vendor/compiler_builtins/build.rs

   1 use std::env;
   2
   3 fn main() {
   4     println!("cargo:rerun-if-changed=build.rs");
   5
   6     let target = env::var("TARGET").unwrap();
   7     let cwd = env::current_dir().unwrap();
   8
   9     println!("cargo:compiler-rt={}", cwd.join("compiler-rt").display());
  10
  11     // Activate libm's unstable features to make full use of Nightly.
  12     println!("cargo:rustc-cfg=feature=\"unstable\"");
  13
  14     // Emscripten's runtime includes all the builtins
  15     if target.contains("emscripten") {
  16         return;
  17     }
  18
  19     // OpenBSD provides compiler_rt by default, use it instead of rebuilding it from source
  20     if target.contains("openbsd") {
  21         println!("cargo:rustc-link-search=native=/usr/lib");
  22         println!("cargo:rustc-link-lib=compiler_rt");
  23         return;
  24     }
  25
  26     // Forcibly enable memory intrinsics on wasm & SGX as we don't have a libc to
  27     // provide them.
  28     if (target.contains("wasm") && !target.contains("wasi"))
  29         || (target.contains("sgx") && target.contains("fortanix"))
  30         || target.contains("-none")
  31         || target.contains("nvptx")
  32     {
  33         println!("cargo:rustc-cfg=feature=\"mem\"");
  34     }
  35
  36     // These targets have hardware unaligned access support.
  37     if target.contains("x86_64")
  38         || target.contains("i686")
  39         || target.contains("aarch64")
  40         || target.contains("bpf")
  41     {
  42         println!("cargo:rustc-cfg=feature=\"mem-unaligned\"");
  43     }
  44
  45     // NOTE we are going to assume that llvm-target, what determines our codegen option, matches the
  46     // target triple. This is usually correct for our built-in targets but can break in presence of
  47     // custom targets, which can have arbitrary names.
  48     let llvm_target = target.split('-').collect::<Vec<_>>();
  49
  50     // Build missing intrinsics from compiler-rt C source code. If we're
  51     // mangling names though we assume that we're also in test mode so we don't
  52     // build anything and we rely on the upstream implementation of compiler-rt
  53     // functions
  54     if !cfg!(feature = "mangled-names") && cfg!(feature = "c") {
  55         // Don't use a C compiler for these targets:
  56         //
  57         // * wasm - clang for wasm is somewhat hard to come by and it's
  58         //   unlikely that the C is really that much better than our own Rust.
  59         // * nvptx - everything is bitcode, not compatible with mixed C/Rust
  60         // * riscv - the rust-lang/rust distribution container doesn't have a C
  61         //   compiler nor is cc-rs ready for compilation to riscv (at this
  62         //   time). This can probably be removed in the future
  63         if !target.contains("wasm") && !target.contains("nvptx") && !target.starts_with("riscv") {
  64             #[cfg(feature = "c")]
  65             c::compile(&llvm_target, &target);
  66         }
  67     }
  68
  69     // To compile intrinsics.rs for thumb targets, where there is no libc
  70     if llvm_target[0].starts_with("thumb") {
  71         println!("cargo:rustc-cfg=thumb")
  72     }
  73
  74     // compiler-rt `cfg`s away some intrinsics for thumbv6m and thumbv8m.base because
  75     // these targets do not have full Thumb-2 support but only original Thumb-1.
  76     // We have to cfg our code accordingly.
  77     if llvm_target[0] == "thumbv6m" || llvm_target[0] == "thumbv8m.base" {
  78         println!("cargo:rustc-cfg=thumb_1")
  79     }
  80
  81     // Only emit the ARM Linux atomic emulation on pre-ARMv6 architectures. This
  82     // includes the old androideabi. It is deprecated but it is available as a
  83     // rustc target (arm-linux-androideabi).
