Merging upstream version 1.76.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

37 files changed, 1442 insertions, 620 deletions

diff --git a/src/bootstrap/Cargo.lock b/src/bootstrap/Cargo.lock
index 57113b0ec..f8e6d629b 100644
--- a/src/bootstrap/Cargo.lock
+++ b/src/bootstrap/Cargo.lock
@@ -55,7 +55,6 @@ dependencies = [
  "cmake",
  "fd-lock",
  "filetime",
- "hex",
  "home",
  "ignore",
  "junction",
@@ -314,12 +313,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "95505c38b4572b2d910cecb0281560f54b440a19336cbbcb27bf6ce6adc6f5a8"
 
 [[package]]
-name = "hex"
-version = "0.4.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7f24254aa9a54b5c858eaee2f5bccdb46aaf0e486a595ed5fd8f86ba55232a70"
-
-[[package]]
 name = "home"
 version = "0.5.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -370,9 +363,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.149"
+version = "0.2.150"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a08173bc88b7955d1b3145aa561539096c421ac8debde8cbc3612ec635fee29b"
+checksum = "89d92a4743f9a61002fae18374ed11e7973f530cb3a3255fb354818118b2203c"
 
 [[package]]
 name = "linux-raw-sys"
diff --git a/src/bootstrap/Cargo.toml b/src/bootstrap/Cargo.toml
index e4d359141..077d1954b 100644
--- a/src/bootstrap/Cargo.toml
+++ b/src/bootstrap/Cargo.toml
@@ -39,10 +39,9 @@ clap = { version = "4.4.7", default-features = false, features = ["std", "usage"
 clap_complete = "4.4.3"
 cmake = "0.1.38"
 filetime = "0.2"
-hex = "0.4"
 home = "0.5.4"
 ignore = "0.4.10"
-libc = "0.2"
+libc = "0.2.150"
 object = { version = "0.32.0", default-features = false, features = ["archive", "coff", "read_core", "unaligned"] }
 once_cell = "1.7.2"
 opener = "0.5"
diff --git a/src/bootstrap/README.md b/src/bootstrap/README.md
index e7998a40a..d0a069f45 100644
--- a/src/bootstrap/README.md
+++ b/src/bootstrap/README.md
@@ -183,7 +183,7 @@ Some general areas that you may be interested in modifying are:
 
 If you make a major change on bootstrap configuration, please remember to:
 
-+ Update `CONFIG_CHANGE_HISTORY` in `src/bootstrap/lib.rs`.
++ Update `CONFIG_CHANGE_HISTORY` in `src/bootstrap/src/utils/change_tracker.rs`.
 * Update `change-id = {pull-request-id}` in `config.example.toml`.
 
 A 'major change' includes
diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index 5a84e37f8..fea194a80 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -616,22 +616,6 @@ class RustBuild(object):
             with output(self.rustc_stamp()) as rust_stamp:
                 rust_stamp.write(key)
 
-    def _download_component_helper(
-        self, filename, pattern, tarball_suffix, rustc_cache,
-    ):
-        key = self.stage0_compiler.date
-
-        tarball = os.path.join(rustc_cache, filename)
-        if not os.path.exists(tarball):
-            get(
-                self.download_url,
-                "dist/{}/{}".format(key, filename),
-                tarball,
-                self.checksums_sha256,
-                verbose=self.verbose,
-            )
-        unpack(tarball, tarball_suffix, self.bin_root(), match=pattern, verbose=self.verbose)
-
     def should_fix_bins_and_dylibs(self):
         """Whether or not `fix_bin_or_dylib` needs to be run; can only be True
         on NixOS or if config.toml has `build.patch-binaries-for-nix` set.
@@ -946,6 +930,8 @@ class RustBuild(object):
         target_linker = self.get_toml("linker", build_section)
         if target_linker is not None:
             env["RUSTFLAGS"] += " -C linker=" + target_linker
+        # When changing this list, also update the corresponding list in `Builder::cargo`
+        # in `src/bootstrap/src/core/builder.rs`.
         env["RUSTFLAGS"] += " -Wrust_2018_idioms -Wunused_lifetimes"
         if self.warnings == "default":
             deny_warnings = self.get_toml("deny-warnings", "rust") != "false"
@@ -1083,6 +1069,11 @@ def bootstrap(args):
         include_file = 'config.{}.toml'.format(profile_aliases.get(profile) or profile)
         include_dir = os.path.join(rust_root, 'src', 'bootstrap', 'defaults')
         include_path = os.path.join(include_dir, include_file)
+
+        if not os.path.exists(include_path):
+            raise Exception("Unrecognized config profile '{}'. Check src/bootstrap/defaults"
+            " for available options.".format(profile))
+
         # HACK: This works because `self.get_toml()` returns the first match it finds for a
         # specific key, so appending our defaults at the end allows the user to override them
         with open(include_path) as included_toml:
diff --git a/src/bootstrap/defaults/config.compiler.toml b/src/bootstrap/defaults/config.compiler.toml
index b98b13119..b27b524b8 100644
--- a/src/bootstrap/defaults/config.compiler.toml
+++ b/src/bootstrap/defaults/config.compiler.toml
@@ -17,4 +17,4 @@ lto = "off"
 
 [llvm]
 # Will download LLVM from CI if available on your platform.
-download-ci-llvm = "if-available"
+download-ci-llvm = "if-unchanged"
diff --git a/src/bootstrap/defaults/config.library.toml b/src/bootstrap/defaults/config.library.toml
index f362c4111..087544397 100644
--- a/src/bootstrap/defaults/config.library.toml
+++ b/src/bootstrap/defaults/config.library.toml
@@ -13,4 +13,4 @@ lto = "off"
 
 [llvm]
 # Will download LLVM from CI if available on your platform.
-download-ci-llvm = "if-available"
+download-ci-llvm = "if-unchanged"
diff --git a/src/bootstrap/defaults/config.tools.toml b/src/bootstrap/defaults/config.tools.toml
index 79424f28d..6e6c36600 100644
--- a/src/bootstrap/defaults/config.tools.toml
+++ b/src/bootstrap/defaults/config.tools.toml
@@ -21,4 +21,4 @@ compiler-docs = true
 
 [llvm]
 # Will download LLVM from CI if available on your platform.
-download-ci-llvm = "if-available"
+download-ci-llvm = "if-unchanged"
diff --git a/src/bootstrap/src/bin/main.rs b/src/bootstrap/src/bin/main.rs
index 0a6072ae1..b1ab8dae5 100644
--- a/src/bootstrap/src/bin/main.rs
+++ b/src/bootstrap/src/bin/main.rs
@@ -5,15 +5,18 @@
 //! parent directory, and otherwise documentation can be found throughout the `build`
 //! directory in each respective module.
 
-#[cfg(all(any(unix, windows), not(target_os = "solaris")))]
 use std::io::Write;
 #[cfg(all(any(unix, windows), not(target_os = "solaris")))]
 use std::process;
-use std::{env, fs};
+use std::{
+    env,
+    fs::{self, OpenOptions},
+    io::{self, BufRead, BufReader, IsTerminal},
+};
 
-#[cfg(all(any(unix, windows), not(target_os = "solaris")))]
-use bootstrap::t;
-use bootstrap::{find_recent_config_change_ids, Build, Config, Subcommand, CONFIG_CHANGE_HISTORY};
+use bootstrap::{
+    find_recent_config_change_ids, t, Build, Config, Subcommand, CONFIG_CHANGE_HISTORY,
+};
 
 fn main() {
     let args = env::args().skip(1).collect::<Vec<_>>();
@@ -23,35 +26,40 @@ fn main() {
     let mut build_lock;
     #[cfg(all(any(unix, windows), not(target_os = "solaris")))]
     let _build_lock_guard;
-    #[cfg(all(any(unix, windows), not(target_os = "solaris")))]
-    // Display PID of process holding the lock
-    // PID will be stored in a lock file
-    {
-        let path = config.out.join("lock");
-        let pid = match fs::read_to_string(&path) {
-            Ok(contents) => contents,
-            Err(_) => String::new(),
-        };
-
-        build_lock =
-            fd_lock::RwLock::new(t!(fs::OpenOptions::new().write(true).create(true).open(&path)));
-        _build_lock_guard = match build_lock.try_write() {
-            Ok(mut lock) => {
-                t!(lock.write(&process::id().to_string().as_ref()));
-                lock
-            }
-            err => {
-                drop(err);
-                println!("WARNING: build directory locked by process {pid}, waiting for lock");
-                let mut lock = t!(build_lock.write());
-                t!(lock.write(&process::id().to_string().as_ref()));
-                lock
-            }
-        };
-    }
 
-    #[cfg(any(not(any(unix, windows)), target_os = "solaris"))]
-    println!("WARNING: file locking not supported for target, not locking build directory");
+    if !config.bypass_bootstrap_lock {
+        // Display PID of process holding the lock
+        // PID will be stored in a lock file
+        #[cfg(all(any(unix, windows), not(target_os = "solaris")))]
+        {
+            let path = config.out.join("lock");
+            let pid = match fs::read_to_string(&path) {
+                Ok(contents) => contents,
+                Err(_) => String::new(),
+            };
+
+            build_lock = fd_lock::RwLock::new(t!(fs::OpenOptions::new()
+                .write(true)
+                .create(true)
+                .open(&path)));
+            _build_lock_guard = match build_lock.try_write() {
+                Ok(mut lock) => {
+                    t!(lock.write(&process::id().to_string().as_ref()));
+                    lock
+                }
+                err => {
+                    drop(err);
+                    println!("WARNING: build directory locked by process {pid}, waiting for lock");
+                    let mut lock = t!(build_lock.write());
+                    t!(lock.write(&process::id().to_string().as_ref()));
+                    lock
+                }
+            };
+        }
+
+        #[cfg(any(not(any(unix, windows)), target_os = "solaris"))]
+        println!("WARNING: file locking not supported for target, not locking build directory");
+    }
 
     // check_version warnings are not printed during setup
     let changelog_suggestion =
@@ -71,6 +79,9 @@ fn main() {
     }
 
     let pre_commit = config.src.join(".git").join("hooks").join("pre-commit");
+    let dump_bootstrap_shims = config.dump_bootstrap_shims;
+    let out_dir = config.out.clone();
+
     Build::new(config).build();
 
     if suggest_setup {
@@ -99,6 +110,29 @@ fn main() {
     if suggest_setup || changelog_suggestion.is_some() {
         println!("NOTE: this message was printed twice to make it more likely to be seen");
     }
+
+    if dump_bootstrap_shims {
+        let dump_dir = out_dir.join("bootstrap-shims-dump");
+        assert!(dump_dir.exists());
+
+        for entry in walkdir::WalkDir::new(&dump_dir) {
+            let entry = t!(entry);
+
+            if !entry.file_type().is_file() {
+                continue;
+            }
+
+            let file = t!(fs::File::open(&entry.path()));
+
+            // To ensure deterministic results we must sort the dump lines.
+            // This is necessary because the order of rustc invocations different
+            // almost all the time.
+            let mut lines: Vec<String> = t!(BufReader::new(&file).lines().collect());
+            lines.sort_by_key(|t| t.to_lowercase());
+            let mut file = t!(OpenOptions::new().write(true).truncate(true).open(&entry.path()));
+            t!(file.write_all(lines.join("\n").as_bytes()));
+        }
+    }
 }
 
 fn check_version(config: &Config) -> Option<String> {
@@ -108,35 +142,46 @@ fn check_version(config: &Config) -> Option<String> {
         msg.push_str("WARNING: The use of `changelog-seen` is deprecated. Please refer to `change-id` option in `config.example.toml` instead.\n");
     }
 
-    let latest_config_id = CONFIG_CHANGE_HISTORY.last().unwrap();
+    let latest_change_id = CONFIG_CHANGE_HISTORY.last().unwrap().change_id;
+    let warned_id_path = config.out.join("bootstrap").join(".last-warned-change-id");
+
     if let Some(id) = config.change_id {
-        if &id == latest_config_id {
+        if id == latest_change_id {
             return None;
         }
 
-        let change_links: Vec<String> = find_recent_config_change_ids(id)
-            .iter()
-            .map(|id| format!("https://github.com/rust-lang/rust/pull/{id}"))
-            .collect();
-        if !change_links.is_empty() {
-            msg.push_str("WARNING: there have been changes to x.py since you last updated.\n");
-            msg.push_str("To see more detail about these changes, visit the following PRs:\n");
-
-            for link in change_links {
-                msg.push_str(&format!("  - {link}\n"));
+        if let Ok(last_warned_id) = fs::read_to_string(&warned_id_path) {
+            if latest_change_id.to_string() == last_warned_id {
+                return None;
             }
+        }
+
+        let changes = find_recent_config_change_ids(id);
+
+        if !changes.is_empty() {
+            msg.push_str("There have been changes to x.py since you last updated:\n");
 
-            msg.push_str("WARNING: there have been changes to x.py since you last updated.\n");
+            for change in changes {
+                msg.push_str(&format!("  [{}] {}\n", change.severity.to_string(), change.summary));
+                msg.push_str(&format!(
+                    "    - PR Link https://github.com/rust-lang/rust/pull/{}\n",
+                    change.change_id
+                ));
+            }
 
             msg.push_str("NOTE: to silence this warning, ");
             msg.push_str(&format!(
-                "update `config.toml` to use `change-id = {latest_config_id}` instead"
+                "update `config.toml` to use `change-id = {latest_change_id}` instead"
             ));
+
+            if io::stdout().is_terminal() && !config.dry_run() {
+                t!(fs::write(warned_id_path, latest_change_id.to_string()));
+            }
         }
     } else {
         msg.push_str("WARNING: The `change-id` is missing in the `config.toml`. This means that you will not be able to track the major changes made to the bootstrap configurations.\n");
         msg.push_str("NOTE: to silence this warning, ");
-        msg.push_str(&format!("add `change-id = {latest_config_id}` at the top of `config.toml`"));
+        msg.push_str(&format!("add `change-id = {latest_change_id}` at the top of `config.toml`"));
     };
 
     Some(msg)
diff --git a/src/bootstrap/src/bin/rustc.rs b/src/bootstrap/src/bin/rustc.rs
index 070a2da6a..38c55b203 100644
--- a/src/bootstrap/src/bin/rustc.rs
+++ b/src/bootstrap/src/bin/rustc.rs
@@ -16,11 +16,11 @@
 //! never get replaced.
 
 use std::env;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::process::{Child, Command};
 use std::time::Instant;
 
-use dylib_util::{dylib_path, dylib_path_var};
+use dylib_util::{dylib_path, dylib_path_var, exe};
 
 #[path = "../utils/bin_helpers.rs"]
 mod bin_helpers;
@@ -29,12 +29,12 @@ mod bin_helpers;
 mod dylib_util;
 
 fn main() {
-    let args = env::args_os().skip(1).collect::<Vec<_>>();
-    let arg = |name| args.windows(2).find(|args| args[0] == name).and_then(|args| args[1].to_str());
+    let orig_args = env::args_os().skip(1).collect::<Vec<_>>();
+    let mut args = orig_args.clone();
+    let arg =
+        |name| orig_args.windows(2).find(|args| args[0] == name).and_then(|args| args[1].to_str());
 
-    // We don't use the stage in this shim, but let's parse it to make sure that we're invoked
-    // by bootstrap, or that we provide a helpful error message if not.
-    bin_helpers::parse_rustc_stage();
+    let stage = bin_helpers::parse_rustc_stage();
     let verbose = bin_helpers::parse_rustc_verbose();
 
     // Detect whether or not we're a build script depending on whether --target
@@ -47,7 +47,8 @@ fn main() {
     // determine the version of the compiler, the real compiler needs to be
     // used. Currently, these two states are differentiated based on whether
     // --target and -vV is/isn't passed.
-    let (rustc, libdir) = if target.is_none() && version.is_none() {
+    let is_build_script = target.is_none() && version.is_none();
+    let (rustc, libdir) = if is_build_script {
         ("RUSTC_SNAPSHOT", "RUSTC_SNAPSHOT_LIBDIR")
     } else {
         ("RUSTC_REAL", "RUSTC_LIBDIR")
@@ -56,12 +57,47 @@ fn main() {
     let sysroot = env::var_os("RUSTC_SYSROOT").expect("RUSTC_SYSROOT was not set");
     let on_fail = env::var_os("RUSTC_ON_FAIL").map(Command::new);
 
-    let rustc = env::var_os(rustc).unwrap_or_else(|| panic!("{:?} was not set", rustc));
+    let rustc_real = env::var_os(rustc).unwrap_or_else(|| panic!("{:?} was not set", rustc));
     let libdir = env::var_os(libdir).unwrap_or_else(|| panic!("{:?} was not set", libdir));
     let mut dylib_path = dylib_path();
     dylib_path.insert(0, PathBuf::from(&libdir));
 
-    let mut cmd = Command::new(rustc);
+    // if we're running clippy, trust cargo-clippy to set clippy-driver appropriately (and don't override it with rustc).
+    // otherwise, substitute whatever cargo thinks rustc should be with RUSTC_REAL.
+    // NOTE: this means we ignore RUSTC in the environment.
+    // FIXME: We might want to consider removing RUSTC_REAL and setting RUSTC directly?
+    // NOTE: we intentionally pass the name of the host, not the target.
+    let host = env::var("CFG_COMPILER_BUILD_TRIPLE").unwrap();
+    let is_clippy = args[0].to_string_lossy().ends_with(&exe("clippy-driver", &host));
+    let rustc_driver = if is_clippy {
+        if is_build_script {
+            // Don't run clippy on build scripts (for one thing, we may not have libstd built with
+            // the appropriate version yet, e.g. for stage 1 std).
+            // Also remove the `clippy-driver` param in addition to the RUSTC param.
+            args.drain(..2);
+            rustc_real
+        } else {
+            args.remove(0)
+        }
+    } else {
+        // Cargo doesn't respect RUSTC_WRAPPER for version information >:(
+        // don't remove the first arg if we're being run as RUSTC instead of RUSTC_WRAPPER.
+        // Cargo also sometimes doesn't pass the `.exe` suffix on Windows - add it manually.
+        let current_exe = env::current_exe().expect("couldn't get path to rustc shim");
+        let arg0 = exe(args[0].to_str().expect("only utf8 paths are supported"), &host);
+        if Path::new(&arg0) == current_exe {
+            args.remove(0);
+        }
+        rustc_real
+    };
+
+    let mut cmd = if let Some(wrapper) = env::var_os("RUSTC_WRAPPER_REAL") {
+        let mut cmd = Command::new(wrapper);
+        cmd.arg(rustc_driver);
+        cmd
+    } else {
+        Command::new(rustc_driver)
+    };
     cmd.args(&args).env(dylib_path_var(), env::join_paths(&dylib_path).unwrap());
 
     // Get the name of the crate we're compiling, if any.
@@ -114,7 +150,7 @@ fn main() {
         {
             cmd.arg("-Ztls-model=initial-exec");
         }
-    } else {
+    } else if std::env::var("MIRI").is_err() {
         // Find any host flags that were passed by bootstrap.
         // The flags are stored in a RUSTC_HOST_FLAGS variable, separated by spaces.
         if let Ok(flags) = std::env::var("RUSTC_HOST_FLAGS") {
@@ -214,6 +250,8 @@ fn main() {
         }
     }
 
+    bin_helpers::maybe_dump(format!("stage{stage}-rustc"), &cmd);
+
     let start = Instant::now();
     let (child, status) = {
         let errmsg = format!("\nFailed to run:\n{cmd:?}\n-------------");
diff --git a/src/bootstrap/src/bin/rustdoc.rs b/src/bootstrap/src/bin/rustdoc.rs
index dbbce6fe2..b4d141518 100644
--- a/src/bootstrap/src/bin/rustdoc.rs
+++ b/src/bootstrap/src/bin/rustdoc.rs
@@ -3,7 +3,6 @@
 //! See comments in `src/bootstrap/rustc.rs` for more information.
 
 use std::env;
-use std::ffi::OsString;
 use std::path::PathBuf;
 use std::process::Command;
 
