Auto merge of rust-lang#117684 - lqd:mcp510-crater, r=<try>

crater: test enabling MCP510

Tests pass at stage1 and 2 with the `x86_64-unknown-linux-gnu` target switched. CI passes in rust-lang#113382 with most `x86_64-unknown-linux-gnu` builders enabled. Bootstrap and the perf collector work.

The crater queue is about to be empty, so it's a good time to do another run with this linker configuration and see if anything changed since the previous run. Surely, some bug-for-bug bfd compatibility differences will remain, but it will good to check with the latest lld anyways.

Note for anyone looking at this PR coming from the crater queue: this is intended to be a low-priority run. If it hasn't started and you need your run started before this one, go ahead and bump your own priority above this.

r? `@ghost`

compiler/rustc_target/src/spec/mod.rs

@@ -625,6 +625,12 @@ impl LinkSelfContainedDefault {
             _ => "crt-objects-fallback",
         }
     }
+
+    /// Creates a `LinkSelfContained` enabling the self-contained linker for target specs (the
+    /// equivalent of `-Clink-self-contained=+linker` on the CLI).
+    pub fn with_linker() -> LinkSelfContainedDefault {
+        LinkSelfContainedDefault::WithComponents(LinkSelfContainedComponents::LINKER)
+    }
 }
 
 bitflags::bitflags! {

compiler/rustc_target/src/spec/x86_64_unknown_linux_gnu.rs

@@ -16,6 +16,12 @@ pub fn target() -> Target {
         | SanitizerSet::THREAD;
     base.supports_xray = true;
 
+    #[cfg(rust_lld)]
+    {
+        base.linker_flavor = LinkerFlavor::Gnu(Cc::Yes, Lld::Yes);
+        base.link_self_contained = crate::spec::LinkSelfContainedDefault::with_linker();
+    }
+
     Target {
         llvm_target: "x86_64-unknown-linux-gnu".into(),
         pointer_width: 64,

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

@@ -1034,6 +1034,10 @@ pub fn rustc_cargo_env(
         cargo.rustflag("--cfg=parallel_compiler");
         cargo.rustdocflag("--cfg=parallel_compiler");
     }
+    if builder.config.lld_enabled {
+        cargo.rustflag("--cfg=rust_lld");
+        cargo.rustdocflag("--cfg=rust_lld");
+    }
     if builder.config.rust_verify_llvm_ir {
         cargo.env("RUSTC_VERIFY_LLVM_IR", "1");
     }

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

@@ -1372,6 +1372,7 @@ impl Config {
         let mut debuginfo_level_tests = None;
         let mut optimize = None;
         let mut omit_git_hash = None;
+        let mut lld_enabled = None;
 
         if let Some(rust) = toml.rust {
             set(&mut config.channel, rust.channel);
@@ -1404,6 +1405,7 @@ impl Config {
             debuginfo_level_std = rust.debuginfo_level_std;
             debuginfo_level_tools = rust.debuginfo_level_tools;
             debuginfo_level_tests = rust.debuginfo_level_tests;
+            lld_enabled = rust.lld;
 
             config.rust_split_debuginfo = rust
                 .split_debuginfo
@@ -1428,7 +1430,6 @@ impl Config {
                 config.incremental = true;
             }
             set(&mut config.use_lld, rust.use_lld);
-            set(&mut config.lld_enabled, rust.lld);
             set(&mut config.llvm_tools_enabled, rust.llvm_tools);
             config.rustc_parallel = rust
                 .parallel_compiler
@@ -1665,6 +1666,26 @@ impl Config {
         config.llvm_plugins = llvm_plugins.unwrap_or(false);
         config.rust_optimize = optimize.unwrap_or(RustOptimize::Bool(true));
 
+        // `x86_64-unknown-linux-gnu` now uses the self-contained linker, so we have to build
+        // our internal lld by default:
+        // - when building our in-tree llvm (the target has not set an `llvm-config`), we're able to
+        //   build rust-lld as well
+        // - when using an external llvm that's downloaded from CI, rust-lld is also packaged there
+        // - otherwise, we're using an external llvm and lld is not available and thus, disabled
+        // - similarly, it's not built or used by this target when asked not to (when the config
+        //   sets `rust.lld = false`)
+        if config.build.triple == "x86_64-unknown-linux-gnu" && config.hosts == &[config.build] {
+            let no_llvm_config = config
+                .target_config
+                .get(&config.build)
+                .is_some_and(|target_config| target_config.llvm_config.is_none());
+            let enable_lld = config.llvm_from_ci || no_llvm_config;
+            // Prefer the config setting in case an explicit opt-out is needed.
+            config.lld_enabled = lld_enabled.unwrap_or(enable_lld);
+        } else {
+            set(&mut config.lld_enabled, lld_enabled);
+        }
+
         let default = debug == Some(true);
         config.rust_debug_assertions = debug_assertions.unwrap_or(default);
         config.rust_debug_assertions_std =

src/bootstrap/src/lib.rs

@@ -117,6 +117,10 @@ const EXTRA_CHECK_CFGS: &[(Option<Mode>, &str, Option<&[&'static str]>)] = &[
     // Needed to avoid the need to copy windows.lib into the sysroot.
     (Some(Mode::Rustc), "windows_raw_dylib", None),
     (Some(Mode::ToolRustc), "windows_raw_dylib", None),
+    // If rustc wants to use rust-lld as the default linker in a target spec.
+    (Some(Mode::Rustc), "rust_lld", None),
+    (Some(Mode::ToolRustc), "rust_lld", None),
+    (Some(Mode::Codegen), "rust_lld", None),
 ];
 
 /// A structure representing a Rust compiler.

src/ci/docker/host-x86_64/dist-x86_64-linux/build-gcc.sh

@@ -3,7 +3,8 @@ set -ex
 
 source shared.sh
 
-GCC=8.5.0
+# Note: in the future when bumping to version 10.1.0, also take care of the sed block below.
+GCC=9.5.0
 
 curl https://ftp.gnu.org/gnu/gcc/gcc-$GCC/gcc-$GCC.tar.xz | xzcat | tar xf -
 cd gcc-$GCC
@@ -22,6 +23,11 @@ cd gcc-$GCC
 # latter host is presented to `wget`! Therefore, we choose to download from the insecure HTTP server
 # instead here.
 #
+# Note: in version 10.1.0, the URL used in `download_prerequisites` has changed from using FTP to
+# using HTTP. When bumping to that gcc version, we can likely remove the sed replacement below, or
+# the expression will need to be updated. That new URL is available at:
+# https://github.com/gcc-mirror/gcc/blob/6e6e3f144a33ae504149dc992453b4f6dea12fdb/contrib/download_prerequisites#L35
+#
 sed -i'' 's|ftp://gcc\.gnu\.org/|https://gcc.gnu.org/|g' ./contrib/download_prerequisites
 
 ./contrib/download_prerequisites