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, PanicStrategy, 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 pub 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 && t.target_vendor == "uwp" {
186 if let Some(ref tool) = msvc_tool {
187 let original_path = tool.path();
188 if let Some(ref root_lib_path) = original_path.ancestors().nth(4) {
189 let arch = match t.arch.as_str() {
190 "x86_64" => Some("x64".to_string()),
191 "x86" => Some("x86".to_string()),
192 "aarch64" => Some("arm64".to_string()),
195 if let Some(ref a) = arch {
196 let mut arg = OsString::from("/LIBPATH:");
197 arg.push(format!("{}\\lib\\{}\\store", root_lib_path.display(), a.to_string()));
200 warn!("arch is not supported");
203 warn!("MSVC root path lib location not found");
206 warn!("link.exe not found");
210 // The compiler's sysroot often has some bundled tools, so add it to the
211 // PATH for the child.
212 let mut new_path = sess.host_filesearch(PathKind::All).get_tools_search_paths();
213 let mut msvc_changed_path = false;
214 if sess.target.target.options.is_like_msvc {
215 if let Some(ref tool) = msvc_tool {
216 cmd.args(tool.args());
217 for &(ref k, ref v) in tool.env() {
219 new_path.extend(env::split_paths(v));
220 msvc_changed_path = true;
228 if !msvc_changed_path {
229 if let Some(path) = env::var_os("PATH") {
230 new_path.extend(env::split_paths(&path));
233 cmd.env("PATH", env::join_paths(new_path).unwrap());
238 pub fn each_linked_rlib(
240 f: &mut dyn FnMut(CrateNum, &Path),
241 ) -> Result<(), String> {
242 let crates = info.used_crates_static.iter();
244 for (ty, list) in info.dependency_formats.iter() {
246 config::CrateType::Executable
247 | config::CrateType::Staticlib
248 | config::CrateType::Cdylib
249 | config::CrateType::ProcMacro => {
256 let fmts = match fmts {
258 None => return Err("could not find formats for rlibs".to_string()),
260 for &(cnum, ref path) in crates {
261 match fmts.get(cnum.as_usize() - 1) {
262 Some(&Linkage::NotLinked) | Some(&Linkage::IncludedFromDylib) => continue,
264 None => return Err("could not find formats for rlibs".to_string()),
266 let name = &info.crate_name[&cnum];
267 let path = match *path {
268 LibSource::Some(ref p) => p,
269 LibSource::MetadataOnly => {
271 "could not find rlib for: `{}`, found rmeta (metadata) file",
275 LibSource::None => return Err(format!("could not find rlib for: `{}`", name)),
282 /// We use a temp directory here to avoid races between concurrent rustc processes,
283 /// such as builds in the same directory using the same filename for metadata while
284 /// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a
285 /// directory being searched for `extern crate` (observing an incomplete file).
286 /// The returned path is the temporary file containing the complete metadata.
287 pub fn emit_metadata<'a>(
289 metadata: &EncodedMetadata,
292 let out_filename = tmpdir.path().join(METADATA_FILENAME);
293 let result = fs::write(&out_filename, &metadata.raw_data);
295 if let Err(e) = result {
296 sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e));
304 // An rlib in its current incarnation is essentially a renamed .a file. The
305 // rlib primarily contains the object file of the crate, but it also contains
306 // all of the object files from native libraries. This is done by unzipping
307 // native libraries and inserting all of the contents into this archive.
308 fn link_rlib<'a, B: ArchiveBuilder<'a>>(
310 codegen_results: &CodegenResults,
315 info!("preparing rlib to {:?}", out_filename);
316 let mut ab = <B as ArchiveBuilder>::new(sess, out_filename, None);
318 for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
322 // Note that in this loop we are ignoring the value of `lib.cfg`. That is,
323 // we may not be configured to actually include a static library if we're
324 // adding it here. That's because later when we consume this rlib we'll
325 // decide whether we actually needed the static library or not.
327 // To do this "correctly" we'd need to keep track of which libraries added
328 // which object files to the archive. We don't do that here, however. The
329 // #[link(cfg(..))] feature is unstable, though, and only intended to get
330 // liblibc working. In that sense the check below just indicates that if
331 // there are any libraries we want to omit object files for at link time we
332 // just exclude all custom object files.
334 // Eventually if we want to stabilize or flesh out the #[link(cfg(..))]
335 // feature then we'll need to figure out how to record what objects were
336 // loaded from the libraries found here and then encode that into the
337 // metadata of the rlib we're generating somehow.
338 for lib in codegen_results.crate_info.used_libraries.iter() {
340 NativeLibraryKind::NativeStatic => {}
341 NativeLibraryKind::NativeStaticNobundle
342 | NativeLibraryKind::NativeFramework
343 | NativeLibraryKind::NativeRawDylib
344 | NativeLibraryKind::NativeUnknown => continue,
346 if let Some(name) = lib.name {
347 ab.add_native_library(name);
351 // After adding all files to the archive, we need to update the
352 // symbol table of the archive.
355 // Note that it is important that we add all of our non-object "magical
356 // files" *after* all of the object files in the archive. The reason for
357 // this is as follows:
359 // * When performing LTO, this archive will be modified to remove
360 // objects from above. The reason for this is described below.
362 // * When the system linker looks at an archive, it will attempt to
363 // determine the architecture of the archive in order to see whether its
366 // The algorithm for this detection is: iterate over the files in the
367 // archive. Skip magical SYMDEF names. Interpret the first file as an
368 // object file. Read architecture from the object file.
370 // * As one can probably see, if "metadata" and "foo.bc" were placed
371 // before all of the objects, then the architecture of this archive would
372 // not be correctly inferred once 'foo.o' is removed.
374 // Basically, all this means is that this code should not move above the
377 RlibFlavor::Normal => {
378 // Instead of putting the metadata in an object file section, rlibs
379 // contain the metadata in a separate file.
380 ab.add_file(&emit_metadata(sess, &codegen_results.metadata, tmpdir));
382 // For LTO purposes, the bytecode of this library is also inserted
385 codegen_results.modules.iter().filter_map(|m| m.bytecode_compressed.as_ref())
387 ab.add_file(bytecode);
390 // After adding all files to the archive, we need to update the
391 // symbol table of the archive. This currently dies on macOS (see
392 // #11162), and isn't necessary there anyway
393 if !sess.target.target.options.is_like_osx {
398 RlibFlavor::StaticlibBase => {
399 let obj = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref());
400 if let Some(obj) = obj {
409 // Create a static archive
411 // This is essentially the same thing as an rlib, but it also involves adding
412 // all of the upstream crates' objects into the archive. This will slurp in
413 // all of the native libraries of upstream dependencies as well.
415 // Additionally, there's no way for us to link dynamic libraries, so we warn
416 // about all dynamic library dependencies that they're not linked in.
