, cxx) = match builder.config.llvm_clang_cl {
        Some(ref cl) => (cl.as_ref(), cl.as_ref()),
        None => (builder.cc(target), builder.cxx(target).unwrap()),
    };

    // Handle msvc + ninja + ccache specially (this is what the bots use)
    if target.contains("msvc") && builder.ninja() && builder.config.ccache.is_some() {
        let mut wrap_cc = env::current_exe().expect("failed to get cwd");
        wrap_cc.set_file_name("sccache-plus-cl.exe");

        cfg.define("CMAKE_C_COMPILER", sanitize_cc(&wrap_cc))
            .define("CMAKE_CXX_COMPILER", sanitize_cc(&wrap_cc));
        cfg.env("SCCACHE_PATH", builder.config.ccache.as_ref().unwrap())
            .env("SCCACHE_TARGET", target.triple)
            .env("SCCACHE_CC", &cc)
            .env("SCCACHE_CXX", &cxx);

        // Building LLVM on MSVC can be a little ludicrous at times. We're so far
        // off the beaten path here that I'm not really sure this is even half
        // supported any more. Here we're trying to:
        //
        // * Build LLVM on MSVC
        // * Build LLVM with `clang-cl` instead of `cl.exe`
        // * Build a project with `sccache`
        // * Build for 32-bit as well
        // * Build with Ninja
        //
        // For `cl.exe` there are different binaries to compile 32/64 bit which
        // we use but for `clang-cl` there's only one which internally
        // multiplexes via flags. As a result it appears that CMake's detection
        // of a compiler's architecture and such on MSVC **doesn't** pass any
        // custom flags we pass in CMAKE_CXX_FLAGS below. This means that if we
        // use `clang-cl.exe` it's always diagnosed as a 64-bit compiler which
        // definitely causes problems since all the env vars are pointing to
        // 32-bit libraries.
        //
        // To hack around this... again... we pass an argument that's
        // unconditionally passed in the sccache shim. This'll get CMake to
        // correctly diagnose it's doing a 32-bit compilation and LLVM will
        // internally configure itself appropriately.
        if builder.config.llvm_clang_cl.is_some() && target.contains("i686") {
            cfg.env("SCCACHE_EXTRA_ARGS", "-m32");
        }
    } else {
        // If ccache is configured we inform the build a little differently how
        // to invoke ccache while also invoking our compilers.
        if use_compiler_launcher {
            if let Some(ref ccache) = builder.config.ccache {
                cfg.define("CMAKE_C_COMPILER_LAUNCHER", ccache)
                    .define("CMAKE_CXX_COMPILER_LAUNCHER", ccache);
            }
        }
        cfg.define("CMAKE_C_COMPILER", sanitize_cc(cc))
            .define("CMAKE_CXX_COMPILER", sanitize_cc(cxx))
            .define("CMAKE_ASM_COMPILER", sanitize_cc(cc));
    }

    cfg.build_arg("-j").build_arg(builder.jobs().to_string());
    let mut cflags: OsString = builder.cflags(target, GitRepo::Llvm, CLang::C).join(" ").into();
    if let Some(ref s) = builder.config.llvm_cflags {
        cflags.push(" ");
        cflags.push(s);
    }
    // Some compiler features used by LLVM (such as thread locals) will not work on a min version below iOS 10.
    if target.contains("apple-ios") {
        if target.contains("86-") {
            cflags.push(" -miphonesimulator-version-min=10.0");
        } else {
            cflags.push(" -miphoneos-version-min=10.0");
        }
    }
    if builder.config.llvm_clang_cl.is_some() {
        cflags.push(&format!(" --target={}", target));
    }
    cfg.define("CMAKE_C_FLAGS", cflags);
    let mut cxxflags: OsString = builder.cflags(target, GitRepo::Llvm, CLang::Cxx).join(" ").into();
    if let Some(ref s) = builder.config.llvm_cxxflags {
        cxxflags.push(" ");
        cxxflags.push(s);
    }
    if builder.config.llvm_clang_cl.is_some() {
        cxxflags.push(&format!(" --target={}", target));
    }
    cfg.define("CMAKE_CXX_FLAGS", cxxflags);
    if let Some(ar) = builder.ar(target) {
        if ar.is_absolute() {
            // LLVM build breaks if `CMAKE_AR` is a relative path, for some reason it
            // tries to resolve this path in the LLVM build directory.
            cfg.define("CMAKE_AR", sanitize_cc(ar));
        }
    }

