build.rs

use std::env;

fn main() {
    println!("cargo:rerun-if-changed=build.rs");

    let target = env::var("TARGET").unwrap();
    let cwd = env::current_dir().unwrap();

    println!("cargo:compiler-rt={}", cwd.join("compiler-rt").display());

    // Activate libm's unstable features to make full use of Nightly.
    println!("cargo:rustc-cfg=feature=\"unstable\"");

    // Emscripten's runtime includes all the builtins
    if target.contains("emscripten") {
        return;
    }

    // OpenBSD provides compiler_rt by default, use it instead of rebuilding it from source
    if target.contains("openbsd") {
        println!("cargo:rustc-link-search=native=/usr/lib");
        println!("cargo:rustc-link-lib=compiler_rt");
        return;
    }

    // Forcibly enable memory intrinsics on wasm32 & SGX as we don't have a libc to
    // provide them.
    if (target.contains("wasm32") && !target.contains("wasi"))
        || (target.contains("sgx") && target.contains("fortanix"))
    {
        println!("cargo:rustc-cfg=feature=\"mem\"");
    }

    // NOTE we are going to assume that llvm-target, what determines our codegen option, matches the
    // target triple. This is usually correct for our built-in targets but can break in presence of
    // custom targets, which can have arbitrary names.
    let llvm_target = target.split('-').collect::<Vec<_>>();

    // Build missing intrinsics from compiler-rt C source code. If we're
    // mangling names though we assume that we're also in test mode so we don't
    // build anything and we rely on the upstream implementation of compiler-rt
    // functions
    if !cfg!(feature = "mangled-names") && cfg!(any(feature = "c-vendor", feature = "c-system")) {
        // Don't use a C compiler for these targets:
        //
        // * wasm32 - clang 8 for wasm is somewhat hard to come by and it's
        //   unlikely that the C is really that much better than our own Rust.
        // * nvptx - everything is bitcode, not compatible with mixed C/Rust
        // * riscv - the rust-lang/rust distribution container doesn't have a C
        //   compiler nor is cc-rs ready for compilation to riscv (at this
        //   time). This can probably be removed in the future
        if !target.contains("wasm32") && !target.contains("nvptx") && !target.starts_with("riscv") {
            #[cfg(feature = "c-vendor")]
            c_vendor::compile(&llvm_target);
            #[cfg(feature = "c-system")]
            c_system::compile(&llvm_target);
        }
    }

    // To compile intrinsics.rs for thumb targets, where there is no libc
    if llvm_target[0].starts_with("thumb") {
        println!("cargo:rustc-cfg=thumb")
    }

    // compiler-rt `cfg`s away some intrinsics for thumbv6m and thumbv8m.base because
    // these targets do not have full Thumb-2 support but only original Thumb-1.
    // We have to cfg our code accordingly.
    if llvm_target[0] == "thumbv6m" || llvm_target[0] == "thumbv8m.base" {
        println!("cargo:rustc-cfg=thumb_1")
    }

    // Only emit the ARM Linux atomic emulation on pre-ARMv6 architectures.
    if llvm_target[0] == "armv4t" || llvm_target[0] == "armv5te" {
        println!("cargo:rustc-cfg=kernel_user_helpers")
    }
}

#[cfg(any(feature = "c-vendor", feature = "c-system"))]
mod sources {
    use std::collections::BTreeMap;
    use std::env;

    pub struct Sources {
        // SYMBOL -> PATH TO SOURCE
        pub map: BTreeMap<&'static str, &'static str>,
    }

    impl Sources {
        fn new() -> Sources {
            Sources {
                map: BTreeMap::new(),
            }
        }

        fn extend(&mut self, sources: &[(&'static str, &'static str)]) {
            // NOTE Some intrinsics have both a generic implementation (e.g.
            // `floatdidf.c`) and an arch optimized implementation
            // (`x86_64/floatdidf.c`). In those cases, we keep the arch optimized
            // implementation and discard the generic implementation. If we don't
            // and keep both implementations, the linker will yell at us about
            // duplicate symbols!
            for (symbol, src) in sources {
                if src.contains("/") {
                    // Arch-optimized implementation (preferred)
                    self.map.insert(symbol, src);
                } else {
                    // Generic implementation
                    if !self.map.contains_key(symbol) {
                        self.map.insert(symbol, src);
                    }
                }
            }
        }

        fn remove(&mut self, symbols: &[&str]) {
            for symbol in symbols {
                self.map.remove(*symbol).unwrap();
            }
        }
    }

