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linker.rs
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linker.rs
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use std::ffi::{OsStr, OsString};
use std::fs::{self, File};
use std::io::prelude::*;
use std::path::{Path, PathBuf};
use std::{env, io, iter, mem, str};
use cc::windows_registry;
use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
use rustc_metadata::{
find_native_static_library, try_find_native_dynamic_library, try_find_native_static_library,
};
use rustc_middle::bug;
use rustc_middle::middle::dependency_format::Linkage;
use rustc_middle::middle::exported_symbols;
use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo, SymbolExportKind};
use rustc_middle::ty::TyCtxt;
use rustc_session::Session;
use rustc_session::config::{self, CrateType, DebugInfo, LinkerPluginLto, Lto, OptLevel, Strip};
use rustc_span::symbol::sym;
use rustc_target::spec::{Cc, LinkOutputKind, LinkerFlavor, Lld};
use tracing::{debug, warn};
use super::command::Command;
use super::symbol_export;
use crate::errors;
#[cfg(test)]
mod tests;
/// Disables non-English messages from localized linkers.
/// Such messages may cause issues with text encoding on Windows (#35785)
/// and prevent inspection of linker output in case of errors, which we occasionally do.
/// This should be acceptable because other messages from rustc are in English anyway,
/// and may also be desirable to improve searchability of the linker diagnostics.
pub(crate) fn disable_localization(linker: &mut Command) {
// No harm in setting both env vars simultaneously.
// Unix-style linkers.
linker.env("LC_ALL", "C");
// MSVC's `link.exe`.
linker.env("VSLANG", "1033");
}
/// The third parameter is for env vars, used on windows to set up the
/// path for MSVC to find its DLLs, and gcc to find its bundled
/// toolchain
pub(crate) fn get_linker<'a>(
sess: &'a Session,
linker: &Path,
flavor: LinkerFlavor,
self_contained: bool,
target_cpu: &'a str,
) -> Box<dyn Linker + 'a> {
// FIXME(cc-rs#1265) pass only target arch to find_tool()
let msvc_tool = windows_registry::find_tool(sess.opts.target_triple.tuple(), "link.exe");
// If our linker looks like a batch script on Windows then to execute this
// we'll need to spawn `cmd` explicitly. This is primarily done to handle
// emscripten where the linker is `emcc.bat` and needs to be spawned as
// `cmd /c emcc.bat ...`.
//
// This worked historically but is needed manually since #42436 (regression
// was tagged as #42791) and some more info can be found on #44443 for
// emscripten itself.
let mut cmd = match linker.to_str() {
Some(linker) if cfg!(windows) && linker.ends_with(".bat") => Command::bat_script(linker),
_ => match flavor {
LinkerFlavor::Gnu(Cc::No, Lld::Yes)
| LinkerFlavor::Darwin(Cc::No, Lld::Yes)
| LinkerFlavor::WasmLld(Cc::No)
| LinkerFlavor::Msvc(Lld::Yes) => Command::lld(linker, flavor.lld_flavor()),
LinkerFlavor::Msvc(Lld::No)
if sess.opts.cg.linker.is_none() && sess.target.linker.is_none() =>
{
Command::new(msvc_tool.as_ref().map_or(linker, |t| t.path()))
}
_ => Command::new(linker),
},
};
// UWP apps have API restrictions enforced during Store submissions.
// To comply with the Windows App Certification Kit,
// MSVC needs to link with the Store versions of the runtime libraries (vcruntime, msvcrt, etc).
let t = &sess.target;
if matches!(flavor, LinkerFlavor::Msvc(..)) && t.vendor == "uwp" {
if let Some(ref tool) = msvc_tool {
let original_path = tool.path();
if let Some(root_lib_path) = original_path.ancestors().nth(4) {
let arch = match t.arch.as_ref() {
"x86_64" => Some("x64"),
"x86" => Some("x86"),
"aarch64" => Some("arm64"),
"arm" => Some("arm"),
_ => None,
};
if let Some(ref a) = arch {
// FIXME: Move this to `fn linker_with_args`.
let mut arg = OsString::from("/LIBPATH:");
arg.push(format!("{}\\lib\\{}\\store", root_lib_path.display(), a));
cmd.arg(&arg);
} else {
warn!("arch is not supported");
}
} else {
warn!("MSVC root path lib location not found");
}
} else {
warn!("link.exe not found");
}
}
// The compiler's sysroot often has some bundled tools, so add it to the
// PATH for the child.