@@ -52,15 +51,6 @@ fn main() {
     if env::var_os("RUSTC_FORCE_UNSTABLE").is_some() {
         cmd.arg("-Z").arg("force-unstable-if-unmarked");
     }
-    if let Some(linker) = env::var_os("RUSTDOC_LINKER") {
-        let mut arg = OsString::from("-Clinker=");
-        arg.push(&linker);
-        cmd.arg(arg);
-    }
-    if let Ok(no_threads) = env::var("RUSTDOC_LLD_NO_THREADS") {
-        cmd.arg("-Clink-arg=-fuse-ld=lld");
-        cmd.arg(format!("-Clink-arg=-Wl,{no_threads}"));
-    }
     // Cargo doesn't pass RUSTDOCFLAGS to proc_macros:
     // https://github.com/rust-lang/cargo/issues/4423
     // Thus, if we are on stage 0, we explicitly set `--cfg=bootstrap`.
@@ -70,9 +60,9 @@ fn main() {
         cmd.arg("--cfg=bootstrap");
     }
     cmd.arg("-Zunstable-options");
-    // #[cfg(bootstrap)]
-    cmd.arg("--check-cfg=values(bootstrap)");
-    // cmd.arg("--check-cfg=cfg(bootstrap)");
+    cmd.arg("--check-cfg=cfg(bootstrap)");
+
+    bin_helpers::maybe_dump(format!("stage{stage}-rustdoc"), &cmd);
 
     if verbose > 1 {
         eprintln!(
diff --git a/src/bootstrap/src/core/build_steps/check.rs b/src/bootstrap/src/core/build_steps/check.rs
index 121925b56..ecaaf91ae 100644
--- a/src/bootstrap/src/core/build_steps/check.rs
+++ b/src/bootstrap/src/core/build_steps/check.rs
@@ -376,12 +376,12 @@ impl Step for RustAnalyzer {
         let compiler = builder.compiler(builder.top_stage, builder.config.build);
         let target = self.target;
 
-        builder.ensure(Std::new(target));
+        builder.ensure(Rustc::new(target, builder));
 
         let mut cargo = prepare_tool_cargo(
             builder,
             compiler,
-            Mode::ToolStd,
+            Mode::ToolRustc,
             target,
             cargo_subcommand(builder.kind),
             "src/tools/rust-analyzer",
@@ -414,7 +414,7 @@ impl Step for RustAnalyzer {
         /// Cargo's output path in a given stage, compiled by a particular
         /// compiler for the specified target.
         fn stamp(builder: &Builder<'_>, compiler: Compiler, target: TargetSelection) -> PathBuf {
-            builder.cargo_out(compiler, Mode::ToolStd, target).join(".rust-analyzer-check.stamp")
+            builder.cargo_out(compiler, Mode::ToolRustc, target).join(".rust-analyzer-check.stamp")
         }
     }
 }
@@ -463,10 +463,6 @@ macro_rules! tool_check_step {
                     cargo.arg("--all-targets");
                 }
 
-                // Enable internal lints for clippy and rustdoc
-                // NOTE: this doesn't enable lints for any other tools unless they explicitly add `#![warn(rustc::internal)]`
-                // See https://github.com/rust-lang/rust/pull/80573#issuecomment-754010776
-                cargo.rustflag("-Zunstable-options");
                 let _guard = builder.msg_check(&concat!(stringify!($name), " artifacts").to_lowercase(), target);
                 run_cargo(
                     builder,
diff --git a/src/bootstrap/src/core/build_steps/clean.rs b/src/bootstrap/src/core/build_steps/clean.rs
index cbb6b5f46..4b993945f 100644
--- a/src/bootstrap/src/core/build_steps/clean.rs
+++ b/src/bootstrap/src/core/build_steps/clean.rs
@@ -145,10 +145,18 @@ fn clean_specific_stage(build: &Build, stage: u32) {
 fn clean_default(build: &Build) {
     rm_rf(&build.out.join("tmp"));
     rm_rf(&build.out.join("dist"));
+    rm_rf(&build.out.join("bootstrap").join(".last-warned-change-id"));
+    rm_rf(&build.out.join("bootstrap-shims-dump"));
     rm_rf(&build.out.join("rustfmt.stamp"));
 
-    for host in &build.hosts {
-        let entries = match build.out.join(host.triple).read_dir() {
+    let mut hosts: Vec<_> = build.hosts.iter().map(|t| build.out.join(t.triple)).collect();
+    // After cross-compilation, artifacts of the host architecture (which may differ from build.host)
+    // might not get removed.
+    // Adding its path (linked one for easier accessibility) will solve this problem.
+    hosts.push(build.out.join("host"));
+
+    for host in hosts {
+        let entries = match host.read_dir() {
             Ok(iter) => iter,
             Err(_) => continue,
         };
diff --git a/src/bootstrap/src/core/build_steps/compile.rs b/src/bootstrap/src/core/build_steps/compile.rs
index 7021a9543..df4d1a43d 100644
--- a/src/bootstrap/src/core/build_steps/compile.rs
+++ b/src/bootstrap/src/core/build_steps/compile.rs
@@ -592,7 +592,9 @@ impl Step for StdLink {
                 .join("stage0/lib/rustlib")
                 .join(&host)
                 .join("codegen-backends");
-            builder.cp_r(&stage0_codegen_backends, &sysroot_codegen_backends);
+            if stage0_codegen_backends.exists() {
+                builder.cp_r(&stage0_codegen_backends, &sysroot_codegen_backends);
+            }
         }
     }
 }
@@ -868,7 +870,7 @@ impl Step for Rustc {
         // 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.use_lld && !compiler.host.contains("msvc") {
+        if builder.config.lld_mode.is_used() && !compiler.host.is_msvc() {
             cargo.rustflag("-Clink-args=-Wl,--icf=all");
         }
 
@@ -885,7 +887,9 @@ impl Step for Rustc {
         } else if let Some(path) = &builder.config.rust_profile_use {
             if compiler.stage == 1 {
                 cargo.rustflag(&format!("-Cprofile-use={path}"));
-                cargo.rustflag("-Cllvm-args=-pgo-warn-missing-function");
+                if builder.is_verbose() {
+                    cargo.rustflag("-Cllvm-args=-pgo-warn-missing-function");
+                }
                 true
             } else {
                 false
@@ -1001,6 +1005,13 @@ pub fn rustc_cargo_env(
         .env("CFG_RELEASE_CHANNEL", &builder.config.channel)
         .env("CFG_VERSION", builder.rust_version());
 
+    // Some tools like Cargo detect their own git information in build scripts. When omit-git-hash
+    // is enabled in config.toml, we pass this environment variable to tell build scripts to avoid
+    // detecting git information on their own.
+    if builder.config.omit_git_hash {
+        cargo.env("CFG_OMIT_GIT_HASH", "1");
+    }
+
     if let Some(backend) = builder.config.default_codegen_backend() {
         cargo.env("CFG_DEFAULT_CODEGEN_BACKEND", backend);
     }
@@ -1078,7 +1089,7 @@ fn rustc_llvm_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelect
     // found. This is to avoid the linker errors about undefined references to
     // `__llvm_profile_instrument_memop` when linking `rustc_driver`.
     let mut llvm_linker_flags = String::new();
-    if builder.config.llvm_profile_generate && target.contains("msvc") {
+    if builder.config.llvm_profile_generate && target.is_msvc() {
         if let Some(ref clang_cl_path) = builder.config.llvm_clang_cl {
             // Add clang's runtime library directory to the search path
             let clang_rt_dir = get_clang_cl_resource_dir(clang_cl_path);
@@ -1103,7 +1114,7 @@ fn rustc_llvm_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelect
     // not for MSVC or macOS
     if builder.config.llvm_static_stdcpp
         && !target.contains("freebsd")
-        && !target.contains("msvc")
+        && !target.is_msvc()
         && !target.contains("apple")
         && !target.contains("solaris")
     {
@@ -1711,7 +1722,7 @@ impl Step for Assemble {
             let dst_exe = exe("rust-lld", target_compiler.host);
             builder.copy(&lld_install.join("bin").join(&src_exe), &libdir_bin.join(&dst_exe));
             let self_contained_lld_dir = libdir_bin.join("gcc-ld");
-            t!(fs::create_dir(&self_contained_lld_dir));
+            t!(fs::create_dir_all(&self_contained_lld_dir));
             let lld_wrapper_exe = builder.ensure(crate::core::build_steps::tool::LldWrapper {
                 compiler: build_compiler,
                 target: target_compiler.host,
@@ -1798,10 +1809,6 @@ pub fn run_cargo(
     is_check: bool,
     rlib_only_metadata: bool,
 ) -> Vec<PathBuf> {
-    if builder.config.dry_run() {
-        return Vec::new();
-    }
-
     // `target_root_dir` looks like $dir/$target/release
     let target_root_dir = stamp.parent().unwrap();
     // `target_deps_dir` looks like $dir/$target/release/deps
@@ -1908,6 +1915,10 @@ pub fn run_cargo(
         crate::exit!(1);
     }
 
+    if builder.config.dry_run() {
+        return Vec::new();
+    }
+
     // Ok now we need to actually find all the files listed in `toplevel`. We've
     // got a list of prefix/extensions and we basically just need to find the
     // most recent file in the `deps` folder corresponding to each one.
@@ -1963,9 +1974,6 @@ pub fn stream_cargo(
     cb: &mut dyn FnMut(CargoMessage<'_>),
 ) -> bool {
     let mut cargo = Command::from(cargo);
-    if builder.config.dry_run() {
-        return true;
-    }
     // Instruct Cargo to give us json messages on stdout, critically leaving
     // stderr as piped so we can get those pretty colors.
     let mut message_format = if builder.config.json_output {
@@ -1984,6 +1992,11 @@ pub fn stream_cargo(
     }
 
     builder.verbose(&format!("running: {cargo:?}"));
+
+    if builder.config.dry_run() {
+        return true;
+    }
+
     let mut child = match cargo.spawn() {
         Ok(child) => child,
         Err(e) => panic!("failed to execute command: {cargo:?}\nERROR: {e}"),
diff --git a/src/bootstrap/src/core/build_steps/dist.rs b/src/bootstrap/src/core/build_steps/dist.rs
index c485481b9..98e267713 100644
--- a/src/bootstrap/src/core/build_steps/dist.rs
+++ b/src/bootstrap/src/core/build_steps/dist.rs
@@ -1319,7 +1319,7 @@ impl Step for CodegenBackend {
                 return None;
             }
 
-            if self.compiler.host.contains("windows") {
+            if self.compiler.host.is_windows() {
                 builder.info(
                     "dist currently disabled for windows by rustc_codegen_cranelift. skipping",
                 );
@@ -1658,7 +1658,7 @@ impl Step for Extended {
             builder.run(&mut cmd);
         }
 
-        if target.contains("windows") {
+        if target.is_windows() {
             let exe = tmp.join("exe");
             let _ = fs::remove_dir_all(&exe);
 
diff --git a/src/bootstrap/src/core/build_steps/doc.rs b/src/bootstrap/src/core/build_steps/doc.rs
index e3fd942fc..cf3f5bc98 100644
--- a/src/bootstrap/src/core/build_steps/doc.rs
+++ b/src/bootstrap/src/core/build_steps/doc.rs
@@ -7,8 +7,9 @@
 //! Everything here is basically just a shim around calling either `rustbook` or
 //! `rustdoc`.
 
-use std::fs;
+use std::io::{self, Write};
 use std::path::{Path, PathBuf};
+use std::{fs, mem};
 
 use crate::core::build_steps::compile;
 use crate::core::build_steps::tool::{self, prepare_tool_cargo, SourceType, Tool};
@@ -388,6 +389,104 @@ impl Step for Standalone {
     }
 }
 
+#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
+pub struct Releases {
+    compiler: Compiler,
+    target: TargetSelection,
+}
+
+impl Step for Releases {
+    type Output = ();
+    const DEFAULT: bool = true;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        let builder = run.builder;
+        run.path("RELEASES.md").alias("releases").default_condition(builder.config.docs)
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(Releases {
+            compiler: run.builder.compiler(run.builder.top_stage, run.builder.config.build),
+            target: run.target,
+        });
+    }
+
+    /// Generates HTML release notes to include in the final docs bundle.
+    ///
+    /// This uses the same stylesheet and other tools as Standalone, but the
+    /// RELEASES.md file is included at the root of the repository and gets
+    /// the headline added. In the end, the conversion is done by Rustdoc.
+    fn run(self, builder: &Builder<'_>) {
+        let target = self.target;
+        let compiler = self.compiler;
+        let _guard = builder.msg_doc(compiler, "releases", target);
+        let out = builder.doc_out(target);
+        t!(fs::create_dir_all(&out));
+
+        builder.ensure(Standalone {
+            compiler: builder.compiler(builder.top_stage, builder.config.build),
+            target,
+        });
+
+        let version_info = builder.ensure(SharedAssets { target: self.target }).version_info;
+
+        let favicon = builder.src.join("src/doc/favicon.inc");
+        let footer = builder.src.join("src/doc/footer.inc");
+        let full_toc = builder.src.join("src/doc/full-toc.inc");
+
+        let html = out.join("releases.html");
+        let tmppath = out.join("releases.md");
+        let inpath = builder.src.join("RELEASES.md");
+        let rustdoc = builder.rustdoc(compiler);
+        if !up_to_date(&inpath, &html)
+            || !up_to_date(&footer, &html)
+            || !up_to_date(&favicon, &html)
+            || !up_to_date(&full_toc, &html)
+            || !(builder.config.dry_run()
+                || up_to_date(&version_info, &html)
+                || up_to_date(&rustdoc, &html))
+        {
+            let mut tmpfile = t!(fs::File::create(&tmppath));
+            t!(tmpfile.write_all(b"% Rust Release Notes\n\n"));
+            t!(io::copy(&mut t!(fs::File::open(&inpath)), &mut tmpfile));
+            mem::drop(tmpfile);
+            let mut cmd = builder.rustdoc_cmd(compiler);
+
+            // Needed for --index-page flag
+            cmd.arg("-Z").arg("unstable-options");
+
+            cmd.arg("--html-after-content")
+                .arg(&footer)
+                .arg("--html-before-content")
+                .arg(&version_info)
+                .arg("--html-in-header")
+                .arg(&favicon)
+                .arg("--markdown-no-toc")
+                .arg("--markdown-css")
+                .arg("rust.css")
+                .arg("--index-page")
+                .arg(&builder.src.join("src/doc/index.md"))
+                .arg("--markdown-playground-url")
+                .arg("https://play.rust-lang.org/")
+                .arg("-o")
+                .arg(&out)
+                .arg(&tmppath);
+
+            if !builder.config.docs_minification {
+                cmd.arg("--disable-minification");
+            }
+
+            builder.run(&mut cmd);
+        }
+
+        // We open doc/RELEASES.html as the default if invoked as `x.py doc --open RELEASES.md`
+        // with no particular explicit doc requested (e.g. library/core).
+        if builder.was_invoked_explicitly::<Self>(Kind::Doc) {
+            builder.open_in_browser(&html);
+        }
+    }
+}
+
 #[derive(Debug, Clone)]
 pub struct SharedAssetsPaths {
     pub version_info: PathBuf,
@@ -897,15 +996,14 @@ tool_doc!(
     in_tree = false,
     crates = [
         "cargo",
+        "cargo-credential",
         "cargo-platform",
-        "cargo-util",
-        "crates-io",
         "cargo-test-macro",
         "cargo-test-support",
-        "cargo-credential",
+        "cargo-util",
+        "crates-io",
         "mdman",
-        // FIXME: this trips a license check in tidy.
-        // "resolver-tests",
+        "rustfix",
     ]
 );
 tool_doc!(Tidy, "tidy", "src/tools/tidy", rustc_tool = false, crates = ["tidy"]);
diff --git a/src/bootstrap/src/core/build_steps/format.rs b/src/bootstrap/src/core/build_steps/format.rs
index 86f1d925f..e792d38b7 100644
--- a/src/bootstrap/src/core/build_steps/format.rs
+++ b/src/bootstrap/src/core/build_steps/format.rs
@@ -142,14 +142,17 @@ pub fn format(build: &Builder<'_>, check: bool, paths: &[PathBuf]) {
         };
         if in_working_tree {
             let untracked_paths_output = output(
-                build.config.git().arg("status").arg("--porcelain").arg("--untracked-files=normal"),
+                build
+                    .config
+                    .git()
+                    .arg("status")
+                    .arg("--porcelain")
+                    .arg("-z")
+                    .arg("--untracked-files=normal"),
+            );
+            let untracked_paths = untracked_paths_output.split_terminator('\0').filter_map(
+                |entry| entry.strip_prefix("?? "), // returns None if the prefix doesn't match
             );
-            let untracked_paths = untracked_paths_output
-                .lines()
-                .filter(|entry| entry.starts_with("??"))
-                .map(|entry| {
-                    entry.split(' ').nth(1).expect("every git status entry should list a path")
-                });
             let mut untracked_count = 0;
             for untracked_path in untracked_paths {
                 println!("skip untracked path {untracked_path} during rustfmt invocations");
diff --git a/src/bootstrap/src/core/build_steps/llvm.rs b/src/bootstrap/src/core/build_steps/llvm.rs
index a1f6fac8a..4b2d3e9ab 100644
--- a/src/bootstrap/src/core/build_steps/llvm.rs
+++ b/src/bootstrap/src/core/build_steps/llvm.rs
@@ -15,12 +15,13 @@ use std::fs::{self, File};
 use std::io;
 use std::path::{Path, PathBuf};
 use std::process::Command;
+use std::sync::OnceLock;
 
 use crate::core::builder::{Builder, RunConfig, ShouldRun, Step};
 use crate::core::config::{Config, TargetSelection};
 use crate::utils::channel;
 use crate::utils::helpers::{self, exe, get_clang_cl_resource_dir, output, t, up_to_date};
-use crate::{CLang, GitRepo, Kind};
+use crate::{generate_smart_stamp_hash, CLang, GitRepo, Kind};
 
 use build_helper::ci::CiEnv;
 use build_helper::git::get_git_merge_base;
@@ -97,7 +98,7 @@ pub fn prebuilt_llvm_config(
     let out_dir = builder.llvm_out(target);
 
     let mut llvm_config_ret_dir = builder.llvm_out(builder.config.build);
-    if !builder.config.build.contains("msvc") || builder.ninja() {
+    if !builder.config.build.is_msvc() || builder.ninja() {
         llvm_config_ret_dir.push("build");
     }
     llvm_config_ret_dir.push("bin");
@@ -105,8 +106,16 @@ pub fn prebuilt_llvm_config(
     let llvm_cmake_dir = out_dir.join("lib/cmake/llvm");
     let res = LlvmResult { llvm_config: build_llvm_config, llvm_cmake_dir };
 
+    static STAMP_HASH_MEMO: OnceLock<String> = OnceLock::new();
+    let smart_stamp_hash = STAMP_HASH_MEMO.get_or_init(|| {
+        generate_smart_stamp_hash(
+            &builder.config.src.join("src/llvm-project"),
+            &builder.in_tree_llvm_info.sha().unwrap_or_default(),
+        )
+    });
+
     let stamp = out_dir.join("llvm-finished-building");
-    let stamp = HashStamp::new(stamp, builder.in_tree_llvm_info.sha());
+    let stamp = HashStamp::new(stamp, Some(smart_stamp_hash));
 
     if stamp.is_done() {
         if stamp.hash.is_none() {
@@ -274,7 +283,7 @@ impl Step for Llvm {
         };
 
         builder.update_submodule(&Path::new("src").join("llvm-project"));
-        if builder.llvm_link_shared() && target.contains("windows") {
+        if builder.llvm_link_shared() && target.is_windows() {
             panic!("shared linking to LLVM is not currently supported on {}", target.triple);
         }
 
@@ -352,7 +361,7 @@ impl Step for Llvm {
         // Disable zstd to avoid a dependency on libzstd.so.
         cfg.define("LLVM_ENABLE_ZSTD", "OFF");
 
-        if !target.contains("windows") {
+        if !target.is_windows() {
             cfg.define("LLVM_ENABLE_ZLIB", "ON");
         } else {
             cfg.define("LLVM_ENABLE_ZLIB", "OFF");
@@ -402,7 +411,7 @@ impl Step for Llvm {
             ldflags.shared.push(" -latomic");
         }
 
