/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- * vim: set ts=8 sts=2 et sw=2 tw=80: * This Source Code Form is subject to the terms of the Mozilla Public * 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/. */ #ifndef jit_VMFunctions_h #define jit_VMFunctions_h #include "mozilla/Assertions.h" #include "mozilla/HashFunctions.h" #include #include #include "jstypes.h" #include "NamespaceImports.h" #include "gc/AllocKind.h" #include "js/ScalarType.h" #include "js/TypeDecls.h" class JSJitInfo; class JSLinearString; namespace js { class AbstractGeneratorObject; class ArrayObject; class GlobalObject; class InterpreterFrame; class LexicalScope; class ClassBodyScope; class MapObject; class NativeObject; class PlainObject; class PropertyName; class SetObject; class Shape; class TypedArrayObject; class WithScope; class MegamorphicCacheEntry; namespace gc { struct Cell; } namespace jit { class BaselineFrame; class InterpreterStubExitFrameLayout; enum DataType : uint8_t { Type_Void, Type_Bool, Type_Int32, Type_Double, Type_Pointer, Type_Cell, Type_Value, Type_Handle }; enum MaybeTailCall : bool { TailCall, NonTailCall }; // [SMDOC] JIT-to-C++ Function Calls. (callVM) // // Sometimes it is easier to reuse C++ code by calling VM's functions. Calling a // function from the VM can be achieved with the use of callWithABI but this is // discouraged when the called functions might trigger exceptions and/or // garbage collections which are expecting to walk the stack. VMFunctions and // callVM are interfaces provided to handle the exception handling and register // the stack end (JITActivation) such that walking the stack is made possible. // // VMFunctionData is a structure which contains the necessary information needed // for generating a trampoline function to make a call (with generateVMWrapper) // and to root the arguments of the function (in TraceJitExitFrame). // VMFunctionData is created with the VMFunctionDataHelper template, which // infers the VMFunctionData fields from the function signature. The rooting and // trampoline code is therefore determined by the arguments of a function and // their locations in the signature of a function. // // VM functions all expect a JSContext* as first argument. This argument is // implicitly provided by the trampoline code (in generateVMWrapper) and used // for creating new objects or reporting errors. If your function does not make // use of a JSContext* argument, then you might probably use a callWithABI // call. // // Functions described using the VMFunction system must conform to a simple // protocol: the return type must have a special "failure" value (for example, // false for bool, or nullptr for Objects). If the function is designed to // return a value that does not meet this requirement - such as // object-or-nullptr, or an integer, an optional, final outParam can be // specified. In this case, the return type must be boolean to indicate // failure. // // JIT Code usage: // // Different JIT compilers in SpiderMonkey have their own implementations of // callVM to call VM functions. However, the general shape of them is that // arguments (excluding the JSContext or trailing out-param) are pushed on to // the stack from right to left (rightmost argument is pushed first). // // Regardless of return value protocol being used (final outParam, or return // value) the generated trampolines ensure the return value ends up in // JSReturnOperand, ReturnReg or ReturnDoubleReg. // // Example: // // The details will differ slightly between the different compilers in // SpiderMonkey, but the general shape of our usage looks like this: // // Suppose we have a function Foo: // // bool Foo(JSContext* cx, HandleObject x, HandleId y, // MutableHandleValue z); // // This function returns true on success, and z is the outparam return