Rollup merge of #79997 - coolreader18:wasm-reactor, r=alexcrichton

Emit a reactor for cdylib target on wasi

Fixes #79199, and relevant to #73432

Implements wasi reactors, as described in WebAssembly/WASI#13 and [`design/application-abi.md`](https://github.com/WebAssembly/WASI/blob/master/design/application-abi.md)

Empty `lib.rs`, `lib.crate-type = ["cdylib"]`:

```shell
$ cargo +reactor build --release --target wasm32-wasi
   Compiling wasm-reactor v0.1.0 (/home/coolreader18/wasm-reactor)
    Finished release [optimized] target(s) in 0.08s
$ wasm-dis target/wasm32-wasi/release/wasm_reactor.wasm >reactor.wat
```
`reactor.wat`:
```wat
(module
 (type $none_=>_none (func))
 (type $i32_=>_none (func (param i32)))
 (type $i32_i32_=>_i32 (func (param i32 i32) (result i32)))
 (type $i32_=>_i32 (func (param i32) (result i32)))
 (type $i32_i32_i32_=>_i32 (func (param i32 i32 i32) (result i32)))
 (import "wasi_snapshot_preview1" "fd_prestat_get" (func $__wasi_fd_prestat_get (param i32 i32) (result i32)))
 (import "wasi_snapshot_preview1" "fd_prestat_dir_name" (func $__wasi_fd_prestat_dir_name (param i32 i32 i32) (result i32)))
 (import "wasi_snapshot_preview1" "proc_exit" (func $__wasi_proc_exit (param i32)))
 (import "wasi_snapshot_preview1" "environ_sizes_get" (func $__wasi_environ_sizes_get (param i32 i32) (result i32)))
 (import "wasi_snapshot_preview1" "environ_get" (func $__wasi_environ_get (param i32 i32) (result i32)))
 (memory $0 17)
 (table $0 1 1 funcref)
 (global $global$0 (mut i32) (i32.const 1048576))
 (global $global$1 i32 (i32.const 1049096))
 (global $global$2 i32 (i32.const 1049096))
 (export "memory" (memory $0))
 (export "_initialize" (func $_initialize))
 (export "__data_end" (global $global$1))
 (export "__heap_base" (global $global$2))
 (func $__wasm_call_ctors
  (call $__wasilibc_initialize_environ_eagerly)
  (call $__wasilibc_populate_preopens)
 )
 (func $_initialize
  (call $__wasm_call_ctors)
 )
 (func $malloc (param $0 i32) (result i32)
  (call $dlmalloc
   (local.get $0)
  )
 )
 ;; lots of dlmalloc, memset/memcpy, & libpreopen code
)
```

I went with repurposing cdylib because I figured that it doesn't make much sense to have a wasi shared library that can't be initialized, and even if someone was using it adding an `_initialize` export is a very small change.

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1276,6 +1276,7 @@ fn exec_linker(
 
 fn link_output_kind(sess: &Session, crate_type: CrateType) -> LinkOutputKind {
     let kind = match (crate_type, sess.crt_static(Some(crate_type)), sess.relocation_model()) {
+        (CrateType::Executable, _, _) if sess.is_wasi_reactor() => LinkOutputKind::WasiReactorExe,
         (CrateType::Executable, false, RelocModel::Pic) => LinkOutputKind::DynamicPicExe,
         (CrateType::Executable, false, _) => LinkOutputKind::DynamicNoPicExe,
         (CrateType::Executable, true, RelocModel::Pic) => LinkOutputKind::StaticPicExe,