-        if target.contains("msvc") {
+        if target.is_msvc() {
             cfg.define("LLVM_USE_CRT_DEBUG", "MT");
             cfg.define("LLVM_USE_CRT_RELEASE", "MT");
             cfg.define("LLVM_USE_CRT_RELWITHDEBINFO", "MT");
@@ -560,11 +569,11 @@ fn check_llvm_version(builder: &Builder<'_>, llvm_config: &Path) {
     let version = output(cmd.arg("--version"));
     let mut parts = version.split('.').take(2).filter_map(|s| s.parse::<u32>().ok());
     if let (Some(major), Some(_minor)) = (parts.next(), parts.next()) {
-        if major >= 15 {
+        if major >= 16 {
             return;
         }
     }
-    panic!("\n\nbad LLVM version: {version}, need >=15.0\n\n")
+    panic!("\n\nbad LLVM version: {version}, need >=16.0\n\n")
 }
 
 fn configure_cmake(
@@ -598,7 +607,7 @@ fn configure_cmake(
             cfg.define("CMAKE_SYSTEM_NAME", "DragonFly");
         } else if target.contains("freebsd") {
             cfg.define("CMAKE_SYSTEM_NAME", "FreeBSD");
-        } else if target.contains("windows") {
+        } else if target.is_windows() {
             cfg.define("CMAKE_SYSTEM_NAME", "Windows");
         } else if target.contains("haiku") {
             cfg.define("CMAKE_SYSTEM_NAME", "Haiku");
@@ -635,7 +644,7 @@ fn configure_cmake(
     }
 
     let sanitize_cc = |cc: &Path| {
-        if target.contains("msvc") {
+        if target.is_msvc() {
             OsString::from(cc.to_str().unwrap().replace("\\", "/"))
         } else {
             cc.as_os_str().to_owned()
@@ -645,7 +654,7 @@ fn configure_cmake(
     // MSVC with CMake uses msbuild by default which doesn't respect these
     // vars that we'd otherwise configure. In that case we just skip this
     // entirely.
-    if target.contains("msvc") && !builder.ninja() {
+    if target.is_msvc() && !builder.ninja() {
         return;
     }
 
@@ -655,7 +664,7 @@ fn configure_cmake(
     };
 
     // Handle msvc + ninja + ccache specially (this is what the bots use)
-    if target.contains("msvc") && builder.ninja() && builder.config.ccache.is_some() {
+    if target.is_msvc() && builder.ninja() && builder.config.ccache.is_some() {
         let mut wrap_cc = env::current_exe().expect("failed to get cwd");
         wrap_cc.set_file_name("sccache-plus-cl.exe");
 
@@ -759,11 +768,11 @@ fn configure_cmake(
     // For distribution we want the LLVM tools to be *statically* linked to libstdc++.
     // We also do this if the user explicitly requested static libstdc++.
     if builder.config.llvm_static_stdcpp
-        && !target.contains("msvc")
+        && !target.is_msvc()
         && !target.contains("netbsd")
         && !target.contains("solaris")
     {
-        if target.contains("apple") || target.contains("windows") {
+        if target.contains("apple") || target.is_windows() {
             ldflags.push_all("-static-libstdc++");
         } else {
             ldflags.push_all("-Wl,-Bsymbolic -static-libstdc++");
@@ -865,7 +874,7 @@ impl Step for Lld {
         // when doing PGO on CI, cmake or clang-cl don't automatically link clang's
         // profiler runtime in. In that case, we need to manually ask cmake to do it, to avoid
         // linking errors, much like LLVM's cmake setup does in that situation.
-        if builder.config.llvm_profile_generate && target.contains("msvc") {
+        if builder.config.llvm_profile_generate && target.is_msvc() {
             if let Some(clang_cl_path) = builder.config.llvm_clang_cl.as_ref() {
                 // Find clang's runtime library directory and push that as a search path to the
                 // cmake linker flags.
@@ -1286,7 +1295,7 @@ impl Step for Libunwind {
                 cfg.define("__LIBUNWIND_IS_NATIVE_ONLY", None);
                 cfg.define("NDEBUG", None);
             }
-            if self.target.contains("windows") {
+            if self.target.is_windows() {
                 cfg.define("_LIBUNWIND_HIDE_SYMBOLS", "1");
                 cfg.define("_LIBUNWIND_IS_NATIVE_ONLY", "1");
             }
diff --git a/src/bootstrap/src/core/build_steps/setup.rs b/src/bootstrap/src/core/build_steps/setup.rs
index 486a1e20f..9c897ae1b 100644
--- a/src/bootstrap/src/core/build_steps/setup.rs
+++ b/src/bootstrap/src/core/build_steps/setup.rs
@@ -1,6 +1,8 @@
 use crate::core::builder::{Builder, RunConfig, ShouldRun, Step};
+use crate::t;
+use crate::utils::change_tracker::CONFIG_CHANGE_HISTORY;
+use crate::utils::helpers::hex_encode;
 use crate::Config;
-use crate::{t, CONFIG_CHANGE_HISTORY};
 use sha2::Digest;
 use std::env::consts::EXE_SUFFIX;
 use std::fmt::Write as _;
@@ -226,7 +228,7 @@ fn setup_config_toml(path: &PathBuf, profile: Profile, config: &Config) {
         return;
     }
 
-    let latest_change_id = CONFIG_CHANGE_HISTORY.last().unwrap();
+    let latest_change_id = CONFIG_CHANGE_HISTORY.last().unwrap().change_id;
     let settings = format!(
         "# Includes one of the default files in src/bootstrap/defaults\n\
     profile = \"{profile}\"\n\
@@ -548,12 +550,13 @@ impl Step for Vscode {
         if config.dry_run() {
             return;
         }
-        t!(create_vscode_settings_maybe(&config));
+        while !t!(create_vscode_settings_maybe(&config)) {}
     }
 }
 
 /// Create a `.vscode/settings.json` file for rustc development, or just print it
-fn create_vscode_settings_maybe(config: &Config) -> io::Result<()> {
+/// If this method should be re-called, it returns `false`.
+fn create_vscode_settings_maybe(config: &Config) -> io::Result<bool> {
     let (current_hash, historical_hashes) = SETTINGS_HASHES.split_last().unwrap();
     let vscode_settings = config.src.join(".vscode").join("settings.json");
     // If None, no settings.json exists
@@ -564,9 +567,9 @@ fn create_vscode_settings_maybe(config: &Config) -> io::Result<()> {
     if let Ok(current) = fs::read_to_string(&vscode_settings) {
         let mut hasher = sha2::Sha256::new();
         hasher.update(&current);
-        let hash = hex::encode(hasher.finalize().as_slice());
+        let hash = hex_encode(hasher.finalize().as_slice());
         if hash == *current_hash {
-            return Ok(());
+            return Ok(true);
         } else if historical_hashes.contains(&hash.as_str()) {
             mismatched_settings = Some(true);
         } else {
@@ -586,13 +589,13 @@ fn create_vscode_settings_maybe(config: &Config) -> io::Result<()> {
         _ => (),
     }
     let should_create = match prompt_user(
-        "Would you like to create/update `settings.json`, or only print suggested settings?: [y/p/N]",
+        "Would you like to create/update settings.json? (Press 'p' to preview values): [y/N]",
     )? {
         Some(PromptResult::Yes) => true,
         Some(PromptResult::Print) => false,
         _ => {
             println!("Ok, skipping settings!");
-            return Ok(());
+            return Ok(true);
         }
     };
     if should_create {
@@ -619,5 +622,5 @@ fn create_vscode_settings_maybe(config: &Config) -> io::Result<()> {
     } else {
         println!("\n{RUST_ANALYZER_SETTINGS}");
     }
-    Ok(())
+    Ok(should_create)
 }
diff --git a/src/bootstrap/src/core/build_steps/synthetic_targets.rs b/src/bootstrap/src/core/build_steps/synthetic_targets.rs
index d2c65b740..9acdcaeb5 100644
--- a/src/bootstrap/src/core/build_steps/synthetic_targets.rs
+++ b/src/bootstrap/src/core/build_steps/synthetic_targets.rs
@@ -59,6 +59,11 @@ fn create_synthetic_target(
     let mut cmd = Command::new(builder.rustc(compiler));
     cmd.arg("--target").arg(base.rustc_target_arg());
     cmd.args(["-Zunstable-options", "--print", "target-spec-json"]);
+
+    // If `rust.channel` is set to either beta or stable, rustc will complain that
+    // we cannot use nightly features. So `RUSTC_BOOTSTRAP` is needed here.
+    cmd.env("RUSTC_BOOTSTRAP", "1");
+
     cmd.stdout(Stdio::piped());
 
     let output = cmd.spawn().unwrap().wait_with_output().unwrap();
diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index d2aa89dee..4eb776625 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -29,8 +29,9 @@ use crate::utils;
 use crate::utils::cache::{Interned, INTERNER};
 use crate::utils::exec::BootstrapCommand;
 use crate::utils::helpers::{
-    self, add_link_lib_path, dylib_path, dylib_path_var, output, t,
-    target_supports_cranelift_backend, up_to_date,
+    self, add_link_lib_path, add_rustdoc_cargo_linker_args, dylib_path, dylib_path_var,
+    linker_args, linker_flags, output, t, target_supports_cranelift_backend, up_to_date,
+    LldThreads,
 };
 use crate::utils::render_tests::{add_flags_and_try_run_tests, try_run_tests};
 use crate::{envify, CLang, DocTests, GitRepo, Mode};
@@ -49,9 +50,9 @@ const MIR_OPT_BLESS_TARGET_MAPPING: &[(&str, &str)] = &[
     ("i686-unknown-linux-musl", "x86_64-unknown-linux-musl"),
     ("i686-pc-windows-msvc", "x86_64-pc-windows-msvc"),
     ("i686-pc-windows-gnu", "x86_64-pc-windows-gnu"),
-    ("i686-apple-darwin", "x86_64-apple-darwin"),
     // ARM Macs don't have a corresponding 32-bit target that they can (easily)
     // build for, so there is no entry for "aarch64-apple-darwin" here.
+    // Likewise, i686 for macOS is no longer possible to build.
 ];
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -271,13 +272,14 @@ impl Step for Cargotest {
 
         let _time = helpers::timeit(&builder);
         let mut cmd = builder.tool_cmd(Tool::CargoTest);
-        builder.run_delaying_failure(
-            cmd.arg(&cargo)
-                .arg(&out_dir)
-                .args(builder.config.test_args())
-                .env("RUSTC", builder.rustc(compiler))
-                .env("RUSTDOC", builder.rustdoc(compiler)),
-        );
+        let mut cmd = cmd
+            .arg(&cargo)
+            .arg(&out_dir)
+            .args(builder.config.test_args())
+            .env("RUSTC", builder.rustc(compiler))
+            .env("RUSTDOC", builder.rustdoc(compiler));
+        add_rustdoc_cargo_linker_args(&mut cmd, builder, compiler.host, LldThreads::No);
+        builder.run_delaying_failure(cmd);
     }
 }
 
@@ -369,7 +371,7 @@ impl Step for RustAnalyzer {
 
         // We don't need to build the whole Rust Analyzer for the proc-macro-srv test suite,
         // but we do need the standard library to be present.
-        builder.ensure(compile::Std::new(compiler, host));
+        builder.ensure(compile::Rustc::new(compiler, host));
 
         let workspace_path = "src/tools/rust-analyzer";
         // until the whole RA test suite runs on `i686`, we only run
@@ -378,7 +380,7 @@ impl Step for RustAnalyzer {
         let mut cargo = tool::prepare_tool_cargo(
             builder,
             compiler,
-            Mode::ToolStd,
+            Mode::ToolRustc,
             host,
             "test",
             crate_path,
@@ -862,15 +864,8 @@ impl Step for RustdocTheme {
             .env("CFG_RELEASE_CHANNEL", &builder.config.channel)
             .env("RUSTDOC_REAL", builder.rustdoc(self.compiler))
             .env("RUSTC_BOOTSTRAP", "1");
-        if let Some(linker) = builder.linker(self.compiler.host) {
-            cmd.env("RUSTDOC_LINKER", linker);
-        }
-        if builder.is_fuse_ld_lld(self.compiler.host) {
-            cmd.env(
-                "RUSTDOC_LLD_NO_THREADS",
-                helpers::lld_flag_no_threads(self.compiler.host.contains("windows")),
-            );
-        }
+        cmd.args(linker_args(builder, self.compiler.host, LldThreads::No));
+
         builder.run_delaying_failure(&mut cmd);
     }
 }
@@ -1005,6 +1000,7 @@ impl Step for RustdocGUI {
         let run = run.suite_path("tests/rustdoc-gui");
         run.lazy_default_condition(Box::new(move || {
             builder.config.nodejs.is_some()
+                && builder.doc_tests != DocTests::Only
                 && builder
                     .config
                     .npm
@@ -1044,6 +1040,8 @@ impl Step for RustdocGUI {
         cmd.env("RUSTDOC", builder.rustdoc(self.compiler))
             .env("RUSTC", builder.rustc(self.compiler));
 
+        add_rustdoc_cargo_linker_args(&mut cmd, builder, self.compiler.host, LldThreads::No);
+
         for path in &builder.paths {
             if let Some(p) = helpers::is_valid_test_suite_arg(path, "tests/rustdoc-gui", builder) {
                 if !p.ends_with(".goml") {
@@ -1162,7 +1160,8 @@ HELP: to skip test's attempt to check tidiness, pass `--skip src/tools/tidy` to
     }
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
-        run.path("src/tools/tidy")
+        let default = run.builder.doc_tests != DocTests::Only;
+        run.path("src/tools/tidy").default_condition(default)
     }
 
     fn make_run(run: RunConfig<'_>) {
@@ -1564,6 +1563,10 @@ impl Step for Compiletest {
     /// compiletest `mode` and `suite` arguments. For example `mode` can be
     /// "run-pass" or `suite` can be something like `debuginfo`.
     fn run(self, builder: &Builder<'_>) {
+        if builder.doc_tests == DocTests::Only {
+            return;
+        }
+
         if builder.top_stage == 0 && env::var("COMPILETEST_FORCE_STAGE0").is_err() {
             eprintln!("\
 ERROR: `--stage 0` runs compiletest on the beta compiler, not your local changes, and will almost always cause tests to fail
@@ -1594,8 +1597,13 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
         // NOTE: Only stage 1 is special cased because we need the rustc_private artifacts to match the
         // running compiler in stage 2 when plugins run.
         let stage_id = if suite == "ui-fulldeps" && compiler.stage == 1 {
-            compiler = builder.compiler(compiler.stage - 1, target);
-            format!("stage{}-{}", compiler.stage + 1, target)
+            // At stage 0 (stage - 1) we are using the beta compiler. Using `self.target` can lead finding
+            // an incorrect compiler path on cross-targets, as the stage 0 beta compiler is always equal
+            // to `build.build` in the configuration.
+            let build = builder.build.build;
+
+            compiler = builder.compiler(compiler.stage - 1, build);
+            format!("stage{}-{}", compiler.stage + 1, build)
         } else {
             format!("stage{}-{}", compiler.stage, target)
         };
@@ -1744,14 +1752,14 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
 
         let mut hostflags = flags.clone();
         hostflags.push(format!("-Lnative={}", builder.test_helpers_out(compiler.host).display()));
-        hostflags.extend(builder.lld_flags(compiler.host));
+        hostflags.extend(linker_flags(builder, compiler.host, LldThreads::No));
         for flag in hostflags {
             cmd.arg("--host-rustcflags").arg(flag);
         }
 
         let mut targetflags = flags;
         targetflags.push(format!("-Lnative={}", builder.test_helpers_out(target).display()));
-        targetflags.extend(builder.lld_flags(target));
+        targetflags.extend(linker_flags(builder, compiler.host, LldThreads::No));
         for flag in targetflags {
             cmd.arg("--target-rustcflags").arg(flag);
         }
@@ -1825,6 +1833,10 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
 
         cmd.arg("--json");
 
+        if builder.config.rust_debug_assertions_std {
+            cmd.arg("--with-debug-assertions");
+        };
+
         let mut llvm_components_passed = false;
         let mut copts_passed = false;
         if builder.config.llvm_enabled() {
@@ -1925,13 +1937,18 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
         //
         // Note that if we encounter `PATH` we make sure to append to our own `PATH`
         // rather than stomp over it.
-        if !builder.config.dry_run() && target.contains("msvc") {
+        if !builder.config.dry_run() && target.is_msvc() {
             for &(ref k, ref v) in builder.cc.borrow()[&target].env() {
                 if k != "PATH" {
                     cmd.env(k, v);
                 }
             }
         }
+
+        // Some UI tests trigger behavior in rustc where it reads $CARGO and changes behavior if it exists.
+        // To make the tests work that rely on it not being set, make sure it is not set.
+        cmd.env_remove("CARGO");
+
         cmd.env("RUSTC_BOOTSTRAP", "1");
         // Override the rustc version used in symbol hashes to reduce the amount of normalization
         // needed when diffing test output.
@@ -2322,6 +2339,8 @@ impl Step for CrateLibrustc {
     }
 
     fn run(self, builder: &Builder<'_>) {
+        builder.ensure(compile::Std::new(self.compiler, self.target));
+
         builder.ensure(Crate {
             compiler: self.compiler,
             target: self.target,
@@ -3057,7 +3076,7 @@ impl Step for TestHelpers {
         // We may have found various cross-compilers a little differently due to our
         // extra configuration, so inform cc of these compilers. Note, though, that
         // on MSVC we still need cc's detection of env vars (ugh).
-        if !target.contains("msvc") {
+        if !target.is_msvc() {
             if let Some(ar) = builder.ar(target) {
                 cfg.archiver(ar);
             }
diff --git a/src/bootstrap/src/core/build_steps/tool.rs b/src/bootstrap/src/core/build_steps/tool.rs
index d1bc05e51..9942f00a0 100644
--- a/src/bootstrap/src/core/build_steps/tool.rs
+++ b/src/bootstrap/src/core/build_steps/tool.rs
@@ -203,6 +203,16 @@ pub fn prepare_tool_cargo(
     if !features.is_empty() {
         cargo.arg("--features").arg(&features.join(", "));
     }
+
+    // Enable internal lints for clippy and rustdoc
+    // NOTE: this doesn't enable lints for any other tools unless they explicitly add `#![warn(rustc::internal)]`
+    // See https://github.com/rust-lang/rust/pull/80573#issuecomment-754010776
+    //
+    // NOTE: We unconditionally set this here to avoid recompiling tools between `x check $tool`
+    // and `x test $tool` executions.
+    // See https://github.com/rust-lang/rust/issues/116538
+    cargo.rustflag("-Zunstable-options");
+
     cargo
 }
 
