diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index f9904cb610d2d..3d46548807705 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -989,21 +989,30 @@ def update_submodules(self):
         slow_submodules = self.get_toml('fast-submodules') == "false"
         start_time = time()
         if slow_submodules:
-            print('Unconditionally updating all submodules')
+            print('Unconditionally updating submodules')
         else:
             print('Updating only changed submodules')
         default_encoding = sys.getdefaultencoding()
-        submodules = [s.split(' ', 1)[1] for s in subprocess.check_output(
-            ["git", "config", "--file",
-             os.path.join(self.rust_root, ".gitmodules"),
-             "--get-regexp", "path"]
-        ).decode(default_encoding).splitlines()]
+        # Only update submodules that are needed to build bootstrap.  These are needed because Cargo
+        # currently requires everything in a workspace to be "locally present" when starting a
+        # build, and will give a hard error if any Cargo.toml files are missing.
+        # FIXME: Is there a way to avoid cloning these eagerly? Bootstrap itself doesn't need to
+        #   share a workspace with any tools - maybe it could be excluded from the workspace?
+        #   That will still require cloning the submodules the second you check the standard
+        #   library, though...
+        # FIXME: Is there a way to avoid hard-coding the submodules required?
+        # WARNING: keep this in sync with the submodules hard-coded in bootstrap/lib.rs
+        submodules = [
+            "src/tools/rust-installer",
+            "src/tools/cargo",
+            "src/tools/rls",
+            "src/tools/miri",
+            "library/backtrace",
+            "library/stdarch"
+        ]
         filtered_submodules = []
         submodules_names = []
         for module in submodules:
-            # This is handled by native::Llvm in rustbuild, not here
-            if module.endswith("llvm-project"):
-                continue
             check = self.check_submodule(module, slow_submodules)
             filtered_submodules.append((module, check))
             submodules_names.append(module)
diff --git a/src/bootstrap/check.rs b/src/bootstrap/check.rs
index 5003d6693f72c..bc106746e57e0 100644
--- a/src/bootstrap/check.rs
+++ b/src/bootstrap/check.rs
@@ -7,7 +7,7 @@ use crate::config::TargetSelection;
 use crate::tool::{prepare_tool_cargo, SourceType};
 use crate::INTERNER;
 use crate::{Compiler, Mode, Subcommand};
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub struct Std {
@@ -72,6 +72,8 @@ impl Step for Std {
     }
 
     fn run(self, builder: &Builder<'_>) {
+        builder.update_submodule(&Path::new("library").join("stdarch"));
+
         let target = self.target;
         let compiler = builder.compiler(builder.top_stage, builder.config.build);
 
diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index 1fae4bee732c0..8c28d0b60fa32 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -79,6 +79,8 @@ impl Step for Std {
             return;
         }
 
+        builder.update_submodule(&Path::new("library").join("stdarch"));
+
         let mut target_deps = builder.ensure(StartupObjects { compiler, target });
 
         let compiler_to_use = builder.compiler_for(compiler.stage, compiler.host, target);
diff --git a/src/bootstrap/doc.rs b/src/bootstrap/doc.rs
index d3f2c87c0d22f..9ec5d4d8ccdb4 100644
--- a/src/bootstrap/doc.rs
+++ b/src/bootstrap/doc.rs
@@ -22,8 +22,17 @@ use crate::config::{Config, TargetSelection};
 use crate::tool::{self, prepare_tool_cargo, SourceType, Tool};
 use crate::util::symlink_dir;
 
+macro_rules! submodule_helper {
+    ($path:expr, submodule) => {
+        $path
+    };
+    ($path:expr, submodule = $submodule:literal) => {
+        $submodule
+    };
+}
+
 macro_rules! book {
-    ($($name:ident, $path:expr, $book_name:expr;)+) => {
+    ($($name:ident, $path:expr, $book_name:expr $(, submodule $(= $submodule:literal)? )? ;)+) => {
         $(
             #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
         pub struct $name {
@@ -46,6 +55,10 @@ macro_rules! book {
             }
 
             fn run(self, builder: &Builder<'_>) {
+                $(
+                    let path = Path::new(submodule_helper!( $path, submodule $( = $submodule )? ));
+                    builder.update_submodule(&path);
+                )?
                 builder.ensure(RustbookSrc {
                     target: self.target,
                     name: INTERNER.intern_str($book_name),
@@ -59,13 +72,16 @@ macro_rules! book {
 