    if let Some(ranlib) = builder.ranlib(target) {
        if ranlib.is_absolute() {
            // LLVM build breaks if `CMAKE_RANLIB` is a relative path, for some reason it
            // tries to resolve this path in the LLVM build directory.
            cfg.define("CMAKE_RANLIB", sanitize_cc(ranlib));
        }
    }

    if let Some(ref flags) = builder.config.llvm_ldflags {
        ldflags.push_all(flags);
    }

    if let Some(flags) = get_var("LDFLAGS", &builder.config.build.triple, &target.triple) {
        ldflags.push_all(&flags);
    }

    // For distribution we want the LLVM tools to be *statically* linked to libstdc++.
    // We also do this if the user explicitly requested static libstdc++.
    if builder.config.llvm_static_stdcpp {
        if !target.contains("msvc") && !target.contains("netbsd") && !target.contains("solaris") {
            if target.contains("apple") || target.contains("windows") {
                ldflags.push_all("-static-libstdc++");
            } else {
                ldflags.push_all("-Wl,-Bsymbolic -static-libstdc++");
            }
        }
    }

    cfg.define("CMAKE_SHARED_LINKER_FLAGS", &ldflags.shared);
    cfg.define("CMAKE_MODULE_LINKER_FLAGS", &ldflags.module);
    cfg.define("CMAKE_EXE_LINKER_FLAGS", &ldflags.exe);

    if env::var_os("SCCACHE_ERROR_LOG").is_some() {
        cfg.env("RUSTC_LOG", "sccache=warn");
    }
}

fn configure_llvm(builder: &Builder<'_>, target: TargetSelection, cfg: &mut cmake::Config) {
    // ThinLTO is only available when building with LLVM, enabling LLD is required.
    // Apple's linker ld64 supports ThinLTO out of the box though, so don't use LLD on Darwin.
    if builder.config.llvm_thin_lto {
        cfg.define("LLVM_ENABLE_LTO", "Thin");
        if !target.contains("apple") {
            cfg.define("LLVM_ENABLE_LLD", "ON");
        }
    }

    if let Some(ref linker) = builder.config.llvm_use_linker {
        cfg.define("LLVM_USE_LINKER", linker);
    }

    if builder.config.llvm_allow_old_toolchain {
        cfg.define("LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN", "YES");
    }
}

// Adapted from https://github.com/alexcrichton/cc-rs/blob/fba7feded71ee4f63cfe885673ead6d7b4f2f454/src/lib.rs#L2347-L2365
fn get_var(var_base: &str, host: &str, target: &str) -> Option<OsString> {
    let kind = if host == target { "HOST" } else { "TARGET" };
    let target_u = target.replace("-", "_");
    env::var_os(&format!("{}_{}", var_base, target))
        .or_else(|| env::var_os(&format!("{}_{}", var_base, target_u)))
        .or_else(|| env::var_os(&format!("{}_{}", kind, var_base)))
        .or_else(|| env::var_os(var_base))
}

#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
pub struct Lld {
    pub target: TargetSelection,
}

impl Step for Lld {
    type Output = PathBuf;
    const ONLY_HOSTS: bool = true;

    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
        run.path("src/llvm-project/lld")
    }

    fn make_run(run: RunConfig<'_>) {
        run.builder.ensure(Lld { target: run.target });
    }

    /// Compile LLD for `target`.
    fn run(self, builder: &Builder<'_>) -> PathBuf {
        if builder.config.dry_run {
            return PathBuf::from("lld-out-dir-test-gen");
        }
        let target = self.target;

        let llvm_config = builder.ensure(Llvm { target: self.target });

        let out_dir = builder.lld_out(target);
        let done_stamp = out_dir.join("lld-finished-building");
        if done_stamp.exists() {
            return out_dir;
        }

        builder.info(&format!("Building LLD for {}", target));
        let _time = util::timeit(&builder);
        t!(fs::create_dir_all(&out_dir));

        let mut cfg = cmake::Config::new(builder.src.join("src/llvm-project/lld"));
        let mut ldflags = LdFlags::default();

