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::{self, CFGuard, CrateType, DebugInfo};
7 use rustc_session::config::{OutputFilenames, OutputType, PrintRequest, Sanitizer};
8 use rustc_session::output::{check_file_is_writeable, invalid_output_for_target, out_filename};
9 use rustc_session::search_paths::PathKind;
10 /// For all the linkers we support, and information they might
11 /// need out of the shared crate context before we get rid of it.
12 use rustc_session::{filesearch, Session};
13 use rustc_span::symbol::Symbol;
14 use rustc_target::spec::{LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, RelroLevel};
16 use super::archive::ArchiveBuilder;
17 use super::command::Command;
18 use super::linker::{self, Linker};
19 use super::rpath::{self, RPathConfig};
20 use crate::{looks_like_rust_object_file, CodegenResults, CrateInfo, METADATA_FILENAME};
22 use cc::windows_registry;
23 use tempfile::{Builder as TempFileBuilder, TempDir};
28 use std::ffi::OsString;
32 use std::path::{Path, PathBuf};
33 use std::process::{ExitStatus, Output, Stdio};
36 pub fn remove(sess: &Session, path: &Path) {
37 if let Err(e) = fs::remove_file(path) {
38 sess.err(&format!("failed to remove {}: {}", path.display(), e));
42 /// Performs the linkage portion of the compilation phase. This will generate all
43 /// of the requested outputs for this compilation session.
44 pub fn link_binary<'a, B: ArchiveBuilder<'a>>(
46 codegen_results: &CodegenResults,
47 outputs: &OutputFilenames,
51 let _timer = sess.timer("link_binary");
52 let output_metadata = sess.opts.output_types.contains_key(&OutputType::Metadata);
53 for &crate_type in sess.crate_types.borrow().iter() {
54 // Ignore executable crates if we have -Z no-codegen, as they will error.
55 if (sess.opts.debugging_opts.no_codegen || !sess.opts.output_types.should_codegen())
57 && crate_type == CrateType::Executable
62 if invalid_output_for_target(sess, crate_type) {
64 "invalid output type `{:?}` for target os `{}`",
66 sess.opts.target_triple
70 sess.time("link_binary_check_files_are_writeable", || {
71 for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
72 check_file_is_writeable(obj, sess);
76 let tmpdir = TempFileBuilder::new()
79 .unwrap_or_else(|err| sess.fatal(&format!("couldn't create a temp dir: {}", err)));
81 if outputs.outputs.should_codegen() {
82 let out_filename = out_filename(sess, crate_type, outputs, crate_name);
85 let _timer = sess.timer("link_rlib");
95 CrateType::Staticlib => {
96 link_staticlib::<B>(sess, codegen_results, &out_filename, &tmpdir);
109 if sess.opts.json_artifact_notifications {
110 sess.parse_sess.span_diagnostic.emit_artifact_notification(&out_filename, "link");
114 if sess.opts.cg.save_temps {
115 let _ = tmpdir.into_path();
119 // Remove the temporary object file and metadata if we aren't saving temps
120 sess.time("link_binary_remove_temps", || {
121 if !sess.opts.cg.save_temps {
122 if sess.opts.output_types.should_codegen()
123 && !preserve_objects_for_their_debuginfo(sess)
125 for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
129 if let Some(ref metadata_module) = codegen_results.metadata_module {
130 if let Some(ref obj) = metadata_module.object {
134 if let Some(ref allocator_module) = codegen_results.allocator_module {
135 if let Some(ref obj) = allocator_module.object {
143 // The third parameter is for env vars, used on windows to set up the
144 // path for MSVC to find its DLLs, and gcc to find its bundled
146 fn get_linker(sess: &Session, linker: &Path, flavor: LinkerFlavor) -> Command {
147 let msvc_tool = windows_registry::find_tool(&sess.opts.target_triple.triple(), "link.exe");
149 // If our linker looks like a batch script on Windows then to execute this
150 // we'll need to spawn `cmd` explicitly. This is primarily done to handle
151 // emscripten where the linker is `emcc.bat` and needs to be spawned as
152 // `cmd /c emcc.bat ...`.
154 // This worked historically but is needed manually since #42436 (regression
155 // was tagged as #42791) and some more info can be found on #44443 for
156 // emscripten itself.
157 let mut cmd = match linker.to_str() {
158 Some(linker) if cfg!(windows) && linker.ends_with(".bat") => Command::bat_script(linker),
160 LinkerFlavor::Lld(f) => Command::lld(linker, f),
162 if sess.opts.cg.linker.is_none() && sess.target.target.options.linker.is_none() =>
164 Command::new(msvc_tool.as_ref().map(|t| t.path()).unwrap_or(linker))
166 _ => Command::new(linker),
170 // UWP apps have API restrictions enforced during Store submissions.
171 // To comply with the Windows App Certification Kit,
172 // MSVC needs to link with the Store versions of the runtime libraries (vcruntime, msvcrt, etc).
173 let t = &sess.target.target;
174 if (flavor == LinkerFlavor::Msvc || flavor == LinkerFlavor::Lld(LldFlavor::Link))
175 && t.target_vendor == "uwp"
177 if let Some(ref tool) = msvc_tool {
178 let original_path = tool.path();
179 if let Some(ref root_lib_path) = original_path.ancestors().nth(4) {
180 let arch = match t.arch.as_str() {
181 "x86_64" => Some("x64".to_string()),
182 "x86" => Some("x86".to_string()),
183 "aarch64" => Some("arm64".to_string()),
186 if let Some(ref a) = arch {
187 // FIXME: Move this to `fn linker_with_args`.
188 let mut arg = OsString::from("/LIBPATH:");
189 arg.push(format!("{}\\lib\\{}\\store", root_lib_path.display(), a.to_string()));
192 warn!("arch is not supported");
195 warn!("MSVC root path lib location not found");
198 warn!("link.exe not found");
202 // The compiler's sysroot often has some bundled tools, so add it to the
203 // PATH for the child.
204 let mut new_path = sess.host_filesearch(PathKind::All).get_tools_search_paths();
205 let mut msvc_changed_path = false;
206 if sess.target.target.options.is_like_msvc {
207 if let Some(ref tool) = msvc_tool {
208 cmd.args(tool.args());
209 for &(ref k, ref v) in tool.env() {
211 new_path.extend(env::split_paths(v));
212 msvc_changed_path = true;
220 if !msvc_changed_path {
221 if let Some(path) = env::var_os("PATH") {
222 new_path.extend(env::split_paths(&path));
225 cmd.env("PATH", env::join_paths(new_path).unwrap());
230 pub fn each_linked_rlib(
232 f: &mut dyn FnMut(CrateNum, &Path),
233 ) -> Result<(), String> {
234 let crates = info.used_crates_static.iter();
236 for (ty, list) in info.dependency_formats.iter() {
238 CrateType::Executable
239 | CrateType::Staticlib
241 | CrateType::ProcMacro => {
248 let fmts = match fmts {
250 None => return Err("could not find formats for rlibs".to_string()),
252 for &(cnum, ref path) in crates {
253 match fmts.get(cnum.as_usize() - 1) {
254 Some(&Linkage::NotLinked | &Linkage::IncludedFromDylib) => continue,
256 None => return Err("could not find formats for rlibs".to_string()),
258 let name = &info.crate_name[&cnum];
259 let path = match *path {
260 LibSource::Some(ref p) => p,
261 LibSource::MetadataOnly => {
263 "could not find rlib for: `{}`, found rmeta (metadata) file",
267 LibSource::None => return Err(format!("could not find rlib for: `{}`", name)),
274 /// We use a temp directory here to avoid races between concurrent rustc processes,
275 /// such as builds in the same directory using the same filename for metadata while
276 /// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a
277 /// directory being searched for `extern crate` (observing an incomplete file).
278 /// The returned path is the temporary file containing the complete metadata.
279 pub fn emit_metadata(sess: &Session, metadata: &EncodedMetadata, tmpdir: &TempDir) -> PathBuf {
280 let out_filename = tmpdir.path().join(METADATA_FILENAME);
281 let result = fs::write(&out_filename, &metadata.raw_data);
283 if let Err(e) = result {
284 sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e));
292 // An rlib in its current incarnation is essentially a renamed .a file. The
293 // rlib primarily contains the object file of the crate, but it also contains
294 // all of the object files from native libraries. This is done by unzipping
295 // native libraries and inserting all of the contents into this archive.
