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Auto merge of #116035 - lqd:mcp-510-target-specs, r=petrochenkov
Allow target specs to use an LLD flavor, and self-contained linking components This PR allows: - target specs to use an LLD linker-flavor: this is needed to switch `x86_64-unknown-linux-gnu` to using LLD, and is currently not possible because the current flavor json serialization fails to roundtrip on the modern linker-flavors. This can e.g. be seen in #115622 (comment) which explains where an `Lld::Yes` is ultimately deserialized into an `Lld::No`. - target specs to declare self-contained linking components: this is needed to switch `x86_64-unknown-linux-gnu` to using `rust-lld` - adds an end-to-end test of a custom target json simulating `x86_64-unknown-linux-gnu` being switched to using `rust-lld` - disables codegen backends from participating because they don't support `-Zgcc-ld=lld` which is the basis of mcp510. r? `@petrochenkov:` if the approach discussed #115622 (comment) and on zulip would work for you: basically, see if we can emit only modern linker flavors in the json specs, but accept both old and new flavors while reading them, to fix the roundtrip issue. The backwards compatible `LinkSelfContainedDefault` variants are still serialized and deserialized in `crt-objects-fallback`, while the spec equivalent of e.g. `-Clink-self-contained=+linker` is serialized into a different json object (with future-proofing to incorporate `crt-objects-fallback` in the future). --- I've been test-driving this in #113382 to test actually switching `x86_64-unknown-linux-gnu` to `rust-lld` (and fix what needs to be fixed in CI, bootstrap, etc), and it seems to work fine.
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+372
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‎compiler/rustc_codegen_ssa/src/back/link.rs

+93-38
Original file line numberDiff line numberDiff line change
@@ -22,7 +22,9 @@ use rustc_session::utils::NativeLibKind;
2222
/// need out of the shared crate context before we get rid of it.
2323
use rustc_session::{filesearch, Session};
2424
use rustc_span::symbol::Symbol;
25-
use rustc_target::spec::crt_objects::{CrtObjects, LinkSelfContainedDefault};
25+
use rustc_target::spec::crt_objects::CrtObjects;
26+
use rustc_target::spec::LinkSelfContainedComponents;
27+
use rustc_target::spec::LinkSelfContainedDefault;
2628
use rustc_target::spec::{Cc, LinkOutputKind, LinkerFlavor, Lld, PanicStrategy};
2729
use rustc_target::spec::{RelocModel, RelroLevel, SanitizerSet, SplitDebuginfo};
2830

@@ -728,6 +730,7 @@ fn link_natively<'a>(
728730
) -> Result<(), ErrorGuaranteed> {
729731
info!("preparing {:?} to {:?}", crate_type, out_filename);
730732
let (linker_path, flavor) = linker_and_flavor(sess);
733+
let self_contained_components = self_contained_components(sess, crate_type);
731734
let mut cmd = linker_with_args(
732735
&linker_path,
733736
flavor,
@@ -737,6 +740,7 @@ fn link_natively<'a>(
737740
tmpdir,
738741
out_filename,
739742
codegen_results,
743+
self_contained_components,
740744
)?;
741745