@@ -603,8 +613,7 @@ pub struct RustAnalyzer {
 }
 
 impl RustAnalyzer {
-    pub const ALLOW_FEATURES: &'static str =
-        "proc_macro_internals,proc_macro_diagnostic,proc_macro_span,proc_macro_span_shrink";
+    pub const ALLOW_FEATURES: &'static str = "rustc_private,proc_macro_internals,proc_macro_diagnostic,proc_macro_span,proc_macro_span_shrink";
 }
 
 impl Step for RustAnalyzer {
@@ -636,7 +645,7 @@ impl Step for RustAnalyzer {
             compiler: self.compiler,
             target: self.target,
             tool: "rust-analyzer",
-            mode: Mode::ToolStd,
+            mode: Mode::ToolRustc,
             path: "src/tools/rust-analyzer",
             extra_features: vec!["rust-analyzer/in-rust-tree".to_owned()],
             is_optional_tool: false,
@@ -824,7 +833,7 @@ impl<'a> Builder<'a> {
         // On MSVC a tool may invoke a C compiler (e.g., compiletest in run-make
         // mode) and that C compiler may need some extra PATH modification. Do
         // so here.
-        if compiler.host.contains("msvc") {
+        if compiler.host.is_msvc() {
             let curpaths = env::var_os("PATH").unwrap_or_default();
             let curpaths = env::split_paths(&curpaths).collect::<Vec<_>>();
             for &(ref k, ref v) in self.cc.borrow()[&compiler.host].env() {
diff --git a/src/bootstrap/src/core/builder.rs b/src/bootstrap/src/core/builder.rs
index cd276674d..e18096443 100644
--- a/src/bootstrap/src/core/builder.rs
+++ b/src/bootstrap/src/core/builder.rs
@@ -10,6 +10,7 @@ use std::io::{BufRead, BufReader};
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
 use std::process::Command;
+use std::sync::OnceLock;
 use std::time::{Duration, Instant};
 
 use crate::core::build_steps::llvm;
@@ -17,19 +18,18 @@ use crate::core::build_steps::tool::{self, SourceType};
 use crate::core::build_steps::{check, clean, compile, dist, doc, install, run, setup, test};
 use crate::core::config::flags::{Color, Subcommand};
 use crate::core::config::{DryRun, SplitDebuginfo, TargetSelection};
+use crate::prepare_behaviour_dump_dir;
 use crate::utils::cache::{Cache, Interned, INTERNER};
-use crate::utils::helpers::{self, add_dylib_path, add_link_lib_path, exe, libdir, output, t};
-use crate::Crate;
+use crate::utils::helpers::{self, add_dylib_path, add_link_lib_path, exe, linker_args};
+use crate::utils::helpers::{libdir, linker_flags, output, t, LldThreads};
 use crate::EXTRA_CHECK_CFGS;
-use crate::{Build, CLang, DocTests, GitRepo, Mode};
+use crate::{Build, CLang, Crate, DocTests, GitRepo, Mode};
 
 pub use crate::Compiler;
-// FIXME:
-// - use std::lazy for `Lazy`
-// - use std::cell for `OnceCell`
-// Once they get stabilized and reach beta.
+
 use clap::ValueEnum;
-use once_cell::sync::{Lazy, OnceCell};
+// FIXME: replace with std::lazy after it gets stabilized and reaches beta
+use once_cell::sync::Lazy;
 
 #[cfg(test)]
 #[path = "../tests/builder.rs"]
@@ -495,7 +495,7 @@ impl<'a> ShouldRun<'a> {
     ///
     /// [`path`]: ShouldRun::path
     pub fn paths(mut self, paths: &[&str]) -> Self {
-        static SUBMODULES_PATHS: OnceCell<Vec<String>> = OnceCell::new();
+        static SUBMODULES_PATHS: OnceLock<Vec<String>> = OnceLock::new();
 
         let init_submodules_paths = |src: &PathBuf| {
             let file = File::open(src.join(".gitmodules")).unwrap();
@@ -810,6 +810,7 @@ impl<'a> Builder<'a> {
                 doc::StyleGuide,
                 doc::Tidy,
                 doc::Bootstrap,
+                doc::Releases,
             ),
             Kind::Dist => describe!(
                 dist::Docs,
@@ -1151,6 +1152,44 @@ impl<'a> Builder<'a> {
         self.ensure(tool::Rustdoc { compiler })
     }
 
+    pub fn cargo_clippy_cmd(&self, run_compiler: Compiler) -> Command {
+        let initial_sysroot_bin = self.initial_rustc.parent().unwrap();
+        // Set PATH to include the sysroot bin dir so clippy can find cargo.
+        // FIXME: once rust-clippy#11944 lands on beta, set `CARGO` directly instead.
+        let path = t!(env::join_paths(
+            // The sysroot comes first in PATH to avoid using rustup's cargo.
+            std::iter::once(PathBuf::from(initial_sysroot_bin))
+                .chain(env::split_paths(&t!(env::var("PATH"))))
+        ));
+
+        if run_compiler.stage == 0 {
+            // `ensure(Clippy { stage: 0 })` *builds* clippy with stage0, it doesn't use the beta clippy.
+            let cargo_clippy = self.build.config.download_clippy();
+            let mut cmd = Command::new(cargo_clippy);
+            cmd.env("PATH", &path);
+            return cmd;
+        }
+
+        let build_compiler = self.compiler(run_compiler.stage - 1, self.build.build);
+        self.ensure(tool::Clippy {
+            compiler: build_compiler,
+            target: self.build.build,
+            extra_features: vec![],
+        });
+        let cargo_clippy = self.ensure(tool::CargoClippy {
+            compiler: build_compiler,
+            target: self.build.build,
+            extra_features: vec![],
+        });
+        let mut dylib_path = helpers::dylib_path();
+        dylib_path.insert(0, self.sysroot(run_compiler).join("lib"));
+
+        let mut cmd = Command::new(cargo_clippy.unwrap());
+        cmd.env(helpers::dylib_path_var(), env::join_paths(&dylib_path).unwrap());
+        cmd.env("PATH", path);
+        cmd
+    }
+
     pub fn rustdoc_cmd(&self, compiler: Compiler) -> Command {
         let mut cmd = Command::new(&self.bootstrap_out.join("rustdoc"));
         cmd.env("RUSTC_STAGE", compiler.stage.to_string())
@@ -1173,9 +1212,7 @@ impl<'a> Builder<'a> {
         cmd.env_remove("MAKEFLAGS");
         cmd.env_remove("MFLAGS");
 
-        if let Some(linker) = self.linker(compiler.host) {
-            cmd.env("RUSTDOC_LINKER", linker);
-        }
+        cmd.args(linker_args(self, compiler.host, LldThreads::Yes));
         cmd
     }
 
@@ -1201,7 +1238,12 @@ impl<'a> Builder<'a> {
         target: TargetSelection,
         cmd: &str,
     ) -> Command {
-        let mut cargo = Command::new(&self.initial_cargo);
+        let mut cargo = if cmd == "clippy" {
+            self.cargo_clippy_cmd(compiler)
+        } else {
+            Command::new(&self.initial_cargo)
+        };
+
         // Run cargo from the source root so it can find .cargo/config.
         // This matters when using vendoring and the working directory is outside the repository.
         cargo.current_dir(&self.src);
@@ -1325,6 +1367,23 @@ impl<'a> Builder<'a> {
             compiler.stage
         };
 
+        // We synthetically interpret a stage0 compiler used to build tools as a
+        // "raw" compiler in that it's the exact snapshot we download. Normally
+        // the stage0 build means it uses libraries build by the stage0
+        // compiler, but for tools we just use the precompiled libraries that
+        // we've downloaded
+        let use_snapshot = mode == Mode::ToolBootstrap;
+        assert!(!use_snapshot || stage == 0 || self.local_rebuild);
+
+        let maybe_sysroot = self.sysroot(compiler);
+        let sysroot = if use_snapshot { self.rustc_snapshot_sysroot() } else { &maybe_sysroot };
+        let libdir = self.rustc_libdir(compiler);
+
+        let sysroot_str = sysroot.as_os_str().to_str().expect("sysroot should be UTF-8");
+        if !matches!(self.config.dry_run, DryRun::SelfCheck) {
+            self.verbose_than(0, &format!("using sysroot {sysroot_str}"));
+        }
+
         let mut rustflags = Rustflags::new(target);
         if stage != 0 {
             if let Ok(s) = env::var("CARGOFLAGS_NOT_BOOTSTRAP") {
@@ -1336,41 +1395,16 @@ impl<'a> Builder<'a> {
                 cargo.args(s.split_whitespace());
             }
             rustflags.env("RUSTFLAGS_BOOTSTRAP");
-            if cmd == "clippy" {
-                // clippy overwrites sysroot if we pass it to cargo.
-                // Pass it directly to clippy instead.
-                // NOTE: this can't be fixed in clippy because we explicitly don't set `RUSTC`,
-                // so it has no way of knowing the sysroot.
-                rustflags.arg("--sysroot");
-                rustflags.arg(
-                    self.sysroot(compiler)
-                        .as_os_str()
-                        .to_str()
-                        .expect("sysroot must be valid UTF-8"),
-                );
-                // Only run clippy on a very limited subset of crates (in particular, not build scripts).
-                cargo.arg("-Zunstable-options");
-                // Explicitly does *not* set `--cfg=bootstrap`, since we're using a nightly clippy.
-                let host_version = Command::new("rustc").arg("--version").output().map_err(|_| ());
-                let output = host_version.and_then(|output| {
-                    if output.status.success() {
-                        Ok(output)
-                    } else {
-                        Err(())
-                    }
-                }).unwrap_or_else(|_| {
-                    eprintln!(
-                        "ERROR: `x.py clippy` requires a host `rustc` toolchain with the `clippy` component"
-                    );
-                    eprintln!("HELP: try `rustup component add clippy`");
-                    crate::exit!(1);
-                });
-                if !t!(std::str::from_utf8(&output.stdout)).contains("nightly") {
-                    rustflags.arg("--cfg=bootstrap");
-                }
-            } else {
-                rustflags.arg("--cfg=bootstrap");
-            }
+            rustflags.arg("--cfg=bootstrap");
+        }
+
+        if cmd == "clippy" {
+            // clippy overwrites sysroot if we pass it to cargo.
+            // Pass it directly to clippy instead.
+            // NOTE: this can't be fixed in clippy because we explicitly don't set `RUSTC`,
+            // so it has no way of knowing the sysroot.
+            rustflags.arg("--sysroot");
+            rustflags.arg(sysroot_str);
         }
 
         let use_new_symbol_mangling = match self.config.rust_new_symbol_mangling {
@@ -1404,9 +1438,6 @@ impl<'a> Builder<'a> {
             rustflags.arg("-Zunstable-options");
         }
 
-        // #[cfg(bootstrap)]
-        let use_new_check_cfg_syntax = self.local_rebuild;
-
         // Enable compile-time checking of `cfg` names, values and Cargo `features`.
         //
         // Note: `std`, `alloc` and `core` imports some dependencies by #[path] (like
@@ -1414,17 +1445,9 @@ impl<'a> Builder<'a> {
         // features but cargo isn't involved in the #[path] process and so cannot pass the
         // complete list of features, so for that reason we don't enable checking of
         // features for std crates.
-        if use_new_check_cfg_syntax {
-            cargo.arg("-Zcheck-cfg");
-            if mode == Mode::Std {
-                rustflags.arg("--check-cfg=cfg(feature,values(any()))");
-            }
-        } else {
-            cargo.arg(if mode != Mode::Std {
-                "-Zcheck-cfg=names,values,output,features"
-            } else {
-                "-Zcheck-cfg=names,values,output"
-            });
+        cargo.arg("-Zcheck-cfg");
+        if mode == Mode::Std {
+            rustflags.arg("--check-cfg=cfg(feature,values(any()))");
         }
 
         // Add extra cfg not defined in/by rustc
@@ -1445,12 +1468,8 @@ impl<'a> Builder<'a> {
                         .collect::<String>(),
                     None => String::new(),
                 };
-                if use_new_check_cfg_syntax {
-                    let values = values.strip_prefix(",").unwrap_or(&values); // remove the first `,`
-                    rustflags.arg(&format!("--check-cfg=cfg({name},values({values}))"));
-                } else {
-                    rustflags.arg(&format!("--check-cfg=values({name}{values})"));
-                }
+                let values = values.strip_prefix(",").unwrap_or(&values); // remove the first `,`
+                rustflags.arg(&format!("--check-cfg=cfg({name},values({values}))"));
             }
         }
 
@@ -1466,11 +1485,7 @@ impl<'a> Builder<'a> {
         // We also declare that the flag is expected, which we need to do to not
         // get warnings about it being unexpected.
         hostflags.arg("-Zunstable-options");
-        if use_new_check_cfg_syntax {
-            hostflags.arg("--check-cfg=cfg(bootstrap)");
-        } else {
-            hostflags.arg("--check-cfg=values(bootstrap)");
-        }
+        hostflags.arg("--check-cfg=cfg(bootstrap)");
 
         // FIXME: It might be better to use the same value for both `RUSTFLAGS` and `RUSTDOCFLAGS`,
         // but this breaks CI. At the very least, stage0 `rustdoc` needs `--cfg bootstrap`. See
@@ -1584,18 +1599,6 @@ impl<'a> Builder<'a> {
 
         let want_rustdoc = self.doc_tests != DocTests::No;
 
-        // We synthetically interpret a stage0 compiler used to build tools as a
-        // "raw" compiler in that it's the exact snapshot we download. Normally
-        // the stage0 build means it uses libraries build by the stage0
-        // compiler, but for tools we just use the precompiled libraries that
-        // we've downloaded
-        let use_snapshot = mode == Mode::ToolBootstrap;
-        assert!(!use_snapshot || stage == 0 || self.local_rebuild);
-
-        let maybe_sysroot = self.sysroot(compiler);
-        let sysroot = if use_snapshot { self.rustc_snapshot_sysroot() } else { &maybe_sysroot };
-        let libdir = self.rustc_libdir(compiler);
-
         // Clear the output directory if the real rustc we're using has changed;
         // Cargo cannot detect this as it thinks rustc is bootstrap/debug/rustc.
         //
@@ -1631,10 +1634,19 @@ impl<'a> Builder<'a> {
             )
             .env("RUSTC_ERROR_METADATA_DST", self.extended_error_dir())
             .env("RUSTC_BREAK_ON_ICE", "1");
-        // Clippy support is a hack and uses the default `cargo-clippy` in path.
-        // Don't override RUSTC so that the `cargo-clippy` in path will be run.
-        if cmd != "clippy" {
-            cargo.env("RUSTC", self.bootstrap_out.join("rustc"));
+
+        // Set RUSTC_WRAPPER to the bootstrap shim, which switches between beta and in-tree
+        // sysroot depending on whether we're building build scripts.
+        // NOTE: we intentionally use RUSTC_WRAPPER so that we can support clippy - RUSTC is not
+        // respected by clippy-driver; RUSTC_WRAPPER happens earlier, before clippy runs.
+        cargo.env("RUSTC_WRAPPER", self.bootstrap_out.join("rustc"));
+        // NOTE: we also need to set RUSTC so cargo can run `rustc -vV`; apparently that ignores RUSTC_WRAPPER >:(
+        cargo.env("RUSTC", self.bootstrap_out.join("rustc"));
+
+        // Someone might have set some previous rustc wrapper (e.g.
+        // sccache) before bootstrap overrode it. Respect that variable.
+        if let Some(existing_wrapper) = env::var_os("RUSTC_WRAPPER") {
+            cargo.env("RUSTC_WRAPPER_REAL", existing_wrapper);
         }
 
         // Dealing with rpath here is a little special, so let's go into some
@@ -1673,10 +1685,7 @@ impl<'a> Builder<'a> {
                 // flesh out rpath support more fully in the future.
                 rustflags.arg("-Zosx-rpath-install-name");
                 Some(format!("-Wl,-rpath,@loader_path/../{libdir}"))
-            } else if !target.contains("windows")
-                && !target.contains("aix")
-                && !target.contains("xous")
-            {
+            } else if !target.is_windows() && !target.contains("aix") && !target.contains("xous") {
                 rustflags.arg("-Clink-args=-Wl,-z,origin");
                 Some(format!("-Wl,-rpath,$ORIGIN/../{libdir}"))
             } else {
@@ -1687,23 +1696,28 @@ impl<'a> Builder<'a> {
             }
         }
 
-        if let Some(host_linker) = self.linker(compiler.host) {
-            hostflags.arg(format!("-Clinker={}", host_linker.display()));
+        cargo.env(profile_var("STRIP"), self.config.rust_strip.to_string());
+
+        if let Some(stack_protector) = &self.config.rust_stack_protector {
+            rustflags.arg(&format!("-Zstack-protector={stack_protector}"));
         }
-        if self.is_fuse_ld_lld(compiler.host) {
-            hostflags.arg("-Clink-args=-fuse-ld=lld");
+
+        for arg in linker_args(self, compiler.host, LldThreads::Yes) {
+            hostflags.arg(&arg);
         }
 
         if let Some(target_linker) = self.linker(target) {
             let target = crate::envify(&target.triple);
             cargo.env(&format!("CARGO_TARGET_{target}_LINKER"), target_linker);
         }
-        if self.is_fuse_ld_lld(target) {
-            rustflags.arg("-Clink-args=-fuse-ld=lld");
+        // We want to set -Clinker using Cargo, therefore we only call `linker_flags` and not
+        // `linker_args` here.
+        for flag in linker_flags(self, target, LldThreads::Yes) {
+            rustflags.arg(&flag);
+        }
+        for arg in linker_args(self, target, LldThreads::Yes) {
+            rustdocflags.arg(&arg);
         }
-        self.lld_flags(target).for_each(|flag| {
-            rustdocflags.arg(&flag);
-        });
 
         if !(["build", "check", "clippy", "fix", "rustc"].contains(&cmd)) && want_rustdoc {
             cargo.env("RUSTDOC_LIBDIR", self.rustc_libdir(compiler));
@@ -1743,10 +1757,8 @@ impl<'a> Builder<'a> {
 
         let split_debuginfo_is_stable = target.contains("linux")
             || target.contains("apple")
-            || (target.contains("msvc")
-                && self.config.rust_split_debuginfo == SplitDebuginfo::Packed)
-            || (target.contains("windows")
-                && self.config.rust_split_debuginfo == SplitDebuginfo::Off);
+            || (target.is_msvc() && self.config.rust_split_debuginfo == SplitDebuginfo::Packed)
+            || (target.is_windows() && self.config.rust_split_debuginfo == SplitDebuginfo::Off);
 
         if !split_debuginfo_is_stable {
             rustflags.arg("-Zunstable-options");
@@ -1804,6 +1816,16 @@ impl<'a> Builder<'a> {
 
         // Enable usage of unstable features
         cargo.env("RUSTC_BOOTSTRAP", "1");
+
+        if self.config.dump_bootstrap_shims {
+            prepare_behaviour_dump_dir(&self.build);
+
+            cargo
+                .env("DUMP_BOOTSTRAP_SHIMS", self.build.out.join("bootstrap-shims-dump"))
+                .env("BUILD_OUT", &self.build.out)
+                .env("CARGO_HOME", t!(home::cargo_home()));
+        };
+
         self.add_rust_test_threads(&mut cargo);
 
         // Almost all of the crates that we compile as part of the bootstrap may
@@ -1892,7 +1914,6 @@ impl<'a> Builder<'a> {
             // some code doesn't go through this `rustc` wrapper.
             lint_flags.push("-Wrust_2018_idioms");
             lint_flags.push("-Wunused_lifetimes");
-            lint_flags.push("-Wsemicolon_in_expressions_from_macros");
 
             if self.config.deny_warnings {
                 lint_flags.push("-Dwarnings");
@@ -1924,7 +1945,7 @@ impl<'a> Builder<'a> {
         // the options through environment variables that are fetched and understood by both.
         //
         // FIXME: the guard against msvc shouldn't need to be here
-        if target.contains("msvc") {
+        if target.is_msvc() {
             if let Some(ref cl) = self.config.llvm_clang_cl {
                 cargo.env("CC", cl).env("CXX", cl);
             }
@@ -1982,6 +2003,16 @@ impl<'a> Builder<'a> {
             rustflags.arg("-Ccontrol-flow-guard");
         }
 
+        // If EHCont Guard is enabled, pass the `-Zehcont-guard` flag to rustc when compiling the
+        // standard library, since this might be linked into the final outputs produced by rustc.
+        // Since this mitigation is only available on Windows, only enable it for the standard
+        // library in case the compiler is run on a non-Windows platform.
+        // This is not needed for stage 0 artifacts because these will only be used for building
+        // the stage 1 compiler.
+        if cfg!(windows) && mode == Mode::Std && self.config.ehcont_guard && compiler.stage >= 1 {
+            rustflags.arg("-Zehcont-guard");
+        }
+
         // For `cargo doc` invocations, make rustdoc print the Rust version into the docs
         // This replaces spaces with tabs because RUSTDOCFLAGS does not
         // support arguments with regular spaces. Hopefully someday Cargo will
@@ -1992,7 +2023,11 @@ impl<'a> Builder<'a> {
         // Environment variables *required* throughout the build
         //
         // FIXME: should update code to not require this env var
+
+        // The host this new compiler will *run* on.
         cargo.env("CFG_COMPILER_HOST_TRIPLE", target.triple);
+        // The host this new compiler is being *built* on.
+        cargo.env("CFG_COMPILER_BUILD_TRIPLE", compiler.host.triple);
 
