1 use rustc_data_structures::fx::FxHashSet;
2 use rustc_fs_util::fix_windows_verbatim_for_gcc;
3 use rustc_hir::def_id::CrateNum;
4 use rustc_middle::middle::cstore::{EncodedMetadata, LibSource, NativeLibrary, NativeLibraryKind};
5 use rustc_middle::middle::dependency_format::Linkage;
6 use rustc_session::config::{
7 self, CFGuard, DebugInfo, OutputFilenames, OutputType, PrintRequest, Sanitizer,
9 use rustc_session::output::{check_file_is_writeable, invalid_output_for_target, out_filename};
10 use rustc_session::search_paths::PathKind;
11 /// For all the linkers we support, and information they might
12 /// need out of the shared crate context before we get rid of it.
13 use rustc_session::{filesearch, Session};
14 use rustc_span::symbol::Symbol;
15 use rustc_target::spec::{LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, RelroLevel};
17 use super::archive::ArchiveBuilder;
18 use super::command::Command;
19 use super::linker::Linker;
20 use super::rpath::{self, RPathConfig};
22 looks_like_rust_object_file, CodegenResults, CrateInfo, METADATA_FILENAME,
23 RLIB_BYTECODE_EXTENSION,
26 use cc::windows_registry;
27 use tempfile::{Builder as TempFileBuilder, TempDir};
32 use std::ffi::OsString;
36 use std::path::{Path, PathBuf};
37 use std::process::{ExitStatus, Output, Stdio};
40 pub fn remove(sess: &Session, path: &Path) {
41 if let Err(e) = fs::remove_file(path) {
42 sess.err(&format!("failed to remove {}: {}", path.display(), e));
46 /// Performs the linkage portion of the compilation phase. This will generate all
47 /// of the requested outputs for this compilation session.
48 pub fn link_binary<'a, B: ArchiveBuilder<'a>>(
50 codegen_results: &CodegenResults,
51 outputs: &OutputFilenames,
55 let _timer = sess.timer("link_binary");
56 let output_metadata = sess.opts.output_types.contains_key(&OutputType::Metadata);
57 for &crate_type in sess.crate_types.borrow().iter() {
58 // Ignore executable crates if we have -Z no-codegen, as they will error.
59 if (sess.opts.debugging_opts.no_codegen || !sess.opts.output_types.should_codegen())
61 && crate_type == config::CrateType::Executable
66 if invalid_output_for_target(sess, crate_type) {
68 "invalid output type `{:?}` for target os `{}`",
70 sess.opts.target_triple
74 sess.time("link_binary_check_files_are_writeable", || {
75 for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
76 check_file_is_writeable(obj, sess);
80 let tmpdir = TempFileBuilder::new()
83 .unwrap_or_else(|err| sess.fatal(&format!("couldn't create a temp dir: {}", err)));
85 if outputs.outputs.should_codegen() {
86 let out_filename = out_filename(sess, crate_type, outputs, crate_name);
88 config::CrateType::Rlib => {
89 let _timer = sess.timer("link_rlib");
99 config::CrateType::Staticlib => {
100 link_staticlib::<B>(sess, codegen_results, &out_filename, &tmpdir);
113 if sess.opts.json_artifact_notifications {
114 sess.parse_sess.span_diagnostic.emit_artifact_notification(&out_filename, "link");
118 if sess.opts.cg.save_temps {
119 let _ = tmpdir.into_path();
123 // Remove the temporary object file and metadata if we aren't saving temps
124 sess.time("link_binary_remove_temps", || {
125 if !sess.opts.cg.save_temps {
126 if sess.opts.output_types.should_codegen()
127 && !preserve_objects_for_their_debuginfo(sess)
129 for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
133 for obj in codegen_results.modules.iter().filter_map(|m| m.bytecode_compressed.as_ref())
137 if let Some(ref metadata_module) = codegen_results.metadata_module {
138 if let Some(ref obj) = metadata_module.object {
142 if let Some(ref allocator_module) = codegen_results.allocator_module {
143 if let Some(ref obj) = allocator_module.object {
146 if let Some(ref bc) = allocator_module.bytecode_compressed {
154 // The third parameter is for env vars, used on windows to set up the
155 // path for MSVC to find its DLLs, and gcc to find its bundled
157 fn get_linker(sess: &Session, linker: &Path, flavor: LinkerFlavor) -> Command {
158 let msvc_tool = windows_registry::find_tool(&sess.opts.target_triple.triple(), "link.exe");
160 // If our linker looks like a batch script on Windows then to execute this
161 // we'll need to spawn `cmd` explicitly. This is primarily done to handle
162 // emscripten where the linker is `emcc.bat` and needs to be spawned as
163 // `cmd /c emcc.bat ...`.
165 // This worked historically but is needed manually since #42436 (regression
166 // was tagged as #42791) and some more info can be found on #44443 for
167 // emscripten itself.
168 let mut cmd = match linker.to_str() {
169 Some(linker) if cfg!(windows) && linker.ends_with(".bat") => Command::bat_script(linker),
171 LinkerFlavor::Lld(f) => Command::lld(linker, f),
173 if sess.opts.cg.linker.is_none() && sess.target.target.options.linker.is_none() =>
175 Command::new(msvc_tool.as_ref().map(|t| t.path()).unwrap_or(linker))
177 _ => Command::new(linker),
181 // UWP apps have API restrictions enforced during Store submissions.
182 // To comply with the Windows App Certification Kit,
183 // MSVC needs to link with the Store versions of the runtime libraries (vcruntime, msvcrt, etc).
184 let t = &sess.target.target;
185 if (flavor == LinkerFlavor::Msvc || flavor == LinkerFlavor::Lld(LldFlavor::Link))
186 && t.target_vendor == "uwp"
188 if let Some(ref tool) = msvc_tool {
189 let original_path = tool.path();
190 if let Some(ref root_lib_path) = original_path.ancestors().nth(4) {
191 let arch = match t.arch.as_str() {
192 "x86_64" => Some("x64".to_string()),
193 "x86" => Some("x86".to_string()),
194 "aarch64" => Some("arm64".to_string()),
197 if let Some(ref a) = arch {
198 // FIXME: Move this to `fn linker_with_args`.
199 let mut arg = OsString::from("/LIBPATH:");
200 arg.push(format!("{}\\lib\\{}\\store", root_lib_path.display(), a.to_string()));
203 warn!("arch is not supported");
206 warn!("MSVC root path lib location not found");
209 warn!("link.exe not found");
213 // The compiler's sysroot often has some bundled tools, so add it to the
214 // PATH for the child.
215 let mut new_path = sess.host_filesearch(PathKind::All).get_tools_search_paths();
216 let mut msvc_changed_path = false;
217 if sess.target.target.options.is_like_msvc {
218 if let Some(ref tool) = msvc_tool {
219 cmd.args(tool.args());
220 for &(ref k, ref v) in tool.env() {
222 new_path.extend(env::split_paths(v));
223 msvc_changed_path = true;
231 if !msvc_changed_path {
232 if let Some(path) = env::var_os("PATH") {
233 new_path.extend(env::split_paths(&path));
236 cmd.env("PATH", env::join_paths(new_path).unwrap());
241 pub fn each_linked_rlib(
243 f: &mut dyn FnMut(CrateNum, &Path),
244 ) -> Result<(), String> {
245 let crates = info.used_crates_static.iter();
247 for (ty, list) in info.dependency_formats.iter() {
249 config::CrateType::Executable
250 | config::CrateType::Staticlib
251 | config::CrateType::Cdylib
252 | config::CrateType::ProcMacro => {
259 let fmts = match fmts {
261 None => return Err("could not find formats for rlibs".to_string()),
263 for &(cnum, ref path) in crates {
264 match fmts.get(cnum.as_usize() - 1) {
265 Some(&Linkage::NotLinked | &Linkage::IncludedFromDylib) => continue,
267 None => return Err("could not find formats for rlibs".to_string()),
269 let name = &info.crate_name[&cnum];
270 let path = match *path {
271 LibSource::Some(ref p) => p,
272 LibSource::MetadataOnly => {
274 "could not find rlib for: `{}`, found rmeta (metadata) file",
278 LibSource::None => return Err(format!("could not find rlib for: `{}`", name)),
285 /// We use a temp directory here to avoid races between concurrent rustc processes,
286 /// such as builds in the same directory using the same filename for metadata while
287 /// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a
288 /// directory being searched for `extern crate` (observing an incomplete file).