    pub fn get_sources(llvm_target: &[&str]) -> Sources {
        let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
        let target_env = env::var("CARGO_CFG_TARGET_ENV").unwrap();
        let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
        let target_vendor = env::var("CARGO_CFG_TARGET_VENDOR").unwrap();

        let mut sources = Sources::new();
        sources.extend(&[
            ("__absvdi2", "absvdi2.c"),
            ("__absvsi2", "absvsi2.c"),
            ("__addvdi3", "addvdi3.c"),
            ("__addvsi3", "addvsi3.c"),
            ("apple_versioning", "apple_versioning.c"),
            ("__clzdi2", "clzdi2.c"),
            ("__clzsi2", "clzsi2.c"),
            ("__cmpdi2", "cmpdi2.c"),
            ("__ctzdi2", "ctzdi2.c"),
            ("__ctzsi2", "ctzsi2.c"),
            ("__divdc3", "divdc3.c"),
            ("__divsc3", "divsc3.c"),
            ("__divxc3", "divxc3.c"),
            ("__extendhfsf2", "extendhfsf2.c"),
            ("__int_util", "int_util.c"),
            ("__muldc3", "muldc3.c"),
            ("__mulsc3", "mulsc3.c"),
            ("__mulvdi3", "mulvdi3.c"),
            ("__mulvsi3", "mulvsi3.c"),
            ("__mulxc3", "mulxc3.c"),
            ("__negdf2", "negdf2.c"),
            ("__negdi2", "negdi2.c"),
            ("__negsf2", "negsf2.c"),
            ("__negvdi2", "negvdi2.c"),
            ("__negvsi2", "negvsi2.c"),
            ("__paritydi2", "paritydi2.c"),
            ("__paritysi2", "paritysi2.c"),
            ("__popcountdi2", "popcountdi2.c"),
            ("__popcountsi2", "popcountsi2.c"),
            ("__powixf2", "powixf2.c"),
            ("__subvdi3", "subvdi3.c"),
            ("__subvsi3", "subvsi3.c"),
            ("__truncdfhf2", "truncdfhf2.c"),
            ("__truncdfsf2", "truncdfsf2.c"),
            ("__truncsfhf2", "truncsfhf2.c"),
            ("__ucmpdi2", "ucmpdi2.c"),
        ]);

        // When compiling in rustbuild (the rust-lang/rust repo) this library
        // also needs to satisfy intrinsics that jemalloc or C in general may
        // need, so include a few more that aren't typically needed by
        // LLVM/Rust.
        if cfg!(feature = "rustbuild") {
            sources.extend(&[("__ffsdi2", "ffsdi2.c")]);
        }

        // On iOS and 32-bit OSX these are all just empty intrinsics, no need to
        // include them.
        if target_os != "ios" && (target_vendor != "apple" || target_arch != "x86") {
            sources.extend(&[
                ("__absvti2", "absvti2.c"),
                ("__addvti3", "addvti3.c"),
                ("__clzti2", "clzti2.c"),
                ("__cmpti2", "cmpti2.c"),
                ("__ctzti2", "ctzti2.c"),
                ("__ffsti2", "ffsti2.c"),
                ("__mulvti3", "mulvti3.c"),
                ("__negti2", "negti2.c"),
                ("__negvti2", "negvti2.c"),
                ("__parityti2", "parityti2.c"),
                ("__popcountti2", "popcountti2.c"),
                ("__subvti3", "subvti3.c"),
                ("__ucmpti2", "ucmpti2.c"),
            ]);
        }

        if target_vendor == "apple" {
            sources.extend(&[
                ("atomic_flag_clear", "atomic_flag_clear.c"),
                ("atomic_flag_clear_explicit", "atomic_flag_clear_explicit.c"),
                ("atomic_flag_test_and_set", "atomic_flag_test_and_set.c"),
                (
                    "atomic_flag_test_and_set_explicit",
                    "atomic_flag_test_and_set_explicit.c",
                ),
                ("atomic_signal_fence", "atomic_signal_fence.c"),
                ("atomic_thread_fence", "atomic_thread_fence.c"),
            ]);
        }