let mut new_path = sess.get_tools_search_paths(self_contained);
let mut msvc_changed_path = false;
if sess.target.is_like_msvc {
if let Some(ref tool) = msvc_tool {
cmd.args(tool.args());
for (k, v) in tool.env() {
if k == "PATH" {
new_path.extend(env::split_paths(v));
msvc_changed_path = true;
} else {
cmd.env(k, v);
}
}
}
}
if !msvc_changed_path {
if let Some(path) = env::var_os("PATH") {
new_path.extend(env::split_paths(&path));
}
}
cmd.env("PATH", env::join_paths(new_path).unwrap());
// FIXME: Move `/LIBPATH` addition for uwp targets from the linker construction
// to the linker args construction.
assert!(cmd.get_args().is_empty() || sess.target.vendor == "uwp");
match flavor {
LinkerFlavor::Unix(Cc::No) if sess.target.os == "l4re" => {
Box::new(L4Bender::new(cmd, sess)) as Box<dyn Linker>
}
LinkerFlavor::Unix(Cc::No) if sess.target.os == "aix" => {
Box::new(AixLinker::new(cmd, sess)) as Box<dyn Linker>
}
LinkerFlavor::WasmLld(Cc::No) => Box::new(WasmLd::new(cmd, sess)) as Box<dyn Linker>,
LinkerFlavor::Gnu(cc, _)
| LinkerFlavor::Darwin(cc, _)
| LinkerFlavor::WasmLld(cc)
| LinkerFlavor::Unix(cc) => Box::new(GccLinker {
cmd,
sess,
target_cpu,
hinted_static: None,
is_ld: cc == Cc::No,
is_gnu: flavor.is_gnu(),
}) as Box<dyn Linker>,
LinkerFlavor::Msvc(..) => Box::new(MsvcLinker { cmd, sess }) as Box<dyn Linker>,
LinkerFlavor::EmCc => Box::new(EmLinker { cmd, sess }) as Box<dyn Linker>,
LinkerFlavor::Bpf => Box::new(BpfLinker { cmd, sess }) as Box<dyn Linker>,
LinkerFlavor::Llbc => Box::new(LlbcLinker { cmd, sess }) as Box<dyn Linker>,
LinkerFlavor::Ptx => Box::new(PtxLinker { cmd, sess }) as Box<dyn Linker>,
}
}
// Note: Ideally neither these helper function, nor the macro-generated inherent methods below
// would exist, and these functions would live in `trait Linker`.
// Unfortunately, adding these functions to `trait Linker` make it `dyn`-incompatible.
// If the methods are added to the trait with `where Self: Sized` bounds, then even a separate
// implementation of them for `dyn Linker {}` wouldn't work due to a conflict with those
// uncallable methods in the trait.
/// Just pass the arguments to the linker as is.
/// It is assumed that they are correctly prepared in advance.
fn verbatim_args<L: Linker + ?Sized>(
l: &mut L,
args: impl IntoIterator<Item: AsRef<OsStr>>,
) -> &mut L {
for arg in args {
l.cmd().arg(arg);
}
l
}
/// Add underlying linker arguments to C compiler command, by wrapping them in
/// `-Wl` or `-Xlinker`.
fn convert_link_args_to_cc_args(cmd: &mut Command, args: impl IntoIterator<Item: AsRef<OsStr>>) {
let mut combined_arg = OsString::from("-Wl");
for arg in args {
// If the argument itself contains a comma, we need to emit it
// as `-Xlinker`, otherwise we can use `-Wl`.
if arg.as_ref().as_encoded_bytes().contains(&b',') {
// Emit current `-Wl` argument, if any has been built.
if combined_arg != OsStr::new("-Wl") {
cmd.arg(combined_arg);
// Begin next `-Wl` argument.
combined_arg = OsString::from("-Wl");
}
// Emit `-Xlinker` argument.
cmd.arg("-Xlinker");
cmd.arg(arg);
} else {
// Append to `-Wl` argument.
combined_arg.push(",");
combined_arg.push(arg);
}
}
// Emit final `-Wl` argument.
if combined_arg != OsStr::new("-Wl") {
cmd.arg(combined_arg);
}
}
/// Arguments for the underlying linker.
/// Add options to pass them through cc wrapper if `Linker` is a cc wrapper.
fn link_args<L: Linker + ?Sized>(l: &mut L, args: impl IntoIterator<Item: AsRef<OsStr>>) -> &mut L {
if !l.is_cc() {
verbatim_args(l, args);
} else {
convert_link_args_to_cc_args(l.cmd(), args);
}
l
}
/// Arguments for the cc wrapper specifically.