742746
linker::disable_localization(&mut cmd);
@@ -812,14 +816,14 @@ fn link_natively<'a>(
812816
"Linker does not support -static-pie command line option. Retrying with -static instead."
813817
);
814818
// Mirror `add_(pre,post)_link_objects` to replace CRT objects.
815-
let self_contained = self_contained(sess, crate_type);
819+
let self_contained_crt_objects = self_contained_components.is_crt_objects_enabled();
816820
let opts = &sess.target;
817-
let pre_objects = if self_contained {
821+
let pre_objects = if self_contained_crt_objects {
818822
&opts.pre_link_objects_self_contained
819823
} else {
820824
&opts.pre_link_objects
821825
};
822-
let post_objects = if self_contained {
826+
let post_objects = if self_contained_crt_objects {
823827
&opts.post_link_objects_self_contained
824828
} else {
825829
&opts.post_link_objects
@@ -830,7 +834,9 @@ fn link_natively<'a>(
830834
.iter()
831835
.copied()
832836
.flatten()
833-
.map(|obj| get_object_file_path(sess, obj, self_contained).into_os_string())
837+
.map(|obj| {
838+
get_object_file_path(sess, obj, self_contained_crt_objects).into_os_string()
839+
})
834840
.collect::<Vec<_>>()
835841
};
836842
let pre_objects_static_pie = get_objects(pre_objects, LinkOutputKind::StaticPicExe);
@@ -1710,26 +1716,43 @@ fn detect_self_contained_mingw(sess: &Session) -> bool {
17101716
/// Various toolchain components used during linking are used from rustc distribution
17111717
/// instead of being found somewhere on the host system.
17121718
/// We only provide such support for a very limited number of targets.
1713-
fn self_contained(sess: &Session, crate_type: CrateType) -> bool {
1714-
if let Some(self_contained) = sess.opts.cg.link_self_contained.explicitly_set {
1715-
if sess.target.link_self_contained == LinkSelfContainedDefault::False {
1716-
sess.emit_err(errors::UnsupportedLinkSelfContained);
1717-
}
1718-
return self_contained;
1719-
}
1719+
fn self_contained_components(sess: &Session, crate_type: CrateType) -> LinkSelfContainedComponents {
1720+
// Turn the backwards compatible bool values for `self_contained` into fully inferred
1721+
// `LinkSelfContainedComponents`.
1722+
let self_contained =
1723+
if let Some(self_contained) = sess.opts.cg.link_self_contained.explicitly_set {
1724+
// Emit an error if the user requested self-contained mode on the CLI but the target
1725+
// explicitly refuses it.
1726+
if sess.target.link_self_contained.is_disabled() {
1727+
sess.emit_err(errors::UnsupportedLinkSelfContained);
1728+
}
1729+
self_contained
1730+
} else {
1731+
match sess.target.link_self_contained {
1732+
LinkSelfContainedDefault::False => false,
1733+
LinkSelfContainedDefault::True => true,
1734+
1735+
LinkSelfContainedDefault::WithComponents(components) => {
1736+
// For target specs with explicitly enabled components, we can return them
1737+
// directly.
1738+
return components;
1739+
}
17201740

1721-
match sess.target.link_self_contained {
1722-
LinkSelfContainedDefault::False => false,
1723-
LinkSelfContainedDefault::True => true,
1724-
// FIXME: Find a better heuristic for "native musl toolchain is available",
1725-
// based on host and linker path, for example.
1726-
// (https://github.com/rust-lang/rust/pull/71769#issuecomment-626330237).
1727-
LinkSelfContainedDefault::Musl => sess.crt_static(Some(crate_type)),
1728-
LinkSelfContainedDefault::Mingw => {
1729-
sess.host == sess.target
1730-
&& sess.target.vendor != "uwp"
1731-
&& detect_self_contained_mingw(&sess)
1732-
}
1741+
// FIXME: Find a better heuristic for "native musl toolchain is available",
1742+
// based on host and linker path, for example.
1743+
// (https://github.com/rust-lang/rust/pull/71769#issuecomment-626330237).
1744+
LinkSelfContainedDefault::InferredForMusl => sess.crt_static(Some(crate_type)),
1745+
LinkSelfContainedDefault::InferredForMingw => {
1746+
sess.host == sess.target
1747+
&& sess.target.vendor != "uwp"
1748+
&& detect_self_contained_mingw(&sess)
1749+
}
1750+
}
1751+
};
1752+
if self_contained {
1753+
LinkSelfContainedComponents::all()
1754+
} else {
1755+
LinkSelfContainedComponents::empty()
17331756
}
17341757
}
17351758

@@ -2030,13 +2053,14 @@ fn linker_with_args<'a>(
20302053
tmpdir: &Path,
20312054
out_filename: &Path,
20322055
codegen_results: &CodegenResults,
2056+
self_contained_components: LinkSelfContainedComponents,
20332057
) -> Result<Command, ErrorGuaranteed> {
2034-
let self_contained = self_contained(sess, crate_type);
2058+
let self_contained_crt_objects = self_contained_components.is_crt_objects_enabled();
20352059
let cmd = &mut *super::linker::get_linker(
20362060
sess,
20372061
path,
20382062
flavor,
2039-
self_contained,
2063+
self_contained_components.are_any_components_enabled(),
20402064
&codegen_results.crate_info.target_cpu,
20412065
);
20422066
let link_output_kind = link_output_kind(sess, crate_type);
@@ -2063,7 +2087,7 @@ fn linker_with_args<'a>(
20632087
// ------------ Object code and libraries, order-dependent ------------
20642088

20652089
// Pre-link CRT objects.
2066-
add_pre_link_objects(cmd, sess, flavor, link_output_kind, self_contained);
2090+
add_pre_link_objects(cmd, sess, flavor, link_output_kind, self_contained_crt_objects);
20672091

