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 add_no_exec(&mut self) {}
134 fn add_as_needed(&mut self) {}
135 fn finalize(&mut self);
138 impl dyn Linker + '_ {
139 pub fn arg(&mut self, arg: impl AsRef<OsStr>) {
143 pub fn args(&mut self, args: impl IntoIterator<Item: AsRef<OsStr>>) {
144 self.cmd().args(args);
147 pub fn take_cmd(&mut self) -> Command {
148 mem::replace(self.cmd(), Command::new(""))
152 pub struct GccLinker<'a> {
155 info: &'a LinkerInfo,
156 hinted_static: bool, // Keeps track of the current hinting mode.
162 impl<'a> GccLinker<'a> {
163 /// Argument that must be passed *directly* to the linker
165 /// These arguments need to be prepended with `-Wl`, when a GCC-style linker is used.
166 fn linker_arg<S>(&mut self, arg: S) -> &mut Self
171 let mut os = OsString::from("-Wl,");
172 os.push(arg.as_ref());
180 fn takes_hints(&self) -> bool {
181 // Really this function only returns true if the underlying linker
182 // configured for a compiler is binutils `ld.bfd` and `ld.gold`. We
183 // don't really have a foolproof way to detect that, so rule out some
184 // platforms where currently this is guaranteed to *not* be the case:
186 // * On OSX they have their own linker, not binutils'
187 // * For WebAssembly the only functional linker is LLD, which doesn't
188 // support hint flags
189 !self.sess.target.is_like_osx && !self.sess.target.is_like_wasm
192 // Some platforms take hints about whether a library is static or dynamic.
193 // For those that support this, we ensure we pass the option if the library
194 // was flagged "static" (most defaults are dynamic) to ensure that if
195 // libfoo.a and libfoo.so both exist that the right one is chosen.
196 fn hint_static(&mut self) {
197 if !self.takes_hints() {
200 if !self.hinted_static {
201 self.linker_arg("-Bstatic");
202 self.hinted_static = true;
206 fn hint_dynamic(&mut self) {
207 if !self.takes_hints() {
210 if self.hinted_static {
211 self.linker_arg("-Bdynamic");
212 self.hinted_static = false;
216 fn push_linker_plugin_lto_args(&mut self, plugin_path: Option<&OsStr>) {
217 if let Some(plugin_path) = plugin_path {
218 let mut arg = OsString::from("-plugin=");
219 arg.push(plugin_path);
220 self.linker_arg(&arg);
223 let opt_level = match self.sess.opts.optimize {
224 config::OptLevel::No => "O0",
225 config::OptLevel::Less => "O1",
226 config::OptLevel::Default | config::OptLevel::Size | config::OptLevel::SizeMin => "O2",
227 config::OptLevel::Aggressive => "O3",
230 self.linker_arg(&format!("-plugin-opt={}", opt_level));
231 let target_cpu = self.target_cpu;
232 self.linker_arg(&format!("-plugin-opt=mcpu={}", target_cpu));
235 fn build_dylib(&mut self, out_filename: &Path) {
236 // On mac we need to tell the linker to let this library be rpathed
237 if self.sess.target.is_like_osx {
238 self.cmd.arg("-dynamiclib");
239 self.linker_arg("-dylib");
241 // Note that the `osx_rpath_install_name` option here is a hack
242 // purely to support rustbuild right now, we should get a more
243 // principled solution at some point to force the compiler to pass
244 // the right `-Wl,-install_name` with an `@rpath` in it.
245 if self.sess.opts.cg.rpath || self.sess.opts.debugging_opts.osx_rpath_install_name {
246 self.linker_arg("-install_name");
247 let mut v = OsString::from("@rpath/");
248 v.push(out_filename.file_name().unwrap());
252 self.cmd.arg("-shared");
253 if self.sess.target.is_like_windows {
254 // The output filename already contains `dll_suffix` so
255 // the resulting import library will have a name in the
256 // form of libfoo.dll.a
258 out_filename.file_name().and_then(|file| file.to_str()).map(|file| {
261 self.sess.target.staticlib_prefix,
263 self.sess.target.staticlib_suffix
266 if let Some(implib_name) = implib_name {
267 let implib = out_filename.parent().map(|dir| dir.join(&implib_name));
268 if let Some(implib) = implib {
269 self.linker_arg(&format!("--out-implib={}", (*implib).to_str().unwrap()));
277 impl<'a> Linker for GccLinker<'a> {
278 fn cmd(&mut self) -> &mut Command {
282 fn set_output_kind(&mut self, output_kind: LinkOutputKind, out_filename: &Path) {
284 LinkOutputKind::DynamicNoPicExe => {
285 if !self.is_ld && self.sess.target.linker_is_gnu {
286 self.cmd.arg("-no-pie");
289 LinkOutputKind::DynamicPicExe => {
290 // `-pie` works for both gcc wrapper and ld.