        if target_env == "msvc" {
            if target_arch == "x86_64" {
                sources.extend(&[
                    ("__floatdisf", "x86_64/floatdisf.c"),
                    ("__floatdixf", "x86_64/floatdixf.c"),
                ]);
            }
        } else {
            // None of these seem to be used on x86_64 windows, and they've all
            // got the wrong ABI anyway, so we want to avoid them.
            if target_os != "windows" {
                if target_arch == "x86_64" {
                    sources.extend(&[
                        ("__floatdisf", "x86_64/floatdisf.c"),
                        ("__floatdixf", "x86_64/floatdixf.c"),
                        ("__floatundidf", "x86_64/floatundidf.S"),
                        ("__floatundisf", "x86_64/floatundisf.S"),
                        ("__floatundixf", "x86_64/floatundixf.S"),
                    ]);
                }
            }

            if target_arch == "x86" {
                sources.extend(&[
                    ("__ashldi3", "i386/ashldi3.S"),
                    ("__ashrdi3", "i386/ashrdi3.S"),
                    ("__divdi3", "i386/divdi3.S"),
                    ("__floatdidf", "i386/floatdidf.S"),
                    ("__floatdisf", "i386/floatdisf.S"),
                    ("__floatdixf", "i386/floatdixf.S"),
                    ("__floatundidf", "i386/floatundidf.S"),
                    ("__floatundisf", "i386/floatundisf.S"),
                    ("__floatundixf", "i386/floatundixf.S"),
                    ("__lshrdi3", "i386/lshrdi3.S"),
                    ("__moddi3", "i386/moddi3.S"),
                    ("__muldi3", "i386/muldi3.S"),
                    ("__udivdi3", "i386/udivdi3.S"),
                    ("__umoddi3", "i386/umoddi3.S"),
                ]);
            }
        }

        if target_arch == "arm" && target_os != "ios" && target_env != "msvc" {
            sources.extend(&[
                ("__aeabi_div0", "arm/aeabi_div0.c"),
                ("__aeabi_drsub", "arm/aeabi_drsub.c"),
                ("__aeabi_frsub", "arm/aeabi_frsub.c"),
                ("__bswapdi2", "arm/bswapdi2.S"),
                ("__bswapsi2", "arm/bswapsi2.S"),
                ("__clzdi2", "arm/clzdi2.S"),
                ("__clzsi2", "arm/clzsi2.S"),
                ("__divmodsi4", "arm/divmodsi4.S"),
                ("__divsi3", "arm/divsi3.S"),
                ("__modsi3", "arm/modsi3.S"),
                ("__switch16", "arm/switch16.S"),
                ("__switch32", "arm/switch32.S"),
                ("__switch8", "arm/switch8.S"),
                ("__switchu8", "arm/switchu8.S"),
                ("__sync_synchronize", "arm/sync_synchronize.S"),
                ("__udivmodsi4", "arm/udivmodsi4.S"),
                ("__udivsi3", "arm/udivsi3.S"),
                ("__umodsi3", "arm/umodsi3.S"),
            ]);

            if target_os == "freebsd" {
                sources.extend(&[("__clear_cache", "clear_cache.c")]);
            }

            // First of all aeabi_cdcmp and aeabi_cfcmp are never called by LLVM.
            // Second are little-endian only, so build fail on big-endian targets.
            // Temporally workaround: exclude these files for big-endian targets.
            if !llvm_target[0].starts_with("thumbeb") && !llvm_target[0].starts_with("armeb") {
                sources.extend(&[
                    ("__aeabi_cdcmp", "arm/aeabi_cdcmp.S"),
                    ("__aeabi_cdcmpeq_check_nan", "arm/aeabi_cdcmpeq_check_nan.c"),
                    ("__aeabi_cfcmp", "arm/aeabi_cfcmp.S"),
                    ("__aeabi_cfcmpeq_check_nan", "arm/aeabi_cfcmpeq_check_nan.c"),
                ]);
            }
        }

