2 use super::command::Command;
3 use super::symbol_export;
4 use rustc_span::symbol::sym;
6 use std::ffi::{OsStr, OsString};
7 use std::fs::{self, File};
8 use std::io::prelude::*;
9 use std::io::{self, BufWriter};
11 use std::path::{Path, PathBuf};
13 use rustc_data_structures::fx::FxHashMap;
14 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
15 use rustc_middle::middle::dependency_format::Linkage;
16 use rustc_middle::ty::TyCtxt;
17 use rustc_serialize::{json, Encoder};
18 use rustc_session::config::{self, CrateType, DebugInfo, LinkerPluginLto, Lto, OptLevel, Strip};
19 use rustc_session::Session;
20 use rustc_span::symbol::Symbol;
21 use rustc_target::spec::{LinkOutputKind, LinkerFlavor, LldFlavor};
23 /// Disables non-English messages from localized linkers.
24 /// Such messages may cause issues with text encoding on Windows (#35785)
25 /// and prevent inspection of linker output in case of errors, which we occasionally do.
26 /// This should be acceptable because other messages from rustc are in English anyway,
27 /// and may also be desirable to improve searchability of the linker diagnostics.
28 pub fn disable_localization(linker: &mut Command) {
29 // No harm in setting both env vars simultaneously.
30 // Unix-style linkers.
31 linker.env("LC_ALL", "C");
33 linker.env("VSLANG", "1033");
36 /// For all the linkers we support, and information they might
37 /// need out of the shared crate context before we get rid of it.
38 #[derive(Encodable, Decodable)]
39 pub struct LinkerInfo {
40 exports: FxHashMap<CrateType, Vec<String>>,
44 pub fn new(tcx: TyCtxt<'_>) -> LinkerInfo {
50 .map(|&c| (c, exported_symbols(tcx, c)))
61 ) -> Box<dyn Linker + 'a> {
63 LinkerFlavor::Lld(LldFlavor::Link) | LinkerFlavor::Msvc => {
64 Box::new(MsvcLinker { cmd, sess, info: self }) as Box<dyn Linker>
66 LinkerFlavor::Em => Box::new(EmLinker { cmd, sess, info: self }) as Box<dyn Linker>,
67 LinkerFlavor::Gcc => Box::new(GccLinker {
74 }) as Box<dyn Linker>,
76 LinkerFlavor::Lld(LldFlavor::Ld)
77 | LinkerFlavor::Lld(LldFlavor::Ld64)
78 | LinkerFlavor::Ld => Box::new(GccLinker {
85 }) as Box<dyn Linker>,
87 LinkerFlavor::Lld(LldFlavor::Wasm) => {
88 Box::new(WasmLd::new(cmd, sess, self)) as Box<dyn Linker>
91 LinkerFlavor::PtxLinker => Box::new(PtxLinker { cmd, sess }) as Box<dyn Linker>,
96 /// Linker abstraction used by `back::link` to build up the command to invoke a
99 /// This trait is the total list of requirements needed by `back::link` and
100 /// represents the meaning of each option being passed down. This trait is then
101 /// used to dispatch on whether a GNU-like linker (generally `ld.exe`) or an
102 /// MSVC linker (e.g., `link.exe`) is being used.
104 fn cmd(&mut self) -> &mut Command;
105 fn set_output_kind(&mut self, output_kind: LinkOutputKind, out_filename: &Path);
106 fn link_dylib(&mut self, lib: Symbol);
107 fn link_rust_dylib(&mut self, lib: Symbol, path: &Path);
108 fn link_framework(&mut self, framework: Symbol);
109 fn link_staticlib(&mut self, lib: Symbol);
110 fn link_rlib(&mut self, lib: &Path);
111 fn link_whole_rlib(&mut self, lib: &Path);
112 fn link_whole_staticlib(&mut self, lib: Symbol, search_path: &[PathBuf]);
113 fn include_path(&mut self, path: &Path);
114 fn framework_path(&mut self, path: &Path);
115 fn output_filename(&mut self, path: &Path);
116 fn add_object(&mut self, path: &Path);
117 fn gc_sections(&mut self, keep_metadata: bool);
118 fn full_relro(&mut self);
119 fn partial_relro(&mut self);
120 fn no_relro(&mut self);
121 fn optimize(&mut self);
122 fn pgo_gen(&mut self);
123 fn control_flow_guard(&mut self);
124 fn debuginfo(&mut self, strip: Strip);
125 fn no_crt_objects(&mut self);
126 fn no_default_libraries(&mut self);
127 fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType);
128 fn subsystem(&mut self, subsystem: &str);
129 fn group_start(&mut self);
130 fn group_end(&mut self);
131 fn linker_plugin_lto(&mut self);
132 fn add_eh_frame_header(&mut self) {}
133 fn finalize(&mut self);
136 impl dyn Linker + '_ {
137 pub fn arg(&mut self, arg: impl AsRef<OsStr>) {
141 pub fn args(&mut self, args: impl IntoIterator<Item: AsRef<OsStr>>) {
142 self.cmd().args(args);
145 pub fn take_cmd(&mut self) -> Command {
146 mem::replace(self.cmd(), Command::new(""))
150 pub struct GccLinker<'a> {
153 info: &'a LinkerInfo,
154 hinted_static: bool, // Keeps track of the current hinting mode.
