Rollup merge of #147046 - Kobzol:bootstrap-ll, r=jieyouxu

Rename `rust.use-lld` to `rust.bootstrap-override-lld`

First part of #146640. The old option is kept for backwards compatibility, we can remove it in ~6 months, as usually.

I'm not sure if the bootstrap prefix is ideal, after all we have a bunch of other configs that only affect bootstrap's behavior and not the built artifacts. Maybe `build.override-lld`? But I don't think it matters that much, as long as it's clear that it is an override, and how does it differ from `rust.lld`.

r? `@jieyouxu`

Author: matthiaskrgr

bootstrap.example.toml

@@ -768,16 +768,15 @@
 # make this default to false.
 #rust.lld = false in all cases, except on `x86_64-unknown-linux-gnu` as described above, where it is true
 
-# Indicates whether LLD will be used to link Rust crates during bootstrap on
-# supported platforms.
+# Indicates if we should override the linker used to link Rust crates during bootstrap to be LLD.
 # If set to `true` or `"external"`, a global `lld` binary that has to be in $PATH
 # will be used.
 # If set to `"self-contained"`, rust-lld from the snapshot compiler will be used.
 #
 # On MSVC, LLD will not be used if we're cross linking.
 #
 # Explicitly setting the linker for a target will override this option when targeting MSVC.
-#rust.use-lld = false
+#rust.bootstrap-override-lld = false
 
 # Indicates whether some LLVM tools, like llvm-objdump, will be made available in the
 # sysroot.
@@ -950,7 +949,7 @@
 # Linker to be used to bootstrap Rust code. Note that the
 # default value is platform specific, and if not specified it may also depend on
 # what platform is crossing to what platform.
-# Setting this will override the `use-lld` option for Rust code when targeting MSVC.
+# Setting this will override the `bootstrap-override-lld` option for Rust code when targeting MSVC.
 #linker = "cc" (path)
 
 # Should rustc and the standard library be built with split debuginfo? Default

src/bootstrap/src/core/build_steps/compile.rs

@@ -1219,7 +1219,7 @@ pub fn rustc_cargo(
     // us a faster startup time. However GNU ld < 2.40 will error if we try to link a shared object
     // with direct references to protected symbols, so for now we only use protected symbols if
     // linking with LLD is enabled.
-    if builder.build.config.lld_mode.is_used() {
+    if builder.build.config.bootstrap_override_lld.is_used() {
         cargo.rustflag("-Zdefault-visibility=protected");
     }
 
@@ -1256,7 +1256,7 @@ pub fn rustc_cargo(
     // is already on by default in MSVC optimized builds, which is interpreted as --icf=all:
     // https://github.com/llvm/llvm-project/blob/3329cec2f79185bafd678f310fafadba2a8c76d2/lld/COFF/Driver.cpp#L1746
     // https://github.com/rust-lang/rust/blob/f22819bcce4abaff7d1246a56eec493418f9f4ee/compiler/rustc_codegen_ssa/src/back/linker.rs#L827
-    if builder.config.lld_mode.is_used() && !build_compiler.host.is_msvc() {
+    if builder.config.bootstrap_override_lld.is_used() && !build_compiler.host.is_msvc() {
         cargo.rustflag("-Clink-args=-Wl,--icf=all");
     }
 

src/bootstrap/src/core/config/config.rs

@@ -41,7 +41,7 @@ use crate::core::config::toml::gcc::Gcc;
 use crate::core::config::toml::install::Install;
 use crate::core::config::toml::llvm::Llvm;
 use crate::core::config::toml::rust::{
-    LldMode, Rust, RustOptimize, check_incompatible_options_for_ci_rustc,
+    BootstrapOverrideLld, Rust, RustOptimize, check_incompatible_options_for_ci_rustc,
     default_lld_opt_in_targets, parse_codegen_backends,
 };
 use crate::core::config::toml::target::Target;
@@ -174,7 +174,7 @@ pub struct Config {
     pub llvm_from_ci: bool,
     pub llvm_build_config: HashMap<String, String>,
 
