[vm] Adds args_n to FFI resolver.

This makes it more closely mirror the Dart_NativeEntryResolver,
and acts as an extra sanity check that signatures (roughly)
align between the FfiNative decl. and the native function.

TEST=Updated runtime/vm/dart_api_impl_test.cc

Change-Id: I40799dc583ec14db14dc453afed4e2d1eb06fced
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/212566
Commit-Queue: Clement Skau <cskau@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>

pkg/vm/lib/transformations/ffi_native.dart

@@ -102,22 +102,26 @@ class FfiNativeTransformer extends Transformer {
     final DartType dartType =
         node.function.computeThisFunctionType(Nullability.nonNullable);
     // Double Function(Double)
-    final nativeType = annotationConst.typeArguments[0];
+    final nativeType = annotationConst.typeArguments[0] as FunctionType;
     // InterfaceType(NativeFunction<Double Function(Double)>*)
     final DartType nativeInterfaceType =
         InterfaceType(nativeFunctionClass, Nullability.legacy, [nativeType]);
 
+    // Derive number of arguments from the native function signature.
+    final args_n = nativeType.positionalParameters.length;
+
     // TODO(dartbug.com/31579): Add `..fileOffset`s once we can handle these in
     // patch files.
 
-    // _ffi_resolver('dart:math', 'Math_sqrt')
+    // _ffi_resolver('dart:math', 'Math_sqrt', 1)
     final resolverInvocation = FunctionInvocation(
         FunctionAccessKind.FunctionType,
         StaticGet(resolverField),
         Arguments([
           ConstantExpression(
               StringConstant(currentLibrary!.importUri.toString())),
-          ConstantExpression(functionName)
+          ConstantExpression(functionName),
+          ConstantExpression(IntConstant(args_n)),
         ]),
         functionType: resolverField.type as FunctionType);
 

runtime/bin/ffi_test/ffi_test_functions_vmspecific.cc

@@ -1094,11 +1094,11 @@ intptr_t ReturnIntPtr(intptr_t x) {
   return x;
 }
 
-static void* FfiNativeResolver(const char* name) {
-  if (strcmp(name, "ReturnIntPtr") == 0) {
+static void* FfiNativeResolver(const char* name, uintptr_t args_n) {
+  if (strcmp(name, "ReturnIntPtr") == 0 && args_n == 1) {
     return reinterpret_cast<void*>(ReturnIntPtr);
   }
-  if (strcmp(name, "IsThreadInGenerated") == 0) {
+  if (strcmp(name, "IsThreadInGenerated") == 0 && args_n == 0) {
     return reinterpret_cast<void*>(IsThreadInGenerated);
   }
   // This should be unreachable in tests.

runtime/include/dart_api.h

@@ -3046,7 +3046,7 @@ typedef const uint8_t* (*Dart_NativeEntrySymbol)(Dart_NativeFunction nf);
  *
  * See Dart_SetFfiNativeResolver.
  */
-typedef void* (*Dart_FfiNativeResolver)(const char* name);
+typedef void* (*Dart_FfiNativeResolver)(const char* name, uintptr_t args_n);
 
 /*
  * ===========

runtime/lib/ffi.cc

@@ -276,7 +276,9 @@ DEFINE_NATIVE_ENTRY(DartApiDLInitializeData, 0, 0) {
 }
 
 // FFI native C function pointer resolver.
-static intptr_t FfiResolve(Dart_Handle lib_url, Dart_Handle name) {
+static intptr_t FfiResolve(Dart_Handle lib_url,
+                           Dart_Handle name,
+                           uintptr_t args_n) {
   DARTSCOPE(Thread::Current());
 
   const String& lib_url_str = Api::UnwrapStringHandle(T->zone(), lib_url);
@@ -296,7 +298,7 @@ static intptr_t FfiResolve(Dart_Handle lib_url, Dart_Handle name) {
     Exceptions::ThrowArgumentError(error);
   }
 
-  auto* f = resolver(function_name.ToCString());
+  auto* f = resolver(function_name.ToCString(), args_n);
   if (f == nullptr) {
     const String& error = String::Handle(String::NewFormatted(
         "Couldn't resolve function: '%s'.", function_name.ToCString()));

runtime/vm/dart_api_impl_test.cc

@@ -9585,8 +9585,9 @@ static intptr_t EchoInt(double x) {
   return x;
 }
 
-static void* FfiNativeResolver(const char* name) {
+static void* FfiNativeResolver(const char* name, uintptr_t args_n) {
   ASSERT(strcmp(name, "EchoInt") == 0);
+  ASSERT(args_n == 1);
   return reinterpret_cast<void*>(EchoInt);
 }
 
@@ -9628,7 +9629,7 @@ TEST_CASE(Dart_SetFfiNativeResolver_MissingResolver) {
       "Invalid argument(s): Library has no handler: 'file:///test-lib'.");
 }
 
-static void* NopResolver(const char* name) {
+static void* NopResolver(const char* name, uintptr_t args_n) {
   return nullptr;
 }
 

sdk/lib/ffi/ffi.dart

@@ -824,11 +824,11 @@ class FfiNative<T> {
 // Bootstrapping native for getting the FFI native C function pointer to look
 // up the FFI resolver.
 @pragma("vm:external-name", "Ffi_GetFfiNativeResolver")
-external Pointer<NativeFunction<IntPtr Function(Handle, Handle)>>
+external Pointer<NativeFunction<IntPtr Function(Handle, Handle, IntPtr)>>
     _get_ffi_native_resolver<T extends NativeFunction>();
 
 // Resolver for FFI Native C function pointers.
 @pragma('vm:entry-point')
-final _ffi_resolver =
-    _get_ffi_native_resolver<NativeFunction<IntPtr Function(Handle, Handle)>>()
-        .asFunction<int Function(Object, Object)>();
+final _ffi_resolver = _get_ffi_native_resolver<
+        NativeFunction<IntPtr Function(Handle, Handle, IntPtr)>>()
+    .asFunction<int Function(Object, Object, int)>();