160 impl<'a> GccLinker<'a> {
161 /// Argument that must be passed *directly* to the linker
163 /// These arguments need to be prepended with `-Wl`, when a GCC-style linker is used.
164 fn linker_arg<S>(&mut self, arg: S) -> &mut Self
169 let mut os = OsString::from("-Wl,");
170 os.push(arg.as_ref());
178 fn takes_hints(&self) -> bool {
179 // Really this function only returns true if the underlying linker
180 // configured for a compiler is binutils `ld.bfd` and `ld.gold`. We
181 // don't really have a foolproof way to detect that, so rule out some
182 // platforms where currently this is guaranteed to *not* be the case:
184 // * On OSX they have their own linker, not binutils'
185 // * For WebAssembly the only functional linker is LLD, which doesn't
186 // support hint flags
187 !self.sess.target.is_like_osx && self.sess.target.arch != "wasm32"
190 // Some platforms take hints about whether a library is static or dynamic.
191 // For those that support this, we ensure we pass the option if the library
192 // was flagged "static" (most defaults are dynamic) to ensure that if
193 // libfoo.a and libfoo.so both exist that the right one is chosen.
194 fn hint_static(&mut self) {
195 if !self.takes_hints() {
198 if !self.hinted_static {
199 self.linker_arg("-Bstatic");
200 self.hinted_static = true;
204 fn hint_dynamic(&mut self) {
205 if !self.takes_hints() {
208 if self.hinted_static {
209 self.linker_arg("-Bdynamic");
210 self.hinted_static = false;
214 fn push_linker_plugin_lto_args(&mut self, plugin_path: Option<&OsStr>) {
215 if let Some(plugin_path) = plugin_path {
216 let mut arg = OsString::from("-plugin=");
217 arg.push(plugin_path);
218 self.linker_arg(&arg);
221 let opt_level = match self.sess.opts.optimize {
222 config::OptLevel::No => "O0",
223 config::OptLevel::Less => "O1",
224 config::OptLevel::Default | config::OptLevel::Size | config::OptLevel::SizeMin => "O2",
225 config::OptLevel::Aggressive => "O3",
228 self.linker_arg(&format!("-plugin-opt={}", opt_level));
229 let target_cpu = self.target_cpu;
230 self.linker_arg(&format!("-plugin-opt=mcpu={}", target_cpu));
233 fn build_dylib(&mut self, out_filename: &Path) {
234 // On mac we need to tell the linker to let this library be rpathed
235 if self.sess.target.is_like_osx {
236 self.cmd.arg("-dynamiclib");
237 self.linker_arg("-dylib");
239 // Note that the `osx_rpath_install_name` option here is a hack
240 // purely to support rustbuild right now, we should get a more
241 // principled solution at some point to force the compiler to pass
242 // the right `-Wl,-install_name` with an `@rpath` in it.
243 if self.sess.opts.cg.rpath || self.sess.opts.debugging_opts.osx_rpath_install_name {
244 self.linker_arg("-install_name");
245 let mut v = OsString::from("@rpath/");
246 v.push(out_filename.file_name().unwrap());
250 self.cmd.arg("-shared");
251 if self.sess.target.is_like_windows {
252 // The output filename already contains `dll_suffix` so
253 // the resulting import library will have a name in the
254 // form of libfoo.dll.a
256 out_filename.file_name().and_then(|file| file.to_str()).map(|file| {
259 self.sess.target.staticlib_prefix,
261 self.sess.target.staticlib_suffix
264 if let Some(implib_name) = implib_name {
265 let implib = out_filename.parent().map(|dir| dir.join(&implib_name));
266 if let Some(implib) = implib {
267 self.linker_arg(&format!("--out-implib={}", (*implib).to_str().unwrap()));
275 impl<'a> Linker for GccLinker<'a> {
276 fn cmd(&mut self) -> &mut Command {
280 fn set_output_kind(&mut self, output_kind: LinkOutputKind, out_filename: &Path) {
282 LinkOutputKind::DynamicNoPicExe => {
283 if !self.is_ld && self.sess.target.linker_is_gnu {
284 self.cmd.arg("-no-pie");
287 LinkOutputKind::DynamicPicExe => {
288 // `-pie` works for both gcc wrapper and ld.
289 self.cmd.arg("-pie");
291 LinkOutputKind::StaticNoPicExe => {
292 // `-static` works for both gcc wrapper and ld.
293 self.cmd.arg("-static");
294 if !self.is_ld && self.sess.target.linker_is_gnu {
295 self.cmd.arg("-no-pie");
298 LinkOutputKind::StaticPicExe => {
300 // Note that combination `-static -pie` doesn't work as expected
301 // for the gcc wrapper, `-static` in that case suppresses `-pie`.
302 self.cmd.arg("-static-pie");
304 // `--no-dynamic-linker` and `-z text` are not strictly necessary for producing
305 // a static pie, but currently passed because gcc and clang pass them.