  84     if llvm_target[0] == "armv4t"
  85         || llvm_target[0] == "armv5te"
  86         || target == "arm-linux-androideabi"
  87     {
  88         println!("cargo:rustc-cfg=kernel_user_helpers")
  89     }
  90 }
  91
  92 #[cfg(feature = "c")]
  93 mod c {
  94     extern crate cc;
  95
  96     use std::collections::{BTreeMap, HashSet};
  97     use std::env;
  98     use std::fs::File;
  99     use std::io::Write;
 100     use std::path::{Path, PathBuf};
 101
 102     struct Sources {
 103         // SYMBOL -> PATH TO SOURCE
 104         map: BTreeMap<&'static str, &'static str>,
 105     }
 106
 107     impl Sources {
 108         fn new() -> Sources {
 109             Sources {
 110                 map: BTreeMap::new(),
 111             }
 112         }
 113
 114         fn extend(&mut self, sources: &[(&'static str, &'static str)]) {
 115             // NOTE Some intrinsics have both a generic implementation (e.g.
 116             // `floatdidf.c`) and an arch optimized implementation
 117             // (`x86_64/floatdidf.c`). In those cases, we keep the arch optimized
 118             // implementation and discard the generic implementation. If we don't
 119             // and keep both implementations, the linker will yell at us about
 120             // duplicate symbols!
 121             for (symbol, src) in sources {
 122                 if src.contains("/") {
 123                     // Arch-optimized implementation (preferred)
 124                     self.map.insert(symbol, src);
 125                 } else {
 126                     // Generic implementation
 127                     if !self.map.contains_key(symbol) {
 128                         self.map.insert(symbol, src);
 129                     }
 130                 }
 131             }
 132         }
 133
 134         fn remove(&mut self, symbols: &[&str]) {
 135             for symbol in symbols {
 136                 self.map.remove(*symbol).unwrap();
 137             }
 138         }
 139     }
 140
 141     /// Compile intrinsics from the compiler-rt C source code
 142     pub fn compile(llvm_target: &[&str], target: &String) {
 143         let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
 144         let target_env = env::var("CARGO_CFG_TARGET_ENV").unwrap();
 145         let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
 146         let target_vendor = env::var("CARGO_CFG_TARGET_VENDOR").unwrap();
 147         let mut consider_float_intrinsics = true;
 148         let cfg = &mut cc::Build::new();
 149
 150         // AArch64 GCCs exit with an error condition when they encounter any kind of floating point
 151         // code if the `nofp` and/or `nosimd` compiler flags have been set.
 152         //
 153         // Therefore, evaluate if those flags are present and set a boolean that causes any
 154         // compiler-rt intrinsics that contain floating point source to be excluded for this target.
 155         if target_arch == "aarch64" {
 156             let cflags_key = String::from("CFLAGS_") + &(target.to_owned().replace("-", "_"));
 157             if let Ok(cflags_value) = env::var(cflags_key) {
 158                 if cflags_value.contains("+nofp") || cflags_value.contains("+nosimd") {
 159                     consider_float_intrinsics = false;
 160                 }
 161             }
 162         }
 163
 164         cfg.warnings(false);
 165
 166         if target_env == "msvc" {
 167             // Don't pull in extra libraries on MSVC
 168             cfg.flag("/Zl");
 169
 170             // Emulate C99 and C++11's __func__ for MSVC prior to 2013 CTP
 171             cfg.define("__func__", Some("__FUNCTION__"));
 172         } else {
 173             // Turn off various features of gcc and such, mostly copying
 174             // compiler-rt's build system already
 175             cfg.flag("-fno-builtin");
 176             cfg.flag("-fvisibility=hidden");
 177             cfg.flag("-ffreestanding");
 178             // Avoid the following warning appearing once **per file**:
 179             // clang: warning: optimization flag '-fomit-frame-pointer' is not supported for target 'armv7' [-Wignored-optimization-argument]
 180             //
 181             // Note that compiler-rt's build system also checks
 182             //
 183             // `check_cxx_compiler_flag(-fomit-frame-pointer COMPILER_RT_HAS_FOMIT_FRAME_POINTER_FLAG)`
 184             //
 185             // in https://github.com/rust-lang/compiler-rt/blob/c8fbcb3/cmake/config-ix.cmake#L19.