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -314,6 +314,10 @@ impl<'a> Linker for GccLinker<'a> {
                 self.cmd.arg("-static");
                 self.build_dylib(out_filename);
             }
+            LinkOutputKind::WasiReactorExe => {
+                self.linker_arg("--entry");
+                self.linker_arg("_initialize");
+            }
         }
         // VxWorks compiler driver introduced `--static-crt` flag specifically for rustc,
         // it switches linking for libc and similar system libraries to static without using
@@ -662,6 +666,9 @@ impl<'a> Linker for MsvcLinker<'a> {
                 arg.push(out_filename.with_extension("dll.lib"));
                 self.cmd.arg(arg);
             }
+            LinkOutputKind::WasiReactorExe => {
+                panic!("can't link as reactor on non-wasi target");
+            }
         }
     }
 
@@ -1085,6 +1092,10 @@ impl<'a> Linker for WasmLd<'a> {
             LinkOutputKind::DynamicDylib | LinkOutputKind::StaticDylib => {
                 self.cmd.arg("--no-entry");
             }
+            LinkOutputKind::WasiReactorExe => {
+                self.cmd.arg("--entry");
+                self.cmd.arg("_initialize");
+            }
         }
     }
 

compiler/rustc_interface/src/tests.rs

@@ -7,7 +7,7 @@ use rustc_session::config::{build_configuration, build_session_options, to_crate
 use rustc_session::config::{rustc_optgroups, ErrorOutputType, ExternLocation, Options, Passes};
 use rustc_session::config::{CFGuard, ExternEntry, LinkerPluginLto, LtoCli, SwitchWithOptPath};
 use rustc_session::config::{
-    Externs, OutputType, OutputTypes, SanitizerSet, SymbolManglingVersion,
+    Externs, OutputType, OutputTypes, SanitizerSet, SymbolManglingVersion, WasiExecModel,
 };
 use rustc_session::lint::Level;
 use rustc_session::search_paths::SearchPath;
@@ -597,6 +597,7 @@ fn test_debugging_options_tracking_hash() {
     tracked!(unleash_the_miri_inside_of_you, true);
     tracked!(use_ctors_section, Some(true));
     tracked!(verify_llvm_ir, true);
+    tracked!(wasi_exec_model, Some(WasiExecModel::Reactor));
 }
 
 #[test]

compiler/rustc_session/src/config.rs

@@ -2172,6 +2172,7 @@ crate mod dep_tracking {
         SymbolManglingVersion, TrimmedDefPaths,
     };
     use crate::lint;
+    use crate::options::WasiExecModel;
     use crate::utils::NativeLibKind;
     use rustc_feature::UnstableFeatures;
     use rustc_span::edition::Edition;
@@ -2227,6 +2228,7 @@ crate mod dep_tracking {
     impl_dep_tracking_hash_via_hash!(Option<RelocModel>);
     impl_dep_tracking_hash_via_hash!(Option<CodeModel>);
     impl_dep_tracking_hash_via_hash!(Option<TlsModel>);
+    impl_dep_tracking_hash_via_hash!(Option<WasiExecModel>);
     impl_dep_tracking_hash_via_hash!(Option<PanicStrategy>);
     impl_dep_tracking_hash_via_hash!(Option<RelroLevel>);
     impl_dep_tracking_hash_via_hash!(Option<lint::Level>);

compiler/rustc_session/src/options.rs

@@ -279,6 +279,7 @@ macro_rules! options {
         pub const parse_tls_model: &str =
             "one of supported TLS models (`rustc --print tls-models`)";
         pub const parse_target_feature: &str = parse_string;
+        pub const parse_wasi_exec_model: &str = "either `command` or `reactor`";
     }
 
     #[allow(dead_code)]
@@ -722,6 +723,15 @@ macro_rules! options {
                 None => false,
             }
         }
+
+        fn parse_wasi_exec_model(slot: &mut Option<WasiExecModel>, v: Option<&str>) -> bool {
+            match v {
+                Some("command")  => *slot = Some(WasiExecModel::Command),
+                Some("reactor") => *slot = Some(WasiExecModel::Reactor),
+                _ => return false,
+            }
+            true
+        }
     }
 ) }
 
