Allow stripping debuginfo from LLVM's shared library

config.example.toml

@@ -56,6 +56,11 @@ changelog-seen = 2
 # Indicates whether an LLVM Release build should include debug info
 #release-debuginfo = false
 
+# When building LLVM as a dynamically linked library, and not explicitly
+# requesting debuginfo, strips the debuginfo it could contain (most often coming
+# from the C++ standard library).
+#strip-debuginfo = false
+
 # Indicates whether the LLVM assertions are enabled or not
 # NOTE: When assertions are disabled, bugs in the integration between rustc and LLVM can lead to
 # unsoundness (segfaults, etc.) in the rustc process itself, not just in the generated code.

src/bootstrap/config.rs

@@ -173,6 +173,7 @@ pub struct Config {
     pub llvm_optimize: bool,
     pub llvm_thin_lto: bool,
     pub llvm_release_debuginfo: bool,
+    pub llvm_strip_debuginfo: bool,
     pub llvm_static_stdcpp: bool,
     /// `None` if `llvm_from_ci` is true and we haven't yet downloaded llvm.
     #[cfg(not(test))]
@@ -823,6 +824,7 @@ define_config! {
         optimize: Option<bool> = "optimize",
         thin_lto: Option<bool> = "thin-lto",
         release_debuginfo: Option<bool> = "release-debuginfo",
+        strip_debuginfo: Option<bool> = "strip-debuginfo",
         assertions: Option<bool> = "assertions",
         tests: Option<bool> = "tests",
         plugins: Option<bool> = "plugins",
@@ -1511,6 +1513,7 @@ impl Config {
             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_strip_debuginfo = llvm.strip_debuginfo.unwrap_or(false);
 
             let asserts = llvm_assertions.unwrap_or(false);
             config.llvm_from_ci = match llvm.download_ci_llvm {
@@ -1552,6 +1555,7 @@ impl Config {
                 check_ci_llvm!(llvm.clang);
                 check_ci_llvm!(llvm.build_config);
                 check_ci_llvm!(llvm.plugins);
+                check_ci_llvm!(llvm.strip_debuginfo);
             }
 
             // NOTE: can never be hit when downloading from CI, since we call `check_ci_llvm!(thin_lto)` above.
@@ -1561,6 +1565,25 @@ impl Config {
                 // the link step) with each stage.
                 config.llvm_link_shared.set(Some(true));
             }
+
+            // Stripping LLVM's debuginfo is only accepted when:
+            // - using a shared library
+            // - not explicitly requesting debuginfo
+            if config.llvm_strip_debuginfo {
+                if config.llvm_release_debuginfo {
+                    panic!(
+                        "enabling `llvm.strip-debuginfo` is incompatible \
+                        with setting `llvm.release-debuginfo`"
+                    );
+                }
+                let llvm_link_shared = config.llvm_link_shared.get().unwrap_or(false);
+                if !llvm_link_shared {
+                    panic!(
+                        "enabling `llvm.strip-debuginfo` is incompatible \
+                        with statically linking LLVM"
+                    );
+                }
+            }
         } else {
             config.llvm_from_ci =
                 config.channel == "dev" && crate::llvm::is_ci_llvm_available(&config, false);

src/bootstrap/llvm.rs

@@ -491,25 +491,53 @@ impl Step for Llvm {
 
         cfg.build();
 
-        // When building LLVM with LLVM_LINK_LLVM_DYLIB for macOS, an unversioned
-        // libLLVM.dylib will be built. However, llvm-config will still look
-        // for a versioned path like libLLVM-14.dylib. Manually create a symbolic
-        // link to make llvm-config happy.
-        if builder.llvm_link_shared() && target.contains("apple-darwin") {
+        // Helper to find the name of LLVM's shared library on darwin and linux.
+        let find_llvm_lib_name = |extension| {
             let mut cmd = Command::new(&res.llvm_config);
             let version = output(cmd.arg("--version"));
             let major = version.split('.').next().unwrap();
-            let lib_name = match llvm_version_suffix {
-                Some(s) => format!("libLLVM-{major}{s}.dylib"),
-                None => format!("libLLVM-{major}.dylib"),
+            let lib_name = match &llvm_version_suffix {
+                Some(version_suffix) => format!("libLLVM-{major}{version_suffix}.{extension}"),
+                None => format!("libLLVM-{major}.{extension}"),
             };
+            lib_name
+        };
 
+        // When building LLVM with LLVM_LINK_LLVM_DYLIB for macOS, an unversioned
+        // libLLVM.dylib will be built. However, llvm-config will still look
+        // for a versioned path like libLLVM-14.dylib. Manually create a symbolic
+        // link to make llvm-config happy.
+        if builder.llvm_link_shared() && target.contains("apple-darwin") {
+            let lib_name = find_llvm_lib_name("dylib");
             let lib_llvm = out_dir.join("build").join("lib").join(lib_name);
             if !lib_llvm.exists() {
                 t!(builder.symlink_file("libLLVM.dylib", &lib_llvm));
             }
         }
 
+        // When building LLVM as a shared library on linux, it can contain debuginfo even when
+        // `llvm.release-debuginfo` is false: some debuginfo can come from the C++ standard library.
+        // If we're asked to do so, strip this debuginfo away.
+        if builder.llvm_link_shared()
+            && target.contains("linux")
+            && builder.config.llvm_strip_debuginfo
+        {
+            // Find the name of the LLVM shared library that we just built.
+            let lib_name = find_llvm_lib_name("so");
+
+            // If the shared library exists in LLVM's `/build/lib/` or `/lib/` folders, strip its
+            // debuginfo. Note: `output` will propagate any errors here.
+            let strip_if_possible = |path: PathBuf| {
+                if path.exists() {
+                    let mut cmd = Command::new("strip");
+                    cmd.arg("--strip-debug").arg(path);
+                    output(&mut cmd);
+                }
+            };
+            strip_if_possible(out_dir.join("lib").join(&lib_name));
+            strip_if_possible(out_dir.join("build").join("lib").join(&lib_name));
+        }
+
         t!(stamp.write());
 
         res

src/ci/docker/host-x86_64/dist-x86_64-linux/Dockerfile

@@ -82,6 +82,7 @@ ENV RUST_CONFIGURE_ARGS \
       --set target.x86_64-unknown-linux-gnu.ranlib=/rustroot/bin/llvm-ranlib \
       --set llvm.thin-lto=true \
       --set llvm.ninja=false \
+      --set llvm.strip-debuginfo=true \
       --set rust.jemalloc \
       --set rust.use-lld=true \
       --set rust.lto=thin