296 fn link_rlib<'a, B: ArchiveBuilder<'a>>(
298 codegen_results: &CodegenResults,
303 info!("preparing rlib to {:?}", out_filename);
304 let mut ab = <B as ArchiveBuilder>::new(sess, out_filename, None);
306 for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
310 // Note that in this loop we are ignoring the value of `lib.cfg`. That is,
311 // we may not be configured to actually include a static library if we're
312 // adding it here. That's because later when we consume this rlib we'll
313 // decide whether we actually needed the static library or not.
315 // To do this "correctly" we'd need to keep track of which libraries added
316 // which object files to the archive. We don't do that here, however. The
317 // #[link(cfg(..))] feature is unstable, though, and only intended to get
318 // liblibc working. In that sense the check below just indicates that if
319 // there are any libraries we want to omit object files for at link time we
320 // just exclude all custom object files.
322 // Eventually if we want to stabilize or flesh out the #[link(cfg(..))]
323 // feature then we'll need to figure out how to record what objects were
324 // loaded from the libraries found here and then encode that into the
325 // metadata of the rlib we're generating somehow.
326 for lib in codegen_results.crate_info.used_libraries.iter() {
328 NativeLibraryKind::NativeStatic => {}
329 NativeLibraryKind::NativeStaticNobundle
330 | NativeLibraryKind::NativeFramework
331 | NativeLibraryKind::NativeRawDylib
332 | NativeLibraryKind::NativeUnknown => continue,
334 if let Some(name) = lib.name {
335 ab.add_native_library(name);
339 // After adding all files to the archive, we need to update the
340 // symbol table of the archive.
343 // Note that it is important that we add all of our non-object "magical
344 // files" *after* all of the object files in the archive. The reason for
345 // this is as follows:
347 // * When performing LTO, this archive will be modified to remove
348 // objects from above. The reason for this is described below.
350 // * When the system linker looks at an archive, it will attempt to
351 // determine the architecture of the archive in order to see whether its
354 // The algorithm for this detection is: iterate over the files in the
355 // archive. Skip magical SYMDEF names. Interpret the first file as an
356 // object file. Read architecture from the object file.
358 // * As one can probably see, if "metadata" and "foo.bc" were placed
359 // before all of the objects, then the architecture of this archive would
360 // not be correctly inferred once 'foo.o' is removed.
362 // Basically, all this means is that this code should not move above the
365 RlibFlavor::Normal => {
366 // Instead of putting the metadata in an object file section, rlibs
367 // contain the metadata in a separate file.
368 ab.add_file(&emit_metadata(sess, &codegen_results.metadata, tmpdir));
370 // After adding all files to the archive, we need to update the
371 // symbol table of the archive. This currently dies on macOS (see
372 // #11162), and isn't necessary there anyway
373 if !sess.target.target.options.is_like_osx {
378 RlibFlavor::StaticlibBase => {
379 let obj = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref());
380 if let Some(obj) = obj {
389 // Create a static archive
391 // This is essentially the same thing as an rlib, but it also involves adding
392 // all of the upstream crates' objects into the archive. This will slurp in
393 // all of the native libraries of upstream dependencies as well.
395 // Additionally, there's no way for us to link dynamic libraries, so we warn
396 // about all dynamic library dependencies that they're not linked in.
398 // There's no need to include metadata in a static archive, so ensure to not
399 // link in the metadata object file (and also don't prepare the archive with a
401 fn link_staticlib<'a, B: ArchiveBuilder<'a>>(
403 codegen_results: &CodegenResults,
408 link_rlib::<B>(sess, codegen_results, RlibFlavor::StaticlibBase, out_filename, tempdir);
409 let mut all_native_libs = vec![];
411 let res = each_linked_rlib(&codegen_results.crate_info, &mut |cnum, path| {
412 let name = &codegen_results.crate_info.crate_name[&cnum];
413 let native_libs = &codegen_results.crate_info.native_libraries[&cnum];
415 // Here when we include the rlib into our staticlib we need to make a
416 // decision whether to include the extra object files along the way.
417 // These extra object files come from statically included native
418 // libraries, but they may be cfg'd away with #[link(cfg(..))].
420 // This unstable feature, though, only needs liblibc to work. The only
421 // use case there is where musl is statically included in liblibc.rlib,
422 // so if we don't want the included version we just need to skip it. As
423 // a result the logic here is that if *any* linked library is cfg'd away
424 // we just skip all object files.
426 // Clearly this is not sufficient for a general purpose feature, and
427 // we'd want to read from the library's metadata to determine which
428 // object files come from where and selectively skip them.
429 let skip_object_files = native_libs
431 .any(|lib| lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib));
435 are_upstream_rust_objects_already_included(sess)
436 && !ignored_for_lto(sess, &codegen_results.crate_info, cnum),
441 all_native_libs.extend(codegen_results.crate_info.native_libraries[&cnum].iter().cloned());
443 if let Err(e) = res {
450 if !all_native_libs.is_empty() {
451 if sess.opts.prints.contains(&PrintRequest::NativeStaticLibs) {
452 print_native_static_libs(sess, &all_native_libs);
457 // Create a dynamic library or executable
459 // This will invoke the system linker/cc to create the resulting file. This
460 // links to all upstream files as well.
461 fn link_natively<'a, B: ArchiveBuilder<'a>>(
463 crate_type: CrateType,
465 codegen_results: &CodegenResults,
469 info!("preparing {:?} to {:?}", crate_type, out_filename);
470 let (linker_path, flavor) = linker_and_flavor(sess);
471 let mut cmd = linker_with_args::<B>(
482 linker::disable_localization(&mut cmd);
484 for &(ref k, ref v) in &sess.target.target.options.link_env {
487 for k in &sess.target.target.options.link_env_remove {
491 if sess.opts.debugging_opts.print_link_args {
492 println!("{:?}", &cmd);
495 // May have not found libraries in the right formats.
496 sess.abort_if_errors();
498 // Invoke the system linker
500 let retry_on_segfault = env::var("RUSTC_RETRY_LINKER_ON_SEGFAULT").is_ok();
505 prog = sess.time("run_linker", || exec_linker(sess, &cmd, out_filename, tmpdir));
506 let output = match prog {
507 Ok(ref output) => output,
510 if output.status.success() {
513 let mut out = output.stderr.clone();
514 out.extend(&output.stdout);
515 let out = String::from_utf8_lossy(&out);
517 // Check to see if the link failed with "unrecognized command line option:
518 // '-no-pie'" for gcc or "unknown argument: '-no-pie'" for clang. If so,
519 // reperform the link step without the -no-pie option. This is safe because
520 // if the linker doesn't support -no-pie then it should not default to
521 // linking executables as pie. Different versions of gcc seem to use
522 // different quotes in the error message so don't check for them.
523 if sess.target.target.options.linker_is_gnu
524 && flavor != LinkerFlavor::Ld
525 && (out.contains("unrecognized command line option")
526 || out.contains("unknown argument"))
527 && out.contains("-no-pie")
528 && cmd.get_args().iter().any(|e| e.to_string_lossy() == "-no-pie")
530 info!("linker output: {:?}", out);
531 warn!("Linker does not support -no-pie command line option. Retrying without.");
532 for arg in cmd.take_args() {
533 if arg.to_string_lossy() != "-no-pie" {
541 // Here's a terribly awful hack that really shouldn't be present in any
542 // compiler. Here an environment variable is supported to automatically
543 // retry the linker invocation if the linker looks like it segfaulted.
545 // Gee that seems odd, normally segfaults are things we want to know
546 // about! Unfortunately though in rust-lang/rust#38878 we're
547 // experiencing the linker segfaulting on Travis quite a bit which is
548 // causing quite a bit of pain to land PRs when they spuriously fail
549 // due to a segfault.
551 // The issue #38878 has some more debugging information on it as well,
552 // but this unfortunately looks like it's just a race condition in
553 // macOS's linker with some thread pool working in the background. It
554 // seems that no one currently knows a fix for this so in the meantime
555 // we're left with this...