value. // // A VM function wrapper for this can be created by adding an entry to // VM_FUNCTION_LIST in VMFunctionList-inl.h: // // _(Foo, js::Foo) // // In the compiler code the call would then be issued like this: // // masm.Push(id); // masm.Push(obj); // // using Fn = bool (*)(JSContext*, HandleObject, HandleId, // MutableHandleValue); // if (!callVM()) { // return false; // } // // After this, the result value is in the return value register. // Data for a VM function. All VMFunctionDatas are stored in a constexpr array. struct VMFunctionData { #if defined(DEBUG) || defined(JS_JITSPEW) // Informative name of the wrapped function. The name should not be present // in release builds in order to save memory. const char* name_; #endif // Note: a maximum of seven root types is supported. enum RootType : uint8_t { RootNone = 0, RootObject, RootString, RootId, RootValue, RootCell, RootBigInt }; // Contains an combination of enumerated types used by the gc for marking // arguments of the VM wrapper. uint64_t argumentRootTypes; enum ArgProperties { WordByValue = 0, DoubleByValue = 1, WordByRef = 2, DoubleByRef = 3, // BitMask version. Word = 0, Double = 1, ByRef = 2 }; // Contains properties about the first 16 arguments. uint32_t argumentProperties; // Which arguments should be passed in float register on platforms that // have them. uint32_t argumentPassedInFloatRegs; // Number of arguments expected, excluding JSContext * as an implicit // first argument and an outparam as a possible implicit final argument. uint8_t explicitArgs; // The root type of the out param if outParam == Type_Handle. RootType outParamRootType; // The outparam may be any Type_*, and must be the final argument to the // function, if not Void. outParam != Void implies that the return type // has a boolean failure mode. DataType outParam; // Type returned by the C function and used by the VMFunction wrapper to // check for failures of the C function. Valid failure/return types are // boolean and object pointers which are asserted inside the VMFunction // constructor. If the C function use an outparam (!= Type_Void), then // the only valid failure/return type is boolean -- object pointers are // pointless because the wrapper will only use it to compare it against // nullptr before discarding its value. DataType returnType; // Number of Values the VM wrapper should pop from the stack when it returns. // Used by baseline IC stubs so that they can use tail calls to call the VM // wrapper. uint8_t extraValuesToPop; // On some architectures, called functions need to explicitly push their // return address, for a tail call, there is nothing to push, so tail-callness // needs to be known at compile time. MaybeTailCall expectTailCall; uint32_t argc() const { // JSContext * + args + (OutParam? *) return 1 + explicitArgc() + ((outParam == Type_Void) ? 0 : 1); } DataType failType() const { return returnType; } // Whether this function returns anything more than a boolean flag for // failures. bool returnsData() const { return returnType == Type_Cell || outParam != Type_Void; } ArgProperties argProperties(uint32_t explicitArg) const { return ArgProperties((argumentProperties >> (2 * explicitArg)) & 3); } RootType argRootType(uint32_t explicitArg) const { return RootType((argumentRootTypes >> (3 * explicitArg)) & 7); } bool argPassedInFloatReg(uint32_t explicitArg) const { return ((argumentPassedInFloatRegs >> explicitArg) & 1) == 1; } #if defined(DEBUG) || defined(JS_JITSPEW) const char* name() const { return name_; } #endif // Return the stack size consumed by explicit arguments. size_t explicitStackSlots() const { size_t stackSlots = explicitArgs; // Fetch all double-word flags of explicit arguments. uint32_t n = ((1 << (explicitArgs * 2)) - 1) // = Explicit argument mask. & 0x55555555 // = Mask double-size