20682092
add_linked_symbol_object(
20692093
cmd,
@@ -2206,7 +2230,7 @@ fn linker_with_args<'a>(
22062230
cmd,
22072231
sess,
22082232
link_output_kind,
2209-
self_contained,
2233+
self_contained_components,
22102234
flavor,
22112235
crate_type,
22122236
codegen_results,
@@ -2222,7 +2246,7 @@ fn linker_with_args<'a>(
22222246
// ------------ Object code and libraries, order-dependent ------------
22232247

22242248
// Post-link CRT objects.
2225-
add_post_link_objects(cmd, sess, link_output_kind, self_contained);
2249+
add_post_link_objects(cmd, sess, link_output_kind, self_contained_crt_objects);
22262250

22272251
// ------------ Late order-dependent options ------------
22282252

@@ -2239,15 +2263,15 @@ fn add_order_independent_options(
22392263
cmd: &mut dyn Linker,
22402264
sess: &Session,
22412265
link_output_kind: LinkOutputKind,
2242-
self_contained: bool,
2266+
self_contained_components: LinkSelfContainedComponents,
22432267
flavor: LinkerFlavor,
22442268
crate_type: CrateType,
22452269
codegen_results: &CodegenResults,
22462270
out_filename: &Path,
22472271
tmpdir: &Path,
22482272
) {
22492273
// Take care of the flavors and CLI options requesting the `lld` linker.
2250-
add_lld_args(cmd, sess, flavor);
2274+
add_lld_args(cmd, sess, flavor, self_contained_components);
22512275

22522276
add_apple_sdk(cmd, sess, flavor);
22532277

@@ -2272,7 +2296,7 @@ fn add_order_independent_options(
22722296
// Make the binary compatible with data execution prevention schemes.
22732297
cmd.add_no_exec();
22742298

2275-
if self_contained {
2299+
if self_contained_components.is_crt_objects_enabled() {
22762300
cmd.no_crt_objects();
22772301
}
22782302

@@ -2303,7 +2327,7 @@ fn add_order_independent_options(
23032327

23042328
cmd.linker_plugin_lto();
23052329

2306-
add_library_search_dirs(cmd, sess, self_contained);
2330+
add_library_search_dirs(cmd, sess, self_contained_components.are_any_components_enabled());
23072331

23082332
cmd.output_filename(out_filename);
23092333

@@ -2953,8 +2977,16 @@ fn get_apple_sdk_root(sdk_name: &str) -> Result<String, errors::AppleSdkRootErro
29532977
/// invoke it:
29542978
/// - when the self-contained linker flag is active: the build of `lld` distributed with rustc,
29552979
/// - or any `lld` available to `cc`.
2956-
fn add_lld_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
2957-
debug!("add_lld_args requested, flavor: '{flavor:?}'");
2980+
fn add_lld_args(
2981+
cmd: &mut dyn Linker,
2982+
sess: &Session,
2983+
flavor: LinkerFlavor,
2984+
self_contained_components: LinkSelfContainedComponents,
2985+
) {
2986+
debug!(
2987+
"add_lld_args requested, flavor: '{:?}', target self-contained components: {:?}",
2988+
flavor, self_contained_components,
2989+
);
29582990

29592991
// If the flavor doesn't use a C/C++ compiler to invoke the linker, or doesn't opt in to `lld`,
29602992
// we don't need to do anything.
@@ -2963,9 +2995,32 @@ fn add_lld_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
29632995
}
29642996