-    pub lld_mode: LldMode,
+    pub bootstrap_override_lld: BootstrapOverrideLld,
     pub lld_enabled: bool,
     pub llvm_tools_enabled: bool,
     pub llvm_bitcode_linker_enabled: bool,
@@ -553,7 +553,8 @@ impl Config {
             frame_pointers: rust_frame_pointers,
             stack_protector: rust_stack_protector,
             strip: rust_strip,
-            lld_mode: rust_lld_mode,
+            bootstrap_override_lld: rust_bootstrap_override_lld,
+            bootstrap_override_lld_legacy: rust_bootstrap_override_lld_legacy,
             std_features: rust_std_features,
             break_on_ice: rust_break_on_ice,
         } = toml.rust.unwrap_or_default();
@@ -601,6 +602,15 @@ impl Config {
 
         let Gcc { download_ci_gcc: gcc_download_ci_gcc } = toml.gcc.unwrap_or_default();
 
+        if rust_bootstrap_override_lld.is_some() && rust_bootstrap_override_lld_legacy.is_some() {
+            panic!(
+                "Cannot use both `rust.use-lld` and `rust.bootstrap-override-lld`. Please use only `rust.bootstrap-override-lld`"
+            );
+        }
+
+        let bootstrap_override_lld =
+            rust_bootstrap_override_lld.or(rust_bootstrap_override_lld_legacy).unwrap_or_default();
+
         if rust_optimize.as_ref().is_some_and(|v| matches!(v, RustOptimize::Bool(false))) {
             eprintln!(
                 "WARNING: setting `optimize` to `false` is known to cause errors and \
@@ -932,7 +942,7 @@ impl Config {
 
         let initial_rustfmt = build_rustfmt.or_else(|| maybe_download_rustfmt(&dwn_ctx, &out));
 
-        if matches!(rust_lld_mode.unwrap_or_default(), LldMode::SelfContained)
+        if matches!(bootstrap_override_lld, BootstrapOverrideLld::SelfContained)
             && !lld_enabled
             && flags_stage.unwrap_or(0) > 0
         {
@@ -1144,6 +1154,7 @@ impl Config {
             backtrace_on_ice: rust_backtrace_on_ice.unwrap_or(false),
             bindir: install_bindir.map(PathBuf::from).unwrap_or("bin".into()),
             bootstrap_cache_path: build_bootstrap_cache_path,
+            bootstrap_override_lld,
             bypass_bootstrap_lock: flags_bypass_bootstrap_lock,
             cargo_info,
             cargo_native_static: build_cargo_native_static.unwrap_or(false),
@@ -1210,7 +1221,6 @@ impl Config {
             libdir: install_libdir.map(PathBuf::from),
             library_docs_private_items: build_library_docs_private_items.unwrap_or(false),
             lld_enabled,
-            lld_mode: rust_lld_mode.unwrap_or_default(),
             lldb: build_lldb.map(PathBuf::from),
             llvm_allow_old_toolchain: llvm_allow_old_toolchain.unwrap_or(false),
             llvm_assertions,

src/bootstrap/src/core/config/mod.rs

@@ -37,7 +37,7 @@ use serde_derive::Deserialize;
 pub use target_selection::TargetSelection;
 pub use toml::BUILDER_CONFIG_FILENAME;
 pub use toml::change_id::ChangeId;
-pub use toml::rust::LldMode;
+pub use toml::rust::BootstrapOverrideLld;
 pub use toml::target::Target;
 
 use crate::Display;

src/bootstrap/src/core/config/tests.rs

@@ -17,7 +17,9 @@ use crate::core::build_steps::clippy::{LintConfig, get_clippy_rules_in_order};
 use crate::core::build_steps::llvm;
 use crate::core::build_steps::llvm::LLVM_INVALIDATION_PATHS;
 use crate::core::config::toml::TomlConfig;
-use crate::core::config::{CompilerBuiltins, LldMode, StringOrBool, Target, TargetSelection};
+use crate::core::config::{
+    BootstrapOverrideLld, CompilerBuiltins, StringOrBool, Target, TargetSelection,
+};
 use crate::utils::tests::git::git_test;
 
 pub(crate) fn parse(config: &str) -> Config {
@@ -298,11 +300,33 @@ fn verify_file_integrity() {
 