        // When building LLD as part of a build with instrumentation on windows, for example
        // when doing PGO on CI, cmake or clang-cl don't automatically link clang's
        // profiler runtime in. In that case, we need to manually ask cmake to do it, to avoid
        // linking errors, much like LLVM's cmake setup does in that situation.
        if builder.config.llvm_profile_generate && target.contains("msvc") {
            if let Some(clang_cl_path) = builder.config.llvm_clang_cl.as_ref() {
                // Find clang's runtime library directory and push that as a search path to the
                // cmake linker flags.
                let clang_rt_dir = get_clang_cl_resource_dir(clang_cl_path);
                ldflags.push_all(&format!("/libpath:{}", clang_rt_dir.display()));
            }
        }

        configure_cmake(builder, target, &mut cfg, true, ldflags);
        configure_llvm(builder, target, &mut cfg);

        // This is an awful, awful hack. Discovered when we migrated to using
        // clang-cl to compile LLVM/LLD it turns out that LLD, when built out of
        // tree, will execute `llvm-config --cmakedir` and then tell CMake about
        // that directory for later processing. Unfortunately if this path has
        // forward slashes in it (which it basically always does on Windows)
        // then CMake will hit a syntax error later on as... something isn't
        // escaped it seems?
        //
        // Instead of attempting to fix this problem in upstream CMake and/or
        // LLVM/LLD we just hack around it here. This thin wrapper will take the
        // output from llvm-config and replace all instances of `\` with `/` to
        // ensure we don't hit the same bugs with escaping. It means that you
        // can't build on a system where your paths require `\` on Windows, but
        // there's probably a lot of reasons you can't do that other than this.
        let llvm_config_shim = env::current_exe().unwrap().with_file_name("llvm-config-wrapper");

        // Re-use the same flags as llvm to control the level of debug information
        // generated for lld.
        let profile = match (builder.config.llvm_optimize, builder.config.llvm_release_debuginfo) {
            (false, _) => "Debug",
            (true, false) => "Release",
            (true, true) => "RelWithDebInfo",
        };

        cfg.out_dir(&out_dir)
            .profile(profile)
            .env("LLVM_CONFIG_REAL", &llvm_config)
            .define("LLVM_CONFIG_PATH", llvm_config_shim)
            .define("LLVM_INCLUDE_TESTS", "OFF");

        // While we're using this horrible workaround to shim the execution of
        // llvm-config, let's just pile on more. I can't seem to figure out how
        // to build LLD as a standalone project and also cross-compile it at the
        // same time. It wants a natively executable `llvm-config` to learn
        // about LLVM, but then it learns about all the host configuration of
        // LLVM and tries to link to host LLVM libraries.
        //
        // To work around that we tell our shim to replace anything with the
        // build target with the actual target instead. This'll break parts of
        // LLD though which try to execute host tools, such as llvm-tblgen, so
        // we specifically tell it where to find those. This is likely super
        // brittle and will break over time. If anyone knows better how to
        // cross-compile LLD it would be much appreciated to fix this!
        if target != builder.config.build {
            cfg.env("LLVM_CONFIG_SHIM_REPLACE", &builder.config.build.triple)
                .env("LLVM_CONFIG_SHIM_REPLACE_WITH", &target.triple)
                .define(
                    "LLVM_TABLEGEN_EXE",
                    llvm_config.with_file_name("llvm-tblgen").with_extension(EXE_EXTENSION),
                );
        }

        // Explicitly set C++ standard, because upstream doesn't do so
        // for standalone builds.
        cfg.define("CMAKE_CXX_STANDARD", "14");

        cfg.build();

        t!(File::create(&done_stamp));
        out_dir
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct TestHelpers {
    pub target: TargetSelection,
}

impl Step for TestHelpers {
    type Output = ();

    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
        run.path("src/test/auxiliary/rust_test_helpers.c")
    }

    fn make_run(run: RunConfig<'_>) {
        run.builder.ensure(TestHelpers { target: run.target })
    }