291 self.cmd.arg("-pie");
293 LinkOutputKind::StaticNoPicExe => {
294 // `-static` works for both gcc wrapper and ld.
295 self.cmd.arg("-static");
296 if !self.is_ld && self.sess.target.linker_is_gnu {
297 self.cmd.arg("-no-pie");
300 LinkOutputKind::StaticPicExe => {
302 // Note that combination `-static -pie` doesn't work as expected
303 // for the gcc wrapper, `-static` in that case suppresses `-pie`.
304 self.cmd.arg("-static-pie");
306 // `--no-dynamic-linker` and `-z text` are not strictly necessary for producing
307 // a static pie, but currently passed because gcc and clang pass them.
308 // The former suppresses the `INTERP` ELF header specifying dynamic linker,
309 // which is otherwise implicitly injected by ld (but not lld).
310 // The latter doesn't change anything, only ensures that everything is pic.
311 self.cmd.args(&["-static", "-pie", "--no-dynamic-linker", "-z", "text"]);
314 LinkOutputKind::DynamicDylib => self.build_dylib(out_filename),
315 LinkOutputKind::StaticDylib => {
316 self.cmd.arg("-static");
317 self.build_dylib(out_filename);
319 LinkOutputKind::WasiReactorExe => {
320 self.linker_arg("--entry");
321 self.linker_arg("_initialize");
324 // VxWorks compiler driver introduced `--static-crt` flag specifically for rustc,
325 // it switches linking for libc and similar system libraries to static without using
326 // any `#[link]` attributes in the `libc` crate, see #72782 for details.
327 // FIXME: Switch to using `#[link]` attributes in the `libc` crate
328 // similarly to other targets.
329 if self.sess.target.os == "vxworks"
332 LinkOutputKind::StaticNoPicExe
333 | LinkOutputKind::StaticPicExe
334 | LinkOutputKind::StaticDylib
337 self.cmd.arg("--static-crt");
341 fn link_dylib(&mut self, lib: Symbol) {
343 self.cmd.arg(format!("-l{}", lib));
345 fn link_staticlib(&mut self, lib: Symbol) {
347 self.cmd.arg(format!("-l{}", lib));
349 fn link_rlib(&mut self, lib: &Path) {
353 fn include_path(&mut self, path: &Path) {
354 self.cmd.arg("-L").arg(path);
356 fn framework_path(&mut self, path: &Path) {
357 self.cmd.arg("-F").arg(path);
359 fn output_filename(&mut self, path: &Path) {
360 self.cmd.arg("-o").arg(path);
362 fn add_object(&mut self, path: &Path) {
365 fn full_relro(&mut self) {
366 self.linker_arg("-zrelro");
367 self.linker_arg("-znow");
369 fn partial_relro(&mut self) {
370 self.linker_arg("-zrelro");
372 fn no_relro(&mut self) {
373 self.linker_arg("-znorelro");
376 fn link_rust_dylib(&mut self, lib: Symbol, _path: &Path) {
378 self.cmd.arg(format!("-l{}", lib));
381 fn link_framework(&mut self, framework: Symbol) {
383 self.cmd.arg("-framework").sym_arg(framework);
386 // Here we explicitly ask that the entire archive is included into the
387 // result artifact. For more details see #15460, but the gist is that
388 // the linker will strip away any unused objects in the archive if we
389 // don't otherwise explicitly reference them. This can occur for
390 // libraries which are just providing bindings, libraries with generic
392 fn link_whole_staticlib(&mut self, lib: Symbol, search_path: &[PathBuf]) {
394 let target = &self.sess.target;
395 if !target.is_like_osx {
396 self.linker_arg("--whole-archive").cmd.arg(format!("-l{}", lib));
397 self.linker_arg("--no-whole-archive");
399 // -force_load is the macOS equivalent of --whole-archive, but it
400 // involves passing the full path to the library to link.
401 self.linker_arg("-force_load");
402 let lib = archive::find_library(lib, search_path, &self.sess);
403 self.linker_arg(&lib);
407 fn link_whole_rlib(&mut self, lib: &Path) {
409 if self.sess.target.is_like_osx {
410 self.linker_arg("-force_load");
411 self.linker_arg(&lib);
413 self.linker_arg("--whole-archive").cmd.arg(lib);
414 self.linker_arg("--no-whole-archive");
418 fn gc_sections(&mut self, keep_metadata: bool) {
419 // The dead_strip option to the linker specifies that functions and data
420 // unreachable by the entry point will be removed. This is quite useful
421 // with Rust's compilation model of compiling libraries at a time into
422 // one object file. For example, this brings hello world from 1.7MB to
425 // Note that this is done for both executables and dynamic libraries. We
426 // won't get much benefit from dylibs because LLVM will have already
427 // stripped away as much as it could. This has not been seen to impact
428 // link times negatively.
