hurd/sigunwind.c

   1 /* longjmp cleanup function for unwinding past signal handlers.
   2 Copyright (C) 1995, 1996 Free Software Foundation, Inc.
   3 This file is part of the GNU C Library.
   4
   5 The GNU C Library is free software; you can redistribute it and/or
   6 modify it under the terms of the GNU Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 License, or (at your option) any later version.
   9
  10 The GNU C Library is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, USA.  */
  19
  20 #include <hurd.h>
  21 #include "thread_state.h"
  22 #include <setjmp.h>
  23 #include <assert.h>
  24
  25
  26 /* _hurd_setup_sighandler puts a link on the `active resources' chain so that
  27    _longjmp_unwind will call this function with the `struct sigcontext *'
  28    describing the context interrupted by the signal, when `longjmp' is jumping
  29    to an environment that unwinds past the interrupted frame.  */
  30
  31 void
  32 _hurdsig_longjmp_from_handler (void *data, jmp_buf env, int val)
  33 {
  34   struct sigcontext *scp = data;
  35   struct hurd_sigstate *ss = _hurd_self_sigstate ();
  36   int onstack;
  37   inline void cleanup (void)
  38     {
  39       /* Destroy the MiG reply port used by the signal handler, and restore
  40          the reply port in use by the thread when interrupted.  */
  41       mach_port_t *reply_port =
  42         (mach_port_t *) __hurd_threadvar_location (_HURD_THREADVAR_MIG_REPLY);
  43       if (*reply_port)
  44         {
  45           mach_port_t port = *reply_port;
  46           /* Assigning MACH_PORT_DEAD here tells libc's mig_get_reply_port
  47              not to get another reply port, but avoids mig_dealloc_reply_port
  48              trying to deallocate it after the receive fails (which it will,
  49              because the reply port will be bogus, regardless).  */
  50           *reply_port = MACH_PORT_DEAD;
  51           __mach_port_destroy (__mach_task_self (), port);
  52         }
  53       *reply_port = scp->sc_reply_port;
  54     }
  55
  56   __spin_lock (&ss->lock);
  57   /* We should only ever be called from _longjmp_unwind (in jmp-unwind.c),
  58      which calls us inside a critical section.  */
  59   assert (__spin_lock_locked (&ss->critical_section_lock));
  60   /* Are we on the alternate signal stack now?  */
  61   onstack = (ss->sigaltstack.ss_flags & SA_ONSTACK);
  62   __spin_unlock (&ss->lock);
  63
  64   if (onstack && ! scp->sc_onstack)
  65     {
  66       /* We are unwinding off the signal stack.  We must use sigreturn to
  67          do it robustly.  Mutate the sigcontext so that when sigreturn
  68          resumes from that context, it will be as if `__longjmp (ENV, VAL)'
  69          were done.  */
  70
  71       struct hurd_userlink *link;
  72
  73       /* Continue _longjmp_unwind's job of running the unwind
  74          forms for frames being unwound, since we will not
  75          return to its loop like this one, which called us.  */
  76       for (link = ss->active_resources;
  77            link && _JMPBUF_UNWINDS (env[0].__jmpbuf, link);
  78            link = link->thread.next)
  79         if (_hurd_userlink_unlink (link))
  80           {
  81             if (link->cleanup == &_hurdsig_longjmp_from_handler)
  82               {
  83                 /* We are unwinding past another signal handler invocation.
  84                    Just finish the cleanup for this (inner) one, and then
  85                    swap SCP to restore to the outer context.  */
  86                 cleanup ();
  87                 scp = link->cleanup_data;
  88               }
  89             else
  90               (*link->cleanup) (link->cleanup_data, env, val);
  91           }
  92
  93 #define sc_machine_thread_state paste(sc_,machine_thread_state)
  94 #define paste(a,b)      paste1(a,b)
  95 #define paste1(a,b)     a##b
  96
  97       /* There are no more unwind forms to be run!
  98          Now we can just have the sigreturn do the longjmp for us.  */
  99       _hurd_longjmp_thread_state
 100         ((struct machine_thread_state *) &scp->sc_machine_thread_state,
 101          env, val);
 102
 103       /* Restore to the same current signal mask.  If sigsetjmp saved the
 104          mask, longjmp has already restored it as desired; if not, we
 105          should leave it as it is.  */
 106       scp->sc_mask = ss->blocked;
 107
 108       /* sigreturn expects the link added by _hurd_setup_sighandler
 109          to still be there, but _longjmp_unwind removed it just before
 110          calling us.  Put it back now so sigreturn can find it.  */
 111       link = (void *) &scp[1];
 112       assert (! link->resource.next && ! link->resource.prevp);
 113       assert (link->thread.next == ss->active_resources);
 114       assert (link->thread.prevp = &ss->active_resources);
 115       if (link->thread.next)
 116         link->thread.next->thread.prevp = &link->thread.next;
 117       ss->active_resources = link;
 118
 119       /* We must momentarily exit the critical section so that sigreturn
 120          does not get upset with us.  But we don't want signal handlers
 121          running right now, because we are presently in the bogus state of
 122          having run all the unwind forms back to ENV's frame, but our SP is
 123          still inside those unwound frames.  */
 124       __spin_lock (&ss->lock);
 125       __spin_unlock (&ss->critical_section_lock);
 126       ss->blocked = ~(sigset_t) 0 & ~_SIG_CANT_MASK;
 127       __spin_unlock (&ss->lock);
 128
 129       /* Restore to the modified signal context that now
 130          performs `longjmp (ENV, VAL)'.  */
 131       __sigreturn (scp);
 132       assert (! "sigreturn returned!");
 133     }
 134
 135   /* We are not unwinding off the alternate signal stack.  So nothing
 136      really funny is going on here.  We can just clean up this handler
 137      frame and let _longjmp_unwind continue unwinding.  */
 138   cleanup ();
 139   ss->intr_port = scp->sc_intr_port;
 140 }