Support building for Wasm/WASI

.github/workflows/build.yml

@@ -247,6 +247,53 @@ jobs:
           path: ./target/libmozjs-${{ matrix.target }}.tar.gz
           name: libmozjs-${{ matrix.target }}.tar.gz
 
+  wasi:
+    name: wasm32-${{ matrix.target }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        target:
+          - wasip1
+          - wasip2
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@master
+        id: toolchain
+        with:
+          toolchain: "1.85.0"
+          targets: "wasm32-${{ matrix.target }}"
+      - uses: bytecodealliance/actions/wasmtime/setup@v1
+      - name: Install WASI-SDK
+        run: |
+          cd /tmp
+          curl --retry 5 --retry-all-errors -OL https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-25/wasi-sdk-25.0-x86_64-linux.tar.gz
+          tar -xzf wasi-sdk-25.0-x86_64-linux.tar.gz
+          mv wasi-sdk-25.0-x86_64-linux wasi-sdk
+      - name: Build
+        run: |
+          cargo +${{ steps.toolchain.outputs.name }} build --no-default-features --features libz-rs,intl --target=wasm32-${{ matrix.target }}
+        env:
+          WASI_SDK_PATH: "/tmp/wasi-sdk"
+      - name: Test
+        run: |
+          export CARGO_TARGET_WASM32_WASIP1_RUNNER="wasmtime run --dir=$PWD::/cwd"
+          export CARGO_TARGET_WASM32_WASIP2_RUNNER="wasmtime run --dir=$PWD::/cwd"
+          cargo +${{ steps.toolchain.outputs.name }} test --tests --examples --no-default-features --features libz-rs,intl --target=wasm32-${{ matrix.target }}
+        env:
+          WASI_SDK_PATH: "/tmp/wasi-sdk"
+      - name: Generate artifact attestation
+        uses: actions/attest-build-provenance@v1
+        if: ${{ inputs.release }}
+        with:
+          subject-path: "./target/libmozjs-wasm32-${{ matrix.target }}.tar.gz"
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          path: ./target/libmozjs-wasm32-${{ matrix.target }}.tar.gz
+          name: libmozjs-wasm32-${{ matrix.target }}.tar.gz
+
   linux-cross-compile:
     name: linux (${{ matrix.target }})
     runs-on: ubuntu-latest

mozjs-sys/Cargo.toml

@@ -2,7 +2,7 @@
 name = "mozjs_sys"
 description = "System crate for the Mozilla SpiderMonkey JavaScript engine."
 repository.workspace = true
-version = "0.140.0-5"
+version = "0.140.0-6"
 authors = ["Mozilla", "The Servo Project Developers"]
 links = "mozjs"
 license.workspace = true

mozjs-sys/build.rs

@@ -45,6 +45,7 @@ const SM_TARGET_ENV_VARS: &'static [&'static str] = &[
     "CXXFLAGS",
     "READELF",
     "OBJCOPY",
+    "WASI_SDK_PATH",
 ];
 
 const EXTRA_FILES: &'static [&'static str] = &["makefile.cargo"];
@@ -60,6 +61,18 @@ fn main() {
     // https://github.com/servo/servo/issues/14759
     env::set_var("MOZ_NO_DEBUG_RTL", "1");
 
+    if let Some(path) = wasi_sdk() {
+        env::set_var(
+            "WASI_SYSROOT",
+            PathBuf::from(&path).join("share").join("wasi-sysroot"),
+        );
+        env::set_var("TARGET_CC", PathBuf::from(&path).join("bin").join("clang"));
+        env::set_var(
+            "TARGET_CXX",
+            PathBuf::from(&path).join("bin").join("clang++"),
+        );
+    }
+
     let out_dir = PathBuf::from(env::var_os("OUT_DIR").unwrap());
     let build_dir = out_dir.join("build");
 
@@ -342,6 +355,12 @@ fn build_bindings(build_dir: &Path, target: BuildTarget) {
         .formatter(Formatter::Rustfmt)
         .clang_args(cc_flags(true));
 