 // NOTE: When adding a book here, make sure to ALSO build the book by
 // adding a build step in `src/bootstrap/builder.rs`!
+// NOTE: Make sure to add the corresponding submodule when adding a new book.
+// FIXME: Make checking for a submodule automatic somehow (maybe by having a list of all submodules
+// and checking against it?).
 book!(
-    CargoBook, "src/tools/cargo/src/doc", "cargo";
-    EditionGuide, "src/doc/edition-guide", "edition-guide";
-    EmbeddedBook, "src/doc/embedded-book", "embedded-book";
-    Nomicon, "src/doc/nomicon", "nomicon";
-    Reference, "src/doc/reference", "reference";
-    RustByExample, "src/doc/rust-by-example", "rust-by-example";
+    CargoBook, "src/tools/cargo/src/doc", "cargo", submodule = "src/tools/cargo";
+    EditionGuide, "src/doc/edition-guide", "edition-guide", submodule;
+    EmbeddedBook, "src/doc/embedded-book", "embedded-book", submodule;
+    Nomicon, "src/doc/nomicon", "nomicon", submodule;
+    Reference, "src/doc/reference", "reference", submodule;
+    RustByExample, "src/doc/rust-by-example", "rust-by-example", submodule;
     RustdocBook, "src/doc/rustdoc", "rustdoc";
 );
 
@@ -197,6 +213,9 @@ impl Step for TheBook {
     /// * Index page
     /// * Redirect pages
     fn run(self, builder: &Builder<'_>) {
+        let relative_path = Path::new("src").join("doc").join("book");
+        builder.update_submodule(&relative_path);
+
         let compiler = self.compiler;
         let target = self.target;
 
@@ -204,7 +223,7 @@ impl Step for TheBook {
         builder.ensure(RustbookSrc {
             target,
             name: INTERNER.intern_str("book"),
-            src: INTERNER.intern_path(builder.src.join("src/doc/book")),
+            src: INTERNER.intern_path(builder.src.join(&relative_path)),
         });
 
         // building older edition redirects
@@ -212,7 +231,7 @@ impl Step for TheBook {
             builder.ensure(RustbookSrc {
                 target,
                 name: INTERNER.intern_string(format!("book/{}", edition)),
-                src: INTERNER.intern_path(builder.src.join("src/doc/book").join(edition)),
+                src: INTERNER.intern_path(builder.src.join(&relative_path).join(edition)),
             });
         }
 
@@ -221,7 +240,7 @@ impl Step for TheBook {
 
         // build the redirect pages
         builder.info(&format!("Documenting book redirect pages ({})", target));
-        for file in t!(fs::read_dir(builder.src.join("src/doc/book/redirects"))) {
+        for file in t!(fs::read_dir(builder.src.join(&relative_path).join("redirects"))) {
             let file = t!(file);
             let path = file.path();
             let path = path.to_str().unwrap();
diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index 69c5de0b40831..6bcdbe3e4bbbb 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -477,17 +477,120 @@ impl Build {
         slice::from_ref(&self.build.triple)
     }
 
+    // modified from `check_submodule` and `update_submodule` in bootstrap.py
+    /// Given a path to the directory of a submodule, update it.
+    ///
+    /// `relative_path` should be relative to the root of the git repository, not an absolute path.
+    pub(crate) fn update_submodule(&self, relative_path: &Path) {
+        fn dir_is_empty(dir: &Path) -> bool {
+            t!(std::fs::read_dir(dir)).next().is_none()
+        }
+
+        if !self.config.submodules {
+            return;
+        }
+
+        let absolute_path = self.config.src.join(relative_path);
+
+        // NOTE: The check for the empty directory is here because when running x.py the first time,
+        // the submodule won't be checked out. Check it out now so we can build it.
+        if !channel::GitInfo::new(false, relative_path).is_git() && !dir_is_empty(&absolute_path) {
+            return;
+        }
+
+        // check_submodule
+        if self.config.fast_submodules {
+            let checked_out_hash = output(
+                Command::new("git").args(&["rev-parse", "HEAD"]).current_dir(&absolute_path),
+            );
+            // update_submodules
+            let recorded = output(
+                Command::new("git")
+                    .args(&["ls-tree", "HEAD"])
+                    .arg(relative_path)
+                    .current_dir(&self.config.src),
+            );
+            let actual_hash = recorded
+                .split_whitespace()
+                .nth(2)
+                .unwrap_or_else(|| panic!("unexpected output `{}`", recorded));
+
+            // update_submodule
+            if actual_hash == checked_out_hash.trim_end() {
+                // already checked out
+                return;
+            }
+        }
+
+        println!("Updating submodule {}", relative_path.display());
+        self.run(
+            Command::new("git")
+                .args(&["submodule", "-q", "sync"])
+                .arg(relative_path)
+                .current_dir(&self.config.src),
+        );
+
+        // Try passing `--progress` to start, then run git again without if that fails.
+        let update = |progress: bool| {
+            let mut git = Command::new("git");
+            git.args(&["submodule", "update", "--init", "--recursive"]);
+            if progress {
+                git.arg("--progress");
+            }
+            git.arg(relative_path).current_dir(&self.config.src);
+            git
+        };
+        // NOTE: doesn't use `try_run` because this shouldn't print an error if it fails.
+        if !update(true).status().map_or(false, |status| status.success()) {
+            self.run(&mut update(false));
+        }
+
+        self.run(Command::new("git").args(&["reset", "-q", "--hard"]).current_dir(&absolute_path));
+        self.run(Command::new("git").args(&["clean", "-qdfx"]).current_dir(absolute_path));
+    }
+
+    /// If any submodule has been initialized already, sync it unconditionally.
+    /// This avoids contributors checking in a submodule change by accident.
+    pub fn maybe_update_submodules(&self) {
+        // WARNING: keep this in sync with the submodules hard-coded in bootstrap.py
+        const BOOTSTRAP_SUBMODULES: &[&str] = &[
+            "src/tools/rust-installer",
+            "src/tools/cargo",
+            "src/tools/rls",
+            "src/tools/miri",
+            "library/backtrace",
+            "library/stdarch",
+        ];
+        // Avoid running git when there isn't a git checkout.
+        if !self.config.submodules {
+            return;
+        }
+        let output = output(
+            Command::new("git")
+                .args(&["config", "--file"])
+                .arg(&self.config.src.join(".gitmodules"))
+                .args(&["--get-regexp", "path"]),
+        );
+        for line in output.lines() {
+            // Look for `submodule.$name.path = $path`
+            // Sample output: `submodule.src/rust-installer.path src/tools/rust-installer`
+            let submodule = Path::new(line.splitn(2, ' ').nth(1).unwrap());
+            // avoid updating submodules twice
+            if !BOOTSTRAP_SUBMODULES.iter().any(|&p| Path::new(p) == submodule)
+                && channel::GitInfo::new(false, submodule).is_git()
+            {
+                self.update_submodule(submodule);
+            }
+        }
+    }
+
     /// Executes the entire build, as configured by the flags and configuration.
     pub fn build(&mut self) {
         unsafe {
             job::setup(self);
         }
 