306 // The former suppresses the `INTERP` ELF header specifying dynamic linker,
307 // which is otherwise implicitly injected by ld (but not lld).
308 // The latter doesn't change anything, only ensures that everything is pic.
309 self.cmd.args(&["-static", "-pie", "--no-dynamic-linker", "-z", "text"]);
312 LinkOutputKind::DynamicDylib => self.build_dylib(out_filename),
313 LinkOutputKind::StaticDylib => {
314 self.cmd.arg("-static");
315 self.build_dylib(out_filename);
317 LinkOutputKind::WasiReactorExe => {
318 self.linker_arg("--entry");
319 self.linker_arg("_initialize");
322 // VxWorks compiler driver introduced `--static-crt` flag specifically for rustc,
323 // it switches linking for libc and similar system libraries to static without using
324 // any `#[link]` attributes in the `libc` crate, see #72782 for details.
325 // FIXME: Switch to using `#[link]` attributes in the `libc` crate
326 // similarly to other targets.
327 if self.sess.target.os == "vxworks"
330 LinkOutputKind::StaticNoPicExe
331 | LinkOutputKind::StaticPicExe
332 | LinkOutputKind::StaticDylib
335 self.cmd.arg("--static-crt");
339 fn link_dylib(&mut self, lib: Symbol) {
341 self.cmd.arg(format!("-l{}", lib));
343 fn link_staticlib(&mut self, lib: Symbol) {
345 self.cmd.arg(format!("-l{}", lib));
347 fn link_rlib(&mut self, lib: &Path) {
351 fn include_path(&mut self, path: &Path) {
352 self.cmd.arg("-L").arg(path);
354 fn framework_path(&mut self, path: &Path) {
355 self.cmd.arg("-F").arg(path);
357 fn output_filename(&mut self, path: &Path) {
358 self.cmd.arg("-o").arg(path);
360 fn add_object(&mut self, path: &Path) {
363 fn full_relro(&mut self) {
364 self.linker_arg("-zrelro");
365 self.linker_arg("-znow");
367 fn partial_relro(&mut self) {
368 self.linker_arg("-zrelro");
370 fn no_relro(&mut self) {
371 self.linker_arg("-znorelro");
374 fn link_rust_dylib(&mut self, lib: Symbol, _path: &Path) {
376 self.cmd.arg(format!("-l{}", lib));
379 fn link_framework(&mut self, framework: Symbol) {
381 self.cmd.arg("-framework").sym_arg(framework);
384 // Here we explicitly ask that the entire archive is included into the
385 // result artifact. For more details see #15460, but the gist is that
386 // the linker will strip away any unused objects in the archive if we
387 // don't otherwise explicitly reference them. This can occur for
388 // libraries which are just providing bindings, libraries with generic
390 fn link_whole_staticlib(&mut self, lib: Symbol, search_path: &[PathBuf]) {
392 let target = &self.sess.target;
393 if !target.is_like_osx {
394 self.linker_arg("--whole-archive").cmd.arg(format!("-l{}", lib));
395 self.linker_arg("--no-whole-archive");
397 // -force_load is the macOS equivalent of --whole-archive, but it
398 // involves passing the full path to the library to link.
399 self.linker_arg("-force_load");
400 let lib = archive::find_library(lib, search_path, &self.sess);
401 self.linker_arg(&lib);
405 fn link_whole_rlib(&mut self, lib: &Path) {
407 if self.sess.target.is_like_osx {
408 self.linker_arg("-force_load");
409 self.linker_arg(&lib);
411 self.linker_arg("--whole-archive").cmd.arg(lib);
412 self.linker_arg("--no-whole-archive");
416 fn gc_sections(&mut self, keep_metadata: bool) {
417 // The dead_strip option to the linker specifies that functions and data
418 // unreachable by the entry point will be removed. This is quite useful
419 // with Rust's compilation model of compiling libraries at a time into
420 // one object file. For example, this brings hello world from 1.7MB to
423 // Note that this is done for both executables and dynamic libraries. We
424 // won't get much benefit from dylibs because LLVM will have already
425 // stripped away as much as it could. This has not been seen to impact
426 // link times negatively.
428 // -dead_strip can't be part of the pre_link_args because it's also used
429 // for partial linking when using multiple codegen units (-r). So we
431 if self.sess.target.is_like_osx {
432 self.linker_arg("-dead_strip");
433 } else if self.sess.target.is_like_solaris {
434 self.linker_arg("-zignore");
436 // If we're building a dylib, we don't use --gc-sections because LLVM
437 // has already done the best it can do, and we also don't want to
438 // eliminate the metadata. If we're building an executable, however,
439 // --gc-sections drops the size of hello world from 1.8MB to 597K, a 67%
441 } else if !keep_metadata {
442 self.linker_arg("--gc-sections");
446 fn optimize(&mut self) {
447 if !self.sess.target.linker_is_gnu {
451 // GNU-style linkers support optimization with -O. GNU ld doesn't
452 // need a numeric argument, but other linkers do.