289 /// The returned path is the temporary file containing the complete metadata.
290 pub fn emit_metadata(sess: &Session, metadata: &EncodedMetadata, tmpdir: &TempDir) -> PathBuf {
291 let out_filename = tmpdir.path().join(METADATA_FILENAME);
292 let result = fs::write(&out_filename, &metadata.raw_data);
294 if let Err(e) = result {
295 sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e));
303 // An rlib in its current incarnation is essentially a renamed .a file. The
304 // rlib primarily contains the object file of the crate, but it also contains
305 // all of the object files from native libraries. This is done by unzipping
306 // native libraries and inserting all of the contents into this archive.
307 fn link_rlib<'a, B: ArchiveBuilder<'a>>(
309 codegen_results: &CodegenResults,
314 info!("preparing rlib to {:?}", out_filename);
315 let mut ab = <B as ArchiveBuilder>::new(sess, out_filename, None);
317 for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
321 // Note that in this loop we are ignoring the value of `lib.cfg`. That is,
322 // we may not be configured to actually include a static library if we're
323 // adding it here. That's because later when we consume this rlib we'll
324 // decide whether we actually needed the static library or not.
326 // To do this "correctly" we'd need to keep track of which libraries added
327 // which object files to the archive. We don't do that here, however. The
328 // #[link(cfg(..))] feature is unstable, though, and only intended to get
329 // liblibc working. In that sense the check below just indicates that if
330 // there are any libraries we want to omit object files for at link time we
331 // just exclude all custom object files.
333 // Eventually if we want to stabilize or flesh out the #[link(cfg(..))]
334 // feature then we'll need to figure out how to record what objects were
335 // loaded from the libraries found here and then encode that into the
336 // metadata of the rlib we're generating somehow.
337 for lib in codegen_results.crate_info.used_libraries.iter() {
339 NativeLibraryKind::NativeStatic => {}
340 NativeLibraryKind::NativeStaticNobundle
341 | NativeLibraryKind::NativeFramework
342 | NativeLibraryKind::NativeRawDylib
343 | NativeLibraryKind::NativeUnknown => continue,
345 if let Some(name) = lib.name {
346 ab.add_native_library(name);
350 // After adding all files to the archive, we need to update the
351 // symbol table of the archive.
354 // Note that it is important that we add all of our non-object "magical
355 // files" *after* all of the object files in the archive. The reason for
356 // this is as follows:
358 // * When performing LTO, this archive will be modified to remove
359 // objects from above. The reason for this is described below.
361 // * When the system linker looks at an archive, it will attempt to
362 // determine the architecture of the archive in order to see whether its
365 // The algorithm for this detection is: iterate over the files in the
366 // archive. Skip magical SYMDEF names. Interpret the first file as an
367 // object file. Read architecture from the object file.
369 // * As one can probably see, if "metadata" and "foo.bc" were placed
370 // before all of the objects, then the architecture of this archive would
371 // not be correctly inferred once 'foo.o' is removed.
373 // Basically, all this means is that this code should not move above the
376 RlibFlavor::Normal => {
377 // Instead of putting the metadata in an object file section, rlibs
378 // contain the metadata in a separate file.
379 ab.add_file(&emit_metadata(sess, &codegen_results.metadata, tmpdir));
381 // For LTO purposes, the bytecode of this library is also inserted
384 codegen_results.modules.iter().filter_map(|m| m.bytecode_compressed.as_ref())
386 ab.add_file(bytecode);
389 // After adding all files to the archive, we need to update the
390 // symbol table of the archive. This currently dies on macOS (see
391 // #11162), and isn't necessary there anyway
392 if !sess.target.target.options.is_like_osx {
397 RlibFlavor::StaticlibBase => {
398 let obj = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref());
399 if let Some(obj) = obj {
408 // Create a static archive
410 // This is essentially the same thing as an rlib, but it also involves adding
411 // all of the upstream crates' objects into the archive. This will slurp in
412 // all of the native libraries of upstream dependencies as well.
414 // Additionally, there's no way for us to link dynamic libraries, so we warn
415 // about all dynamic library dependencies that they're not linked in.
417 // There's no need to include metadata in a static archive, so ensure to not
418 // link in the metadata object file (and also don't prepare the archive with a
420 fn link_staticlib<'a, B: ArchiveBuilder<'a>>(
422 codegen_results: &CodegenResults,
427 link_rlib::<B>(sess, codegen_results, RlibFlavor::StaticlibBase, out_filename, tempdir);
428 let mut all_native_libs = vec![];
430 let res = each_linked_rlib(&codegen_results.crate_info, &mut |cnum, path| {
431 let name = &codegen_results.crate_info.crate_name[&cnum];
432 let native_libs = &codegen_results.crate_info.native_libraries[&cnum];
434 // Here when we include the rlib into our staticlib we need to make a
435 // decision whether to include the extra object files along the way.
436 // These extra object files come from statically included native
437 // libraries, but they may be cfg'd away with #[link(cfg(..))].
439 // This unstable feature, though, only needs liblibc to work. The only
440 // use case there is where musl is statically included in liblibc.rlib,
441 // so if we don't want the included version we just need to skip it. As
442 // a result the logic here is that if *any* linked library is cfg'd away
443 // we just skip all object files.
445 // Clearly this is not sufficient for a general purpose feature, and
446 // we'd want to read from the library's metadata to determine which
447 // object files come from where and selectively skip them.
448 let skip_object_files = native_libs
450 .any(|lib| lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib));
454 are_upstream_rust_objects_already_included(sess)
455 && !ignored_for_lto(sess, &codegen_results.crate_info, cnum),
460 all_native_libs.extend(codegen_results.crate_info.native_libraries[&cnum].iter().cloned());
462 if let Err(e) = res {
469 if !all_native_libs.is_empty() {
470 if sess.opts.prints.contains(&PrintRequest::NativeStaticLibs) {
471 print_native_static_libs(sess, &all_native_libs);
476 // Create a dynamic library or executable
478 // This will invoke the system linker/cc to create the resulting file. This
479 // links to all upstream files as well.
480 fn link_natively<'a, B: ArchiveBuilder<'a>>(
482 crate_type: config::CrateType,
484 codegen_results: &CodegenResults,
488 info!("preparing {:?} to {:?}", crate_type, out_filename);
489 let (linker_path, flavor) = linker_and_flavor(sess);
490 let mut cmd = linker_with_args::<B>(
501 for &(ref k, ref v) in &sess.target.target.options.link_env {
504 for k in &sess.target.target.options.link_env_remove {
508 if sess.opts.debugging_opts.print_link_args {
509 println!("{:?}", &cmd);
512 // May have not found libraries in the right formats.
513 sess.abort_if_errors();
515 // Invoke the system linker
517 let retry_on_segfault = env::var("RUSTC_RETRY_LINKER_ON_SEGFAULT").is_ok();
522 prog = sess.time("run_linker", || exec_linker(sess, &cmd, out_filename, tmpdir));
523 let output = match prog {
524 Ok(ref output) => output,
527 if output.status.success() {
530 let mut out = output.stderr.clone();
531 out.extend(&output.stdout);
532 let out = String::from_utf8_lossy(&out);
534 // Check to see if the link failed with "unrecognized command line option:
535 // '-no-pie'" for gcc or "unknown argument: '-no-pie'" for clang. If so,
536 // reperform the link step without the -no-pie option. This is safe because
537 // if the linker doesn't support -no-pie then it should not default to
538 // linking executables as pie. Different versions of gcc seem to use
539 // different quotes in the error message so don't check for them.
540 if sess.target.target.options.linker_is_gnu
541 && flavor != LinkerFlavor::Ld
542 && (out.contains("unrecognized command line option")
543 || out.contains("unknown argument"))
544 && out.contains("-no-pie")
545 && cmd.get_args().iter().any(|e| e.to_string_lossy() == "-no-pie")
547 info!("linker output: {:?}", out);
548 warn!("Linker does not support -no-pie command line option. Retrying without.");
549 for arg in cmd.take_args() {
550 if arg.to_string_lossy() != "-no-pie" {
558 // Here's a terribly awful hack that really shouldn't be present in any
559 // compiler. Here an environment variable is supported to automatically
560 // retry the linker invocation if the linker looks like it segfaulted.