556 if !retry_on_segfault || i > 3 {
559 let msg_segv = "clang: error: unable to execute command: Segmentation fault: 11";
560 let msg_bus = "clang: error: unable to execute command: Bus error: 10";
561 if out.contains(msg_segv) || out.contains(msg_bus) {
563 "looks like the linker segfaulted when we tried to call it, \
564 automatically retrying again. cmd = {:?}, out = {}.",
570 if is_illegal_instruction(&output.status) {
572 "looks like the linker hit an illegal instruction when we \
573 tried to call it, automatically retrying again. cmd = {:?}, ]\
574 out = {}, status = {}.",
575 cmd, out, output.status,
581 fn is_illegal_instruction(status: &ExitStatus) -> bool {
582 use std::os::unix::prelude::*;
583 status.signal() == Some(libc::SIGILL)
587 fn is_illegal_instruction(_status: &ExitStatus) -> bool {
594 fn escape_string(s: &[u8]) -> String {
595 str::from_utf8(s).map(|s| s.to_owned()).unwrap_or_else(|_| {
596 let mut x = "Non-UTF-8 output: ".to_string();
597 x.extend(s.iter().flat_map(|&b| ascii::escape_default(b)).map(char::from));
601 if !prog.status.success() {
602 let mut output = prog.stderr.clone();
603 output.extend_from_slice(&prog.stdout);
604 sess.struct_err(&format!(
605 "linking with `{}` failed: {}",
606 linker_path.display(),
609 .note(&format!("{:?}", &cmd))
610 .note(&escape_string(&output))
612 sess.abort_if_errors();
614 info!("linker stderr:\n{}", escape_string(&prog.stderr));
615 info!("linker stdout:\n{}", escape_string(&prog.stdout));
618 let linker_not_found = e.kind() == io::ErrorKind::NotFound;
620 let mut linker_error = {
621 if linker_not_found {
622 sess.struct_err(&format!("linker `{}` not found", linker_path.display()))
624 sess.struct_err(&format!(
625 "could not exec the linker `{}`",
626 linker_path.display()
631 linker_error.note(&e.to_string());
633 if !linker_not_found {
634 linker_error.note(&format!("{:?}", &cmd));
639 if sess.target.target.options.is_like_msvc && linker_not_found {
640 sess.note_without_error(
641 "the msvc targets depend on the msvc linker \
642 but `link.exe` was not found",
644 sess.note_without_error(
645 "please ensure that VS 2013, VS 2015, VS 2017 or VS 2019 \
646 was installed with the Visual C++ option",
649 sess.abort_if_errors();
653 // On macOS, debuggers need this utility to get run to do some munging of
654 // the symbols. Note, though, that if the object files are being preserved
655 // for their debug information there's no need for us to run dsymutil.
656 if sess.target.target.options.is_like_osx
657 && sess.opts.debuginfo != DebugInfo::None
658 && !preserve_objects_for_their_debuginfo(sess)
660 if let Err(e) = Command::new("dsymutil").arg(out_filename).output() {
661 sess.fatal(&format!("failed to run dsymutil: {}", e))
666 fn link_sanitizer_runtime(sess: &Session, crate_type: CrateType, linker: &mut dyn Linker) {
667 let sanitizer = match &sess.opts.debugging_opts.sanitizer {
672 if crate_type != CrateType::Executable {
676 let name = match sanitizer {
677 Sanitizer::Address => "asan",
678 Sanitizer::Leak => "lsan",
679 Sanitizer::Memory => "msan",
680 Sanitizer::Thread => "tsan",
683 let default_sysroot = filesearch::get_or_default_sysroot();
685 filesearch::make_target_lib_path(&default_sysroot, sess.opts.target_triple.triple());
686 let channel = option_env!("CFG_RELEASE_CHANNEL")
687 .map(|channel| format!("-{}", channel))
688 .unwrap_or_default();
690 match sess.opts.target_triple.triple() {
691 "x86_64-apple-darwin" => {
692 // On Apple platforms, the sanitizer is always built as a dylib, and
693 // LLVM will link to `@rpath/*.dylib`, so we need to specify an
694 // rpath to the library as well (the rpath should be absolute, see
695 // PR #41352 for details).
696 let libname = format!("rustc{}_rt.{}", channel, name);
697 let rpath = default_tlib.to_str().expect("non-utf8 component in path");
698 linker.args(&["-Wl,-rpath", "-Xlinker", rpath]);
699 linker.link_dylib(Symbol::intern(&libname));
701 "x86_64-unknown-linux-gnu" | "x86_64-fuchsia" | "aarch64-fuchsia" => {
702 let filename = format!("librustc{}_rt.{}.a", channel, name);
703 let path = default_tlib.join(&filename);
704 linker.link_whole_rlib(&path);
710 /// Returns a boolean indicating whether the specified crate should be ignored
713 /// Crates ignored during LTO are not lumped together in the "massive object
714 /// file" that we create and are linked in their normal rlib states. See
715 /// comments below for what crates do not participate in LTO.
717 /// It's unusual for a crate to not participate in LTO. Typically only
718 /// compiler-specific and unstable crates have a reason to not participate in
720 pub fn ignored_for_lto(sess: &Session, info: &CrateInfo, cnum: CrateNum) -> bool {
721 // If our target enables builtin function lowering in LLVM then the
722 // crates providing these functions don't participate in LTO (e.g.
723 // no_builtins or compiler builtins crates).
724 !sess.target.target.options.no_builtins
725 && (info.compiler_builtins == Some(cnum) || info.is_no_builtins.contains(&cnum))
728 fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
731 linker: Option<PathBuf>,
732 flavor: Option<LinkerFlavor>,
733 ) -> Option<(PathBuf, LinkerFlavor)> {
734 match (linker, flavor) {
735 (Some(linker), Some(flavor)) => Some((linker, flavor)),
736 // only the linker flavor is known; use the default linker for the selected flavor
737 (None, Some(flavor)) => Some((
738 PathBuf::from(match flavor {
739 LinkerFlavor::Em => {
746 LinkerFlavor::Gcc => {
747 if cfg!(any(target_os = "solaris", target_os = "illumos")) {
748 // On historical Solaris systems, "cc" may have
749 // been Sun Studio, which is not flag-compatible
750 // with "gcc". This history casts a long shadow,
751 // and many modern illumos distributions today
752 // ship GCC as "gcc" without also making it
753 // available as "cc".
759 LinkerFlavor::Ld => "ld",
760 LinkerFlavor::Msvc => "link.exe",
761 LinkerFlavor::Lld(_) => "lld",
762 LinkerFlavor::PtxLinker => "rust-ptx-linker",
766 (Some(linker), None) => {
767 let stem = linker.file_stem().and_then(|stem| stem.to_str()).unwrap_or_else(|| {
768 sess.fatal("couldn't extract file stem from specified linker")
771 let flavor = if stem == "emcc" {
773 } else if stem == "gcc"
774 || stem.ends_with("-gcc")
776 || stem.ends_with("-clang")
779 } else if stem == "ld" || stem == "ld.lld" || stem.ends_with("-ld") {
781 } else if stem == "link" || stem == "lld-link" {
783 } else if stem == "lld" || stem == "rust-lld" {
784 LinkerFlavor::Lld(sess.target.target.options.lld_flavor)
786 // fall back to the value in the target spec
787 sess.target.target.linker_flavor
790 Some((linker, flavor))
792 (None, None) => None,
796 // linker and linker flavor specified via command line have precedence over what the target
797 // specification specifies
798 if let Some(ret) = infer_from(sess, sess.opts.cg.linker.clone(), sess.opts.cg.linker_flavor) {
802 if let Some(ret) = infer_from(
804 sess.target.target.options.linker.clone().map(PathBuf::from),
805 Some(sess.target.target.linker_flavor),
810 bug!("Not enough information provided to determine how to invoke the linker");
813 /// Returns a boolean indicating whether we should preserve the object files on
814 /// the filesystem for their debug information. This is often useful with
815 /// split-dwarf like schemes.
816 fn preserve_objects_for_their_debuginfo(sess: &Session) -> bool {
817 // If the objects don't have debuginfo there's nothing to preserve.
818 if sess.opts.debuginfo == config::DebugInfo::None {
822 // If we're only producing artifacts that are archives, no need to preserve
823 // the objects as they're losslessly contained inside the archives.
