hurd/sigunwind.c

   1 /* longjmp cleanup function for unwinding past signal handlers.
   2 Copyright (C) 1995 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         __mach_port_destroy (__mach_task_self (), *reply_port);
  45       *reply_port = scp->sc_reply_port;
  46     }
  47
  48   __spin_lock (&ss->lock);
  49   /* We should only ever be called from _longjmp_unwind (in jmp-unwind.c),
  50      which calls us inside a critical section.  */
  51   assert (ss->critical_section);
  52   /* Are we on the alternate signal stack now?  */
  53   onstack = (ss->sigaltstack.ss_flags & SA_ONSTACK);
  54   __spin_unlock (&ss->lock);
  55
  56   if (onstack && ! scp->sc_onstack)
  57     {
  58       /* We are unwinding off the signal stack.  We must use sigreturn to
  59          do it robustly.  Mutate the sigcontext so that when sigreturn
  60          resumes from that context, it will be as if `__longjmp (ENV, VAL)'
  61          were done.  */
  62
  63       struct hurd_userlink *link;
  64
  65       /* Continue _longjmp_unwind's job of running the unwind
  66          forms for frames being unwound, since we will not
  67          return to its loop like this one, which called us.  */
  68       for (link = ss->active_resources;
  69            link && _JMPBUF_UNWINDS (env[0].__jmpbuf, link);
  70            link = link->thread.next)
  71         if (_hurd_userlink_unlink (link))
  72           {
  73             if (link->cleanup == &_hurdsig_longjmp_from_handler)
  74               {
  75                 /* We are unwinding past another signal handler invocation.
  76                    Just finish the cleanup for this (inner) one, and then
  77                    swap SCP to restore to the outer context.  */
  78                 cleanup ();
  79                 scp = link->cleanup_data;
  80               }
  81             else
  82               (*link->cleanup) (link->cleanup_data, env, val);
  83           }
  84
  85 #define sc_machine_thread_state paste(sc_,machine_thread_state)
  86 #define paste(a,b)      paste1(a,b)
  87 #define paste1(a,b)     a##b
  88
  89       /* There are no more unwind forms to be run!
  90          Now we can just have the sigreturn do the longjmp for us.  */
  91       _hurd_longjmp_thread_state
  92         ((struct machine_thread_state *) &scp->sc_machine_thread_state,
  93          env, val);
  94
  95       /* Restore to the same current signal mask.  If sigsetjmp saved the
  96          mask, longjmp has already restored it as desired; if not, we
  97          should leave it as it is.  */
  98       scp->sc_mask = ss->blocked;
  99
 100       /* sigreturn expects the link added by _hurd_setup_sighandler
 101          to still be there, but _longjmp_unwind removed it just before
 102          calling us.  Put it back now so sigreturn can find it.  */
 103       link = (void *) &scp[1];
 104       assert (! link->resource.next && ! link->resource.prevp);
 105       assert (link->thread.next == ss->active_resources);
 106       assert (link->thread.prevp = &ss->active_resources);
 107       if (link->thread.next)
 108         link->thread.next->thread.prevp = &link->thread.next;
 109       ss->active_resources = link;
 110
 111       /* We must momentarily exit the critical section so that sigreturn
 112          does not get upset with us.  But we don't want signal handlers
 113          running right now, because we are presently in the bogus state of
 114          having run all the unwind forms back to ENV's frame, but our SP is
 115          still inside those unwound frames.  */
 116       __spin_lock (&ss->lock);
 117       ss->critical_section = 0;
 118       ss->blocked = ~(sigset_t) 0 & ~_SIG_CANT_MASK;
 119       __spin_unlock (&ss->lock);
 120
 121       /* Restore to the modified signal context that now
 122          performs `longjmp (ENV, VAL)'.  */
 123       __sigreturn (scp);
 124       assert (! "sigreturn returned!");
 125     }
 126
 127   /* We are not unwinding off the alternate signal stack.  So nothing
 128      really funny is going on here.  We can just clean up this handler
 129      frame and let _longjmp_unwind continue unwinding.  */
 130   cleanup ();
 131   ss->intr_port = scp->sc_intr_port;
 132 }