         // Set this for all builds to make sure doc builds also get it.
         cargo.env("CFG_RELEASE_CHANNEL", &self.config.channel);
diff --git a/src/bootstrap/src/core/config/config.rs b/src/bootstrap/src/core/config/config.rs
index 0a9175aa3..f1e1b89d9 100644
--- a/src/bootstrap/src/core/config/config.rs
+++ b/src/bootstrap/src/core/config/config.rs
@@ -17,6 +17,7 @@ use std::io::IsTerminal;
 use std::path::{Path, PathBuf};
 use std::process::Command;
 use std::str::FromStr;
+use std::sync::OnceLock;
 
 use crate::core::build_steps::compile::CODEGEN_BACKEND_PREFIX;
 use crate::core::build_steps::llvm;
@@ -25,7 +26,6 @@ use crate::utils::cache::{Interned, INTERNER};
 use crate::utils::channel::{self, GitInfo};
 use crate::utils::helpers::{exe, output, t};
 use build_helper::exit;
-use once_cell::sync::OnceCell;
 use semver::Version;
 use serde::{Deserialize, Deserializer};
 use serde_derive::Deserialize;
@@ -105,6 +105,39 @@ impl Display for DebuginfoLevel {
     }
 }
 
+/// LLD in bootstrap works like this:
+/// - 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`
+/// 2) MSVC
+/// - Self-contained: `-Clinker=<path to rust-lld>`
+/// - External: `-Clinker=lld`
+#[derive(Default, Copy, Clone)]
+pub enum LldMode {
+    /// Do not use LLD
+    #[default]
+    Unused,
+    /// Use `rust-lld` from the compiler's sysroot
+    SelfContained,
+    /// Use an externally provided `lld` binary.
+    /// Note that the linker name cannot be overridden, the binary has to be named `lld` and it has
+    /// to be in $PATH.
+    External,
+}
+
+impl LldMode {
+    pub fn is_used(&self) -> bool {
+        match self {
+            LldMode::SelfContained | LldMode::External => true,
+            LldMode::Unused => false,
+        }
+    }
+}
+
 /// Global configuration for the entire build and/or bootstrap.
 ///
 /// This structure is parsed from `config.toml`, and some of the fields are inferred from `git` or build-time parameters.
@@ -117,6 +150,7 @@ impl Display for DebuginfoLevel {
 pub struct Config {
     pub changelog_seen: Option<usize>, // FIXME: Deprecated field. Remove it at 2024.
     pub change_id: Option<usize>,
+    pub bypass_bootstrap_lock: bool,
     pub ccache: Option<String>,
     /// Call Build::ninja() instead of this.
     pub ninja_in_file: bool,
@@ -159,6 +193,7 @@ pub struct Config {
     pub cmd: Subcommand,
     pub incremental: bool,
     pub dry_run: DryRun,
+    pub dump_bootstrap_shims: bool,
     /// Arguments appearing after `--` to be forwarded to tools,
     /// e.g. `--fix-broken` or test arguments.
     pub free_args: Vec<String>,
@@ -198,7 +233,7 @@ pub struct Config {
     pub llvm_from_ci: bool,
     pub llvm_build_config: HashMap<String, String>,
 
-    pub use_lld: bool,
+    pub lld_mode: LldMode,
     pub lld_enabled: bool,
     pub llvm_tools_enabled: bool,
 
@@ -222,6 +257,8 @@ pub struct Config {
     pub rust_debuginfo_level_tests: DebuginfoLevel,
     pub rust_split_debuginfo: SplitDebuginfo,
     pub rust_rpath: bool,
+    pub rust_strip: bool,
+    pub rust_stack_protector: Option<String>,
     pub rustc_parallel: bool,
     pub rustc_default_linker: Option<String>,
     pub rust_optimize_tests: bool,
@@ -248,6 +285,7 @@ pub struct Config {
     pub local_rebuild: bool,
     pub jemalloc: bool,
     pub control_flow_guard: bool,
+    pub ehcont_guard: bool,
 
     // dist misc
     pub dist_sign_folder: Option<PathBuf>,
@@ -383,10 +421,10 @@ impl std::str::FromStr for SplitDebuginfo {
 impl SplitDebuginfo {
     /// Returns the default `-Csplit-debuginfo` value for the current target. See the comment for
     /// `rust.split-debuginfo` in `config.example.toml`.
-    fn default_for_platform(target: &str) -> Self {
+    fn default_for_platform(target: TargetSelection) -> Self {
         if target.contains("apple") {
             SplitDebuginfo::Unpacked
-        } else if target.contains("windows") {
+        } else if target.is_windows() {
             SplitDebuginfo::Packed
         } else {
             SplitDebuginfo::Off
@@ -485,6 +523,14 @@ impl TargetSelection {
     pub fn is_synthetic(&self) -> bool {
         self.synthetic
     }
+
+    pub fn is_msvc(&self) -> bool {
+        self.contains("msvc")
+    }
+
+    pub fn is_windows(&self) -> bool {
+        self.contains("windows")
+    }
 }
 
 impl fmt::Display for TargetSelection {
@@ -853,7 +899,6 @@ define_config! {
 define_config! {
     struct Dist {
         sign_folder: Option<String> = "sign-folder",
-        gpg_password_file: Option<String> = "gpg-password-file",
         upload_addr: Option<String> = "upload-addr",
         src_tarball: Option<bool> = "src-tarball",
         missing_tools: Option<bool> = "missing-tools",
@@ -973,6 +1018,44 @@ enum StringOrInt<'a> {
     String(&'a str),
     Int(i64),
 }
+
+impl<'de> Deserialize<'de> for LldMode {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct LldModeVisitor;
+
+        impl<'de> serde::de::Visitor<'de> for LldModeVisitor {
+            type Value = LldMode;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+                formatter.write_str("one of true, 'self-contained' or 'external'")
+            }
+
+            fn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>
+            where
+                E: serde::de::Error,
+            {
+                Ok(if v { LldMode::External } else { LldMode::Unused })
+            }
+
+            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),
+                    _ => Err(E::custom("unknown mode {v}")),
+                }
+            }
+        }
+
+        deserializer.deserialize_any(LldModeVisitor)
+    }
+}
+
 define_config! {
     /// TOML representation of how the Rust build is configured.
     struct Rust {
@@ -991,7 +1074,6 @@ define_config! {
         debuginfo_level_tools: Option<DebuginfoLevel> = "debuginfo-level-tools",
         debuginfo_level_tests: Option<DebuginfoLevel> = "debuginfo-level-tests",
         split_debuginfo: Option<String> = "split-debuginfo",
-        run_dsymutil: Option<bool> = "run-dsymutil",
         backtrace: Option<bool> = "backtrace",
         incremental: Option<bool> = "incremental",
         parallel_compiler: Option<bool> = "parallel-compiler",
@@ -1000,6 +1082,8 @@ define_config! {
         description: Option<String> = "description",
         musl_root: Option<String> = "musl-root",
         rpath: Option<bool> = "rpath",
+        strip: Option<bool> = "strip",
+        stack_protector: Option<String> = "stack-protector",
         verbose_tests: Option<bool> = "verbose-tests",
         optimize_tests: Option<bool> = "optimize-tests",
         codegen_tests: Option<bool> = "codegen-tests",
@@ -1008,7 +1092,7 @@ define_config! {
         save_toolstates: Option<String> = "save-toolstates",
         codegen_backends: Option<Vec<String>> = "codegen-backends",
         lld: Option<bool> = "lld",
-        use_lld: Option<bool> = "use-lld",
+        lld_mode: Option<LldMode> = "use-lld",
         llvm_tools: Option<bool> = "llvm-tools",
         deny_warnings: Option<bool> = "deny-warnings",
         backtrace_on_ice: Option<bool> = "backtrace-on-ice",
@@ -1019,6 +1103,7 @@ define_config! {
         test_compare_mode: Option<bool> = "test-compare-mode",
         llvm_libunwind: Option<String> = "llvm-libunwind",
         control_flow_guard: Option<bool> = "control-flow-guard",
+        ehcont_guard: Option<bool> = "ehcont-guard",
         new_symbol_mangling: Option<bool> = "new-symbol-mangling",
         profile_generate: Option<String> = "profile-generate",
         profile_use: Option<String> = "profile-use",
@@ -1057,6 +1142,7 @@ define_config! {
 impl Config {
     pub fn default_opts() -> Config {
         let mut config = Config::default();
+        config.bypass_bootstrap_lock = false;
         config.llvm_optimize = true;
         config.ninja_in_file = true;
         config.llvm_static_stdcpp = false;
@@ -1067,6 +1153,7 @@ impl Config {
         config.docs = true;
         config.docs_minification = true;
         config.rust_rpath = true;
+        config.rust_strip = false;
         config.channel = "dev".to_string();
         config.codegen_tests = true;
         config.rust_dist_src = true;
@@ -1128,6 +1215,7 @@ impl Config {
         config.cmd = flags.cmd;
         config.incremental = flags.incremental;
         config.dry_run = if flags.dry_run { DryRun::UserSelected } else { DryRun::Disabled };
+        config.dump_bootstrap_shims = flags.dump_bootstrap_shims;
         config.keep_stage = flags.keep_stage;
         config.keep_stage_std = flags.keep_stage_std;
         config.color = flags.color;
@@ -1135,6 +1223,7 @@ impl Config {
         config.llvm_profile_use = flags.llvm_profile_use;
         config.llvm_profile_generate = flags.llvm_profile_generate;
         config.enable_bolt_settings = flags.enable_bolt_settings;
+        config.bypass_bootstrap_lock = flags.bypass_bootstrap_lock;
 
         // Infer the rest of the configuration.
 
@@ -1264,12 +1353,56 @@ impl Config {
         config.changelog_seen = toml.changelog_seen;
         config.change_id = toml.change_id;
 
-        let build = toml.build.unwrap_or_default();
-        if let Some(file_build) = build.build {
+        let Build {
+            build,
+            host,
+            target,
+            build_dir,
+            cargo,
+            rustc,
+            rustfmt,
+            docs,
+            compiler_docs,
+            library_docs_private_items,
+            docs_minification,
+            submodules,
+            gdb,
+            nodejs,
+            npm,
+            python,
+            reuse,
+            locked_deps,
+            vendor,
+            full_bootstrap,
+            extended,
+            tools,
+            verbose,
+            sanitizers,
+            profiler,
+            cargo_native_static,
+            low_priority,
+            configure_args,
+            local_rebuild,
+            print_step_timings,
+            print_step_rusage,
+            check_stage,
+            doc_stage,
+            build_stage,
+            test_stage,
+            install_stage,
+            dist_stage,
+            bench_stage,
+            patch_binaries_for_nix,
+            // This field is only used by bootstrap.py
+            metrics: _,
+            android_ndk,
+        } = toml.build.unwrap_or_default();
+
+        if let Some(file_build) = build {
             config.build = TargetSelection::from_user(&file_build);
         };
 
-        set(&mut config.out, flags.build_dir.or_else(|| build.build_dir.map(PathBuf::from)));
+        set(&mut config.out, flags.build_dir.or_else(|| build_dir.map(PathBuf::from)));
         // NOTE: Bootstrap spawns various commands with different working directories.
         // To avoid writing to random places on the file system, `config.out` needs to be an absolute path.
         if !config.out.is_absolute() {
@@ -1277,7 +1410,7 @@ impl Config {
             config.out = crate::utils::helpers::absolute(&config.out);
         }
 
-        config.initial_rustc = if let Some(rustc) = build.rustc {
+        config.initial_rustc = if let Some(rustc) = rustc {
             if !flags.skip_stage0_validation {
                 config.check_build_rustc_version(&rustc);
             }
@@ -1287,8 +1420,7 @@ impl Config {
             config.out.join(config.build.triple).join("stage0/bin/rustc")
         };
 
-        config.initial_cargo = build
-            .cargo
+        config.initial_cargo = cargo
             .map(|cargo| {
                 t!(PathBuf::from(cargo).canonicalize(), "`initial_cargo` not found on disk")
             })
@@ -1303,14 +1435,14 @@ impl Config {
 
         config.hosts = if let Some(TargetSelectionList(arg_host)) = flags.host {
             arg_host
-        } else if let Some(file_host) = build.host {
+        } else if let Some(file_host) = host {
             file_host.iter().map(|h| TargetSelection::from_user(h)).collect()
         } else {
             vec![config.build]
         };
         config.targets = if let Some(TargetSelectionList(arg_target)) = flags.target {
             arg_target
-        } else if let Some(file_target) = build.target {
+        } else if let Some(file_target) = target {
             file_target.iter().map(|h| TargetSelection::from_user(h)).collect()
         } else {
             // If target is *not* configured, then default to the host
@@ -1318,43 +1450,44 @@ impl Config {
             config.hosts.clone()
         };
 
-        config.nodejs = build.nodejs.map(PathBuf::from);
-        config.npm = build.npm.map(PathBuf::from);
-        config.gdb = build.gdb.map(PathBuf::from);
-        config.python = build.python.map(PathBuf::from);
-        config.reuse = build.reuse.map(PathBuf::from);
-        config.submodules = build.submodules;
-        config.android_ndk = build.android_ndk;
-        set(&mut config.low_priority, build.low_priority);
-        set(&mut config.compiler_docs, build.compiler_docs);
-        set(&mut config.library_docs_private_items, build.library_docs_private_items);
-        set(&mut config.docs_minification, build.docs_minification);
-        set(&mut config.docs, build.docs);
-        set(&mut config.locked_deps, build.locked_deps);
-        set(&mut config.vendor, build.vendor);
-        set(&mut config.full_bootstrap, build.full_bootstrap);
-        set(&mut config.extended, build.extended);
-        config.tools = build.tools;
-        set(&mut config.verbose, build.verbose);
-        set(&mut config.sanitizers, build.sanitizers);
-        set(&mut config.profiler, build.profiler);
-        set(&mut config.cargo_native_static, build.cargo_native_static);
-        set(&mut config.configure_args, build.configure_args);
-        set(&mut config.local_rebuild, build.local_rebuild);
-        set(&mut config.print_step_timings, build.print_step_timings);
-        set(&mut config.print_step_rusage, build.print_step_rusage);
-        config.patch_binaries_for_nix = build.patch_binaries_for_nix;
+        config.nodejs = nodejs.map(PathBuf::from);
+        config.npm = npm.map(PathBuf::from);
+        config.gdb = gdb.map(PathBuf::from);
+        config.python = python.map(PathBuf::from);
+        config.reuse = reuse.map(PathBuf::from);
+        config.submodules = submodules;
+        config.android_ndk = android_ndk;
+        set(&mut config.low_priority, low_priority);
+        set(&mut config.compiler_docs, compiler_docs);
+        set(&mut config.library_docs_private_items, library_docs_private_items);
+        set(&mut config.docs_minification, docs_minification);
+        set(&mut config.docs, docs);
+        set(&mut config.locked_deps, locked_deps);
+        set(&mut config.vendor, vendor);
+        set(&mut config.full_bootstrap, full_bootstrap);
+        set(&mut config.extended, extended);
+        config.tools = tools;
+        set(&mut config.verbose, verbose);
+        set(&mut config.sanitizers, sanitizers);
+        set(&mut config.profiler, profiler);
+        set(&mut config.cargo_native_static, cargo_native_static);
+        set(&mut config.configure_args, configure_args);
+        set(&mut config.local_rebuild, local_rebuild);
+        set(&mut config.print_step_timings, print_step_timings);
+        set(&mut config.print_step_rusage, print_step_rusage);
+        config.patch_binaries_for_nix = patch_binaries_for_nix;
 
         config.verbose = cmp::max(config.verbose, flags.verbose as usize);
 
         if let Some(install) = toml.install {
-            config.prefix = install.prefix.map(PathBuf::from);
-            config.sysconfdir = install.sysconfdir.map(PathBuf::from);
-            config.datadir = install.datadir.map(PathBuf::from);
-            config.docdir = install.docdir.map(PathBuf::from);
-            set(&mut config.bindir, install.bindir.map(PathBuf::from));
-            config.libdir = install.libdir.map(PathBuf::from);
-            config.mandir = install.mandir.map(PathBuf::from);
+            let Install { prefix, sysconfdir, docdir, bindir, libdir, mandir, datadir } = install;
+            config.prefix = prefix.map(PathBuf::from);
+            config.sysconfdir = sysconfdir.map(PathBuf::from);
+            config.datadir = datadir.map(PathBuf::from);
+            config.docdir = docdir.map(PathBuf::from);
+            set(&mut config.bindir, bindir.map(PathBuf::from));
+            config.libdir = libdir.map(PathBuf::from);
+            config.mandir = mandir.map(PathBuf::from);
         }
 
         // Store off these values as options because if they're not provided
@@ -1377,9 +1510,63 @@ impl Config {
         let mut omit_git_hash = None;
 
         if let Some(rust) = toml.rust {
-            set(&mut config.channel, rust.channel);
-
-            config.download_rustc_commit = config.download_ci_rustc_commit(rust.download_rustc);
+            let Rust {
+                optimize: optimize_toml,
+                debug: debug_toml,
+                codegen_units,
+                codegen_units_std,
+                debug_assertions: debug_assertions_toml,
+                debug_assertions_std: debug_assertions_std_toml,
+                overflow_checks: overflow_checks_toml,
+                overflow_checks_std: overflow_checks_std_toml,
+                debug_logging: debug_logging_toml,
+                debuginfo_level: debuginfo_level_toml,
+                debuginfo_level_rustc: debuginfo_level_rustc_toml,
+                debuginfo_level_std: debuginfo_level_std_toml,
+                debuginfo_level_tools: debuginfo_level_tools_toml,
+                debuginfo_level_tests: debuginfo_level_tests_toml,
+                split_debuginfo,
+                backtrace,
+                incremental,
+                parallel_compiler,
+                default_linker,
+                channel,
+                description,
+                musl_root,
+                rpath,
+                verbose_tests,
+                optimize_tests,
+                codegen_tests,
+                omit_git_hash: omit_git_hash_toml,
+                dist_src,
+                save_toolstates,
+                codegen_backends,
+                lld,
+                llvm_tools,
+                deny_warnings,
+                backtrace_on_ice,
+                verify_llvm_ir,
+                thin_lto_import_instr_limit,
+                remap_debuginfo,
+                jemalloc,
+                test_compare_mode,
+                llvm_libunwind,
+                control_flow_guard,
+                ehcont_guard,
+                new_symbol_mangling,
+                profile_generate,
+                profile_use,
+                download_rustc,
+                lto,
+                validate_mir_opts,
+                stack_protector,
+                strip,
+                lld_mode,
+            } = rust;
+
+            set(&mut config.channel, channel);
+
+            config.download_rustc_commit = config.download_ci_rustc_commit(download_rustc);
             // This list is incomplete, please help by expanding it!
             if config.download_rustc_commit.is_some() {
                 // We need the channel used by the downloaded compiler to match the one we set for rustdoc;
@@ -1396,67 +1583,77 @@ impl Config {
                 }
             }
 
