Several updates to try cross-compiling from gcc to clang

compiler/rustc_target/src/spec/windows_gnu_base.rs

@@ -16,13 +16,34 @@ pub fn opts() -> TargetOptions {
         ],
     );
 
+    let mut late_link_args = LinkArgs::new();
     let mut late_link_args_dynamic = LinkArgs::new();
     let mut late_link_args_static = LinkArgs::new();
+    // Order of `late_link_args*` was found through trial and error to work with various
+    // mingw-w64 versions (not tested on the CI). It's expected to change from time to time.
+    let mingw_libs = vec![
+        "-lmsvcrt".to_string(),
+        "-lmingwex".to_string(),
+        "-lmingw32".to_string(),
+        "-lgcc".to_string(), // alas, mingw* libraries above depend on libgcc
+        // mingw's msvcrt is a weird hybrid import library and static library.
+        // And it seems that the linker fails to use import symbols from msvcrt
+        // that are required from functions in msvcrt in certain cases. For example
+        // `_fmode` that is used by an implementation of `__p__fmode` in x86_64.
+        // The library is purposely listed twice to fix that.
+        //
+        // See https://github.com/rust-lang/rust/pull/47483 for some more details.
+        "-lmsvcrt".to_string(),
+        "-luser32".to_string(),
+        "-lkernel32".to_string(),
+    ];
+    late_link_args.insert(LinkerFlavor::Gcc, mingw_libs.clone());
+    late_link_args.insert(LinkerFlavor::Lld(LldFlavor::Ld), mingw_libs);
     let dynamic_unwind_libs = vec![
         // If any of our crates are dynamically linked then we need to use
         // the shared libgcc_s-dw2-1.dll. This is required to support
         // unwinding across DLL boundaries.
-        "-l:libunwind.dll.a".to_string(),
+        "-lgcc_s".to_string(),
     ];
     late_link_args_dynamic.insert(LinkerFlavor::Gcc, dynamic_unwind_libs.clone());
     late_link_args_dynamic.insert(LinkerFlavor::Lld(LldFlavor::Ld), dynamic_unwind_libs);
@@ -32,7 +53,8 @@ pub fn opts() -> TargetOptions {
         // binaries to be redistributed without the libgcc_s-dw2-1.dll
         // dependency, but unfortunately break unwinding across DLL
         // boundaries when unwinding across FFI boundaries.
-        "-l:libunwind.a".to_string(),
+        "-lgcc_eh".to_string(),
+        "-l:libpthread.a".to_string(),
     ];
     late_link_args_static.insert(LinkerFlavor::Gcc, static_unwind_libs.clone());
     late_link_args_static.insert(LinkerFlavor::Lld(LldFlavor::Ld), static_unwind_libs);
@@ -42,8 +64,7 @@ pub fn opts() -> TargetOptions {
         env: "gnu".to_string(),
         vendor: "pc".to_string(),
         // FIXME(#13846) this should be enabled for windows
-        function_sections: true,
-        no_default_libraries: false,
+        function_sections: false,
         linker: Some("gcc".to_string()),
         dynamic_linking: true,
         executables: true,
@@ -59,6 +80,7 @@ pub fn opts() -> TargetOptions {
         pre_link_objects_fallback: crt_objects::pre_mingw_fallback(),
         post_link_objects_fallback: crt_objects::post_mingw_fallback(),
         crt_objects_fallback: Some(CrtObjectsFallback::Mingw),
+        late_link_args,
         late_link_args_dynamic,
         late_link_args_static,
         abi_return_struct_as_int: true,

src/bootstrap/bootstrap.py

@@ -470,11 +470,12 @@ def download_toolchain(self, stage0=True, rustc_channel=None):
             with output(self.rustc_stamp(stage0)) as rust_stamp:
                 rust_stamp.write(key)
 
-            gcc_libs_hack = '{}/missing-libs-hack'.format(self.rust_root)
-            gcc_libs_hack_dest = '{}/rustlib/{}/lib'.format(lib_dir, self.build)
-            shutil.copy(gcc_libs_hack + '/libgcc.a', gcc_libs_hack_dest)
-            shutil.copy(gcc_libs_hack + '/libgcc_eh.a', gcc_libs_hack_dest)
-            shutil.copy(gcc_libs_hack + '/libgcc_s.a', gcc_libs_hack_dest)
+            #gcc_libs_hack = '{}/missing-libs-hack'.format(self.rust_root)
+            #gcc_libs_hack_dest = '{}/rustlib/{}/lib'.format(lib_dir, self.build)
+            #shutil.copy(gcc_libs_hack + '/libgcc.a', gcc_libs_hack_dest)
+            #shutil.copy(gcc_libs_hack + '/libgcc_eh.a', gcc_libs_hack_dest)
+            #shutil.copy(gcc_libs_hack + '/libgcc_s.a', gcc_libs_hack_dest)
+            #shutil.copy(gcc_libs_hack + '/libstdc++.a', gcc_libs_hack_dest)
 