-        // If the LLVM submodule has been initialized already, sync it unconditionally. This avoids
-        // contributors checking in a submodule change by accident.
-        if self.in_tree_llvm_info.is_git() {
-            native::update_llvm_submodule(self);
-        }
+        self.maybe_update_submodules();
 
         if let Subcommand::Format { check, paths } = &self.config.cmd {
             return format::format(self, *check, &paths);
diff --git a/src/bootstrap/native.rs b/src/bootstrap/native.rs
index 0be42d9b23486..1be414b29a1ae 100644
--- a/src/bootstrap/native.rs
+++ b/src/bootstrap/native.rs
@@ -21,7 +21,7 @@ use build_helper::{output, t};
 use crate::builder::{Builder, RunConfig, ShouldRun, Step};
 use crate::config::TargetSelection;
 use crate::util::{self, exe};
-use crate::{Build, GitRepo};
+use crate::GitRepo;
 use build_helper::up_to_date;
 
 pub struct Meta {
@@ -91,86 +91,6 @@ pub fn prebuilt_llvm_config(
     Err(Meta { stamp, build_llvm_config, out_dir, root: root.into() })
 }
 
-// modified from `check_submodule` and `update_submodule` in bootstrap.py
-pub(crate) fn update_llvm_submodule(build: &Build) {
-    let llvm_project = &Path::new("src").join("llvm-project");
-
-    fn dir_is_empty(dir: &Path) -> bool {
-        t!(std::fs::read_dir(dir)).next().is_none()
-    }
-
-    if !build.config.submodules {
-        return;
-    }
-
-    // NOTE: The check for the empty directory is here because when running x.py
-    // the first time, the llvm submodule won't be checked out. Check it out
-    // now so we can build it.
-    if !build.in_tree_llvm_info.is_git() && !dir_is_empty(&build.config.src.join(llvm_project)) {
-        return;
-    }
-
-    // check_submodule
-    if build.config.fast_submodules {
-        let checked_out_hash = output(
-            Command::new("git")
-                .args(&["rev-parse", "HEAD"])
-                .current_dir(build.config.src.join(llvm_project)),
-        );
-        // update_submodules
-        let recorded = output(
-            Command::new("git")
-                .args(&["ls-tree", "HEAD"])
-                .arg(llvm_project)
-                .current_dir(&build.config.src),
-        );
-        let actual_hash = recorded
-            .split_whitespace()
-            .nth(2)
-            .unwrap_or_else(|| panic!("unexpected output `{}`", recorded));
-
-        // update_submodule
-        if actual_hash == checked_out_hash.trim_end() {
-            // already checked out
-            return;
-        }
-    }
-
-    println!("Updating submodule {}", llvm_project.display());
-    build.run(
-        Command::new("git")
-            .args(&["submodule", "-q", "sync"])
-            .arg(llvm_project)
-            .current_dir(&build.config.src),
-    );
-
-    // Try passing `--progress` to start, then run git again without if that fails.
-    let update = |progress: bool| {
-        let mut git = Command::new("git");
-        git.args(&["submodule", "update", "--init", "--recursive"]);
-        if progress {
-            git.arg("--progress");
-        }
-        git.arg(llvm_project).current_dir(&build.config.src);
-        git
-    };
-    // NOTE: doesn't use `try_run` because this shouldn't print an error if it fails.
-    if !update(true).status().map_or(false, |status| status.success()) {
-        build.run(&mut update(false));
-    }
-
-    build.run(
-        Command::new("git")
-            .args(&["reset", "-q", "--hard"])
-            .current_dir(build.config.src.join(llvm_project)),
-    );
-    build.run(
-        Command::new("git")
-            .args(&["clean", "-qdfx"])
-            .current_dir(build.config.src.join(llvm_project)),
-    );
-}
-
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
 pub struct Llvm {
     pub target: TargetSelection,
@@ -208,9 +128,7 @@ impl Step for Llvm {
                 Err(m) => m,
             };
 