        if llvm_target[0] == "armv7" {
            sources.extend(&[
                ("__sync_fetch_and_add_4", "arm/sync_fetch_and_add_4.S"),
                ("__sync_fetch_and_add_8", "arm/sync_fetch_and_add_8.S"),
                ("__sync_fetch_and_and_4", "arm/sync_fetch_and_and_4.S"),
                ("__sync_fetch_and_and_8", "arm/sync_fetch_and_and_8.S"),
                ("__sync_fetch_and_max_4", "arm/sync_fetch_and_max_4.S"),
                ("__sync_fetch_and_max_8", "arm/sync_fetch_and_max_8.S"),
                ("__sync_fetch_and_min_4", "arm/sync_fetch_and_min_4.S"),
                ("__sync_fetch_and_min_8", "arm/sync_fetch_and_min_8.S"),
                ("__sync_fetch_and_nand_4", "arm/sync_fetch_and_nand_4.S"),
                ("__sync_fetch_and_nand_8", "arm/sync_fetch_and_nand_8.S"),
                ("__sync_fetch_and_or_4", "arm/sync_fetch_and_or_4.S"),
                ("__sync_fetch_and_or_8", "arm/sync_fetch_and_or_8.S"),
                ("__sync_fetch_and_sub_4", "arm/sync_fetch_and_sub_4.S"),
                ("__sync_fetch_and_sub_8", "arm/sync_fetch_and_sub_8.S"),
                ("__sync_fetch_and_umax_4", "arm/sync_fetch_and_umax_4.S"),
                ("__sync_fetch_and_umax_8", "arm/sync_fetch_and_umax_8.S"),
                ("__sync_fetch_and_umin_4", "arm/sync_fetch_and_umin_4.S"),
                ("__sync_fetch_and_umin_8", "arm/sync_fetch_and_umin_8.S"),
                ("__sync_fetch_and_xor_4", "arm/sync_fetch_and_xor_4.S"),
                ("__sync_fetch_and_xor_8", "arm/sync_fetch_and_xor_8.S"),
            ]);
        }

        if llvm_target.last().unwrap().ends_with("eabihf") {
            if !llvm_target[0].starts_with("thumbv7em")
                && !llvm_target[0].starts_with("thumbv8m.main")
            {
                // The FPU option chosen for these architectures in cc-rs, ie:
                //     -mfpu=fpv4-sp-d16 for thumbv7em
                //     -mfpu=fpv5-sp-d16 for thumbv8m.main
                // do not support double precision floating points conversions so the files
                // that include such instructions are not included for these targets.
                sources.extend(&[
                    ("__fixdfsivfp", "arm/fixdfsivfp.S"),
                    ("__fixunsdfsivfp", "arm/fixunsdfsivfp.S"),
                    ("__floatsidfvfp", "arm/floatsidfvfp.S"),
                    ("__floatunssidfvfp", "arm/floatunssidfvfp.S"),
                ]);
            }

            sources.extend(&[
                ("__fixsfsivfp", "arm/fixsfsivfp.S"),
                ("__fixunssfsivfp", "arm/fixunssfsivfp.S"),
                ("__floatsisfvfp", "arm/floatsisfvfp.S"),
                ("__floatunssisfvfp", "arm/floatunssisfvfp.S"),
                ("__floatunssisfvfp", "arm/floatunssisfvfp.S"),
                ("__restore_vfp_d8_d15_regs", "arm/restore_vfp_d8_d15_regs.S"),
                ("__save_vfp_d8_d15_regs", "arm/save_vfp_d8_d15_regs.S"),
                ("__negdf2vfp", "arm/negdf2vfp.S"),
                ("__negsf2vfp", "arm/negsf2vfp.S"),
            ]);
        }

        if target_arch == "aarch64" {
            sources.extend(&[
                ("__comparetf2", "comparetf2.c"),
                ("__extenddftf2", "extenddftf2.c"),
                ("__extendsftf2", "extendsftf2.c"),
                ("__fixtfdi", "fixtfdi.c"),
                ("__fixtfsi", "fixtfsi.c"),
                ("__fixtfti", "fixtfti.c"),
                ("__fixunstfdi", "fixunstfdi.c"),
                ("__fixunstfsi", "fixunstfsi.c"),
                ("__fixunstfti", "fixunstfti.c"),
                ("__floatditf", "floatditf.c"),
                ("__floatsitf", "floatsitf.c"),
                ("__floatunditf", "floatunditf.c"),
                ("__floatunsitf", "floatunsitf.c"),
                ("__trunctfdf2", "trunctfdf2.c"),
                ("__trunctfsf2", "trunctfsf2.c"),
            ]);

            if target_os != "windows" {
                sources.extend(&[("__multc3", "multc3.c")]);
            }
        }

        // Remove the assembly implementations that won't compile for the target
        if llvm_target[0] == "thumbv6m" || llvm_target[0] == "thumbv8m.base" {
            let mut to_remove = Vec::new();
            for (k, v) in sources.map.iter() {
                if v.ends_with(".S") {
                    to_remove.push(*k);
                }
            }
            sources.remove(&to_remove);

