feat: add a histrical wit-bindgen

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "wit-bindgen-gen-spidermonkey"
+version = "0.1.0"
+authors = ["Nick Fitzgerald <fitzgen@gmail.com>"]
+edition = "2018"
+
+[lib]
+test = false
+doctest = false
+
+[dependencies]
+lazy_static = "1.4.0"
+structopt = { version = "0.3", optional = true }
+wasm-encoder = "0.8.0"
+wit-bindgen-gen-core = { path = "../gen-core" }
+heck = "0.3"
+
+[dev-dependencies]
+test-helpers = { path = '../test-helpers', features = ['wit-bindgen-gen-spidermonkey'] }
+wasmparser = "0.80"

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/build.rs

@@ -0,0 +1,4 @@
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+    // this build script is currently only here so OUT_DIR is set for testing.
+}

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/.gitignore

@@ -0,0 +1,7 @@
+spidermonkey-*
+lib/*
+*.o
+spidermonkey.initial.wasm
+wasi-sdk-12.0
+mozbuild
+.exports

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/Makefile

@@ -0,0 +1,142 @@
+SM_REPO := https://github.com/fitzgen/gecko-dev
+SM_COMMIT := dafd3165f45c55023ece4787a86444029e4f475e
+
+# TODO: support building `spidermonkey.wasm` on other OSes. But for some reason
+# the resulting `.wasm` binary is slower when the host compiler is on macOS.
+WASI_SDK_URL := https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-12/wasi-sdk-12.0-linux.tar.gz
+
+CC := $(CURDIR)/wasi-sdk-12.0/bin/clang
+CXX := $(CURDIR)/wasi-sdk-12.0/bin/clang++
+
+# Set this to `1` to enable logging via all the `SMW_LOG(...)` calls.
+LOGGING := 0
+
+# Set this to `-DDEBUG` and uncomment the `--enable-debug` line in `mozconfig`
+# to enable debug builds of SpiderMonkey.
+DEBUG := ""
+
+# Set this to `""` in debug mode for better debugging.
+OPT := "-O2"
+
+CFLAGS := \
+	--sysroot=$(CURDIR)/wasi-sdk-12.0/share/wasi-sysroot \
+	-Wall \
+	--target=wasm32-unknown-wasi \
+	-Ispidermonkey-$(SM_COMMIT)/obj-wasm32-unknown-wasi/dist/include \
+	-I$(CURDIR)/include \
+	$(DEBUG) \
+	$(OPT) \
+	-DLOGGING=$(LOGGING)
+
+CXXFLAGS := \
+	$(CFLAGS) \
+	-fno-exceptions \
+	-std=c++17
+
+# Local object files.
+LOCAL_OBJECTS := $(patsubst %.cpp,%.o,$(wildcard *.cpp))
+
+# Object files needed within SpiderMonkey's obj dir.
+SM_OBJECTS := \
+	js/src/build/libjs_static.a \
+	memory/build/Unified_cpp_memory_build0.o \
+	memory/mozalloc/mozalloc_abort.o \
+	memory/mozalloc/Unified_cpp_memory_mozalloc0.o \
+	mfbt/Unified_cpp_mfbt0.o \
+	mfbt/Unified_cpp_mfbt1.o \
+	mfbt/lz4.o \
+	mfbt/lz4frame.o \
+	mfbt/lz4hc.o \
+	mfbt/xxhash.o \
+	mozglue/misc/AutoProfilerLabel.o \
+	mozglue/misc/ConditionVariable_noop.o \
+	mozglue/misc/Decimal.o \
+	mozglue/misc/MmapFaultHandler.o \
+	mozglue/misc/Mutex_noop.o \
+	mozglue/misc/Printf.o \
+	mozglue/misc/StackWalk.o \
+	mozglue/misc/TimeStamp.o \
+	mozglue/misc/TimeStamp_posix.o \
+	mozglue/misc/Uptime.o \
+	modules/zlib/src/compress.o \
+	modules/zlib/src/gzclose.o \
+	modules/zlib/src/infback.o \
+	modules/zlib/src/uncompr.o \
+	wasm32-wasi/release/libjsrust.a
+
+# The `./lib/*` copies of SpiderMonkey's object files that we check into the
+# repo.
+SM_LIB_OBJECTS := $(shell echo $(SM_OBJECTS) | xargs -d' ' -I{} basename {} | xargs -I{} echo lib/{})
+
+.PHONY: all clean clean-all clean-spidermonkey clean-wasi-sdk
+
+all: spidermonkey.wasm
+	@echo "Done!"
+
+spidermonkey.initial.wasm: $(SM_LIB_OBJECTS) $(LOCAL_OBJECTS)
+	$(CXX) $(CXXFLAGS) \
+		-mexec-model=reactor \
+		$(LOCAL_OBJECTS) \
+		$(SM_LIB_OBJECTS) \
+		-o spidermonkey.initial.wasm \
+		-Wl,--export-dynamic \
+		-Wl,--growable-table \
+		-Wl,--export-table \
+		-Wl,--gc-sections
+
+spidermonkey.wasm: spidermonkey.initial.wasm
+	# Uncomment this `wasm-opt` invocation and comment the following one out to
+	# enable better debugging.
+	#
+	# wasm-opt -g --duplicate-import-elimination spidermonkey.initial.wasm -o spidermonkey.wasm
+	wasm-opt -O2 --strip-dwarf --duplicate-import-elimination spidermonkey.initial.wasm -o spidermonkey.wasm
+
+
+# Build all `*.cpp` files into `*.o` files.
+%.o: %.cpp $(SM_LIB_OBJECTS)
+	$(CXX) $(CXXFLAGS) -c $< -o $@
+
+# Actually build SpiderMonkey.
+$(SM_LIB_OBJECTS): spidermonkey-$(SM_COMMIT) mozbuild wasi-sdk-12.0 mozconfig
+	cd spidermonkey-$(SM_COMMIT) \
+		&& MOZBUILD_STATE_PATH=$(CURDIR)/mozbuild MOZCONFIG=$(CURDIR)/mozconfig ./mach build
+	mkdir -p lib
+	for x in $(SM_OBJECTS); do \
+	    cp spidermonkey-$(SM_COMMIT)/obj-wasm32-unknown-wasi/$$x lib/; \
+	done
+
+# Clone `mozilla-central` at the `SM_COMMIT` commit.
+spidermonkey-$(SM_COMMIT):
+	-rm -rf spidermonkey-temp
+	mkdir spidermonkey-temp
+	cd spidermonkey-temp \
+		&& git init \
+		&& git remote add origin $(SM_REPO) \
+		&& git fetch origin $(SM_COMMIT) \
+		&& git checkout $(SM_COMMIT)
+	mv spidermonkey-temp spidermonkey-$(SM_COMMIT)
+
+mozbuild: spidermonkey-$(SM_COMMIT)
+	-mkdir mozbuild
+	cd spidermonkey-$(SM_COMMIT) \
+		&& MOZBUILD_STATE_PATH=$(CURDIR)/mozbuild ./mach bootstrap --application-choice js --no-system-changes \
+		|| rm -rf $(CURDIR)/mozbuild
+
+wasi-sdk-12.0:
+	curl -L $(WASI_SDK_URL) | tar -x -z
+
+clean-all: clean clean-spidermonkey clean-wasi-sdk
+
+clean-wasi-sdk:
+	-rm -rf wasi-sdk-12.0
+
+clean-spidermonkey:
+	-rm -rf spidermonkey-$(SM_COMMIT)
+	-rm -rf spidermonkey-$(SM_COMMIT)/obj-wasm32-unknown-wasi/
+	-rm -rf mozbuild
+
+clean:
+	@echo 'Only cleaning our own artifacts, not upstream deps. Run `make clean-{all,spidermonkey,wasi-sdk}` to clean others.'
+	-rm -rf spidermonkey-temp
+	-rm -rf ./*.o
+	-rm -rf spidermonkey.wasm

