hphp/runtime/base/rds-header.h

   1 /*
   2    +----------------------------------------------------------------------+
   3    | HipHop for PHP                                                       |
   4    +----------------------------------------------------------------------+
   5    | Copyright (c) 2010-2014 Facebook, Inc. (http://www.facebook.com)     |
   6    +----------------------------------------------------------------------+
   7    | This source file is subject to version 3.01 of the PHP license,      |
   8    | that is bundled with this package in the file LICENSE, and is        |
   9    | available through the world-wide-web at the following url:           |
  10    | http://www.php.net/license/3_01.txt                                  |
  11    | If you did not receive a copy of the PHP license and are unable to   |
  12    | obtain it through the world-wide-web, please send a note to          |
  13    | license@php.net so we can mail you a copy immediately.               |
  14    +----------------------------------------------------------------------+
  15 */
  16
  17 #ifndef incl_HPHP_RUNTIME_RDS_HEADER_H_
  18 #define incl_HPHP_RUNTIME_RDS_HEADER_H_
  19
  20 #include <atomic>
  21 #include <cstddef>
  22
  23 #include "hphp/runtime/base/rds.h"
  24 #include "hphp/runtime/base/types.h"
  25 #include "hphp/runtime/vm/bytecode.h"
  26
  27 namespace HPHP {
  28
  29 /*
  30  * Do not access this struct directly from RDS::header(). Use the accessors in
  31  * runtime/vm/vm-regs.h.
  32  */
  33 struct VMRegs {
  34   /* VM evaluation stack. Grows down in memory in multiples of 16 bytes - the
  35    * size of a TypedValue. */
  36   Stack stack;
  37
  38   /* VM frame pointer. Contains information about the current executing
  39    * function, class context, caller, and a base pointer for accessing local
  40    * variables. */
  41   ActRec* fp;
  42
  43   /* VM program counter. Points to the beginning of the currently executing
  44    * bytecode instruction. */
  45   PC pc;
  46 };
  47
  48 namespace RDS {
  49
  50 /*
  51  * Statically layed-out header that goes at the front of RDS.
  52  */
  53 struct Header {
  54   /*
  55    * Surprise flags.  May be written by other threads.  At various
  56    * points, the runtime will check whether this word is non-zero, and
  57    * if so go to a slow path to handle unusual conditions (e.g. OOM).
  58    */
  59   std::atomic<ssize_t> conditionFlags;
  60
  61   VMRegs vmRegs;
  62 };
  63
  64 /*
  65  * Access to the statically layed out header.
  66  */
  67 inline Header* header() {
  68   return static_cast<Header*>(tl_base);
  69 }
  70
  71 constexpr ptrdiff_t kConditionFlagsOff = offsetof(Header, conditionFlags);
  72 constexpr ptrdiff_t kVmRegsOff         = offsetof(Header, vmRegs);
  73 constexpr ptrdiff_t kVmspOff           = kVmRegsOff + offsetof(VMRegs, stack) +
  74                                            Stack::topOfStackOffset();
  75 constexpr ptrdiff_t kVmfpOff           = kVmRegsOff + offsetof(VMRegs, fp);
  76 constexpr ptrdiff_t kVmpcOff           = kVmRegsOff + offsetof(VMRegs, pc);
  77
  78 } }
  79
  80 #endif