args. & argumentProperties; // Add the number of double-word flags. (expect a few loop // iteration) while (n) { stackSlots++; n &= n - 1; } return stackSlots; } // Double-size argument which are passed by value are taking the space // of 2 C arguments. This function is used to compute the number of // argument expected by the C function. This is not the same as // explicitStackSlots because reference to stack slots may take one less // register in the total count. size_t explicitArgc() const { size_t stackSlots = explicitArgs; // Fetch all explicit arguments. uint32_t n = ((1 << (explicitArgs * 2)) - 1) // = Explicit argument mask. & argumentProperties; // Filter double-size arguments (0x5 = 0b0101) and remove (& ~) // arguments passed by reference (0b1010 >> 1 == 0b0101). n = (n & 0x55555555) & ~(n >> 1); // Add the number of double-word transfered by value. (expect a few // loop iteration) while (n) { stackSlots++; n &= n - 1; } return stackSlots; } size_t doubleByRefArgs() const { size_t count = 0; // Fetch all explicit arguments. uint32_t n = ((1 << (explicitArgs * 2)) - 1) // = Explicit argument mask. & argumentProperties; // Filter double-size arguments (0x5 = 0b0101) and take (&) only // arguments passed by reference (0b1010 >> 1 == 0b0101). n = (n & 0x55555555) & (n >> 1); // Add the number of double-word transfered by refference. (expect a // few loop iterations) while (n) { count++; n &= n - 1; } return count; } constexpr VMFunctionData(const char* name, uint32_t explicitArgs, uint32_t argumentProperties, uint32_t argumentPassedInFloatRegs, uint64_t argRootTypes, DataType outParam, RootType outParamRootType, DataType returnType, uint8_t extraValuesToPop = 0, MaybeTailCall expectTailCall = NonTailCall) : #if defined(DEBUG) || defined(JS_JITSPEW) name_(name), #endif argumentRootTypes(argRootTypes), argumentProperties(argumentProperties), argumentPassedInFloatRegs(argumentPassedInFloatRegs), explicitArgs(explicitArgs), outParamRootType(outParamRootType), outParam(outParam), returnType(returnType), extraValuesToPop(extraValuesToPop), expectTailCall(expectTailCall) { // Check for valid failure/return type. MOZ_ASSERT_IF(outParam != Type_Void, returnType == Type_Void || returnType == Type_Bool); MOZ_ASSERT(returnType == Type_Void || returnType == Type_Bool || returnType == Type_Cell); } constexpr VMFunctionData(const VMFunctionData& o) = default; }; // Extract the last element of a list of types. template struct LastArg; template <> struct LastArg<> { using Type = void; }; template struct LastArg { using Type = HeadType; }; template struct LastArg { using Type = typename LastArg::Type; }; [[nodiscard]] bool InvokeFunction(JSContext* cx, HandleObject obj0, bool constructing, bool ignoresReturnValue, uint32_t argc, Value* argv, MutableHandleValue rval); bool InvokeFromInterpreterStub(JSContext* cx, InterpreterStubExitFrameLayout* frame); void* GetContextSensitiveInterpreterStub(); bool CheckOverRecursed(JSContext* cx); bool CheckOverRecursedBaseline(JSContext* cx, BaselineFrame* frame); [[nodiscard]] bool MutatePrototype(JSContext* cx, Handle obj, HandleValue value); enum class EqualityKind : bool { NotEqual, Equal }; template bool StringsEqual(JSContext* cx, HandleString lhs, HandleString rhs, bool* res); enum class ComparisonKind : bool { GreaterThanOrEqual, LessThan }; template bool StringsCompare(JSContext* cx, HandleString lhs, HandleString rhs, bool* res); [[nodiscard]] bool ArrayPushDensePure(JSContext* cx, ArrayObject* arr, Value* v); JSString* ArrayJoin(JSContext* cx, HandleObject array, HandleString sep); [[nodiscard]] bool SetArrayLength(JSContext* cx, HandleObject obj, HandleValue value, bool strict); [[nodiscard]] bool CharCodeAt(JSContext* cx, HandleString str, int32_t index, uint32_t* code); JSLinearString* StringFromCharCode(JSContext* cx, int32_t