 186             cfg.flag_if_supported("-fomit-frame-pointer");
 187             cfg.define("VISIBILITY_HIDDEN", None);
 188         }
 189
 190         let mut sources = Sources::new();
 191         sources.extend(&[
 192             ("__absvdi2", "absvdi2.c"),
 193             ("__absvsi2", "absvsi2.c"),
 194             ("__addvdi3", "addvdi3.c"),
 195             ("__addvsi3", "addvsi3.c"),
 196             ("__clzdi2", "clzdi2.c"),
 197             ("__clzsi2", "clzsi2.c"),
 198             ("__cmpdi2", "cmpdi2.c"),
 199             ("__ctzdi2", "ctzdi2.c"),
 200             ("__ctzsi2", "ctzsi2.c"),
 201             ("__int_util", "int_util.c"),
 202             ("__mulvdi3", "mulvdi3.c"),
 203             ("__mulvsi3", "mulvsi3.c"),
 204             ("__negdi2", "negdi2.c"),
 205             ("__negvdi2", "negvdi2.c"),
 206             ("__negvsi2", "negvsi2.c"),
 207             ("__paritydi2", "paritydi2.c"),
 208             ("__paritysi2", "paritysi2.c"),
 209             ("__popcountdi2", "popcountdi2.c"),
 210             ("__popcountsi2", "popcountsi2.c"),
 211             ("__subvdi3", "subvdi3.c"),
 212             ("__subvsi3", "subvsi3.c"),
 213             ("__ucmpdi2", "ucmpdi2.c"),
 214         ]);
 215
 216         if consider_float_intrinsics {
 217             sources.extend(&[
 218                 ("__divdc3", "divdc3.c"),
 219                 ("__divsc3", "divsc3.c"),
 220                 ("__divxc3", "divxc3.c"),
 221                 ("__extendhfsf2", "extendhfsf2.c"),
 222                 ("__muldc3", "muldc3.c"),
 223                 ("__mulsc3", "mulsc3.c"),
 224                 ("__mulxc3", "mulxc3.c"),
 225                 ("__negdf2", "negdf2.c"),
 226                 ("__negsf2", "negsf2.c"),
 227                 ("__powixf2", "powixf2.c"),
 228                 ("__truncdfhf2", "truncdfhf2.c"),
 229                 ("__truncsfhf2", "truncsfhf2.c"),
 230             ]);
 231         }
 232
 233         // When compiling in rustbuild (the rust-lang/rust repo) this library
 234         // also needs to satisfy intrinsics that jemalloc or C in general may
 235         // need, so include a few more that aren't typically needed by
 236         // LLVM/Rust.
 237         if cfg!(feature = "rustbuild") {
 238             sources.extend(&[("__ffsdi2", "ffsdi2.c")]);
 239         }
 240
 241         // On iOS and 32-bit OSX these are all just empty intrinsics, no need to
 242         // include them.
 243         if target_os != "ios"
 244             && target_os != "watchos"
 245             && (target_vendor != "apple" || target_arch != "x86")
 246         {
 247             sources.extend(&[
 248                 ("__absvti2", "absvti2.c"),
 249                 ("__addvti3", "addvti3.c"),
 250                 ("__clzti2", "clzti2.c"),
 251                 ("__cmpti2", "cmpti2.c"),
 252                 ("__ctzti2", "ctzti2.c"),
 253                 ("__ffsti2", "ffsti2.c"),
 254                 ("__mulvti3", "mulvti3.c"),
 255                 ("__negti2", "negti2.c"),
 256                 ("__parityti2", "parityti2.c"),
 257                 ("__popcountti2", "popcountti2.c"),
 258                 ("__subvti3", "subvti3.c"),
 259                 ("__ucmpti2", "ucmpti2.c"),
 260             ]);
 261
 262             if consider_float_intrinsics {
 263                 sources.extend(&[("__negvti2", "negvti2.c")]);
 264             }
 265         }
 266
 267         if target_vendor == "apple" {
 268             sources.extend(&[
 269                 ("atomic_flag_clear", "atomic_flag_clear.c"),
 270                 ("atomic_flag_clear_explicit", "atomic_flag_clear_explicit.c"),
 271                 ("atomic_flag_test_and_set", "atomic_flag_test_and_set.c"),
 272                 (
 273                     "atomic_flag_test_and_set_explicit",
 274                     "atomic_flag_test_and_set_explicit.c",
 275                 ),
 276                 ("atomic_signal_fence", "atomic_signal_fence.c"),
 277                 ("atomic_thread_fence", "atomic_thread_fence.c"),
 278             ]);
 279         }
 280
 281         if target_env == "msvc" {
 282             if target_arch == "x86_64" {
 283                 sources.extend(&[("__floatdixf", "x86_64/floatdixf.c")]);
 284             }
 285         } else {
 286             // None of these seem to be used on x86_64 windows, and they've all
 287             // got the wrong ABI anyway, so we want to avoid them.