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/README.md

@@ -0,0 +1,13 @@
+# `spidermonkey.wasm`
+
+This directory contains the source code for `spidermonkey.wasm`, which is an
+embedding of the SpiderMonkey JavaScript engine for targeting `wasm32-wasi` and
+use with `wit-bindgen-gen-spidermonkey`. It exports a variety of helper
+functions that are used by `wit-bindgen-gen-spidermonkey`'s generated glue
+code. These helpers are typically named something like `SMW_whatever_function`.
+
+## Building `spidermonkey.wasm`
+
+```
+make
+```

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/abort.cpp

@@ -0,0 +1,46 @@
+#include <stdlib.h>
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Winvalid-offsetof"
+#include "js/Exception.h"
+#pragma clang diagnostic pop
+
+#include "smw/abort.h"
+#include "smw/cx.h"
+#include "smw/dump.h"
+
+namespace smw {
+
+void abort(const char* msg) {
+    abort(get_js_context(), msg);
+}
+
+void abort(JSContext *cx, const char* msg) {
+    fprintf(stderr, "Error: %s", msg);
+
+    if (JS_IsExceptionPending(cx))  {
+        fprintf(stderr, ":");
+        JS::ExceptionStack exception(cx);
+        if (!JS::GetPendingExceptionStack(cx, &exception)) {
+            fprintf(stderr, " failed to get pending exception value and stack\n");
+        } else {
+            fprintf(stderr, "\n  exception value: ");
+            if (!dump_value(cx, exception.exception(), stderr)) {
+                fprintf(stderr, "<failed to dump value>");
+            }
+            fprintf(stderr, "\n  exception stack:\n");
+            if (!dump_stack(cx, exception.stack(), stderr)) {
+                fprintf(stderr, "<failed to dump stack>\n");
+            }
+        }
+    } else {
+        fprintf(stderr, "\n");
+    }
+
+    // TODO: check for unhandled promise rejections.
+
+    fflush(stderr);
+    ::abort();
+}
+
+} // namespace smw