code); JSLinearString* StringFromCharCodeNoGC(JSContext* cx, int32_t code); JSString* StringFromCodePoint(JSContext* cx, int32_t codePoint); JSLinearString* LinearizeForCharAccessPure(JSString* str); JSLinearString* LinearizeForCharAccess(JSContext* cx, JSString* str); [[nodiscard]] bool SetProperty(JSContext* cx, HandleObject obj, Handle name, HandleValue value, bool strict, jsbytecode* pc); [[nodiscard]] bool InterruptCheck(JSContext* cx); JSObject* NewStringObject(JSContext* cx, HandleString str); bool OperatorIn(JSContext* cx, HandleValue key, HandleObject obj, bool* out); [[nodiscard]] bool GetIntrinsicValue(JSContext* cx, Handle name, MutableHandleValue rval); [[nodiscard]] bool CreateThisFromIC(JSContext* cx, HandleObject callee, HandleObject newTarget, MutableHandleValue rval); [[nodiscard]] bool CreateThisFromIon(JSContext* cx, HandleObject callee, HandleObject newTarget, MutableHandleValue rval); void PostWriteBarrier(JSRuntime* rt, js::gc::Cell* cell); void PostGlobalWriteBarrier(JSRuntime* rt, GlobalObject* obj); enum class IndexInBounds { Yes, Maybe }; template void PostWriteElementBarrier(JSRuntime* rt, JSObject* obj, int32_t index); // If |str| represents an int32, assign it to |result| and return true. // Otherwise return false. bool GetInt32FromStringPure(JSContext* cx, JSString* str, int32_t* result); // If |str| is an index in the range [0, INT32_MAX], return it. If the string // is not an index in this range, return -1. int32_t GetIndexFromString(JSString* str); JSObject* WrapObjectPure(JSContext* cx, JSObject* obj); [[nodiscard]] bool DebugPrologue(JSContext* cx, BaselineFrame* frame); [[nodiscard]] bool DebugEpilogue(JSContext* cx, BaselineFrame* frame, const jsbytecode* pc, bool ok); [[nodiscard]] bool DebugEpilogueOnBaselineReturn(JSContext* cx, BaselineFrame* frame, const jsbytecode* pc); void FrameIsDebuggeeCheck(BaselineFrame* frame); JSObject* CreateGeneratorFromFrame(JSContext* cx, BaselineFrame* frame); JSObject* CreateGenerator(JSContext* cx, HandleFunction, HandleScript, HandleObject, HandleObject); [[nodiscard]] bool NormalSuspend(JSContext* cx, HandleObject obj, BaselineFrame* frame, uint32_t frameSize, const jsbytecode* pc); [[nodiscard]] bool FinalSuspend(JSContext* cx, HandleObject obj, const jsbytecode* pc); [[nodiscard]] bool InterpretResume(JSContext* cx, HandleObject obj, Value* stackValues, MutableHandleValue rval); [[nodiscard]] bool DebugAfterYield(JSContext* cx, BaselineFrame* frame); [[nodiscard]] bool GeneratorThrowOrReturn( JSContext* cx, BaselineFrame* frame, Handle genObj, HandleValue arg, int32_t resumeKindArg); [[nodiscard]] bool GlobalDeclInstantiationFromIon(JSContext* cx, HandleScript script, const jsbytecode* pc); [[nodiscard]] bool InitFunctionEnvironmentObjects(JSContext* cx, BaselineFrame* frame); [[nodiscard]] bool NewArgumentsObject(JSContext* cx, BaselineFrame* frame, MutableHandleValue res); ArrayObject* NewArrayObjectEnsureDenseInitLength(JSContext* cx, int32_t count); JSObject* InitRestParameter(JSContext* cx, uint32_t length, Value* rest, HandleObject res); [[nodiscard]] bool HandleDebugTrap(JSContext* cx, BaselineFrame* frame, const uint8_t* retAddr); [[nodiscard]] bool OnDebuggerStatement(JSContext* cx, BaselineFrame* frame); [[nodiscard]] bool GlobalHasLiveOnDebuggerStatement(JSContext* cx); [[nodiscard]] bool EnterWith(JSContext* cx, BaselineFrame* frame, HandleValue val, Handle templ); [[nodiscard]] bool LeaveWith(JSContext* cx, BaselineFrame* frame); [[nodiscard]] bool PushLexicalEnv(JSContext* cx, BaselineFrame* frame, Handle scope); [[nodiscard]] bool PushClassBodyEnv(JSContext* cx, BaselineFrame* frame, Handle scope); [[nodiscard]] bool DebugLeaveThenPopLexicalEnv(JSContext* cx, BaselineFrame* frame, const jsbytecode* pc); [[nodiscard]] bool FreshenLexicalEnv(JSContext* cx, BaselineFrame* frame); [[nodiscard]] bool