418 // There's no need to include metadata in a static archive, so ensure to not
419 // link in the metadata object file (and also don't prepare the archive with a
421 fn link_staticlib<'a, B: ArchiveBuilder<'a>>(
423 codegen_results: &CodegenResults,
428 link_rlib::<B>(sess, codegen_results, RlibFlavor::StaticlibBase, out_filename, tempdir);
429 let mut all_native_libs = vec![];
431 let res = each_linked_rlib(&codegen_results.crate_info, &mut |cnum, path| {
432 let name = &codegen_results.crate_info.crate_name[&cnum];
433 let native_libs = &codegen_results.crate_info.native_libraries[&cnum];
435 // Here when we include the rlib into our staticlib we need to make a
436 // decision whether to include the extra object files along the way.
437 // These extra object files come from statically included native
438 // libraries, but they may be cfg'd away with #[link(cfg(..))].
440 // This unstable feature, though, only needs liblibc to work. The only
441 // use case there is where musl is statically included in liblibc.rlib,
442 // so if we don't want the included version we just need to skip it. As
443 // a result the logic here is that if *any* linked library is cfg'd away
444 // we just skip all object files.
446 // Clearly this is not sufficient for a general purpose feature, and
447 // we'd want to read from the library's metadata to determine which
448 // object files come from where and selectively skip them.
449 let skip_object_files = native_libs
451 .any(|lib| lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib));
455 are_upstream_rust_objects_already_included(sess)
456 && !ignored_for_lto(sess, &codegen_results.crate_info, cnum),
461 all_native_libs.extend(codegen_results.crate_info.native_libraries[&cnum].iter().cloned());
463 if let Err(e) = res {
470 if !all_native_libs.is_empty() {
471 if sess.opts.prints.contains(&PrintRequest::NativeStaticLibs) {
472 print_native_static_libs(sess, &all_native_libs);
477 // Create a dynamic library or executable
479 // This will invoke the system linker/cc to create the resulting file. This
480 // links to all upstream files as well.
481 fn link_natively<'a, B: ArchiveBuilder<'a>>(
483 crate_type: config::CrateType,
485 codegen_results: &CodegenResults,
489 info!("preparing {:?} to {:?}", crate_type, out_filename);
490 let (linker_path, flavor) = linker_and_flavor(sess);
491 let mut cmd = linker_with_args::<B>(
502 for &(ref k, ref v) in &sess.target.target.options.link_env {
505 for k in &sess.target.target.options.link_env_remove {
509 if sess.opts.debugging_opts.print_link_args {
510 println!("{:?}", &cmd);
513 // May have not found libraries in the right formats.
514 sess.abort_if_errors();
516 // Invoke the system linker
518 let retry_on_segfault = env::var("RUSTC_RETRY_LINKER_ON_SEGFAULT").is_ok();
523 prog = sess.time("run_linker", || exec_linker(sess, &cmd, out_filename, tmpdir));
524 let output = match prog {
525 Ok(ref output) => output,
528 if output.status.success() {
531 let mut out = output.stderr.clone();
532 out.extend(&output.stdout);
533 let out = String::from_utf8_lossy(&out);
535 // Check to see if the link failed with "unrecognized command line option:
536 // '-no-pie'" for gcc or "unknown argument: '-no-pie'" for clang. If so,
537 // reperform the link step without the -no-pie option. This is safe because
538 // if the linker doesn't support -no-pie then it should not default to
539 // linking executables as pie. Different versions of gcc seem to use
540 // different quotes in the error message so don't check for them.
541 if sess.target.target.options.linker_is_gnu
542 && flavor != LinkerFlavor::Ld
543 && (out.contains("unrecognized command line option")
544 || out.contains("unknown argument"))
545 && out.contains("-no-pie")
546 && cmd.get_args().iter().any(|e| e.to_string_lossy() == "-no-pie")
548 info!("linker output: {:?}", out);
549 warn!("Linker does not support -no-pie command line option. Retrying without.");
550 for arg in cmd.take_args() {
551 if arg.to_string_lossy() != "-no-pie" {
559 // Here's a terribly awful hack that really shouldn't be present in any
560 // compiler. Here an environment variable is supported to automatically
561 // retry the linker invocation if the linker looks like it segfaulted.
563 // Gee that seems odd, normally segfaults are things we want to know
564 // about! Unfortunately though in rust-lang/rust#38878 we're
565 // experiencing the linker segfaulting on Travis quite a bit which is
566 // causing quite a bit of pain to land PRs when they spuriously fail
567 // due to a segfault.
569 // The issue #38878 has some more debugging information on it as well,
570 // but this unfortunately looks like it's just a race condition in
571 // macOS's linker with some thread pool working in the background. It
572 // seems that no one currently knows a fix for this so in the meantime
573 // we're left with this...
574 if !retry_on_segfault || i > 3 {
577 let msg_segv = "clang: error: unable to execute command: Segmentation fault: 11";
578 let msg_bus = "clang: error: unable to execute command: Bus error: 10";
579 if out.contains(msg_segv) || out.contains(msg_bus) {
581 "looks like the linker segfaulted when we tried to call it, \
582 automatically retrying again. cmd = {:?}, out = {}.",
588 if is_illegal_instruction(&output.status) {
590 "looks like the linker hit an illegal instruction when we \
591 tried to call it, automatically retrying again. cmd = {:?}, ]\
592 out = {}, status = {}.",
593 cmd, out, output.status,
599 fn is_illegal_instruction(status: &ExitStatus) -> bool {
600 use std::os::unix::prelude::*;
601 status.signal() == Some(libc::SIGILL)
605 fn is_illegal_instruction(_status: &ExitStatus) -> bool {
612 fn escape_string(s: &[u8]) -> String {
613 str::from_utf8(s).map(|s| s.to_owned()).unwrap_or_else(|_| {
614 let mut x = "Non-UTF-8 output: ".to_string();
615 x.extend(s.iter().flat_map(|&b| ascii::escape_default(b)).map(char::from));
619 if !prog.status.success() {
620 let mut output = prog.stderr.clone();
621 output.extend_from_slice(&prog.stdout);
622 sess.struct_err(&format!(
623 "linking with `{}` failed: {}",
624 linker_path.display(),
627 .note(&format!("{:?}", &cmd))
628 .note(&escape_string(&output))
630 sess.abort_if_errors();
632 info!("linker stderr:\n{}", escape_string(&prog.stderr));
633 info!("linker stdout:\n{}", escape_string(&prog.stdout));
636 let linker_not_found = e.kind() == io::ErrorKind::NotFound;
638 let mut linker_error = {
639 if linker_not_found {
640 sess.struct_err(&format!("linker `{}` not found", linker_path.display()))
642 sess.struct_err(&format!(
643 "could not exec the linker `{}`",
644 linker_path.display()
649 linker_error.note(&e.to_string());
651 if !linker_not_found {
652 linker_error.note(&format!("{:?}", &cmd));
657 if sess.target.target.options.is_like_msvc && linker_not_found {
658 sess.note_without_error(
659 "the msvc targets depend on the msvc linker \
660 but `link.exe` was not found",
662 sess.note_without_error(
663 "please ensure that VS 2013, VS 2015, VS 2017 or VS 2019 \
664 was installed with the Visual C++ option",
667 sess.abort_if_errors();
671 // On macOS, debuggers need this utility to get run to do some munging of
672 // the symbols. Note, though, that if the object files are being preserved
673 // for their debug information there's no need for us to run dsymutil.
