The Tor Browser: js/src/vm/ArgumentsObject.h@6474c204b198 (annotated)

js/src/vm/ArgumentsObject.h@6474c204b198 (annotated)

js/src/vm/ArgumentsObject.h

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
  * vim: set ts=8 sts=4 et sw=4 tw=99:
  * 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 vm_ArgumentsObject_h
 #define vm_ArgumentsObject_h
 #include "mozilla/MemoryReporting.h"
 #include "jsobj.h"
 #include "gc/Barrier.h"
 namespace js {
 class AbstractFramePtr;
 class ScriptFrameIter;
 namespace jit {
 class IonJSFrameLayout;
 }
 /*
  * ArgumentsData stores the initial indexed arguments provided to the
  * corresponding and that function itself.  It is used to store arguments[i]
  * and arguments.callee -- up until the corresponding property is modified,
  * when the relevant value is flagged to memorialize the modification.
  */
 struct ArgumentsData
 {
     /*
      * numArgs = Max(numFormalArgs, numActualArgs)
      * The array 'args' has numArgs elements.
      */
     unsigned    numArgs;
     /*
      * arguments.callee, or MagicValue(JS_OVERWRITTEN_CALLEE) if
      * arguments.callee has been modified.
      */
     HeapValue   callee;
     /* The script for the function containing this arguments object. */
     JSScript    *script;
     /*
      * Pointer to an array of bits indicating, for every argument in 'slots',
      * whether the element has been deleted. See isElementDeleted comment.
      */
     size_t      *deletedBits;
     /*
      * This array holds either the current argument value or the magic
      * forwarding value. The latter means that the function has both a
      * CallObject and an ArgumentsObject AND the particular formal variable is
      * aliased by the CallObject. In such cases, the CallObject holds the
      * canonical value so any element access to the arguments object should load
      * the value out of the CallObject (which is pointed to by MAYBE_CALL_SLOT).
      */
     HeapValue   args[1];
     /* For jit use: */
     static ptrdiff_t offsetOfArgs() { return offsetof(ArgumentsData, args); }
 };
 // Maximum supported value of arguments.length. This bounds the maximum
 // number of arguments that can be supplied to Function.prototype.apply.
 // This value also bounds the number of elements parsed in an array
 // initialiser.
 static const unsigned ARGS_LENGTH_MAX = 500 * 1000;
 /*
  * ArgumentsObject instances represent |arguments| objects created to store
  * function arguments when a function is called.  It's expensive to create such
  * objects if they're never used, so they're only created when they are
  * potentially used.
  *
  * Arguments objects are complicated because, for non-strict mode code, they
  * must alias any named arguments which were provided to the function.  Gnarly
  * example:
  *
  *   function f(a, b, c, d)
  *   {
  *     arguments[0] = "seta";
  *     assertEq(a, "seta");
  *     b = "setb";
  *     assertEq(arguments[1], "setb");
  *     c = "setc";
  *     assertEq(arguments[2], undefined);
  *     arguments[3] = "setd";
  *     assertEq(d, undefined);
  *   }
  *   f("arga", "argb");
  *
  * ES5's strict mode behaves more sanely, and named arguments don't alias
  * elements of an arguments object.
  *
  * ArgumentsObject instances use the following reserved slots:
  *
  *   INITIAL_LENGTH_SLOT
  *     Stores the initial value of arguments.length, plus a bit indicating
  *     whether arguments.length has been modified.  Use initialLength() and
  *     hasOverriddenLength() to access these values.  If arguments.length has
  *     been modified, then the current value of arguments.length is stored in
  *     another slot associated with a new property.
  *   DATA_SLOT
  *     Stores an ArgumentsData*, described above.
  */
 class ArgumentsObject : public JSObject
 {
   protected:
     static const uint32_t INITIAL_LENGTH_SLOT = 0;
     static const uint32_t DATA_SLOT = 1;
     static const uint32_t MAYBE_CALL_SLOT = 2;
   public:
     static const uint32_t LENGTH_OVERRIDDEN_BIT = 0x1;
     static const uint32_t PACKED_BITS_COUNT = 1;
   protected:
     template <typename CopyArgs>
     static ArgumentsObject *create(JSContext *cx, HandleScript script, HandleFunction callee,
                                    unsigned numActuals, CopyArgs &copy);
     ArgumentsData *data() const {
         return reinterpret_cast<ArgumentsData *>(getFixedSlot(DATA_SLOT).toPrivate());
     }
   public:
     static const uint32_t RESERVED_SLOTS = 3;
     static const gc::AllocKind FINALIZE_KIND = gc::FINALIZE_OBJECT4_BACKGROUND;
     /* Create an arguments object for a frame that is expecting them. */
     static ArgumentsObject *createExpected(JSContext *cx, AbstractFramePtr frame);
     /*
      * Purposefully disconnect the returned arguments object from the frame
      * by always creating a new copy that does not alias formal parameters.
      * This allows function-local analysis to determine that formals are
      * not aliased and generally simplifies arguments objects.
      */
     static ArgumentsObject *createUnexpected(JSContext *cx, ScriptFrameIter &iter);
     static ArgumentsObject *createUnexpected(JSContext *cx, AbstractFramePtr frame);
 #if defined(JS_ION)
     static ArgumentsObject *createForIon(JSContext *cx, jit::IonJSFrameLayout *frame,
                                          HandleObject scopeChain);
 #endif
     /*
      * Return the initial length of the arguments.  This may differ from the
      * current value of arguments.length!
      */
     uint32_t initialLength() const {
         uint32_t argc = uint32_t(getFixedSlot(INITIAL_LENGTH_SLOT).toInt32()) >> PACKED_BITS_COUNT;