/// Check that it's indeed a cc wrapper and pass verbatim.
fn cc_args<L: Linker + ?Sized>(l: &mut L, args: impl IntoIterator<Item: AsRef<OsStr>>) -> &mut L {
assert!(l.is_cc());
verbatim_args(l, args)
}
/// Arguments supported by both underlying linker and cc wrapper, pass verbatim.
fn link_or_cc_args<L: Linker + ?Sized>(
l: &mut L,
args: impl IntoIterator<Item: AsRef<OsStr>>,
) -> &mut L {
verbatim_args(l, args)
}
macro_rules! generate_arg_methods {
($($ty:ty)*) => { $(
impl $ty {
#[allow(unused)]
pub(crate) fn verbatim_args(&mut self, args: impl IntoIterator<Item: AsRef<OsStr>>) -> &mut Self {
verbatim_args(self, args)
}
#[allow(unused)]
pub(crate) fn verbatim_arg(&mut self, arg: impl AsRef<OsStr>) -> &mut Self {
verbatim_args(self, iter::once(arg))
}
#[allow(unused)]
pub(crate) fn link_args(&mut self, args: impl IntoIterator<Item: AsRef<OsStr>>) -> &mut Self {
link_args(self, args)
}
#[allow(unused)]
pub(crate) fn link_arg(&mut self, arg: impl AsRef<OsStr>) -> &mut Self {
link_args(self, iter::once(arg))
}
#[allow(unused)]
pub(crate) fn cc_args(&mut self, args: impl IntoIterator<Item: AsRef<OsStr>>) -> &mut Self {
cc_args(self, args)
}
#[allow(unused)]
pub(crate) fn cc_arg(&mut self, arg: impl AsRef<OsStr>) -> &mut Self {
cc_args(self, iter::once(arg))
}
#[allow(unused)]
pub(crate) fn link_or_cc_args(&mut self, args: impl IntoIterator<Item: AsRef<OsStr>>) -> &mut Self {
link_or_cc_args(self, args)
}
#[allow(unused)]
pub(crate) fn link_or_cc_arg(&mut self, arg: impl AsRef<OsStr>) -> &mut Self {
link_or_cc_args(self, iter::once(arg))
}
}
)* }
}
generate_arg_methods! {
GccLinker<'_>
MsvcLinker<'_>
EmLinker<'_>
WasmLd<'_>
L4Bender<'_>
AixLinker<'_>
LlbcLinker<'_>
PtxLinker<'_>
BpfLinker<'_>
dyn Linker + '_
}
/// Linker abstraction used by `back::link` to build up the command to invoke a
/// linker.
///
/// This trait is the total list of requirements needed by `back::link` and
/// represents the meaning of each option being passed down. This trait is then
/// used to dispatch on whether a GNU-like linker (generally `ld.exe`) or an
/// MSVC linker (e.g., `link.exe`) is being used.
pub(crate) trait Linker {
fn cmd(&mut self) -> &mut Command;
fn is_cc(&self) -> bool {
false
}
fn set_output_kind(
&mut self,
output_kind: LinkOutputKind,
crate_type: CrateType,
out_filename: &Path,
);
fn link_dylib_by_name(&mut self, _name: &str, _verbatim: bool, _as_needed: bool) {
bug!("dylib linked with unsupported linker")
}
fn link_dylib_by_path(&mut self, _path: &Path, _as_needed: bool) {
bug!("dylib linked with unsupported linker")
}
fn link_framework_by_name(&mut self, _name: &str, _verbatim: bool, _as_needed: bool) {
bug!("framework linked with unsupported linker")
}
fn link_staticlib_by_name(&mut self, name: &str, verbatim: bool, whole_archive: bool);
fn link_staticlib_by_path(&mut self, path: &Path, whole_archive: bool);
fn include_path(&mut self, path: &Path) {
link_or_cc_args(link_or_cc_args(self, &["-L"]), &[path]);
}
fn framework_path(&mut self, _path: &Path) {
bug!("framework path set with unsupported linker")
}
fn output_filename(&mut self, path: &Path) {
link_or_cc_args(link_or_cc_args(self, &["-o"]), &[path]);
}
fn add_object(&mut self, path: &Path) {
link_or_cc_args(self, &[path]);
}
fn gc_sections(&mut self, keep_metadata: bool);
fn no_gc_sections(&mut self);
fn full_relro(&mut self);
fn partial_relro(&mut self);
fn no_relro(&mut self);
fn optimize(&mut self);
fn pgo_gen(&mut self);
fn control_flow_guard(&mut self);
fn ehcont_guard(&mut self);
fn debuginfo(&mut self, strip: Strip, natvis_debugger_visualizers: &[PathBuf]);
fn no_crt_objects(&mut self);
fn no_default_libraries(&mut self);
fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType, symbols: &[String]);
fn subsystem(&mut self, subsystem: &str);
fn linker_plugin_lto(&mut self);
fn add_eh_frame_header(&mut self) {}
fn add_no_exec(&mut self) {}
fn add_as_needed(&mut self) {}
fn reset_per_library_state(&mut self) {}
}
impl dyn Linker + '_ {
pub(crate) fn take_cmd(&mut self) -> Command {
mem::replace(self.cmd(), Command::new(""))
}
}
struct GccLinker<'a> {
cmd: Command,
sess: &'a Session,
target_cpu: &'a str,
hinted_static: Option<bool>, // Keeps track of the current hinting mode.