    /// Compiles the `rust_test_helpers.c` library which we used in various
    /// `run-pass` tests for ABI testing.
    fn run(self, builder: &Builder<'_>) {
        if builder.config.dry_run {
            return;
        }
        // The x86_64-fortanix-unknown-sgx target doesn't have a working C
        // toolchain. However, some x86_64 ELF objects can be linked
        // without issues. Use this hack to compile the test helpers.
        let target = if self.target == "x86_64-fortanix-unknown-sgx" {
            TargetSelection::from_user("x86_64-unknown-linux-gnu")
        } else {
            self.target
        };
        let dst = builder.test_helpers_out(target);
        let src = builder.src.join("src/test/auxiliary/rust_test_helpers.c");
        if up_to_date(&src, &dst.join("librust_test_helpers.a")) {
            return;
        }

        builder.info("Building test helpers");
        t!(fs::create_dir_all(&dst));
        let mut cfg = cc::Build::new();
        // FIXME: Workaround for https://github.com/emscripten-core/emscripten/issues/9013
        if target.contains("emscripten") {
            cfg.pic(false);
        }

        // We may have found various cross-compilers a little differently due to our
        // extra configuration, so inform cc of these compilers. Note, though, that
        // on MSVC we still need cc's detection of env vars (ugh).
        if !target.contains("msvc") {
            if let Some(ar) = builder.ar(target) {
                cfg.archiver(ar);
            }
            cfg.compiler(builder.cc(target));
        }
        cfg.cargo_metadata(false)
            .out_dir(&dst)
            .target(&target.triple)
            .host(&builder.config.build.triple)
            .opt_level(0)
            .warnings(false)
            .debug(false)
            .file(builder.src.join("src/test/auxiliary/rust_test_helpers.c"))
            .compile("rust_test_helpers");
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct Sanitizers {
    pub target: TargetSelection,
}

impl Step for Sanitizers {
    type Output = Vec<SanitizerRuntime>;

    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
        run.alias("sanitizers")
    }

    fn make_run(run: RunConfig<'_>) {
        run.builder.ensure(Sanitizers { target: run.target });
    }

    /// Builds sanitizer runtime libraries.
    fn run(self, builder: &Builder<'_>) -> Self::Output {
        let compiler_rt_dir = builder.src.join("src/llvm-project/compiler-rt");
        if !compiler_rt_dir.exists() {
            return Vec::new();
        }

        let out_dir = builder.native_dir(self.target).join("sanitizers");
        let runtimes = supported_sanitizers(&out_dir, self.target, &builder.config.channel);
        if runtimes.is_empty() {
            return runtimes;
        }

        let llvm_config = builder.ensure(Llvm { target: builder.config.build });
        if builder.config.dry_run {
            return runtimes;
        }

        let stamp = out_dir.join("sanitizers-finished-building");
        let stamp = HashStamp::new(stamp, builder.in_tree_llvm_info.sha());

        if stamp.is_done() {
            if stamp.hash.is_none() {
                builder.info(&format!(
                    "Rebuild sanitizers by removing the file `{}`",
                    stamp.path.display()
                ));
            }
            return runtimes;
        }

        builder.info(&format!("Building sanitizers for {}", self.target));
        t!(stamp.remove());
        let _time = util::timeit(&builder);

        let mut cfg = cmake::Config::new(&compiler_rt_dir);
        cfg.profile("Release");
        cfg.define("CMAKE_C_COMPILER_TARGET", self.target.triple);
        cfg.define("COMPILER_RT_BUILD_BUILTINS", "OFF");
        cfg.define("COMPILER_RT_BUILD_CRT", "OFF");
        cfg.define("COMPILER_RT_BUILD_LIBFUZZER", "OFF");
        cfg.define("COMPILER_RT_BUILD_PROFILE", "OFF");
        cfg.define("COMPILER_RT_BUILD_SANITIZERS", "ON");
        cfg.define("COMPILER_RT_BUILD_XRAY", "OFF");
        cfg.define("COMPILER_RT_DEFAULT_TARGET_ONLY", "ON");
        cfg.define("COMPILER_RT_USE_LIBCXX", "OFF");
        cfg.define("LLVM_CONFIG_PATH", &llvm_config);