 #[test]
 fn rust_lld() {
-    assert!(matches!(parse("").lld_mode, LldMode::Unused));
-    assert!(matches!(parse("rust.use-lld = \"self-contained\"").lld_mode, LldMode::SelfContained));
-    assert!(matches!(parse("rust.use-lld = \"external\"").lld_mode, LldMode::External));
-    assert!(matches!(parse("rust.use-lld = true").lld_mode, LldMode::External));
-    assert!(matches!(parse("rust.use-lld = false").lld_mode, LldMode::Unused));
+    assert!(matches!(parse("").bootstrap_override_lld, BootstrapOverrideLld::None));
+    assert!(matches!(
+        parse("rust.bootstrap-override-lld = \"self-contained\"").bootstrap_override_lld,
+        BootstrapOverrideLld::SelfContained
+    ));
+    assert!(matches!(
+        parse("rust.bootstrap-override-lld = \"external\"").bootstrap_override_lld,
+        BootstrapOverrideLld::External
+    ));
+    assert!(matches!(
+        parse("rust.bootstrap-override-lld = true").bootstrap_override_lld,
+        BootstrapOverrideLld::External
+    ));
+    assert!(matches!(
+        parse("rust.bootstrap-override-lld = false").bootstrap_override_lld,
+        BootstrapOverrideLld::None
+    ));
+
+    // Also check the legacy options
+    assert!(matches!(
+        parse("rust.use-lld = true").bootstrap_override_lld,
+        BootstrapOverrideLld::External
+    ));
+    assert!(matches!(
+        parse("rust.use-lld = false").bootstrap_override_lld,
+        BootstrapOverrideLld::None
+    ));
 }
 
 #[test]

src/bootstrap/src/core/config/toml/rust.rs

@@ -45,7 +45,9 @@ define_config! {
         codegen_backends: Option<Vec<String>> = "codegen-backends",
         llvm_bitcode_linker: Option<bool> = "llvm-bitcode-linker",
         lld: Option<bool> = "lld",
-        lld_mode: Option<LldMode> = "use-lld",
+        bootstrap_override_lld: Option<BootstrapOverrideLld> = "bootstrap-override-lld",
+        // FIXME: Remove this option in Spring 2026
+        bootstrap_override_lld_legacy: Option<BootstrapOverrideLld> = "use-lld",
         llvm_tools: Option<bool> = "llvm-tools",
         deny_warnings: Option<bool> = "deny-warnings",
         backtrace_on_ice: Option<bool> = "backtrace-on-ice",
@@ -70,22 +72,33 @@ define_config! {
     }
 }
 
-/// LLD in bootstrap works like this:
-/// - Self-contained lld: use `rust-lld` from the compiler's sysroot
+/// Determines if we should override the linker used for linking Rust code built
+/// during the bootstrapping process to be LLD.
+///
+/// The primary use-case for this is to make local (re)builds of Rust code faster
+/// when using bootstrap.
+///
+/// This does not affect the *behavior* of the built/distributed compiler when invoked
+/// outside of bootstrap.
+/// It might affect its performance/binary size though, as that can depend on the
+/// linker that links rustc.
+///
+/// There are two ways of overriding the linker to be LLD:
+/// - Self-contained LLD: use `rust-lld` from the compiler's sysroot
 /// - External: use an external `lld` binary
 ///
 /// It is configured depending on the target:
 /// 1) Everything except MSVC
-/// - Self-contained: `-Clinker-flavor=gnu-lld-cc -Clink-self-contained=+linker`
-/// - External: `-Clinker-flavor=gnu-lld-cc`
+/// - Self-contained: `-Clinker-features=+lld -Clink-self-contained=+linker`
+/// - External: `-Clinker-features=+lld`
 /// 2) MSVC
 /// - Self-contained: `-Clinker=<path to rust-lld>`
 /// - External: `-Clinker=lld`
 #[derive(Copy, Clone, Default, Debug, PartialEq)]
-pub enum LldMode {
-    /// Do not use LLD
+pub enum BootstrapOverrideLld {
+    /// Do not override the linker LLD
     #[default]
-    Unused,
+    None,
     /// Use `rust-lld` from the compiler's sysroot
     SelfContained,
     /// Use an externally provided `lld` binary.
@@ -94,24 +107,24 @@ pub enum LldMode {
     External,
 }
 
-impl LldMode {
+impl BootstrapOverrideLld {
     pub fn is_used(&self) -> bool {
         match self {
-            LldMode::SelfContained | LldMode::External => true,
-            LldMode::Unused => false,
+            BootstrapOverrideLld::SelfContained | BootstrapOverrideLld::External => true,
+            BootstrapOverrideLld::None => false,
         }
     }
 }
 