-            debug = rust.debug;
-            debug_assertions = rust.debug_assertions;
-            debug_assertions_std = rust.debug_assertions_std;
-            overflow_checks = rust.overflow_checks;
-            overflow_checks_std = rust.overflow_checks_std;
-            debug_logging = rust.debug_logging;
-            debuginfo_level = rust.debuginfo_level;
-            debuginfo_level_rustc = rust.debuginfo_level_rustc;
-            debuginfo_level_std = rust.debuginfo_level_std;
-            debuginfo_level_tools = rust.debuginfo_level_tools;
-            debuginfo_level_tests = rust.debuginfo_level_tests;
-
-            config.rust_split_debuginfo = rust
-                .split_debuginfo
+            debug = debug_toml;
+            debug_assertions = debug_assertions_toml;
+            debug_assertions_std = debug_assertions_std_toml;
+            overflow_checks = overflow_checks_toml;
+            overflow_checks_std = overflow_checks_std_toml;
+            debug_logging = debug_logging_toml;
+            debuginfo_level = debuginfo_level_toml;
+            debuginfo_level_rustc = debuginfo_level_rustc_toml;
+            debuginfo_level_std = debuginfo_level_std_toml;
+            debuginfo_level_tools = debuginfo_level_tools_toml;
+            debuginfo_level_tests = debuginfo_level_tests_toml;
+
+            config.rust_split_debuginfo = split_debuginfo
                 .as_deref()
                 .map(SplitDebuginfo::from_str)
                 .map(|v| v.expect("invalid value for rust.split_debuginfo"))
-                .unwrap_or(SplitDebuginfo::default_for_platform(&config.build.triple));
-            optimize = rust.optimize;
-            omit_git_hash = rust.omit_git_hash;
-            config.rust_new_symbol_mangling = rust.new_symbol_mangling;
-            set(&mut config.rust_optimize_tests, rust.optimize_tests);
-            set(&mut config.codegen_tests, rust.codegen_tests);
-            set(&mut config.rust_rpath, rust.rpath);
-            set(&mut config.jemalloc, rust.jemalloc);
-            set(&mut config.test_compare_mode, rust.test_compare_mode);
-            set(&mut config.backtrace, rust.backtrace);
-            config.description = rust.description;
-            set(&mut config.rust_dist_src, rust.dist_src);
-            set(&mut config.verbose_tests, rust.verbose_tests);
+                .unwrap_or(SplitDebuginfo::default_for_platform(config.build));
+            optimize = optimize_toml;
+            omit_git_hash = omit_git_hash_toml;
+            config.rust_new_symbol_mangling = new_symbol_mangling;
+            set(&mut config.rust_optimize_tests, optimize_tests);
+            set(&mut config.codegen_tests, codegen_tests);
+            set(&mut config.rust_rpath, rpath);
+            set(&mut config.rust_strip, strip);
+            config.rust_stack_protector = stack_protector;
+            set(&mut config.jemalloc, jemalloc);
+            set(&mut config.test_compare_mode, test_compare_mode);
+            set(&mut config.backtrace, backtrace);
+            config.description = description;
+            set(&mut config.rust_dist_src, dist_src);
+            set(&mut config.verbose_tests, verbose_tests);
             // in the case "false" is set explicitly, do not overwrite the command line args
-            if let Some(true) = rust.incremental {
+            if let Some(true) = incremental {
                 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
-                .unwrap_or(config.channel == "dev" || config.channel == "nightly");
-            config.rustc_default_linker = rust.default_linker;
-            config.musl_root = rust.musl_root.map(PathBuf::from);
-            config.save_toolstates = rust.save_toolstates.map(PathBuf::from);
+            set(&mut config.lld_mode, lld_mode);
+            set(&mut config.lld_enabled, lld);
+
+            if matches!(config.lld_mode, LldMode::SelfContained)
+                && !config.lld_enabled
+                && flags.stage.unwrap_or(0) > 0
+            {
+                panic!(
+                    "Trying to use self-contained lld as a linker, but LLD is not being added to the sysroot. Enable it with rust.lld = true."
+                );
+            }
+
+            set(&mut config.llvm_tools_enabled, llvm_tools);
+            config.rustc_parallel =
+                parallel_compiler.unwrap_or(config.channel == "dev" || config.channel == "nightly");
+            config.rustc_default_linker = default_linker;
+            config.musl_root = musl_root.map(PathBuf::from);
+            config.save_toolstates = save_toolstates.map(PathBuf::from);
             set(
                 &mut config.deny_warnings,
                 match flags.warnings {
                     Warnings::Deny => Some(true),
                     Warnings::Warn => Some(false),
-                    Warnings::Default => rust.deny_warnings,
+                    Warnings::Default => deny_warnings,
                 },
             );
-            set(&mut config.backtrace_on_ice, rust.backtrace_on_ice);
-            set(&mut config.rust_verify_llvm_ir, rust.verify_llvm_ir);
-            config.rust_thin_lto_import_instr_limit = rust.thin_lto_import_instr_limit;
-            set(&mut config.rust_remap_debuginfo, rust.remap_debuginfo);
-            set(&mut config.control_flow_guard, rust.control_flow_guard);
-            config.llvm_libunwind_default = rust
-                .llvm_libunwind
-                .map(|v| v.parse().expect("failed to parse rust.llvm-libunwind"));
-
-            if let Some(ref backends) = rust.codegen_backends {
+            set(&mut config.backtrace_on_ice, backtrace_on_ice);
+            set(&mut config.rust_verify_llvm_ir, verify_llvm_ir);
+            config.rust_thin_lto_import_instr_limit = thin_lto_import_instr_limit;
+            set(&mut config.rust_remap_debuginfo, remap_debuginfo);
+            set(&mut config.control_flow_guard, control_flow_guard);
+            set(&mut config.ehcont_guard, ehcont_guard);
+            config.llvm_libunwind_default =
+                llvm_libunwind.map(|v| v.parse().expect("failed to parse rust.llvm-libunwind"));
+
+            if let Some(ref backends) = codegen_backends {
                 let available_backends = vec!["llvm", "cranelift", "gcc"];
 
                 config.rust_codegen_backends = backends.iter().map(|s| {
@@ -1474,16 +1671,13 @@ impl Config {
                 }).collect();
             }
 
-            config.rust_codegen_units = rust.codegen_units.map(threads_from_config);
-            config.rust_codegen_units_std = rust.codegen_units_std.map(threads_from_config);
-            config.rust_profile_use = flags.rust_profile_use.or(rust.profile_use);
-            config.rust_profile_generate = flags.rust_profile_generate.or(rust.profile_generate);
-            config.rust_lto = rust
-                .lto
-                .as_deref()
-                .map(|value| RustcLto::from_str(value).unwrap())
-                .unwrap_or_default();
-            config.rust_validate_mir_opts = rust.validate_mir_opts;
+            config.rust_codegen_units = codegen_units.map(threads_from_config);
+            config.rust_codegen_units_std = codegen_units_std.map(threads_from_config);
+            config.rust_profile_use = flags.rust_profile_use.or(profile_use);
+            config.rust_profile_generate = flags.rust_profile_generate.or(profile_generate);
+            config.rust_lto =
+                lto.as_deref().map(|value| RustcLto::from_str(value).unwrap()).unwrap_or_default();
+            config.rust_validate_mir_opts = validate_mir_opts;
         } else {
             config.rust_profile_use = flags.rust_profile_use;
             config.rust_profile_generate = flags.rust_profile_generate;
@@ -1497,43 +1691,71 @@ impl Config {
         config.rust_info = GitInfo::new(config.omit_git_hash, &config.src);
 
         if let Some(llvm) = toml.llvm {
-            match llvm.ccache {
+            let Llvm {
+                optimize: optimize_toml,
+                thin_lto,
+                release_debuginfo,
+                assertions,
+                tests,
+                plugins,
+                ccache,
+                static_libstdcpp,
+                ninja,
+                targets,
+                experimental_targets,
+                link_jobs,
+                link_shared,
+                version_suffix,
+                clang_cl,
+                cflags,
+                cxxflags,
+                ldflags,
+                use_libcxx,
+                use_linker,
+                allow_old_toolchain,
+                polly,
+                clang,
+                enable_warnings,
+                download_ci_llvm,
+                build_config,
+            } = llvm;
+            match ccache {
                 Some(StringOrBool::String(ref s)) => config.ccache = Some(s.to_string()),
                 Some(StringOrBool::Bool(true)) => {
                     config.ccache = Some("ccache".to_string());
                 }
                 Some(StringOrBool::Bool(false)) | None => {}
             }
-            set(&mut config.ninja_in_file, llvm.ninja);
-            llvm_assertions = llvm.assertions;
-            llvm_tests = llvm.tests;
-            llvm_plugins = llvm.plugins;
-            set(&mut config.llvm_optimize, llvm.optimize);
-            set(&mut config.llvm_thin_lto, llvm.thin_lto);
-            set(&mut config.llvm_release_debuginfo, llvm.release_debuginfo);
-            set(&mut config.llvm_static_stdcpp, llvm.static_libstdcpp);
-            if let Some(v) = llvm.link_shared {
+            set(&mut config.ninja_in_file, ninja);
+            llvm_assertions = assertions;
+            llvm_tests = tests;
+            llvm_plugins = plugins;
+            set(&mut config.llvm_optimize, optimize_toml);
+            set(&mut config.llvm_thin_lto, thin_lto);
+            set(&mut config.llvm_release_debuginfo, release_debuginfo);
+            set(&mut config.llvm_static_stdcpp, static_libstdcpp);
+            if let Some(v) = link_shared {
                 config.llvm_link_shared.set(Some(v));
             }
-            config.llvm_targets = llvm.targets.clone();
-            config.llvm_experimental_targets = llvm.experimental_targets.clone();
-            config.llvm_link_jobs = llvm.link_jobs;
-            config.llvm_version_suffix = llvm.version_suffix.clone();
-            config.llvm_clang_cl = llvm.clang_cl.clone();
-
-            config.llvm_cflags = llvm.cflags.clone();
-            config.llvm_cxxflags = llvm.cxxflags.clone();
-            config.llvm_ldflags = llvm.ldflags.clone();
-            set(&mut config.llvm_use_libcxx, llvm.use_libcxx);
-            config.llvm_use_linker = llvm.use_linker.clone();
-            config.llvm_allow_old_toolchain = llvm.allow_old_toolchain.unwrap_or(false);
-            config.llvm_polly = llvm.polly.unwrap_or(false);
-            config.llvm_clang = llvm.clang.unwrap_or(false);
-            config.llvm_enable_warnings = llvm.enable_warnings.unwrap_or(false);
-            config.llvm_build_config = llvm.build_config.clone().unwrap_or(Default::default());
+            config.llvm_targets = targets.clone();
+            config.llvm_experimental_targets = experimental_targets.clone();
+            config.llvm_link_jobs = link_jobs;
+            config.llvm_version_suffix = version_suffix.clone();
+            config.llvm_clang_cl = clang_cl.clone();
+
+            config.llvm_cflags = cflags.clone();
+            config.llvm_cxxflags = cxxflags.clone();
+            config.llvm_ldflags = ldflags.clone();
+            set(&mut config.llvm_use_libcxx, use_libcxx);
+            config.llvm_use_linker = use_linker.clone();
+            config.llvm_allow_old_toolchain = allow_old_toolchain.unwrap_or(false);
+            config.llvm_polly = polly.unwrap_or(false);
+            config.llvm_clang = clang.unwrap_or(false);
+            config.llvm_enable_warnings = enable_warnings.unwrap_or(false);
+            config.llvm_build_config = build_config.clone().unwrap_or(Default::default());
 
             let asserts = llvm_assertions.unwrap_or(false);
-            config.llvm_from_ci = config.parse_download_ci_llvm(llvm.download_ci_llvm, asserts);
+            config.llvm_from_ci = config.parse_download_ci_llvm(download_ci_llvm, asserts);
 
             if config.llvm_from_ci {
                 // None of the LLVM options, except assertions, are supported
@@ -1542,39 +1764,38 @@ impl Config {
                 // explicitly set. The defaults and CI defaults don't
                 // necessarily match but forcing people to match (somewhat
                 // arbitrary) CI configuration locally seems bad/hard.
-                check_ci_llvm!(llvm.optimize);
-                check_ci_llvm!(llvm.thin_lto);
-                check_ci_llvm!(llvm.release_debuginfo);
+                check_ci_llvm!(optimize_toml);
+                check_ci_llvm!(thin_lto);
+                check_ci_llvm!(release_debuginfo);
                 // CI-built LLVM can be either dynamic or static. We won't know until we download it.
-                check_ci_llvm!(llvm.link_shared);
-                check_ci_llvm!(llvm.static_libstdcpp);
-                check_ci_llvm!(llvm.targets);
-                check_ci_llvm!(llvm.experimental_targets);
-                check_ci_llvm!(llvm.link_jobs);
-                check_ci_llvm!(llvm.clang_cl);
-                check_ci_llvm!(llvm.version_suffix);
-                check_ci_llvm!(llvm.cflags);
-                check_ci_llvm!(llvm.cxxflags);
-                check_ci_llvm!(llvm.ldflags);
-                check_ci_llvm!(llvm.use_libcxx);
-                check_ci_llvm!(llvm.use_linker);
-                check_ci_llvm!(llvm.allow_old_toolchain);
-                check_ci_llvm!(llvm.polly);
-                check_ci_llvm!(llvm.clang);
-                check_ci_llvm!(llvm.build_config);
-                check_ci_llvm!(llvm.plugins);
+                check_ci_llvm!(link_shared);
+                check_ci_llvm!(static_libstdcpp);
+                check_ci_llvm!(targets);
+                check_ci_llvm!(experimental_targets);
+                check_ci_llvm!(link_jobs);
+                check_ci_llvm!(clang_cl);
+                check_ci_llvm!(version_suffix);
+                check_ci_llvm!(cflags);
+                check_ci_llvm!(cxxflags);
+                check_ci_llvm!(ldflags);
+                check_ci_llvm!(use_libcxx);
+                check_ci_llvm!(use_linker);
+                check_ci_llvm!(allow_old_toolchain);
+                check_ci_llvm!(polly);
+                check_ci_llvm!(clang);
+                check_ci_llvm!(build_config);
+                check_ci_llvm!(plugins);
             }
 
             // NOTE: can never be hit when downloading from CI, since we call `check_ci_llvm!(thin_lto)` above.
-            if config.llvm_thin_lto && llvm.link_shared.is_none() {
+            if config.llvm_thin_lto && link_shared.is_none() {
                 // If we're building with ThinLTO on, by default we want to link
                 // to LLVM shared, to avoid re-doing ThinLTO (which happens in
                 // the link step) with each stage.
                 config.llvm_link_shared.set(Some(true));
             }
         } else {
-            config.llvm_from_ci = config.channel == "dev"
-                && crate::core::build_steps::llvm::is_ci_llvm_available(&config, false);
+            config.llvm_from_ci = config.parse_download_ci_llvm(None, false);
         }
 
         if let Some(t) = toml.target {
@@ -1632,17 +1853,26 @@ impl Config {
             build_target.llvm_filecheck = Some(ci_llvm_bin.join(exe("FileCheck", config.build)));
         }
 
-        if let Some(t) = toml.dist {
-            config.dist_sign_folder = t.sign_folder.map(PathBuf::from);
-            config.dist_upload_addr = t.upload_addr;
-            config.dist_compression_formats = t.compression_formats;
-            set(&mut config.dist_compression_profile, t.compression_profile);
-            set(&mut config.rust_dist_src, t.src_tarball);
-            set(&mut config.missing_tools, t.missing_tools);
-            set(&mut config.dist_include_mingw_linker, t.include_mingw_linker)
+        if let Some(dist) = toml.dist {
+            let Dist {
+                sign_folder,
+                upload_addr,
+                src_tarball,
+                missing_tools,
+                compression_formats,
+                compression_profile,
+                include_mingw_linker,
+            } = dist;
+            config.dist_sign_folder = sign_folder.map(PathBuf::from);
+            config.dist_upload_addr = upload_addr;
+            config.dist_compression_formats = compression_formats;
+            set(&mut config.dist_compression_profile, compression_profile);
+            set(&mut config.rust_dist_src, src_tarball);
+            set(&mut config.missing_tools, missing_tools);
+            set(&mut config.dist_include_mingw_linker, include_mingw_linker)
         }
 
-        if let Some(r) = build.rustfmt {
+        if let Some(r) = rustfmt {
             *config.initial_rustfmt.borrow_mut() = if r.exists() {
                 RustfmtState::SystemToolchain(r)
             } else {
@@ -1683,20 +1913,20 @@ impl Config {
         let download_rustc = config.download_rustc_commit.is_some();
         // See https://github.com/rust-lang/compiler-team/issues/326
         config.stage = match config.cmd {
-            Subcommand::Check { .. } => flags.stage.or(build.check_stage).unwrap_or(0),
+            Subcommand::Check { .. } => flags.stage.or(check_stage).unwrap_or(0),
             // `download-rustc` only has a speed-up for stage2 builds. Default to stage2 unless explicitly overridden.
             Subcommand::Doc { .. } => {
-                flags.stage.or(build.doc_stage).unwrap_or(if download_rustc { 2 } else { 0 })
+                flags.stage.or(doc_stage).unwrap_or(if download_rustc { 2 } else { 0 })
             }
             Subcommand::Build { .. } => {
-                flags.stage.or(build.build_stage).unwrap_or(if download_rustc { 2 } else { 1 })
+                flags.stage.or(build_stage).unwrap_or(if download_rustc { 2 } else { 1 })
             }
             Subcommand::Test { .. } => {
-                flags.stage.or(build.test_stage).unwrap_or(if download_rustc { 2 } else { 1 })
+                flags.stage.or(test_stage).unwrap_or(if download_rustc { 2 } else { 1 })
             }
-            Subcommand::Bench { .. } => flags.stage.or(build.bench_stage).unwrap_or(2),
-            Subcommand::Dist { .. } => flags.stage.or(build.dist_stage).unwrap_or(2),
-            Subcommand::Install { .. } => flags.stage.or(build.install_stage).unwrap_or(2),
+            Subcommand::Bench { .. } => flags.stage.or(bench_stage).unwrap_or(2),
+            Subcommand::Dist { .. } => flags.stage.or(dist_stage).unwrap_or(2),
+            Subcommand::Install { .. } => flags.stage.or(install_stage).unwrap_or(2),
             // These are all bootstrap tools, which don't depend on the compiler.
             // The stage we pass shouldn't matter, but use 0 just in case.
             Subcommand::Clean { .. }
@@ -1738,7 +1968,7 @@ impl Config {
         config
     }
 
-    pub(crate) fn dry_run(&self) -> bool {
+    pub fn dry_run(&self) -> bool {
         match self.dry_run {
             DryRun::Disabled => false,
             DryRun::SelfCheck | DryRun::UserSelected => true,
@@ -1904,7 +2134,7 @@ impl Config {
     }
 
     pub(crate) fn download_rustc_commit(&self) -> Option<&str> {
-        static DOWNLOAD_RUSTC: OnceCell<Option<String>> = OnceCell::new();
+        static DOWNLOAD_RUSTC: OnceLock<Option<String>> = OnceLock::new();
         if self.dry_run() && DOWNLOAD_RUSTC.get().is_none() {
             // avoid trying to actually download the commit
             return self.download_rustc_commit.as_deref();
@@ -2110,27 +2340,30 @@ impl Config {
         download_ci_llvm: Option<StringOrBool>,
         asserts: bool,
     ) -> bool {
+        let if_unchanged = || {
+            // Git is needed to track modifications here, but tarball source is not available.
+            // If not modified here or built through tarball source, we maintain consistency
+            // with '"if available"'.
+            if !self.rust_info.is_from_tarball()
+                && self
+                    .last_modified_commit(&["src/llvm-project"], "download-ci-llvm", true)
+                    .is_none()
+            {
+                // there are some untracked changes in the the given paths.
+                false
+            } else {
+                llvm::is_ci_llvm_available(&self, asserts)
+            }
+        };
         match download_ci_llvm {
-            None => self.channel == "dev" && llvm::is_ci_llvm_available(&self, asserts),
+            None => self.channel == "dev" && if_unchanged(),
             Some(StringOrBool::Bool(b)) => b,
+            // FIXME: "if-available" is deprecated. Remove this block later (around mid 2024)
+            // to not break builds between the recent-to-old checkouts.
             Some(StringOrBool::String(s)) if s == "if-available" => {
                 llvm::is_ci_llvm_available(&self, asserts)
             }
-            Some(StringOrBool::String(s)) if s == "if-unchanged" => {
-                // Git is needed to track modifications here, but tarball source is not available.
-                // If not modified here or built through tarball source, we maintain consistency
-                // with '"if available"'.
-                if !self.rust_info.is_from_tarball()
-                    && self
-                        .last_modified_commit(&["src/llvm-project"], "download-ci-llvm", true)
-                        .is_none()
-                {
-                    // there are some untracked changes in the the given paths.
-                    false
-                } else {
-                    llvm::is_ci_llvm_available(&self, asserts)
-                }
-            }
+            Some(StringOrBool::String(s)) if s == "if-unchanged" => if_unchanged(),
             Some(StringOrBool::String(other)) => {
                 panic!("unrecognized option for download-ci-llvm: {:?}", other)
             }
diff --git a/src/bootstrap/src/core/config/flags.rs b/src/bootstrap/src/core/config/flags.rs
index 2a301007a..0b1372608 100644
--- a/src/bootstrap/src/core/config/flags.rs
+++ b/src/bootstrap/src/core/config/flags.rs
@@ -85,6 +85,9 @@ pub struct Flags {
     #[arg(global(true), long)]
     /// dry run; don't build anything
     pub dry_run: bool,
+    /// Indicates whether to dump the work done from bootstrap shims
+    #[arg(global(true), long)]
+    pub dump_bootstrap_shims: bool,
     #[arg(global(true), value_hint = clap::ValueHint::Other, long, value_name = "N")]
     /// stage to build (indicates compiler to use/test, e.g., stage 0 uses the
     /// bootstrap compiler, stage 1 the stage 0 rustc artifacts, etc.)
@@ -133,6 +136,13 @@ pub struct Flags {
     /// whether to use color in cargo and rustc output
     pub color: Color,
 