453 if self.sess.opts.optimize == config::OptLevel::Default
454 || self.sess.opts.optimize == config::OptLevel::Aggressive
456 self.linker_arg("-O1");
460 fn pgo_gen(&mut self) {
461 if !self.sess.target.linker_is_gnu {
465 // If we're doing PGO generation stuff and on a GNU-like linker, use the
466 // "-u" flag to properly pull in the profiler runtime bits.
468 // This is because LLVM otherwise won't add the needed initialization
469 // for us on Linux (though the extra flag should be harmless if it
472 // See https://reviews.llvm.org/D14033 and https://reviews.llvm.org/D14030.
474 // Though it may be worth to try to revert those changes upstream, since
475 // the overhead of the initialization should be minor.
477 self.cmd.arg("__llvm_profile_runtime");
480 fn control_flow_guard(&mut self) {}
482 fn debuginfo(&mut self, strip: Strip) {
485 Strip::Debuginfo => {
486 // MacOS linker does not support longhand argument --strip-debug
487 self.linker_arg("-S");
490 // MacOS linker does not support longhand argument --strip-all
491 self.linker_arg("-s");
496 fn no_crt_objects(&mut self) {
498 self.cmd.arg("-nostartfiles");
502 fn no_default_libraries(&mut self) {
504 self.cmd.arg("-nodefaultlibs");
508 fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType) {
509 // Symbol visibility in object files typically takes care of this.
510 if crate_type == CrateType::Executable && self.sess.target.override_export_symbols.is_none()
515 // We manually create a list of exported symbols to ensure we don't expose any more.
516 // The object files have far more public symbols than we actually want to export,
517 // so we hide them all here.
519 if !self.sess.target.limit_rdylib_exports {
523 if crate_type == CrateType::ProcMacro {
527 let is_windows = self.sess.target.is_like_windows;
528 let mut arg = OsString::new();
529 let path = tmpdir.join(if is_windows { "list.def" } else { "list" });
531 debug!("EXPORTED SYMBOLS:");
533 if self.sess.target.is_like_osx {
534 // Write a plain, newline-separated list of symbols
535 let res: io::Result<()> = try {
536 let mut f = BufWriter::new(File::create(&path)?);
537 for sym in self.info.exports[&crate_type].iter() {
539 writeln!(f, "_{}", sym)?;
542 if let Err(e) = res {
543 self.sess.fatal(&format!("failed to write lib.def file: {}", e));
545 } else if is_windows {
546 let res: io::Result<()> = try {
547 let mut f = BufWriter::new(File::create(&path)?);
549 // .def file similar to MSVC one but without LIBRARY section
550 // because LD doesn't like when it's empty
551 writeln!(f, "EXPORTS")?;
552 for symbol in self.info.exports[&crate_type].iter() {
553 debug!(" _{}", symbol);
554 writeln!(f, " {}", symbol)?;
557 if let Err(e) = res {
558 self.sess.fatal(&format!("failed to write list.def file: {}", e));
561 // Write an LD version script
562 let res: io::Result<()> = try {
563 let mut f = BufWriter::new(File::create(&path)?);
565 if !self.info.exports[&crate_type].is_empty() {
566 writeln!(f, " global:")?;
567 for sym in self.info.exports[&crate_type].iter() {
569 writeln!(f, " {};", sym)?;
572 writeln!(f, "\n local:\n *;\n}};")?;
574 if let Err(e) = res {
575 self.sess.fatal(&format!("failed to write version script: {}", e));
579 if self.sess.target.is_like_osx {
583 arg.push("-exported_symbols_list,");
584 } else if self.sess.target.is_like_solaris {
593 // Both LD and LLD accept export list in *.def file form, there are no flags required
595 arg.push("--version-script=")
603 fn subsystem(&mut self, subsystem: &str) {
604 self.linker_arg("--subsystem");
605 self.linker_arg(&subsystem);
608 fn finalize(&mut self) {
609 self.hint_dynamic(); // Reset to default before returning the composed command line.
612 fn group_start(&mut self) {
613 if self.takes_hints() {
614 self.linker_arg("--start-group");
618 fn group_end(&mut self) {
619 if self.takes_hints() {
620 self.linker_arg("--end-group");
624 fn linker_plugin_lto(&mut self) {
625 match self.sess.opts.cg.linker_plugin_lto {
626 LinkerPluginLto::Disabled => {
629 LinkerPluginLto::LinkerPluginAuto => {
630 self.push_linker_plugin_lto_args(None);
632 LinkerPluginLto::LinkerPlugin(ref path) => {
633 self.push_linker_plugin_lto_args(Some(path.as_os_str()));
638 // Add the `GNU_EH_FRAME` program header which is required to locate unwinding information.
639 // Some versions of `gcc` add it implicitly, some (e.g. `musl-gcc`) don't,
640 // so we just always add it.