 288             if target_os != "windows" {
 289                 if target_arch == "x86_64" {
 290                     sources.extend(&[
 291                         ("__floatdixf", "x86_64/floatdixf.c"),
 292                         ("__floatundixf", "x86_64/floatundixf.S"),
 293                     ]);
 294                 }
 295             }
 296
 297             if target_arch == "x86" {
 298                 sources.extend(&[
 299                     ("__ashldi3", "i386/ashldi3.S"),
 300                     ("__ashrdi3", "i386/ashrdi3.S"),
 301                     ("__divdi3", "i386/divdi3.S"),
 302                     ("__floatdixf", "i386/floatdixf.S"),
 303                     ("__floatundixf", "i386/floatundixf.S"),
 304                     ("__lshrdi3", "i386/lshrdi3.S"),
 305                     ("__moddi3", "i386/moddi3.S"),
 306                     ("__muldi3", "i386/muldi3.S"),
 307                     ("__udivdi3", "i386/udivdi3.S"),
 308                     ("__umoddi3", "i386/umoddi3.S"),
 309                 ]);
 310             }
 311         }
 312
 313         if target_arch == "arm"
 314             && target_os != "ios"
 315             && target_os != "watchos"
 316             && target_env != "msvc"
 317         {
 318             sources.extend(&[
 319                 ("__aeabi_div0", "arm/aeabi_div0.c"),
 320                 ("__aeabi_drsub", "arm/aeabi_drsub.c"),
 321                 ("__aeabi_frsub", "arm/aeabi_frsub.c"),
 322                 ("__bswapdi2", "arm/bswapdi2.S"),
 323                 ("__bswapsi2", "arm/bswapsi2.S"),
 324                 ("__clzdi2", "arm/clzdi2.S"),
 325                 ("__clzsi2", "arm/clzsi2.S"),
 326                 ("__divmodsi4", "arm/divmodsi4.S"),
 327                 ("__divsi3", "arm/divsi3.S"),
 328                 ("__modsi3", "arm/modsi3.S"),
 329                 ("__switch16", "arm/switch16.S"),
 330                 ("__switch32", "arm/switch32.S"),
 331                 ("__switch8", "arm/switch8.S"),
 332                 ("__switchu8", "arm/switchu8.S"),
 333                 ("__sync_synchronize", "arm/sync_synchronize.S"),
 334                 ("__udivmodsi4", "arm/udivmodsi4.S"),
 335                 ("__udivsi3", "arm/udivsi3.S"),
 336                 ("__umodsi3", "arm/umodsi3.S"),
 337             ]);
 338
 339             if target_os == "freebsd" {
 340                 sources.extend(&[("__clear_cache", "clear_cache.c")]);
 341             }
 342
 343             // First of all aeabi_cdcmp and aeabi_cfcmp are never called by LLVM.
 344             // Second are little-endian only, so build fail on big-endian targets.
 345             // Temporally workaround: exclude these files for big-endian targets.
