root/trampolines.cpp

DEFINITIONS

1. sbrk_wrapper
2. sbrk_trampoline
3. _dmtcp_setup_trampolines

   1 /****************************************************************************
   2  *   Copyright (C) 2006-2013 by Tyler Denniston and Kapil Arya              *
   3  *   tyler@ccs.neu.edu and kapil@ccs.neu.edu                                *
   4  *                                                                          *
   5  *  This file is part of DMTCP.                                             *
   6  *                                                                          *
   7  *  DMTCP is free software: you can redistribute it and/or                  *
   8  *  modify it under the terms of the GNU Lesser General Public License as   *
   9  *  published by the Free Software Foundation, either version 3 of the      *
  10  *  License, or (at your option) any later version.                         *
  11  *                                                                          *
  12  *  DMTCP is distributed in the hope that it will be useful,                *
  13  *  but WITHOUT ANY WARRANTY; without even the implied warranty of          *
  14  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the           *
  15  *  GNU Lesser General Public License for more details.                     *
  16  *                                                                          *
  17  *  You should have received a copy of the GNU Lesser General Public        *
  18  *  License along with DMTCP:dmtcp/src.  If not, see                        *
  19  *  <http://www.gnu.org/licenses/>.                                         *
  20  ****************************************************************************/
  22 #include "trampolines.h"
  23 #include "syscallwrappers.h"
  24 #include "../jalib/jassert.h"
  26 static trampoline_info_t sbrk_trampoline_info;
  28 /* All calls by glibc to extend or shrink the heap go through __sbrk(). On
  29  * restart, the kernel may extend the end of data beyond where we want it. So
  30  * sbrk will present an abstraction corresponding to the original end of heap
  31  * before restart. FIXME: Potentially a user could call brk() directly, in
  32  * which case we would want a wrapper for that too. */
  33 static void *sbrk_wrapper(intptr_t increment)
  34 {
  35   static void *curbrk = NULL;
  36   void *oldbrk = NULL;
  37   /* Initialize curbrk. */
  38   if (curbrk == NULL) {
  39     /* The man page says syscall returns int, but unistd.h says long int. */
  40     long retval = syscall(SYS_brk, NULL);
curbrk = (void *)retval;
  42   }
oldbrk = curbrk;
curbrk = (void *)((char *)curbrk + increment);
  45   if (increment > 0) {
syscall(SYS_brk, curbrk);
  47   }
  48   return oldbrk;
  49 }
  51 /* Calls to sbrk will land here. */
  52 static void *sbrk_trampoline(intptr_t increment)
  53 {
  54   /* Unpatch sbrk. */
  55   UNINSTALL_TRAMPOLINE(sbrk_trampoline_info);
  56   void *retval = sbrk_wrapper(increment);
  57   /* Repatch sbrk. */
  58   INSTALL_TRAMPOLINE(sbrk_trampoline_info);
  59   return retval;
  60 }
  62 /* Any trampolines which should be installed are done so via this function.
  63    Called from DmtcpWorker constructor. */
  64 void _dmtcp_setup_trampolines()
  65 {
  66   dmtcp_setup_trampoline("sbrk", (void*) &sbrk_trampoline,
  67                          &sbrk_trampoline_info);
  68 }