562 // Gee that seems odd, normally segfaults are things we want to know
563 // about! Unfortunately though in rust-lang/rust#38878 we're
564 // experiencing the linker segfaulting on Travis quite a bit which is
565 // causing quite a bit of pain to land PRs when they spuriously fail
566 // due to a segfault.
568 // The issue #38878 has some more debugging information on it as well,
569 // but this unfortunately looks like it's just a race condition in
570 // macOS's linker with some thread pool working in the background. It
571 // seems that no one currently knows a fix for this so in the meantime
572 // we're left with this...
573 if !retry_on_segfault || i > 3 {
576 let msg_segv = "clang: error: unable to execute command: Segmentation fault: 11";
577 let msg_bus = "clang: error: unable to execute command: Bus error: 10";
578 if out.contains(msg_segv) || out.contains(msg_bus) {
580 "looks like the linker segfaulted when we tried to call it, \
581 automatically retrying again. cmd = {:?}, out = {}.",
587 if is_illegal_instruction(&output.status) {
589 "looks like the linker hit an illegal instruction when we \
590 tried to call it, automatically retrying again. cmd = {:?}, ]\
591 out = {}, status = {}.",
592 cmd, out, output.status,
598 fn is_illegal_instruction(status: &ExitStatus) -> bool {
599 use std::os::unix::prelude::*;
600 status.signal() == Some(libc::SIGILL)
604 fn is_illegal_instruction(_status: &ExitStatus) -> bool {
611 fn escape_string(s: &[u8]) -> String {
612 str::from_utf8(s).map(|s| s.to_owned()).unwrap_or_else(|_| {
613 let mut x = "Non-UTF-8 output: ".to_string();
614 x.extend(s.iter().flat_map(|&b| ascii::escape_default(b)).map(char::from));
618 if !prog.status.success() {
619 let mut output = prog.stderr.clone();
620 output.extend_from_slice(&prog.stdout);
621 sess.struct_err(&format!(
622 "linking with `{}` failed: {}",
623 linker_path.display(),
626 .note(&format!("{:?}", &cmd))
627 .note(&escape_string(&output))
629 sess.abort_if_errors();
631 info!("linker stderr:\n{}", escape_string(&prog.stderr));
632 info!("linker stdout:\n{}", escape_string(&prog.stdout));
635 let linker_not_found = e.kind() == io::ErrorKind::NotFound;
637 let mut linker_error = {
638 if linker_not_found {
639 sess.struct_err(&format!("linker `{}` not found", linker_path.display()))
641 sess.struct_err(&format!(
642 "could not exec the linker `{}`",
643 linker_path.display()
648 linker_error.note(&e.to_string());
650 if !linker_not_found {
651 linker_error.note(&format!("{:?}", &cmd));
656 if sess.target.target.options.is_like_msvc && linker_not_found {
657 sess.note_without_error(
658 "the msvc targets depend on the msvc linker \
659 but `link.exe` was not found",
661 sess.note_without_error(
662 "please ensure that VS 2013, VS 2015, VS 2017 or VS 2019 \
663 was installed with the Visual C++ option",
666 sess.abort_if_errors();
670 // On macOS, debuggers need this utility to get run to do some munging of
671 // the symbols. Note, though, that if the object files are being preserved
672 // for their debug information there's no need for us to run dsymutil.
673 if sess.target.target.options.is_like_osx
674 && sess.opts.debuginfo != DebugInfo::None
675 && !preserve_objects_for_their_debuginfo(sess)
677 if let Err(e) = Command::new("dsymutil").arg(out_filename).output() {
678 sess.fatal(&format!("failed to run dsymutil: {}", e))
683 fn link_sanitizer_runtime(sess: &Session, crate_type: config::CrateType, linker: &mut dyn Linker) {
684 let sanitizer = match &sess.opts.debugging_opts.sanitizer {
689 if crate_type != config::CrateType::Executable {
693 let name = match sanitizer {
694 Sanitizer::Address => "asan",
695 Sanitizer::Leak => "lsan",
696 Sanitizer::Memory => "msan",
697 Sanitizer::Thread => "tsan",
700 let default_sysroot = filesearch::get_or_default_sysroot();
702 filesearch::make_target_lib_path(&default_sysroot, sess.opts.target_triple.triple());
703 let channel = option_env!("CFG_RELEASE_CHANNEL")
704 .map(|channel| format!("-{}", channel))
705 .unwrap_or_default();
707 match sess.opts.target_triple.triple() {
708 "x86_64-apple-darwin" => {
709 // On Apple platforms, the sanitizer is always built as a dylib, and
710 // LLVM will link to `@rpath/*.dylib`, so we need to specify an
711 // rpath to the library as well (the rpath should be absolute, see
712 // PR #41352 for details).
713 let libname = format!("rustc{}_rt.{}", channel, name);
714 let rpath = default_tlib.to_str().expect("non-utf8 component in path");
715 linker.args(&["-Wl,-rpath", "-Xlinker", rpath]);
716 linker.link_dylib(Symbol::intern(&libname));
718 "x86_64-unknown-linux-gnu" | "x86_64-fuchsia" | "aarch64-fuchsia" => {
719 let filename = format!("librustc{}_rt.{}.a", channel, name);
720 let path = default_tlib.join(&filename);
721 linker.link_whole_rlib(&path);
727 /// Returns a boolean indicating whether the specified crate should be ignored
730 /// Crates ignored during LTO are not lumped together in the "massive object
731 /// file" that we create and are linked in their normal rlib states. See
732 /// comments below for what crates do not participate in LTO.
734 /// It's unusual for a crate to not participate in LTO. Typically only
735 /// compiler-specific and unstable crates have a reason to not participate in
737 pub fn ignored_for_lto(sess: &Session, info: &CrateInfo, cnum: CrateNum) -> bool {
738 // If our target enables builtin function lowering in LLVM then the
739 // crates providing these functions don't participate in LTO (e.g.
740 // no_builtins or compiler builtins crates).
741 !sess.target.target.options.no_builtins
742 && (info.compiler_builtins == Some(cnum) || info.is_no_builtins.contains(&cnum))
745 fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
748 linker: Option<PathBuf>,
749 flavor: Option<LinkerFlavor>,
750 ) -> Option<(PathBuf, LinkerFlavor)> {
751 match (linker, flavor) {
752 (Some(linker), Some(flavor)) => Some((linker, flavor)),
753 // only the linker flavor is known; use the default linker for the selected flavor
754 (None, Some(flavor)) => Some((
755 PathBuf::from(match flavor {
756 LinkerFlavor::Em => {
763 LinkerFlavor::Gcc => {
764 if cfg!(any(target_os = "solaris", target_os = "illumos")) {
765 // On historical Solaris systems, "cc" may have
766 // been Sun Studio, which is not flag-compatible
767 // with "gcc". This history casts a long shadow,
768 // and many modern illumos distributions today
769 // ship GCC as "gcc" without also making it
770 // available as "cc".
776 LinkerFlavor::Ld => "ld",
777 LinkerFlavor::Msvc => "link.exe",
778 LinkerFlavor::Lld(_) => "lld",
779 LinkerFlavor::PtxLinker => "rust-ptx-linker",
783 (Some(linker), None) => {
784 let stem = linker.file_stem().and_then(|stem| stem.to_str()).unwrap_or_else(|| {
785 sess.fatal("couldn't extract file stem from specified linker")
788 let flavor = if stem == "emcc" {
790 } else if stem == "gcc"
791 || stem.ends_with("-gcc")
793 || stem.ends_with("-clang")
796 } else if stem == "ld" || stem == "ld.lld" || stem.ends_with("-ld") {
798 } else if stem == "link" || stem == "lld-link" {
800 } else if stem == "lld" || stem == "rust-lld" {
801 LinkerFlavor::Lld(sess.target.target.options.lld_flavor)
803 // fall back to the value in the target spec
804 sess.target.target.linker_flavor
807 Some((linker, flavor))
809 (None, None) => None,
813 // linker and linker flavor specified via command line have precedence over what the target
814 // specification specifies
815 if let Some(ret) = infer_from(sess, sess.opts.cg.linker.clone(), sess.opts.cg.linker_flavor) {
819 if let Some(ret) = infer_from(
821 sess.target.target.options.linker.clone().map(PathBuf::from),
822 Some(sess.target.target.linker_flavor),
827 bug!("Not enough information provided to determine how to invoke the linker");
830 /// Returns a boolean indicating whether we should preserve the object files on
831 /// the filesystem for their debug information. This is often useful with
832 /// split-dwarf like schemes.
