LCOV - code coverage report
Current view: directory - js/src/vm - ArgumentsObject.h (source / functions) Found Hit Coverage
Test: app.info Lines: 9 9 100.0 %
Date: 2012-04-07 Functions: 3 3 100.0 %

       1                 : /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
       2                 :  * vim: set ts=8 sw=4 et tw=78:
       3                 :  *
       4                 :  * ***** BEGIN LICENSE BLOCK *****
       5                 :  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
       6                 :  *
       7                 :  * The contents of this file are subject to the Mozilla Public License Version
       8                 :  * 1.1 (the "License"); you may not use this file except in compliance with
       9                 :  * the License. You may obtain a copy of the License at
      10                 :  * http://www.mozilla.org/MPL/
      11                 :  *
      12                 :  * Software distributed under the License is distributed on an "AS IS" basis,
      13                 :  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
      14                 :  * for the specific language governing rights and limitations under the
      15                 :  * License.
      16                 :  *
      17                 :  * The Original Code is SpiderMonkey arguments object code.
      18                 :  *
      19                 :  * The Initial Developer of the Original Code is
      20                 :  * the Mozilla Foundation.
      21                 :  * Portions created by the Initial Developer are Copyright (C) 2011
      22                 :  * the Initial Developer. All Rights Reserved.
      23                 :  *
      24                 :  * Contributor(s):
      25                 :  *   Jeff Walden <jwalden+code@mit.edu> (original author)
      26                 :  *   Luke Wagner <luke@mozilla.com>
      27                 :  *
      28                 :  * Alternatively, the contents of this file may be used under the terms of
      29                 :  * either of the GNU General Public License Version 2 or later (the "GPL"),
      30                 :  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
      31                 :  * in which case the provisions of the GPL or the LGPL are applicable instead
      32                 :  * of those above. If you wish to allow use of your version of this file only
      33                 :  * under the terms of either the GPL or the LGPL, and not to allow others to
      34                 :  * use your version of this file under the terms of the MPL, indicate your
      35                 :  * decision by deleting the provisions above and replace them with the notice
      36                 :  * and other provisions required by the GPL or the LGPL. If you do not delete
      37                 :  * the provisions above, a recipient may use your version of this file under
      38                 :  * the terms of any one of the MPL, the GPL or the LGPL.
      39                 :  *
      40                 :  * ***** END LICENSE BLOCK ***** */
      41                 : 
      42                 : #ifndef ArgumentsObject_h___
      43                 : #define ArgumentsObject_h___
      44                 : 
      45                 : #include "jsfun.h"
      46                 : 
      47                 : namespace js {
      48                 : 
      49                 : /*
      50                 :  * ArgumentsData stores the initial indexed arguments provided to the
      51                 :  * corresponding and that function itself.  It is used to store arguments[i]
      52                 :  * and arguments.callee -- up until the corresponding property is modified,
      53                 :  * when the relevant value is overwritten with MagicValue(JS_ARGS_HOLE) to
      54                 :  * memorialize the modification.
      55                 :  */
      56                 : struct ArgumentsData
      57                 : {
      58                 :     /*
      59                 :      * arguments.callee, or MagicValue(JS_ARGS_HOLE) if arguments.callee has
      60                 :      * been modified.
      61                 :      */
      62                 :     HeapValue   callee;
      63                 : 
      64                 :     /*
      65                 :      * Pointer to an array of bits indicating, for every argument in 'slots',
      66                 :      * whether the element has been deleted. See isElementDeleted comment.
      67                 :      */
      68                 :     size_t      *deletedBits;
      69                 : 
      70                 :     /*
      71                 :      * Values of the arguments for this object, or MagicValue(JS_ARGS_HOLE) if
      72                 :      * the indexed argument has been modified.
      73                 :      */
      74                 :     HeapValue   slots[1];
      75                 : };
      76                 : 
      77                 : /*
      78                 :  * ArgumentsObject instances represent |arguments| objects created to store
      79                 :  * function arguments when a function is called.  It's expensive to create such
      80                 :  * objects if they're never used, so they're only created lazily.  (See
      81                 :  * js::StackFrame::setArgsObj and friends.)
      82                 :  *
      83                 :  * Arguments objects are complicated because, for non-strict mode code, they
      84                 :  * must alias any named arguments which were provided to the function.  Gnarly
      85                 :  * example:
      86                 :  *
      87                 :  *   function f(a, b, c, d)
      88                 :  *   {
      89                 :  *     arguments[0] = "seta";
      90                 :  *     assertEq(a, "seta");
      91                 :  *     b = "setb";
      92                 :  *     assertEq(arguments[1], "setb");
      93                 :  *     c = "setc";
      94                 :  *     assertEq(arguments[2], undefined);
      95                 :  *     arguments[3] = "setd";
      96                 :  *     assertEq(d, undefined);
      97                 :  *   }
      98                 :  *   f("arga", "argb");
      99                 :  *
     100                 :  * ES5's strict mode behaves more sanely, and named arguments don't alias
     101                 :  * elements of an arguments object.
