src/leave-setcontext.c

   1 /* Leaving a signal handler executing on the alternate stack.
   2    Copyright (C) 2002  Bruno Haible <bruno@clisp.org>
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software Foundation,
  16    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  17
  18 #include <signal.h>
  19 #include <ucontext.h>
  20
  21 void
  22 sigsegv_reset_onstack_flag (void)
  23 {
  24   ucontext_t uc;
  25
  26   if (getcontext (&uc) >= 0)
  27     /* getcontext returns twice.  We are interested in the returned context
  28        only the first time, i.e. when the SS_ONSTACK bit is set.  */
  29     if (uc.uc_stack.ss_flags & SS_ONSTACK)
  30       {
  31         uc.uc_stack.ss_flags &= ~SS_ONSTACK;
  32         /* Note that setcontext() does not refill uc.  Therefore if
  33            setcontext() keeps SS_ONSTACK set in the kernel, either
  34            setcontext() will return -1 or getcontext() will return a
  35            second time, with the SS_ONSTACK bit being cleared.  */
  36         setcontext (&uc);
  37       }
  38 }