833 fn preserve_objects_for_their_debuginfo(sess: &Session) -> bool {
834 // If the objects don't have debuginfo there's nothing to preserve.
835 if sess.opts.debuginfo == config::DebugInfo::None {
839 // If we're only producing artifacts that are archives, no need to preserve
840 // the objects as they're losslessly contained inside the archives.
841 let output_linked = sess
845 .any(|&x| x != config::CrateType::Rlib && x != config::CrateType::Staticlib);
850 // If we're on OSX then the equivalent of split dwarf is turned on by
851 // default. The final executable won't actually have any debug information
852 // except it'll have pointers to elsewhere. Historically we've always run
853 // `dsymutil` to "link all the dwarf together" but this is actually sort of
854 // a bummer for incremental compilation! (the whole point of split dwarf is
855 // that you don't do this sort of dwarf link).
857 // Basically as a result this just means that if we're on OSX and we're
858 // *not* running dsymutil then the object files are the only source of truth
859 // for debug information, so we must preserve them.
860 if sess.target.target.options.is_like_osx {
861 return !sess.opts.debugging_opts.run_dsymutil;
867 pub fn archive_search_paths(sess: &Session) -> Vec<PathBuf> {
868 sess.target_filesearch(PathKind::Native).search_path_dirs()
876 fn print_native_static_libs(sess: &Session, all_native_libs: &[NativeLibrary]) {
877 let lib_args: Vec<_> = all_native_libs
879 .filter(|l| relevant_lib(sess, l))
881 let name = lib.name?;
883 NativeLibraryKind::NativeStaticNobundle | NativeLibraryKind::NativeUnknown => {
884 if sess.target.target.options.is_like_msvc {
885 Some(format!("{}.lib", name))
887 Some(format!("-l{}", name))
890 NativeLibraryKind::NativeFramework => {
891 // ld-only syntax, since there are no frameworks in MSVC
892 Some(format!("-framework {}", name))
894 // These are included, no need to print them
895 NativeLibraryKind::NativeStatic | NativeLibraryKind::NativeRawDylib => None,
899 if !lib_args.is_empty() {
900 sess.note_without_error(
901 "Link against the following native artifacts when linking \
902 against this static library. The order and any duplication \
903 can be significant on some platforms.",
905 // Prefix for greppability
906 sess.note_without_error(&format!("native-static-libs: {}", &lib_args.join(" ")));
910 // Because windows-gnu target is meant to be self-contained for pure Rust code it bundles
911 // own mingw-w64 libraries. These libraries are usually not compatible with mingw-w64
912 // installed in the system. This breaks many cases where Rust is mixed with other languages
913 // (e.g. *-sys crates).
914 // We prefer system mingw-w64 libraries if they are available to avoid this issue.
915 fn get_crt_libs_path(sess: &Session) -> Option<PathBuf> {
916 fn find_exe_in_path<P>(exe_name: P) -> Option<PathBuf>
920 for dir in env::split_paths(&env::var_os("PATH")?) {
921 let full_path = dir.join(&exe_name);
922 if full_path.is_file() {
923 return Some(fix_windows_verbatim_for_gcc(&full_path));
929 fn probe(sess: &Session) -> Option<PathBuf> {
930 if let (linker, LinkerFlavor::Gcc) = linker_and_flavor(&sess) {
931 let linker_path = if cfg!(windows) && linker.extension().is_none() {
932 linker.with_extension("exe")
936 if let Some(linker_path) = find_exe_in_path(linker_path) {
937 let mingw_arch = match &sess.target.target.arch {
938 x if x == "x86" => "i686",
941 let mingw_bits = &sess.target.target.target_pointer_width;
942 let mingw_dir = format!("{}-w64-mingw32", mingw_arch);
943 // Here we have path/bin/gcc but we need path/
944 let mut path = linker_path;
947 // Loosely based on Clang MinGW driver
948 let probe_paths = vec![
949 path.join(&mingw_dir).join("lib"), // Typical path
950 path.join(&mingw_dir).join("sys-root/mingw/lib"), // Rare path
952 "lib/mingw/tools/install/mingw{}/{}/lib",
953 &mingw_bits, &mingw_dir
954 )), // Chocolatey is creative
956 for probe_path in probe_paths {
957 if probe_path.join("crt2.o").exists() {
958 return Some(probe_path);
966 let mut system_library_path = sess.system_library_path.borrow_mut();
967 match &*system_library_path {
968 Some(Some(compiler_libs_path)) => Some(compiler_libs_path.clone()),
971 let path = probe(sess);
972 *system_library_path = Some(path.clone());
978 fn get_object_file_path(sess: &Session, name: &str) -> PathBuf {
979 // prefer system {,dll}crt2.o libs, see get_crt_libs_path comment for more details
980 if sess.target.target.llvm_target.contains("windows-gnu") {
981 if let Some(compiler_libs_path) = get_crt_libs_path(sess) {
982 let file_path = compiler_libs_path.join(name);
983 if file_path.exists() {
988 let fs = sess.target_filesearch(PathKind::Native);
989 let file_path = fs.get_lib_path().join(name);
990 if file_path.exists() {
993 for search_path in fs.search_paths() {
994 let file_path = search_path.dir.join(name);
995 if file_path.exists() {
1005 out_filename: &Path,
1007 ) -> io::Result<Output> {
1008 // When attempting to spawn the linker we run a risk of blowing out the
1009 // size limits for spawning a new process with respect to the arguments
1010 // we pass on the command line.
1012 // Here we attempt to handle errors from the OS saying "your list of
1013 // arguments is too big" by reinvoking the linker again with an `@`-file
1014 // that contains all the arguments. The theory is that this is then
1015 // accepted on all linkers and the linker will read all its options out of
1016 // there instead of looking at the command line.
1017 if !cmd.very_likely_to_exceed_some_spawn_limit() {
1018 match cmd.command().stdout(Stdio::piped()).stderr(Stdio::piped()).spawn() {
1020 let output = child.wait_with_output();
1021 flush_linked_file(&output, out_filename)?;
1024 Err(ref e) if command_line_too_big(e) => {
1025 info!("command line to linker was too big: {}", e);
1027 Err(e) => return Err(e),
1031 info!("falling back to passing arguments to linker via an @-file");
1032 let mut cmd2 = cmd.clone();
1033 let mut args = String::new();
1034 for arg in cmd2.take_args() {
1037 arg: arg.to_str().unwrap(),
1038 is_like_msvc: sess.target.target.options.is_like_msvc,
1042 args.push_str("\n");
1044 let file = tmpdir.join("linker-arguments");
1045 let bytes = if sess.target.target.options.is_like_msvc {
1046 let mut out = Vec::with_capacity((1 + args.len()) * 2);
1047 // start the stream with a UTF-16 BOM
1048 for c in std::iter::once(0xFEFF).chain(args.encode_utf16()) {
1049 // encode in little endian
1051 out.push((c >> 8) as u8);
1057 fs::write(&file, &bytes)?;
1058 cmd2.arg(format!("@{}", file.display()));
1059 info!("invoking linker {:?}", cmd2);
1060 let output = cmd2.output();
1061 flush_linked_file(&output, out_filename)?;
1065 fn flush_linked_file(_: &io::Result<Output>, _: &Path) -> io::Result<()> {
1070 fn flush_linked_file(
1071 command_output: &io::Result<Output>,
1072 out_filename: &Path,
1073 ) -> io::Result<()> {
1074 // On Windows, under high I/O load, output buffers are sometimes not flushed,
1075 // even long after process exit, causing nasty, non-reproducible output bugs.
1077 // File::sync_all() calls FlushFileBuffers() down the line, which solves the problem.