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/bindgen.cpp

@@ -0,0 +1,452 @@
+/*!
+ * This module implements the intrinsics used by code emitted in the
+ * `wit_bindgen_gen_spidermonkey::Bindgen` trait implementation.
+ */
+
+#include <assert.h>
+#include <cmath>
+#include <stdlib.h>
+
+#include "smw/abort.h"
+#include "smw/cx.h"
+#include "smw/logging.h"
+#include "smw/wasm.h"
+
+#include "mozilla/UniquePtr.h"
+#include "jsapi.h"
+#include "js/Array.h"
+#include "js/Conversions.h"
+#include "js/ForOfIterator.h"
+#include "js/Modules.h"
+
+#ifdef LOGGING
+#include "js/friend/DumpFunctions.h"
+#endif
+
+namespace smw {
+
+using UniqueChars = mozilla::UniquePtr<char[]>;
+
+using PersistentRootedValueVector = JS::PersistentRooted<JS::GCVector<JS::Value>>;
+
+// Used for general Wasm<-->JS conversions.
+static PersistentRootedValueVector* OPERANDS;
+
+// Used for holding arguments to JS calls.
+static PersistentRootedValueVector* ARGS;
+
+// Used for holding returns from Wasm calls.
+static PersistentRootedValueVector* RETS;
+
+void init_operands(JSContext* cx) {
+    assert(!OPERANDS && "OPERANDS must only be initialized once");
+    OPERANDS = new PersistentRootedValueVector(cx, cx);
+    if (!OPERANDS) {
+        abort(cx, "failed to allocate OPERANDS");
+    }
+
+    assert(!ARGS && "ARGS must only be initialized once");
+    ARGS = new PersistentRootedValueVector(cx, cx);
+    if (!ARGS) {
+        abort(cx, "failed to allocate ARGS");
+    }
+
+    assert(!RETS && "RETS must only be initialized once");
+    RETS = new PersistentRootedValueVector(cx, cx);
+    if (!RETS) {
+        abort(cx, "failed to allocate RETS");
+    }
+}
+
+PersistentRootedValueVector& operands() {
+    assert(OPERANDS && OPERANDS->initialized() && "OPERANDS must be initialized");
+    return *OPERANDS;
+}
+
+void save_operand(size_t dest, JS::HandleValue val) {
+#if LOGGING==1
+    SMW_LOG("operands[%zu] = ", dest);
+    js::DumpValue(val, stderr);
+#endif // LOGGING==1
+
+    JSContext* cx = get_js_context();
+
+    if (operands().length() <= dest) {
+        size_t needed_capacity = 1 + dest - operands().length();
+        if (!operands().reserve(needed_capacity)) {
+            abort("failed to reserve capacity for the OPERANDS vector");
+        }
+        if (dest == operands().length()) {
+            bool ok = operands().append(val);
+            assert(ok && "already reserved space");
+            return;
+        }
+        JS::RootedValue placeholder(cx, JS::UndefinedValue());
+        for (size_t i = 0; i < needed_capacity; i++) {
+            bool ok = operands().append(placeholder);
+            assert(ok && "already reserved space");
+        }
+    }
+
+    operands()[dest].set(val);
+}
+
+PersistentRootedValueVector& args() {
+    assert(ARGS && ARGS->initialized() && "ARGS must be initialized");
+    return *ARGS;
+}
+
+PersistentRootedValueVector& rets() {
+    assert(RETS && RETS->initialized() && "RETS must be initialized");
+    return *RETS;
+}
+
+WASM_EXPORT
+void canonical_abi_free(void* ptr, size_t size, size_t align) {
+    (void) size;
+    (void) align;
+    free(ptr);
+}
+
+WASM_EXPORT
+void* canonical_abi_realloc(void* ptr, size_t old_size, size_t align, size_t new_size) {
+    (void) old_size;
+    (void) align;
+    return realloc(ptr, new_size);
+}
+
+WASM_EXPORT
+void SMW_fill_operands(unsigned argc, JS::Value* vp) {
+    SMW_LOG("SMW_fill_operands(argc = %d, vp = %p)\n", argc, vp);
+
+    JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+
+    if (!operands().reserve(size_t(args.length()))) {
+        abort(get_js_context(), "failed to reserve space in the operands vector");
+    }
+    for (unsigned i = 0; i < args.length(); i++) {
+#if LOGGING==1
+        SMW_LOG("operands[%d] = ", i);
+        js::DumpValue(args.get(i), stderr);
+#endif // LOGGING==1
+
+        bool ok = operands().append(args.get(i));
+        assert(ok && "already reserved space");
+    }
+}
+
+WASM_EXPORT
+void SMW_clear_operands() {
+    SMW_LOG("SMW_clear_operands\n");
+    operands().clear();
+}
+
+WASM_EXPORT
+void SMW_push_arg(size_t i) {
+    SMW_LOG("SMW_push_arg(i = %zu)\n", i);
+    if (!args().append(operands()[i])) {
+        abort("failed to push arg");
+    }
+}
+
+WASM_EXPORT
+void SMW_call(char *funcName, size_t funcNameLen, size_t numResults, size_t dest) {
+#ifdef LOGGING
+    SMW_LOG("SMW_call(funcName = %p \"", funcName);
+    for (size_t i = 0; i < funcNameLen; i++) {
+        SMW_LOG("%c", funcName[i]);
+    }
+    SMW_LOG("\", funcNameLen = %zu, numResults = %zu, dest = %zu)\n",
+            funcNameLen,
+            numResults,
+            dest);
+#endif
+
+    UniqueChars uniqFuncName(funcName);
+
+    JSContext *cx = get_js_context();
+
+    JS::RootedString funcNameAtom(cx, JS_AtomizeStringN(cx, uniqFuncName.get(), funcNameLen));
+    if (!funcNameAtom) {
+        abort(cx, "failed to atomize function name");
+    }
+
+    JS::RootedObject module(cx, get_user_module());
+    JS::RootedValue exportVal(cx);
+    bool hasExport = false;
+    if (!JS::GetModuleExport(cx, module, funcNameAtom, &exportVal, &hasExport)) {
+        abort(cx, "failed to get module export");
+    }
+    if (!hasExport) {
+        // TODO: include the export name in this message to help users debug
+        // which export they're missing.
+        abort(cx, "user module does not have the requested export");
+    }
+
+    JS::RootedFunction exportFunc(cx, JS_ValueToFunction(cx, exportVal));
+    if (!exportFunc) {
+        // TODO: include the export name in this message.
+        abort(cx, "exported value is not a function");
+    }
+
+    // XXX: we have to copy ARGS into a `JS::RootedVector<JS::Value>` because
+    // `JS::Call` takes a `JS::HandleValueArray` and you can't construct that
+    // from a `JS::PersistentRooted<JS::GCVector<JS::Value>>`, only a
+    // `JS::RootedVector<JS::Value>`. And we can't make `ARGS` a
+    // `JS::RootedVector<JS::Value>` because it is a global, not an on-stack
+    // RAII value as required by `JS::RootedVector<JS::Value>`. Gross!
+    JS::RootedVector<JS::Value> argsVector(cx);
+    if (!argsVector.reserve(args().length())) {
+        abort(cx, "failed to reserve space for arguments vector");
+    }
+    for (size_t i = 0; i < args().length(); i++) {
+        bool ok = argsVector.append(args()[i]);
+        assert(ok && "already reserved space");
+    }
+
+    JS::RootedObject thisObj(cx);
+    JS::RootedValue result(cx);
+    if (!JS::Call(cx, thisObj, exportFunc, argsVector, &result)) {
+        // TODO: include the export name in this message.
+        abort(cx, "calling export function failed");
+    }
+
+    args().clear();
+
+    if (numResults == 0) {
+        // Nothing to push onto the operands vector.
+    } else if (numResults == 1) {
+        save_operand(dest, result);
+    } else {
+        // Treat the "physical" return value as an iterator and unpack the
+        // "logical" return values from within it. This allows JS to return
+        // multiple WIT values as an array or any other iterable.
+        JS::ForOfIterator iter(cx);