        // On Darwin targets the sanitizer runtimes are build as universal binaries.
        // Unfortunately sccache currently lacks support to build them successfully.
        // Disable compiler launcher on Darwin targets to avoid potential issues.
        let use_compiler_launcher = !self.target.contains("apple-darwin");
        configure_cmake(builder, self.target, &mut cfg, use_compiler_launcher, LdFlags::default());

        t!(fs::create_dir_all(&out_dir));
        cfg.out_dir(out_dir);

        for runtime in &runtimes {
            cfg.build_target(&runtime.cmake_target);
            cfg.build();
        }
        t!(stamp.write());

        runtimes
    }
}

#[derive(Clone, Debug)]
pub struct SanitizerRuntime {
    /// CMake target used to build the runtime.
    pub cmake_target: String,
    /// Path to the built runtime library.
    pub path: PathBuf,
    /// Library filename that will be used rustc.
    pub name: String,
}

/// Returns sanitizers available on a given target.
fn supported_sanitizers(
    out_dir: &Path,
    target: TargetSelection,
    channel: &str,
) -> Vec<SanitizerRuntime> {
    let darwin_libs = |os: &str, components: &[&str]| -> Vec<SanitizerRuntime> {
        components
            .iter()
            .map(move |c| SanitizerRuntime {
                cmake_target: format!("clang_rt.{}_{}_dynamic", c, os),
                path: out_dir
                    .join(&format!("build/lib/darwin/libclang_rt.{}_{}_dynamic.dylib", c, os)),
                name: format!("librustc-{}_rt.{}.dylib", channel, c),
            })
            .collect()
    };

    let common_libs = |os: &str, arch: &str, components: &[&str]| -> Vec<SanitizerRuntime> {
        components
            .iter()
            .map(move |c| SanitizerRuntime {
                cmake_target: format!("clang_rt.{}-{}", c, arch),
                path: out_dir.join(&format!("build/lib/{}/libclang_rt.{}-{}.a", os, c, arch)),
                name: format!("librustc-{}_rt.{}.a", channel, c),
            })
            .collect()
    };

    match &*target.triple {
        "aarch64-apple-darwin" => darwin_libs("osx", &["asan", "lsan", "tsan"]),
        "aarch64-fuchsia" => common_libs("fuchsia", "aarch64", &["asan"]),
        "aarch64-unknown-linux-gnu" => {
            common_libs("linux", "aarch64", &["asan", "lsan", "msan", "tsan", "hwasan"])
        }
        "x86_64-apple-darwin" => darwin_libs("osx", &["asan", "lsan", "tsan"]),
        "x86_64-fuchsia" => common_libs("fuchsia", "x86_64", &["asan"]),
        "x86_64-unknown-freebsd" => common_libs("freebsd", "x86_64", &["asan", "msan", "tsan"]),
        "x86_64-unknown-netbsd" => {
            common_libs("netbsd", "x86_64", &["asan", "lsan", "msan", "tsan"])
        }
        "x86_64-unknown-illumos" => common_libs("illumos", "x86_64", &["asan"]),
        "x86_64-pc-solaris" => common_libs("solaris", "x86_64", &["asan"]),
        "x86_64-unknown-linux-gnu" => {
            common_libs("linux", "x86_64", &["asan", "lsan", "msan", "tsan"])
        }
        "x86_64-unknown-linux-musl" => {
            common_libs("linux", "x86_64", &["asan", "lsan", "msan", "tsan"])
        }
        _ => Vec::new(),
    }
}

struct HashStamp {
    path: PathBuf,
    hash: Option<Vec<u8>>,
}

impl HashStamp {
    fn new(path: PathBuf, hash: Option<&str>) -> Self {
        HashStamp { path, hash: hash.map(|s| s.as_bytes().to_owned()) }
    }

    fn is_done(&self) -> bool {
        match fs::read(&self.path) {
            Ok(h) => self.hash.as_deref().unwrap_or(b"") == h.as_slice(),
            Err(e) if e.kind() == io::ErrorKind::NotFound => false,
            Err(e) => {
                panic!("failed to read stamp file `{}`: {}", self.path.display(), e);
            }
        }
    }

    fn remove(&self) -> io::Result<()> {
        match fs::remove_file(&self.path) {
            Ok(()) => Ok(()),
            Err(e) => {
                if e.kind() == io::ErrorKind::NotFound {
                    Ok(())
                } else {
                    Err(e)
                }
            }
        }
    }

    fn write(&self) -> io::Result<()> {
        fs::write(&self.path, self.hash.as_deref().unwrap_or(b""))
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct CrtBeginEnd {
    pub target: TargetSelection,
}

impl Step for CrtBeginEnd {
    type Output = PathBuf;

