Auto merge of #78959 - petrochenkov:likeuefi, r=nagisa

rustc_target: Mark UEFI targets as `is_like_windows`/`is_like_msvc`

And document what `is_like_windows` and `is_like_msvc` actually mean in more detail.

Addresses FIXMEs left from https://github.com/rust-lang/rust/pull/71030.
r? `@nagisa`

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -925,9 +925,7 @@ unsafe fn embed_bitcode(
         || cgcx.opts.target_triple.triple().starts_with("asmjs")
     {
         // nothing to do here
-    } else if cgcx.opts.target_triple.triple().contains("windows")
-        || cgcx.opts.target_triple.triple().contains("uefi")
-    {
+    } else if cgcx.is_pe_coff {
         let asm = "
             .section .llvmbc,\"n\"
             .section .llvmcmd,\"n\"

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -307,6 +307,7 @@ pub struct CodegenContext<B: WriteBackendMethods> {
     pub allocator_module_config: Arc<ModuleConfig>,
     pub tm_factory: TargetMachineFactory<B>,
     pub msvc_imps_needed: bool,
+    pub is_pe_coff: bool,
     pub target_pointer_width: u32,
     pub target_arch: String,
     pub debuginfo: config::DebugInfo,
@@ -1022,6 +1023,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
         tm_factory: TargetMachineFactory(backend.target_machine_factory(tcx.sess, ol)),
         total_cgus,
         msvc_imps_needed: msvc_imps_needed(tcx),
+        is_pe_coff: tcx.sess.target.is_like_windows,
         target_pointer_width: tcx.sess.target.pointer_width,
         target_arch: tcx.sess.target.arch.clone(),
         debuginfo: tcx.sess.opts.debuginfo,

compiler/rustc_target/src/spec/mod.rs

@@ -822,10 +822,23 @@ pub struct TargetOptions {
     /// Only useful for compiling against Illumos/Solaris,
     /// as they have a different set of linker flags. Defaults to false.
     pub is_like_solaris: bool,
-    /// Whether the target toolchain is like Windows'. Only useful for compiling against Windows,
-    /// only really used for figuring out how to find libraries, since Windows uses its own
-    /// library naming convention. Defaults to false.
+    /// Whether the target is like Windows.
+    /// This is a combination of several more specific properties represented as a single flag:
+    ///   - The target uses a Windows ABI,
+    ///   - uses PE/COFF as a format for object code,
+    ///   - uses Windows-style dllexport/dllimport for shared libraries,
+    ///   - uses import libraries and .def files for symbol exports,
+    ///   - executables support setting a subsystem.
     pub is_like_windows: bool,
+    /// Whether the target is like MSVC.
+    /// This is a combination of several more specific properties represented as a single flag:
+    ///   - The target has all the properties from `is_like_windows`
+    ///     (for in-tree targets "is_like_msvc ⇒ is_like_windows" is ensured by a unit test),
+    ///   - has some MSVC-specific Windows ABI properties,
+    ///   - uses a link.exe-like linker,
+    ///   - uses CodeView/PDB for debuginfo and natvis for its visualization,
+    ///   - uses SEH-based unwinding,
+    ///   - supports control flow guard mechanism.
     pub is_like_msvc: bool,
     /// Whether the target toolchain is like Emscripten's. Only useful for compiling with
     /// Emscripten toolchain.

compiler/rustc_target/src/spec/tests/tests_impl.rs

@@ -8,6 +8,7 @@ pub(super) fn test_target(target: Target) {
 
 impl Target {
     fn check_consistency(&self) {
+        assert!(self.is_like_windows || !self.is_like_msvc);
         // Check that LLD with the given flavor is treated identically to the linker it emulates.
         // If your target really needs to deviate from the rules below, except it and document the
         // reasons.
@@ -16,6 +17,7 @@ impl Target {
                 || self.linker_flavor == LinkerFlavor::Lld(LldFlavor::Link),
             self.lld_flavor == LldFlavor::Link,
         );
+        assert_eq!(self.is_like_msvc, self.lld_flavor == LldFlavor::Link);
         for args in &[
             &self.pre_link_args,
             &self.late_link_args,

compiler/rustc_target/src/spec/uefi_msvc_base.rs

@@ -46,15 +46,6 @@ pub fn opts() -> TargetOptions {
         stack_probes: true,
         singlethread: true,
         linker: Some("rust-lld".to_string()),
-        // FIXME: This should likely be `true` inherited from `msvc_base`
-        // because UEFI follows Windows ABI and uses PE/COFF.
-        // The `false` is probably causing ABI bugs right now.
-        is_like_windows: false,
-        // FIXME: This should likely be `true` inherited from `msvc_base`
-        // because UEFI follows Windows ABI and uses PE/COFF.
-        // The `false` is probably causing ABI bugs right now.
-        is_like_msvc: false,
-
         ..base
     }
 }