824 let output_linked = sess
828 .any(|&x| x != CrateType::Rlib && x != CrateType::Staticlib);
833 // If we're on OSX then the equivalent of split dwarf is turned on by
834 // default. The final executable won't actually have any debug information
835 // except it'll have pointers to elsewhere. Historically we've always run
836 // `dsymutil` to "link all the dwarf together" but this is actually sort of
837 // a bummer for incremental compilation! (the whole point of split dwarf is
838 // that you don't do this sort of dwarf link).
840 // Basically as a result this just means that if we're on OSX and we're
841 // *not* running dsymutil then the object files are the only source of truth
842 // for debug information, so we must preserve them.
843 if sess.target.target.options.is_like_osx {
844 return !sess.opts.debugging_opts.run_dsymutil;
850 pub fn archive_search_paths(sess: &Session) -> Vec<PathBuf> {
851 sess.target_filesearch(PathKind::Native).search_path_dirs()
859 fn print_native_static_libs(sess: &Session, all_native_libs: &[NativeLibrary]) {
860 let lib_args: Vec<_> = all_native_libs
862 .filter(|l| relevant_lib(sess, l))
864 let name = lib.name?;
866 NativeLibraryKind::NativeStaticNobundle | NativeLibraryKind::NativeUnknown => {
867 if sess.target.target.options.is_like_msvc {
868 Some(format!("{}.lib", name))
870 Some(format!("-l{}", name))
873 NativeLibraryKind::NativeFramework => {
874 // ld-only syntax, since there are no frameworks in MSVC
875 Some(format!("-framework {}", name))
877 // These are included, no need to print them
878 NativeLibraryKind::NativeStatic | NativeLibraryKind::NativeRawDylib => None,
882 if !lib_args.is_empty() {
883 sess.note_without_error(
884 "Link against the following native artifacts when linking \
885 against this static library. The order and any duplication \
886 can be significant on some platforms.",
888 // Prefix for greppability
889 sess.note_without_error(&format!("native-static-libs: {}", &lib_args.join(" ")));
893 // Because windows-gnu target is meant to be self-contained for pure Rust code it bundles
894 // own mingw-w64 libraries. These libraries are usually not compatible with mingw-w64
895 // installed in the system. This breaks many cases where Rust is mixed with other languages
896 // (e.g. *-sys crates).
897 // We prefer system mingw-w64 libraries if they are available to avoid this issue.
898 fn get_crt_libs_path(sess: &Session) -> Option<PathBuf> {
899 fn find_exe_in_path<P>(exe_name: P) -> Option<PathBuf>
903 for dir in env::split_paths(&env::var_os("PATH")?) {
904 let full_path = dir.join(&exe_name);
905 if full_path.is_file() {
906 return Some(fix_windows_verbatim_for_gcc(&full_path));
912 fn probe(sess: &Session) -> Option<PathBuf> {
913 if let (linker, LinkerFlavor::Gcc) = linker_and_flavor(&sess) {
914 let linker_path = if cfg!(windows) && linker.extension().is_none() {
915 linker.with_extension("exe")
919 if let Some(linker_path) = find_exe_in_path(linker_path) {
920 let mingw_arch = match &sess.target.target.arch {
921 x if x == "x86" => "i686",
924 let mingw_bits = &sess.target.target.target_pointer_width;
925 let mingw_dir = format!("{}-w64-mingw32", mingw_arch);
926 // Here we have path/bin/gcc but we need path/
927 let mut path = linker_path;
930 // Loosely based on Clang MinGW driver
931 let probe_paths = vec![
932 path.join(&mingw_dir).join("lib"), // Typical path
933 path.join(&mingw_dir).join("sys-root/mingw/lib"), // Rare path
935 "lib/mingw/tools/install/mingw{}/{}/lib",
936 &mingw_bits, &mingw_dir
937 )), // Chocolatey is creative
939 for probe_path in probe_paths {
940 if probe_path.join("crt2.o").exists() {
941 return Some(probe_path);
949 let mut system_library_path = sess.system_library_path.borrow_mut();
950 match &*system_library_path {
951 Some(Some(compiler_libs_path)) => Some(compiler_libs_path.clone()),
954 let path = probe(sess);
955 *system_library_path = Some(path.clone());
961 fn get_object_file_path(sess: &Session, name: &str) -> PathBuf {
962 // prefer system {,dll}crt2.o libs, see get_crt_libs_path comment for more details
963 if sess.target.target.llvm_target.contains("windows-gnu") {
964 if let Some(compiler_libs_path) = get_crt_libs_path(sess) {
965 let file_path = compiler_libs_path.join(name);
966 if file_path.exists() {
971 let fs = sess.target_filesearch(PathKind::Native);
972 let file_path = fs.get_lib_path().join(name);
973 if file_path.exists() {
976 for search_path in fs.search_paths() {
977 let file_path = search_path.dir.join(name);
978 if file_path.exists() {
990 ) -> io::Result<Output> {
991 // When attempting to spawn the linker we run a risk of blowing out the
992 // size limits for spawning a new process with respect to the arguments
993 // we pass on the command line.
995 // Here we attempt to handle errors from the OS saying "your list of
996 // arguments is too big" by reinvoking the linker again with an `@`-file
997 // that contains all the arguments. The theory is that this is then
998 // accepted on all linkers and the linker will read all its options out of
999 // there instead of looking at the command line.
1000 if !cmd.very_likely_to_exceed_some_spawn_limit() {
1001 match cmd.command().stdout(Stdio::piped()).stderr(Stdio::piped()).spawn() {
1003 let output = child.wait_with_output();
1004 flush_linked_file(&output, out_filename)?;
1007 Err(ref e) if command_line_too_big(e) => {
1008 info!("command line to linker was too big: {}", e);
1010 Err(e) => return Err(e),
1014 info!("falling back to passing arguments to linker via an @-file");
1015 let mut cmd2 = cmd.clone();
1016 let mut args = String::new();
1017 for arg in cmd2.take_args() {
1020 arg: arg.to_str().unwrap(),
1021 is_like_msvc: sess.target.target.options.is_like_msvc,
1025 args.push_str("\n");
1027 let file = tmpdir.join("linker-arguments");
1028 let bytes = if sess.target.target.options.is_like_msvc {
1029 let mut out = Vec::with_capacity((1 + args.len()) * 2);
1030 // start the stream with a UTF-16 BOM
1031 for c in std::iter::once(0xFEFF).chain(args.encode_utf16()) {
1032 // encode in little endian
1034 out.push((c >> 8) as u8);
1040 fs::write(&file, &bytes)?;
1041 cmd2.arg(format!("@{}", file.display()));
1042 info!("invoking linker {:?}", cmd2);
1043 let output = cmd2.output();
1044 flush_linked_file(&output, out_filename)?;
1048 fn flush_linked_file(_: &io::Result<Output>, _: &Path) -> io::Result<()> {
1053 fn flush_linked_file(
1054 command_output: &io::Result<Output>,
1055 out_filename: &Path,
1056 ) -> io::Result<()> {
1057 // On Windows, under high I/O load, output buffers are sometimes not flushed,
1058 // even long after process exit, causing nasty, non-reproducible output bugs.
1060 // File::sync_all() calls FlushFileBuffers() down the line, which solves the problem.
1062 // А full writeup of the original Chrome bug can be found at
1063 // randomascii.wordpress.com/2018/02/25/compiler-bug-linker-bug-windows-kernel-bug/amp
1065 if let &Ok(ref out) = command_output {
1066 if out.status.success() {
1067 if let Ok(of) = fs::OpenOptions::new().write(true).open(out_filename) {
1077 fn command_line_too_big(err: &io::Error) -> bool {
1078 err.raw_os_error() == Some(::libc::E2BIG)
1082 fn command_line_too_big(err: &io::Error) -> bool {
1083 const ERROR_FILENAME_EXCED_RANGE: i32 = 206;
1084 err.raw_os_error() == Some(ERROR_FILENAME_EXCED_RANGE)
1092 impl<'a> fmt::Display for Escape<'a> {
1093 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1094 if self.is_like_msvc {
1095 // This is "documented" at
1096 // https://docs.microsoft.com/en-us/cpp/build/reference/at-specify-a-linker-response-file
1098 // Unfortunately there's not a great specification of the
1099 // syntax I could find online (at least) but some local
1100 // testing showed that this seemed sufficient-ish to catch
1101 // at least a few edge cases.