+        if (!iter.init(result)) {
+            // TODO: include the export name in this message.
+            abort(cx, "failed to convert return value to iterable");
+        }
+        JS::RootedValue val(cx);
+        bool done = false;
+        for (size_t i = 0; i < numResults; i++) {
+            if (done) {
+                // TODO: include the export name in this message.
+                abort(cx, "function's returned iterator did not yield enough return values");
+            }
+            if (!iter.next(&val, &done)) {
+                // TODO: include the export name in this message.
+                abort(cx, "failed to get the next value out of the return values iterator");
+            }
+            save_operand(dest + i, val);
+        }
+    }
+}
+
+WASM_EXPORT
+void SMW_push_return_value(size_t i) {
+    SMW_LOG("SMW_push_return_value(i = %zu)\n", i);
+    if (!rets().append(operands()[i])) {
+        abort(get_js_context(), "failed to push arg");
+    }
+}
+
+WASM_EXPORT
+void SMW_finish_returns(unsigned argc, JS::Value* vp) {
+    SMW_LOG("SMW_finish_returns(argc = %d, vp = %p)\n", argc, vp);
+
+    JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+    switch (rets().length()) {
+    case 0: {
+        break;
+    }
+    case 1: {
+        args.rval().set(rets().back());
+        break;
+    }
+    default: {
+        JSContext* cx = get_js_context();
+        JS::RootedVector<JS::Value> elems(cx);
+        if (!elems.reserve(rets().length())) {
+            abort(cx, "failed to reserve space for results vector");
+        }
+        for (size_t i = 0; i < rets().length(); i++) {
+            bool ok = elems.append(rets()[i]);
+            assert(ok && "already reserved space");
+        }
+        JS::RootedObject arr(cx, JS::NewArrayObject(cx, elems));
+        if (!arr) {
+            abort(cx, "failed to allocate array for function's return values");
+        }
+        args.rval().setObject(*arr.get());
+        break;
+    }
+    }
+
+    rets().clear();
+}
+
+WASM_EXPORT
+uint32_t SMW_i32_from_u32(size_t i) {
+    SMW_LOG("SMW_i32_from_u32(i = %zu)\n", i);
+
+    JSContext* cx = get_js_context();
+    JS::RootedValue val(cx, operands()[i]);
+    double number = 0.0;
+    if (!JS::ToNumber(cx, val, &number)) {
+        abort(cx, "failed to convert value to number");
+    }
+    number = std::round(number);
+    return uint32_t(number);
+}
+
+WASM_EXPORT
+void SMW_u32_from_i32(uint32_t x, size_t dest) {
+    SMW_LOG("SMW_u32_from_i32(x = %ull, dest = %zu)\n", x, dest);
+
+    JSContext* cx = get_js_context();
+    JS::RootedValue val(cx, JS::NumberValue(x));
+    save_operand(dest, val);
+}
+
+WASM_EXPORT
+void SMW_string_canon_lower(uint32_t* ret_ptr, size_t i) {
+    SMW_LOG("SMW_string_canon_lower(ret_ptr = %p, i = %zu)\n", ret_ptr, i);
+
+    JSContext* cx = get_js_context();
+    JS::RootedValue strVal(cx, operands()[i]);
+    if (!strVal.isString()) {
+        abort(cx, "value is not a string");
+    }
+    JS::RootedString str(cx, strVal.toString());
+    JS::Rooted<JSLinearString*> linearStr(cx, JS_EnsureLinearString(cx, str));
+    if (!linearStr) {
+        abort(cx, "failed to linearize JS string");
+    }
+
+    size_t len = JS::GetDeflatedUTF8StringLength(linearStr);
+    char* ptr = static_cast<char*>(malloc(len));
+    if (!ptr) {
+        abort(cx, "out of memory");
+    }
+
+    size_t num_written = JS::DeflateStringToUTF8Buffer(linearStr, mozilla::Span(ptr, len));
+    assert(num_written == len);
+
+    ret_ptr[0] = reinterpret_cast<uint32_t>(ptr);
+    ret_ptr[1] = static_cast<uint32_t>(len);
+}
+
+WASM_EXPORT
+void SMW_string_canon_lift(char* ptr, size_t len, size_t dest) {
+    SMW_LOG("SMW_string_canon_lift(ptr = %p, len = %zu, dest = %zu)\n", ptr, len, dest);
+
+    JSContext* cx = get_js_context();
+    JS::RootedString str(cx, JS_NewStringCopyUTF8N(cx, JS::UTF8Chars(ptr, len)));
+    if (!str) {
+        abort(cx, "failed to create JS string from UTF-8 buffer");
+    }
+    JS::RootedValue strVal(cx, JS::StringValue(str));
+    save_operand(dest, strVal);
+}
+
+WASM_EXPORT
+uint32_t SMW_spread_into_array(size_t i) {
+    SMW_LOG("SMW_spread_into_array; i = %zu\n", i);
+
+    JSContext* cx = get_js_context();
+
+    JS::RootedValue iterable(cx, operands()[i]);
+    bool is_array = false;
+    if (!JS::IsArrayObject(cx, iterable, &is_array)) {
+        abort(cx, "failed to check if object is an array");
+    }
+
+    if (is_array) {
+        JS::RootedObject arr(cx, &iterable.toObject());
+        uint32_t length = 0;
+        if (!JS::GetArrayLength(cx, arr, &length)) {
+            abort(cx, "failed to get array length");
+        }
+        return length;
+    }
+
+    JS::RootedVector<JS::Value> elems(cx);
+    JS::ForOfIterator iter(cx);
+    if (!iter.init(iterable)) {
+        abort(cx, "failed to convert operand value to iterable");
+    }
+    JS::RootedValue val(cx);
+    bool done = false;
+    while (!done) {
+        if (!iter.next(&val, &done)) {
+            abort(cx, "failed to get the next value out of iterator");
+        }
+        if (done) {
+            break;
+        }
+        if (!elems.append(val)) {
+            abort(cx, "failed to append value to vector");
+        }
+    }
+
+    JS::RootedObject arr(cx, JS::NewArrayObject(cx, elems));
+    if (!arr) {
+        abort(cx, "failed to allocate JS array object");
+    }
+    operands()[i].setObject(*arr);
+
+    return elems.length();
+}
+
+WASM_EXPORT
+void SMW_get_array_element(size_t array, size_t index, size_t dest) {
+    SMW_LOG("SMW_get_array_element(array = %zu, index = %zu, dest = %zu)\n", array, index, dest);
+
+    JSContext* cx = get_js_context();
+
+    JS::RootedValue array_val(cx, operands()[array]);
+    assert(array_val.isObject());
+    JS::RootedObject array_obj(cx, &array_val.toObject());
+    JS::RootedValue elem(cx);
+    if (!JS_GetElement(cx, array_obj, index, &elem)) {
+        abort(cx, "failed to get array element");
+    }
+
+    save_operand(dest, elem);
+}
+
+WASM_EXPORT
+void SMW_new_array(size_t dest) {
+    SMW_LOG("SMW_new_array(dest = %zu)\n", dest);
+
+    JSContext* cx = get_js_context();
+    JS::RootedObject arr(cx, JS::NewArrayObject(cx, 0));
+    if (!arr) {
+        abort(cx, "failed to allocate a new JS array object");
+    }
+    JS::RootedValue arr_val(cx, JS::ObjectValue(*arr));
+    save_operand(dest, arr_val);
+}
+
+WASM_EXPORT
+void SMW_array_push(size_t array, size_t elem) {
+    SMW_LOG("SMW_array_push(array = %zu, elem = %zu)\n", array, elem);
+
+    JSContext* cx = get_js_context();
+
+    JS::RootedValue array_val(cx, operands()[array]);
+    assert(array_val.isObject());
+    JS::RootedObject array_obj(cx, &array_val.toObject());
+
+    uint32_t length = 0;
+    if (!JS::GetArrayLength(cx, array_obj, &length)) {
+        abort(cx, "failed to get JS array object length");
+    }
+
+    JS::RootedValue elem_val(cx, operands()[elem]);
+    if (!JS_SetElement(cx, array_obj, length, elem_val)) {
+        abort(cx, "failed to set JS array element");
+    }
+}
+
+} // namespace smw