 346             if !llvm_target[0].starts_with("thumbeb") && !llvm_target[0].starts_with("armeb") {
 347                 sources.extend(&[
 348                     ("__aeabi_cdcmp", "arm/aeabi_cdcmp.S"),
 349                     ("__aeabi_cdcmpeq_check_nan", "arm/aeabi_cdcmpeq_check_nan.c"),
 350                     ("__aeabi_cfcmp", "arm/aeabi_cfcmp.S"),
 351                     ("__aeabi_cfcmpeq_check_nan", "arm/aeabi_cfcmpeq_check_nan.c"),
 352                 ]);
 353             }
 354         }
 355
 356         if llvm_target[0] == "armv7" {
 357             sources.extend(&[
 358                 ("__sync_fetch_and_add_4", "arm/sync_fetch_and_add_4.S"),
 359                 ("__sync_fetch_and_add_8", "arm/sync_fetch_and_add_8.S"),
 360                 ("__sync_fetch_and_and_4", "arm/sync_fetch_and_and_4.S"),
 361                 ("__sync_fetch_and_and_8", "arm/sync_fetch_and_and_8.S"),
 362                 ("__sync_fetch_and_max_4", "arm/sync_fetch_and_max_4.S"),
 363                 ("__sync_fetch_and_max_8", "arm/sync_fetch_and_max_8.S"),
 364                 ("__sync_fetch_and_min_4", "arm/sync_fetch_and_min_4.S"),
 365                 ("__sync_fetch_and_min_8", "arm/sync_fetch_and_min_8.S"),
 366                 ("__sync_fetch_and_nand_4", "arm/sync_fetch_and_nand_4.S"),
 367                 ("__sync_fetch_and_nand_8", "arm/sync_fetch_and_nand_8.S"),
 368                 ("__sync_fetch_and_or_4", "arm/sync_fetch_and_or_4.S"),
 369                 ("__sync_fetch_and_or_8", "arm/sync_fetch_and_or_8.S"),
 370                 ("__sync_fetch_and_sub_4", "arm/sync_fetch_and_sub_4.S"),
 371                 ("__sync_fetch_and_sub_8", "arm/sync_fetch_and_sub_8.S"),
 372                 ("__sync_fetch_and_umax_4", "arm/sync_fetch_and_umax_4.S"),
 373                 ("__sync_fetch_and_umax_8", "arm/sync_fetch_and_umax_8.S"),
 374                 ("__sync_fetch_and_umin_4", "arm/sync_fetch_and_umin_4.S"),
 375                 ("__sync_fetch_and_umin_8", "arm/sync_fetch_and_umin_8.S"),
 376                 ("__sync_fetch_and_xor_4", "arm/sync_fetch_and_xor_4.S"),
 377                 ("__sync_fetch_and_xor_8", "arm/sync_fetch_and_xor_8.S"),
 378             ]);
 379         }
 380
 381         if llvm_target.last().unwrap().ends_with("eabihf") {
 382             if !llvm_target[0].starts_with("thumbv7em")
 383                 && !llvm_target[0].starts_with("thumbv8m.main")
 384             {
 385                 // The FPU option chosen for these architectures in cc-rs, ie:
 386                 //     -mfpu=fpv4-sp-d16 for thumbv7em
 387                 //     -mfpu=fpv5-sp-d16 for thumbv8m.main
 388                 // do not support double precision floating points conversions so the files
 389                 // that include such instructions are not included for these targets.