430 // -dead_strip can't be part of the pre_link_args because it's also used
431 // for partial linking when using multiple codegen units (-r). So we
433 if self.sess.target.is_like_osx {
434 self.linker_arg("-dead_strip");
435 } else if self.sess.target.is_like_solaris {
436 self.linker_arg("-zignore");
438 // If we're building a dylib, we don't use --gc-sections because LLVM
439 // has already done the best it can do, and we also don't want to
440 // eliminate the metadata. If we're building an executable, however,
441 // --gc-sections drops the size of hello world from 1.8MB to 597K, a 67%
443 } else if !keep_metadata {
444 self.linker_arg("--gc-sections");
448 fn optimize(&mut self) {
449 if !self.sess.target.linker_is_gnu {
453 // GNU-style linkers support optimization with -O. GNU ld doesn't
454 // need a numeric argument, but other linkers do.
455 if self.sess.opts.optimize == config::OptLevel::Default
456 || self.sess.opts.optimize == config::OptLevel::Aggressive
458 self.linker_arg("-O1");
462 fn pgo_gen(&mut self) {
463 if !self.sess.target.linker_is_gnu {
467 // If we're doing PGO generation stuff and on a GNU-like linker, use the
468 // "-u" flag to properly pull in the profiler runtime bits.
470 // This is because LLVM otherwise won't add the needed initialization
471 // for us on Linux (though the extra flag should be harmless if it
474 // See https://reviews.llvm.org/D14033 and https://reviews.llvm.org/D14030.
476 // Though it may be worth to try to revert those changes upstream, since
477 // the overhead of the initialization should be minor.
479 self.cmd.arg("__llvm_profile_runtime");
482 fn control_flow_guard(&mut self) {}
484 fn debuginfo(&mut self, strip: Strip) {
487 Strip::Debuginfo => {
488 // MacOS linker does not support longhand argument --strip-debug
489 self.linker_arg("-S");
492 // MacOS linker does not support longhand argument --strip-all
493 self.linker_arg("-s");
498 fn no_crt_objects(&mut self) {
500 self.cmd.arg("-nostartfiles");
504 fn no_default_libraries(&mut self) {
506 self.cmd.arg("-nodefaultlibs");
510 fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType) {
511 // Symbol visibility in object files typically takes care of this.
512 if crate_type == CrateType::Executable && self.sess.target.override_export_symbols.is_none()
517 // We manually create a list of exported symbols to ensure we don't expose any more.
518 // The object files have far more public symbols than we actually want to export,
519 // so we hide them all here.
521 if !self.sess.target.limit_rdylib_exports {
525 if crate_type == CrateType::ProcMacro {
529 let is_windows = self.sess.target.is_like_windows;
530 let mut arg = OsString::new();
531 let path = tmpdir.join(if is_windows { "list.def" } else { "list" });
533 debug!("EXPORTED SYMBOLS:");
535 if self.sess.target.is_like_osx {
536 // Write a plain, newline-separated list of symbols
537 let res: io::Result<()> = try {
538 let mut f = BufWriter::new(File::create(&path)?);
539 for sym in self.info.exports[&crate_type].iter() {
541 writeln!(f, "_{}", sym)?;
544 if let Err(e) = res {
545 self.sess.fatal(&format!("failed to write lib.def file: {}", e));
547 } else if is_windows {
548 let res: io::Result<()> = try {
549 let mut f = BufWriter::new(File::create(&path)?);
551 // .def file similar to MSVC one but without LIBRARY section
552 // because LD doesn't like when it's empty
553 writeln!(f, "EXPORTS")?;
554 for symbol in self.info.exports[&crate_type].iter() {
555 debug!(" _{}", symbol);
556 writeln!(f, " {}", symbol)?;
559 if let Err(e) = res {
560 self.sess.fatal(&format!("failed to write list.def file: {}", e));
563 // Write an LD version script
564 let res: io::Result<()> = try {
565 let mut f = BufWriter::new(File::create(&path)?);
567 if !self.info.exports[&crate_type].is_empty() {
568 writeln!(f, " global:")?;
569 for sym in self.info.exports[&crate_type].iter() {
571 writeln!(f, " {};", sym)?;
574 writeln!(f, "\n local:\n *;\n}};")?;
576 if let Err(e) = res {
577 self.sess.fatal(&format!("failed to write version script: {}", e));
581 if self.sess.target.is_like_osx {
585 arg.push("-exported_symbols_list,");
586 } else if self.sess.target.is_like_solaris {
595 // Both LD and LLD accept export list in *.def file form, there are no flags required
597 arg.push("--version-script=")
605 fn subsystem(&mut self, subsystem: &str) {
606 self.linker_arg("--subsystem");
607 self.linker_arg(&subsystem);
610 fn finalize(&mut self) {
611 self.hint_dynamic(); // Reset to default before returning the composed command line.