674 if sess.target.target.options.is_like_osx
675 && sess.opts.debuginfo != DebugInfo::None
676 && !preserve_objects_for_their_debuginfo(sess)
678 if let Err(e) = Command::new("dsymutil").arg(out_filename).output() {
679 sess.fatal(&format!("failed to run dsymutil: {}", e))
684 fn link_sanitizer_runtime(sess: &Session, crate_type: config::CrateType, linker: &mut dyn Linker) {
685 let sanitizer = match &sess.opts.debugging_opts.sanitizer {
690 if crate_type != config::CrateType::Executable {
694 let name = match sanitizer {
695 Sanitizer::Address => "asan",
696 Sanitizer::Leak => "lsan",
697 Sanitizer::Memory => "msan",
698 Sanitizer::Thread => "tsan",
701 let default_sysroot = filesearch::get_or_default_sysroot();
703 filesearch::make_target_lib_path(&default_sysroot, sess.opts.target_triple.triple());
704 let channel = option_env!("CFG_RELEASE_CHANNEL")
705 .map(|channel| format!("-{}", channel))
706 .unwrap_or_default();
708 match sess.opts.target_triple.triple() {
709 "x86_64-apple-darwin" => {
710 // On Apple platforms, the sanitizer is always built as a dylib, and
711 // LLVM will link to `@rpath/*.dylib`, so we need to specify an
712 // rpath to the library as well (the rpath should be absolute, see
713 // PR #41352 for details).
714 let libname = format!("rustc{}_rt.{}", channel, name);
715 let rpath = default_tlib.to_str().expect("non-utf8 component in path");
716 linker.args(&["-Wl,-rpath", "-Xlinker", rpath]);
717 linker.link_dylib(Symbol::intern(&libname));
719 "x86_64-unknown-linux-gnu" | "x86_64-fuchsia" | "aarch64-fuchsia" => {
720 let filename = format!("librustc{}_rt.{}.a", channel, name);
721 let path = default_tlib.join(&filename);
722 linker.link_whole_rlib(&path);
728 /// Returns a boolean indicating whether the specified crate should be ignored
731 /// Crates ignored during LTO are not lumped together in the "massive object
732 /// file" that we create and are linked in their normal rlib states. See
733 /// comments below for what crates do not participate in LTO.
735 /// It's unusual for a crate to not participate in LTO. Typically only
736 /// compiler-specific and unstable crates have a reason to not participate in
738 pub fn ignored_for_lto(sess: &Session, info: &CrateInfo, cnum: CrateNum) -> bool {
739 // If our target enables builtin function lowering in LLVM then the
740 // crates providing these functions don't participate in LTO (e.g.
741 // no_builtins or compiler builtins crates).
742 !sess.target.target.options.no_builtins
743 && (info.compiler_builtins == Some(cnum) || info.is_no_builtins.contains(&cnum))
746 pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
749 linker: Option<PathBuf>,
750 flavor: Option<LinkerFlavor>,
751 ) -> Option<(PathBuf, LinkerFlavor)> {
752 match (linker, flavor) {
753 (Some(linker), Some(flavor)) => Some((linker, flavor)),
754 // only the linker flavor is known; use the default linker for the selected flavor
755 (None, Some(flavor)) => Some((
756 PathBuf::from(match flavor {
757 LinkerFlavor::Em => {
764 LinkerFlavor::Gcc => {
765 if cfg!(target_os = "solaris") {
766 // On historical Solaris systems, "cc" may have
767 // been Sun Studio, which is not flag-compatible
768 // with "gcc". This history casts a long shadow,
769 // and many modern illumos distributions today
770 // ship GCC as "gcc" without also making it
771 // available as "cc".
777 LinkerFlavor::Ld => "ld",
778 LinkerFlavor::Msvc => "link.exe",
779 LinkerFlavor::Lld(_) => "lld",
780 LinkerFlavor::PtxLinker => "rust-ptx-linker",
784 (Some(linker), None) => {
785 let stem = linker.file_stem().and_then(|stem| stem.to_str()).unwrap_or_else(|| {
786 sess.fatal("couldn't extract file stem from specified linker")
789 let flavor = if stem == "emcc" {
791 } else if stem == "gcc"
792 || stem.ends_with("-gcc")
794 || stem.ends_with("-clang")
797 } else if stem == "ld" || stem == "ld.lld" || stem.ends_with("-ld") {
799 } else if stem == "link" || stem == "lld-link" {
801 } else if stem == "lld" || stem == "rust-lld" {
802 LinkerFlavor::Lld(sess.target.target.options.lld_flavor)
804 // fall back to the value in the target spec
805 sess.target.target.linker_flavor
808 Some((linker, flavor))
810 (None, None) => None,
814 // linker and linker flavor specified via command line have precedence over what the target
815 // specification specifies
816 if let Some(ret) = infer_from(sess, sess.opts.cg.linker.clone(), sess.opts.cg.linker_flavor) {
820 if let Some(ret) = infer_from(
822 sess.target.target.options.linker.clone().map(PathBuf::from),
823 Some(sess.target.target.linker_flavor),
828 bug!("Not enough information provided to determine how to invoke the linker");
831 /// Returns a boolean indicating whether we should preserve the object files on
832 /// the filesystem for their debug information. This is often useful with
833 /// split-dwarf like schemes.
834 pub fn preserve_objects_for_their_debuginfo(sess: &Session) -> bool {
835 // If the objects don't have debuginfo there's nothing to preserve.
836 if sess.opts.debuginfo == config::DebugInfo::None {
840 // If we're only producing artifacts that are archives, no need to preserve
841 // the objects as they're losslessly contained inside the archives.
842 let output_linked = sess
846 .any(|&x| x != config::CrateType::Rlib && x != config::CrateType::Staticlib);
851 // If we're on OSX then the equivalent of split dwarf is turned on by
852 // default. The final executable won't actually have any debug information
853 // except it'll have pointers to elsewhere. Historically we've always run
854 // `dsymutil` to "link all the dwarf together" but this is actually sort of
855 // a bummer for incremental compilation! (the whole point of split dwarf is
856 // that you don't do this sort of dwarf link).
858 // Basically as a result this just means that if we're on OSX and we're
859 // *not* running dsymutil then the object files are the only source of truth
860 // for debug information, so we must preserve them.