641 fn add_eh_frame_header(&mut self) {
642 self.linker_arg("--eh-frame-hdr");
646 pub struct MsvcLinker<'a> {
649 info: &'a LinkerInfo,
652 impl<'a> Linker for MsvcLinker<'a> {
653 fn cmd(&mut self) -> &mut Command {
657 fn set_output_kind(&mut self, output_kind: LinkOutputKind, out_filename: &Path) {
659 LinkOutputKind::DynamicNoPicExe
660 | LinkOutputKind::DynamicPicExe
661 | LinkOutputKind::StaticNoPicExe
662 | LinkOutputKind::StaticPicExe => {}
663 LinkOutputKind::DynamicDylib | LinkOutputKind::StaticDylib => {
664 self.cmd.arg("/DLL");
665 let mut arg: OsString = "/IMPLIB:".into();
666 arg.push(out_filename.with_extension("dll.lib"));
669 LinkOutputKind::WasiReactorExe => {
670 panic!("can't link as reactor on non-wasi target");
675 fn link_rlib(&mut self, lib: &Path) {
678 fn add_object(&mut self, path: &Path) {
682 fn gc_sections(&mut self, _keep_metadata: bool) {
683 // MSVC's ICF (Identical COMDAT Folding) link optimization is
684 // slow for Rust and thus we disable it by default when not in
685 // optimization build.
686 if self.sess.opts.optimize != config::OptLevel::No {
687 self.cmd.arg("/OPT:REF,ICF");
689 // It is necessary to specify NOICF here, because /OPT:REF
690 // implies ICF by default.
691 self.cmd.arg("/OPT:REF,NOICF");
695 fn link_dylib(&mut self, lib: Symbol) {
696 self.cmd.arg(&format!("{}.lib", lib));
699 fn link_rust_dylib(&mut self, lib: Symbol, path: &Path) {
700 // When producing a dll, the MSVC linker may not actually emit a
701 // `foo.lib` file if the dll doesn't actually export any symbols, so we
702 // check to see if the file is there and just omit linking to it if it's
704 let name = format!("{}.dll.lib", lib);
705 if fs::metadata(&path.join(&name)).is_ok() {
710 fn link_staticlib(&mut self, lib: Symbol) {
711 self.cmd.arg(&format!("{}.lib", lib));
714 fn full_relro(&mut self) {
718 fn partial_relro(&mut self) {
722 fn no_relro(&mut self) {
726 fn no_crt_objects(&mut self) {
730 fn no_default_libraries(&mut self) {
731 self.cmd.arg("/NODEFAULTLIB");
734 fn include_path(&mut self, path: &Path) {
735 let mut arg = OsString::from("/LIBPATH:");
740 fn output_filename(&mut self, path: &Path) {
741 let mut arg = OsString::from("/OUT:");
746 fn framework_path(&mut self, _path: &Path) {
747 bug!("frameworks are not supported on windows")
749 fn link_framework(&mut self, _framework: Symbol) {
750 bug!("frameworks are not supported on windows")
753 fn link_whole_staticlib(&mut self, lib: Symbol, _search_path: &[PathBuf]) {
754 self.link_staticlib(lib);
755 self.cmd.arg(format!("/WHOLEARCHIVE:{}.lib", lib));
757 fn link_whole_rlib(&mut self, path: &Path) {
758 self.link_rlib(path);
759 let mut arg = OsString::from("/WHOLEARCHIVE:");
763 fn optimize(&mut self) {
764 // Needs more investigation of `/OPT` arguments
767 fn pgo_gen(&mut self) {
768 // Nothing needed here.
771 fn control_flow_guard(&mut self) {
772 self.cmd.arg("/guard:cf");
775 fn debuginfo(&mut self, strip: Strip) {
778 // This will cause the Microsoft linker to generate a PDB file
779 // from the CodeView line tables in the object files.
780 self.cmd.arg("/DEBUG");
782 // This will cause the Microsoft linker to embed .natvis info into the PDB file
783 let natvis_dir_path = self.sess.sysroot.join("lib\\rustlib\\etc");
784 if let Ok(natvis_dir) = fs::read_dir(&natvis_dir_path) {
785 for entry in natvis_dir {
788 let path = entry.path();
789 if path.extension() == Some("natvis".as_ref()) {
790 let mut arg = OsString::from("/NATVIS:");
797 .warn(&format!("error enumerating natvis directory: {}", err));
803 Strip::Debuginfo | Strip::Symbols => {
804 self.cmd.arg("/DEBUG:NONE");
809 // Currently the compiler doesn't use `dllexport` (an LLVM attribute) to
810 // export symbols from a dynamic library. When building a dynamic library,
811 // however, we're going to want some symbols exported, so this function
812 // generates a DEF file which lists all the symbols.
814 // The linker will read this `*.def` file and export all the symbols from
815 // the dynamic library. Note that this is not as simple as just exporting
816 // all the symbols in the current crate (as specified by `codegen.reachable`)
817 // but rather we also need to possibly export the symbols of upstream
818 // crates. Upstream rlibs may be linked statically to this dynamic library,
819 // in which case they may continue to transitively be used and hence need
820 // their symbols exported.
821 fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType) {
822 // Symbol visibility takes care of this typically
823 if crate_type == CrateType::Executable {
827 let path = tmpdir.join("lib.def");
828 let res: io::Result<()> = try {
829 let mut f = BufWriter::new(File::create(&path)?);
831 // Start off with the standard module name header and then go
832 // straight to exports.