614 fn group_start(&mut self) {
615 if self.takes_hints() {
616 self.linker_arg("--start-group");
620 fn group_end(&mut self) {
621 if self.takes_hints() {
622 self.linker_arg("--end-group");
626 fn linker_plugin_lto(&mut self) {
627 match self.sess.opts.cg.linker_plugin_lto {
628 LinkerPluginLto::Disabled => {
631 LinkerPluginLto::LinkerPluginAuto => {
632 self.push_linker_plugin_lto_args(None);
634 LinkerPluginLto::LinkerPlugin(ref path) => {
635 self.push_linker_plugin_lto_args(Some(path.as_os_str()));
640 // Add the `GNU_EH_FRAME` program header which is required to locate unwinding information.
641 // Some versions of `gcc` add it implicitly, some (e.g. `musl-gcc`) don't,
642 // so we just always add it.
643 fn add_eh_frame_header(&mut self) {
644 self.linker_arg("--eh-frame-hdr");
647 fn add_no_exec(&mut self) {
648 if self.sess.target.is_like_windows {
649 self.linker_arg("--nxcompat");
650 } else if self.sess.target.linker_is_gnu {
651 self.linker_arg("-znoexecstack");
655 fn add_as_needed(&mut self) {
656 if self.sess.target.linker_is_gnu {
657 self.linker_arg("--as-needed");
662 pub struct MsvcLinker<'a> {
665 info: &'a LinkerInfo,
668 impl<'a> Linker for MsvcLinker<'a> {
669 fn cmd(&mut self) -> &mut Command {
673 fn set_output_kind(&mut self, output_kind: LinkOutputKind, out_filename: &Path) {
675 LinkOutputKind::DynamicNoPicExe
676 | LinkOutputKind::DynamicPicExe
677 | LinkOutputKind::StaticNoPicExe
678 | LinkOutputKind::StaticPicExe => {}
679 LinkOutputKind::DynamicDylib | LinkOutputKind::StaticDylib => {
680 self.cmd.arg("/DLL");
681 let mut arg: OsString = "/IMPLIB:".into();
682 arg.push(out_filename.with_extension("dll.lib"));
685 LinkOutputKind::WasiReactorExe => {
686 panic!("can't link as reactor on non-wasi target");
691 fn link_rlib(&mut self, lib: &Path) {
694 fn add_object(&mut self, path: &Path) {
698 fn gc_sections(&mut self, _keep_metadata: bool) {
699 // MSVC's ICF (Identical COMDAT Folding) link optimization is
700 // slow for Rust and thus we disable it by default when not in
701 // optimization build.
702 if self.sess.opts.optimize != config::OptLevel::No {
703 self.cmd.arg("/OPT:REF,ICF");
705 // It is necessary to specify NOICF here, because /OPT:REF
706 // implies ICF by default.
707 self.cmd.arg("/OPT:REF,NOICF");
711 fn link_dylib(&mut self, lib: Symbol) {
712 self.cmd.arg(&format!("{}.lib", lib));
715 fn link_rust_dylib(&mut self, lib: Symbol, path: &Path) {
716 // When producing a dll, the MSVC linker may not actually emit a
717 // `foo.lib` file if the dll doesn't actually export any symbols, so we
718 // check to see if the file is there and just omit linking to it if it's
720 let name = format!("{}.dll.lib", lib);
721 if fs::metadata(&path.join(&name)).is_ok() {
726 fn link_staticlib(&mut self, lib: Symbol) {
727 self.cmd.arg(&format!("{}.lib", lib));
730 fn full_relro(&mut self) {
734 fn partial_relro(&mut self) {
738 fn no_relro(&mut self) {
742 fn no_crt_objects(&mut self) {
746 fn no_default_libraries(&mut self) {
747 self.cmd.arg("/NODEFAULTLIB");
750 fn include_path(&mut self, path: &Path) {
751 let mut arg = OsString::from("/LIBPATH:");
756 fn output_filename(&mut self, path: &Path) {
757 let mut arg = OsString::from("/OUT:");
762 fn framework_path(&mut self, _path: &Path) {
763 bug!("frameworks are not supported on windows")
765 fn link_framework(&mut self, _framework: Symbol) {
766 bug!("frameworks are not supported on windows")
769 fn link_whole_staticlib(&mut self, lib: Symbol, _search_path: &[PathBuf]) {
770 self.link_staticlib(lib);
771 self.cmd.arg(format!("/WHOLEARCHIVE:{}.lib", lib));
773 fn link_whole_rlib(&mut self, path: &Path) {
774 self.link_rlib(path);
775 let mut arg = OsString::from("/WHOLEARCHIVE:");
779 fn optimize(&mut self) {
780 // Needs more investigation of `/OPT` arguments
783 fn pgo_gen(&mut self) {
784 // Nothing needed here.