1079 // А full writeup of the original Chrome bug can be found at
1080 // randomascii.wordpress.com/2018/02/25/compiler-bug-linker-bug-windows-kernel-bug/amp
1082 if let &Ok(ref out) = command_output {
1083 if out.status.success() {
1084 if let Ok(of) = fs::OpenOptions::new().write(true).open(out_filename) {
1094 fn command_line_too_big(err: &io::Error) -> bool {
1095 err.raw_os_error() == Some(::libc::E2BIG)
1099 fn command_line_too_big(err: &io::Error) -> bool {
1100 const ERROR_FILENAME_EXCED_RANGE: i32 = 206;
1101 err.raw_os_error() == Some(ERROR_FILENAME_EXCED_RANGE)
1109 impl<'a> fmt::Display for Escape<'a> {
1110 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1111 if self.is_like_msvc {
1112 // This is "documented" at
1113 // https://docs.microsoft.com/en-us/cpp/build/reference/at-specify-a-linker-response-file
1115 // Unfortunately there's not a great specification of the
1116 // syntax I could find online (at least) but some local
1117 // testing showed that this seemed sufficient-ish to catch
1118 // at least a few edge cases.
1120 for c in self.arg.chars() {
1122 '"' => write!(f, "\\{}", c)?,
1123 c => write!(f, "{}", c)?,
1128 // This is documented at https://linux.die.net/man/1/ld, namely:
1130 // > Options in file are separated by whitespace. A whitespace
1131 // > character may be included in an option by surrounding the
1132 // > entire option in either single or double quotes. Any
1133 // > character (including a backslash) may be included by
1134 // > prefixing the character to be included with a backslash.
1136 // We put an argument on each line, so all we need to do is
1137 // ensure the line is interpreted as one whole argument.
1138 for c in self.arg.chars() {
1140 '\\' | ' ' => write!(f, "\\{}", c)?,
1141 c => write!(f, "{}", c)?,
1150 /// Add begin object files defined by the target spec.
1151 fn add_pre_link_objects(cmd: &mut dyn Linker, sess: &Session, crate_type: config::CrateType) {
1152 let pre_link_objects = if crate_type == config::CrateType::Executable {
1153 &sess.target.target.options.pre_link_objects_exe
1155 &sess.target.target.options.pre_link_objects_dll
1157 for obj in pre_link_objects {
1158 cmd.add_object(&get_object_file_path(sess, obj));
1161 if crate_type == config::CrateType::Executable && sess.crt_static(Some(crate_type)) {
1162 for obj in &sess.target.target.options.pre_link_objects_exe_crt {
1163 cmd.add_object(&get_object_file_path(sess, obj));
1168 /// Add end object files defined by the target spec.
1169 fn add_post_link_objects(cmd: &mut dyn Linker, sess: &Session, crate_type: config::CrateType) {
1170 for obj in &sess.target.target.options.post_link_objects {
1171 cmd.add_object(&get_object_file_path(sess, obj));
1173 if sess.crt_static(Some(crate_type)) {
1174 for obj in &sess.target.target.options.post_link_objects_crt {
1175 cmd.add_object(&get_object_file_path(sess, obj));
1180 /// Add arbitrary "pre-link" args defined by the target spec or from command line.
1181 /// FIXME: Determine where exactly these args need to be inserted.
1182 fn add_pre_link_args(
1183 cmd: &mut dyn Linker,
1185 flavor: LinkerFlavor,
1186 crate_type: config::CrateType,
1188 if let Some(args) = sess.target.target.options.pre_link_args.get(&flavor) {
1191 if let Some(args) = sess.target.target.options.pre_link_args_crt.get(&flavor) {
1192 if sess.crt_static(Some(crate_type)) {
1196 cmd.args(&sess.opts.debugging_opts.pre_link_args);
1199 /// Add arbitrary "user defined" args defined from command line and by `#[link_args]` attributes.
1200 /// FIXME: Determine where exactly these args need to be inserted.
1201 fn add_user_defined_link_args(
1202 cmd: &mut dyn Linker,
1204 codegen_results: &CodegenResults,
1206 cmd.args(&sess.opts.cg.link_args);
1207 cmd.args(&*codegen_results.crate_info.link_args);
1210 /// Add arbitrary "late link" args defined by the target spec.
1211 /// FIXME: Determine where exactly these args need to be inserted.
1212 fn add_late_link_args(
1213 cmd: &mut dyn Linker,
1215 flavor: LinkerFlavor,
1216 crate_type: config::CrateType,
1217 codegen_results: &CodegenResults,
1219 if let Some(args) = sess.target.target.options.late_link_args.get(&flavor) {
1222 let any_dynamic_crate = crate_type == config::CrateType::Dylib
1223 || codegen_results.crate_info.dependency_formats.iter().any(|(ty, list)| {
1224 *ty == crate_type && list.iter().any(|&linkage| linkage == Linkage::Dynamic)
1226 if any_dynamic_crate {
1227 if let Some(args) = sess.target.target.options.late_link_args_dynamic.get(&flavor) {
1231 if let Some(args) = sess.target.target.options.late_link_args_static.get(&flavor) {
1237 /// Add arbitrary "post-link" args defined by the target spec.
1238 /// FIXME: Determine where exactly these args need to be inserted.
1239 fn add_post_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
1240 if let Some(args) = sess.target.target.options.post_link_args.get(&flavor) {
1245 /// Add object files containing code from the current crate.
1246 fn add_local_crate_regular_objects(cmd: &mut dyn Linker, codegen_results: &CodegenResults) {
1247 for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
1248 cmd.add_object(obj);
1252 /// Add object files for allocator code linked once for the whole crate tree.
1253 fn add_local_crate_allocator_objects(cmd: &mut dyn Linker, codegen_results: &CodegenResults) {
1254 if let Some(obj) = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref()) {
1255 cmd.add_object(obj);
1259 /// Add object files containing metadata for the current crate.
1260 fn add_local_crate_metadata_objects(
1261 cmd: &mut dyn Linker,
1262 crate_type: config::CrateType,
1263 codegen_results: &CodegenResults,
1265 // When linking a dynamic library, we put the metadata into a section of the
1266 // executable. This metadata is in a separate object file from the main
1267 // object file, so we link that in here.
1268 if crate_type == config::CrateType::Dylib || crate_type == config::CrateType::ProcMacro {
1269 if let Some(obj) = codegen_results.metadata_module.as_ref().and_then(|m| m.object.as_ref())
1271 cmd.add_object(obj);
1276 /// Link native libraries corresponding to the current crate and all libraries corresponding to
1277 /// all its dependency crates.
1278 /// FIXME: Consider combining this with the functions above adding object files for the local crate.
1279 fn link_local_crate_native_libs_and_dependent_crate_libs<'a, B: ArchiveBuilder<'a>>(
1280 cmd: &mut dyn Linker,
1282 crate_type: config::CrateType,
1283 codegen_results: &CodegenResults,
1286 // Take careful note of the ordering of the arguments we pass to the linker
1287 // here. Linkers will assume that things on the left depend on things to the
1288 // right. Things on the right cannot depend on things on the left. This is
1289 // all formally implemented in terms of resolving symbols (libs on the right
1290 // resolve unknown symbols of libs on the left, but not vice versa).
1292 // For this reason, we have organized the arguments we pass to the linker as
1295 // 1. The local object that LLVM just generated
1296 // 2. Local native libraries
1297 // 3. Upstream rust libraries
1298 // 4. Upstream native libraries
1300 // The rationale behind this ordering is that those items lower down in the
1301 // list can't depend on items higher up in the list. For example nothing can
1302 // depend on what we just generated (e.g., that'd be a circular dependency).
1303 // Upstream rust libraries are not allowed to depend on our local native
1304 // libraries as that would violate the structure of the DAG, in that
1305 // scenario they are required to link to them as well in a shared fashion.
1307 // Note that upstream rust libraries may contain native dependencies as
1308 // well, but they also can't depend on what we just started to add to the
1309 // link line. And finally upstream native libraries can't depend on anything
1310 // in this DAG so far because they're only dylibs and dylibs can only depend
1311 // on other dylibs (e.g., other native deps).
1313 // If -Zlink-native-libraries=false is set, then the assumption is that an
1314 // external build system already has the native dependencies defined, and it
1315 // will provide them to the linker itself.
1316 if sess.opts.debugging_opts.link_native_libraries {
1317 add_local_native_libraries(cmd, sess, codegen_results);
1319 add_upstream_rust_crates::<B>(cmd, sess, codegen_results, crate_type, tmpdir);
1320 if sess.opts.debugging_opts.link_native_libraries {
1321 add_upstream_native_libraries(cmd, sess, codegen_results, crate_type);
1325 /// Add sysroot and other globally set directories to the directory search list.