861 if sess.target.target.options.is_like_osx {
862 match sess.opts.debugging_opts.run_dsymutil {
863 // dsymutil is not being run, preserve objects
864 Some(false) => return true,
866 // dsymutil is being run, no need to preserve the objects
867 Some(true) => return false,
869 // The default historical behavior was to always run dsymutil, so
870 // we're preserving that temporarily, but we're likely to switch the
872 None => return false,
879 pub fn archive_search_paths(sess: &Session) -> Vec<PathBuf> {
880 sess.target_filesearch(PathKind::Native).search_path_dirs()
888 pub fn print_native_static_libs(sess: &Session, all_native_libs: &[NativeLibrary]) {
889 let lib_args: Vec<_> = all_native_libs
891 .filter(|l| relevant_lib(sess, l))
893 let name = lib.name?;
895 NativeLibraryKind::NativeStaticNobundle | NativeLibraryKind::NativeUnknown => {
896 if sess.target.target.options.is_like_msvc {
897 Some(format!("{}.lib", name))
899 Some(format!("-l{}", name))
902 NativeLibraryKind::NativeFramework => {
903 // ld-only syntax, since there are no frameworks in MSVC
904 Some(format!("-framework {}", name))
906 // These are included, no need to print them
907 NativeLibraryKind::NativeStatic | NativeLibraryKind::NativeRawDylib => None,
911 if !lib_args.is_empty() {
912 sess.note_without_error(
913 "Link against the following native artifacts when linking \
914 against this static library. The order and any duplication \
915 can be significant on some platforms.",
917 // Prefix for greppability
918 sess.note_without_error(&format!("native-static-libs: {}", &lib_args.join(" ")));
922 // Because windows-gnu target is meant to be self-contained for pure Rust code it bundles
923 // own mingw-w64 libraries. These libraries are usually not compatible with mingw-w64
924 // installed in the system. This breaks many cases where Rust is mixed with other languages
925 // (e.g. *-sys crates).
926 // We prefer system mingw-w64 libraries if they are available to avoid this issue.
927 fn get_crt_libs_path(sess: &Session) -> Option<PathBuf> {
928 fn find_exe_in_path<P>(exe_name: P) -> Option<PathBuf>
932 for dir in env::split_paths(&env::var_os("PATH")?) {
933 let full_path = dir.join(&exe_name);
934 if full_path.is_file() {
935 return Some(fix_windows_verbatim_for_gcc(&full_path));
941 fn probe(sess: &Session) -> Option<PathBuf> {
942 if let (linker, LinkerFlavor::Gcc) = linker_and_flavor(&sess) {
943 let linker_path = if cfg!(windows) && linker.extension().is_none() {
944 linker.with_extension("exe")
948 if let Some(linker_path) = find_exe_in_path(linker_path) {
949 let mingw_arch = match &sess.target.target.arch {
950 x if x == "x86" => "i686",
953 let mingw_bits = &sess.target.target.target_pointer_width;
954 let mingw_dir = format!("{}-w64-mingw32", mingw_arch);
955 // Here we have path/bin/gcc but we need path/
956 let mut path = linker_path;
959 // Loosely based on Clang MinGW driver
960 let probe_paths = vec![
961 path.join(&mingw_dir).join("lib"), // Typical path
962 path.join(&mingw_dir).join("sys-root/mingw/lib"), // Rare path
964 "lib/mingw/tools/install/mingw{}/{}/lib",
965 &mingw_bits, &mingw_dir
966 )), // Chocolatey is creative
968 for probe_path in probe_paths {
969 if probe_path.join("crt2.o").exists() {
970 return Some(probe_path);
978 let mut system_library_path = sess.system_library_path.borrow_mut();
979 match &*system_library_path {
980 Some(Some(compiler_libs_path)) => Some(compiler_libs_path.clone()),
983 let path = probe(sess);
984 *system_library_path = Some(path.clone());
990 pub fn get_file_path(sess: &Session, name: &str) -> PathBuf {
991 // prefer system {,dll}crt2.o libs, see get_crt_libs_path comment for more details
992 if sess.target.target.llvm_target.contains("windows-gnu") {
993 if let Some(compiler_libs_path) = get_crt_libs_path(sess) {
994 let file_path = compiler_libs_path.join(name);
995 if file_path.exists() {
1000 let fs = sess.target_filesearch(PathKind::Native);
1001 let file_path = fs.get_lib_path().join(name);
1002 if file_path.exists() {
1005 for search_path in fs.search_paths() {
1006 let file_path = search_path.dir.join(name);
1007 if file_path.exists() {
1017 out_filename: &Path,
1019 ) -> io::Result<Output> {
1020 // When attempting to spawn the linker we run a risk of blowing out the
1021 // size limits for spawning a new process with respect to the arguments
1022 // we pass on the command line.
1024 // Here we attempt to handle errors from the OS saying "your list of
1025 // arguments is too big" by reinvoking the linker again with an `@`-file
1026 // that contains all the arguments. The theory is that this is then
1027 // accepted on all linkers and the linker will read all its options out of
1028 // there instead of looking at the command line.
1029 if !cmd.very_likely_to_exceed_some_spawn_limit() {
1030 match cmd.command().stdout(Stdio::piped()).stderr(Stdio::piped()).spawn() {
1032 let output = child.wait_with_output();
1033 flush_linked_file(&output, out_filename)?;
1036 Err(ref e) if command_line_too_big(e) => {
1037 info!("command line to linker was too big: {}", e);
1039 Err(e) => return Err(e),
1043 info!("falling back to passing arguments to linker via an @-file");
1044 let mut cmd2 = cmd.clone();
1045 let mut args = String::new();
1046 for arg in cmd2.take_args() {
1049 arg: arg.to_str().unwrap(),
1050 is_like_msvc: sess.target.target.options.is_like_msvc,
1054 args.push_str("\n");
1056 let file = tmpdir.join("linker-arguments");
1057 let bytes = if sess.target.target.options.is_like_msvc {
1058 let mut out = Vec::with_capacity((1 + args.len()) * 2);
1059 // start the stream with a UTF-16 BOM
1060 for c in std::iter::once(0xFEFF).chain(args.encode_utf16()) {
1061 // encode in little endian
1063 out.push((c >> 8) as u8);
1069 fs::write(&file, &bytes)?;
1070 cmd2.arg(format!("@{}", file.display()));
1071 info!("invoking linker {:?}", cmd2);
1072 let output = cmd2.output();
1073 flush_linked_file(&output, out_filename)?;
1077 fn flush_linked_file(_: &io::Result<Output>, _: &Path) -> io::Result<()> {
1082 fn flush_linked_file(
1083 command_output: &io::Result<Output>,
1084 out_filename: &Path,
1085 ) -> io::Result<()> {
1086 // On Windows, under high I/O load, output buffers are sometimes not flushed,
1087 // even long after process exit, causing nasty, non-reproducible output bugs.
1089 // File::sync_all() calls FlushFileBuffers() down the line, which solves the problem.