         JS_ASSERT(argc <= ARGS_LENGTH_MAX);
         return argc;
     }
     /* The script for the function containing this arguments object. */
     JSScript *containingScript() const {
         return data()->script;
     }
     /* True iff arguments.length has been assigned or its attributes changed. */
     bool hasOverriddenLength() const {
         const Value &v = getFixedSlot(INITIAL_LENGTH_SLOT);
         return v.toInt32() & LENGTH_OVERRIDDEN_BIT;
     }
     void markLengthOverridden() {
         uint32_t v = getFixedSlot(INITIAL_LENGTH_SLOT).toInt32() | LENGTH_OVERRIDDEN_BIT;
         setFixedSlot(INITIAL_LENGTH_SLOT, Int32Value(v));
     }
     /*
      * Because the arguments object is a real object, its elements may be
      * deleted. This is implemented by setting a 'deleted' flag for the arg
      * which is read by argument object resolve and getter/setter hooks.
      *
      * NB: an element, once deleted, stays deleted. Thus:
      *
      *   function f(x) { delete arguments[0]; arguments[0] = 42; return x }
      *   assertEq(f(1), 1);
      *
      * This works because, once a property is deleted from an arguments object,
      * it gets regular properties with regular getters/setters that don't alias
      * ArgumentsData::slots.
      */
     bool isElementDeleted(uint32_t i) const {
         JS_ASSERT(i < data()->numArgs);
         if (i >= initialLength())
             return false;
         return IsBitArrayElementSet(data()->deletedBits, initialLength(), i);
     }
     bool isAnyElementDeleted() const {
         return IsAnyBitArrayElementSet(data()->deletedBits, initialLength());
     }
     void markElementDeleted(uint32_t i) {
         SetBitArrayElement(data()->deletedBits, initialLength(), i);
     }
     /*
      * An ArgumentsObject serves two roles:
      *  - a real object, accessed through regular object operations, e.g..,
      *    JSObject::getElement corresponding to 'arguments[i]';
      *  - a VM-internal data structure, storing the value of arguments (formal
      *    and actual) that are accessed directly by the VM when a reading the
      *    value of a formal parameter.
      * There are two ways to access the ArgumentsData::args corresponding to
      * these two use cases:
      *  - object access should use elements(i) which will take care of
      *    forwarding when the value is the magic forwarding value;
      *  - VM argument access should use arg(i) which will assert that the
      *    value is not the magic forwarding value (since, if such forwarding was
      *    needed, the frontend should have emitted JSOP_GETALIASEDVAR).
      */
     const Value &element(uint32_t i) const;
     inline void setElement(JSContext *cx, uint32_t i, const Value &v);
     const Value &arg(unsigned i) const {
         JS_ASSERT(i < data()->numArgs);
         const Value &v = data()->args[i];
         JS_ASSERT(!v.isMagic());
         return v;
     }
     void setArg(unsigned i, const Value &v) {
         JS_ASSERT(i < data()->numArgs);
         HeapValue &lhs = data()->args[i];
         JS_ASSERT(!lhs.isMagic());
         lhs = v;
     }
     /*
      * Attempt to speedily and efficiently access the i-th element of this
      * arguments object.  Return true if the element was speedily returned.
      * Return false if the element must be looked up more slowly using
      * getProperty or some similar method. The second overload copies the
      * elements [start, start + count) into the locations starting at 'vp'.
      *
      * NB: Returning false does not indicate error!
      */
     bool maybeGetElement(uint32_t i, MutableHandleValue vp) {
         if (i >= initialLength() || isElementDeleted(i))
             return false;
         vp.set(element(i));
         return true;
     }
     inline bool maybeGetElements(uint32_t start, uint32_t count, js::Value *vp);
     /*
      * Measures things hanging off this ArgumentsObject that are counted by the
      * |miscSize| argument in JSObject::sizeOfExcludingThis().
      */
     size_t sizeOfMisc(mozilla::MallocSizeOf mallocSizeOf) const {
         return mallocSizeOf(data());
     }
     static void finalize(FreeOp *fop, JSObject *obj);
     static void trace(JSTracer *trc, JSObject *obj);
     /* For jit use: */
     static size_t getDataSlotOffset() {
         return getFixedSlotOffset(DATA_SLOT);
     }
     static size_t getInitialLengthSlotOffset() {
         return getFixedSlotOffset(INITIAL_LENGTH_SLOT);
     }
     static void MaybeForwardToCallObject(AbstractFramePtr frame, JSObject *obj, ArgumentsData *data);
 #if defined(JS_ION)
     static void MaybeForwardToCallObject(jit::IonJSFrameLayout *frame, HandleObject callObj,
                                          JSObject *obj, ArgumentsData *data);
 #endif
 };
 class NormalArgumentsObject : public ArgumentsObject
 {
   public:
     static const Class class_;
     /*
      * Stores arguments.callee, or MagicValue(JS_ARGS_HOLE) if the callee has
      * been cleared.
      */
     const js::Value &callee() const {
         return data()->callee;
     }
     /* Clear the location storing arguments.callee's initial value. */
     void clearCallee() {
         data()->callee.set(zone(), MagicValue(JS_OVERWRITTEN_CALLEE));
     }
 };
 class StrictArgumentsObject : public ArgumentsObject
 {
   public:
     static const Class class_;
 };
 } // namespace js
 template<>
 inline bool
 JSObject::is<js::ArgumentsObject>() const
 {
     return is<js::NormalArgumentsObject>() || is<js::StrictArgumentsObject>();
 }
 #endif /* vm_ArgumentsObject_h */

The Tor Browser / annotate

js/src/vm/ArgumentsObject.h@6474c204b198 (annotated)

js/src/vm/ArgumentsObject.h