            // But use some generic implementations where possible
            sources.extend(&[("__clzdi2", "clzdi2.c"), ("__clzsi2", "clzsi2.c")])
        }

        if llvm_target[0] == "thumbv7m" || llvm_target[0] == "thumbv7em" {
            sources.remove(&["__aeabi_cdcmp", "__aeabi_cfcmp"]);
        }

        sources
    }
}

#[cfg(feature = "c-vendor")]
mod c_vendor {
    extern crate cc;

    use sources;
    use std::env;
    use std::path::PathBuf;

    /// Compile intrinsics from the compiler-rt C source code
    pub fn compile(llvm_target: &[&str]) {
        let target_env = env::var("CARGO_CFG_TARGET_ENV").unwrap();
        let cfg = &mut cc::Build::new();
        cfg.warnings(false);

        if target_env == "msvc" {
            // Don't pull in extra libraries on MSVC
            cfg.flag("/Zl");

            // Emulate C99 and C++11's __func__ for MSVC prior to 2013 CTP
            cfg.define("__func__", Some("__FUNCTION__"));
        } else {
            // Turn off various features of gcc and such, mostly copying
            // compiler-rt's build system already
            cfg.flag("-fno-builtin");
            cfg.flag("-fvisibility=hidden");
            cfg.flag("-ffreestanding");
            // Avoid the following warning appearing once **per file**:
            // clang: warning: optimization flag '-fomit-frame-pointer' is not supported for target 'armv7' [-Wignored-optimization-argument]
            //
            // Note that compiler-rt's build system also checks
            //
            // `check_cxx_compiler_flag(-fomit-frame-pointer COMPILER_RT_HAS_FOMIT_FRAME_POINTER_FLAG)`
            //
            // in https://github.com/rust-lang/compiler-rt/blob/c8fbcb3/cmake/config-ix.cmake#L19.
            cfg.flag_if_supported("-fomit-frame-pointer");
            cfg.define("VISIBILITY_HIDDEN", None);
        }

        // When compiling the C code we require the user to tell us where the
        // source code is, and this is largely done so when we're compiling as
        // part of rust-lang/rust we can use the same llvm-project repository as
        // rust-lang/rust.
        let root = match env::var_os("RUST_COMPILER_RT_ROOT") {
            Some(s) => PathBuf::from(s),
            None => panic!("RUST_COMPILER_RT_ROOT is not set"),
        };
        if !root.exists() {
            panic!("RUST_COMPILER_RT_ROOT={} does not exist", root.display());
        }

        // Support deterministic builds by remapping the __FILE__ prefix if the
        // compiler supports it.  This fixes the nondeterminism caused by the
        // use of that macro in lib/builtins/int_util.h in compiler-rt.
        cfg.flag_if_supported(&format!("-ffile-prefix-map={}=.", root.display()));

        let sources = sources::get_sources(llvm_target);
        let src_dir = root.join("lib/builtins");
        for (sym, src) in sources.map.iter() {
            let src = src_dir.join(src);
            cfg.file(&src);
            println!("cargo:rerun-if-changed={}", src.display());
            println!("cargo:rustc-cfg={}=\"optimized-c\"", sym);
        }

        cfg.compile("libcompiler-rt.a");
    }
}

#[cfg(feature = "c-system")]
mod c_system {
    extern crate ar;

    use std::collections::HashMap;
    use std::env;
    use std::fs::File;
    use std::path::{Path, PathBuf};
    use std::process::{Command, Output};
    use std::str;

    use sources;

    fn success_output(err: &str, cmd: &mut Command) -> Output {
        let output = cmd.output().expect(err);
        let status = output.status;
        if !status.success() {
            panic!("{}: {:?}", err, status.code());
        }
        output
    }

    // This can be obtained by adding the line:
    //   message(STATUS "All builtin supported architectures: ${ALL_BUILTIN_SUPPORTED_ARCH}")
    // to the bottom of compiler-rt/cmake/builtin-config-ix.cmake, then running
    // cmake and looking at the output.
    const ALL_SUPPORTED_ARCHES : &'static str = "i386;x86_64;arm;armhf;armv6m;armv7m;armv7em;armv7;armv7s;armv7k;aarch64;hexagon;mips;mipsel;mips64;mips64el;powerpc64;powerpc64le;riscv32;riscv64;wasm32;wasm64";