// Link as ld
is_ld: bool,
is_gnu: bool,
}
impl<'a> GccLinker<'a> {
fn takes_hints(&self) -> bool {
// Really this function only returns true if the underlying linker
// configured for a compiler is binutils `ld.bfd` and `ld.gold`. We
// don't really have a foolproof way to detect that, so rule out some
// platforms where currently this is guaranteed to *not* be the case:
//
// * On OSX they have their own linker, not binutils'
// * For WebAssembly the only functional linker is LLD, which doesn't
// support hint flags
!self.sess.target.is_like_osx && !self.sess.target.is_like_wasm
}
// Some platforms take hints about whether a library is static or dynamic.
// For those that support this, we ensure we pass the option if the library
// was flagged "static" (most defaults are dynamic) to ensure that if
// libfoo.a and libfoo.so both exist that the right one is chosen.
fn hint_static(&mut self) {
if !self.takes_hints() {
return;
}
if self.hinted_static != Some(true) {
self.link_arg("-Bstatic");
self.hinted_static = Some(true);
}
}
fn hint_dynamic(&mut self) {
if !self.takes_hints() {
return;
}
if self.hinted_static != Some(false) {
self.link_arg("-Bdynamic");
self.hinted_static = Some(false);
}
}
fn push_linker_plugin_lto_args(&mut self, plugin_path: Option<&OsStr>) {
if let Some(plugin_path) = plugin_path {
let mut arg = OsString::from("-plugin=");
arg.push(plugin_path);
self.link_arg(&arg);
}
let opt_level = match self.sess.opts.optimize {
config::OptLevel::No => "O0",
config::OptLevel::Less => "O1",
config::OptLevel::Default | config::OptLevel::Size | config::OptLevel::SizeMin => "O2",
config::OptLevel::Aggressive => "O3",
};
if let Some(path) = &self.sess.opts.unstable_opts.profile_sample_use {
self.link_arg(&format!("-plugin-opt=sample-profile={}", path.display()));
};
self.link_args(&[
&format!("-plugin-opt={opt_level}"),
&format!("-plugin-opt=mcpu={}", self.target_cpu),
]);
}
fn build_dylib(&mut self, crate_type: CrateType, out_filename: &Path) {
// On mac we need to tell the linker to let this library be rpathed
if self.sess.target.is_like_osx {
if self.is_cc() {
// `-dynamiclib` makes `cc` pass `-dylib` to the linker.
self.cc_arg("-dynamiclib");
} else {
self.link_arg("-dylib");
// Clang also sets `-dynamic`, but that's implied by `-dylib`, so unnecessary.
}
// Note that the `osx_rpath_install_name` option here is a hack
// purely to support bootstrap right now, we should get a more
// principled solution at some point to force the compiler to pass
// the right `-Wl,-install_name` with an `@rpath` in it.
