sysdeps/mach/hurd/i386/sigreturn.c

   1 /* Copyright (C) 1991-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library 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 GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 register int *sp asm ("%esp");
  19
  20 #include <hurd.h>
  21 #include <hurd/signal.h>
  22 #include <hurd/msg.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25
  26 /* This is run on the thread stack after restoring it, to be able to
  27    unlock SS off sigstack.  */
  28 static void
  29 __sigreturn2 (int *usp, struct sigcontext *scp)
  30 {
  31   mach_port_t reply_port;
  32   struct hurd_sigstate *ss;
  33
  34   /* We know the sigstate must be initialized by the call below, but the
  35      compiler does not.  Help it out a little bit by eliding the check that
  36      _hurd_self_sigstate makes otherwise.  */
  37   ss = THREAD_GETMEM (THREAD_SELF, _hurd_sigstate);
  38   _hurd_sigstate_unlock (ss);
  39
  40   /* Destroy the MiG reply port used by the signal handler, and restore the
  41      reply port in use by the thread when interrupted.
  42
  43      We cannot use the original reply port for our RPCs that we do here, since
  44      we could unexpectedly receive/consume a reply message meant for the user
  45      (in particular, msg_sig_post_reply), and also since we would deallocate
  46      the port if *our* RPC fails, which we don't want to do since the user
  47      still has the old name.  And so, temporarily set MACH_PORT_DEAD as our
  48      reply name, and make sure destroying the port is the very last RPC we
  49      do.  */
  50   reply_port = THREAD_GETMEM (THREAD_SELF, reply_port);
  51   THREAD_SETMEM (THREAD_SELF, reply_port, MACH_PORT_DEAD);
  52   if (__glibc_likely (MACH_PORT_VALID (reply_port)))
  53     (void) __mach_port_mod_refs (__mach_task_self (), reply_port,
  54                                  MACH_PORT_RIGHT_RECEIVE, -1);
  55   THREAD_SETMEM (THREAD_SELF, reply_port, scp->sc_reply_port);
  56
  57   sp = usp;
  58 #define A(line) asm volatile (#line)
  59   /* The members in the sigcontext are arranged in this order
  60      so we can pop them easily.  */
  61
  62   /* Pop the segment registers (except %cs and %ss, done last).  */
  63   A (popl %gs);
  64   A (popl %fs);
  65   A (popl %es);
  66   A (popl %ds);
  67   /* Pop the general registers.  */
  68   A (popa);
  69   /* Pop the processor flags.  */
  70   A (popf);
  71   /* Return to the saved PC.  */
  72   A (ret);
  73
  74   /* Firewall.  */
  75   A (hlt);
  76 #undef A
  77   __builtin_unreachable ();
  78 }
  79
  80 int
  81 __sigreturn (struct sigcontext *scp)
  82 {
  83   struct hurd_sigstate *ss;
  84   struct hurd_userlink *link = (void *) &scp[1];
  85
  86   if (__glibc_unlikely (scp == NULL || (scp->sc_mask & _SIG_CANT_MASK)))
  87     return __hurd_fail (EINVAL);
  88
  89   ss = _hurd_self_sigstate ();
  90   _hurd_sigstate_lock (ss);
  91
  92   /* Remove the link on the `active resources' chain added by
  93      _hurd_setup_sighandler.  Its purpose was to make sure
  94      that we got called; now we have, it is done.  */
  95   _hurd_userlink_unlink (link);
  96
  97   /* Restore the set of blocked signals, and the intr_port slot.  */
  98   ss->blocked = scp->sc_mask;
  99   ss->intr_port = scp->sc_intr_port;
 100
 101   /* Check for pending signals that were blocked by the old set.  */
 102   if (_hurd_sigstate_pending (ss) & ~ss->blocked)
 103     {
 104       /* There are pending signals that just became unblocked.  Wake up the
 105          signal thread to deliver them.  But first, squirrel away SCP where
 106          the signal thread will notice it if it runs another handler, and
 107          arrange to have us called over again in the new reality.  */
 108       ss->context = scp;
 109       _hurd_sigstate_unlock (ss);
 110       __msg_sig_post (_hurd_msgport, 0, 0, __mach_task_self ());
 111       /* If a pending signal was handled, sig_post never returned.
 112          If it did return, the pending signal didn't run a handler;
 113          proceed as usual.  */
 114       _hurd_sigstate_lock (ss);
 115       ss->context = NULL;
 116     }
 117
 118   if (scp->sc_onstack)
 119     ss->sigaltstack.ss_flags &= ~SS_ONSTACK;
 120
 121   if (scp->sc_fpused)
 122     /* Restore the FPU state.  Mach conveniently stores the state
 123        in the format the i387 `frstor' instruction uses to restore it.  */
 124     asm volatile ("frstor %0" : : "m" (scp->sc_fpsave));
 125
 126   {
 127     /* There are convenient instructions to pop state off the stack, so we
 128        copy the registers onto the user's stack, switch there, pop and
 129        return.  */
 130
 131     int usp_arg, *usp = (int *) scp->sc_uesp;
 132
 133     *--usp = scp->sc_eip;
 134     *--usp = scp->sc_efl;
 135     memcpy (usp -= 12, &scp->sc_i386_thread_state, 12 * sizeof (int));
 136     usp_arg = (int) usp;
 137
 138     *--usp = (int) scp;
 139     /* Pass usp to __sigreturn2 so it can unwind itself easily.  */
 140     *--usp = usp_arg;
 141     /* Bogus return address for __sigreturn2 */
 142     *--usp = 0;
 143     *--usp = (int) __sigreturn2;
 144
 145     /* Restore thread stack */
 146     sp = usp;
 147     /* Return into __sigreturn2.  */
 148     asm volatile ("ret");
 149     /* Firewall.  */
 150     asm volatile ("hlt");
 151   }
 152
 153   /* NOTREACHED */
 154   return -1;
 155 }
 156
 157 weak_alias (__sigreturn, sigreturn)