    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
        run.path("src/llvm-project/compiler-rt/lib/crt")
    }

    fn make_run(run: RunConfig<'_>) {
        run.builder.ensure(CrtBeginEnd { target: run.target });
    }

    /// Build crtbegin.o/crtend.o for musl target.
    fn run(self, builder: &Builder<'_>) -> Self::Output {
        let out_dir = builder.native_dir(self.target).join("crt");

        if builder.config.dry_run {
            return out_dir;
        }

        let crtbegin_src = builder.src.join("src/llvm-project/compiler-rt/lib/crt/crtbegin.c");
        let crtend_src = builder.src.join("src/llvm-project/compiler-rt/lib/crt/crtend.c");
        if up_to_date(&crtbegin_src, &out_dir.join("crtbegin.o"))
            && up_to_date(&crtend_src, &out_dir.join("crtendS.o"))
        {
            return out_dir;
        }

        builder.info("Building crtbegin.o and crtend.o");
        t!(fs::create_dir_all(&out_dir));

        let mut cfg = cc::Build::new();

        if let Some(ar) = builder.ar(self.target) {
            cfg.archiver(ar);
        }
        cfg.compiler(builder.cc(self.target));
        cfg.cargo_metadata(false)
            .out_dir(&out_dir)
            .target(&self.target.triple)
            .host(&builder.config.build.triple)
            .warnings(false)
            .debug(false)
            .opt_level(3)
            .file(crtbegin_src)
            .file(crtend_src);

        // Those flags are defined in src/llvm-project/compiler-rt/lib/crt/CMakeLists.txt
        // Currently only consumer of those objects is musl, which use .init_array/.fini_array
        // instead of .ctors/.dtors
        cfg.flag("-std=c11")
            .define("CRT_HAS_INITFINI_ARRAY", None)
            .define("EH_USE_FRAME_REGISTRY", None);

        cfg.compile("crt");

        t!(fs::copy(out_dir.join("crtbegin.o"), out_dir.join("crtbeginS.o")));
        t!(fs::copy(out_dir.join("crtend.o"), out_dir.join("crtendS.o")));
        out_dir
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct Libunwind {
    pub target: TargetSelection,
}

impl Step for Libunwind {
    type Output = PathBuf;

    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
        run.path("src/llvm-project/libunwind")
    }

    fn make_run(run: RunConfig<'_>) {
        run.builder.ensure(Libunwind { target: run.target });
    }

    /// Build linunwind.a
    fn run(self, builder: &Builder<'_>) -> Self::Output {
        if builder.config.dry_run {
            return PathBuf::new();
        }

        let out_dir = builder.native_dir(self.target).join("libunwind");
        let root = builder.src.join("src/llvm-project/libunwind");

        if up_to_date(&root, &out_dir.join("libunwind.a")) {
            return out_dir;
        }

        builder.info(&format!("Building libunwind.a for {}", self.target.triple));
        t!(fs::create_dir_all(&out_dir));

        let mut cc_cfg = cc::Build::new();
        let mut cpp_cfg = cc::Build::new();

        cpp_cfg.cpp(true);
        cpp_cfg.cpp_set_stdlib(None);
        cpp_cfg.flag("-nostdinc++");
        cpp_cfg.flag("-fno-exceptions");
        cpp_cfg.flag("-fno-rtti");
        cpp_cfg.flag_if_supported("-fvisibility-global-new-delete-hidden");

        for cfg in [&mut cc_cfg, &mut cpp_cfg].iter_mut() {
            if let Some(ar) = builder.ar(self.target) {
                cfg.archiver(ar);
            }
            cfg.target(&self.target.triple);
            cfg.host(&builder.config.build.triple);
            cfg.warnings(false);
            cfg.debug(false);
            // get_compiler() need set opt_level first.
            cfg.opt_level(3);
            cfg.flag("-fstrict-aliasing");
            cfg.flag("-funwind-tables");
            cfg.flag("-fvisibility=hidden");
            cfg.define("_LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS", None);
            cfg.include(root.join("include"));
            cfg.cargo_metadata(false);
            cfg.out_dir(&out_dir);

            if self.target.contains("x86_64-fortanix-unknown-sgx") {
                cfg.static_flag(true);
                cfg.flag("-fno-stack-protector");
                cfg.flag("-ffreestanding");
                cfg.flag("-fexceptions");