787 fn control_flow_guard(&mut self) {
788 self.cmd.arg("/guard:cf");
791 fn debuginfo(&mut self, strip: Strip) {
794 // This will cause the Microsoft linker to generate a PDB file
795 // from the CodeView line tables in the object files.
796 self.cmd.arg("/DEBUG");
798 // This will cause the Microsoft linker to embed .natvis info into the PDB file
799 let natvis_dir_path = self.sess.sysroot.join("lib\\rustlib\\etc");
800 if let Ok(natvis_dir) = fs::read_dir(&natvis_dir_path) {
801 for entry in natvis_dir {
804 let path = entry.path();
805 if path.extension() == Some("natvis".as_ref()) {
806 let mut arg = OsString::from("/NATVIS:");
813 .warn(&format!("error enumerating natvis directory: {}", err));
819 Strip::Debuginfo | Strip::Symbols => {
820 self.cmd.arg("/DEBUG:NONE");
825 // Currently the compiler doesn't use `dllexport` (an LLVM attribute) to
826 // export symbols from a dynamic library. When building a dynamic library,
827 // however, we're going to want some symbols exported, so this function
828 // generates a DEF file which lists all the symbols.
830 // The linker will read this `*.def` file and export all the symbols from
831 // the dynamic library. Note that this is not as simple as just exporting
832 // all the symbols in the current crate (as specified by `codegen.reachable`)
833 // but rather we also need to possibly export the symbols of upstream
834 // crates. Upstream rlibs may be linked statically to this dynamic library,
835 // in which case they may continue to transitively be used and hence need
836 // their symbols exported.
837 fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType) {
838 // Symbol visibility takes care of this typically
839 if crate_type == CrateType::Executable {
843 let path = tmpdir.join("lib.def");
844 let res: io::Result<()> = try {
845 let mut f = BufWriter::new(File::create(&path)?);
847 // Start off with the standard module name header and then go
848 // straight to exports.
849 writeln!(f, "LIBRARY")?;
850 writeln!(f, "EXPORTS")?;
851 for symbol in self.info.exports[&crate_type].iter() {
852 debug!(" _{}", symbol);
853 writeln!(f, " {}", symbol)?;
856 if let Err(e) = res {
857 self.sess.fatal(&format!("failed to write lib.def file: {}", e));
859 let mut arg = OsString::from("/DEF:");
864 fn subsystem(&mut self, subsystem: &str) {
865 // Note that previous passes of the compiler validated this subsystem,
866 // so we just blindly pass it to the linker.
867 self.cmd.arg(&format!("/SUBSYSTEM:{}", subsystem));
869 // Windows has two subsystems we're interested in right now, the console
870 // and windows subsystems. These both implicitly have different entry
871 // points (starting symbols). The console entry point starts with
872 // `mainCRTStartup` and the windows entry point starts with
873 // `WinMainCRTStartup`. These entry points, defined in system libraries,
874 // will then later probe for either `main` or `WinMain`, respectively to
875 // start the application.