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/cx.cpp

@@ -0,0 +1,33 @@
+#include <assert.h>
+
+#include "smw/cx.h"
+
+#include "jsapi.h"
+
+namespace smw {
+
+static JSContext* CONTEXT = nullptr;
+
+void init_js_context(JSContext *cx) {
+    assert(!CONTEXT && "CONTEXT should only be initialized once");
+    CONTEXT = cx;
+}
+
+JSContext *get_js_context() {
+    assert(CONTEXT && "CONTEXT should be initialized");
+    return CONTEXT;
+}
+
+static JS::PersistentRooted<JSObject*> USER_MODULE;
+
+void init_user_module(JSContext* cx, JSObject* user_module) {
+    assert(!USER_MODULE && "USER_MODULE should only be initialized once");
+    USER_MODULE.init(cx, user_module);
+}
+
+JSObject* get_user_module() {
+    assert(USER_MODULE && "USER_MODULE should be initialized");
+    return USER_MODULE;
+}
+
+} // namespace smw

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/dump.cpp

@@ -0,0 +1,48 @@
+#include "smw/dump.h"
+
+#include <assert.h>
+#include "jsapi.h"
+#include "smw/wasm.h"
+
+namespace smw {
+
+static JS::UniqueChars stringify_value(JSContext *cx, JS::HandleValue val) {
+    JS::RootedString str(cx, JS_ValueToSource(cx, val));
+    if (!str) {
+        return nullptr;
+    }
+    return JS_EncodeStringToUTF8(cx, str);
+}
+
+bool dump_value(JSContext *cx, JS::HandleValue val, FILE* fp) {
+    JS::UniqueChars str = stringify_value(cx, val);
+    if (!str) {
+        return false;
+    }
+    fprintf(fp, "%s\n", str.get());
+    return true;
+}
+
+bool dump_stack(JSContext *cx, JS::HandleObject stack, FILE* fp) {
+    JS::RootedString str(cx);
+    size_t indent = 4;
+    if (!JS::BuildStackString(cx, nullptr, stack, &str, indent)) {
+        return false;
+    }
+
+    JS::UniqueChars utf8 = JS_EncodeStringToUTF8(cx, str);
+    if (!utf8) {
+        return false;
+    }
+
+    fprintf(fp, "%s\n", utf8.get());
+    return true;
+}
+
+WASM_EXPORT
+int32_t dump_i32(int32_t x) {
+    fprintf(stderr, "dump_i32: %d\n", x);
+    return x;
+}
+
+} // namespace smw

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/include/smw/abort.h

@@ -0,0 +1,16 @@
+#ifndef _smw_abort_h
+#define _smw_abort_h
+
+struct JSContext;
+
+namespace smw {
+
+/**
+ * Print the given error message and abort.
+ */
+void abort(const char* msg);
+void abort(JSContext *cx, const char* msg);
+
+}
+
+#endif // _smw_abort_h

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/include/smw/bindgen.h

@@ -0,0 +1,12 @@
+#ifndef _smw_bindgen_h
+#define _smw_bindgen_h
+
+struct JSContext;
+
+namespace smw {
+
+void init_operands(JSContext* cx);
+
+}
+
+#endif // _smw_bindgen_h

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/include/smw/cx.h

@@ -0,0 +1,17 @@
+#ifndef _smw_cx_h
+#define _smw_cx_h
+
+struct JSContext;
+class JSObject;
+
+namespace smw {
+
+void init_js_context(JSContext* cx);
+JSContext* get_js_context();
+
+void init_user_module(JSContext* cx, JSObject* user_module);
+JSObject* get_user_module();
+
+}
+
+#endif // _smw_cx_h

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/include/smw/dump.h

@@ -0,0 +1,27 @@
+#ifndef _smw_dump_h
+#define _smw_dump_h
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Winvalid-offsetof"
+
+#include "js/TypeDecls.h"
+#include "js/Value.h"
+
+#pragma clang diagnostic pop
+
+namespace smw {
+
+/**
+ * Dump a human-readable representation of the given JS value to the given file.
+ */
+bool dump_value(JSContext *cx, JS::HandleValue val, FILE* fp);
+
+/**
+ * Dump a human-readable representation of the given JS exception stack to the
+ * given file.
+ */
+bool dump_stack(JSContext *cx, JS::HandleObject stack, FILE* fp);
+
+}
+
+#endif // _smw_dump_h

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/include/smw/logging.h

@@ -0,0 +1,15 @@
+#ifndef _smw_logging_h
+#define _smw_logging_h
+
+#if LOGGING==1
+
+#include <stdio.h>
+#define SMW_LOG(msg, ...) fprintf(stderr, msg, ##__VA_ARGS__)
+
+#else // LOGGING==1
+
+#define SMW_LOG(msg, ...) do { } while(false)
+
+#endif // LOGGING==1
+
+#endif // _smw_logging_h