@@ -1166,9 +1176,17 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "in general, enable more debug printouts (default: no)"),
     verify_llvm_ir: bool = (false, parse_bool, [TRACKED],
         "verify LLVM IR (default: no)"),
+    wasi_exec_model: Option<WasiExecModel> = (None, parse_wasi_exec_model, [TRACKED],
+        "whether to build a wasi command or reactor"),
 
     // This list is in alphabetical order.
     //
     // If you add a new option, please update:
-    // - src/librustc_interface/tests.rs
+    // - compiler/rustc_interface/src/tests.rs
+}
+
+#[derive(Clone, Hash)]
+pub enum WasiExecModel {
+    Command,
+    Reactor,
 }

compiler/rustc_session/src/session.rs

@@ -796,6 +796,14 @@ impl Session {
         self.opts.debugging_opts.tls_model.unwrap_or(self.target.tls_model)
     }
 
+    pub fn is_wasi_reactor(&self) -> bool {
+        self.target.options.os == "wasi"
+            && matches!(
+                self.opts.debugging_opts.wasi_exec_model,
+                Some(config::WasiExecModel::Reactor)
+            )
+    }
+
     pub fn must_not_eliminate_frame_pointers(&self) -> bool {
         // "mcount" function relies on stack pointer.
         // See <https://sourceware.org/binutils/docs/gprof/Implementation.html>.

compiler/rustc_target/src/spec/crt_objects.rs

@@ -5,15 +5,16 @@
 //! The `crtx` ones are generally distributed with libc and the `begin/end` ones with gcc.
 //! See <https://dev.gentoo.org/~vapier/crt.txt> for some more details.
 //!
-//! | Pre-link CRT objects | glibc                  | musl                   | bionic           | mingw             | wasi |
-//! |----------------------|------------------------|------------------------|------------------|-------------------|------|
-//! | dynamic-nopic-exe    | crt1, crti, crtbegin   | crt1, crti, crtbegin   | crtbegin_dynamic | crt2, crtbegin    | crt1 |
-//! | dynamic-pic-exe      | Scrt1, crti, crtbeginS | Scrt1, crti, crtbeginS | crtbegin_dynamic | crt2, crtbegin    | crt1 |
-//! | static-nopic-exe     | crt1, crti, crtbeginT  | crt1, crti, crtbegin   | crtbegin_static  | crt2, crtbegin    | crt1 |
-//! | static-pic-exe       | rcrt1, crti, crtbeginS | rcrt1, crti, crtbeginS | crtbegin_dynamic | crt2, crtbegin    | crt1 |
-//! | dynamic-dylib        | crti, crtbeginS        | crti, crtbeginS        | crtbegin_so      | dllcrt2, crtbegin | -    |
-//! | static-dylib (gcc)   | crti, crtbeginT        | crti, crtbeginS        | crtbegin_so      | dllcrt2, crtbegin | -    |
-//! | static-dylib (clang) | crti, crtbeginT        | N/A                    | crtbegin_static  | dllcrt2, crtbegin | -    |
+//! | Pre-link CRT objects | glibc                  | musl                   | bionic           | mingw             | wasi         |
+//! |----------------------|------------------------|------------------------|------------------|-------------------|--------------|
+//! | dynamic-nopic-exe    | crt1, crti, crtbegin   | crt1, crti, crtbegin   | crtbegin_dynamic | crt2, crtbegin    | crt1         |
+//! | dynamic-pic-exe      | Scrt1, crti, crtbeginS | Scrt1, crti, crtbeginS | crtbegin_dynamic | crt2, crtbegin    | crt1         |
+//! | static-nopic-exe     | crt1, crti, crtbeginT  | crt1, crti, crtbegin   | crtbegin_static  | crt2, crtbegin    | crt1         |
+//! | static-pic-exe       | rcrt1, crti, crtbeginS | rcrt1, crti, crtbeginS | crtbegin_dynamic | crt2, crtbegin    | crt1         |
+//! | dynamic-dylib        | crti, crtbeginS        | crti, crtbeginS        | crtbegin_so      | dllcrt2, crtbegin | -            |
+//! | static-dylib (gcc)   | crti, crtbeginT        | crti, crtbeginS        | crtbegin_so      | dllcrt2, crtbegin | -            |
+//! | static-dylib (clang) | crti, crtbeginT        | N/A                    | crtbegin_static  | dllcrt2, crtbegin | -            |
+//! | wasi-reactor-exe     | N/A                    | N/A                    | N/A              | N/A               | crt1-reactor |
 //!
 //! | Post-link CRT objects | glibc         | musl          | bionic         | mingw  | wasi |
 //! |-----------------------|---------------|---------------|----------------|--------|------|
@@ -105,6 +106,7 @@ pub(super) fn pre_wasi_fallback() -> CrtObjects {
         (LinkOutputKind::DynamicPicExe, &["crt1.o"]),
         (LinkOutputKind::StaticNoPicExe, &["crt1.o"]),
         (LinkOutputKind::StaticPicExe, &["crt1.o"]),
+        (LinkOutputKind::WasiReactorExe, &["crt1-reactor.o"]),
     ])
 }
 