         if self.rustfmt() and self.rustfmt().startswith(bin_root) and (
             not os.path.exists(self.rustfmt())

src/bootstrap/dist.rs

@@ -184,7 +184,7 @@ fn make_win_dist(
         "libm.a",
         "libmingw32.a",
         "libmingwex.a",
-        //"libstdc++.a",
+        "libstdc++.a",
         "libiconv.a",
         "libmoldname.a",
         "libpthread.a",

x86_64-pc-windows-gnu.json

@@ -0,0 +1,137 @@
+{
+    "abi-return-struct-as-int": true,
+    "allows-weak-linkage": false,
+    "arch": "x86_64",
+    "crt-objects-fallback": "mingw",
+    "data-layout": "e-m:w-p:64:64-i32:32-i64:64-i128:128-n32:64-S128",
+    "dll-prefix": "",
+    "dll-suffix": ".dll",
+    "dynamic-linking": true,
+    "eh-frame-header": false,
+    "emit-debug-gdb-scripts": false,
+    "env": "gnu",
+    "exe-suffix": ".exe",
+    "executables": true,
+    "is-builtin": false,
+    "is-like-windows": true,
+    "late-link-args-dynamic": {
+        "gcc": [
+            "-l:libunwind.dll.a"
+        ],
+        "ld.lld": [
+            "-l:libunwind.dll.a"
+        ]
+    },
+    "late-link-args-static": {
+        "gcc": [
+            "-l:libunwind.a"
+        ],
+        "ld.lld": [
+            "-l:libunwind.a"
+        ]
+    },
+    "linker": "x86_64-w64-mingw32-clang",
+    "llvm-target": "x86_64-pc-windows-gnu",
+    "max-atomic-width": 64,
+    "no-default-libraries": false,
+    "os": "windows",
+    "post-link-objects": {
+        "dynamic-dylib": [
+            "rsend.o"
+        ],
+        "dynamic-nopic-exe": [
+            "rsend.o"
+        ],
+        "dynamic-pic-exe": [
+            "rsend.o"
+        ],
+        "static-dylib": [
+            "rsend.o"
+        ],
+        "static-nopic-exe": [
+            "rsend.o"
+        ],
+        "static-pic-exe": [
+            "rsend.o"
+        ]
+    },
+    "post-link-objects-fallback": {
+        "dynamic-dylib": [
+            "rsend.o"
+        ],
+        "dynamic-nopic-exe": [
+            "rsend.o"
+        ],
+        "dynamic-pic-exe": [
+            "rsend.o"
+        ],
+        "static-dylib": [
+            "rsend.o"
+        ],
+        "static-nopic-exe": [
+            "rsend.o"
+        ],
+        "static-pic-exe": [
+            "rsend.o"
+        ]
+    },
+    "pre-link-args": {
+        "gcc": [
+            "-fno-use-linker-plugin",
+            "-Wl,--dynamicbase",
+            "-Wl,--disable-auto-image-base"
+        ]
+    },
+    "pre-link-objects": {
+        "dynamic-dylib": [
+            "rsbegin.o"
+        ],
+        "dynamic-nopic-exe": [
+            "rsbegin.o"
+        ],
+        "dynamic-pic-exe": [
+            "rsbegin.o"
+        ],
+        "static-dylib": [
+            "rsbegin.o"
+        ],
+        "static-nopic-exe": [
+            "rsbegin.o"
+        ],
+        "static-pic-exe": [
+            "rsbegin.o"
+        ]
+    },
+    "pre-link-objects-fallback": {
+        "dynamic-dylib": [
+            "dllcrt2.o",
+            "rsbegin.o"
+        ],
+        "dynamic-nopic-exe": [
+            "crt2.o",
+            "rsbegin.o"
+        ],
+        "dynamic-pic-exe": [
+            "crt2.o",
+            "rsbegin.o"
+        ],
+        "static-dylib": [
+            "dllcrt2.o",
+            "rsbegin.o"
+        ],
+        "static-nopic-exe": [
+            "crt2.o",
+            "rsbegin.o"
+        ],
+        "static-pic-exe": [
+            "crt2.o",
+            "rsbegin.o"
+        ]
+    },
+    "requires-uwtable": true,
+    "target-family": [
+        "windows"
+    ],
+    "target-pointer-width": "64",
+    "vendor": "pc"
+}