1103 for c in self.arg.chars() {
1105 '"' => write!(f, "\\{}", c)?,
1106 c => write!(f, "{}", c)?,
1111 // This is documented at https://linux.die.net/man/1/ld, namely:
1113 // > Options in file are separated by whitespace. A whitespace
1114 // > character may be included in an option by surrounding the
1115 // > entire option in either single or double quotes. Any
1116 // > character (including a backslash) may be included by
1117 // > prefixing the character to be included with a backslash.
1119 // We put an argument on each line, so all we need to do is
1120 // ensure the line is interpreted as one whole argument.
1121 for c in self.arg.chars() {
1123 '\\' | ' ' => write!(f, "\\{}", c)?,
1124 c => write!(f, "{}", c)?,
1133 /// Add begin object files defined by the target spec.
1134 fn add_pre_link_objects(cmd: &mut dyn Linker, sess: &Session, crate_type: CrateType) {
1135 let pre_link_objects = if crate_type == CrateType::Executable {
1136 &sess.target.target.options.pre_link_objects_exe
1138 &sess.target.target.options.pre_link_objects_dll
1140 for obj in pre_link_objects {
1141 cmd.add_object(&get_object_file_path(sess, obj));
1144 if crate_type == CrateType::Executable && sess.crt_static(Some(crate_type)) {
1145 for obj in &sess.target.target.options.pre_link_objects_exe_crt {
1146 cmd.add_object(&get_object_file_path(sess, obj));
1151 /// Add end object files defined by the target spec.
1152 fn add_post_link_objects(cmd: &mut dyn Linker, sess: &Session, crate_type: CrateType) {
1153 for obj in &sess.target.target.options.post_link_objects {
1154 cmd.add_object(&get_object_file_path(sess, obj));
1156 if sess.crt_static(Some(crate_type)) {
1157 for obj in &sess.target.target.options.post_link_objects_crt {
1158 cmd.add_object(&get_object_file_path(sess, obj));
1163 /// Add arbitrary "pre-link" args defined by the target spec or from command line.
1164 /// FIXME: Determine where exactly these args need to be inserted.
1165 fn add_pre_link_args(
1166 cmd: &mut dyn Linker,
1168 flavor: LinkerFlavor,
1169 crate_type: CrateType,
1171 if let Some(args) = sess.target.target.options.pre_link_args.get(&flavor) {
1174 if let Some(args) = sess.target.target.options.pre_link_args_crt.get(&flavor) {
1175 if sess.crt_static(Some(crate_type)) {
1179 cmd.args(&sess.opts.debugging_opts.pre_link_args);
1182 /// Add a link script embedded in the target, if applicable.
1184 cmd: &mut dyn Linker,
1187 crate_type: CrateType,
1189 match (crate_type, &sess.target.target.options.link_script) {
1190 (CrateType::Cdylib | CrateType::Executable, Some(script)) => {
1191 if !sess.target.target.options.linker_is_gnu {
1192 sess.fatal("can only use link script when linking with GNU-like linker");
1195 let file_name = ["rustc", &sess.target.target.llvm_target, "linkfile.ld"].join("-");
1197 let path = tmpdir.join(file_name);
1198 if let Err(e) = fs::write(&path, script) {
1199 sess.fatal(&format!("failed to write link script to {}: {}", path.display(), e));
1202 cmd.arg("--script");
1209 /// Add arbitrary "user defined" args defined from command line and by `#[link_args]` attributes.
1210 /// FIXME: Determine where exactly these args need to be inserted.
1211 fn add_user_defined_link_args(
1212 cmd: &mut dyn Linker,
1214 codegen_results: &CodegenResults,
1216 cmd.args(&sess.opts.cg.link_args);
1217 cmd.args(&*codegen_results.crate_info.link_args);
1220 /// Add arbitrary "late link" args defined by the target spec.
1221 /// FIXME: Determine where exactly these args need to be inserted.
1222 fn add_late_link_args(
1223 cmd: &mut dyn Linker,
1225 flavor: LinkerFlavor,
1226 crate_type: CrateType,
1227 codegen_results: &CodegenResults,
1229 if let Some(args) = sess.target.target.options.late_link_args.get(&flavor) {
1232 let any_dynamic_crate = crate_type == CrateType::Dylib
1233 || codegen_results.crate_info.dependency_formats.iter().any(|(ty, list)| {
1234 *ty == crate_type && list.iter().any(|&linkage| linkage == Linkage::Dynamic)
1236 if any_dynamic_crate {
1237 if let Some(args) = sess.target.target.options.late_link_args_dynamic.get(&flavor) {
1241 if let Some(args) = sess.target.target.options.late_link_args_static.get(&flavor) {
1247 /// Add arbitrary "post-link" args defined by the target spec.
1248 /// FIXME: Determine where exactly these args need to be inserted.
1249 fn add_post_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
1250 if let Some(args) = sess.target.target.options.post_link_args.get(&flavor) {
1255 /// Add object files containing code from the current crate.
1256 fn add_local_crate_regular_objects(cmd: &mut dyn Linker, codegen_results: &CodegenResults) {
1257 for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
1258 cmd.add_object(obj);
1262 /// Add object files for allocator code linked once for the whole crate tree.
1263 fn add_local_crate_allocator_objects(cmd: &mut dyn Linker, codegen_results: &CodegenResults) {
1264 if let Some(obj) = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref()) {
1265 cmd.add_object(obj);
1269 /// Add object files containing metadata for the current crate.
1270 fn add_local_crate_metadata_objects(
1271 cmd: &mut dyn Linker,
1272 crate_type: CrateType,
1273 codegen_results: &CodegenResults,
1275 // When linking a dynamic library, we put the metadata into a section of the
1276 // executable. This metadata is in a separate object file from the main
1277 // object file, so we link that in here.
1278 if crate_type == CrateType::Dylib || crate_type == CrateType::ProcMacro {
1279 if let Some(obj) = codegen_results.metadata_module.as_ref().and_then(|m| m.object.as_ref())
1281 cmd.add_object(obj);
1286 /// Link native libraries corresponding to the current crate and all libraries corresponding to
1287 /// all its dependency crates.
1288 /// FIXME: Consider combining this with the functions above adding object files for the local crate.
1289 fn link_local_crate_native_libs_and_dependent_crate_libs<'a, B: ArchiveBuilder<'a>>(
1290 cmd: &mut dyn Linker,
1292 crate_type: CrateType,
1293 codegen_results: &CodegenResults,
1296 // Take careful note of the ordering of the arguments we pass to the linker
1297 // here. Linkers will assume that things on the left depend on things to the
1298 // right. Things on the right cannot depend on things on the left. This is
1299 // all formally implemented in terms of resolving symbols (libs on the right
1300 // resolve unknown symbols of libs on the left, but not vice versa).
1302 // For this reason, we have organized the arguments we pass to the linker as
1305 // 1. The local object that LLVM just generated
1306 // 2. Local native libraries
1307 // 3. Upstream rust libraries
1308 // 4. Upstream native libraries
1310 // The rationale behind this ordering is that those items lower down in the
1311 // list can't depend on items higher up in the list. For example nothing can
1312 // depend on what we just generated (e.g., that'd be a circular dependency).
1313 // Upstream rust libraries are not allowed to depend on our local native
1314 // libraries as that would violate the structure of the DAG, in that
1315 // scenario they are required to link to them as well in a shared fashion.
1317 // Note that upstream rust libraries may contain native dependencies as
1318 // well, but they also can't depend on what we just started to add to the
1319 // link line. And finally upstream native libraries can't depend on anything
1320 // in this DAG so far because they're only dylibs and dylibs can only depend
1321 // on other dylibs (e.g., other native deps).
1323 // If -Zlink-native-libraries=false is set, then the assumption is that an
1324 // external build system already has the native dependencies defined, and it
1325 // will provide them to the linker itself.
1326 if sess.opts.debugging_opts.link_native_libraries {
1327 add_local_native_libraries(cmd, sess, codegen_results);
1329 add_upstream_rust_crates::<B>(cmd, sess, codegen_results, crate_type, tmpdir);
1330 if sess.opts.debugging_opts.link_native_libraries {
1331 add_upstream_native_libraries(cmd, sess, codegen_results, crate_type);
1335 /// Add sysroot and other globally set directories to the directory search list.