1091 // А full writeup of the original Chrome bug can be found at
1092 // randomascii.wordpress.com/2018/02/25/compiler-bug-linker-bug-windows-kernel-bug/amp
1094 if let &Ok(ref out) = command_output {
1095 if out.status.success() {
1096 if let Ok(of) = fs::OpenOptions::new().write(true).open(out_filename) {
1106 fn command_line_too_big(err: &io::Error) -> bool {
1107 err.raw_os_error() == Some(::libc::E2BIG)
1111 fn command_line_too_big(err: &io::Error) -> bool {
1112 const ERROR_FILENAME_EXCED_RANGE: i32 = 206;
1113 err.raw_os_error() == Some(ERROR_FILENAME_EXCED_RANGE)
1121 impl<'a> fmt::Display for Escape<'a> {
1122 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1123 if self.is_like_msvc {
1124 // This is "documented" at
1125 // https://docs.microsoft.com/en-us/cpp/build/reference/at-specify-a-linker-response-file
1127 // Unfortunately there's not a great specification of the
1128 // syntax I could find online (at least) but some local
1129 // testing showed that this seemed sufficient-ish to catch
1130 // at least a few edge cases.
1132 for c in self.arg.chars() {
1134 '"' => write!(f, "\\{}", c)?,
1135 c => write!(f, "{}", c)?,
1140 // This is documented at https://linux.die.net/man/1/ld, namely:
1142 // > Options in file are separated by whitespace. A whitespace
1143 // > character may be included in an option by surrounding the
1144 // > entire option in either single or double quotes. Any
1145 // > character (including a backslash) may be included by
1146 // > prefixing the character to be included with a backslash.
1148 // We put an argument on each line, so all we need to do is
1149 // ensure the line is interpreted as one whole argument.
1150 for c in self.arg.chars() {
1152 '\\' | ' ' => write!(f, "\\{}", c)?,
1153 c => write!(f, "{}", c)?,
1162 fn linker_with_args<'a, B: ArchiveBuilder<'a>>(
1164 flavor: LinkerFlavor,
1166 crate_type: config::CrateType,
1168 out_filename: &Path,
1169 codegen_results: &CodegenResults,
1172 let base_cmd = get_linker(sess, path, flavor);
1173 // FIXME: Move `/LIBPATH` addition for uwp targets from the linker construction
1174 // to the linker args construction.
1175 assert!(base_cmd.get_args().is_empty() || sess.target.target.target_vendor == "uwp");
1176 let cmd = &mut *codegen_results.linker_info.to_linker(base_cmd, &sess, flavor, target_cpu);
1178 if let Some(args) = sess.target.target.options.pre_link_args.get(&flavor) {
1181 if let Some(args) = sess.target.target.options.pre_link_args_crt.get(&flavor) {
1182 if sess.crt_static(Some(crate_type)) {
1186 cmd.args(&sess.opts.debugging_opts.pre_link_args);
1188 if sess.target.target.options.is_like_fuchsia {
1189 let prefix = match sess.opts.debugging_opts.sanitizer {
1190 Some(Sanitizer::Address) => "asan/",
1193 cmd.arg(format!("--dynamic-linker={}ld.so.1", prefix));
1196 let pre_link_objects = if crate_type == config::CrateType::Executable {
1197 &sess.target.target.options.pre_link_objects_exe
1199 &sess.target.target.options.pre_link_objects_dll
1201 for obj in pre_link_objects {
1202 cmd.arg(get_file_path(sess, obj));
1205 if crate_type == config::CrateType::Executable && sess.crt_static(Some(crate_type)) {
1206 for obj in &sess.target.target.options.pre_link_objects_exe_crt {
1207 cmd.arg(get_file_path(sess, obj));
1211 if sess.target.target.options.is_like_emscripten {
1213 cmd.arg(if sess.panic_strategy() == PanicStrategy::Abort {
1214 "DISABLE_EXCEPTION_CATCHING=1"
1216 "DISABLE_EXCEPTION_CATCHING=0"
1220 link_sanitizer_runtime(sess, crate_type, cmd);
1222 // Linker plugins should be specified early in the list of arguments
1223 cmd.linker_plugin_lto();
1225 // The default library location, we need this to find the runtime.
1226 // The location of crates will be determined as needed.
1227 let lib_path = sess.target_filesearch(PathKind::All).get_lib_path();
1229 // target descriptor
1230 let t = &sess.target.target;
1232 // prefer system mingw-w64 libs, see get_crt_libs_path comment for more details
1233 if cfg!(windows) && sess.target.target.llvm_target.contains("windows-gnu") {
1234 if let Some(compiler_libs_path) = get_crt_libs_path(sess) {
1235 cmd.include_path(&compiler_libs_path);
1239 cmd.include_path(&fix_windows_verbatim_for_gcc(&lib_path));
1241 for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
1242 cmd.add_object(obj);
1244 cmd.output_filename(out_filename);
1246 if crate_type == config::CrateType::Executable && sess.target.target.options.is_like_windows {
1247 if let Some(ref s) = codegen_results.windows_subsystem {
1252 // If we're building something like a dynamic library then some platforms
1253 // need to make sure that all symbols are exported correctly from the
1255 cmd.export_symbols(tmpdir, crate_type);
1257 // When linking a dynamic library, we put the metadata into a section of the
1258 // executable. This metadata is in a separate object file from the main
1259 // object file, so we link that in here.
1260 if crate_type == config::CrateType::Dylib || crate_type == config::CrateType::ProcMacro {
1261 let obj = codegen_results.metadata_module.as_ref().and_then(|m| m.object.as_ref());
1262 if let Some(obj) = obj {
1263 cmd.add_object(obj);
1267 let obj = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref());
1268 if let Some(obj) = obj {
1269 cmd.add_object(obj);
1272 // Try to strip as much out of the generated object by removing unused
1273 // sections if possible. See more comments in linker.rs
1274 if !sess.opts.cg.link_dead_code {
1275 let keep_metadata = crate_type == config::CrateType::Dylib;
1276 cmd.gc_sections(keep_metadata);
1279 let attr_link_args = codegen_results.crate_info.link_args.iter();
1280 let user_link_args = sess.opts.cg.link_args.iter().chain(attr_link_args);
1282 if crate_type == config::CrateType::Executable {
1283 let mut position_independent_executable = false;
1285 if t.options.position_independent_executables {
1287 && !sess.crt_static(Some(crate_type))
1288 && !user_link_args.clone().any(|x| x == "-static")
1290 position_independent_executable = true;
1294 if position_independent_executable {
1295 cmd.position_independent_executable();
1297 // recent versions of gcc can be configured to generate position
1298 // independent executables by default. We have to pass -no-pie to
1299 // explicitly turn that off. Not applicable to ld.
1300 if sess.target.target.options.linker_is_gnu && flavor != LinkerFlavor::Ld {
1301 cmd.no_position_independent_executable();
1306 let relro_level = match sess.opts.debugging_opts.relro_level {
1307 Some(level) => level,
1308 None => t.options.relro_level,
1311 RelroLevel::Full => {
1314 RelroLevel::Partial => {
1315 cmd.partial_relro();
1317 RelroLevel::Off => {
1320 RelroLevel::None => {}
1323 // Pass optimization flags down to the linker.
1326 // Pass debuginfo flags down to the linker.