                // easiest way to undefine since no API available in cc::Build to undefine
                cfg.flag("-U_FORTIFY_SOURCE");
                cfg.define("_FORTIFY_SOURCE", "0");
                cfg.define("RUST_SGX", "1");
                cfg.define("__NO_STRING_INLINES", None);
                cfg.define("__NO_MATH_INLINES", None);
                cfg.define("_LIBUNWIND_IS_BAREMETAL", None);
                cfg.define("__LIBUNWIND_IS_NATIVE_ONLY", None);
                cfg.define("NDEBUG", None);
            }
            if self.target.contains("windows") {
                cfg.define("_LIBUNWIND_HIDE_SYMBOLS", "1");
                cfg.define("_LIBUNWIND_IS_NATIVE_ONLY", "1");
            }
        }

        cc_cfg.compiler(builder.cc(self.target));
        if let Ok(cxx) = builder.cxx(self.target) {
            cpp_cfg.compiler(cxx);
        } else {
            cc_cfg.compiler(builder.cc(self.target));
        }

        // Don't set this for clang
        // By default, Clang builds C code in GNU C17 mode.
        // By default, Clang builds C++ code according to the C++98 standard,
        // with many C++11 features accepted as extensions.
        if cc_cfg.get_compiler().is_like_gnu() {
            cc_cfg.flag("-std=c99");
        }
        if cpp_cfg.get_compiler().is_like_gnu() {
            cpp_cfg.flag("-std=c++11");
        }

        if self.target.contains("x86_64-fortanix-unknown-sgx") || self.target.contains("musl") {
            // use the same GCC C compiler command to compile C++ code so we do not need to setup the
            // C++ compiler env variables on the builders.
            // Don't set this for clang++, as clang++ is able to compile this without libc++.
            if cpp_cfg.get_compiler().is_like_gnu() {
                cpp_cfg.cpp(false);
                cpp_cfg.compiler(builder.cc(self.target));
            }
        }

        let mut c_sources = vec![
            "Unwind-sjlj.c",
            "UnwindLevel1-gcc-ext.c",
            "UnwindLevel1.c",
            "UnwindRegistersRestore.S",
            "UnwindRegistersSave.S",
        ];

        let cpp_sources = vec!["Unwind-EHABI.cpp", "Unwind-seh.cpp", "libunwind.cpp"];
        let cpp_len = cpp_sources.len();

        if self.target.contains("x86_64-fortanix-unknown-sgx") {
            c_sources.push("UnwindRustSgx.c");
        }

        for src in c_sources {
            cc_cfg.file(root.join("src").join(src).canonicalize().unwrap());
        }

        for src in &cpp_sources {
            cpp_cfg.file(root.join("src").join(src).canonicalize().unwrap());
        }

        cpp_cfg.compile("unwind-cpp");

        // FIXME: https://github.com/alexcrichton/cc-rs/issues/545#issuecomment-679242845
        let mut count = 0;
        for entry in fs::read_dir(&out_dir).unwrap() {
            let file = entry.unwrap().path().canonicalize().unwrap();
            if file.is_file() && file.extension() == Some(OsStr::new("o")) {
                // file name starts with "Unwind-EHABI", "Unwind-seh" or "libunwind"
                let file_name = file.file_name().unwrap().to_str().expect("UTF-8 file name");
                if cpp_sources.iter().any(|f| file_name.starts_with(&f[..f.len() - 4])) {
                    cc_cfg.object(&file);
                    count += 1;
                }
            }
        }
        assert_eq!(cpp_len, count, "Can't get object files from {:?}", &out_dir);

        cc_cfg.compile("unwind");
        out_dir
    }
}