1326 fn add_library_search_dirs(cmd: &mut dyn Linker, sess: &Session) {
1327 // Prefer system mingw-w64 libs, see get_crt_libs_path comment for more details.
1328 if cfg!(windows) && sess.target.target.llvm_target.contains("windows-gnu") {
1329 if let Some(compiler_libs_path) = get_crt_libs_path(sess) {
1330 cmd.include_path(&compiler_libs_path);
1334 // The default library location, we need this to find the runtime.
1335 // The location of crates will be determined as needed.
1336 let lib_path = sess.target_filesearch(PathKind::All).get_lib_path();
1337 cmd.include_path(&fix_windows_verbatim_for_gcc(&lib_path));
1340 /// Add options requesting executables to be position-independent or not position-independent.
1341 fn add_position_independent_executable_args(
1342 cmd: &mut dyn Linker,
1344 flavor: LinkerFlavor,
1345 crate_type: config::CrateType,
1346 codegen_results: &CodegenResults,
1348 if crate_type != config::CrateType::Executable {
1352 if sess.target.target.options.position_independent_executables {
1353 let attr_link_args = &*codegen_results.crate_info.link_args;
1354 let mut user_defined_link_args = sess.opts.cg.link_args.iter().chain(attr_link_args);
1355 if sess.relocation_model() == RelocModel::Pic
1356 && !sess.crt_static(Some(crate_type))
1357 && !user_defined_link_args.any(|x| x == "-static")
1359 cmd.position_independent_executable();
1364 // Recent versions of gcc can be configured to generate position
1365 // independent executables by default. We have to pass -no-pie to
1366 // explicitly turn that off. Not applicable to ld.
1367 if sess.target.target.options.linker_is_gnu && flavor != LinkerFlavor::Ld {
1368 cmd.no_position_independent_executable();
1372 /// Add options making relocation sections in the produced ELF files read-only
1373 /// and suppressing lazy binding.
1374 fn add_relro_args(cmd: &mut dyn Linker, sess: &Session) {
1375 match sess.opts.debugging_opts.relro_level.unwrap_or(sess.target.target.options.relro_level) {
1376 RelroLevel::Full => cmd.full_relro(),
1377 RelroLevel::Partial => cmd.partial_relro(),
1378 RelroLevel::Off => cmd.no_relro(),
1379 RelroLevel::None => {}
1383 /// Add library search paths used at runtime by dynamic linkers.
1385 cmd: &mut dyn Linker,
1387 codegen_results: &CodegenResults,
1388 out_filename: &Path,
1390 // FIXME (#2397): At some point we want to rpath our guesses as to
1391 // where extern libraries might live, based on the
1392 // addl_lib_search_paths
1393 if sess.opts.cg.rpath {
1394 let target_triple = sess.opts.target_triple.triple();
1395 let mut get_install_prefix_lib_path = || {
1396 let install_prefix = option_env!("CFG_PREFIX").expect("CFG_PREFIX");
1397 let tlib = filesearch::relative_target_lib_path(&sess.sysroot, target_triple);
1398 let mut path = PathBuf::from(install_prefix);
1403 let mut rpath_config = RPathConfig {
1404 used_crates: &codegen_results.crate_info.used_crates_dynamic,
1405 out_filename: out_filename.to_path_buf(),
1406 has_rpath: sess.target.target.options.has_rpath,
1407 is_like_osx: sess.target.target.options.is_like_osx,
1408 linker_is_gnu: sess.target.target.options.linker_is_gnu,
1409 get_install_prefix_lib_path: &mut get_install_prefix_lib_path,
1411 cmd.args(&rpath::get_rpath_flags(&mut rpath_config));
1415 /// Produce the linker command line containing linker path and arguments.
1416 /// `NO-OPT-OUT` marks the arguments that cannot be removed from the command line
1417 /// by the user without creating a custom target specification.
1418 /// `OBJECT-FILES` specify whether the arguments can add object files.
1419 /// `CUSTOMIZATION-POINT` means that arbitrary arguments defined by the user
1420 /// or by the target spec can be inserted here.
1421 /// `AUDIT-ORDER` - need to figure out whether the option is order-dependent or not.
1422 fn linker_with_args<'a, B: ArchiveBuilder<'a>>(
1424 flavor: LinkerFlavor,
1426 crate_type: config::CrateType,
1428 out_filename: &Path,
1429 codegen_results: &CodegenResults,
1432 let base_cmd = get_linker(sess, path, flavor);
1433 // FIXME: Move `/LIBPATH` addition for uwp targets from the linker construction
1434 // to the linker args construction.
1435 assert!(base_cmd.get_args().is_empty() || sess.target.target.target_vendor == "uwp");
1436 let cmd = &mut *codegen_results.linker_info.to_linker(base_cmd, &sess, flavor, target_cpu);
1438 // NO-OPT-OUT, OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT
1439 add_pre_link_args(cmd, sess, flavor, crate_type);
1441 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1442 if sess.target.target.options.is_like_fuchsia {
1443 let prefix = match sess.opts.debugging_opts.sanitizer {
1444 Some(Sanitizer::Address) => "asan/",
1447 cmd.arg(format!("--dynamic-linker={}ld.so.1", prefix));
1450 // NO-OPT-OUT, OBJECT-FILES-YES
1451 add_pre_link_objects(cmd, sess, crate_type);
1453 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1454 if sess.target.target.options.is_like_emscripten {
1456 cmd.arg(if sess.panic_strategy() == PanicStrategy::Abort {
1457 "DISABLE_EXCEPTION_CATCHING=1"
1459 "DISABLE_EXCEPTION_CATCHING=0"
1463 // OBJECT-FILES-YES, AUDIT-ORDER
1464 link_sanitizer_runtime(sess, crate_type, cmd);
1466 // OBJECT-FILES-NO, AUDIT-ORDER
1467 // Linker plugins should be specified early in the list of arguments
1468 // FIXME: How "early" exactly?
1469 cmd.linker_plugin_lto();
1471 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1472 // FIXME: Order-dependent, at least relatively to other args adding searh directories.
1473 add_library_search_dirs(cmd, sess);
1476 add_local_crate_regular_objects(cmd, codegen_results);
1478 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1479 cmd.output_filename(out_filename);
1481 // OBJECT-FILES-NO, AUDIT-ORDER
1482 if crate_type == config::CrateType::Executable && sess.target.target.options.is_like_windows {
1483 if let Some(ref s) = codegen_results.windows_subsystem {
1488 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1489 // If we're building something like a dynamic library then some platforms
1490 // need to make sure that all symbols are exported correctly from the
1492 cmd.export_symbols(tmpdir, crate_type);
1495 add_local_crate_metadata_objects(cmd, crate_type, codegen_results);
1498 add_local_crate_allocator_objects(cmd, codegen_results);
1500 // OBJECT-FILES-NO, AUDIT-ORDER
1501 // FIXME: Order dependent, applies to the following objects. Where should it be placed?
1502 // Try to strip as much out of the generated object by removing unused
1503 // sections if possible. See more comments in linker.rs
1504 if !sess.opts.cg.link_dead_code {
1505 let keep_metadata = crate_type == config::CrateType::Dylib;
1506 cmd.gc_sections(keep_metadata);
1509 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1510 add_position_independent_executable_args(cmd, sess, flavor, crate_type, codegen_results);
1512 // OBJECT-FILES-NO, AUDIT-ORDER
1513 add_relro_args(cmd, sess);
1515 // OBJECT-FILES-NO, AUDIT-ORDER
1516 // Pass optimization flags down to the linker.
1519 // OBJECT-FILES-NO, AUDIT-ORDER
1520 // Pass debuginfo flags down to the linker.
1523 // OBJECT-FILES-NO, AUDIT-ORDER
1524 // We want to prevent the compiler from accidentally leaking in any system libraries,
1525 // so by default we tell linkers not to link to any default libraries.
1526 if !sess.opts.cg.default_linker_libraries && sess.target.target.options.no_default_libraries {
1527 cmd.no_default_libraries();
1531 link_local_crate_native_libs_and_dependent_crate_libs::<B>(
1539 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1540 // Tell the linker what we're doing.