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/include/smw/wasm.h

@@ -0,0 +1,18 @@
+#ifndef _smw_wasm_h
+#define _smw_wasm_h
+
+/**
+ * An attribute for making a function exported from the final Wasm binary.
+ *
+ * Example usage:
+ *
+ *     WASM_EXPORT
+ *     int add(int a, int b) {
+ *         return a + b;
+ *     }
+ */
+#define WASM_EXPORT                             \
+    __attribute__((visibility("default")))      \
+    extern "C"
+
+#endif // _smw_wasm_h

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/initialize.cpp

@@ -0,0 +1,380 @@
+/*!
+ * JS engine initialization and JS top-level evaluation.
+ *
+ * This file contains the code to start up the JS engine, define import-able
+ * modules from VM functions, and evaluate the user JS.
+ */
+
+#include <assert.h>
+#include <stdlib.h>
+
+#include "smw/abort.h"
+#include "smw/bindgen.h"
+#include "smw/cx.h"
+#include "smw/wasm.h"
+
+#include "js/AllocPolicy.h"
+#include "js/CompilationAndEvaluation.h"
+#include "js/GCAPI.h"
+#include "js/GCVector.h"
+#include "js/Initialization.h"
+#include "js/Modules.h"
+#include "js/Promise.h"
+#include "js/Realm.h"
+#include "js/SourceText.h"
+#include "js/TypeDecls.h"
+#include "js/Warnings.h"
+#include "jsapi.h"
+#include "jsfriendapi.h"
+
+namespace smw {
+
+using UniqueChars = mozilla::UniquePtr<char[]>;
+
+bool INITIALIZED = false;
+JS::PersistentRootedObject GLOBAL;
+
+static JSClass global_class = {
+    "global",
+    JSCLASS_GLOBAL_FLAGS,
+    &JS::DefaultGlobalClassOps
+};
+
+/**
+ * Compile the given JS source as a module in the context of the given global.
+ *
+ * Takes ownership of `jsSource`.
+ *
+ * Does not take ownership of `jsFileName`.
+ *
+ * Sets `outModule` to the resulting source text module record object.
+ */
+bool compile_js_module(JSContext *cx,
+                       const char *jsFileName,
+                       char *jsSource,
+                       size_t jsSourceLen,
+                       JS::MutableHandleObject outModule) {
+    JS::CompileOptions copts(cx);
+    copts
+        .setFileAndLine(jsFileName, 1)
+        .setNoScriptRval(true)
+        .setForceFullParse();
+
+    JS::SourceText<mozilla::Utf8Unit> srcBuf;
+    if (!srcBuf.init(cx, jsSource, jsSourceLen, JS::SourceOwnership::TakeOwnership)) {
+        return false;
+    }
+
+    JS::RootedObject module(cx);
+
+    // Disabling generational GC during compilation seems to slightly reduce
+    // the number of pages touched post-wizening. (Whereas disabling it
+    // during execution meaningfully increases it, which is why this is
+    // scoped to just compilation.)
+    JS::AutoDisableGenerationalGC noGgc(cx);
+    module = JS::CompileModule(cx, copts, srcBuf);
+    if (!module) {
+        return false;
+    }
+
+    outModule.set(module);
+    return true;
+}
+
+/**
+ * A synthesized module that exports `JSNative` functions.
+ */
+struct SynthesizedModule {
+    JS::Heap<JSString*> moduleName;
+    JS::Heap<JSObject*> moduleObject;
+
+    SynthesizedModule(JS::HandleString moduleName, JS::HandleObject moduleObject)
+        : moduleName(moduleName)
+        , moduleObject(moduleObject)
+    { }
+
+    void trace(JSTracer* tracer) {
+        JS::TraceEdge(tracer, &moduleObject, "SynthesizedModule.moduleObject");
+    }
+};
+
+JS::PersistentRooted<JS::GCVector<SynthesizedModule, 0, js::SystemAllocPolicy>> MODULES;
+
+JSObject* module_resolve_hook(JSContext *cx,
+                              JS::HandleValue referencing_private,
+                              JS::HandleObject module_request) {
+    JS::RootedString specifier(cx, JS::GetModuleRequestSpecifier(cx, module_request));
+    if (!specifier) {
+        abort(cx, "failed to get module request specifier");
+    }
+
+    size_t len = MODULES.length();
+    for (size_t i = 0; i < len; i++) {
+        JS::RootedObject it_module(cx, MODULES[i].get().moduleObject);
+        JS::RootedString it_name(cx, MODULES[i].get().moduleName);
+        int32_t result = 0;
+        if (!JS_CompareStrings(cx, it_name, specifier, &result)) {
+            abort(cx, "failed to compare module specifier to registered module name");
+        }
+        if (result == 0) {
+            return it_module.get();
+        }
+    }
+
+
+    JS::UniqueChars utf8 = JS_EncodeStringToUTF8(cx, specifier);
+    if (!utf8) {
+        JS_ReportErrorASCII(cx, "failed to find module import");
+        return nullptr;
+    }
+    JS_ReportErrorASCII(cx, "failed to find module import: `%s`", utf8.get());
+    return nullptr;
+}
+
+JS::RealmOptions make_realm_options() {
+    JS::RealmOptions options;
+    options
+        .creationOptions()
+        .setStreamsEnabled(true)
+        .setReadableByteStreamsEnabled(true)
+        .setBYOBStreamReadersEnabled(true)
+        .setReadableStreamPipeToEnabled(true)
+        .setWritableStreamsEnabled(true)
+        .setIteratorHelpersEnabled(true)
+        .setWeakRefsEnabled(JS::WeakRefSpecifier::EnabledWithoutCleanupSome);
+    return options;
+}
+
+bool init_js(JSContext *cx) {
+    if (!js::UseInternalJobQueues(cx)) {
+        return false;
+    }
+
+    if (!JS::InitSelfHostedCode(cx)) {
+        return false;
+    }
+
+    JS::RealmOptions options = make_realm_options();
+
+    JS::DisableIncrementalGC(cx);
+
+    JS::RootedObject global(cx, JS_NewGlobalObject(cx, &global_class, nullptr,
+                                                   JS::FireOnNewGlobalHook, options));
+    if (!global) {
+        return false;
+    }
+
+    JS::EnterRealm(cx, global);
+
+    if (!JS::InitRealmStandardClasses(cx)) {
+        return false;
+    }
+
+    // JS::SetPromiseRejectionTrackerCallback(cx, rejection_tracker);
+
+    JS::SetModuleResolveHook(JS_GetRuntime(cx), module_resolve_hook);
+
+    GLOBAL.init(cx, global);
+    return true;
+}
+
+// static void report_warning(JSContext *cx, JSErrorReport *report) {
+//     JS::PrintError(stderr, report, true);
+//     if (!report->isWarning()) {
+//         ::abort();
+//     }
+// }
+
+/**
+ * Initialize the JS engine and evaluate the top-level of the given JavaScript