compiler/rustc_target/src/spec/mod.rs

@@ -408,6 +408,8 @@ pub enum LinkOutputKind {
     DynamicDylib,
     /// Dynamic library with bundled libc ("statically linked").
     StaticDylib,
+    /// WASI module with a lifetime past the _initialize entry point
+    WasiReactorExe,
 }
 
 impl LinkOutputKind {
@@ -419,6 +421,7 @@ impl LinkOutputKind {
             LinkOutputKind::StaticPicExe => "static-pic-exe",
             LinkOutputKind::DynamicDylib => "dynamic-dylib",
             LinkOutputKind::StaticDylib => "static-dylib",
+            LinkOutputKind::WasiReactorExe => "wasi-reactor-exe",
         }
     }
 
@@ -430,6 +433,7 @@ impl LinkOutputKind {
             "static-pic-exe" => LinkOutputKind::StaticPicExe,
             "dynamic-dylib" => LinkOutputKind::DynamicDylib,
             "static-dylib" => LinkOutputKind::StaticDylib,
+            "wasi-reactor-exe" => LinkOutputKind::WasiReactorExe,
             _ => return None,
         })
     }
@@ -1378,7 +1382,7 @@ impl Target {
                         let kind = LinkOutputKind::from_str(&k).ok_or_else(|| {
                             format!("{}: '{}' is not a valid value for CRT object kind. \
                                      Use '(dynamic,static)-(nopic,pic)-exe' or \
-                                     '(dynamic,static)-dylib'", name, k)
+                                     '(dynamic,static)-dylib' or 'wasi-reactor-exe'", name, k)
                         })?;
 
                         let v = v.as_array().ok_or_else(||

src/bootstrap/compile.rs

@@ -188,14 +188,16 @@ fn copy_self_contained_objects(
         }
     } else if target.ends_with("-wasi") {
         let srcdir = builder.wasi_root(target).unwrap().join("lib/wasm32-wasi");
-        copy_and_stamp(
-            builder,
-            &libdir_self_contained,
-            &srcdir,
-            "crt1.o",
-            &mut target_deps,
-            DependencyType::TargetSelfContained,
-        );
+        for &obj in &["crt1.o", "crt1-reactor.o"] {
+            copy_and_stamp(
+                builder,
+                &libdir_self_contained,
+                &srcdir,
+                obj,
+                &mut target_deps,
+                DependencyType::TargetSelfContained,
+            );
+        }
     } else if target.contains("windows-gnu") {
         for obj in ["crt2.o", "dllcrt2.o"].iter() {
             let src = compiler_file(builder, builder.cc(target), target, obj);