-        if !builder.config.dry_run {
-            update_llvm_submodule(builder);
-        }
+        builder.update_submodule(&Path::new("src").join("llvm-project"));
         if builder.config.llvm_link_shared
             && (target.contains("windows") || target.contains("apple-darwin"))
         {
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 61ffae47e2ad0..50980d25cb288 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -1833,7 +1833,10 @@ impl Step for RustcGuide {
     }
 
     fn run(self, builder: &Builder<'_>) {
-        let src = builder.src.join("src/doc/rustc-dev-guide");
+        let relative_path = Path::new("src").join("doc").join("rustc-dev-guide");
+        builder.update_submodule(&relative_path);
+
+        let src = builder.src.join(relative_path);
         let mut rustbook_cmd = builder.tool_cmd(Tool::Rustbook);
         let toolstate = if try_run(builder, rustbook_cmd.arg("linkcheck").arg(&src)) {
             ToolState::TestPass
diff --git a/src/bootstrap/tool.rs b/src/bootstrap/tool.rs
index aa7fe658df320..f5e3f61dcc88f 100644
--- a/src/bootstrap/tool.rs
+++ b/src/bootstrap/tool.rs
@@ -1,7 +1,7 @@
 use std::collections::HashSet;
 use std::env;
 use std::fs;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::process::{exit, Command};
 
 use build_helper::t;
@@ -670,7 +670,8 @@ macro_rules! tool_extended {
        $path:expr,
        $tool_name:expr,
        stable = $stable:expr,
-       $(in_tree = $in_tree:expr,)*
+       $(in_tree = $in_tree:expr,)?
+       $(submodule = $submodule:literal,)?
        $extra_deps:block;)+) => {
         $(
             #[derive(Debug, Clone, Hash, PartialEq, Eq)]
@@ -714,6 +715,7 @@ macro_rules! tool_extended {
             #[allow(unused_mut)]
             fn run(mut $sel, $builder: &Builder<'_>) -> Option<PathBuf> {
                 $extra_deps
+                $( $builder.update_submodule(&Path::new("src").join("tools").join($submodule)); )?
                 $builder.ensure(ToolBuild {
                     compiler: $sel.compiler,
                     target: $sel.target,
@@ -736,6 +738,8 @@ macro_rules! tool_extended {
 
 // Note: tools need to be also added to `Builder::get_step_descriptions` in `builder.rs`
 // to make `./x.py build <tool>` work.
+// Note: Most submodule updates for tools are handled by bootstrap.py, since they're needed just to
+// invoke Cargo to build bootstrap. See the comment there for more details.
 tool_extended!((self, builder),
     Cargofmt, rustfmt, "src/tools/rustfmt", "cargo-fmt", stable=true, in_tree=true, {};
     CargoClippy, clippy, "src/tools/clippy", "cargo-clippy", stable=true, in_tree=true, {};
@@ -752,7 +756,7 @@ tool_extended!((self, builder),
     };
     RustDemangler, rust_demangler, "src/tools/rust-demangler", "rust-demangler", stable=false, in_tree=true, {};
     Rustfmt, rustfmt, "src/tools/rustfmt", "rustfmt", stable=true, in_tree=true, {};
-    RustAnalyzer, rust_analyzer, "src/tools/rust-analyzer/crates/rust-analyzer", "rust-analyzer", stable=false, {};
+    RustAnalyzer, rust_analyzer, "src/tools/rust-analyzer/crates/rust-analyzer", "rust-analyzer", stable=false, submodule="rust-analyzer", {};
 );
 
 impl<'a> Builder<'a> {