+    #[arg(global(true), long)]
+    /// Bootstrap uses this value to decide whether it should bypass locking the build process.
+    /// This is rarely needed (e.g., compiling the std library for different targets in parallel).
+    ///
+    /// Unless you know exactly what you are doing, you probably don't need this.
+    pub bypass_bootstrap_lock: bool,
+
     /// whether rebuilding llvm should be skipped, overriding `skip-rebuld` in config.toml
     #[arg(global(true), long, value_name = "VALUE")]
     pub llvm_skip_rebuild: Option<bool>,
diff --git a/src/bootstrap/src/core/download.rs b/src/bootstrap/src/core/download.rs
index 3327aed96..ec404ab85 100644
--- a/src/bootstrap/src/core/download.rs
+++ b/src/bootstrap/src/core/download.rs
@@ -5,18 +5,18 @@ use std::{
     io::{BufRead, BufReader, BufWriter, ErrorKind, Write},
     path::{Path, PathBuf},
     process::{Command, Stdio},
+    sync::OnceLock,
 };
 
 use build_helper::ci::CiEnv;
-use once_cell::sync::OnceCell;
 use xz2::bufread::XzDecoder;
 
-use crate::core::build_steps::llvm::detect_llvm_sha;
 use crate::core::config::RustfmtMetadata;
 use crate::utils::helpers::{check_run, exe, program_out_of_date};
+use crate::{core::build_steps::llvm::detect_llvm_sha, utils::helpers::hex_encode};
 use crate::{t, Config};
 
-static SHOULD_FIX_BINS_AND_DYLIBS: OnceCell<bool> = OnceCell::new();
+static SHOULD_FIX_BINS_AND_DYLIBS: OnceLock<bool> = OnceLock::new();
 
 /// `Config::try_run` wrapper for this module to avoid warnings on `try_run`, since we don't have access to a `builder` yet.
 fn try_run(config: &Config, cmd: &mut Command) -> Result<(), ()> {
@@ -131,7 +131,7 @@ impl Config {
         println!("attempting to patch {}", fname.display());
 
         // Only build `.nix-deps` once.
-        static NIX_DEPS_DIR: OnceCell<PathBuf> = OnceCell::new();
+        static NIX_DEPS_DIR: OnceLock<PathBuf> = OnceLock::new();
         let mut nix_build_succeeded = true;
         let nix_deps_dir = NIX_DEPS_DIR.get_or_init(|| {
             // Run `nix-build` to "build" each dependency (which will likely reuse
@@ -208,7 +208,10 @@ impl Config {
             Some(other) => panic!("unsupported protocol {other} in {url}"),
             None => panic!("no protocol in {url}"),
         }
-        t!(std::fs::rename(&tempfile, dest_path));
+        t!(
+            std::fs::rename(&tempfile, dest_path),
+            format!("failed to rename {tempfile:?} to {dest_path:?}")
+        );
     }
 
     fn download_http_with_retries(&self, tempfile: &Path, url: &str, help_on_error: &str) {
@@ -342,7 +345,7 @@ impl Config {
             reader.consume(l);
         }
 
-        let checksum = hex::encode(hasher.finalize().as_slice());
+        let checksum = hex_encode(hasher.finalize().as_slice());
         let verified = checksum == expected;
 
         if !verified {
@@ -375,6 +378,32 @@ enum DownloadSource {
 
 /// Functions that are only ever called once, but named for clarify and to avoid thousand-line functions.
 impl Config {
+    pub(crate) fn download_clippy(&self) -> PathBuf {
+        self.verbose("downloading stage0 clippy artifacts");
+
+        let date = &self.stage0_metadata.compiler.date;
+        let version = &self.stage0_metadata.compiler.version;
+        let host = self.build;
+
+        let bin_root = self.out.join(host.triple).join("stage0");
+        let clippy_stamp = bin_root.join(".clippy-stamp");
+        let cargo_clippy = bin_root.join("bin").join(exe("cargo-clippy", host));
+        if cargo_clippy.exists() && !program_out_of_date(&clippy_stamp, &date) {
+            return cargo_clippy;
+        }
+
+        let filename = format!("clippy-{version}-{host}.tar.xz");
+        self.download_component(DownloadSource::Dist, filename, "clippy-preview", date, "stage0");
+        if self.should_fix_bins_and_dylibs() {
+            self.fix_bin_or_dylib(&cargo_clippy);
+            self.fix_bin_or_dylib(&cargo_clippy.with_file_name(exe("clippy-driver", host)));
+        }
+
+        cargo_clippy
+    }
+
+    /// NOTE: rustfmt is a completely different toolchain than the bootstrap compiler, so it can't
+    /// reuse target directories or artifacts
     pub(crate) fn maybe_download_rustfmt(&self) -> Option<PathBuf> {
         let RustfmtMetadata { date, version } = self.stage0_metadata.rustfmt.as_ref()?;
         let channel = format!("{version}-{date}");
@@ -544,6 +573,10 @@ impl Config {
         key: &str,
         destination: &str,
     ) {
+        if self.dry_run() {
+            return;
+        }
+
         let cache_dst = self.out.join("cache");
         let cache_dir = cache_dst.join(key);
         if !cache_dir.exists() {
diff --git a/src/bootstrap/src/core/sanity.rs b/src/bootstrap/src/core/sanity.rs
index eec3be66a..9101d94ea 100644
--- a/src/bootstrap/src/core/sanity.rs
+++ b/src/bootstrap/src/core/sanity.rs
@@ -237,7 +237,7 @@ than building it.
             }
         }
 
-        if need_cmake && target.contains("msvc") {
+        if need_cmake && target.is_msvc() {
             // There are three builds of cmake on windows: MSVC, MinGW, and
             // Cygwin. The Cygwin build does not have generators for Visual
             // Studio, so detect that here and error.
diff --git a/src/bootstrap/src/lib.rs b/src/bootstrap/src/lib.rs
index 33b8f1a7c..871318de5 100644
--- a/src/bootstrap/src/lib.rs
+++ b/src/bootstrap/src/lib.rs
@@ -25,18 +25,20 @@ use std::io;
 use std::path::{Path, PathBuf};
 use std::process::{Command, Output, Stdio};
 use std::str;
+use std::sync::OnceLock;
 
 use build_helper::ci::{gha, CiEnv};
 use build_helper::exit;
 use build_helper::util::fail;
 use filetime::FileTime;
-use once_cell::sync::OnceCell;
+use sha2::digest::Digest;
 use termcolor::{ColorChoice, StandardStream, WriteColor};
 use utils::channel::GitInfo;
+use utils::helpers::hex_encode;
 
 use crate::core::builder;
 use crate::core::builder::Kind;
-use crate::core::config::flags;
+use crate::core::config::{flags, LldMode};
 use crate::core::config::{DryRun, Target};
 use crate::core::config::{LlvmLibunwind, TargetSelection};
 use crate::utils::cache::{Interned, INTERNER};
@@ -46,9 +48,10 @@ use crate::utils::helpers::{self, dir_is_empty, exe, libdir, mtime, output, syml
 mod core;
 mod utils;
 
-pub use crate::core::builder::PathSet;
-pub use crate::core::config::flags::Subcommand;
-pub use crate::core::config::Config;
+pub use core::builder::PathSet;
+pub use core::config::flags::Subcommand;
+pub use core::config::Config;
+pub use utils::change_tracker::{find_recent_config_change_ids, CONFIG_CHANGE_HISTORY};
 
 const LLVM_TOOLS: &[&str] = &[
     "llvm-cov",      // used to generate coverage report
@@ -69,36 +72,25 @@ const LLVM_TOOLS: &[&str] = &[
 /// LLD file names for all flavors.
 const LLD_FILE_NAMES: &[&str] = &["ld.lld", "ld64.lld", "lld-link", "wasm-ld"];
 
-/// Keeps track of major changes made to the bootstrap configuration.
-///
-/// These values also represent the IDs of the PRs that caused major changes.
-/// You can visit `https://github.com/rust-lang/rust/pull/{any-id-from-the-list}` to
-/// check for more details regarding each change.
-///
-/// If you make any major changes (such as adding new values or changing default values),
-/// please ensure that the associated PR ID is added to the end of this list.
-/// This is necessary because the list must be sorted by the merge date.
-pub const CONFIG_CHANGE_HISTORY: &[usize] = &[115898, 116998, 117435, 116881];
-
 /// Extra --check-cfg to add when building
 /// (Mode restriction, config name, config values (if any))
 const EXTRA_CHECK_CFGS: &[(Option<Mode>, &str, Option<&[&'static str]>)] = &[
     (None, "bootstrap", None),
     (Some(Mode::Rustc), "parallel_compiler", None),
     (Some(Mode::ToolRustc), "parallel_compiler", None),
+    (Some(Mode::ToolRustc), "rust_analyzer", None),
+    (Some(Mode::ToolStd), "rust_analyzer", None),
     (Some(Mode::Codegen), "parallel_compiler", None),
     (Some(Mode::Std), "stdarch_intel_sde", None),
     (Some(Mode::Std), "no_fp_fmt_parse", None),
     (Some(Mode::Std), "no_global_oom_handling", None),
     (Some(Mode::Std), "no_rc", None),
     (Some(Mode::Std), "no_sync", None),
-    (Some(Mode::Std), "freebsd12", None),
-    (Some(Mode::Std), "freebsd13", None),
     (Some(Mode::Std), "backtrace_in_libstd", None),
     /* Extra values not defined in the built-in targets yet, but used in std */
     (Some(Mode::Std), "target_env", Some(&["libnx"])),
     // (Some(Mode::Std), "target_os", Some(&[])),
-    (Some(Mode::Std), "target_arch", Some(&["asmjs", "spirv", "nvptx", "xtensa"])),
+    (Some(Mode::Std), "target_arch", Some(&["spirv", "nvptx", "xtensa"])),
     /* Extra names used by dependencies */
     // FIXME: Used by serde_json, but we should not be triggering on external dependencies.
     (Some(Mode::Rustc), "no_btreemap_remove_entry", None),
@@ -873,7 +865,7 @@ impl Build {
             }
         } else {
             let base = self.llvm_out(target).join("build");
-            let base = if !self.ninja() && target.contains("msvc") {
+            let base = if !self.ninja() && target.is_msvc() {
                 if self.config.llvm_optimize {
                     if self.config.llvm_release_debuginfo {
                         base.join("RelWithDebInfo")
@@ -915,7 +907,7 @@ impl Build {
 
     /// Returns the sysroot of the snapshot compiler.
     fn rustc_snapshot_sysroot(&self) -> &Path {
-        static SYSROOT_CACHE: OnceCell<PathBuf> = once_cell::sync::OnceCell::new();
+        static SYSROOT_CACHE: OnceLock<PathBuf> = OnceLock::new();
         SYSROOT_CACHE.get_or_init(|| {
             let mut rustc = Command::new(&self.initial_rustc);
             rustc.args(&["--print", "sysroot"]);
@@ -1266,35 +1258,27 @@ impl Build {
             Some(self.cxx.borrow()[&target].path().into())
         } else if target != self.config.build
             && helpers::use_host_linker(target)
-            && !target.contains("msvc")
+            && !target.is_msvc()
         {
             Some(self.cc(target))
-        } else if self.config.use_lld && !self.is_fuse_ld_lld(target) && self.build == target {
-            Some(self.initial_lld.clone())
+        } else if self.config.lld_mode.is_used()
+            && self.is_lld_direct_linker(target)
+            && self.build == target
+        {
+            match self.config.lld_mode {
+                LldMode::SelfContained => Some(self.initial_lld.clone()),
+                LldMode::External => Some("lld".into()),
+                LldMode::Unused => None,
+            }
         } else {
             None
         }
     }
 
-    // LLD is used through `-fuse-ld=lld` rather than directly.
+    // Is LLD configured directly through `-Clinker`?
     // Only MSVC targets use LLD directly at the moment.
-    fn is_fuse_ld_lld(&self, target: TargetSelection) -> bool {
-        self.config.use_lld && !target.contains("msvc")
-    }
-
-    fn lld_flags(&self, target: TargetSelection) -> impl Iterator<Item = String> {
-        let mut options = [None, None];
-
-        if self.config.use_lld {
-            if self.is_fuse_ld_lld(target) {
-                options[0] = Some("-Clink-arg=-fuse-ld=lld".to_string());
-            }
-
-            let no_threads = helpers::lld_flag_no_threads(target.contains("windows"));
-            options[1] = Some(format!("-Clink-arg=-Wl,{no_threads}"));
-        }
-
-        IntoIterator::into_iter(options).flatten()
+    fn is_lld_direct_linker(&self, target: TargetSelection) -> bool {
+        target.is_msvc()
     }
 
     /// Returns if this target should statically link the C runtime, if specified
@@ -1775,7 +1759,7 @@ to download LLVM rather than building it.
         // In these cases we automatically enable Ninja if we find it in the
         // environment.
         if !self.config.ninja_in_file
-            && self.config.build.contains("msvc")
+            && self.config.build.is_msvc()
             && cmd_finder.maybe_have("ninja").is_some()
         {
             return true;
@@ -1849,26 +1833,63 @@ fn envify(s: &str) -> String {
         .collect()
 }
 
-pub fn find_recent_config_change_ids(current_id: usize) -> Vec<usize> {
-    if !CONFIG_CHANGE_HISTORY.contains(&current_id) {
-        // If the current change-id is greater than the most recent one, return
-        // an empty list (it may be due to switching from a recent branch to an
-        // older one); otherwise, return the full list (assuming the user provided
-        // the incorrect change-id by accident).
-        if let Some(max_id) = CONFIG_CHANGE_HISTORY.iter().max() {
-            if &current_id > max_id {
-                return Vec::new();
-            }
-        }
+/// Computes a hash representing the state of a repository/submodule and additional input.
+///
+/// It uses `git diff` for the actual changes, and `git status` for including the untracked
+/// files in the specified directory. The additional input is also incorporated into the
+/// computation of the hash.
+///
+/// # Parameters
+///
+/// - `dir`: A reference to the directory path of the target repository/submodule.
+/// - `additional_input`: An additional input to be included in the hash.
+///
+/// # Panics
+///
+/// In case of errors during `git` command execution (e.g., in tarball sources), default values
+/// are used to prevent panics.
+pub fn generate_smart_stamp_hash(dir: &Path, additional_input: &str) -> String {
+    let diff = Command::new("git")
+        .current_dir(dir)
+        .arg("diff")
+        .output()
+        .map(|o| String::from_utf8(o.stdout).unwrap_or_default())
+        .unwrap_or_default();
+
+    let status = Command::new("git")
+        .current_dir(dir)
+        .arg("status")
+        .arg("--porcelain")
+        .arg("-z")
+        .arg("--untracked-files=normal")
+        .output()
+        .map(|o| String::from_utf8(o.stdout).unwrap_or_default())
+        .unwrap_or_default();
+
+    let mut hasher = sha2::Sha256::new();
+
+    hasher.update(diff);
+    hasher.update(status);
+    hasher.update(additional_input);
+
+    hex_encode(hasher.finalize().as_slice())
+}
 
-        return CONFIG_CHANGE_HISTORY.to_vec();
-    }
+/// Ensures that the behavior dump directory is properly initialized.
+pub fn prepare_behaviour_dump_dir(build: &Build) {
+    static INITIALIZED: OnceLock<bool> = OnceLock::new();
 
-    let index = CONFIG_CHANGE_HISTORY.iter().position(|&id| id == current_id).unwrap();
+    let dump_path = build.out.join("bootstrap-shims-dump");
 
-    CONFIG_CHANGE_HISTORY
-        .iter()
-        .skip(index + 1) // Skip the current_id and IDs before it
-        .cloned()
-        .collect()
+    let initialized = INITIALIZED.get().unwrap_or_else(|| &false);
+    if !initialized {
+        // clear old dumps
+        if dump_path.exists() {
+            t!(fs::remove_dir_all(&dump_path));
+        }
+
+        t!(fs::create_dir_all(&dump_path));
+
+        t!(INITIALIZED.set(true));
+    }
 }
diff --git a/src/bootstrap/src/tests/builder.rs b/src/bootstrap/src/tests/builder.rs
index 96139f7b0..700ebcf5e 100644
--- a/src/bootstrap/src/tests/builder.rs
+++ b/src/bootstrap/src/tests/builder.rs
@@ -1,6 +1,6 @@
 use super::*;
-use crate::core::config::{Config, DryRun, TargetSelection};
 use crate::core::build_steps::doc::DocumentationFormat;
+use crate::core::config::{Config, DryRun, TargetSelection};
 use std::thread;
 
 fn configure(cmd: &str, host: &[&str], target: &[&str]) -> Config {
@@ -156,22 +156,6 @@ fn alias_and_path_for_library() {
     assert_eq!(first(cache.all::<doc::Std>()), &[doc_std!(A => A, stage = 0)]);
 }
 
-#[test]
-fn test_beta_rev_parsing() {
-    use crate::utils::helpers::extract_beta_rev;
-
-    // single digit revision
-    assert_eq!(extract_beta_rev("1.99.9-beta.7 (xxxxxx)"), Some("7".to_string()));
-    // multiple digits
-    assert_eq!(extract_beta_rev("1.99.9-beta.777 (xxxxxx)"), Some("777".to_string()));
-    // nightly channel (no beta revision)
-    assert_eq!(extract_beta_rev("1.99.9-nightly (xxxxxx)"), None);
-    // stable channel (no beta revision)
-    assert_eq!(extract_beta_rev("1.99.9 (xxxxxxx)"), None);
-    // invalid string
-    assert_eq!(extract_beta_rev("invalid"), None);
-}
-
 mod defaults {
     use super::{configure, first, run_build};
     use crate::core::builder::*;
diff --git a/src/bootstrap/src/tests/config.rs b/src/bootstrap/src/tests/config.rs
index 59bd52a94..6f4323438 100644
--- a/src/bootstrap/src/tests/config.rs
+++ b/src/bootstrap/src/tests/config.rs
@@ -1,5 +1,5 @@
-use crate::core::config::TomlConfig;
 use super::{Config, Flags};
+use crate::core::config::{LldMode, TomlConfig};
 
 use clap::CommandFactory;
 use serde::Deserialize;
@@ -24,19 +24,19 @@ fn download_ci_llvm() {
     }
 
     let parse_llvm = |s| parse(s).llvm_from_ci;
-    let if_available = parse_llvm("llvm.download-ci-llvm = \"if-available\"");
+    let if_unchanged = parse_llvm("llvm.download-ci-llvm = \"if-unchanged\"");
 
     assert!(parse_llvm("llvm.download-ci-llvm = true"));
     assert!(!parse_llvm("llvm.download-ci-llvm = false"));
-    assert_eq!(parse_llvm(""), if_available);
-    assert_eq!(parse_llvm("rust.channel = \"dev\""), if_available);
+    assert_eq!(parse_llvm(""), if_unchanged);
+    assert_eq!(parse_llvm("rust.channel = \"dev\""), if_unchanged);
     assert!(!parse_llvm("rust.channel = \"stable\""));
-    assert!(parse_llvm("build.build = \"x86_64-unknown-linux-gnu\""));
-    assert!(parse_llvm(
-        "llvm.assertions = true \r\n build.build = \"x86_64-unknown-linux-gnu\" \r\n llvm.download-ci-llvm = \"if-available\""
-    ));
+    assert_eq!(parse_llvm("build.build = \"x86_64-unknown-linux-gnu\""), if_unchanged);
+    assert_eq!(parse_llvm(
+        "llvm.assertions = true \r\n build.build = \"x86_64-unknown-linux-gnu\" \r\n llvm.download-ci-llvm = \"if-unchanged\""
+    ), if_unchanged);
     assert!(!parse_llvm(
-        "llvm.assertions = true \r\n build.build = \"aarch64-apple-darwin\" \r\n llvm.download-ci-llvm = \"if-available\""
+        "llvm.assertions = true \r\n build.build = \"aarch64-apple-darwin\" \r\n llvm.download-ci-llvm = \"if-unchanged\""
     ));
 }
 