if self.sess.opts.cg.rpath || self.sess.opts.unstable_opts.osx_rpath_install_name {
let mut rpath = OsString::from("@rpath/");
rpath.push(out_filename.file_name().unwrap());
self.link_arg("-install_name").link_arg(rpath);
}
} else {
self.link_or_cc_arg("-shared");
if let Some(name) = out_filename.file_name() {
if self.sess.target.is_like_windows {
// The output filename already contains `dll_suffix` so
// the resulting import library will have a name in the
// form of libfoo.dll.a
let mut implib_name = OsString::from(&*self.sess.target.staticlib_prefix);
implib_name.push(name);
implib_name.push(&*self.sess.target.staticlib_suffix);
let mut out_implib = OsString::from("--out-implib=");
out_implib.push(out_filename.with_file_name(implib_name));
self.link_arg(out_implib);
} else if crate_type == CrateType::Dylib {
// When dylibs are linked by a full path this value will get into `DT_NEEDED`
// instead of the full path, so the library can be later found in some other
// location than that specific path.
let mut soname = OsString::from("-soname=");
soname.push(name);
self.link_arg(soname);
}
}
}
}
fn with_as_needed(&mut self, as_needed: bool, f: impl FnOnce(&mut Self)) {
if !as_needed {
if self.sess.target.is_like_osx {
// FIXME(81490): ld64 doesn't support these flags but macOS 11
// has -needed-l{} / -needed_library {}
// but we have no way to detect that here.
self.sess.dcx().emit_warn(errors::Ld64UnimplementedModifier);
} else if self.is_gnu && !self.sess.target.is_like_windows {
self.link_arg("--no-as-needed");
} else {
self.sess.dcx().emit_warn(errors::LinkerUnsupportedModifier);
}
}
f(self);
if !as_needed {
if self.sess.target.is_like_osx {
// See above FIXME comment
} else if self.is_gnu && !self.sess.target.is_like_windows {
self.link_arg("--as-needed");
}
}
}
}
impl<'a> Linker for GccLinker<'a> {
fn cmd(&mut self) -> &mut Command {
&mut self.cmd
}
fn is_cc(&self) -> bool {
!self.is_ld
}
fn set_output_kind(
&mut self,
output_kind: LinkOutputKind,
crate_type: CrateType,
out_filename: &Path,
) {
match output_kind {
LinkOutputKind::DynamicNoPicExe => {
if !self.is_ld && self.is_gnu {
self.cc_arg("-no-pie");
}
}
LinkOutputKind::DynamicPicExe => {
// noop on windows w/ gcc & ld, error w/ lld
if !self.sess.target.is_like_windows {
// `-pie` works for both gcc wrapper and ld.
self.link_or_cc_arg("-pie");
}
}
LinkOutputKind::StaticNoPicExe => {
// `-static` works for both gcc wrapper and ld.
self.link_or_cc_arg("-static");
if !self.is_ld && self.is_gnu {
self.cc_arg("-no-pie");
}
}
LinkOutputKind::StaticPicExe => {
if !self.is_ld {
// Note that combination `-static -pie` doesn't work as expected
// for the gcc wrapper, `-static` in that case suppresses `-pie`.
self.cc_arg("-static-pie");
} else {
// `--no-dynamic-linker` and `-z text` are not strictly necessary for producing
// a static pie, but currently passed because gcc and clang pass them.
// The former suppresses the `INTERP` ELF header specifying dynamic linker,
// which is otherwise implicitly injected by ld (but not lld).
// The latter doesn't change anything, only ensures that everything is pic.
self.link_args(&["-static", "-pie", "--no-dynamic-linker", "-z", "text"]);
}
}
LinkOutputKind::DynamicDylib => self.build_dylib(crate_type, out_filename),
LinkOutputKind::StaticDylib => {
self.link_or_cc_arg("-static");
self.build_dylib(crate_type, out_filename);
}
LinkOutputKind::WasiReactorExe => {
self.link_args(&["--entry", "_initialize"]);
}
}
// VxWorks compiler driver introduced `--static-crt` flag specifically for rustc,
// it switches linking for libc and similar system libraries to static without using
// any `#[link]` attributes in the `libc` crate, see #72782 for details.
// FIXME: Switch to using `#[link]` attributes in the `libc` crate
// similarly to other targets.
if self.sess.target.os == "vxworks"
&& matches!(
output_kind,
LinkOutputKind::StaticNoPicExe
| LinkOutputKind::StaticPicExe
| LinkOutputKind::StaticDylib
)
{
self.cc_arg("--static-crt");
}
}
fn link_dylib_by_name(&mut self, name: &str, verbatim: bool, as_needed: bool) {
if self.sess.target.os == "illumos" && name == "c" {
// libc will be added via late_link_args on illumos so that it will
// appear last in the library search order.
