Source/JavaScriptCore/runtime/DirectArguments.cpp

/*
 * Copyright (C) 2015-2018 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
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#include "config.h"
#include "DirectArguments.h"

#include "CodeBlock.h"
#include "GenericArgumentsInlines.h"

namespace JSC {

STATIC_ASSERT_IS_TRIVIALLY_DESTRUCTIBLE(DirectArguments);

const ClassInfo DirectArguments::s_info = { "Arguments", &Base::s_info, nullptr, nullptr, CREATE_METHOD_TABLE(DirectArguments) };

DirectArguments::DirectArguments(VM& vm, Structure* structure, unsigned length, unsigned capacity)
    : GenericArguments(vm, structure)
    , m_length(length)
    , m_minCapacity(capacity)
{
    // When we construct the object from C++ code, we expect the capacity to be at least as large as
    // length. JIT-allocated DirectArguments objects play evil tricks, though.
    ASSERT(capacity >= length);
}

DirectArguments* DirectArguments::createUninitialized(
    VM& vm, Structure* structure, unsigned length, unsigned capacity)
{
    DirectArguments* result =
        new (NotNull, allocateCell<DirectArguments>(vm.heap, allocationSize(capacity)))
        DirectArguments(vm, structure, length, capacity);
    result->finishCreation(vm);
    return result;
}

DirectArguments* DirectArguments::create(VM& vm, Structure* structure, unsigned length, unsigned capacity)
{
    DirectArguments* result = createUninitialized(vm, structure, length, capacity);
    
    for (unsigned i = capacity; i--;)
        result->storage()[i].setUndefined();
    
    return result;
}

DirectArguments* DirectArguments::createByCopying(JSGlobalObject* globalObject, CallFrame* callFrame)
{
    VM& vm = globalObject->vm();
    
    unsigned length = callFrame->argumentCount();
    unsigned capacity = std::max(length, static_cast<unsigned>(callFrame->codeBlock()->numParameters() - 1));
    DirectArguments* result = createUninitialized(
        vm, globalObject->directArgumentsStructure(), length, capacity);
    
    for (unsigned i = capacity; i--;)
        result->storage()[i].set(vm, result, callFrame->getArgumentUnsafe(i));
    
    result->setCallee(vm, jsCast<JSFunction*>(callFrame->jsCallee()));
    
    return result;
}

size_t DirectArguments::estimatedSize(JSCell* cell, VM& vm)
{
    DirectArguments* thisObject = jsCast<DirectArguments*>(cell);
    size_t mappedArgumentsSize = thisObject->m_mappedArguments ? thisObject->mappedArgumentsSize() * sizeof(bool) : 0;
    size_t modifiedArgumentsSize = thisObject->m_modifiedArgumentsDescriptor ? thisObject->m_length * sizeof(bool) : 0;
    return Base::estimatedSize(cell, vm) + mappedArgumentsSize + modifiedArgumentsSize;
}

void DirectArguments::visitChildren(JSCell* thisCell, SlotVisitor& visitor)
{
    DirectArguments* thisObject = static_cast<DirectArguments*>(thisCell);
    ASSERT_GC_OBJECT_INHERITS(thisObject, info());
    Base::visitChildren(thisObject, visitor);

    visitor.appendValues(thisObject->storage(), std::max(thisObject->m_length, thisObject->m_minCapacity));
    visitor.append(thisObject->m_callee);

    if (thisObject->m_mappedArguments)
        visitor.markAuxiliary(thisObject->m_mappedArguments.get(thisObject->internalLength()));
    GenericArguments<DirectArguments>::visitChildren(thisCell, visitor);
}

Structure* DirectArguments::createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
{
    return Structure::create(vm, globalObject, prototype, TypeInfo(DirectArgumentsType, StructureFlags), info());
}

void DirectArguments::overrideThings(JSGlobalObject* globalObject)
{
    VM& vm = globalObject->vm();
    auto scope = DECLARE_THROW_SCOPE(vm);

    RELEASE_ASSERT(!m_mappedArguments);
    
    putDirect(vm, vm.propertyNames->length, jsNumber(m_length), static_cast<unsigned>(PropertyAttribute::DontEnum));
    putDirect(vm, vm.propertyNames->callee, m_callee.get(), static_cast<unsigned>(PropertyAttribute::DontEnum));
    putDirect(vm, vm.propertyNames->iteratorSymbol, globalObject->arrayProtoValuesFunction(), static_cast<unsigned>(PropertyAttribute::DontEnum));
    
    void* backingStore = vm.gigacageAuxiliarySpace(m_mappedArguments.kind).allocateNonVirtual(vm, mappedArgumentsSize(), nullptr, AllocationFailureMode::ReturnNull);
    if (UNLIKELY(!backingStore)) {
        throwOutOfMemoryError(globalObject, scope);
        return;
    }
    bool* overrides = static_cast<bool*>(backingStore);
    m_mappedArguments.set(vm, this, overrides, internalLength());
    for (unsigned i = internalLength(); i--;)
        overrides[i] = false;
}

void DirectArguments::overrideThingsIfNecessary(JSGlobalObject* globalObject)
{
    if (!m_mappedArguments)
        overrideThings(globalObject);
}

void DirectArguments::unmapArgument(JSGlobalObject* globalObject, unsigned index)
{
    VM& vm = globalObject->vm();
    auto scope = DECLARE_THROW_SCOPE(vm);

    overrideThingsIfNecessary(globalObject);
    RETURN_IF_EXCEPTION(scope, void());

    m_mappedArguments.at(index, internalLength()) = true;
}

void DirectArguments::copyToArguments(JSGlobalObject* globalObject, JSValue* firstElementDest, unsigned offset, unsigned length)
{
    if (!m_mappedArguments) {
        unsigned limit = std::min(length + offset, m_length);
        unsigned i;
        for (i = offset; i < limit; ++i)
            firstElementDest[i - offset] = storage()[i].get();
        for (; i < length; ++i)
            firstElementDest[i - offset] = get(globalObject, i);
        return;
    }

    GenericArguments::copyToArguments(globalObject, firstElementDest, offset, length);
}

unsigned DirectArguments::mappedArgumentsSize()
{
    // We always allocate something; in the relatively uncommon case of overriding an empty argument we
    // still allocate so that m_mappedArguments is non-null. We use that to indicate that the other properties
    // (length, etc) are overridden.
    return WTF::roundUpToMultipleOf<8>(m_length ? m_length : 1);
}

} // namespace JSC