hurd/sigunwind.c

   1 /* longjmp cleanup function for unwinding past signal handlers.
   2    Copyright (C) 1995-2015 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 Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <hurd.h>
  20 #include <thread_state.h>
  21 #include <jmpbuf-unwind.h>
  22 #include <assert.h>
  23 #include <stdint.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 & SS_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       inline uintptr_t demangle_ptr (uintptr_t x)
  74         {
  75 # ifdef PTR_DEMANGLE
  76           PTR_DEMANGLE (x);
  77 # endif
  78           return x;
  79         }
  80
  81       /* Continue _longjmp_unwind's job of running the unwind
  82          forms for frames being unwound, since we will not
  83          return to its loop like this one, which called us.  */
  84       for (link = ss->active_resources;
  85            link && _JMPBUF_UNWINDS (env[0].__jmpbuf, link, demangle_ptr);
  86            link = link->thread.next)
  87         if (_hurd_userlink_unlink (link))
  88           {
  89             if (link->cleanup == &_hurdsig_longjmp_from_handler)
  90               {
  91                 /* We are unwinding past another signal handler invocation.
  92                    Just finish the cleanup for this (inner) one, and then
  93                    swap SCP to restore to the outer context.  */
  94                 cleanup ();
  95                 scp = link->cleanup_data;
  96               }
  97             else
  98               (*link->cleanup) (link->cleanup_data, env, val);
  99           }
 100
 101 #define sc_machine_thread_state paste(sc_,machine_thread_state)
 102 #define paste(a,b)      paste1(a,b)
 103 #define paste1(a,b)     a##b
 104
 105       /* There are no more unwind forms to be run!
 106          Now we can just have the sigreturn do the longjmp for us.  */
 107       _hurd_longjmp_thread_state
 108         ((struct machine_thread_state *) &scp->sc_machine_thread_state,
 109          env, val);
 110
 111       /* Restore to the same current signal mask.  If sigsetjmp saved the
 112          mask, longjmp has already restored it as desired; if not, we
 113          should leave it as it is.  */
 114       scp->sc_mask = ss->blocked;
 115
 116       /* sigreturn expects the link added by _hurd_setup_sighandler
 117          to still be there, but _longjmp_unwind removed it just before
 118          calling us.  Put it back now so sigreturn can find it.  */
 119       link = (void *) &scp[1];
 120       assert (! link->resource.next && ! link->resource.prevp);
 121       assert (link->thread.next == ss->active_resources);
 122       assert (link->thread.prevp == &ss->active_resources);
 123       if (link->thread.next)
 124         link->thread.next->thread.prevp = &link->thread.next;
 125       ss->active_resources = link;
 126
 127       /* We must momentarily exit the critical section so that sigreturn
 128          does not get upset with us.  But we don't want signal handlers
 129          running right now, because we are presently in the bogus state of
 130          having run all the unwind forms back to ENV's frame, but our SP is
 131          still inside those unwound frames.  */
 132       __spin_lock (&ss->lock);
 133       __spin_unlock (&ss->critical_section_lock);
 134       ss->blocked = ~(sigset_t) 0 & ~_SIG_CANT_MASK;
 135       __spin_unlock (&ss->lock);
 136
 137       /* Restore to the modified signal context that now
 138          performs `longjmp (ENV, VAL)'.  */
 139       __sigreturn (scp);
 140       assert (! "sigreturn returned!");
 141     }
 142
 143   /* We are not unwinding off the alternate signal stack.  So nothing
 144      really funny is going on here.  We can just clean up this handler
 145      frame and let _longjmp_unwind continue unwinding.  */
 146   cleanup ();
 147   ss->intr_port = scp->sc_intr_port;
 148 }