@@ -217,3 +217,12 @@ fn verify_file_integrity() {
 
     remove_file(tempfile).unwrap();
 }
+
+#[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));
+}
diff --git a/src/bootstrap/src/tests/helpers.rs b/src/bootstrap/src/tests/helpers.rs
new file mode 100644
index 000000000..afe18aeba
--- /dev/null
+++ b/src/bootstrap/src/tests/helpers.rs
@@ -0,0 +1,59 @@
+use crate::utils::helpers::{extract_beta_rev, hex_encode, make};
+use std::path::PathBuf;
+
+#[test]
+fn test_make() {
+    for (host, make_path) in vec![
+        ("dragonfly", PathBuf::from("gmake")),
+        ("netbsd", PathBuf::from("gmake")),
+        ("freebsd", PathBuf::from("gmake")),
+        ("openbsd", PathBuf::from("gmake")),
+        ("linux", PathBuf::from("make")),
+        // for checking the default
+        ("_", PathBuf::from("make")),
+    ] {
+        assert_eq!(make(host), make_path);
+    }
+}
+
+#[cfg(unix)]
+#[test]
+fn test_absolute_unix() {
+    use crate::utils::helpers::absolute_unix;
+
+    // Test an absolute path
+    let path = PathBuf::from("/home/user/file.txt");
+    assert_eq!(absolute_unix(&path).unwrap(), PathBuf::from("/home/user/file.txt"));
+
+    // Test an absolute path with double leading slashes
+    let path = PathBuf::from("//root//file.txt");
+    assert_eq!(absolute_unix(&path).unwrap(), PathBuf::from("//root/file.txt"));
+
+    // Test a relative path
+    let path = PathBuf::from("relative/path");
+    assert_eq!(
+        absolute_unix(&path).unwrap(),
+        std::env::current_dir().unwrap().join("relative/path")
+    );
+}
+
+#[test]
+fn test_beta_rev_parsing() {
+    // single digit revision
+    assert_eq!(extract_beta_rev("1.99.9-beta.7 (xxxxxx)"), Some("7".to_string()));
+    // multiple digits
+    assert_eq!(extract_beta_rev("1.99.9-beta.777 (xxxxxx)"), Some("777".to_string()));
+    // nightly channel (no beta revision)
+    assert_eq!(extract_beta_rev("1.99.9-nightly (xxxxxx)"), None);
+    // stable channel (no beta revision)
+    assert_eq!(extract_beta_rev("1.99.9 (xxxxxxx)"), None);
+    // invalid string
+    assert_eq!(extract_beta_rev("invalid"), None);
+}
+
+#[test]
+fn test_string_to_hex_encode() {
+    let input_string = "Hello, World!";
+    let hex_string = hex_encode(input_string);
+    assert_eq!(hex_string, "48656c6c6f2c20576f726c6421");
+}
diff --git a/src/bootstrap/src/tests/setup.rs b/src/bootstrap/src/tests/setup.rs
index 0fe6e4a46..3e4d66c74 100644
--- a/src/bootstrap/src/tests/setup.rs
+++ b/src/bootstrap/src/tests/setup.rs
@@ -1,11 +1,12 @@
 use super::{RUST_ANALYZER_SETTINGS, SETTINGS_HASHES};
+use crate::utils::helpers::hex_encode;
 use sha2::Digest;
 
 #[test]
 fn check_matching_settings_hash() {
     let mut hasher = sha2::Sha256::new();
     hasher.update(&RUST_ANALYZER_SETTINGS);
-    let hash = hex::encode(hasher.finalize().as_slice());
+    let hash = hex_encode(hasher.finalize().as_slice());
     assert_eq!(
         &hash,
         SETTINGS_HASHES.last().unwrap(),
diff --git a/src/bootstrap/src/utils/bin_helpers.rs b/src/bootstrap/src/utils/bin_helpers.rs
index c90fd2805..9c4e039ea 100644
--- a/src/bootstrap/src/utils/bin_helpers.rs
+++ b/src/bootstrap/src/utils/bin_helpers.rs
@@ -2,14 +2,18 @@
 //! dependency on the bootstrap library. This reduces the binary size and
 //! improves compilation time by reducing the linking time.
 
+use std::env;
+use std::fs::OpenOptions;
+use std::io::Write;
+use std::process::Command;
+use std::str::FromStr;
+
 /// Parses the value of the "RUSTC_VERBOSE" environment variable and returns it as a `usize`.
 /// If it was not defined, returns 0 by default.
 ///
 /// Panics if "RUSTC_VERBOSE" is defined with the value that is not an unsigned integer.
 pub(crate) fn parse_rustc_verbose() -> usize {
-    use std::str::FromStr;
-
-    match std::env::var("RUSTC_VERBOSE") {
+    match env::var("RUSTC_VERBOSE") {
         Ok(s) => usize::from_str(&s).expect("RUSTC_VERBOSE should be an integer"),
         Err(_) => 0,
     }
@@ -19,10 +23,29 @@ pub(crate) fn parse_rustc_verbose() -> usize {
 ///
 /// If "RUSTC_STAGE" was not set, the program will be terminated with 101.
 pub(crate) fn parse_rustc_stage() -> String {
-    std::env::var("RUSTC_STAGE").unwrap_or_else(|_| {
+    env::var("RUSTC_STAGE").unwrap_or_else(|_| {
         // Don't panic here; it's reasonable to try and run these shims directly. Give a helpful error instead.
         eprintln!("rustc shim: FATAL: RUSTC_STAGE was not set");
         eprintln!("rustc shim: NOTE: use `x.py build -vvv` to see all environment variables set by bootstrap");
         std::process::exit(101);
     })
 }
+
+/// Writes the command invocation to a file if `DUMP_BOOTSTRAP_SHIMS` is set during bootstrap.
+///
+/// Before writing it, replaces user-specific values to create generic dumps for cross-environment
+/// comparisons.
+pub(crate) fn maybe_dump(dump_name: String, cmd: &Command) {
+    if let Ok(dump_dir) = env::var("DUMP_BOOTSTRAP_SHIMS") {
+        let dump_file = format!("{dump_dir}/{dump_name}");
+
+        let mut file =
+            OpenOptions::new().create(true).write(true).append(true).open(&dump_file).unwrap();
+
+        let cmd_dump = format!("{:?}\n", cmd);
+        let cmd_dump = cmd_dump.replace(&env::var("BUILD_OUT").unwrap(), "${BUILD_OUT}");
+        let cmd_dump = cmd_dump.replace(&env::var("CARGO_HOME").unwrap(), "${CARGO_HOME}");
+
+        file.write_all(cmd_dump.as_bytes()).expect("Unable to write file");
+    }
+}
diff --git a/src/bootstrap/src/utils/cc_detect.rs b/src/bootstrap/src/utils/cc_detect.rs
index 52b36ce75..fb5b9d8c8 100644
--- a/src/bootstrap/src/utils/cc_detect.rs
+++ b/src/bootstrap/src/utils/cc_detect.rs
@@ -39,7 +39,7 @@ fn cc2ar(cc: &Path, target: TargetSelection) -> Option<PathBuf> {
         Some(PathBuf::from(ar))
     } else if let Some(ar) = env::var_os("AR") {
         Some(PathBuf::from(ar))
-    } else if target.contains("msvc") {
+    } else if target.is_msvc() {
         None
     } else if target.contains("musl") {
         Some(PathBuf::from("ar"))
@@ -78,7 +78,7 @@ fn new_cc_build(build: &Build, target: TargetSelection) -> cc::Build {
             cfg.static_crt(a);
         }
         None => {
-            if target.contains("msvc") {
+            if target.is_msvc() {
                 cfg.static_crt(true);
             }
             if target.contains("musl") {
diff --git a/src/bootstrap/src/utils/change_tracker.rs b/src/bootstrap/src/utils/change_tracker.rs
new file mode 100644
index 000000000..8b53a6154
--- /dev/null
+++ b/src/bootstrap/src/utils/change_tracker.rs
@@ -0,0 +1,99 @@
+//! This module facilitates the tracking system for major changes made to the bootstrap,
+//! with the goal of keeping developers synchronized with important modifications in
+//! the bootstrap.
+
+#[derive(Clone, Debug)]
+pub struct ChangeInfo {
+    /// Represents the ID of PR caused major change on bootstrap.
+    pub change_id: usize,
+    pub severity: ChangeSeverity,
+    /// Provides a short summary of the change that will guide developers
+    /// on "how to handle/behave" in response to the changes.
+    pub summary: &'static str,
+}
+
+#[derive(Clone, Debug)]
+pub enum ChangeSeverity {
+    /// Used when build configurations continue working as before.
+    Info,
+    /// Used when the default value of an option changes, or support for an option is removed entirely,
+    /// potentially requiring developers to update their build configurations.
+    Warning,
+}
+
+impl ToString for ChangeSeverity {
+    fn to_string(&self) -> String {
+        match self {
+            ChangeSeverity::Info => "INFO".to_string(),
+            ChangeSeverity::Warning => "WARNING".to_string(),
+        }
+    }
+}
+
+pub fn find_recent_config_change_ids(current_id: usize) -> Vec<ChangeInfo> {
+    if !CONFIG_CHANGE_HISTORY.iter().any(|config| config.change_id == current_id) {
+        // If the current change-id is greater than the most recent one, return
+        // an empty list (it may be due to switching from a recent branch to an
+        // older one); otherwise, return the full list (assuming the user provided
+        // the incorrect change-id by accident).
+        if let Some(config) = CONFIG_CHANGE_HISTORY.iter().max_by_key(|config| config.change_id) {
+            if &current_id > &config.change_id {
+                return Vec::new();
+            }
+        }
+
+        return CONFIG_CHANGE_HISTORY.to_vec();
+    }
+
+    let index =
+        CONFIG_CHANGE_HISTORY.iter().position(|config| config.change_id == current_id).unwrap();
+
+    CONFIG_CHANGE_HISTORY
+        .iter()
+        .skip(index + 1) // Skip the current_id and IDs before it
+        .cloned()
+        .collect()
+}
+
+/// Keeps track of major changes made to the bootstrap configuration.
+///
+/// If you make any major changes (such as adding new values or changing default values),
+/// please ensure adding `ChangeInfo` to the end(because the list must be sorted by the merge date)
+/// of this list.
+pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
+    ChangeInfo {
+        change_id: 115898,
+        severity: ChangeSeverity::Info,
+        summary: "Implementation of this change-tracking system. Ignore this.",
+    },
+    ChangeInfo {
+        change_id: 116998,
+        severity: ChangeSeverity::Info,
+        summary: "Removed android-ndk r15 support in favor of android-ndk r25b.",
+    },
+    ChangeInfo {
+        change_id: 117435,
+        severity: ChangeSeverity::Info,
+        summary: "New option `rust.parallel-compiler` added to config.toml.",
+    },
+    ChangeInfo {
+        change_id: 116881,
+        severity: ChangeSeverity::Warning,
+        summary: "Default value of `download-ci-llvm` was changed for `codegen` profile.",
+    },
+    ChangeInfo {
+        change_id: 117813,
+        severity: ChangeSeverity::Info,
+        summary: "Use of the `if-available` value for `download-ci-llvm` is deprecated; prefer using the new `if-unchanged` value.",
+    },
+    ChangeInfo {
+        change_id: 116278,
+        severity: ChangeSeverity::Info,
+        summary: "The `rust.use-lld` configuration now has different options ('external'/true or 'self-contained'), and its behaviour has changed.",
+    },
+    ChangeInfo {
+        change_id: 118703,
+        severity: ChangeSeverity::Info,
+        summary: "Removed rust.run_dsymutil and dist.gpg_password_file config options, as they were unused.",
+    },
+];
diff --git a/src/bootstrap/src/utils/dylib.rs b/src/bootstrap/src/utils/dylib.rs
index 279a6a010..b6e7aec17 100644
--- a/src/bootstrap/src/utils/dylib.rs
+++ b/src/bootstrap/src/utils/dylib.rs
@@ -25,3 +25,16 @@ pub fn dylib_path() -> Vec<std::path::PathBuf> {
     };
     std::env::split_paths(&var).collect()
 }
+
+/// Given an executable called `name`, return the filename for the
+/// executable for a particular target.
+#[allow(dead_code)]
+pub fn exe(name: &str, target: &str) -> String {
+    if target.contains("windows") {
+        format!("{name}.exe")
+    } else if target.contains("uefi") {
+        format!("{name}.efi")
+    } else {
+        name.to_string()
+    }
+}
diff --git a/src/bootstrap/src/utils/helpers.rs b/src/bootstrap/src/utils/helpers.rs
index 5bc81f2d9..0c4297db6 100644
--- a/src/bootstrap/src/utils/helpers.rs
+++ b/src/bootstrap/src/utils/helpers.rs
@@ -5,19 +5,25 @@
 
 use build_helper::util::fail;
 use std::env;
+use std::ffi::OsStr;
 use std::fs;
 use std::io;
 use std::path::{Path, PathBuf};
 use std::process::{Command, Stdio};
 use std::str;
+use std::sync::OnceLock;
 use std::time::{Instant, SystemTime, UNIX_EPOCH};
 
 use crate::core::builder::Builder;
 use crate::core::config::{Config, TargetSelection};
-use crate::OnceCell;
+use crate::LldMode;
 
 pub use crate::utils::dylib::{dylib_path, dylib_path_var};
 
+#[cfg(test)]
+#[path = "../tests/helpers.rs"]
+mod tests;
+
 /// A helper macro to `unwrap` a result except also print out details like:
 ///
 /// * The file/line of the panic
@@ -44,16 +50,8 @@ macro_rules! t {
 }
 pub use t;
 
-/// Given an executable called `name`, return the filename for the
-/// executable for a particular target.
 pub fn exe(name: &str, target: TargetSelection) -> String {
-    if target.contains("windows") {
-        format!("{name}.exe")
-    } else if target.contains("uefi") {
-        format!("{name}.efi")
-    } else {
-        name.to_string()
-    }
+    crate::utils::dylib::exe(name, &target.triple)
 }
 
 /// Returns `true` if the file name given looks like a dynamic library.
@@ -70,7 +68,7 @@ pub fn is_debug_info(name: &str) -> bool {
 /// Returns the corresponding relative library directory that the compiler's
 /// dylibs will be found in.
 pub fn libdir(target: TargetSelection) -> &'static str {
-    if target.contains("windows") { "bin" } else { "lib" }
+    if target.is_windows() { "bin" } else { "lib" }
 }
 
 /// Adds a list of lookup paths to `cmd`'s dynamic library lookup path.
@@ -189,7 +187,7 @@ pub fn target_supports_cranelift_backend(target: TargetSelection) -> bool {
             || target.contains("aarch64")
             || target.contains("s390x")
             || target.contains("riscv64gc")
-    } else if target.contains("darwin") || target.contains("windows") {
+    } else if target.contains("darwin") || target.is_windows() {
         target.contains("x86_64")
     } else {
         false
@@ -443,17 +441,29 @@ pub fn get_clang_cl_resource_dir(clang_cl_path: &str) -> PathBuf {
     clang_rt_dir.to_path_buf()
 }
 
-pub fn lld_flag_no_threads(is_windows: bool) -> &'static str {
-    static LLD_NO_THREADS: OnceCell<(&'static str, &'static str)> = OnceCell::new();
-    let (windows, other) = LLD_NO_THREADS.get_or_init(|| {
-        let out = output(Command::new("lld").arg("-flavor").arg("ld").arg("--version"));
-        let newer = match (out.find(char::is_numeric), out.find('.')) {
-            (Some(b), Some(e)) => out.as_str()[b..e].parse::<i32>().ok().unwrap_or(14) > 10,
+/// Returns a flag that configures LLD to use only a single thread.
+/// If we use an external LLD, we need to find out which version is it to know which flag should we
+/// pass to it (LLD older than version 10 had a different flag).
+fn lld_flag_no_threads(lld_mode: LldMode, is_windows: bool) -> &'static str {
+    static LLD_NO_THREADS: OnceLock<(&'static str, &'static str)> = OnceLock::new();
+
+    let new_flags = ("/threads:1", "--threads=1");
+    let old_flags = ("/no-threads", "--no-threads");
+
+    let (windows_flag, other_flag) = LLD_NO_THREADS.get_or_init(|| {
+        let newer_version = match lld_mode {
+            LldMode::External => {
+                let out = output(Command::new("lld").arg("-flavor").arg("ld").arg("--version"));
+                match (out.find(char::is_numeric), out.find('.')) {
+                    (Some(b), Some(e)) => out.as_str()[b..e].parse::<i32>().ok().unwrap_or(14) > 10,
+                    _ => true,
+                }
+            }
             _ => true,
         };
-        if newer { ("/threads:1", "--threads=1") } else { ("/no-threads", "--no-threads") }
+        if newer_version { new_flags } else { old_flags }
     });
-    if is_windows { windows } else { other }
+    if is_windows { windows_flag } else { other_flag }
 }
 
 pub fn dir_is_empty(dir: &Path) -> bool {
@@ -470,3 +480,75 @@ pub fn extract_beta_rev(version: &str) -> Option<String> {
 
     count
 }
+
+pub enum LldThreads {
+    Yes,
+    No,
+}
+
+/// Returns the linker arguments for rustc/rustdoc for the given builder and target.
+pub fn linker_args(
+    builder: &Builder<'_>,
+    target: TargetSelection,
+    lld_threads: LldThreads,
+) -> Vec<String> {
+    let mut args = linker_flags(builder, target, lld_threads);
+
+    if let Some(linker) = builder.linker(target) {
+        args.push(format!("-Clinker={}", linker.display()));
+    }
+
+    args
+}
+
+/// Returns the linker arguments for rustc/rustdoc for the given builder and target, without the
+/// -Clinker flag.
+pub fn linker_flags(
+    builder: &Builder<'_>,
+    target: TargetSelection,
+    lld_threads: LldThreads,
+) -> Vec<String> {
+    let mut args = vec![];
+    if !builder.is_lld_direct_linker(target) && builder.config.lld_mode.is_used() {
+        args.push(String::from("-Clink-arg=-fuse-ld=lld"));
+
+        if matches!(lld_threads, LldThreads::No) {
+            args.push(format!(
+                "-Clink-arg=-Wl,{}",
+                lld_flag_no_threads(builder.config.lld_mode, target.is_windows())
+            ));
+        }
+    }
+    args
+}
+
+pub fn add_rustdoc_cargo_linker_args(
+    cmd: &mut Command,
+    builder: &Builder<'_>,
+    target: TargetSelection,
+    lld_threads: LldThreads,
+) {
+    let args = linker_args(builder, target, lld_threads);
+    let mut flags = cmd
+        .get_envs()
+        .find_map(|(k, v)| if k == OsStr::new("RUSTDOCFLAGS") { v } else { None })
+        .unwrap_or_default()
+        .to_os_string();
+    for arg in args {
+        if !flags.is_empty() {
+            flags.push(" ");
+        }
+        flags.push(arg);
+    }
+    if !flags.is_empty() {
+        cmd.env("RUSTDOCFLAGS", flags);
+    }
+}
+
+/// Converts `T` into a hexadecimal `String`.
+pub fn hex_encode<T>(input: T) -> String
+where
+    T: AsRef<[u8]>,
+{
+    input.as_ref().iter().map(|x| format!("{:02x}", x)).collect()
+}
diff --git a/src/bootstrap/src/utils/mod.rs b/src/bootstrap/src/utils/mod.rs
index 8ca22d008..cb535f0e1 100644
--- a/src/bootstrap/src/utils/mod.rs
+++ b/src/bootstrap/src/utils/mod.rs
@@ -4,6 +4,7 @@
 
 pub(crate) mod cache;
 pub(crate) mod cc_detect;
+pub(crate) mod change_tracker;
 pub(crate) mod channel;
 pub(crate) mod dylib;
 pub(crate) mod exec;