DebugLeaveThenFreshenLexicalEnv(JSContext* cx, BaselineFrame* frame, const jsbytecode* pc); [[nodiscard]] bool RecreateLexicalEnv(JSContext* cx, BaselineFrame* frame); [[nodiscard]] bool DebugLeaveThenRecreateLexicalEnv(JSContext* cx, BaselineFrame* frame, const jsbytecode* pc); [[nodiscard]] bool DebugLeaveLexicalEnv(JSContext* cx, BaselineFrame* frame, const jsbytecode* pc); [[nodiscard]] bool PushVarEnv(JSContext* cx, BaselineFrame* frame, Handle scope); [[nodiscard]] bool InitBaselineFrameForOsr(BaselineFrame* frame, InterpreterFrame* interpFrame, uint32_t numStackValues); JSString* StringReplace(JSContext* cx, HandleString string, HandleString pattern, HandleString repl); void AssertValidBigIntPtr(JSContext* cx, JS::BigInt* bi); void AssertValidObjectPtr(JSContext* cx, JSObject* obj); void AssertValidStringPtr(JSContext* cx, JSString* str); void AssertValidSymbolPtr(JSContext* cx, JS::Symbol* sym); void AssertValidValue(JSContext* cx, Value* v); void JitValuePreWriteBarrier(JSRuntime* rt, Value* vp); void JitStringPreWriteBarrier(JSRuntime* rt, JSString** stringp); void JitObjectPreWriteBarrier(JSRuntime* rt, JSObject** objp); void JitShapePreWriteBarrier(JSRuntime* rt, Shape** shapep); bool ObjectIsCallable(JSObject* obj); bool ObjectIsConstructor(JSObject* obj); [[nodiscard]] bool ThrowRuntimeLexicalError(JSContext* cx, unsigned errorNumber); [[nodiscard]] bool ThrowBadDerivedReturnOrUninitializedThis(JSContext* cx, HandleValue v); [[nodiscard]] bool BaselineGetFunctionThis(JSContext* cx, BaselineFrame* frame, MutableHandleValue res); [[nodiscard]] bool CallNativeGetter(JSContext* cx, HandleFunction callee, HandleValue receiver, MutableHandleValue result); bool CallDOMGetter(JSContext* cx, const JSJitInfo* jitInfo, HandleObject obj, MutableHandleValue result); bool CallDOMSetter(JSContext* cx, const JSJitInfo* jitInfo, HandleObject obj, HandleValue value); [[nodiscard]] bool CallNativeSetter(JSContext* cx, HandleFunction callee, HandleObject obj, HandleValue rhs); [[nodiscard]] bool EqualStringsHelperPure(JSString* str1, JSString* str2); void HandleCodeCoverageAtPC(BaselineFrame* frame, jsbytecode* pc); void HandleCodeCoverageAtPrologue(BaselineFrame* frame); bool GetNativeDataPropertyPure(JSContext* cx, JSObject* obj, PropertyKey id, MegamorphicCacheEntry* entry, Value* vp); bool GetNativeDataPropertyPureWithCacheLookup(JSContext* cx, JSObject* obj, PropertyKey id, MegamorphicCacheEntry* entry, Value* vp); bool GetNativeDataPropertyByValuePure(JSContext* cx, JSObject* obj, MegamorphicCacheEntry* cacheEntry, Value* vp); template bool HasNativeDataPropertyPure(JSContext* cx, JSObject* obj, MegamorphicCacheEntry* cacheEntry, Value* vp); bool HasNativeElementPure(JSContext* cx, NativeObject* obj, int32_t index, Value* vp); bool ObjectHasGetterSetterPure(JSContext* cx, JSObject* objArg, jsid id, GetterSetter* getterSetter); template bool SetElementMegamorphic(JSContext* cx, HandleObject obj, HandleValue index, HandleValue value, bool strict); template bool SetPropertyMegamorphic(JSContext* cx, HandleObject obj, HandleId id, HandleValue value, bool strict); JSString* TypeOfNameObject(JSObject* obj, JSRuntime* rt); bool GetPrototypeOf(JSContext* cx, HandleObject target, MutableHandleValue rval); bool DoConcatStringObject(JSContext* cx, HandleValue lhs, HandleValue rhs, MutableHandleValue res); bool IsPossiblyWrappedTypedArray(JSContext* cx, JSObject* obj, bool* result); void* AllocateDependentString(JSContext* cx); void* AllocateFatInlineString(JSContext* cx); void* AllocateBigIntNoGC(JSContext* cx, bool requestMinorGC); void AllocateAndInitTypedArrayBuffer(JSContext* cx, TypedArrayObject* obj, int32_t count); void* CreateMatchResultFallbackFunc(JSContext* cx, gc::AllocKind kind, size_t nDynamicSlots); #ifdef JS_GC_PROBES void TraceCreateObject(JSObject* obj); #endif