Disallow direct call of host functions (#723)

Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>

examples/multiple-results/multiple-results.go

@@ -37,20 +37,12 @@ func main() {
 	r := wazero.NewRuntime()
 	defer r.Close(ctx) // This closes everything this Runtime created.
 
-	// Add a module that uses offset parameters for multiple results.
-
-	// ... defined in WebAssembly.
+	// Add a module that uses offset parameters for multiple results defined in WebAssembly.
 	wasm, err := resultOffsetWasmFunctions(ctx, r)
 	if err != nil {
 		log.Panicln(err)
 	}
 
-	// ... defined in Go.
-	host, err := resultOffsetHostFunctions(ctx, r)
-	if err != nil {
-		log.Panicln(err)
-	}
-
 	// wazero enables WebAssembly 1.0 by default. Opt-in to other features:
 	runtimeWithMultiValue := wazero.NewRuntimeWithConfig(
 		wazero.NewRuntimeConfig().WithFeatureMultiValue(true),
@@ -66,13 +58,13 @@ func main() {
 	}
 
 	// ... defined in Go.
-	hostWithMultiValue, err := multiValueHostFunctions(ctx, runtimeWithMultiValue)
+	multiValueFromImportedHost, err := multiValueFromImportedHostWasmFunctions(ctx, runtimeWithMultiValue)
 	if err != nil {
 		log.Panicln(err)
 	}
 
 	// Call the function from each module and print the results to the console.
-	for _, mod := range []api.Module{wasm, host, wasmWithMultiValue, hostWithMultiValue} {
+	for _, mod := range []api.Module{wasm, wasmWithMultiValue, multiValueFromImportedHost} {
 		getAge := mod.ExportedFunction("call_get_age")
 		results, err := getAge.Call(ctx)
 		if err != nil {
@@ -83,36 +75,6 @@ func main() {
 	}
 }
 
-// resultOffsetHostFunctions defines host functions that illustrate multiple
-// results using a technique compatible with any WebAssembly 1.0 runtime.
-//
-// To return a value in WASM written to a result parameter, you have to define
-// memory and pass a location to write the result. At the end of your function,
-// you load that location.
-func resultOffsetHostFunctions(ctx context.Context, r wazero.Runtime) (api.Module, error) {
-	return r.NewModuleBuilder("result-offset/host").
-		// To use result parameters, we need scratch memory. Allocate the least
-		// possible: 1 page (64KB).
-		ExportMemoryWithMax("mem", 1, 1).
-		// get_age returns a result, while a second result is written to memory.
-		ExportFunction("get_age", func(ctx context.Context, m api.Module, resultOffsetAge uint32) (errno uint32) {
-			if m.Memory().WriteUint64Le(ctx, resultOffsetAge, 37) {
-				return 0
-			}
-			return 1 // overflow
-		}).
-		// Now, define a function that shows the Wasm mechanics returning
-		// something written to a result parameter. The caller provides a
-		// memory offset to the callee, so that it knows where to write the
-		// second result.
-		ExportFunction("call_get_age", func(ctx context.Context, m api.Module) (age uint64) {
-			resultOffsetAge := uint32(8) // arbitrary memory offset (in bytes)
-			_, _ = m.ExportedFunction("get_age").Call(ctx, uint64(resultOffsetAge))
-			age, _ = m.Memory().ReadUint64Le(ctx, resultOffsetAge)
-			return
-		}).Instantiate(ctx, r)
-}
-
 // resultOffsetWasm was generated by the following:
 //
 //	cd testdata; wat2wasm --debug-names result_offset.wat
@@ -126,23 +88,6 @@ func resultOffsetWasmFunctions(ctx context.Context, r wazero.Runtime) (api.Modul
 	return r.InstantiateModuleFromBinary(ctx, resultOffsetWasm)
 }
 
-// multiValueHostFunctions defines Wasm functions that illustrate multiple
-// results using the "multiple-results" feature.
-func multiValueHostFunctions(ctx context.Context, r wazero.Runtime) (api.Module, error) {
-	return r.NewModuleBuilder("multi-value/host").
-		// Define a function that returns two results
-		ExportFunction("get_age", func() (age uint64, errno uint32) {
-			age = 37
-			errno = 0
-			return
-		}).
-		// Now, define a function that returns only the first result.
-		ExportFunction("call_get_age", func(ctx context.Context, m api.Module) (age uint64) {
-			results, _ := m.ExportedFunction("get_age").Call(ctx)
-			return results[0]
-		}).Instantiate(ctx, r)
-}
-
 // multiValueWasm was generated by the following:
 //
 //	cd testdata; wat2wasm --debug-names multi_value.wat
@@ -155,3 +100,21 @@ var multiValueWasm []byte
 func multiValueWasmFunctions(ctx context.Context, r wazero.Runtime) (api.Module, error) {
 	return r.InstantiateModuleFromBinary(ctx, multiValueWasm)
 }
+
+// multiValueWasm was generated by the following:
+//
+//	cd testdata; wat2wasm --debug-names multi_value_imported.wat
+//
+//go:embed testdata/multi_value_imported.wasm
+var multiValueFromImportedHostWasm []byte
+
+func multiValueFromImportedHostWasmFunctions(ctx context.Context, r wazero.Runtime) (api.Module, error) {
+	r.NewModuleBuilder("multi-value/host").
+		// Define a function that returns two results
+		ExportFunction("get_age", func() (age uint64, errno uint32) {
+			age = 37
+			errno = 0
+			return
+		}).Instantiate(ctx, r)
+	return r.InstantiateModuleFromBinary(ctx, multiValueFromImportedHostWasm)
+}

examples/multiple-results/multiple-results_test.go

@@ -13,8 +13,7 @@ import (
 func Test_main(t *testing.T) {
 	stdout, _ := maintester.TestMain(t, main, "multiple-results")
 	require.Equal(t, `result-offset/wasm: age=37
-result-offset/host: age=37
 multi-value/wasm: age=37
-multi-value/host: age=37
+multi-value/imported_host: age=37
 `, stdout)
 }

examples/multiple-results/testdata/multi_value_imported.wat

@@ -0,0 +1,12 @@
+;; multiValueWasmFunctions defines Wasm functions that illustrate multiple
+;; results using the "multiple-results" feature.
+(module $multi-value/imported_host
+  ;; Imports the `get_age` function from `multi-value/host` defined in the host.
+  (func $get_age (import "multi-value/host" "get_age") (result (;age;) i64 (;errno;) i32))
+
+  ;; Now, define a function that returns only the first result.
+  (func (export "call_get_age") (result i64)
+    call $get_age ;; stack = [37, errno] result of get_age
+    drop          ;; stack = [37]
+  )
+)