Make llvm-libunwind a per-target option

config.toml.example

@@ -605,16 +605,9 @@ changelog-seen = 2
 # development of NLL
 #test-compare-mode = false
 
-# Use LLVM libunwind as the implementation for Rust's unwinder.
-# Accepted values are 'in-tree' (formerly true), 'system' or 'no' (formerly false).
-# This option only applies for Linux and Fuchsia targets.
-# On Linux target, if crt-static is not enabled, 'no' means dynamic link to
-# `libgcc_s.so`, 'in-tree' means static link to the in-tree build of llvm libunwind
-# and 'system' means dynamic link to `libunwind.so`. If crt-static is enabled,
-# the behavior is depend on the libc. On musl target, 'no' and 'in-tree' both
-# means static link to the in-tree build of llvm libunwind, and 'system' means
-# static link to `libunwind.a` provided by system. Due to the limitation of glibc,
-# it must link to `libgcc_eh.a` to get a working output, and this option have no effect.
+# Global default for llvm-libunwind for all targets. See the target-specific
+# documentation for llvm-libunwind below. Note that the target-specific
+# option will override this if set.
 #llvm-libunwind = 'no'
 
 # Enable Windows Control Flow Guard checks in the standard library.
@@ -671,6 +664,18 @@ changelog-seen = 2
 # not, you can specify an explicit file name for it.
 #llvm-filecheck = "/path/to/llvm-version/bin/FileCheck"
 
+# Use LLVM libunwind as the implementation for Rust's unwinder.
+# Accepted values are 'in-tree' (formerly true), 'system' or 'no' (formerly false).
+# This option only applies for Linux and Fuchsia targets.
+# On Linux target, if crt-static is not enabled, 'no' means dynamic link to
+# `libgcc_s.so`, 'in-tree' means static link to the in-tree build of llvm libunwind
+# and 'system' means dynamic link to `libunwind.so`. If crt-static is enabled,
+# the behavior is depend on the libc. On musl target, 'no' and 'in-tree' both
+# means static link to the in-tree build of llvm libunwind, and 'system' means
+# static link to `libunwind.a` provided by system. Due to the limitation of glibc,
+# it must link to `libgcc_eh.a` to get a working output, and this option have no effect.
+#llvm-libunwind = 'no' if Linux, 'in-tree' if Fuchsia
+
 # If this target is for Android, this option will be required to specify where
 # the NDK for the target lives. This is used to find the C compiler to link and
 # build native code.

src/bootstrap/compile.rs

@@ -176,7 +176,7 @@ fn copy_third_party_objects(
 
     if target == "x86_64-fortanix-unknown-sgx"
         || target.contains("pc-windows-gnullvm")
-        || builder.config.llvm_libunwind == LlvmLibunwind::InTree
+        || builder.config.llvm_libunwind(target) == LlvmLibunwind::InTree
             && (target.contains("linux") || target.contains("fuchsia"))
     {
         let libunwind_path =

src/bootstrap/config.rs

@@ -67,7 +67,6 @@ pub struct Config {
     pub rustc_error_format: Option<String>,
     pub json_output: bool,
     pub test_compare_mode: bool,
-    pub llvm_libunwind: LlvmLibunwind,
     pub color: Color,
     pub patch_binaries_for_nix: bool,
 
@@ -151,6 +150,7 @@ pub struct Config {
     pub rust_profile_generate: Option<String>,
     pub llvm_profile_use: Option<String>,
     pub llvm_profile_generate: bool,
+    pub llvm_libunwind_default: Option<LlvmLibunwind>,
 
     pub build: TargetSelection,
     pub hosts: Vec<TargetSelection>,
@@ -342,6 +342,7 @@ pub struct Target {
     pub llvm_config: Option<PathBuf>,
     /// Some(path to FileCheck) if one was specified.
     pub llvm_filecheck: Option<PathBuf>,
+    pub llvm_libunwind: Option<LlvmLibunwind>,
     pub cc: Option<PathBuf>,
     pub cxx: Option<PathBuf>,
     pub ar: Option<PathBuf>,
@@ -680,6 +681,7 @@ define_config! {
         linker: Option<String> = "linker",
         llvm_config: Option<String> = "llvm-config",
         llvm_filecheck: Option<String> = "llvm-filecheck",
+        llvm_libunwind: Option<String> = "llvm-libunwind",
         android_ndk: Option<String> = "android-ndk",
         sanitizers: Option<bool> = "sanitizers",
         profiler: Option<bool> = "profiler",
@@ -1043,10 +1045,6 @@ impl Config {
             set(&mut config.rust_rpath, rust.rpath);
             set(&mut config.jemalloc, rust.jemalloc);
             set(&mut config.test_compare_mode, rust.test_compare_mode);
-            config.llvm_libunwind = rust
-                .llvm_libunwind
-                .map(|v| v.parse().expect("failed to parse rust.llvm-libunwind"))
-                .unwrap_or_default();
             set(&mut config.backtrace, rust.backtrace);
             set(&mut config.channel, rust.channel);
             config.description = rust.description;
@@ -1069,6 +1067,9 @@ impl Config {
             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 {
                 config.rust_codegen_backends =
@@ -1095,6 +1096,10 @@ impl Config {
                 if let Some(ref s) = cfg.llvm_filecheck {
                     target.llvm_filecheck = Some(config.src.join(s));
                 }
+                target.llvm_libunwind = cfg
+                    .llvm_libunwind
+                    .as_ref()
+                    .map(|v| v.parse().expect("failed to parse rust.llvm-libunwind"));
                 if let Some(ref s) = cfg.android_ndk {
                     target.ndk = Some(config.src.join(s));
                 }
@@ -1328,6 +1333,14 @@ impl Config {
         self.rust_codegen_backends.contains(&INTERNER.intern_str("llvm"))
     }
 
+    pub fn llvm_libunwind(&self, target: TargetSelection) -> LlvmLibunwind {
+        self.target_config
+            .get(&target)
+            .and_then(|t| t.llvm_libunwind)
+            .or(self.llvm_libunwind_default)
+            .unwrap_or(LlvmLibunwind::No)
+    }
+
     pub fn submodules(&self, rust_info: &GitInfo) -> bool {
         self.submodules.unwrap_or(rust_info.is_git())
     }

src/bootstrap/lib.rs

@@ -720,7 +720,7 @@ impl Build {
     fn std_features(&self, target: TargetSelection) -> String {
         let mut features = "panic-unwind".to_string();
 
-        match self.config.llvm_libunwind {
+        match self.config.llvm_libunwind(target) {
             LlvmLibunwind::InTree => features.push_str(" llvm-libunwind"),
             LlvmLibunwind::System => features.push_str(" system-llvm-libunwind"),
             LlvmLibunwind::No => {}