 390                 sources.extend(&[
 391                     ("__fixdfsivfp", "arm/fixdfsivfp.S"),
 392                     ("__fixunsdfsivfp", "arm/fixunsdfsivfp.S"),
 393                     ("__floatsidfvfp", "arm/floatsidfvfp.S"),
 394                     ("__floatunssidfvfp", "arm/floatunssidfvfp.S"),
 395                 ]);
 396             }
 397
 398             sources.extend(&[
 399                 ("__fixsfsivfp", "arm/fixsfsivfp.S"),
 400                 ("__fixunssfsivfp", "arm/fixunssfsivfp.S"),
 401                 ("__floatsisfvfp", "arm/floatsisfvfp.S"),
 402                 ("__floatunssisfvfp", "arm/floatunssisfvfp.S"),
 403                 ("__floatunssisfvfp", "arm/floatunssisfvfp.S"),
 404                 ("__restore_vfp_d8_d15_regs", "arm/restore_vfp_d8_d15_regs.S"),
 405                 ("__save_vfp_d8_d15_regs", "arm/save_vfp_d8_d15_regs.S"),
 406                 ("__negdf2vfp", "arm/negdf2vfp.S"),
 407                 ("__negsf2vfp", "arm/negsf2vfp.S"),
 408             ]);
 409         }
 410
 411         if target_arch == "aarch64" && consider_float_intrinsics {
 412             sources.extend(&[
 413                 ("__comparetf2", "comparetf2.c"),
 414                 ("__extenddftf2", "extenddftf2.c"),
 415                 ("__extendsftf2", "extendsftf2.c"),
 416                 ("__fixtfdi", "fixtfdi.c"),
 417                 ("__fixtfsi", "fixtfsi.c"),
 418                 ("__fixtfti", "fixtfti.c"),
 419                 ("__fixunstfdi", "fixunstfdi.c"),
 420                 ("__fixunstfsi", "fixunstfsi.c"),
 421                 ("__fixunstfti", "fixunstfti.c"),
 422                 ("__floatditf", "floatditf.c"),
 423                 ("__floatsitf", "floatsitf.c"),
 424                 ("__floatunditf", "floatunditf.c"),
 425                 ("__floatunsitf", "floatunsitf.c"),
 426                 ("__trunctfdf2", "trunctfdf2.c"),
 427                 ("__trunctfsf2", "trunctfsf2.c"),
 428                 ("__addtf3", "addtf3.c"),
 429                 ("__multf3", "multf3.c"),
 430                 ("__subtf3", "subtf3.c"),
 431                 ("__divtf3", "divtf3.c"),
 432                 ("__powitf2", "powitf2.c"),
 433                 ("__fe_getround", "fp_mode.c"),
 434                 ("__fe_raise_inexact", "fp_mode.c"),
 435             ]);
 436
 437             if target_os != "windows" {
 438                 sources.extend(&[("__multc3", "multc3.c")]);
 439             }
 440         }
 441
 442         if target_arch == "mips" {
 443             sources.extend(&[("__bswapsi2", "bswapsi2.c")]);
 444         }
 445
 446         if target_arch == "mips64" {
 447             sources.extend(&[
 448                 ("__extenddftf2", "extenddftf2.c"),
 449                 ("__netf2", "comparetf2.c"),
 450                 ("__addtf3", "addtf3.c"),
 451                 ("__multf3", "multf3.c"),
 452                 ("__subtf3", "subtf3.c"),
 453                 ("__fixtfsi", "fixtfsi.c"),
 454                 ("__floatsitf", "floatsitf.c"),
 455                 ("__fixunstfsi", "fixunstfsi.c"),
 456                 ("__floatunsitf", "floatunsitf.c"),
 457                 ("__fe_getround", "fp_mode.c"),
 458                 ("__divtf3", "divtf3.c"),
 459                 ("__trunctfdf2", "trunctfdf2.c"),
 460             ]);
 461         }
 462
 463         // Remove the assembly implementations that won't compile for the target
 464         if llvm_target[0] == "thumbv6m" || llvm_target[0] == "thumbv8m.base" {
 465             let mut to_remove = Vec::new();
 466             for (k, v) in sources.map.iter() {
 467                 if v.ends_with(".S") {
 468                     to_remove.push(*k);
 469                 }
 470             }
 471             sources.remove(&to_remove);
 472
 473             // But use some generic implementations where possible
 474             sources.extend(&[("__clzdi2", "clzdi2.c"), ("__clzsi2", "clzsi2.c")])
 475         }
 476
 477         if llvm_target[0] == "thumbv7m" || llvm_target[0] == "thumbv7em" {
 478             sources.remove(&["__aeabi_cdcmp", "__aeabi_cfcmp"]);
 479         }
 480
 481         // Android uses emulated TLS so we need a runtime support function.
 482         if target_os == "android" {
 483             sources.extend(&[("__emutls_get_address", "emutls.c")]);
 484
 485             // Work around a bug in the NDK headers (fixed in
 486             // https://r.android.com/2038949 which will be released in a future
 487             // NDK version) by providing a definition of LONG_BIT.
 488             cfg.define("LONG_BIT", "(8 * sizeof(long))");
 489         }
 490
 491         // When compiling the C code we require the user to tell us where the
 492         // source code is, and this is largely done so when we're compiling as
 493         // part of rust-lang/rust we can use the same llvm-project repository as
 494         // rust-lang/rust.