1541 if crate_type != config::CrateType::Executable {
1542 cmd.build_dylib(out_filename);
1544 if crate_type == config::CrateType::Executable && sess.crt_static(Some(crate_type)) {
1545 cmd.build_static_executable();
1548 // OBJECT-FILES-NO, AUDIT-ORDER
1549 if sess.opts.cg.profile_generate.enabled() {
1553 // OBJECT-FILES-NO, AUDIT-ORDER
1554 if sess.opts.debugging_opts.control_flow_guard != CFGuard::Disabled {
1555 cmd.control_flow_guard();
1558 // OBJECT-FILES-NO, AUDIT-ORDER
1559 add_rpath_args(cmd, sess, codegen_results, out_filename);
1561 // OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT
1562 add_user_defined_link_args(cmd, sess, codegen_results);
1564 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1567 // NO-OPT-OUT, OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT
1568 add_late_link_args(cmd, sess, flavor, crate_type, codegen_results);
1570 // NO-OPT-OUT, OBJECT-FILES-YES
1571 add_post_link_objects(cmd, sess, crate_type);
1573 // NO-OPT-OUT, OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT
1574 add_post_link_args(cmd, sess, flavor);
1579 // # Native library linking
1581 // User-supplied library search paths (-L on the command line). These are
1582 // the same paths used to find Rust crates, so some of them may have been
1583 // added already by the previous crate linking code. This only allows them
1584 // to be found at compile time so it is still entirely up to outside
1585 // forces to make sure that library can be found at runtime.
1587 // Also note that the native libraries linked here are only the ones located
1588 // in the current crate. Upstream crates with native library dependencies
1589 // may have their native library pulled in above.
1590 fn add_local_native_libraries(
1591 cmd: &mut dyn Linker,
1593 codegen_results: &CodegenResults,
1595 let filesearch = sess.target_filesearch(PathKind::All);
1596 for search_path in filesearch.search_paths() {
1597 match search_path.kind {
1598 PathKind::Framework => {
1599 cmd.framework_path(&search_path.dir);
1602 cmd.include_path(&fix_windows_verbatim_for_gcc(&search_path.dir));
1608 codegen_results.crate_info.used_libraries.iter().filter(|l| relevant_lib(sess, l));
1610 let search_path = archive_search_paths(sess);
1611 for lib in relevant_libs {
1612 let name = match lib.name {
1617 NativeLibraryKind::NativeUnknown => cmd.link_dylib(name),
1618 NativeLibraryKind::NativeFramework => cmd.link_framework(name),
1619 NativeLibraryKind::NativeStaticNobundle => cmd.link_staticlib(name),
1620 NativeLibraryKind::NativeStatic => cmd.link_whole_staticlib(name, &search_path),
1621 NativeLibraryKind::NativeRawDylib => {
1622 // FIXME(#58713): Proper handling for raw dylibs.
1623 bug!("raw_dylib feature not yet implemented");
1629 // # Rust Crate linking
1631 // Rust crates are not considered at all when creating an rlib output. All
1632 // dependencies will be linked when producing the final output (instead of
1633 // the intermediate rlib version)
1634 fn add_upstream_rust_crates<'a, B: ArchiveBuilder<'a>>(
1635 cmd: &mut dyn Linker,
1637 codegen_results: &CodegenResults,
1638 crate_type: config::CrateType,
1641 // All of the heavy lifting has previously been accomplished by the
1642 // dependency_format module of the compiler. This is just crawling the
1643 // output of that module, adding crates as necessary.
1645 // Linking to a rlib involves just passing it to the linker (the linker
1646 // will slurp up the object files inside), and linking to a dynamic library
1647 // involves just passing the right -l flag.
1649 let (_, data) = codegen_results
1653 .find(|(ty, _)| *ty == crate_type)
1654 .expect("failed to find crate type in dependency format list");
1656 // Invoke get_used_crates to ensure that we get a topological sorting of
1658 let deps = &codegen_results.crate_info.used_crates_dynamic;
1660 // There's a few internal crates in the standard library (aka libcore and
1661 // libstd) which actually have a circular dependence upon one another. This
1662 // currently arises through "weak lang items" where libcore requires things
1663 // like `rust_begin_unwind` but libstd ends up defining it. To get this
1664 // circular dependence to work correctly in all situations we'll need to be
1665 // sure to correctly apply the `--start-group` and `--end-group` options to
1666 // GNU linkers, otherwise if we don't use any other symbol from the standard
1667 // library it'll get discarded and the whole application won't link.
1669 // In this loop we're calculating the `group_end`, after which crate to
1670 // pass `--end-group` and `group_start`, before which crate to pass
1671 // `--start-group`. We currently do this by passing `--end-group` after
1672 // the first crate (when iterating backwards) that requires a lang item
1673 // defined somewhere else. Once that's set then when we've defined all the
1674 // necessary lang items we'll pass `--start-group`.
1676 // Note that this isn't amazing logic for now but it should do the trick
1677 // for the current implementation of the standard library.
1678 let mut group_end = None;
1679 let mut group_start = None;
1680 // Crates available for linking thus far.
1681 let mut available = FxHashSet::default();
1682 // Crates required to satisfy dependencies discovered so far.
1683 let mut required = FxHashSet::default();
1685 let info = &codegen_results.crate_info;
1686 for &(cnum, _) in deps.iter().rev() {
1687 if let Some(missing) = info.missing_lang_items.get(&cnum) {
1688 let missing_crates = missing.iter().map(|i| info.lang_item_to_crate.get(i).copied());
1689 required.extend(missing_crates);
1692 required.insert(Some(cnum));
1693 available.insert(Some(cnum));
1695 if required.len() > available.len() && group_end.is_none() {
1696 group_end = Some(cnum);
1698 if required.len() == available.len() && group_end.is_some() {
1699 group_start = Some(cnum);
1704 // If we didn't end up filling in all lang items from upstream crates then
1705 // we'll be filling it in with our crate. This probably means we're the
1706 // standard library itself, so skip this for now.
1707 if group_end.is_some() && group_start.is_none() {
1711 let mut compiler_builtins = None;
1713 for &(cnum, _) in deps.iter() {
1714 if group_start == Some(cnum) {
1718 // We may not pass all crates through to the linker. Some crates may
1719 // appear statically in an existing dylib, meaning we'll pick up all the
1720 // symbols from the dylib.
1721 let src = &codegen_results.crate_info.used_crate_source[&cnum];
1722 match data[cnum.as_usize() - 1] {
1723 _ if codegen_results.crate_info.profiler_runtime == Some(cnum) => {
1724 add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
1726 // compiler-builtins are always placed last to ensure that they're
1727 // linked correctly.
1728 _ if codegen_results.crate_info.compiler_builtins == Some(cnum) => {
1729 assert!(compiler_builtins.is_none());
1730 compiler_builtins = Some(cnum);
1732 Linkage::NotLinked | Linkage::IncludedFromDylib => {}
1733 Linkage::Static => {
1734 add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
1736 Linkage::Dynamic => add_dynamic_crate(cmd, sess, &src.dylib.as_ref().unwrap().0),
1739 if group_end == Some(cnum) {
1744 // compiler-builtins are always placed last to ensure that they're
1745 // linked correctly.
1746 // We must always link the `compiler_builtins` crate statically. Even if it
1747 // was already "included" in a dylib (e.g., `libstd` when `-C prefer-dynamic`
1749 if let Some(cnum) = compiler_builtins {
1750 add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
1753 // Converts a library file-stem into a cc -l argument
1754 fn unlib<'a>(config: &config::Config, stem: &'a str) -> &'a str {
1755 if stem.starts_with("lib") && !config.target.options.is_like_windows {
1762 // Adds the static "rlib" versions of all crates to the command line.
1763 // There's a bit of magic which happens here specifically related to LTO and
1764 // dynamic libraries. Specifically:
1766 // * For LTO, we remove upstream object files.
1767 // * For dylibs we remove metadata and bytecode from upstream rlibs
1769 // When performing LTO, almost(*) all of the bytecode from the upstream
1770 // libraries has already been included in our object file output. As a
1771 // result we need to remove the object files in the upstream libraries so
1772 // the linker doesn't try to include them twice (or whine about duplicate
1773 // symbols). We must continue to include the rest of the rlib, however, as
1774 // it may contain static native libraries which must be linked in.