+    if env::var("TARGET").unwrap().contains("wasi") {
+        builder = builder
+            .clang_arg("--sysroot")
+            .clang_arg(env::var("WASI_SYSROOT").unwrap().to_string());
+    }
+
     if target == BuildTarget::JSGlue {
         builder = builder
             .parse_callbacks(Box::new(JSGlueCargoCallbacks::default()))
@@ -437,9 +456,15 @@ fn link_static_lib_binaries(build_dir: &Path) {
         println!("cargo:rustc-link-lib=c++");
     } else if target.contains("windows") && target.contains("gnu") {
         println!("cargo:rustc-link-lib=stdc++");
-    } else if !target.contains("windows") {
+    } else if !target.contains("windows") && !target.contains("wasi") {
+        // The build works without this for WASI, and specifying it means
+        // needing to use the WASI-SDK's clang for linking, which is annoying.
         println!("cargo:rustc-link-lib=stdc++")
     }
+
+    if target.contains("wasi") {
+        println!("cargo:rustc-link-lib=wasi-emulated-getpid");
+    }
 }
 
 fn link_bindgen_static_lib_binaries(build_dir: &Path) {
@@ -518,6 +543,13 @@ fn cc_flags(bindgen: bool) -> Vec<&'static str> {
         if env::var_os("CARGO_FEATURE_PROFILEMOZJS").is_some() {
             flags.push("-fno-omit-frame-pointer");
         }
+
+        if target.contains("wasi") {
+            // Unconditionally target p1 for now. Even if the application
+            // targets p2, an adapter will take care of it.
+            flags.push("--target=wasm32-wasip1");
+            flags.push("-fvisibility=default");
+        }
     }
 
     flags.extend(&["-DSTATIC_JS_API", "-DRUST_BINDGEN"]);
@@ -541,6 +573,10 @@ fn cc_flags(bindgen: bool) -> Vec<&'static str> {
         flags.push("-stdlib=libc++");
     }
 
+    if target.contains("wasi") {
+        flags.push("-D_WASI_EMULATED_GETPID");
+    }
+
     flags
 }
 
@@ -561,6 +597,14 @@ fn js_config_path(build_dir: &Path) -> String {
         .to_string()
 }
 
+fn wasi_sdk() -> Option<OsString> {
+    if env::var("TARGET").unwrap().contains("wasi") {
+        get_cc_rs_env_os("WASI_SDK_PATH")
+    } else {
+        None
+    }
+}
+
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 enum BuildTarget {
     JSApi,

mozjs-sys/makefile.cargo

@@ -20,7 +20,13 @@ ifeq (,$(CARGO_FEATURE_INTL))
 endif
 
 ifneq (,$(CARGO_FEATURE_DEBUGMOZJS))
-	CONFIGURE_FLAGS += --enable-debug --disable-optimize --enable-gczeal
+	CONFIGURE_FLAGS += --enable-debug --enable-gczeal
+	ifneq (,$(findstring -wasi,$(TARGET)))
+		# wasm-opt chokes on -O0 builds.
+		CONFIGURE_FLAGS += --enable-optimize=-O1
+	else
+		CONFIGURE_FLAGS += --disable-optimize
+	endif
 endif
 
 ifneq (,$(CARGO_FEATURE_PROFILEMOZJS))
@@ -29,6 +35,9 @@ endif
 
 ifneq (,$(CARGO_FEATURE_LIBZ_RS))
 	CONFIGURE_FLAGS += --enable-libz-rs
+else ifneq (,$(findstring wasi,$(TARGET)))
+	# system libz is not available on wasi
+	CONFIGURE_FLAGS += --enable-libz-rs
 endif
 
 ifneq (,$(CCACHE))
@@ -76,6 +85,32 @@ ifneq ($(HOST),$(TARGET))
 		TARGET = aarch64-linux-gnu
 	endif
 