bool DoStringToInt64(JSContext* cx, HandleString str, uint64_t* res); #if JS_BITS_PER_WORD == 32 BigInt* CreateBigIntFromInt64(JSContext* cx, uint32_t low, uint32_t high); BigInt* CreateBigIntFromUint64(JSContext* cx, uint32_t low, uint32_t high); #else BigInt* CreateBigIntFromInt64(JSContext* cx, uint64_t i64); BigInt* CreateBigIntFromUint64(JSContext* cx, uint64_t i64); #endif template bool BigIntEqual(BigInt* x, BigInt* y); template bool BigIntCompare(BigInt* x, BigInt* y); template bool BigIntNumberEqual(BigInt* x, double y); template bool BigIntNumberCompare(BigInt* x, double y); template bool NumberBigIntCompare(double x, BigInt* y); template bool BigIntStringEqual(JSContext* cx, HandleBigInt x, HandleString y, bool* res); template bool BigIntStringCompare(JSContext* cx, HandleBigInt x, HandleString y, bool* res); template bool StringBigIntCompare(JSContext* cx, HandleString x, HandleBigInt y, bool* res); BigInt* BigIntAsIntN(JSContext* cx, HandleBigInt x, int32_t bits); BigInt* BigIntAsUintN(JSContext* cx, HandleBigInt x, int32_t bits); using AtomicsCompareExchangeFn = int32_t (*)(TypedArrayObject*, size_t, int32_t, int32_t); using AtomicsReadWriteModifyFn = int32_t (*)(TypedArrayObject*, size_t, int32_t); AtomicsCompareExchangeFn AtomicsCompareExchange(Scalar::Type elementType); AtomicsReadWriteModifyFn AtomicsExchange(Scalar::Type elementType); AtomicsReadWriteModifyFn AtomicsAdd(Scalar::Type elementType); AtomicsReadWriteModifyFn AtomicsSub(Scalar::Type elementType); AtomicsReadWriteModifyFn AtomicsAnd(Scalar::Type elementType); AtomicsReadWriteModifyFn AtomicsOr(Scalar::Type elementType); AtomicsReadWriteModifyFn AtomicsXor(Scalar::Type elementType); BigInt* AtomicsLoad64(JSContext* cx, TypedArrayObject* typedArray, size_t index); void AtomicsStore64(TypedArrayObject* typedArray, size_t index, const BigInt* value); BigInt* AtomicsCompareExchange64(JSContext* cx, TypedArrayObject* typedArray, size_t index, const BigInt* expected, const BigInt* replacement); BigInt* AtomicsExchange64(JSContext* cx, TypedArrayObject* typedArray, size_t index, const BigInt* value); BigInt* AtomicsAdd64(JSContext* cx, TypedArrayObject* typedArray, size_t index, const BigInt* value); BigInt* AtomicsAnd64(JSContext* cx, TypedArrayObject* typedArray, size_t index, const BigInt* value); BigInt* AtomicsOr64(JSContext* cx, TypedArrayObject* typedArray, size_t index, const BigInt* value); BigInt* AtomicsSub64(JSContext* cx, TypedArrayObject* typedArray, size_t index, const BigInt* value); BigInt* AtomicsXor64(JSContext* cx, TypedArrayObject* typedArray, size_t index, const BigInt* value); JSAtom* AtomizeStringNoGC(JSContext* cx, JSString* str); bool SetObjectHas(JSContext* cx, HandleObject obj, HandleValue key, bool* rval); bool MapObjectHas(JSContext* cx, HandleObject obj, HandleValue key, bool* rval); bool MapObjectGet(JSContext* cx, HandleObject obj, HandleValue key, MutableHandleValue rval); void AssertSetObjectHash(JSContext* cx, SetObject* obj, const Value* value, mozilla::HashNumber actualHash); void AssertMapObjectHash(JSContext* cx, MapObject* obj, const Value* value, mozilla::HashNumber actualHash); void AssertPropertyLookup(NativeObject* obj, PropertyKey id, uint32_t slot); // Functions used when JS_MASM_VERBOSE is enabled. void AssumeUnreachable(const char* output); void Printf0(const char* output); void Printf1(const char* output, uintptr_t value); enum class TailCallVMFunctionId; enum class VMFunctionId; extern const VMFunctionData& GetVMFunction(VMFunctionId id); extern const VMFunctionData& GetVMFunction(TailCallVMFunctionId id); } // namespace jit } // namespace js #if defined(JS_CODEGEN_ARM) extern "C" { extern MOZ_EXPORT int64_t __aeabi_idivmod(int, int); extern MOZ_EXPORT int64_t __aeabi_uidivmod(int, int); } #endif #endif /* jit_VMFunctions_h */