1336 fn add_library_search_dirs(cmd: &mut dyn Linker, sess: &Session) {
1337 // Prefer system mingw-w64 libs, see get_crt_libs_path comment for more details.
1338 if cfg!(windows) && sess.target.target.llvm_target.contains("windows-gnu") {
1339 if let Some(compiler_libs_path) = get_crt_libs_path(sess) {
1340 cmd.include_path(&compiler_libs_path);
1344 // The default library location, we need this to find the runtime.
1345 // The location of crates will be determined as needed.
1346 let lib_path = sess.target_filesearch(PathKind::All).get_lib_path();
1347 cmd.include_path(&fix_windows_verbatim_for_gcc(&lib_path));
1350 /// Add options requesting executables to be position-independent or not position-independent.
1351 fn add_position_independent_executable_args(
1352 cmd: &mut dyn Linker,
1354 flavor: LinkerFlavor,
1355 crate_type: CrateType,
1356 codegen_results: &CodegenResults,
1358 if crate_type != CrateType::Executable {
1362 if sess.target.target.options.position_independent_executables {
1363 let attr_link_args = &*codegen_results.crate_info.link_args;
1364 let mut user_defined_link_args = sess.opts.cg.link_args.iter().chain(attr_link_args);
1365 if sess.relocation_model() == RelocModel::Pic
1366 && !sess.crt_static(Some(crate_type))
1367 && !user_defined_link_args.any(|x| x == "-static")
1369 cmd.position_independent_executable();
1374 // Recent versions of gcc can be configured to generate position
1375 // independent executables by default. We have to pass -no-pie to
1376 // explicitly turn that off. Not applicable to ld.
1377 if sess.target.target.options.linker_is_gnu && flavor != LinkerFlavor::Ld {
1378 cmd.no_position_independent_executable();
1382 /// Add options making relocation sections in the produced ELF files read-only
1383 /// and suppressing lazy binding.
1384 fn add_relro_args(cmd: &mut dyn Linker, sess: &Session) {
1385 match sess.opts.debugging_opts.relro_level.unwrap_or(sess.target.target.options.relro_level) {
1386 RelroLevel::Full => cmd.full_relro(),
1387 RelroLevel::Partial => cmd.partial_relro(),
1388 RelroLevel::Off => cmd.no_relro(),
1389 RelroLevel::None => {}
1393 /// Add library search paths used at runtime by dynamic linkers.
1395 cmd: &mut dyn Linker,
1397 codegen_results: &CodegenResults,
1398 out_filename: &Path,
1400 // FIXME (#2397): At some point we want to rpath our guesses as to
1401 // where extern libraries might live, based on the
1402 // addl_lib_search_paths
1403 if sess.opts.cg.rpath {
1404 let target_triple = sess.opts.target_triple.triple();
1405 let mut get_install_prefix_lib_path = || {
1406 let install_prefix = option_env!("CFG_PREFIX").expect("CFG_PREFIX");
1407 let tlib = filesearch::relative_target_lib_path(&sess.sysroot, target_triple);
1408 let mut path = PathBuf::from(install_prefix);
1413 let mut rpath_config = RPathConfig {
1414 used_crates: &codegen_results.crate_info.used_crates_dynamic,
1415 out_filename: out_filename.to_path_buf(),
1416 has_rpath: sess.target.target.options.has_rpath,
1417 is_like_osx: sess.target.target.options.is_like_osx,
1418 linker_is_gnu: sess.target.target.options.linker_is_gnu,
1419 get_install_prefix_lib_path: &mut get_install_prefix_lib_path,
1421 cmd.args(&rpath::get_rpath_flags(&mut rpath_config));
1425 /// Produce the linker command line containing linker path and arguments.
1426 /// `NO-OPT-OUT` marks the arguments that cannot be removed from the command line
1427 /// by the user without creating a custom target specification.
1428 /// `OBJECT-FILES` specify whether the arguments can add object files.
1429 /// `CUSTOMIZATION-POINT` means that arbitrary arguments defined by the user
1430 /// or by the target spec can be inserted here.
1431 /// `AUDIT-ORDER` - need to figure out whether the option is order-dependent or not.
1432 fn linker_with_args<'a, B: ArchiveBuilder<'a>>(
1434 flavor: LinkerFlavor,
1436 crate_type: CrateType,
1438 out_filename: &Path,
1439 codegen_results: &CodegenResults,
1442 let base_cmd = get_linker(sess, path, flavor);
1443 // FIXME: Move `/LIBPATH` addition for uwp targets from the linker construction
1444 // to the linker args construction.
1445 assert!(base_cmd.get_args().is_empty() || sess.target.target.target_vendor == "uwp");
1446 let cmd = &mut *codegen_results.linker_info.to_linker(base_cmd, &sess, flavor, target_cpu);
1448 // NO-OPT-OUT, OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT
1449 add_pre_link_args(cmd, sess, flavor, crate_type);
1452 add_link_script(cmd, sess, tmpdir, crate_type);
1454 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1455 if sess.target.target.options.is_like_fuchsia {
1456 let prefix = match sess.opts.debugging_opts.sanitizer {
1457 Some(Sanitizer::Address) => "asan/",
1460 cmd.arg(format!("--dynamic-linker={}ld.so.1", prefix));
1463 // NO-OPT-OUT, OBJECT-FILES-YES
1464 add_pre_link_objects(cmd, sess, crate_type);
1466 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1467 if sess.target.target.options.is_like_emscripten {
1469 cmd.arg(if sess.panic_strategy() == PanicStrategy::Abort {
1470 "DISABLE_EXCEPTION_CATCHING=1"
1472 "DISABLE_EXCEPTION_CATCHING=0"
1476 // OBJECT-FILES-YES, AUDIT-ORDER
1477 link_sanitizer_runtime(sess, crate_type, cmd);
1479 // OBJECT-FILES-NO, AUDIT-ORDER
1480 // Linker plugins should be specified early in the list of arguments
1481 // FIXME: How "early" exactly?
1482 cmd.linker_plugin_lto();
1484 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1485 // FIXME: Order-dependent, at least relatively to other args adding searh directories.
1486 add_library_search_dirs(cmd, sess);
1489 add_local_crate_regular_objects(cmd, codegen_results);
1491 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1492 cmd.output_filename(out_filename);
1494 // OBJECT-FILES-NO, AUDIT-ORDER
1495 if crate_type == CrateType::Executable && sess.target.target.options.is_like_windows {
1496 if let Some(ref s) = codegen_results.windows_subsystem {
1501 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1502 // If we're building something like a dynamic library then some platforms
1503 // need to make sure that all symbols are exported correctly from the
1505 cmd.export_symbols(tmpdir, crate_type);
1508 add_local_crate_metadata_objects(cmd, crate_type, codegen_results);
1511 add_local_crate_allocator_objects(cmd, codegen_results);
1513 // OBJECT-FILES-NO, AUDIT-ORDER
1514 // FIXME: Order dependent, applies to the following objects. Where should it be placed?
1515 // Try to strip as much out of the generated object by removing unused
1516 // sections if possible. See more comments in linker.rs
1517 if !sess.opts.cg.link_dead_code {
1518 let keep_metadata = crate_type == CrateType::Dylib;
1519 cmd.gc_sections(keep_metadata);
1522 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1523 add_position_independent_executable_args(cmd, sess, flavor, crate_type, codegen_results);
1525 // OBJECT-FILES-NO, AUDIT-ORDER
1526 add_relro_args(cmd, sess);
1528 // OBJECT-FILES-NO, AUDIT-ORDER
1529 // Pass optimization flags down to the linker.
1532 // OBJECT-FILES-NO, AUDIT-ORDER
1533 // Pass debuginfo flags down to the linker.
1536 // OBJECT-FILES-NO, AUDIT-ORDER
1537 // We want to prevent the compiler from accidentally leaking in any system libraries,
1538 // so by default we tell linkers not to link to any default libraries.
1539 if !sess.opts.cg.default_linker_libraries && sess.target.target.options.no_default_libraries {
1540 cmd.no_default_libraries();
1544 link_local_crate_native_libs_and_dependent_crate_libs::<B>(
1552 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1553 // Tell the linker what we're doing.