1329 // We want to, by default, prevent the compiler from accidentally leaking in
1330 // any system libraries, so we may explicitly ask linkers to not link to any
1331 // libraries by default. Note that this does not happen for windows because
1332 // windows pulls in some large number of libraries and I couldn't quite
1333 // figure out which subset we wanted.
1335 // This is all naturally configurable via the standard methods as well.
1336 if !sess.opts.cg.default_linker_libraries.unwrap_or(false) && t.options.no_default_libraries {
1337 cmd.no_default_libraries();
1340 // Take careful note of the ordering of the arguments we pass to the linker
1341 // here. Linkers will assume that things on the left depend on things to the
1342 // right. Things on the right cannot depend on things on the left. This is
1343 // all formally implemented in terms of resolving symbols (libs on the right
1344 // resolve unknown symbols of libs on the left, but not vice versa).
1346 // For this reason, we have organized the arguments we pass to the linker as
1349 // 1. The local object that LLVM just generated
1350 // 2. Local native libraries
1351 // 3. Upstream rust libraries
1352 // 4. Upstream native libraries
1354 // The rationale behind this ordering is that those items lower down in the
1355 // list can't depend on items higher up in the list. For example nothing can
1356 // depend on what we just generated (e.g., that'd be a circular dependency).
1357 // Upstream rust libraries are not allowed to depend on our local native
1358 // libraries as that would violate the structure of the DAG, in that
1359 // scenario they are required to link to them as well in a shared fashion.
1361 // Note that upstream rust libraries may contain native dependencies as
1362 // well, but they also can't depend on what we just started to add to the
1363 // link line. And finally upstream native libraries can't depend on anything
1364 // in this DAG so far because they're only dylibs and dylibs can only depend
1365 // on other dylibs (e.g., other native deps).
1367 // If -Zlink-native-libraries=false is set, then the assumption is that an
1368 // external build system already has the native dependencies defined, and it
1369 // will provide them to the linker itself.
1370 if sess.opts.debugging_opts.link_native_libraries.unwrap_or(true) {
1371 add_local_native_libraries(cmd, sess, codegen_results);
1373 add_upstream_rust_crates::<B>(cmd, sess, codegen_results, crate_type, tmpdir);
1374 if sess.opts.debugging_opts.link_native_libraries.unwrap_or(true) {
1375 add_upstream_native_libraries(cmd, sess, codegen_results, crate_type);
1377 // Tell the linker what we're doing.
1378 if crate_type != config::CrateType::Executable {
1379 cmd.build_dylib(out_filename);
1381 if crate_type == config::CrateType::Executable && sess.crt_static(Some(crate_type)) {
1382 cmd.build_static_executable();
1385 if sess.opts.cg.profile_generate.enabled() {
1389 if sess.opts.debugging_opts.control_flow_guard != CFGuard::Disabled {
1390 cmd.control_flow_guard();
1393 // FIXME (#2397): At some point we want to rpath our guesses as to
1394 // where extern libraries might live, based on the
1395 // addl_lib_search_paths
1396 if sess.opts.cg.rpath {
1397 let target_triple = sess.opts.target_triple.triple();
1398 let mut get_install_prefix_lib_path = || {
1399 let install_prefix = option_env!("CFG_PREFIX").expect("CFG_PREFIX");
1400 let tlib = filesearch::relative_target_lib_path(&sess.sysroot, target_triple);
1401 let mut path = PathBuf::from(install_prefix);
1406 let mut rpath_config = RPathConfig {
1407 used_crates: &codegen_results.crate_info.used_crates_dynamic,
1408 out_filename: out_filename.to_path_buf(),
1409 has_rpath: sess.target.target.options.has_rpath,
1410 is_like_osx: sess.target.target.options.is_like_osx,
1411 linker_is_gnu: sess.target.target.options.linker_is_gnu,
1412 get_install_prefix_lib_path: &mut get_install_prefix_lib_path,
1414 cmd.args(&rpath::get_rpath_flags(&mut rpath_config));
1417 // Finally add all the linker arguments provided on the command line along
1418 // with any #[link_args] attributes found inside the crate
1419 cmd.args(user_link_args);
1423 if let Some(args) = sess.target.target.options.late_link_args.get(&flavor) {
1426 let any_dynamic_crate = crate_type == config::CrateType::Dylib
1427 || codegen_results.crate_info.dependency_formats.iter().any(|(ty, list)| {
1428 *ty == crate_type && list.iter().any(|&linkage| linkage == Linkage::Dynamic)
1430 if any_dynamic_crate {
1431 if let Some(args) = sess.target.target.options.late_link_args_dynamic.get(&flavor) {
1435 if let Some(args) = sess.target.target.options.late_link_args_static.get(&flavor) {
1439 for obj in &sess.target.target.options.post_link_objects {
1440 cmd.arg(get_file_path(sess, obj));
1442 if sess.crt_static(Some(crate_type)) {
1443 for obj in &sess.target.target.options.post_link_objects_crt {
1444 cmd.arg(get_file_path(sess, obj));
1447 if let Some(args) = sess.target.target.options.post_link_args.get(&flavor) {
1454 // # Native library linking
1456 // User-supplied library search paths (-L on the command line). These are
1457 // the same paths used to find Rust crates, so some of them may have been
1458 // added already by the previous crate linking code. This only allows them
1459 // to be found at compile time so it is still entirely up to outside
1460 // forces to make sure that library can be found at runtime.
1462 // Also note that the native libraries linked here are only the ones located
1463 // in the current crate. Upstream crates with native library dependencies
1464 // may have their native library pulled in above.
1465 pub fn add_local_native_libraries(
1466 cmd: &mut dyn Linker,
1468 codegen_results: &CodegenResults,
1470 let filesearch = sess.target_filesearch(PathKind::All);
1471 for search_path in filesearch.search_paths() {
1472 match search_path.kind {
1473 PathKind::Framework => {
1474 cmd.framework_path(&search_path.dir);
1477 cmd.include_path(&fix_windows_verbatim_for_gcc(&search_path.dir));
1483 codegen_results.crate_info.used_libraries.iter().filter(|l| relevant_lib(sess, l));
1485 let search_path = archive_search_paths(sess);
1486 for lib in relevant_libs {
1487 let name = match lib.name {
1492 NativeLibraryKind::NativeUnknown => cmd.link_dylib(name),
1493 NativeLibraryKind::NativeFramework => cmd.link_framework(name),
1494 NativeLibraryKind::NativeStaticNobundle => cmd.link_staticlib(name),
1495 NativeLibraryKind::NativeStatic => cmd.link_whole_staticlib(name, &search_path),
1496 NativeLibraryKind::NativeRawDylib => {
1497 // FIXME(#58713): Proper handling for raw dylibs.