    // This function recreates the logic of getArchNameForCompilerRTLib,
    // defined in clang/lib/Driver/ToolChain.cpp.
    fn get_arch_name_for_compiler_rtlib() -> String {
        let target = env::var("TARGET").unwrap();
        let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
        let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
        let r = match target_arch.as_str() {
            "arm" => {
                if target.ends_with("eabihf") && target_os != "windows" {
                    "armhf"
                } else {
                    "arm"
                }
            }
            "x86" => {
                if target_os == "android" {
                    "i686"
                } else {
                    "i386"
                }
            }
            _ => target_arch.as_str(),
        };
        r.to_string()
    }

    fn find_library<I>(dirs: I, libname: &str) -> Result<PathBuf, Vec<String>>
    where
        I: Iterator<Item = PathBuf>,
    {
        let mut paths = Vec::new();
        for dir in dirs {
            let try_path = dir.join(format!("lib{}.a", libname));
            if try_path.exists() {
                return Ok(try_path.to_path_buf());
            } else {
                paths.push(format!("{:?}", try_path))
            }
        }
        Err(paths)
    }

    /// Link against system clang runtime libraries
    pub fn compile(llvm_target: &[&str]) {
        let target = env::var("TARGET").unwrap();
        let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
        let compiler_rt_arch = get_arch_name_for_compiler_rtlib();
        let out_dir = env::var("OUT_DIR").unwrap();

        if ALL_SUPPORTED_ARCHES
            .split(";")
            .find(|x| *x == compiler_rt_arch)
            == None
        {
            return;
        }

        println!("cargo:rerun-if-env-changed=CLANG");
        println!("cargo:rerun-if-env-changed=LLVM_CONFIG");

        let fullpath = if let Ok(clang) = env::var("CLANG") {
            let output = success_output(
                "failed to find clang's compiler-rt",
                Command::new(clang)
                    .arg(format!("--target={}", target))
                    .arg("--rtlib=compiler-rt")
                    .arg("--print-libgcc-file-name"),
            );
            let path = str::from_utf8(&output.stdout).unwrap().trim_end();
            Path::new(path).to_path_buf()
        } else if let Ok(llvm_config) = env::var("LLVM_CONFIG") {
            // fallback if clang is not installed
            let (subpath, libname) = match target_os.as_str() {
                "linux" => ("linux", format!("clang_rt.builtins-{}", &compiler_rt_arch)),
                "macos" => ("darwin", "clang_rt.builtins_osx_dynamic".to_string()),
                _ => panic!("unsupported target os: {}", target_os),
            };
            let output = success_output(
                "failed to find llvm-config's lib dir",
                Command::new(llvm_config).arg("--libdir"),
            );
            let libdir = str::from_utf8(&output.stdout).unwrap().trim_end();
            let paths = std::fs::read_dir(Path::new(libdir).join("clang"))
                .unwrap()
                .map(|e| e.unwrap().path().join("lib").join(subpath));
            match find_library(paths, &libname) {
                Ok(p) => p,
                Err(paths) => panic!(
                    "failed to find llvm-config's compiler-rt: {}",
                    paths.join(":")
                ),
            }
        } else {
            panic!("neither CLANG nor LLVM_CONFIG could be read");
        };

        let mut index = 0;
        let mut files = HashMap::new();
        let mut orig = ar::Archive::new(File::open(&fullpath).unwrap());
        while let Some(entry_result) = orig.next_entry() {
            let entry = entry_result.unwrap();
            let name = str::from_utf8(entry.header().identifier()).unwrap();
            files.insert(name.to_owned(), index);
            index += 1;
        }

        let sources = sources::get_sources(llvm_target);
        let mut new =
            ar::Builder::new(File::create(Path::new(&out_dir).join("libcompiler-rt.a")).unwrap());
        for (sym, _src) in sources.map.iter() {
            let &i = {
                let sym_ = if sym.starts_with("__") {
                    &sym[2..]
                } else {
                    &sym
                };
                match files.get(&format!("{}.c.o", sym_)) {
                    Some(i) => i,
                    None => match files.get(&format!("{}.S.o", sym_)) {
                        Some(i) => i,
                        None => panic!("could not find expected symbol {} in {:?}", sym, &fullpath),
                    },
                }
            };
            let mut entry = orig.jump_to_entry(i).unwrap();
            // TODO: ar really should have an append_entry to avoid the clone
            new.append(&entry.header().clone(), &mut entry).unwrap();
            println!("cargo:rustc-cfg={}=\"optimized-c\"", sym);
        }

        println!("cargo:rustc-link-search=native={}", out_dir);
        println!("cargo:rustc-link-lib=static={}", "compiler-rt");
    }
}