runtime/StackAlignment.h

   1 /*
   2  * Copyright (C) 2013 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef StackAlignment_h
  27 #define StackAlignment_h
  28
  29 #include "JSCJSValue.h"
  30 #include "JSStack.h"
  31 #include <wtf/MathExtras.h>
  32
  33 namespace JSC {
  34
  35 // NB. Different platforms may have different requirements here. But 16 bytes is very common.
  36 inline unsigned stackAlignmentBytes() { return 16; }
  37
  38 inline unsigned stackAlignmentRegisters()
  39 {
  40     return stackAlignmentBytes() / sizeof(EncodedJSValue);
  41 }
  42
  43 // Align argument count taking into account the CallFrameHeaderSize may be
  44 // an "unaligned" count of registers.
  45 inline unsigned roundArgumentCountToAlignFrame(unsigned argumentCount)
  46 {
  47     return WTF::roundUpToMultipleOf(stackAlignmentRegisters(), argumentCount + JSStack::CallFrameHeaderSize) - JSStack::CallFrameHeaderSize;
  48 }
  49
  50 // Align local register count to make the last local end on a stack aligned address given the
  51 // CallFrame is at an address that is stack aligned minus JSStack::CallerFrameAndPCSize
  52 inline unsigned roundLocalRegisterCountForFramePointerOffset(unsigned localRegisterCount)
  53 {
  54     return WTF::roundUpToMultipleOf(stackAlignmentRegisters(), localRegisterCount + JSStack::CallerFrameAndPCSize) - JSStack::CallerFrameAndPCSize;
  55 }
  56
  57 inline unsigned logStackAlignmentRegisters()
  58 {
  59     return WTF::fastLog2(stackAlignmentRegisters());
  60 }
  61
  62 } // namespace JSC
  63
  64 #endif // StackAlignment_h
  65