// FIXME: This should be replaced by a more complete and generic
// mechanism for controlling the order of library arguments passed
// to the linker.
return;
}
self.hint_dynamic();
self.with_as_needed(as_needed, |this| {
let colon = if verbatim && this.is_gnu { ":" } else { "" };
this.link_or_cc_arg(format!("-l{colon}{name}"));
});
}
fn link_dylib_by_path(&mut self, path: &Path, as_needed: bool) {
self.hint_dynamic();
self.with_as_needed(as_needed, |this| {
this.link_or_cc_arg(path);
})
}
fn link_framework_by_name(&mut self, name: &str, _verbatim: bool, as_needed: bool) {
self.hint_dynamic();
if !as_needed {
// FIXME(81490): ld64 as of macOS 11 supports the -needed_framework
// flag but we have no way to detect that here.
// self.link_or_cc_arg("-needed_framework").link_or_cc_arg(name);
self.sess.dcx().emit_warn(errors::Ld64UnimplementedModifier);
}
self.link_or_cc_args(&["-framework", name]);
}
fn link_staticlib_by_name(&mut self, name: &str, verbatim: bool, whole_archive: bool) {
self.hint_static();
let colon = if verbatim && self.is_gnu { ":" } else { "" };
if !whole_archive {
self.link_or_cc_arg(format!("-l{colon}{name}"));
} else if self.sess.target.is_like_osx {
// -force_load is the macOS equivalent of --whole-archive, but it
// involves passing the full path to the library to link.
self.link_arg("-force_load");
self.link_arg(find_native_static_library(name, verbatim, self.sess));
} else {
self.link_arg("--whole-archive")
.link_or_cc_arg(format!("-l{colon}{name}"))
.link_arg("--no-whole-archive");
}
}
fn link_staticlib_by_path(&mut self, path: &Path, whole_archive: bool) {
self.hint_static();
if !whole_archive {
self.link_or_cc_arg(path);
} else if self.sess.target.is_like_osx {
self.link_arg("-force_load").link_arg(path);
} else {
self.link_arg("--whole-archive").link_arg(path).link_arg("--no-whole-archive");
}
}
fn framework_path(&mut self, path: &Path) {
self.link_or_cc_arg("-F").link_or_cc_arg(path);
}
fn full_relro(&mut self) {
self.link_args(&["-z", "relro", "-z", "now"]);
}
fn partial_relro(&mut self) {
self.link_args(&["-z", "relro"]);
}
fn no_relro(&mut self) {
self.link_args(&["-z", "norelro"]);
}
fn gc_sections(&mut self, keep_metadata: bool) {
// The dead_strip option to the linker specifies that functions and data
// unreachable by the entry point will be removed. This is quite useful
// with Rust's compilation model of compiling libraries at a time into
// one object file. For example, this brings hello world from 1.7MB to
// 458K.
//
// Note that this is done for both executables and dynamic libraries. We
// won't get much benefit from dylibs because LLVM will have already
// stripped away as much as it could. This has not been seen to impact
// link times negatively.
//
// -dead_strip can't be part of the pre_link_args because it's also used
// for partial linking when using multiple codegen units (-r). So we
// insert it here.
if self.sess.target.is_like_osx {
self.link_arg("-dead_strip");
// If we're building a dylib, we don't use --gc-sections because LLVM
// has already done the best it can do, and we also don't want to
// eliminate the metadata. If we're building an executable, however,
// --gc-sections drops the size of hello world from 1.8MB to 597K, a 67%
// reduction.
} else if (self.is_gnu || self.sess.target.is_like_wasm) && !keep_metadata {
self.link_arg("--gc-sections");
}
}
fn no_gc_sections(&mut self) {
if self.is_gnu || self.sess.target.is_like_wasm {
self.link_arg("--no-gc-sections");
}
}
fn optimize(&mut self) {
if !self.is_gnu && !self.sess.target.is_like_wasm {
return;
}
// GNU-style linkers support optimization with -O. GNU ld doesn't
// need a numeric argument, but other linkers do.
if self.sess.opts.optimize == config::OptLevel::Default
|| self.sess.opts.optimize == config::OptLevel::Aggressive
{
self.link_arg("-O1");
}
}
fn pgo_gen(&mut self) {
if !self.is_gnu {
return;
}
// If we're doing PGO generation stuff and on a GNU-like linker, use the
// "-u" flag to properly pull in the profiler runtime bits.
//
// This is because LLVM otherwise won't add the needed initialization
// for us on Linux (though the extra flag should be harmless if it
// does).
//
// See https://reviews.llvm.org/D14033 and https://reviews.llvm.org/D14030.