833 writeln!(f, "LIBRARY")?;
834 writeln!(f, "EXPORTS")?;
835 for symbol in self.info.exports[&crate_type].iter() {
836 debug!(" _{}", symbol);
837 writeln!(f, " {}", symbol)?;
840 if let Err(e) = res {
841 self.sess.fatal(&format!("failed to write lib.def file: {}", e));
843 let mut arg = OsString::from("/DEF:");
848 fn subsystem(&mut self, subsystem: &str) {
849 // Note that previous passes of the compiler validated this subsystem,
850 // so we just blindly pass it to the linker.
851 self.cmd.arg(&format!("/SUBSYSTEM:{}", subsystem));
853 // Windows has two subsystems we're interested in right now, the console
854 // and windows subsystems. These both implicitly have different entry
855 // points (starting symbols). The console entry point starts with
856 // `mainCRTStartup` and the windows entry point starts with
857 // `WinMainCRTStartup`. These entry points, defined in system libraries,
858 // will then later probe for either `main` or `WinMain`, respectively to
859 // start the application.
861 // In Rust we just always generate a `main` function so we want control
862 // to always start there, so we force the entry point on the windows
863 // subsystem to be `mainCRTStartup` to get everything booted up
866 // For more information see RFC #1665
867 if subsystem == "windows" {
868 self.cmd.arg("/ENTRY:mainCRTStartup");
872 fn finalize(&mut self) {}
874 // MSVC doesn't need group indicators
875 fn group_start(&mut self) {}
876 fn group_end(&mut self) {}
878 fn linker_plugin_lto(&mut self) {
883 pub struct EmLinker<'a> {
886 info: &'a LinkerInfo,
889 impl<'a> Linker for EmLinker<'a> {
890 fn cmd(&mut self) -> &mut Command {
894 fn set_output_kind(&mut self, _output_kind: LinkOutputKind, _out_filename: &Path) {}
896 fn include_path(&mut self, path: &Path) {
897 self.cmd.arg("-L").arg(path);
900 fn link_staticlib(&mut self, lib: Symbol) {
901 self.cmd.arg("-l").sym_arg(lib);
904 fn output_filename(&mut self, path: &Path) {
905 self.cmd.arg("-o").arg(path);
908 fn add_object(&mut self, path: &Path) {
912 fn link_dylib(&mut self, lib: Symbol) {
913 // Emscripten always links statically
914 self.link_staticlib(lib);
917 fn link_whole_staticlib(&mut self, lib: Symbol, _search_path: &[PathBuf]) {
919 self.link_staticlib(lib);
922 fn link_whole_rlib(&mut self, lib: &Path) {
927 fn link_rust_dylib(&mut self, lib: Symbol, _path: &Path) {
928 self.link_dylib(lib);
931 fn link_rlib(&mut self, lib: &Path) {
932 self.add_object(lib);
935 fn full_relro(&mut self) {
939 fn partial_relro(&mut self) {
943 fn no_relro(&mut self) {
947 fn framework_path(&mut self, _path: &Path) {
948 bug!("frameworks are not supported on Emscripten")
951 fn link_framework(&mut self, _framework: Symbol) {
952 bug!("frameworks are not supported on Emscripten")
955 fn gc_sections(&mut self, _keep_metadata: bool) {
959 fn optimize(&mut self) {
960 // Emscripten performs own optimizations
961 self.cmd.arg(match self.sess.opts.optimize {
962 OptLevel::No => "-O0",
963 OptLevel::Less => "-O1",
964 OptLevel::Default => "-O2",
965 OptLevel::Aggressive => "-O3",
966 OptLevel::Size => "-Os",
967 OptLevel::SizeMin => "-Oz",
969 // Unusable until https://github.com/rust-lang/rust/issues/38454 is resolved
970 self.cmd.args(&["--memory-init-file", "0"]);
973 fn pgo_gen(&mut self) {
974 // noop, but maybe we need something like the gnu linker?
977 fn control_flow_guard(&mut self) {}
979 fn debuginfo(&mut self, _strip: Strip) {
980 // Preserve names or generate source maps depending on debug info
981 self.cmd.arg(match self.sess.opts.debuginfo {
982 DebugInfo::None => "-g0",
983 DebugInfo::Limited => "-g3",
984 DebugInfo::Full => "-g4",
988 fn no_crt_objects(&mut self) {}
990 fn no_default_libraries(&mut self) {
991 self.cmd.args(&["-s", "DEFAULT_LIBRARY_FUNCS_TO_INCLUDE=[]"]);
994 fn export_symbols(&mut self, _tmpdir: &Path, crate_type: CrateType) {
995 let symbols = &self.info.exports[&crate_type];
997 debug!("EXPORTED SYMBOLS:");
1001 let mut arg = OsString::from("EXPORTED_FUNCTIONS=");
1002 let mut encoded = String::new();
1005 let mut encoder = json::Encoder::new(&mut encoded);
1006 let res = encoder.emit_seq(symbols.len(), |encoder| {
1007 for (i, sym) in symbols.iter().enumerate() {
1008 encoder.emit_seq_elt(i, |encoder| encoder.emit_str(&("_".to_owned() + sym)))?;
1012 if let Err(e) = res {
1013 self.sess.fatal(&format!("failed to encode exported symbols: {}", e));
1016 debug!("{}", encoded);
1022 fn subsystem(&mut self, _subsystem: &str) {
1026 fn finalize(&mut self) {}
1028 // Appears not necessary on Emscripten
1029 fn group_start(&mut self) {}
1030 fn group_end(&mut self) {}
1032 fn linker_plugin_lto(&mut self) {
1037 pub struct WasmLd<'a> {
1040 info: &'a LinkerInfo,
1043 impl<'a> WasmLd<'a> {
1044 fn new(mut cmd: Command, sess: &'a Session, info: &'a LinkerInfo) -> WasmLd<'a> {
1045 // If the atomics feature is enabled for wasm then we need a whole bunch
1048 // * `--shared-memory` - the link won't even succeed without this, flags
1049 // the one linear memory as `shared`
1051 // * `--max-memory=1G` - when specifying a shared memory this must also
1052 // be specified. We conservatively choose 1GB but users should be able
1053 // to override this with `-C link-arg`.