+ * source.
+ *
+ * Takes ownership of its parameters.
+ */
+WASM_EXPORT
+void SMW_initialize_engine() {
+    assert(!INITIALIZED);
+
+    bool ok = true;
+
+    ok = JS_Init();
+    assert(ok && "JS_Init failed");
+
+    JSContext *cx = JS_NewContext(JS::DefaultHeapMaxBytes);
+    assert(cx != nullptr && "JS_NewContext failed");
+    init_js_context(cx);
+
+    // JS::SetWarningReporter(cx, report_warning);
+
+    if (!init_js(cx)) {
+        abort(cx, "initializing the JavaScript engine failed");
+    }
+
+    init_operands(cx);
+
+    MODULES.init(cx);
+    INITIALIZED = true;
+}
+
+class ModuleBuilder {
+    JS::PersistentRootedString moduleName;
+    JS::PersistentRooted<JS::IdValueVector> exports;
+
+public:
+    /**
+     * Construct a new `ModuleBuilder` and take ownership of `moduleName`.
+     */
+    ModuleBuilder(JSContext *cx, JS::HandleString moduleName)
+        : moduleName(cx, moduleName)
+        , exports(cx, cx)
+    {
+        assert(moduleName && "moduleName must not be nullptr");
+    }
+
+    /**
+     * Add an exported function to this module and take ownership of `funcName`.
+     */
+    void add_export(const char *funcName, size_t funcNameLen, JSNative func, unsigned numArgs) {
+        assert(funcName && "function name must not be nullptr");
+        assert(funcNameLen > 0 && "function name length must be greater than zero");
+        assert(func && "the function must not be nullptr");
+
+        JSContext *cx = get_js_context();
+
+        JS::RootedString jsFuncName(cx, JS_NewStringCopyN(cx, funcName, funcNameLen));
+        if (!jsFuncName) {
+            abort(cx, "failed to create new JS string");
+        }
+
+        JS::RootedId funcNameId(cx);
+        if (!JS_StringToId(cx, jsFuncName, &funcNameId)) {
+            abort(cx, "failed to convert string to id");
+        }
+
+        JS::RootedFunction jsFunc(cx, JS_NewFunction(cx, func, numArgs, 0, funcName));
+        if (!jsFunc) {
+            abort(cx, "failed to create new JS function");
+        }
+
+        JS::RootedObject jsFuncObj(cx, JS_GetFunctionObject(jsFunc));
+        assert(jsFuncObj && "getting function object is infallible");
+        JS::RootedValue jsFuncVal(cx, JS::ObjectValue(*jsFuncObj));
+
+        if (!exports.append(JS::IdValuePair(funcNameId, jsFuncVal))) {
+            abort(cx, "failed to append export to exports list");
+        }
+    }
+
+    void finish() {
+        JSContext *cx = get_js_context();
+
+        JS::RootedObject module(cx, JS::CreateModule(cx, exports));
+        if (!module) {
+            abort(cx, "failed to create synthetic module");
+        }
+
+        if (!MODULES.append(SynthesizedModule(moduleName, module))) {
+            abort(cx, "failed to append to MODULES");
+        }
+
+        delete this;
+    }
+};
+
+WASM_EXPORT
+ModuleBuilder *SMW_new_module_builder(char *module_name, size_t module_name_len) {
+    auto unique_module_name = UniqueChars(module_name);
+
+    JSContext *cx = get_js_context();
+
+    JS::RootedString js_module_name(cx, JS_NewStringCopyN(cx, unique_module_name.get(), module_name_len));
+    if (!js_module_name) {
+        abort(cx, "failed to allocate JS string");
+    }
+
+    auto b = new ModuleBuilder(cx, js_module_name);
+    if (!b) {
+        abort(cx, "failed to create new ModuleBuilder");
+    }
+
+    return b;
+}
+
+WASM_EXPORT
+void SMW_module_builder_add_export(ModuleBuilder *builder,
+                                   char *funcName,
+                                   size_t funcNameLen,
+                                   JSNative func,
+                                   unsigned numArgs) {
+    assert(builder && "builder must not be nullptr");
+    assert(funcName && "funcName must not be nullptr");
+    assert(funcNameLen > 0 && "funcNameLen must be greater than 0");
+    assert(func && "func must not be nullptr");
+
+    auto uniqFuncName = UniqueChars(funcName);
+    builder->add_export(uniqFuncName.get(), funcNameLen, func, numArgs);
+}
+
+WASM_EXPORT
+void SMW_finish_module_builder(ModuleBuilder *builder) {
+    builder->finish();
+}
+
+WASM_EXPORT
+void SMW_eval_module(char *jsFileName, char *jsSource, size_t jsSourceLen) {
+    JSContext *cx = get_js_context();
+
+    assert(GLOBAL && "GLOBAL should be initialized");
+    JS::RootedObject global(cx, GLOBAL);
+    JSAutoRealm autoRealm(cx, global);
+
+    JS::RootedObject module(cx);
+    if (!compile_js_module(cx, jsFileName, jsSource, jsSourceLen, &module)) {
+        abort(cx, "module compilation failed");
+    }
+
+    if (!JS::ModuleInstantiate(cx, module)) {
+        abort(cx, "failed to instantiate module");
+    }
+
+    JS::RootedValue result(cx);
+    if (!JS::ModuleEvaluate(cx, module, &result)) {
+        abort(cx, "failed to evaluate module");
+    }
+
+    // TODO: if `result` is a promise because of top-level await, then don't
+    // return until the micro task queue is empty.
+    if (result.isObject()) {
+        JS::RootedObject resultObj(cx, &result.toObject());
+        if (!JS::IsPromiseObject(resultObj)) {
+            goto done_handling_promise;
+        }
+        switch (JS::GetPromiseState(resultObj)) {
+        case JS::PromiseState::Fulfilled: {
+            JS::RootedValue promiseResolution(cx, JS::GetPromiseResult(resultObj));
+            break;
+        }
+        case JS::PromiseState::Rejected: {
+            JS::RootedValue promiseRejection(cx, JS::GetPromiseResult(resultObj));
+            JS_SetPendingException(cx, promiseRejection);
+            abort(cx, "module evaluation failed");
+        }
+        case JS::PromiseState::Pending: {
+            abort(cx, "module evaluation returned a pending promise, but top-level await isn't enabled yet");
+        }
+        default:
+            abort(cx, "module evaluation returned a promise in an unknown promise state");
+        }
+    }
+
+  done_handling_promise:
+
+    init_user_module(cx, module);
+
+    JS::PrepareForFullGC(cx);
+    JS::NonIncrementalGC(cx, JS::GCOptions::Shrink, JS::GCReason::API);
+
+    free(jsFileName);
+}
+
+} // namespace smw