//
// Though it may be worth to try to revert those changes upstream, since
// the overhead of the initialization should be minor.
self.link_or_cc_args(&["-u", "__llvm_profile_runtime"]);
}
fn control_flow_guard(&mut self) {}
fn ehcont_guard(&mut self) {}
fn debuginfo(&mut self, strip: Strip, _: &[PathBuf]) {
// MacOS linker doesn't support stripping symbols directly anymore.
if self.sess.target.is_like_osx {
return;
}
match strip {
Strip::None => {}
Strip::Debuginfo => {
// The illumos linker does not support --strip-debug although
// it does support --strip-all as a compatibility alias for -s.
// The --strip-debug case is handled by running an external
// `strip` utility as a separate step after linking.
if !self.sess.target.is_like_solaris {
self.link_arg("--strip-debug");
}
}
Strip::Symbols => {
self.link_arg("--strip-all");
}
}
match self.sess.opts.unstable_opts.debuginfo_compression {
config::DebugInfoCompression::None => {}
config::DebugInfoCompression::Zlib => {
self.link_arg("--compress-debug-sections=zlib");
}
config::DebugInfoCompression::Zstd => {
self.link_arg("--compress-debug-sections=zstd");
}
}
}
fn no_crt_objects(&mut self) {
if !self.is_ld {
self.cc_arg("-nostartfiles");
}
}
fn no_default_libraries(&mut self) {
if !self.is_ld {
self.cc_arg("-nodefaultlibs");
}
}
fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType, symbols: &[String]) {
// Symbol visibility in object files typically takes care of this.
if crate_type == CrateType::Executable {
let should_export_executable_symbols =
self.sess.opts.unstable_opts.export_executable_symbols;
if self.sess.target.override_export_symbols.is_none()
&& !should_export_executable_symbols
{
return;
}
}
// We manually create a list of exported symbols to ensure we don't expose any more.
// The object files have far more public symbols than we actually want to export,
// so we hide them all here.
if !self.sess.target.limit_rdylib_exports {
return;
}
let is_windows = self.sess.target.is_like_windows;
let path = tmpdir.join(if is_windows { "list.def" } else { "list" });
debug!("EXPORTED SYMBOLS:");
if self.sess.target.is_like_osx {
// Write a plain, newline-separated list of symbols
let res: io::Result<()> = try {
let mut f = File::create_buffered(&path)?;
for sym in symbols {
debug!(" _{sym}");
writeln!(f, "_{sym}")?;
}
};
if let Err(error) = res {
self.sess.dcx().emit_fatal(errors::LibDefWriteFailure { error });
}
} else if is_windows {
let res: io::Result<()> = try {
let mut f = File::create_buffered(&path)?;
// .def file similar to MSVC one but without LIBRARY section
// because LD doesn't like when it's empty
writeln!(f, "EXPORTS")?;
for symbol in symbols {
debug!(" _{symbol}");
writeln!(f, " {symbol}")?;
}
};
if let Err(error) = res {
self.sess.dcx().emit_fatal(errors::LibDefWriteFailure { error });
}
} else {
// Write an LD version script
let res: io::Result<()> = try {
let mut f = File::create_buffered(&path)?;
writeln!(f, "{{")?;
if !symbols.is_empty() {
writeln!(f, " global:")?;
for sym in symbols {
debug!(" {sym};");
writeln!(f, " {sym};")?;
}
}
writeln!(f, "\n local:\n *;\n}};")?;
};
if let Err(error) = res {
self.sess.dcx().emit_fatal(errors::VersionScriptWriteFailure { error });
}
}
if self.sess.target.is_like_osx {
self.link_arg("-exported_symbols_list").link_arg(path);
} else if self.sess.target.is_like_solaris {
self.link_arg("-M").link_arg(path);
} else if is_windows {
self.link_arg(path);
} else {
let mut arg = OsString::from("--version-script=");
arg.push(path);
self.link_arg(arg).link_arg("--no-undefined-version");
}
}
fn subsystem(&mut self, subsystem: &str) {
self.link_args(&["--subsystem", subsystem]);
}
fn reset_per_library_state(&mut self) {
self.hint_dynamic(); // Reset to default before returning the composed command line.
}
fn linker_plugin_lto(&mut self) {
match self.sess.opts.cg.linker_plugin_lto {
LinkerPluginLto::Disabled => {
// Nothing to do
}
LinkerPluginLto::LinkerPluginAuto => {
self.push_linker_plugin_lto_args(None);
}
LinkerPluginLto::LinkerPlugin(ref path) => {
self.push_linker_plugin_lto_args(Some(path.as_os_str()));
}
}
}
// Add the `GNU_EH_FRAME` program header which is required to locate unwinding information.