     102                 :  *
     103                 :  * ArgumentsObject instances use the following reserved slots:
     104                 :  *
     105                 :  *   INITIAL_LENGTH_SLOT
     106                 :  *     Stores the initial value of arguments.length, plus a bit indicating
     107                 :  *     whether arguments.length has been modified.  Use initialLength() and
     108                 :  *     hasOverriddenLength() to access these values.  If arguments.length has
     109                 :  *     been modified, then the current value of arguments.length is stored in
     110                 :  *     another slot associated with a new property.
     111                 :  *   DATA_SLOT
     112                 :  *     Stores an ArgumentsData* storing argument values and the callee, or
     113                 :  *     sentinels for any of these if the corresponding property is modified.
     114                 :  *     Use callee() to access the callee/sentinel, and use
     115                 :  *     element/addressOfElement/setElement to access the values stored in
     116                 :  *     the ArgumentsData.  If you're simply looking to get arguments[i],
     117                 :  *     however, use getElement or getElements to avoid spreading arguments
     118                 :  *     object implementation details around too much.
     119                 :  *   STACK_FRAME_SLOT
     120                 :  *     Stores the function's stack frame for non-strict arguments objects until
     121                 :  *     the function returns, when it is replaced with null.  When an arguments
     122                 :  *     object is created on-trace its private is JS_ARGUMENTS_OBJECT_ON_TRACE,
     123                 :  *     and when the trace exits its private is replaced with the stack frame or
     124                 :  *     null, as appropriate. This slot is used by strict arguments objects as
     125                 :  *     well, but the slot is always null. Conceptually it would be better to
     126                 :  *     remove this oddity, but preserving it allows us to work with arguments
     127                 :  *     objects of either kind more abstractly, so we keep it for now.
     128                 :  */
     129                 : class ArgumentsObject : public JSObject
     130                 : {
     131                 :     static const uint32_t INITIAL_LENGTH_SLOT = 0;
     132                 :     static const uint32_t DATA_SLOT = 1;
     133                 :     static const uint32_t STACK_FRAME_SLOT = 2;
     134                 : 
     135                 :     /* Lower-order bit stolen from the length slot. */
     136                 :     static const uint32_t LENGTH_OVERRIDDEN_BIT = 0x1;
     137                 :     static const uint32_t PACKED_BITS_COUNT = 1;
     138                 : 
     139                 :     void initInitialLength(uint32_t length);
     140                 :     void initData(ArgumentsData *data);
     141                 :     static ArgumentsObject *create(JSContext *cx, uint32_t argc, JSObject &callee);
     142                 : 
     143                 :   public:
     144                 :     static const uint32_t RESERVED_SLOTS = 3;
     145                 :     static const gc::AllocKind FINALIZE_KIND = gc::FINALIZE_OBJECT4;
     146                 : 
     147                 :     /* Create an arguments object for a frame that is expecting them. */
     148                 :     static bool create(JSContext *cx, StackFrame *fp);
     149                 : 
     150                 :     /*
     151                 :      * Purposefully disconnect the returned arguments object from the frame
     152                 :      * by always creating a new copy that does not alias formal parameters.
     153                 :      * This allows function-local analysis to determine that formals are
     154                 :      * not aliased and generally simplifies arguments objects.
     155                 :      */
     156                 :     static ArgumentsObject *createUnexpected(JSContext *cx, StackFrame *fp);
     157                 : 
     158                 :     /*
     159                 :      * Return the initial length of the arguments.  This may differ from the
     160                 :      * current value of arguments.length!
     161                 :      */
     162                 :     inline uint32_t initialLength() const;
     163                 : 
     164                 :     /* True iff arguments.length has been assigned or its attributes changed. */
     165                 :     inline bool hasOverriddenLength() const;
     166                 :     inline void markLengthOverridden();
     167                 : 
     168                 :     /*
     169                 :      * Attempt to speedily and efficiently access the i-th element of this
     170                 :      * arguments object.  Return true if the element was speedily returned.
     171                 :      * Return false if the element must be looked up more slowly using
     172                 :      * getProperty or some similar method.
     173                 :      *
     174                 :      * NB: Returning false does not indicate error!