1554 if crate_type != CrateType::Executable {
1555 cmd.build_dylib(out_filename);
1557 if crate_type == CrateType::Executable && sess.crt_static(Some(crate_type)) {
1558 cmd.build_static_executable();
1561 // OBJECT-FILES-NO, AUDIT-ORDER
1562 if sess.opts.cg.profile_generate.enabled() {
1566 // OBJECT-FILES-NO, AUDIT-ORDER
1567 if sess.opts.debugging_opts.control_flow_guard != CFGuard::Disabled {
1568 cmd.control_flow_guard();
1571 // OBJECT-FILES-NO, AUDIT-ORDER
1572 add_rpath_args(cmd, sess, codegen_results, out_filename);
1574 // OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT
1575 add_user_defined_link_args(cmd, sess, codegen_results);
1577 // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
1580 // NO-OPT-OUT, OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT
1581 add_late_link_args(cmd, sess, flavor, crate_type, codegen_results);
1583 // NO-OPT-OUT, OBJECT-FILES-YES
1584 add_post_link_objects(cmd, sess, crate_type);
1586 // NO-OPT-OUT, OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT
1587 add_post_link_args(cmd, sess, flavor);
1592 // # Native library linking
1594 // User-supplied library search paths (-L on the command line). These are
1595 // the same paths used to find Rust crates, so some of them may have been
1596 // added already by the previous crate linking code. This only allows them
1597 // to be found at compile time so it is still entirely up to outside
1598 // forces to make sure that library can be found at runtime.
1600 // Also note that the native libraries linked here are only the ones located
1601 // in the current crate. Upstream crates with native library dependencies
1602 // may have their native library pulled in above.
1603 fn add_local_native_libraries(
1604 cmd: &mut dyn Linker,
1606 codegen_results: &CodegenResults,
1608 let filesearch = sess.target_filesearch(PathKind::All);
1609 for search_path in filesearch.search_paths() {
1610 match search_path.kind {
1611 PathKind::Framework => {
1612 cmd.framework_path(&search_path.dir);
1615 cmd.include_path(&fix_windows_verbatim_for_gcc(&search_path.dir));
1621 codegen_results.crate_info.used_libraries.iter().filter(|l| relevant_lib(sess, l));
1623 let search_path = archive_search_paths(sess);
1624 for lib in relevant_libs {
1625 let name = match lib.name {
1630 NativeLibraryKind::NativeUnknown => cmd.link_dylib(name),
1631 NativeLibraryKind::NativeFramework => cmd.link_framework(name),
1632 NativeLibraryKind::NativeStaticNobundle => cmd.link_staticlib(name),
1633 NativeLibraryKind::NativeStatic => cmd.link_whole_staticlib(name, &search_path),
1634 NativeLibraryKind::NativeRawDylib => {
1635 // FIXME(#58713): Proper handling for raw dylibs.
1636 bug!("raw_dylib feature not yet implemented");
1642 // # Rust Crate linking
1644 // Rust crates are not considered at all when creating an rlib output. All
1645 // dependencies will be linked when producing the final output (instead of
1646 // the intermediate rlib version)
1647 fn add_upstream_rust_crates<'a, B: ArchiveBuilder<'a>>(
1648 cmd: &mut dyn Linker,
1650 codegen_results: &CodegenResults,
1651 crate_type: CrateType,
1654 // All of the heavy lifting has previously been accomplished by the
1655 // dependency_format module of the compiler. This is just crawling the
1656 // output of that module, adding crates as necessary.
1658 // Linking to a rlib involves just passing it to the linker (the linker
1659 // will slurp up the object files inside), and linking to a dynamic library
1660 // involves just passing the right -l flag.
1662 let (_, data) = codegen_results
1666 .find(|(ty, _)| *ty == crate_type)
1667 .expect("failed to find crate type in dependency format list");
1669 // Invoke get_used_crates to ensure that we get a topological sorting of
1671 let deps = &codegen_results.crate_info.used_crates_dynamic;
1673 // There's a few internal crates in the standard library (aka libcore and
1674 // libstd) which actually have a circular dependence upon one another. This
1675 // currently arises through "weak lang items" where libcore requires things
1676 // like `rust_begin_unwind` but libstd ends up defining it. To get this
1677 // circular dependence to work correctly in all situations we'll need to be
1678 // sure to correctly apply the `--start-group` and `--end-group` options to
1679 // GNU linkers, otherwise if we don't use any other symbol from the standard
1680 // library it'll get discarded and the whole application won't link.
1682 // In this loop we're calculating the `group_end`, after which crate to
1683 // pass `--end-group` and `group_start`, before which crate to pass
1684 // `--start-group`. We currently do this by passing `--end-group` after
1685 // the first crate (when iterating backwards) that requires a lang item
1686 // defined somewhere else. Once that's set then when we've defined all the
1687 // necessary lang items we'll pass `--start-group`.
1689 // Note that this isn't amazing logic for now but it should do the trick
1690 // for the current implementation of the standard library.
1691 let mut group_end = None;
1692 let mut group_start = None;
1693 // Crates available for linking thus far.
1694 let mut available = FxHashSet::default();
1695 // Crates required to satisfy dependencies discovered so far.
1696 let mut required = FxHashSet::default();
1698 let info = &codegen_results.crate_info;
1699 for &(cnum, _) in deps.iter().rev() {
1700 if let Some(missing) = info.missing_lang_items.get(&cnum) {
1701 let missing_crates = missing.iter().map(|i| info.lang_item_to_crate.get(i).copied());
1702 required.extend(missing_crates);
1705 required.insert(Some(cnum));
1706 available.insert(Some(cnum));
1708 if required.len() > available.len() && group_end.is_none() {
1709 group_end = Some(cnum);
1711 if required.len() == available.len() && group_end.is_some() {
1712 group_start = Some(cnum);
1717 // If we didn't end up filling in all lang items from upstream crates then
1718 // we'll be filling it in with our crate. This probably means we're the
1719 // standard library itself, so skip this for now.
1720 if group_end.is_some() && group_start.is_none() {
1724 let mut compiler_builtins = None;
1726 for &(cnum, _) in deps.iter() {
1727 if group_start == Some(cnum) {
1731 // We may not pass all crates through to the linker. Some crates may
1732 // appear statically in an existing dylib, meaning we'll pick up all the
1733 // symbols from the dylib.
1734 let src = &codegen_results.crate_info.used_crate_source[&cnum];
1735 match data[cnum.as_usize() - 1] {
1736 _ if codegen_results.crate_info.profiler_runtime == Some(cnum) => {
1737 add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
1739 // compiler-builtins are always placed last to ensure that they're
1740 // linked correctly.
1741 _ if codegen_results.crate_info.compiler_builtins == Some(cnum) => {
1742 assert!(compiler_builtins.is_none());
1743 compiler_builtins = Some(cnum);
1745 Linkage::NotLinked | Linkage::IncludedFromDylib => {}
1746 Linkage::Static => {
1747 add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
1749 Linkage::Dynamic => add_dynamic_crate(cmd, sess, &src.dylib.as_ref().unwrap().0),
1752 if group_end == Some(cnum) {
1757 // compiler-builtins are always placed last to ensure that they're
1758 // linked correctly.
1759 // We must always link the `compiler_builtins` crate statically. Even if it
1760 // was already "included" in a dylib (e.g., `libstd` when `-C prefer-dynamic`
1762 if let Some(cnum) = compiler_builtins {
1763 add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
1766 // Converts a library file-stem into a cc -l argument
1767 fn unlib<'a>(config: &config::Config, stem: &'a str) -> &'a str {
1768 if stem.starts_with("lib") && !config.target.options.is_like_windows {
1775 // Adds the static "rlib" versions of all crates to the command line.
1776 // There's a bit of magic which happens here specifically related to LTO and
1777 // dynamic libraries. Specifically:
1779 // * For LTO, we remove upstream object files.
1780 // * For dylibs we remove metadata and bytecode from upstream rlibs
1782 // When performing LTO, almost(*) all of the bytecode from the upstream
1783 // libraries has already been included in our object file output. As a
1784 // result we need to remove the object files in the upstream libraries so
1785 // the linker doesn't try to include them twice (or whine about duplicate
1786 // symbols). We must continue to include the rest of the rlib, however, as
1787 // it may contain static native libraries which must be linked in.