 495         let root = match env::var_os("RUST_COMPILER_RT_ROOT") {
 496             Some(s) => PathBuf::from(s),
 497             None => panic!("RUST_COMPILER_RT_ROOT is not set"),
 498         };
 499         if !root.exists() {
 500             panic!("RUST_COMPILER_RT_ROOT={} does not exist", root.display());
 501         }
 502
 503         // Support deterministic builds by remapping the __FILE__ prefix if the
 504         // compiler supports it.  This fixes the nondeterminism caused by the
 505         // use of that macro in lib/builtins/int_util.h in compiler-rt.
 506         cfg.flag_if_supported(&format!("-ffile-prefix-map={}=.", root.display()));
 507
 508         // Include out-of-line atomics for aarch64, which are all generated by supplying different
 509         // sets of flags to the same source file.
 510         // Note: Out-of-line aarch64 atomics are not supported by the msvc toolchain (#430).
 511         let src_dir = root.join("lib/builtins");
 512         if target_arch == "aarch64" && target_env != "msvc" {
 513             // See below for why we're building these as separate libraries.
 514             build_aarch64_out_of_line_atomics_libraries(&src_dir, cfg);
 515
 516             // Some run-time CPU feature detection is necessary, as well.
 517             sources.extend(&[("__aarch64_have_lse_atomics", "cpu_model.c")]);
 518         }
 519
 520         let mut added_sources = HashSet::new();
 521         for (sym, src) in sources.map.iter() {
 522             let src = src_dir.join(src);
 523             if added_sources.insert(src.clone()) {
 524                 cfg.file(&src);
 525                 println!("cargo:rerun-if-changed={}", src.display());
 526             }
 527             println!("cargo:rustc-cfg={}=\"optimized-c\"", sym);
 528         }
 529
 530         cfg.compile("libcompiler-rt.a");
 531     }
 532
 533     fn build_aarch64_out_of_line_atomics_libraries(builtins_dir: &Path, cfg: &mut cc::Build) {
 534         let out_dir = PathBuf::from(env::var("OUT_DIR").unwrap());
 535         let outlined_atomics_file = builtins_dir.join("aarch64/lse.S");
 536         println!("cargo:rerun-if-changed={}", outlined_atomics_file.display());
 537
 538         cfg.include(&builtins_dir);
 539
 540         for instruction_type in &["cas", "swp", "ldadd", "ldclr", "ldeor", "ldset"] {
 541             for size in &[1, 2, 4, 8, 16] {
 542                 if *size == 16 && *instruction_type != "cas" {
 543                     continue;
 544                 }
 545
 546                 for (model_number, model_name) in
 547                     &[(1, "relax"), (2, "acq"), (3, "rel"), (4, "acq_rel")]
 548                 {
 549                     // The original compiler-rt build system compiles the same
 550                     // source file multiple times with different compiler
 551                     // options. Here we do something slightly different: we
 552                     // create multiple .S files with the proper #defines and
 553                     // then include the original file.
 554                     //
 555                     // This is needed because the cc crate doesn't allow us to
 556                     // override the name of object files and libtool requires
 557                     // all objects in an archive to have unique names.
 558                     let path =
 559                         out_dir.join(format!("lse_{}{}_{}.S", instruction_type, size, model_name));
 560                     let mut file = File::create(&path).unwrap();
 561                     writeln!(file, "#define L_{}", instruction_type).unwrap();
 562                     writeln!(file, "#define SIZE {}", size).unwrap();
 563                     writeln!(file, "#define MODEL {}", model_number).unwrap();
 564                     writeln!(
 565                         file,
 566                         "#include \"{}\"",
 567                         outlined_atomics_file.canonicalize().unwrap().display()
 568                     )
 569                     .unwrap();
 570                     drop(file);
 571                     cfg.file(path);
 572
 573                     let sym = format!("__aarch64_{}{}_{}", instruction_type, size, model_name);
 574                     println!("cargo:rustc-cfg={}=\"optimized-c\"", sym);
 575                 }
 576             }
 577         }
 578     }
 579 }