877 // In Rust we just always generate a `main` function so we want control
878 // to always start there, so we force the entry point on the windows
879 // subsystem to be `mainCRTStartup` to get everything booted up
882 // For more information see RFC #1665
883 if subsystem == "windows" {
884 self.cmd.arg("/ENTRY:mainCRTStartup");
888 fn finalize(&mut self) {}
890 // MSVC doesn't need group indicators
891 fn group_start(&mut self) {}
892 fn group_end(&mut self) {}
894 fn linker_plugin_lto(&mut self) {
898 fn add_no_exec(&mut self) {
899 self.cmd.arg("/NXCOMPAT");
903 pub struct EmLinker<'a> {
906 info: &'a LinkerInfo,
909 impl<'a> Linker for EmLinker<'a> {
910 fn cmd(&mut self) -> &mut Command {
914 fn set_output_kind(&mut self, _output_kind: LinkOutputKind, _out_filename: &Path) {}
916 fn include_path(&mut self, path: &Path) {
917 self.cmd.arg("-L").arg(path);
920 fn link_staticlib(&mut self, lib: Symbol) {
921 self.cmd.arg("-l").sym_arg(lib);
924 fn output_filename(&mut self, path: &Path) {
925 self.cmd.arg("-o").arg(path);
928 fn add_object(&mut self, path: &Path) {
932 fn link_dylib(&mut self, lib: Symbol) {
933 // Emscripten always links statically
934 self.link_staticlib(lib);
937 fn link_whole_staticlib(&mut self, lib: Symbol, _search_path: &[PathBuf]) {
939 self.link_staticlib(lib);
942 fn link_whole_rlib(&mut self, lib: &Path) {
947 fn link_rust_dylib(&mut self, lib: Symbol, _path: &Path) {
948 self.link_dylib(lib);
951 fn link_rlib(&mut self, lib: &Path) {
952 self.add_object(lib);
955 fn full_relro(&mut self) {
959 fn partial_relro(&mut self) {
963 fn no_relro(&mut self) {
967 fn framework_path(&mut self, _path: &Path) {
968 bug!("frameworks are not supported on Emscripten")
971 fn link_framework(&mut self, _framework: Symbol) {
972 bug!("frameworks are not supported on Emscripten")
975 fn gc_sections(&mut self, _keep_metadata: bool) {
979 fn optimize(&mut self) {
980 // Emscripten performs own optimizations
981 self.cmd.arg(match self.sess.opts.optimize {
982 OptLevel::No => "-O0",
983 OptLevel::Less => "-O1",
984 OptLevel::Default => "-O2",
985 OptLevel::Aggressive => "-O3",
986 OptLevel::Size => "-Os",
987 OptLevel::SizeMin => "-Oz",
989 // Unusable until https://github.com/rust-lang/rust/issues/38454 is resolved
990 self.cmd.args(&["--memory-init-file", "0"]);
993 fn pgo_gen(&mut self) {
994 // noop, but maybe we need something like the gnu linker?
997 fn control_flow_guard(&mut self) {}
999 fn debuginfo(&mut self, _strip: Strip) {
1000 // Preserve names or generate source maps depending on debug info
1001 self.cmd.arg(match self.sess.opts.debuginfo {
1002 DebugInfo::None => "-g0",
1003 DebugInfo::Limited => "-g3",
1004 DebugInfo::Full => "-g4",
1008 fn no_crt_objects(&mut self) {}
1010 fn no_default_libraries(&mut self) {
1011 self.cmd.args(&["-s", "DEFAULT_LIBRARY_FUNCS_TO_INCLUDE=[]"]);
1014 fn export_symbols(&mut self, _tmpdir: &Path, crate_type: CrateType) {
1015 let symbols = &self.info.exports[&crate_type];
1017 debug!("EXPORTED SYMBOLS:");
1021 let mut arg = OsString::from("EXPORTED_FUNCTIONS=");
1022 let mut encoded = String::new();
1025 let mut encoder = json::Encoder::new(&mut encoded);
1026 let res = encoder.emit_seq(symbols.len(), |encoder| {
1027 for (i, sym) in symbols.iter().enumerate() {
1028 encoder.emit_seq_elt(i, |encoder| encoder.emit_str(&("_".to_owned() + sym)))?;
1032 if let Err(e) = res {
1033 self.sess.fatal(&format!("failed to encode exported symbols: {}", e));
1036 debug!("{}", encoded);
1042 fn subsystem(&mut self, _subsystem: &str) {
1046 fn finalize(&mut self) {}
1048 // Appears not necessary on Emscripten
1049 fn group_start(&mut self) {}
1050 fn group_end(&mut self) {}
1052 fn linker_plugin_lto(&mut self) {
1057 pub struct WasmLd<'a> {
1060 info: &'a LinkerInfo,
1063 impl<'a> WasmLd<'a> {
1064 fn new(mut cmd: Command, sess: &'a Session, info: &'a LinkerInfo) -> WasmLd<'a> {
1065 // If the atomics feature is enabled for wasm then we need a whole bunch
1068 // * `--shared-memory` - the link won't even succeed without this, flags
1069 // the one linear memory as `shared`
1071 // * `--max-memory=1G` - when specifying a shared memory this must also
1072 // be specified. We conservatively choose 1GB but users should be able
1073 // to override this with `-C link-arg`.