1498 bug!("raw_dylib feature not yet implemented");
1504 // # Rust Crate linking
1506 // Rust crates are not considered at all when creating an rlib output. All
1507 // dependencies will be linked when producing the final output (instead of
1508 // the intermediate rlib version)
1509 fn add_upstream_rust_crates<'a, B: ArchiveBuilder<'a>>(
1510 cmd: &mut dyn Linker,
1512 codegen_results: &CodegenResults,
1513 crate_type: config::CrateType,
1516 // All of the heavy lifting has previously been accomplished by the
1517 // dependency_format module of the compiler. This is just crawling the
1518 // output of that module, adding crates as necessary.
1520 // Linking to a rlib involves just passing it to the linker (the linker
1521 // will slurp up the object files inside), and linking to a dynamic library
1522 // involves just passing the right -l flag.
1524 let (_, data) = codegen_results
1528 .find(|(ty, _)| *ty == crate_type)
1529 .expect("failed to find crate type in dependency format list");
1531 // Invoke get_used_crates to ensure that we get a topological sorting of
1533 let deps = &codegen_results.crate_info.used_crates_dynamic;
1535 // There's a few internal crates in the standard library (aka libcore and
1536 // libstd) which actually have a circular dependence upon one another. This
1537 // currently arises through "weak lang items" where libcore requires things
1538 // like `rust_begin_unwind` but libstd ends up defining it. To get this
1539 // circular dependence to work correctly in all situations we'll need to be
1540 // sure to correctly apply the `--start-group` and `--end-group` options to
1541 // GNU linkers, otherwise if we don't use any other symbol from the standard
1542 // library it'll get discarded and the whole application won't link.
1544 // In this loop we're calculating the `group_end`, after which crate to
1545 // pass `--end-group` and `group_start`, before which crate to pass
1546 // `--start-group`. We currently do this by passing `--end-group` after
1547 // the first crate (when iterating backwards) that requires a lang item
1548 // defined somewhere else. Once that's set then when we've defined all the
1549 // necessary lang items we'll pass `--start-group`.
1551 // Note that this isn't amazing logic for now but it should do the trick
1552 // for the current implementation of the standard library.
1553 let mut group_end = None;
1554 let mut group_start = None;
1555 // Crates available for linking thus far.
1556 let mut available = FxHashSet::default();
1557 // Crates required to satisfy dependencies discovered so far.
1558 let mut required = FxHashSet::default();
1560 let info = &codegen_results.crate_info;
1561 for &(cnum, _) in deps.iter().rev() {
1562 if let Some(missing) = info.missing_lang_items.get(&cnum) {
1563 let missing_crates = missing.iter().map(|i| info.lang_item_to_crate.get(i).copied());
1564 required.extend(missing_crates);
1567 required.insert(Some(cnum));
1568 available.insert(Some(cnum));
1570 if required.len() > available.len() && group_end.is_none() {
1571 group_end = Some(cnum);
1573 if required.len() == available.len() && group_end.is_some() {
1574 group_start = Some(cnum);
1579 // If we didn't end up filling in all lang items from upstream crates then
1580 // we'll be filling it in with our crate. This probably means we're the
1581 // standard library itself, so skip this for now.
1582 if group_end.is_some() && group_start.is_none() {
1586 let mut compiler_builtins = None;
1588 for &(cnum, _) in deps.iter() {
1589 if group_start == Some(cnum) {
1593 // We may not pass all crates through to the linker. Some crates may
1594 // appear statically in an existing dylib, meaning we'll pick up all the
1595 // symbols from the dylib.
1596 let src = &codegen_results.crate_info.used_crate_source[&cnum];
1597 match data[cnum.as_usize() - 1] {
1598 _ if codegen_results.crate_info.profiler_runtime == Some(cnum) => {
1599 add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
1601 // compiler-builtins are always placed last to ensure that they're
1602 // linked correctly.
1603 _ if codegen_results.crate_info.compiler_builtins == Some(cnum) => {
1604 assert!(compiler_builtins.is_none());
1605 compiler_builtins = Some(cnum);
1607 Linkage::NotLinked | Linkage::IncludedFromDylib => {}
1608 Linkage::Static => {
1609 add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
1611 Linkage::Dynamic => add_dynamic_crate(cmd, sess, &src.dylib.as_ref().unwrap().0),
1614 if group_end == Some(cnum) {
1619 // compiler-builtins are always placed last to ensure that they're
1620 // linked correctly.
1621 // We must always link the `compiler_builtins` crate statically. Even if it
1622 // was already "included" in a dylib (e.g., `libstd` when `-C prefer-dynamic`
1624 if let Some(cnum) = compiler_builtins {
1625 add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
1628 // Converts a library file-stem into a cc -l argument
1629 fn unlib<'a>(config: &config::Config, stem: &'a str) -> &'a str {
1630 if stem.starts_with("lib") && !config.target.options.is_like_windows {
1637 // Adds the static "rlib" versions of all crates to the command line.
1638 // There's a bit of magic which happens here specifically related to LTO and
1639 // dynamic libraries. Specifically:
1641 // * For LTO, we remove upstream object files.
1642 // * For dylibs we remove metadata and bytecode from upstream rlibs
1644 // When performing LTO, almost(*) all of the bytecode from the upstream
1645 // libraries has already been included in our object file output. As a
1646 // result we need to remove the object files in the upstream libraries so
1647 // the linker doesn't try to include them twice (or whine about duplicate
1648 // symbols). We must continue to include the rest of the rlib, however, as
1649 // it may contain static native libraries which must be linked in.
1651 // (*) Crates marked with `#![no_builtins]` don't participate in LTO and
1652 // their bytecode wasn't included. The object files in those libraries must
1653 // still be passed to the linker.
1655 // When making a dynamic library, linkers by default don't include any
1656 // object files in an archive if they're not necessary to resolve the link.
1657 // We basically want to convert the archive (rlib) to a dylib, though, so we
1658 // *do* want everything included in the output, regardless of whether the
1659 // linker thinks it's needed or not. As a result we must use the
1660 // --whole-archive option (or the platform equivalent). When using this
1661 // option the linker will fail if there are non-objects in the archive (such
1662 // as our own metadata and/or bytecode). All in all, for rlibs to be
1663 // entirely included in dylibs, we need to remove all non-object files.
1665 // Note, however, that if we're not doing LTO or we're not producing a dylib
1666 // (aka we're making an executable), we can just pass the rlib blindly to
1667 // the linker (fast) because it's fine if it's not actually included as
1668 // we're at the end of the dependency chain.