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/malloc.cpp

@@ -0,0 +1,18 @@
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "smw/abort.h"
+#include "smw/wasm.h"
+
+namespace smw {
+
+WASM_EXPORT
+void* SMW_malloc(size_t size) {
+    auto p = malloc(size);
+    if (p == nullptr) {
+        abort("out of memory");
+    }
+    return p;
+}
+
+} // namespace smw

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/spidermonkey-wasm/mozconfig

@@ -0,0 +1,27 @@
+WASI_SDK="$(pwd)/../wasi-sdk-12.0"
+
+CC="$WASI_SDK/bin/clang --sysroot=$WASI_SDK/share/wasi-sysroot"
+CXX="$WASI_SDK/bin/clang++ --sysroot=$WASI_SDK/share/wasi-sysroot"
+AR="$WASI_SDK/bin/ar"
+
+HOST_CC=gcc
+HOST_CXX=g++
+
+ac_add_options --enable-application=js
+ac_add_options --target=wasm32-unknown-wasi
+
+ac_add_options --without-system-zlib
+ac_add_options --without-intl-api
+
+ac_add_options --disable-jit
+ac_add_options --disable-shared-js
+ac_add_options --disable-shared-memory
+
+# Comment out `--enable-optimize` and `--disable-debug` and then uncomment
+# `--enable-debug` to switch to debug builds of SpiderMonkey. Also update
+# `DEFINE=` in the `Makefile`.
+ac_add_options --enable-optimize
+ac_add_options --disable-debug
+# ac_add_options --enable-debug
+
+mk_add_options AUTOCLOBBER=1

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/src/data_segments.rs

@@ -0,0 +1,72 @@
+//! Assigning static locations for data segments we will emit in the glue Wasm
+//! module.
+
+use std::convert::TryFrom;
+
+#[derive(Debug)]
+pub struct DataSegments {
+    data: wasm_encoder::DataSection,
+    next_offset: u32,
+    memory: u32,
+}
+
+impl DataSegments {
+    /// Create a new collection of data segments for the given memory.
+    pub fn new(memory: u32) -> DataSegments {
+        DataSegments {
+            data: wasm_encoder::DataSection::new(),
+            next_offset: 0,
+            memory,
+        }
+    }
+
+    /// Add a new segment to this `DataSegments`, returning the assigned offset
+    /// in memory.
+    pub fn add<S>(&mut self, segment: S) -> u32
+    where
+        S: IntoIterator<Item = u8>,
+        S::IntoIter: ExactSizeIterator,
+    {
+        let segment = segment.into_iter();
+        let offset = self.reserve_space(u32::try_from(segment.len()).unwrap());
+        self.data.active(
+            self.memory,
+            &wasm_encoder::Instruction::I32Const(offset as i32),
+            segment,
+        );
+        offset
+    }
+
+    /// Reserve space in memory but don't emit any data segment to initialize
+    /// it.
+    ///
+    /// This effectively lets you add zero-initialized data segments, reserve
+    /// space for return pointer areas, or define shadow stack regions.
+    pub fn reserve_space(&mut self, num_bytes: u32) -> u32 {
+        // Leave an empty byte between each data segment. This helps when
+        // staring at disassemblies and heap dumps.
+        self.next_offset += 1;
+
+        let offset = self.next_offset;
+        self.next_offset += num_bytes;
+
+        offset
+    }
+
+    /// Get the memory type required to hold these data segments.
+    pub fn memory_type(&self) -> wasm_encoder::MemoryType {
+        const WASM_PAGE_SIZE: u32 = 65_536;
+        wasm_encoder::MemoryType {
+            minimum: ((self.next_offset + WASM_PAGE_SIZE - 1) / WASM_PAGE_SIZE).into(),
+            maximum: None,
+            memory64: false,
+        }
+    }
+
+    /// Take the constructed data section.
+    ///
+    /// No more data segments should be added after this is called.
+    pub fn take_data(&mut self) -> wasm_encoder::DataSection {
+        std::mem::replace(&mut self.data, wasm_encoder::DataSection::new())
+    }
+}

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/tests/codegen-smw.rs

@@ -0,0 +1,31 @@
+use std::path::Path;
+
+mod imports {
+    test_helpers::codegen_spidermonkey_import!(
+        // TODO: should support more of the `*.wit` test suite
+        "strings.wit"
+        "simple-lists.wit"
+        "simple-functions.wit"
+    );
+}
+
+mod exports {
+    test_helpers::codegen_spidermonkey_export!(
+        // TODO: should support more of the `*.wit` test suite
+        "strings.wit"
+        "simple-lists.wit"
+        "simple-functions.wit"
+    );
+}
+
+fn verify(dir: &str, _name: &str) {
+    let wasm = std::fs::read(Path::new(dir).join("foo.wasm")).unwrap();
+    let mut validator = wasmparser::Validator::new();
+    validator.wasm_features(wasmparser::WasmFeatures {
+        bulk_memory: true,
+        module_linking: true,
+        multi_memory: true,
+        ..wasmparser::WasmFeatures::default()
+    });
+    validator.validate_all(&wasm).expect("wasm isn't valid");
+}