1055 // * `--import-memory` - it doesn't make much sense for memory to be
1056 // exported in a threaded module because typically you're
1057 // sharing memory and instantiating the module multiple times. As a
1058 // result if it were exported then we'd just have no sharing.
1060 // * `--export=__wasm_init_memory` - when using `--passive-segments` the
1061 // linker will synthesize this function, and so we need to make sure
1062 // that our usage of `--export` below won't accidentally cause this
1063 // function to get deleted.
1065 // * `--export=*tls*` - when `#[thread_local]` symbols are used these
1066 // symbols are how the TLS segments are initialized and configured.
1067 if sess.target_features.contains(&sym::atomics) {
1068 cmd.arg("--shared-memory");
1069 cmd.arg("--max-memory=1073741824");
1070 cmd.arg("--import-memory");
1071 cmd.arg("--export=__wasm_init_memory");
1072 cmd.arg("--export=__wasm_init_tls");
1073 cmd.arg("--export=__tls_size");
1074 cmd.arg("--export=__tls_align");
1075 cmd.arg("--export=__tls_base");
1077 WasmLd { cmd, sess, info }
1081 impl<'a> Linker for WasmLd<'a> {
1082 fn cmd(&mut self) -> &mut Command {
1086 fn set_output_kind(&mut self, output_kind: LinkOutputKind, _out_filename: &Path) {
1088 LinkOutputKind::DynamicNoPicExe
1089 | LinkOutputKind::DynamicPicExe
1090 | LinkOutputKind::StaticNoPicExe
1091 | LinkOutputKind::StaticPicExe => {}
1092 LinkOutputKind::DynamicDylib | LinkOutputKind::StaticDylib => {
1093 self.cmd.arg("--no-entry");
1095 LinkOutputKind::WasiReactorExe => {
1096 self.cmd.arg("--entry");
1097 self.cmd.arg("_initialize");
1102 fn link_dylib(&mut self, lib: Symbol) {
1103 self.cmd.arg("-l").sym_arg(lib);
1106 fn link_staticlib(&mut self, lib: Symbol) {
1107 self.cmd.arg("-l").sym_arg(lib);
1110 fn link_rlib(&mut self, lib: &Path) {
1114 fn include_path(&mut self, path: &Path) {
1115 self.cmd.arg("-L").arg(path);
1118 fn framework_path(&mut self, _path: &Path) {
1119 panic!("frameworks not supported")
1122 fn output_filename(&mut self, path: &Path) {
1123 self.cmd.arg("-o").arg(path);
1126 fn add_object(&mut self, path: &Path) {
1130 fn full_relro(&mut self) {}
1132 fn partial_relro(&mut self) {}
1134 fn no_relro(&mut self) {}
1136 fn link_rust_dylib(&mut self, lib: Symbol, _path: &Path) {
1137 self.cmd.arg("-l").sym_arg(lib);
1140 fn link_framework(&mut self, _framework: Symbol) {
1141 panic!("frameworks not supported")
1144 fn link_whole_staticlib(&mut self, lib: Symbol, _search_path: &[PathBuf]) {
1145 self.cmd.arg("-l").sym_arg(lib);
1148 fn link_whole_rlib(&mut self, lib: &Path) {
1152 fn gc_sections(&mut self, _keep_metadata: bool) {
1153 self.cmd.arg("--gc-sections");
1156 fn optimize(&mut self) {
1157 self.cmd.arg(match self.sess.opts.optimize {
1158 OptLevel::No => "-O0",
1159 OptLevel::Less => "-O1",
1160 OptLevel::Default => "-O2",
1161 OptLevel::Aggressive => "-O3",
1162 // Currently LLD doesn't support `Os` and `Oz`, so pass through `O2`
1164 OptLevel::Size => "-O2",
1165 OptLevel::SizeMin => "-O2",
1169 fn pgo_gen(&mut self) {}
1171 fn debuginfo(&mut self, strip: Strip) {
1174 Strip::Debuginfo => {
1175 self.cmd.arg("--strip-debug");
1178 self.cmd.arg("--strip-all");
1183 fn control_flow_guard(&mut self) {}
1185 fn no_crt_objects(&mut self) {}
1187 fn no_default_libraries(&mut self) {}
1189 fn export_symbols(&mut self, _tmpdir: &Path, crate_type: CrateType) {
1190 for sym in self.info.exports[&crate_type].iter() {
1191 self.cmd.arg("--export").arg(&sym);
1194 // LLD will hide these otherwise-internal symbols since it only exports
1195 // symbols explicity passed via the `--export` flags above and hides all
1196 // others. Various bits and pieces of tooling use this, so be sure these
1197 // symbols make their way out of the linker as well.