1669 fn add_static_crate<'a, B: ArchiveBuilder<'a>>(
1670 cmd: &mut dyn Linker,
1672 codegen_results: &CodegenResults,
1674 crate_type: config::CrateType,
1677 let src = &codegen_results.crate_info.used_crate_source[&cnum];
1678 let cratepath = &src.rlib.as_ref().unwrap().0;
1680 // See the comment above in `link_staticlib` and `link_rlib` for why if
1681 // there's a static library that's not relevant we skip all object
1683 let native_libs = &codegen_results.crate_info.native_libraries[&cnum];
1684 let skip_native = native_libs
1686 .any(|lib| lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib));
1688 if (!are_upstream_rust_objects_already_included(sess)
1689 || ignored_for_lto(sess, &codegen_results.crate_info, cnum))
1690 && crate_type != config::CrateType::Dylib
1693 cmd.link_rlib(&fix_windows_verbatim_for_gcc(cratepath));
1697 let dst = tmpdir.join(cratepath.file_name().unwrap());
1698 let name = cratepath.file_name().unwrap().to_str().unwrap();
1699 let name = &name[3..name.len() - 5]; // chop off lib/.rlib
1701 sess.prof.generic_activity_with_arg("link_altering_rlib", name).run(|| {
1702 let mut archive = <B as ArchiveBuilder>::new(sess, &dst, Some(cratepath));
1703 archive.update_symbols();
1705 let mut any_objects = false;
1706 for f in archive.src_files() {
1707 if f.ends_with(RLIB_BYTECODE_EXTENSION) || f == METADATA_FILENAME {
1708 archive.remove_file(&f);
1712 let canonical = f.replace("-", "_");
1713 let canonical_name = name.replace("-", "_");
1715 let is_rust_object =
1716 canonical.starts_with(&canonical_name) && looks_like_rust_object_file(&f);
1718 // If we've been requested to skip all native object files
1719 // (those not generated by the rust compiler) then we can skip
1720 // this file. See above for why we may want to do this.
1721 let skip_because_cfg_say_so = skip_native && !is_rust_object;
1723 // If we're performing LTO and this is a rust-generated object
1724 // file, then we don't need the object file as it's part of the
1725 // LTO module. Note that `#![no_builtins]` is excluded from LTO,
1726 // though, so we let that object file slide.
1727 let skip_because_lto = are_upstream_rust_objects_already_included(sess)
1729 && (sess.target.target.options.no_builtins
1730 || !codegen_results.crate_info.is_no_builtins.contains(&cnum));
1732 if skip_because_cfg_say_so || skip_because_lto {
1733 archive.remove_file(&f);
1744 // If we're creating a dylib, then we need to include the
1745 // whole of each object in our archive into that artifact. This is
1746 // because a `dylib` can be reused as an intermediate artifact.
1748 // Note, though, that we don't want to include the whole of a
1749 // compiler-builtins crate (e.g., compiler-rt) because it'll get
1750 // repeatedly linked anyway.
1751 if crate_type == config::CrateType::Dylib
1752 && codegen_results.crate_info.compiler_builtins != Some(cnum)
1754 cmd.link_whole_rlib(&fix_windows_verbatim_for_gcc(&dst));
1756 cmd.link_rlib(&fix_windows_verbatim_for_gcc(&dst));
1761 // Same thing as above, but for dynamic crates instead of static crates.
1762 fn add_dynamic_crate(cmd: &mut dyn Linker, sess: &Session, cratepath: &Path) {
1763 // Just need to tell the linker about where the library lives and
1765 let parent = cratepath.parent();
1766 if let Some(dir) = parent {
1767 cmd.include_path(&fix_windows_verbatim_for_gcc(dir));
1769 let filestem = cratepath.file_stem().unwrap().to_str().unwrap();
1770 cmd.link_rust_dylib(
1771 Symbol::intern(&unlib(&sess.target, filestem)),
1772 parent.unwrap_or(Path::new("")),
1777 // Link in all of our upstream crates' native dependencies. Remember that
1778 // all of these upstream native dependencies are all non-static
1779 // dependencies. We've got two cases then:
1781 // 1. The upstream crate is an rlib. In this case we *must* link in the
1782 // native dependency because the rlib is just an archive.
1784 // 2. The upstream crate is a dylib. In order to use the dylib, we have to
1785 // have the dependency present on the system somewhere. Thus, we don't
1786 // gain a whole lot from not linking in the dynamic dependency to this
1789 // The use case for this is a little subtle. In theory the native
1790 // dependencies of a crate are purely an implementation detail of the crate
1791 // itself, but the problem arises with generic and inlined functions. If a
1792 // generic function calls a native function, then the generic function must
1793 // be instantiated in the target crate, meaning that the native symbol must
1794 // also be resolved in the target crate.
1795 pub fn add_upstream_native_libraries(
1796 cmd: &mut dyn Linker,
1798 codegen_results: &CodegenResults,
1799 crate_type: config::CrateType,
1801 // Be sure to use a topological sorting of crates because there may be
1802 // interdependencies between native libraries. When passing -nodefaultlibs,
1803 // for example, almost all native libraries depend on libc, so we have to
1804 // make sure that's all the way at the right (liblibc is near the base of
1805 // the dependency chain).
1807 // This passes RequireStatic, but the actual requirement doesn't matter,
1808 // we're just getting an ordering of crate numbers, we're not worried about
1810 let (_, data) = codegen_results
1814 .find(|(ty, _)| *ty == crate_type)
1815 .expect("failed to find crate type in dependency format list");
1817 let crates = &codegen_results.crate_info.used_crates_static;
1818 for &(cnum, _) in crates {
1819 for lib in codegen_results.crate_info.native_libraries[&cnum].iter() {
1820 let name = match lib.name {
1824 if !relevant_lib(sess, &lib) {
1828 NativeLibraryKind::NativeUnknown => cmd.link_dylib(name),
1829 NativeLibraryKind::NativeFramework => cmd.link_framework(name),
1830 NativeLibraryKind::NativeStaticNobundle => {
1831 // Link "static-nobundle" native libs only if the crate they originate from
1832 // is being linked statically to the current crate. If it's linked dynamically
1833 // or is an rlib already included via some other dylib crate, the symbols from
1834 // native libs will have already been included in that dylib.
1835 if data[cnum.as_usize() - 1] == Linkage::Static {
1836 cmd.link_staticlib(name)
1839 // ignore statically included native libraries here as we've
1840 // already included them when we included the rust library
1842 NativeLibraryKind::NativeStatic => {}
1843 NativeLibraryKind::NativeRawDylib => {
1844 // FIXME(#58713): Proper handling for raw dylibs.
1845 bug!("raw_dylib feature not yet implemented");
1852 pub fn relevant_lib(sess: &Session, lib: &NativeLibrary) -> bool {
1854 Some(ref cfg) => rustc_attr::cfg_matches(cfg, &sess.parse_sess, None),
1859 pub fn are_upstream_rust_objects_already_included(sess: &Session) -> bool {
1861 config::Lto::Fat => true,
1862 config::Lto::Thin => {
1863 // If we defer LTO to the linker, we haven't run LTO ourselves, so
1864 // any upstream object files have not been copied yet.
1865 !sess.opts.cg.linker_plugin_lto.enabled()
1867 config::Lto::No | config::Lto::ThinLocal => false,
1871 fn is_pic(sess: &Session) -> bool {
1872 let reloc_model_arg = match sess.opts.cg.relocation_model {
1873 Some(ref s) => &s[..],
1874 None => &sess.target.target.options.relocation_model[..],
1877 reloc_model_arg == "pic"