     175                 :      */
     176                 :     inline bool getElement(uint32_t i, js::Value *vp);
     177                 : 
     178                 :     /*
     179                 :      * Attempt to speedily and efficiently get elements [start, start + count)
     180                 :      * of this arguments object into the locations starting at |vp|.  Return
     181                 :      * true if all elements were copied.  Return false if the elements must be
     182                 :      * gotten more slowly, perhaps using a getProperty or some similar method
     183                 :      * in a loop.
     184                 :      *
     185                 :      * NB: Returning false does not indicate error!
     186                 :      */
     187                 :     inline bool getElements(uint32_t start, uint32_t count, js::Value *vp);
     188                 : 
     189                 :     inline js::ArgumentsData *data() const;
     190                 : 
     191                 :     /*
     192                 :      * Because the arguments object is a real object, its elements may be
     193                 :      * deleted. This is implemented by setting a 'deleted' flag for the arg
     194                 :      * which is read by argument object resolve and getter/setter hooks.
     195                 :      *
     196                 :      * NB: an element, once deleted, stays deleted. Thus:
     197                 :      *
     198                 :      *   function f(x) { delete arguments[0]; arguments[0] = 42; return x }
     199                 :      *   assertEq(f(1), 1);
     200                 :      *
     201                 :      * This works because, once a property is deleted from an arguments object,
     202                 :      * it gets regular properties with regular getters/setters that don't alias
     203                 :      * ArgumentsData::slots.
     204                 :      */
     205                 :     inline bool isElementDeleted(uint32_t i) const;
     206                 :     inline bool isAnyElementDeleted() const;
     207                 :     inline void markElementDeleted(uint32_t i);
     208                 : 
     209                 :     inline const js::Value &element(uint32_t i) const;
     210                 :     inline void setElement(uint32_t i, const js::Value &v);
     211                 : 
     212                 :     /* The stack frame for this ArgumentsObject, if the frame is still active. */
     213                 :     inline js::StackFrame *maybeStackFrame() const;
     214                 :     inline void setStackFrame(js::StackFrame *frame);
     215                 : 
     216                 :     /*
     217                 :      * Measures things hanging off this ArgumentsObject that are counted by the
     218                 :      * |miscSize| argument in JSObject::sizeOfExcludingThis().
     219                 :      */
     220                 :     inline size_t sizeOfMisc(JSMallocSizeOfFun mallocSizeOf) const;
     221                 : };
     222                 : 
     223                 : class NormalArgumentsObject : public ArgumentsObject
     224                 : {
     225                 :   public:
     226                 :     /*
     227                 :      * Stores arguments.callee, or MagicValue(JS_ARGS_HOLE) if the callee has
     228                 :      * been cleared.
     229                 :      */
     230                 :     inline const js::Value &callee() const;
     231                 : 
     232                 :     /* Clear the location storing arguments.callee's initial value. */
     233                 :     inline void clearCallee();
     234                 : 
     235                 :     /*
     236                 :      * Return 'arguments[index]' for some unmodified NormalArgumentsObject of
     237                 :      * 'fp' (the actual instance of 'arguments' doesn't matter so it does not
     238                 :      * have to be passed or even created).
     239                 :      */
     240                 :     static bool optimizedGetElem(JSContext *cx, StackFrame *fp, const Value &elem, Value *vp);
     241                 : };
     242                 : 
     243                 : class StrictArgumentsObject : public ArgumentsObject
     244                 : {};
     245                 : 
     246                 : } // namespace js
     247                 : 
     248                 : js::NormalArgumentsObject &
     249            9034 : JSObject::asNormalArguments()
     250                 : {
     251            9034 :     JS_ASSERT(isNormalArguments());
     252            9034 :     return *static_cast<js::NormalArgumentsObject *>(this);
     253                 : }
     254                 : 
     255                 : js::StrictArgumentsObject &
     256            1628 : JSObject::asStrictArguments()
     257                 : {
     258            1628 :     JS_ASSERT(isStrictArguments());
     259            1628 :     return *static_cast<js::StrictArgumentsObject *>(this);
     260                 : }
     261                 : 
     262                 : js::ArgumentsObject &
     263         1286964 : JSObject::asArguments()
     264                 : {
     265         1286964 :     JS_ASSERT(isArguments());
     266         1286964 :     return *static_cast<js::ArgumentsObject *>(this);
     267                 : }
     268                 : 
     269                 : const js::ArgumentsObject &
     270                 : JSObject::asArguments() const
     271                 : {
     272                 :     JS_ASSERT(isArguments());
     273                 :     return *static_cast<const js::ArgumentsObject *>(this);
     274                 : }
     275                 : 
     276                 : #endif /* ArgumentsObject_h___ */

Generated by: LCOV version 1.7