1075 // * `--import-memory` - it doesn't make much sense for memory to be
1076 // exported in a threaded module because typically you're
1077 // sharing memory and instantiating the module multiple times. As a
1078 // result if it were exported then we'd just have no sharing.
1080 // * `--export=__wasm_init_memory` - when using `--passive-segments` the
1081 // linker will synthesize this function, and so we need to make sure
1082 // that our usage of `--export` below won't accidentally cause this
1083 // function to get deleted.
1085 // * `--export=*tls*` - when `#[thread_local]` symbols are used these
1086 // symbols are how the TLS segments are initialized and configured.
1087 if sess.target_features.contains(&sym::atomics) {
1088 cmd.arg("--shared-memory");
1089 cmd.arg("--max-memory=1073741824");
1090 cmd.arg("--import-memory");
1091 cmd.arg("--export=__wasm_init_memory");
1092 cmd.arg("--export=__wasm_init_tls");
1093 cmd.arg("--export=__tls_size");
1094 cmd.arg("--export=__tls_align");
1095 cmd.arg("--export=__tls_base");
1097 WasmLd { cmd, sess, info }
1101 impl<'a> Linker for WasmLd<'a> {
1102 fn cmd(&mut self) -> &mut Command {
1106 fn set_output_kind(&mut self, output_kind: LinkOutputKind, _out_filename: &Path) {
1108 LinkOutputKind::DynamicNoPicExe
1109 | LinkOutputKind::DynamicPicExe
1110 | LinkOutputKind::StaticNoPicExe
1111 | LinkOutputKind::StaticPicExe => {}
1112 LinkOutputKind::DynamicDylib | LinkOutputKind::StaticDylib => {
1113 self.cmd.arg("--no-entry");
1115 LinkOutputKind::WasiReactorExe => {
1116 self.cmd.arg("--entry");
1117 self.cmd.arg("_initialize");
1122 fn link_dylib(&mut self, lib: Symbol) {
1123 self.cmd.arg("-l").sym_arg(lib);
1126 fn link_staticlib(&mut self, lib: Symbol) {
1127 self.cmd.arg("-l").sym_arg(lib);
1130 fn link_rlib(&mut self, lib: &Path) {
1134 fn include_path(&mut self, path: &Path) {
1135 self.cmd.arg("-L").arg(path);
1138 fn framework_path(&mut self, _path: &Path) {
1139 panic!("frameworks not supported")
1142 fn output_filename(&mut self, path: &Path) {
1143 self.cmd.arg("-o").arg(path);
1146 fn add_object(&mut self, path: &Path) {
1150 fn full_relro(&mut self) {}
1152 fn partial_relro(&mut self) {}
1154 fn no_relro(&mut self) {}
1156 fn link_rust_dylib(&mut self, lib: Symbol, _path: &Path) {
1157 self.cmd.arg("-l").sym_arg(lib);
1160 fn link_framework(&mut self, _framework: Symbol) {
1161 panic!("frameworks not supported")
1164 fn link_whole_staticlib(&mut self, lib: Symbol, _search_path: &[PathBuf]) {
1165 self.cmd.arg("-l").sym_arg(lib);
1168 fn link_whole_rlib(&mut self, lib: &Path) {
1172 fn gc_sections(&mut self, _keep_metadata: bool) {
1173 self.cmd.arg("--gc-sections");
1176 fn optimize(&mut self) {
1177 self.cmd.arg(match self.sess.opts.optimize {
1178 OptLevel::No => "-O0",
1179 OptLevel::Less => "-O1",
1180 OptLevel::Default => "-O2",
1181 OptLevel::Aggressive => "-O3",
1182 // Currently LLD doesn't support `Os` and `Oz`, so pass through `O2`
1184 OptLevel::Size => "-O2",
1185 OptLevel::SizeMin => "-O2",
1189 fn pgo_gen(&mut self) {}
1191 fn debuginfo(&mut self, strip: Strip) {
1194 Strip::Debuginfo => {
1195 self.cmd.arg("--strip-debug");
1198 self.cmd.arg("--strip-all");
1203 fn control_flow_guard(&mut self) {}
1205 fn no_crt_objects(&mut self) {}
1207 fn no_default_libraries(&mut self) {}
1209 fn export_symbols(&mut self, _tmpdir: &Path, crate_type: CrateType) {
1210 for sym in self.info.exports[&crate_type].iter() {
1211 self.cmd.arg("--export").arg(&sym);
1214 // LLD will hide these otherwise-internal symbols since it only exports
1215 // symbols explicity passed via the `--export` flags above and hides all
1216 // others. Various bits and pieces of tooling use this, so be sure these
1217 // symbols make their way out of the linker as well.