1198 self.cmd.arg("--export=__heap_base");
1199 self.cmd.arg("--export=__data_end");
1202 fn subsystem(&mut self, _subsystem: &str) {}
1204 fn finalize(&mut self) {}
1206 // Not needed for now with LLD
1207 fn group_start(&mut self) {}
1208 fn group_end(&mut self) {}
1210 fn linker_plugin_lto(&mut self) {
1211 // Do nothing for now
1215 fn exported_symbols(tcx: TyCtxt<'_>, crate_type: CrateType) -> Vec<String> {
1216 if let Some(ref exports) = tcx.sess.target.override_export_symbols {
1217 return exports.clone();
1220 let mut symbols = Vec::new();
1222 let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
1223 for &(symbol, level) in tcx.exported_symbols(LOCAL_CRATE).iter() {
1224 if level.is_below_threshold(export_threshold) {
1225 symbols.push(symbol_export::symbol_name_for_instance_in_crate(
1233 let formats = tcx.dependency_formats(LOCAL_CRATE);
1234 let deps = formats.iter().find_map(|(t, list)| (*t == crate_type).then_some(list)).unwrap();
1236 for (index, dep_format) in deps.iter().enumerate() {
1237 let cnum = CrateNum::new(index + 1);
1238 // For each dependency that we are linking to statically ...
1239 if *dep_format == Linkage::Static {
1240 // ... we add its symbol list to our export list.
1241 for &(symbol, level) in tcx.exported_symbols(cnum).iter() {
1242 if !level.is_below_threshold(export_threshold) {
1246 symbols.push(symbol_export::symbol_name_for_instance_in_crate(tcx, symbol, cnum));
1254 /// Much simplified and explicit CLI for the NVPTX linker. The linker operates
1255 /// with bitcode and uses LLVM backend to generate a PTX assembly.
1256 pub struct PtxLinker<'a> {
1261 impl<'a> Linker for PtxLinker<'a> {
1262 fn cmd(&mut self) -> &mut Command {
1266 fn set_output_kind(&mut self, _output_kind: LinkOutputKind, _out_filename: &Path) {}
1268 fn link_rlib(&mut self, path: &Path) {
1269 self.cmd.arg("--rlib").arg(path);
1272 fn link_whole_rlib(&mut self, path: &Path) {
1273 self.cmd.arg("--rlib").arg(path);
1276 fn include_path(&mut self, path: &Path) {
1277 self.cmd.arg("-L").arg(path);
1280 fn debuginfo(&mut self, _strip: Strip) {
1281 self.cmd.arg("--debug");
1284 fn add_object(&mut self, path: &Path) {
1285 self.cmd.arg("--bitcode").arg(path);
1288 fn optimize(&mut self) {
1289 match self.sess.lto() {
1290 Lto::Thin | Lto::Fat | Lto::ThinLocal => {
1291 self.cmd.arg("-Olto");
1298 fn output_filename(&mut self, path: &Path) {
1299 self.cmd.arg("-o").arg(path);
1302 fn finalize(&mut self) {
1303 // Provide the linker with fallback to internal `target-cpu`.
1304 self.cmd.arg("--fallback-arch").arg(match self.sess.opts.cg.target_cpu {
1306 None => &self.sess.target.cpu,
1310 fn link_dylib(&mut self, _lib: Symbol) {
1311 panic!("external dylibs not supported")
1314 fn link_rust_dylib(&mut self, _lib: Symbol, _path: &Path) {
1315 panic!("external dylibs not supported")
1318 fn link_staticlib(&mut self, _lib: Symbol) {
1319 panic!("staticlibs not supported")
1322 fn link_whole_staticlib(&mut self, _lib: Symbol, _search_path: &[PathBuf]) {
1323 panic!("staticlibs not supported")
1326 fn framework_path(&mut self, _path: &Path) {
1327 panic!("frameworks not supported")
1330 fn link_framework(&mut self, _framework: Symbol) {
1331 panic!("frameworks not supported")
1334 fn full_relro(&mut self) {}
1336 fn partial_relro(&mut self) {}
1338 fn no_relro(&mut self) {}
1340 fn gc_sections(&mut self, _keep_metadata: bool) {}
1342 fn pgo_gen(&mut self) {}
1344 fn no_crt_objects(&mut self) {}
1346 fn no_default_libraries(&mut self) {}
1348 fn control_flow_guard(&mut self) {}
1350 fn export_symbols(&mut self, _tmpdir: &Path, _crate_type: CrateType) {}
1352 fn subsystem(&mut self, _subsystem: &str) {}
1354 fn group_start(&mut self) {}
1356 fn group_end(&mut self) {}
1358 fn linker_plugin_lto(&mut self) {}