1776 // (*) Crates marked with `#![no_builtins]` don't participate in LTO and
1777 // their bytecode wasn't included. The object files in those libraries must
1778 // still be passed to the linker.
1780 // When making a dynamic library, linkers by default don't include any
1781 // object files in an archive if they're not necessary to resolve the link.
1782 // We basically want to convert the archive (rlib) to a dylib, though, so we
1783 // *do* want everything included in the output, regardless of whether the
1784 // linker thinks it's needed or not. As a result we must use the
1785 // --whole-archive option (or the platform equivalent). When using this
1786 // option the linker will fail if there are non-objects in the archive (such
1787 // as our own metadata and/or bytecode). All in all, for rlibs to be
1788 // entirely included in dylibs, we need to remove all non-object files.
1790 // Note, however, that if we're not doing LTO or we're not producing a dylib
1791 // (aka we're making an executable), we can just pass the rlib blindly to
1792 // the linker (fast) because it's fine if it's not actually included as
1793 // we're at the end of the dependency chain.
1794 fn add_static_crate<'a, B: ArchiveBuilder<'a>>(
1795 cmd: &mut dyn Linker,
1797 codegen_results: &CodegenResults,
1799 crate_type: config::CrateType,
1802 let src = &codegen_results.crate_info.used_crate_source[&cnum];
1803 let cratepath = &src.rlib.as_ref().unwrap().0;
1805 // See the comment above in `link_staticlib` and `link_rlib` for why if
1806 // there's a static library that's not relevant we skip all object
1808 let native_libs = &codegen_results.crate_info.native_libraries[&cnum];
1809 let skip_native = native_libs
1811 .any(|lib| lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib));
1813 if (!are_upstream_rust_objects_already_included(sess)
1814 || ignored_for_lto(sess, &codegen_results.crate_info, cnum))
1815 && crate_type != config::CrateType::Dylib
1818 cmd.link_rlib(&fix_windows_verbatim_for_gcc(cratepath));
1822 let dst = tmpdir.join(cratepath.file_name().unwrap());
1823 let name = cratepath.file_name().unwrap().to_str().unwrap();
1824 let name = &name[3..name.len() - 5]; // chop off lib/.rlib
1826 sess.prof.generic_activity_with_arg("link_altering_rlib", name).run(|| {
1827 let mut archive = <B as ArchiveBuilder>::new(sess, &dst, Some(cratepath));
1828 archive.update_symbols();
1830 let mut any_objects = false;
1831 for f in archive.src_files() {
1832 if f.ends_with(RLIB_BYTECODE_EXTENSION) || f == METADATA_FILENAME {
1833 archive.remove_file(&f);
1837 let canonical = f.replace("-", "_");
1838 let canonical_name = name.replace("-", "_");
1840 let is_rust_object =
1841 canonical.starts_with(&canonical_name) && looks_like_rust_object_file(&f);
1843 // If we've been requested to skip all native object files
1844 // (those not generated by the rust compiler) then we can skip
1845 // this file. See above for why we may want to do this.
1846 let skip_because_cfg_say_so = skip_native && !is_rust_object;
1848 // If we're performing LTO and this is a rust-generated object
1849 // file, then we don't need the object file as it's part of the
1850 // LTO module. Note that `#![no_builtins]` is excluded from LTO,
1851 // though, so we let that object file slide.
1852 let skip_because_lto = are_upstream_rust_objects_already_included(sess)
1854 && (sess.target.target.options.no_builtins
1855 || !codegen_results.crate_info.is_no_builtins.contains(&cnum));
1857 if skip_because_cfg_say_so || skip_because_lto {
1858 archive.remove_file(&f);
1869 // If we're creating a dylib, then we need to include the
1870 // whole of each object in our archive into that artifact. This is
1871 // because a `dylib` can be reused as an intermediate artifact.
1873 // Note, though, that we don't want to include the whole of a
1874 // compiler-builtins crate (e.g., compiler-rt) because it'll get
1875 // repeatedly linked anyway.
1876 if crate_type == config::CrateType::Dylib
1877 && codegen_results.crate_info.compiler_builtins != Some(cnum)
1879 cmd.link_whole_rlib(&fix_windows_verbatim_for_gcc(&dst));
1881 cmd.link_rlib(&fix_windows_verbatim_for_gcc(&dst));
1886 // Same thing as above, but for dynamic crates instead of static crates.
1887 fn add_dynamic_crate(cmd: &mut dyn Linker, sess: &Session, cratepath: &Path) {
1888 // Just need to tell the linker about where the library lives and
1890 let parent = cratepath.parent();
1891 if let Some(dir) = parent {
1892 cmd.include_path(&fix_windows_verbatim_for_gcc(dir));
1894 let filestem = cratepath.file_stem().unwrap().to_str().unwrap();
1895 cmd.link_rust_dylib(
1896 Symbol::intern(&unlib(&sess.target, filestem)),
1897 parent.unwrap_or(Path::new("")),
1902 // Link in all of our upstream crates' native dependencies. Remember that
1903 // all of these upstream native dependencies are all non-static
1904 // dependencies. We've got two cases then:
1906 // 1. The upstream crate is an rlib. In this case we *must* link in the
1907 // native dependency because the rlib is just an archive.
1909 // 2. The upstream crate is a dylib. In order to use the dylib, we have to
1910 // have the dependency present on the system somewhere. Thus, we don't
1911 // gain a whole lot from not linking in the dynamic dependency to this
1914 // The use case for this is a little subtle. In theory the native
1915 // dependencies of a crate are purely an implementation detail of the crate
1916 // itself, but the problem arises with generic and inlined functions. If a
1917 // generic function calls a native function, then the generic function must
1918 // be instantiated in the target crate, meaning that the native symbol must
1919 // also be resolved in the target crate.
1920 fn add_upstream_native_libraries(
1921 cmd: &mut dyn Linker,
1923 codegen_results: &CodegenResults,
1924 crate_type: config::CrateType,
1926 // Be sure to use a topological sorting of crates because there may be
1927 // interdependencies between native libraries. When passing -nodefaultlibs,
1928 // for example, almost all native libraries depend on libc, so we have to
1929 // make sure that's all the way at the right (liblibc is near the base of
1930 // the dependency chain).
1932 // This passes RequireStatic, but the actual requirement doesn't matter,
1933 // we're just getting an ordering of crate numbers, we're not worried about
1935 let (_, data) = codegen_results
1939 .find(|(ty, _)| *ty == crate_type)
1940 .expect("failed to find crate type in dependency format list");
1942 let crates = &codegen_results.crate_info.used_crates_static;
1943 for &(cnum, _) in crates {
1944 for lib in codegen_results.crate_info.native_libraries[&cnum].iter() {
1945 let name = match lib.name {
1949 if !relevant_lib(sess, &lib) {
1953 NativeLibraryKind::NativeUnknown => cmd.link_dylib(name),
1954 NativeLibraryKind::NativeFramework => cmd.link_framework(name),
1955 NativeLibraryKind::NativeStaticNobundle => {
1956 // Link "static-nobundle" native libs only if the crate they originate from
1957 // is being linked statically to the current crate. If it's linked dynamically
1958 // or is an rlib already included via some other dylib crate, the symbols from
1959 // native libs will have already been included in that dylib.
1960 if data[cnum.as_usize() - 1] == Linkage::Static {
1961 cmd.link_staticlib(name)
1964 // ignore statically included native libraries here as we've
1965 // already included them when we included the rust library
1967 NativeLibraryKind::NativeStatic => {}
1968 NativeLibraryKind::NativeRawDylib => {
1969 // FIXME(#58713): Proper handling for raw dylibs.
1970 bug!("raw_dylib feature not yet implemented");
1977 fn relevant_lib(sess: &Session, lib: &NativeLibrary) -> bool {
1979 Some(ref cfg) => rustc_attr::cfg_matches(cfg, &sess.parse_sess, None),
1984 fn are_upstream_rust_objects_already_included(sess: &Session) -> bool {
1986 config::Lto::Fat => true,
1987 config::Lto::Thin => {
1988 // If we defer LTO to the linker, we haven't run LTO ourselves, so
1989 // any upstream object files have not been copied yet.
1990 !sess.opts.cg.linker_plugin_lto.enabled()
1992 config::Lto::No | config::Lto::ThinLocal => false,