text: /*
   * Copyright (C) 2015-2016 Apple Inc. All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
   * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
   * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
   */
  
  #pragma once
  
  #include "GenericArguments.h"
  #include "JSLexicalEnvironment.h"
  
  namespace JSC {
  
  // This is an Arguments-class object that we create when you say "arguments" inside a function,
  // and one or more of the arguments may be captured in the function's activation. The function
  // will copy its formally declared arguments into the activation and then create this object. This
  // object will store the overflow arguments, if there are any. This object will use the symbol
  // table's ScopedArgumentsTable and the activation, or its overflow storage, to handle all indexed
  // lookups.
  class ScopedArguments : public GenericArguments<ScopedArguments> {
  private:
      ScopedArguments(VM&, Structure*, unsigned totalLength);
      void finishCreation(VM&, JSFunction* callee, ScopedArgumentsTable*, JSLexicalEnvironment*);
  
  public:
      template<typename CellType>
      static CompleteSubspace* subspaceFor(VM& vm)
      {
          RELEASE_ASSERT(!CellType::needsDestruction);
          return &vm.jsValueGigacageCellSpace;
      }
  
      // Creates an arguments object but leaves it uninitialized. This is dangerous if we GC right
      // after allocation.
      static ScopedArguments* createUninitialized(VM&, Structure*, JSFunction* callee, ScopedArgumentsTable*, JSLexicalEnvironment*, unsigned totalLength);
      
      // Creates an arguments object and initializes everything to the empty value. Use this if you
      // cannot guarantee that you'll immediately initialize all of the elements.
      static ScopedArguments* create(VM&, Structure*, JSFunction* callee, ScopedArgumentsTable*, JSLexicalEnvironment*, unsigned totalLength);
      
      // Creates an arguments object by copying the arguments from the stack.
      static ScopedArguments* createByCopying(ExecState*, ScopedArgumentsTable*, JSLexicalEnvironment*);
      
      // Creates an arguments object by copying the arguments from a well-defined stack location.
      static ScopedArguments* createByCopyingFrom(VM&, Structure*, Register* argumentsStart, unsigned totalLength, JSFunction* callee, ScopedArgumentsTable*, JSLexicalEnvironment*);
      
      static void visitChildren(JSCell*, SlotVisitor&);
      
      uint32_t internalLength() const
      {
          return m_totalLength;
      }
      
      uint32_t length(ExecState* exec) const
      {
          VM& vm = exec->vm();
          if (UNLIKELY(m_overrodeThings))
              return get(exec, vm.propertyNames->length).toUInt32(exec);
          return internalLength();
      }
      
      bool isMappedArgument(uint32_t i) const
      {
          if (i >= m_totalLength)
              return false;
          unsigned namedLength = m_table->length();
          if (i < namedLength)
              return !!m_table->get(i);
          return !!overflowStorage()[i - namedLength].get();
      }
  
      bool isMappedArgumentInDFG(uint32_t i) const
      {
          return isMappedArgument(i);
      }
      
      JSValue getIndexQuickly(uint32_t i) const
      {
          ASSERT_WITH_SECURITY_IMPLICATION(isMappedArgument(i));
          unsigned namedLength = m_table->length();
          if (i < namedLength)
              return m_scope->variableAt(m_table->get(i)).get();
          return overflowStorage()[i - namedLength].get();
      }
  
      void setIndexQuickly(VM& vm, uint32_t i, JSValue value)
      {
          ASSERT_WITH_SECURITY_IMPLICATION(isMappedArgument(i));
          unsigned namedLength = m_table->length();
          if (i < namedLength)
              m_scope->variableAt(m_table->get(i)).set(vm, m_scope.get(), value);
          else
              overflowStorage()[i - namedLength].set(vm, this, value);
      }
  
      WriteBarrier<JSFunction>& callee()
      {
          return m_callee;
      }
  
      bool overrodeThings() const { return m_overrodeThings; }
      void overrideThings(VM&);
      void overrideThingsIfNecessary(VM&);
      void unmapArgument(VM&, uint32_t index);
      
      void initModifiedArgumentsDescriptorIfNecessary(VM& vm)
      {
          GenericArguments<ScopedArguments>::initModifiedArgumentsDescriptorIfNecessary(vm, m_table->length());
      }
  
      void setModifiedArgumentDescriptor(VM& vm, unsigned index)
      {
          GenericArguments<ScopedArguments>::setModifiedArgumentDescriptor(vm, index, m_table->length());
      }
  
      bool isModifiedArgumentDescriptor(unsigned index)
      {
          return GenericArguments<ScopedArguments>::isModifiedArgumentDescriptor(index, m_table->length());
      }
  
      void copyToArguments(ExecState*, VirtualRegister firstElementDest, unsigned offset, unsigned length);
  
      DECLARE_INFO;
      
      static Structure* createStructure(VM&, JSGlobalObject*, JSValue prototype);
      
      static ptrdiff_t offsetOfOverrodeThings() { return OBJECT_OFFSETOF(ScopedArguments, m_overrodeThings); }
      static ptrdiff_t offsetOfTotalLength() { return OBJECT_OFFSETOF(ScopedArguments, m_totalLength); }
      static ptrdiff_t offsetOfTable() { return OBJECT_OFFSETOF(ScopedArguments, m_table); }
      static ptrdiff_t offsetOfScope() { return OBJECT_OFFSETOF(ScopedArguments, m_scope); }
      
      static size_t overflowStorageOffset()
      {
          return WTF::roundUpToMultipleOf<sizeof(WriteBarrier<Unknown>)>(sizeof(ScopedArguments));
      }
      
      static size_t allocationSize(Checked<size_t> overflowArgumentsLength)
      {
          return (overflowStorageOffset() + sizeof(WriteBarrier<Unknown>) * overflowArgumentsLength).unsafeGet();
      }
  
  private:
      WriteBarrier<Unknown>* overflowStorage() const
      {
          return bitwise_cast<WriteBarrier<Unknown>*>(bitwise_cast<char*>(this) + overflowStorageOffset());
      }
      
      bool m_overrodeThings; // True if length, callee, and caller are fully materialized in the object.
      unsigned m_totalLength; // The length of declared plus overflow arguments.
      WriteBarrier<JSFunction> m_callee;
      WriteBarrier<ScopedArgumentsTable> m_table;
      WriteBarrier<JSLexicalEnvironment> m_scope;
  };
  
  } // namespace JSC
  