29652997
// 1. Implement the "self-contained" part of this feature by adding rustc distribution
2966-
// directories to the tool's search path:
2967-
// - if the self-contained linker is enabled on the CLI.
2968-
if sess.opts.cg.link_self_contained.is_linker_enabled() {
2998+
// directories to the tool's search path, depending on a mix between what users can specify on
2999+
// the CLI, and what the target spec enables (as it can't disable components):
3000+
// - if the self-contained linker is enabled on the CLI or by the target spec,
3001+
// - and if the self-contained linker is not disabled on the CLI.
3002+
let self_contained_cli = sess.opts.cg.link_self_contained.is_linker_enabled();
3003+
let self_contained_target = self_contained_components.is_linker_enabled();
3004+
3005+
// FIXME: in the future, codegen backends may need to have more control over this process: they
3006+
// don't always support all the features the linker expects here, and vice versa. For example,
3007+
// at the time of writing this, lld expects a newer style of aarch64 TLS relocations that
3008+
// cranelift doesn't implement yet. That in turn can impact whether linking would succeed on
3009+
// such a target when using the `cg_clif` backend and lld.
3010+
//
3011+
// Until interactions between backends and linker features are expressible, we limit target
3012+
// specs to opt-in to lld only when we're on the llvm backend, where it's expected to work and
3013+
// tested on CI. As usual, the CLI still has precedence over this, so that users and developers
3014+
// can still override this default when needed (e.g. for tests).
3015+
let uses_llvm_backend =
3016+
matches!(sess.opts.unstable_opts.codegen_backend.as_deref(), None | Some("llvm"));
3017+
if !uses_llvm_backend && !self_contained_cli && sess.opts.cg.linker_flavor.is_none() {
3018+
// We bail if we're not using llvm and lld was not explicitly requested on the CLI.
3019+
return;
3020+
}
3021+
3022+
let self_contained_linker = self_contained_cli || self_contained_target;
3023+
if self_contained_linker && !sess.opts.cg.link_self_contained.is_linker_disabled() {
29693024
for path in sess.get_tools_search_paths(false) {
29703025
cmd.arg({
29713026
let mut arg = OsString::from("-B");

‎compiler/rustc_target/src/spec/crt_objects.rs

-38
Original file line numberDiff line numberDiff line change
@@ -40,11 +40,9 @@
4040
//! but not gcc's. As a result rustc cannot link with C++ static libraries (#36710)
4141
//! when linking in self-contained mode.
4242
43-
use crate::json::{Json, ToJson};
4443
use crate::spec::LinkOutputKind;
4544
use std::borrow::Cow;
4645
use std::collections::BTreeMap;
47-
use std::str::FromStr;
4846

4947
pub type CrtObjects = BTreeMap<LinkOutputKind, Vec<Cow<'static, str>>>;
5048

@@ -123,39 +121,3 @@ pub(super) fn pre_wasi_self_contained() -> CrtObjects {
123121
pub(super) fn post_wasi_self_contained() -> CrtObjects {
124122
new(&[])
125123
}
126-
127-
/// Which logic to use to determine whether to use self-contained linking mode
128-
/// if `-Clink-self-contained` is not specified explicitly.
129-
#[derive(Clone, Copy, PartialEq, Hash, Debug)]
130-
pub enum LinkSelfContainedDefault {
131-
False,
132-
True,
133-
Musl,
134-
Mingw,
135-
}
136-
137-
impl FromStr for LinkSelfContainedDefault {
138-
type Err = ();
139-
140-
fn from_str(s: &str) -> Result<LinkSelfContainedDefault, ()> {
141-
Ok(match s {
142-
"false" => LinkSelfContainedDefault::False,
143-
"true" | "wasm" => LinkSelfContainedDefault::True,
144-
"musl" => LinkSelfContainedDefault::Musl,
145-
"mingw" => LinkSelfContainedDefault::Mingw,
146-
_ => return Err(()),
147-
})
148-
}
149-
}
150-
151-
impl ToJson for LinkSelfContainedDefault {
152-
fn to_json(&self) -> Json {
153-
match *self {
154-
LinkSelfContainedDefault::False => "false",
155-
LinkSelfContainedDefault::True => "true",
156-
LinkSelfContainedDefault::Musl => "musl",
157-
LinkSelfContainedDefault::Mingw => "mingw",
158-
}
159-
.to_json()
160-
}
161-
}

‎compiler/rustc_target/src/spec/linux_musl_base.rs

+3-3
Original file line numberDiff line numberDiff line change
@@ -1,13 +1,13 @@
1-
use crate::spec::crt_objects::{self, LinkSelfContainedDefault};
2-
use crate::spec::TargetOptions;
1+
use crate::spec::crt_objects;
2+
use crate::spec::{LinkSelfContainedDefault, TargetOptions};
33

44
pub fn opts() -> TargetOptions {
55
let mut base = super::linux_base::opts();
66

77
base.env = "musl".into();
88
base.pre_link_objects_self_contained = crt_objects::pre_musl_self_contained();
99
base.post_link_objects_self_contained = crt_objects::post_musl_self_contained();
10-
base.link_self_contained = LinkSelfContainedDefault::Musl;
10+
base.link_self_contained = LinkSelfContainedDefault::InferredForMusl;
1111

1212
// These targets statically link libc by default
1313
base.crt_static_default = true;

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