+    ifneq (,$(findstring -wasi,$(TARGET)))
+        ifeq (,$(WASI_SDK_PATH))
+            $(error WASI_SDK_PATH environment variable must be set when building for wasm32)
+        endif
+        WASI_SYSROOT = $(WASI_SDK_PATH)/share/wasi-sysroot
+        CC = $(WASI_SDK_PATH)/bin/clang
+        CPP = $(WASI_SDK_PATH)/bin/clang -E
+        CXX = $(WASI_SDK_PATH)/bin/clang++
+        AR = $(WASI_SDK_PATH)/bin/ar
+        HOST_CC = clang
+        HOST_CXX = clang++
+        CONFIGURE_FLAGS += \
+            --enable-portable-baseline-interp \
+            --disable-clang-plugin \
+            --disable-jit \
+            --disable-shared-memory \
+            --with-sysroot=$(WASI_SDK_PATH)/share/wasi-sysroot \
+            $(NULL)
+        # LTO makes `cargo test --wasm32-wasi` take a very very long time. Since build scripts
+        # don't have a way to detect if the build is for `cargo test`, enable LTO for release
+        # builds only.
+        ifneq (debug,$(PROFILE))
+            CONFIGURE_FLAGS += --lto=thin
+        endif
+    endif
+
 	ifeq (android,$(findstring android,$(TARGET)))
 		# Force use of lld on android. Mozilla build system tries to use
 		# gold or bfd linker on Android to support their 'elfhack'functionality in
@@ -154,7 +189,7 @@ all: maybe-configure
 JSSRC := '$(SRC_DIR)'/js/src
 # Keep track of all input variables to configure, so we don't skip reconfigure
 # when we do need to reconfigure
-CONFIGURE_INPUTS := "$(CC)$(CFLAGS)$(CPP)$(CPPFLAGS)$(CXX)$(CXXFLAGS)$(AS)$(AR)$(CONFIGURE_FLAGS)"
+CONFIGURE_INPUTS := "$(CC)$(CFLAGS)$(CPP)$(CPPFLAGS)$(CXX)$(CXXFLAGS)$(AS)$(AR)$(HOST_CC)$(HOST_CXX)$(WASI_SYSROOT)$(CONFIGURE_FLAGS)"
 LAST_CONFIGURE_INPUTS := "$(shell cat reconfigure.inputs)"
 maybe-configure:
 	[[ $(JSSRC)/configure -ot $(JSSRC)/configure.in ]] && touch $(JSSRC)/configure || true
@@ -165,6 +200,9 @@ maybe-configure:
 	  CC="$(CC)" CFLAGS="$(CFLAGS)" \
 	  CPP="$(CPP)" CPPFLAGS="$(CPPFLAGS)" \
 	  CXX="$(CXX)" CXXFLAGS="$(CXXFLAGS)" \
+	  HOST_CC="$(HOST_CC)" \
+	  HOST_CXX="$(HOST_CXX)" \
+	  WASI_SYSROOT="$(WASI_SYSROOT)" \
 	  AS="$(AS)" AR="$(AR)" \
 	  $(JSSRC)/configure $(strip $(CONFIGURE_FLAGS)) || (cat config.log && exit 1) ; \
 	fi

mozjs-sys/src/jsglue.cpp

@@ -883,7 +883,7 @@ bool AppendToRootedObjectVector(JS::PersistentRootedObjectVector* v,
 
 void DeleteRootedObjectVector(JS::PersistentRootedObjectVector* v) { delete v; }
 
-#if defined(__linux__)
+#if defined(__linux__) || defined(__wasi__)
 #  include <malloc.h>
 #elif defined(__APPLE__)
 #  include <malloc/malloc.h>
@@ -897,7 +897,7 @@ void DeleteRootedObjectVector(JS::PersistentRootedObjectVector* v) { delete v; }
 
 // SpiderMonkey-in-Rust currently uses system malloc, not jemalloc.
 static size_t MallocSizeOf(const void* aPtr) {
-#if defined(__linux__)
+#if defined(__linux__) || defined(__wasi__)
   return malloc_usable_size((void*)aPtr);
 #elif defined(__APPLE__)
   return malloc_size((void*)aPtr);

mozjs/Cargo.toml

@@ -27,7 +27,10 @@ libc.workspace = true
 log = "0.4"
 mozjs_sys = { path = "../mozjs-sys" }
 
-[dev-dependencies]
+[target.'cfg(target_arch = "wasm32")'.dev-dependencies]
+criterion = { version = "0.6", default-features = false, features = ["html_reports"] }
+
+[target.'cfg(not(target_arch = "wasm32"))'.dev-dependencies]
 criterion = "0.6"
 
 [build-dependencies]

mozjs/examples/wasm.rs

@@ -6,6 +6,9 @@
 //! and do some setup on both of these. You also need to enter a "realm"
 //! (environment within one global object) before you can execute code.
 
+// The wasm example does not work on wasm32 targets.
+#![cfg(not(target_arch = "wasm32"))]
+
 use ::std::ptr;
 use ::std::ptr::null_mut;
 

mozjs/tests/runtime.rs

@@ -2,6 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#![cfg(not(target_arch = "wasm32"))]
+
 use std::ptr;
 use std::sync::mpsc::channel;
 use std::thread;