-impl<'de> Deserialize<'de> for LldMode {
+impl<'de> Deserialize<'de> for BootstrapOverrideLld {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
     {
         struct LldModeVisitor;
 
         impl serde::de::Visitor<'_> for LldModeVisitor {
-            type Value = LldMode;
+            type Value = BootstrapOverrideLld;
 
             fn expecting(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
                 formatter.write_str("one of true, 'self-contained' or 'external'")
@@ -121,16 +134,16 @@ impl<'de> Deserialize<'de> for LldMode {
             where
                 E: serde::de::Error,
             {
-                Ok(if v { LldMode::External } else { LldMode::Unused })
+                Ok(if v { BootstrapOverrideLld::External } else { BootstrapOverrideLld::None })
             }
 
             fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
             where
                 E: serde::de::Error,
             {
                 match v {
-                    "external" => Ok(LldMode::External),
-                    "self-contained" => Ok(LldMode::SelfContained),
+                    "external" => Ok(BootstrapOverrideLld::External),
+                    "self-contained" => Ok(BootstrapOverrideLld::SelfContained),
                     _ => Err(E::custom(format!("unknown mode {v}"))),
                 }
             }
@@ -311,7 +324,6 @@ pub fn check_incompatible_options_for_ci_rustc(
         lto,
         stack_protector,
         strip,
-        lld_mode,
         jemalloc,
         rpath,
         channel,
@@ -359,6 +371,8 @@ pub fn check_incompatible_options_for_ci_rustc(
         frame_pointers: _,
         break_on_ice: _,
         parallel_frontend_threads: _,
+        bootstrap_override_lld: _,
+        bootstrap_override_lld_legacy: _,
     } = ci_rust_config;
 
     // There are two kinds of checks for CI rustc incompatible options:
@@ -374,7 +388,6 @@ pub fn check_incompatible_options_for_ci_rustc(
     err!(current_rust_config.debuginfo_level_rustc, debuginfo_level_rustc, "rust");
     err!(current_rust_config.rpath, rpath, "rust");
     err!(current_rust_config.strip, strip, "rust");
-    err!(current_rust_config.lld_mode, lld_mode, "rust");
     err!(current_rust_config.llvm_tools, llvm_tools, "rust");
     err!(current_rust_config.llvm_bitcode_linker, llvm_bitcode_linker, "rust");
     err!(current_rust_config.jemalloc, jemalloc, "rust");

src/bootstrap/src/lib.rs

@@ -35,7 +35,7 @@ use utils::exec::ExecutionContext;
 
 use crate::core::builder;
 use crate::core::builder::Kind;
-use crate::core::config::{DryRun, LldMode, LlvmLibunwind, TargetSelection, flags};
+use crate::core::config::{BootstrapOverrideLld, DryRun, LlvmLibunwind, TargetSelection, flags};
 use crate::utils::exec::{BootstrapCommand, command};
 use crate::utils::helpers::{self, dir_is_empty, exe, libdir, set_file_times, split_debuginfo};
 
@@ -1370,14 +1370,14 @@ impl Build {
             && !target.is_msvc()
         {
             Some(self.cc(target))
-        } else if self.config.lld_mode.is_used()
+        } else if self.config.bootstrap_override_lld.is_used()
             && self.is_lld_direct_linker(target)
             && self.host_target == target
         {
-            match self.config.lld_mode {
-                LldMode::SelfContained => Some(self.initial_lld.clone()),
-                LldMode::External => Some("lld".into()),
-                LldMode::Unused => None,
+            match self.config.bootstrap_override_lld {
+                BootstrapOverrideLld::SelfContained => Some(self.initial_lld.clone()),
+                BootstrapOverrideLld::External => Some("lld".into()),
+                BootstrapOverrideLld::None => None,
             }
         } else {
             None

src/bootstrap/src/utils/change_tracker.rs

@@ -556,4 +556,9 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
         severity: ChangeSeverity::Info,
         summary: "New option `build.windows-rc` that will override which resource compiler on Windows will be used to compile Rust.",
     },
+    ChangeInfo {
+        change_id: 99999,
+        severity: ChangeSeverity::Warning,
+        summary: "The `rust.use-lld` option has been renamed to `rust.bootstrap-override-lld`. Note that it only serves for overriding the linker used when building Rust code in bootstrap to be LLD.",
+    },
 ];