1218 self.cmd.arg("--export=__heap_base");
1219 self.cmd.arg("--export=__data_end");
1222 fn subsystem(&mut self, _subsystem: &str) {}
1224 fn finalize(&mut self) {}
1226 // Not needed for now with LLD
1227 fn group_start(&mut self) {}
1228 fn group_end(&mut self) {}
1230 fn linker_plugin_lto(&mut self) {
1231 // Do nothing for now
1235 fn exported_symbols(tcx: TyCtxt<'_>, crate_type: CrateType) -> Vec<String> {
1236 if let Some(ref exports) = tcx.sess.target.override_export_symbols {
1237 return exports.clone();
1240 let mut symbols = Vec::new();
1242 let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
1243 for &(symbol, level) in tcx.exported_symbols(LOCAL_CRATE).iter() {
1244 if level.is_below_threshold(export_threshold) {
1245 symbols.push(symbol_export::symbol_name_for_instance_in_crate(
1253 let formats = tcx.dependency_formats(LOCAL_CRATE);
1254 let deps = formats.iter().find_map(|(t, list)| (*t == crate_type).then_some(list)).unwrap();
1256 for (index, dep_format) in deps.iter().enumerate() {
1257 let cnum = CrateNum::new(index + 1);
1258 // For each dependency that we are linking to statically ...
1259 if *dep_format == Linkage::Static {
1260 // ... we add its symbol list to our export list.
1261 for &(symbol, level) in tcx.exported_symbols(cnum).iter() {
1262 if !level.is_below_threshold(export_threshold) {
1266 symbols.push(symbol_export::symbol_name_for_instance_in_crate(tcx, symbol, cnum));
1274 /// Much simplified and explicit CLI for the NVPTX linker. The linker operates
1275 /// with bitcode and uses LLVM backend to generate a PTX assembly.
1276 pub struct PtxLinker<'a> {
1281 impl<'a> Linker for PtxLinker<'a> {
1282 fn cmd(&mut self) -> &mut Command {
1286 fn set_output_kind(&mut self, _output_kind: LinkOutputKind, _out_filename: &Path) {}
1288 fn link_rlib(&mut self, path: &Path) {
1289 self.cmd.arg("--rlib").arg(path);
1292 fn link_whole_rlib(&mut self, path: &Path) {
1293 self.cmd.arg("--rlib").arg(path);
1296 fn include_path(&mut self, path: &Path) {
1297 self.cmd.arg("-L").arg(path);
1300 fn debuginfo(&mut self, _strip: Strip) {
1301 self.cmd.arg("--debug");
1304 fn add_object(&mut self, path: &Path) {
1305 self.cmd.arg("--bitcode").arg(path);
1308 fn optimize(&mut self) {
1309 match self.sess.lto() {
1310 Lto::Thin | Lto::Fat | Lto::ThinLocal => {
1311 self.cmd.arg("-Olto");
1318 fn output_filename(&mut self, path: &Path) {
1319 self.cmd.arg("-o").arg(path);
1322 fn finalize(&mut self) {
1323 // Provide the linker with fallback to internal `target-cpu`.
1324 self.cmd.arg("--fallback-arch").arg(match self.sess.opts.cg.target_cpu {
1326 None => &self.sess.target.cpu,
1330 fn link_dylib(&mut self, _lib: Symbol) {
1331 panic!("external dylibs not supported")
1334 fn link_rust_dylib(&mut self, _lib: Symbol, _path: &Path) {
1335 panic!("external dylibs not supported")
1338 fn link_staticlib(&mut self, _lib: Symbol) {
1339 panic!("staticlibs not supported")
1342 fn link_whole_staticlib(&mut self, _lib: Symbol, _search_path: &[PathBuf]) {
1343 panic!("staticlibs not supported")
1346 fn framework_path(&mut self, _path: &Path) {
1347 panic!("frameworks not supported")
1350 fn link_framework(&mut self, _framework: Symbol) {
1351 panic!("frameworks not supported")
1354 fn full_relro(&mut self) {}
1356 fn partial_relro(&mut self) {}
1358 fn no_relro(&mut self) {}
1360 fn gc_sections(&mut self, _keep_metadata: bool) {}
1362 fn pgo_gen(&mut self) {}
1364 fn no_crt_objects(&mut self) {}
1366 fn no_default_libraries(&mut self) {}
1368 fn control_flow_guard(&mut self) {}
1370 fn export_symbols(&mut self, _tmpdir: &Path, _crate_type: CrateType) {}
1372 fn subsystem(&mut self, _subsystem: &str) {}
1374 fn group_start(&mut self) {}
1376 fn group_end(&mut self) {}
1378 fn linker_plugin_lto(&mut self) {}