// Some versions of `gcc` add it implicitly, some (e.g. `musl-gcc`) don't,
// so we just always add it.
fn add_eh_frame_header(&mut self) {
self.link_arg("--eh-frame-hdr");
}
fn add_no_exec(&mut self) {
if self.sess.target.is_like_windows {
self.link_arg("--nxcompat");
} else if self.is_gnu {
self.link_args(&["-z", "noexecstack"]);
}
}
fn add_as_needed(&mut self) {
if self.is_gnu && !self.sess.target.is_like_windows {
self.link_arg("--as-needed");
} else if self.sess.target.is_like_solaris {
// -z ignore is the Solaris equivalent to the GNU ld --as-needed option
self.link_args(&["-z", "ignore"]);
}
}
}
struct MsvcLinker<'a> {
cmd: Command,
sess: &'a Session,
}
impl<'a> Linker for MsvcLinker<'a> {
fn cmd(&mut self) -> &mut Command {
&mut self.cmd
}
fn set_output_kind(
&mut self,
output_kind: LinkOutputKind,
_crate_type: CrateType,
out_filename: &Path,
) {
match output_kind {
LinkOutputKind::DynamicNoPicExe
| LinkOutputKind::DynamicPicExe
| LinkOutputKind::StaticNoPicExe
| LinkOutputKind::StaticPicExe => {}
LinkOutputKind::DynamicDylib | LinkOutputKind::StaticDylib => {
self.link_arg("/DLL");
let mut arg: OsString = "/IMPLIB:".into();
arg.push(out_filename.with_extension("dll.lib"));
self.link_arg(arg);
}
LinkOutputKind::WasiReactorExe => {
panic!("can't link as reactor on non-wasi target");
}
}
}
fn link_dylib_by_name(&mut self, name: &str, verbatim: bool, _as_needed: bool) {
// On MSVC-like targets rustc supports import libraries using alternative naming
// scheme (`libfoo.a`) unsupported by linker, search for such libraries manually.
if let Some(path) = try_find_native_dynamic_library(self.sess, name, verbatim) {
self.link_arg(path);
} else {
self.link_arg(format!("{}{}", name, if verbatim { "" } else { ".lib" }));
}
}
fn link_dylib_by_path(&mut self, path: &Path, _as_needed: bool) {
// When producing a dll, MSVC linker may not emit an implib file if the dll doesn't export
// any symbols, so we skip linking if the implib file is not present.
let implib_path = path.with_extension("dll.lib");
if implib_path.exists() {
self.link_or_cc_arg(implib_path);
}
}
fn link_staticlib_by_name(&mut self, name: &str, verbatim: bool, whole_archive: bool) {
// On MSVC-like targets rustc supports static libraries using alternative naming
// scheme (`libfoo.a`) unsupported by linker, search for such libraries manually.
if let Some(path) = try_find_native_static_library(self.sess, name, verbatim) {
self.link_staticlib_by_path(&path, whole_archive);
} else {
let prefix = if whole_archive { "/WHOLEARCHIVE:" } else { "" };
let suffix = if verbatim { "" } else { ".lib" };
self.link_arg(format!("{prefix}{name}{suffix}"));
}
}
fn link_staticlib_by_path(&mut self, path: &Path, whole_archive: bool) {
if !whole_archive {
self.link_arg(path);
} else {
let mut arg = OsString::from("/WHOLEARCHIVE:");
arg.push(path);
self.link_arg(arg);
}
}
fn gc_sections(&mut self, _keep_metadata: bool) {
// MSVC's ICF (Identical COMDAT Folding) link optimization is
// slow for Rust and thus we disable it by default when not in
// optimization build.
if self.sess.opts.optimize != config::OptLevel::No {
self.link_arg("/OPT:REF,ICF");
} else {
// It is necessary to specify NOICF here, because /OPT:REF
// implies ICF by default.
self.link_arg("/OPT:REF,NOICF");
}
}
fn no_gc_sections(&mut self) {
self.link_arg("/OPT:NOREF,NOICF");
}
fn full_relro(&mut self) {
// noop
}
fn partial_relro(&mut self) {
// noop
}
fn no_relro(&mut self) {
// noop
}
fn no_crt_objects(&mut self) {
// noop
}