1789 // (*) Crates marked with `#![no_builtins]` don't participate in LTO and
1790 // their bytecode wasn't included. The object files in those libraries must
1791 // still be passed to the linker.
1793 // When making a dynamic library, linkers by default don't include any
1794 // object files in an archive if they're not necessary to resolve the link.
1795 // We basically want to convert the archive (rlib) to a dylib, though, so we
1796 // *do* want everything included in the output, regardless of whether the
1797 // linker thinks it's needed or not. As a result we must use the
1798 // --whole-archive option (or the platform equivalent). When using this
1799 // option the linker will fail if there are non-objects in the archive (such
1800 // as our own metadata and/or bytecode). All in all, for rlibs to be
1801 // entirely included in dylibs, we need to remove all non-object files.
1803 // Note, however, that if we're not doing LTO or we're not producing a dylib
1804 // (aka we're making an executable), we can just pass the rlib blindly to
1805 // the linker (fast) because it's fine if it's not actually included as
1806 // we're at the end of the dependency chain.
1807 fn add_static_crate<'a, B: ArchiveBuilder<'a>>(
1808 cmd: &mut dyn Linker,
1810 codegen_results: &CodegenResults,
1812 crate_type: CrateType,
1815 let src = &codegen_results.crate_info.used_crate_source[&cnum];
1816 let cratepath = &src.rlib.as_ref().unwrap().0;
1818 // See the comment above in `link_staticlib` and `link_rlib` for why if
1819 // there's a static library that's not relevant we skip all object
1821 let native_libs = &codegen_results.crate_info.native_libraries[&cnum];
1822 let skip_native = native_libs
1824 .any(|lib| lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib));
1826 if (!are_upstream_rust_objects_already_included(sess)
1827 || ignored_for_lto(sess, &codegen_results.crate_info, cnum))
1828 && crate_type != CrateType::Dylib
1831 cmd.link_rlib(&fix_windows_verbatim_for_gcc(cratepath));
1835 let dst = tmpdir.join(cratepath.file_name().unwrap());
1836 let name = cratepath.file_name().unwrap().to_str().unwrap();
1837 let name = &name[3..name.len() - 5]; // chop off lib/.rlib
1839 sess.prof.generic_activity_with_arg("link_altering_rlib", name).run(|| {
1840 let mut archive = <B as ArchiveBuilder>::new(sess, &dst, Some(cratepath));
1841 archive.update_symbols();
1843 let mut any_objects = false;
1844 for f in archive.src_files() {
1845 if f == METADATA_FILENAME {
1846 archive.remove_file(&f);
1850 let canonical = f.replace("-", "_");
1851 let canonical_name = name.replace("-", "_");
1853 let is_rust_object =
1854 canonical.starts_with(&canonical_name) && looks_like_rust_object_file(&f);
1856 // If we've been requested to skip all native object files
1857 // (those not generated by the rust compiler) then we can skip
1858 // this file. See above for why we may want to do this.
1859 let skip_because_cfg_say_so = skip_native && !is_rust_object;
1861 // If we're performing LTO and this is a rust-generated object
1862 // file, then we don't need the object file as it's part of the
1863 // LTO module. Note that `#![no_builtins]` is excluded from LTO,
1864 // though, so we let that object file slide.
1865 let skip_because_lto = are_upstream_rust_objects_already_included(sess)
1867 && (sess.target.target.options.no_builtins
1868 || !codegen_results.crate_info.is_no_builtins.contains(&cnum));
1870 if skip_because_cfg_say_so || skip_because_lto {
1871 archive.remove_file(&f);
1882 // If we're creating a dylib, then we need to include the
1883 // whole of each object in our archive into that artifact. This is
1884 // because a `dylib` can be reused as an intermediate artifact.
1886 // Note, though, that we don't want to include the whole of a
1887 // compiler-builtins crate (e.g., compiler-rt) because it'll get
1888 // repeatedly linked anyway.
1889 if crate_type == CrateType::Dylib
1890 && codegen_results.crate_info.compiler_builtins != Some(cnum)
1892 cmd.link_whole_rlib(&fix_windows_verbatim_for_gcc(&dst));
1894 cmd.link_rlib(&fix_windows_verbatim_for_gcc(&dst));
1899 // Same thing as above, but for dynamic crates instead of static crates.
1900 fn add_dynamic_crate(cmd: &mut dyn Linker, sess: &Session, cratepath: &Path) {
1901 // Just need to tell the linker about where the library lives and
1903 let parent = cratepath.parent();
1904 if let Some(dir) = parent {
1905 cmd.include_path(&fix_windows_verbatim_for_gcc(dir));
1907 let filestem = cratepath.file_stem().unwrap().to_str().unwrap();
1908 cmd.link_rust_dylib(
1909 Symbol::intern(&unlib(&sess.target, filestem)),
1910 parent.unwrap_or(Path::new("")),
1915 // Link in all of our upstream crates' native dependencies. Remember that
1916 // all of these upstream native dependencies are all non-static
1917 // dependencies. We've got two cases then:
1919 // 1. The upstream crate is an rlib. In this case we *must* link in the
1920 // native dependency because the rlib is just an archive.
1922 // 2. The upstream crate is a dylib. In order to use the dylib, we have to
1923 // have the dependency present on the system somewhere. Thus, we don't
1924 // gain a whole lot from not linking in the dynamic dependency to this
1927 // The use case for this is a little subtle. In theory the native
1928 // dependencies of a crate are purely an implementation detail of the crate
1929 // itself, but the problem arises with generic and inlined functions. If a
1930 // generic function calls a native function, then the generic function must
1931 // be instantiated in the target crate, meaning that the native symbol must
1932 // also be resolved in the target crate.
1933 fn add_upstream_native_libraries(
1934 cmd: &mut dyn Linker,
1936 codegen_results: &CodegenResults,
1937 crate_type: CrateType,
1939 // Be sure to use a topological sorting of crates because there may be
1940 // interdependencies between native libraries. When passing -nodefaultlibs,
1941 // for example, almost all native libraries depend on libc, so we have to
1942 // make sure that's all the way at the right (liblibc is near the base of
1943 // the dependency chain).
1945 // This passes RequireStatic, but the actual requirement doesn't matter,
1946 // we're just getting an ordering of crate numbers, we're not worried about
1948 let (_, data) = codegen_results
1952 .find(|(ty, _)| *ty == crate_type)
1953 .expect("failed to find crate type in dependency format list");
1955 let crates = &codegen_results.crate_info.used_crates_static;
1956 for &(cnum, _) in crates {
1957 for lib in codegen_results.crate_info.native_libraries[&cnum].iter() {
1958 let name = match lib.name {
1962 if !relevant_lib(sess, &lib) {
1966 NativeLibraryKind::NativeUnknown => cmd.link_dylib(name),
1967 NativeLibraryKind::NativeFramework => cmd.link_framework(name),
1968 NativeLibraryKind::NativeStaticNobundle => {
1969 // Link "static-nobundle" native libs only if the crate they originate from
1970 // is being linked statically to the current crate. If it's linked dynamically
1971 // or is an rlib already included via some other dylib crate, the symbols from
1972 // native libs will have already been included in that dylib.
1973 if data[cnum.as_usize() - 1] == Linkage::Static {
1974 cmd.link_staticlib(name)
1977 // ignore statically included native libraries here as we've
1978 // already included them when we included the rust library
1980 NativeLibraryKind::NativeStatic => {}
1981 NativeLibraryKind::NativeRawDylib => {
1982 // FIXME(#58713): Proper handling for raw dylibs.
1983 bug!("raw_dylib feature not yet implemented");
1990 fn relevant_lib(sess: &Session, lib: &NativeLibrary) -> bool {
1992 Some(ref cfg) => rustc_attr::cfg_matches(cfg, &sess.parse_sess, None),
1997 fn are_upstream_rust_objects_already_included(sess: &Session) -> bool {
1999 config::Lto::Fat => true,
2000 config::Lto::Thin => {
2001 // If we defer LTO to the linker, we haven't run LTO ourselves, so
2002 // any upstream object files have not been copied yet.
2003 !sess.opts.cg.linker_plugin_lto.enabled()
2005 config::Lto::No | config::Lto::ThinLocal => false,