lib/libc/gen/ucontext.c

   1 /*
   2  * Copyright (c) 2007 Matthew T. Emmerton <matt@gsicomp.on.ca>
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Neither the name of the author nor the names of its contributors
  11  *    may be used to endorse or promote products derived from this software
  12  *    without specific prior written permission.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  *
  26  * $DragonFly: src/lib/libc/gen/ucontext.c,v 1.1 2007/01/16 07:16:23 dillon Exp $
  27  */
  28
  29 #include <sys/cdefs.h>
  30 #include <sys/param.h>
  31 #include <sys/signal.h>
  32 #include <sys/ucontext.h>
  33
  34 #include <errno.h>
  35 #include <stdarg.h>
  36 #include <stdlib.h>
  37 #include <unistd.h>
  38 #include <signal.h>
  39
  40 /* Prototypes */
  41 __weak_reference(_swapcontext, swapcontext);
  42 __weak_reference(_setcontext, setcontext);
  43
  44 int get_mcontext(mcontext_t *);
  45 int set_mcontext(const mcontext_t *);
  46
  47 /*
  48  * We need to block most signals during a context switch so we do not
  49  * dispatch a signal vector during a context switch.
  50  */
  51 static sigset_t sigset_block_all;
  52
  53 static void __sigset_block_all_setup(void) __attribute__ ((constructor));
  54
  55 static void
  56 __sigset_block_all_setup(void)
  57 {
  58         sigfillset(&sigset_block_all);
  59         sigdelset(&sigset_block_all, SIGSEGV);
  60         sigdelset(&sigset_block_all, SIGBUS);
  61         sigdelset(&sigset_block_all, SIGILL);
  62 }
  63
  64 /*
  65  * Save the calling context in (oucp) then switch to (ucp).
  66  *
  67  * Block all signals while switching contexts.  get_mcontext() returns zero
  68  * when retrieving a context.
  69  *
  70  * When some other thread calls set_mcontext() to resume our thread,
  71  * the resume point causes get_mcontext() to return non-zero to us.
  72  * Signals will be blocked and we must restore the signal mask before
  73  * returning.
  74  */
  75 int
  76 _swapcontext(ucontext_t *oucp, const ucontext_t *ucp)
  77 {
  78         int ret;
  79
  80         ret = _sigprocmask(SIG_BLOCK, &sigset_block_all, &oucp->uc_sigmask);
  81         if (ret == 0) {
  82                 if (get_mcontext(&oucp->uc_mcontext) == 0) {
  83                         ret = set_mcontext(&ucp->uc_mcontext);
  84                 } else {
  85                         ret = _sigprocmask(SIG_SETMASK, &oucp->uc_sigmask, NULL);
  86                 }
  87         }
  88         return(ret);
  89 }
  90
  91 /*
  92  * Switch to the target context.  The current signal mask is saved in ucp
  93  * and all signals are blocked.  The call to set_mcontext() causes the
  94  * specified context to be switched to (usually resuming as a return from
  95  * the get_mcontext() procedure).  The current context is thrown away.
  96  *
  97  * The target context being resumed is responsible for restoring the
  98  * signal mask appropriate for the target context.
  99  */
 100 int
 101 _setcontext(ucontext_t *ucp)
 102 {
 103         int ret;
 104
 105         ret = _sigprocmask(SIG_BLOCK, &sigset_block_all, &ucp->uc_sigmask);
 106         if (ret == 0)
 107                 ret = set_mcontext(&ucp->uc_mcontext);
 108         return(ret);
 109 }
 110