sysdeps/mach/hurd/i386/trampoline.c

   1 /* Set thread_state for sighandler, and sigcontext to recover.  i386 version.
   2 Copyright (C) 1994, 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/signal.h>
  21 #include <hurd/userlink.h>
  22 #include "thread_state.h"
  23 #include <assert.h>
  24 #include <errno.h>
  25 #include "hurdfault.h"
  26
  27
  28 struct mach_msg_trap_args
  29   {
  30     void *retaddr;              /* Address mach_msg_trap will return to.  */
  31     /* This is the order of arguments to mach_msg_trap.  */
  32     mach_msg_header_t *msg;
  33     mach_msg_option_t option;
  34     mach_msg_size_t send_size;
  35     mach_msg_size_t rcv_size;
  36     mach_port_t rcv_name;
  37     mach_msg_timeout_t timeout;
  38     mach_port_t notify;
  39   };
  40
  41 struct sigcontext *
  42 _hurd_setup_sighandler (struct hurd_sigstate *ss, __sighandler_t handler,
  43                         int signo, long int sigcode,
  44                         volatile int rpc_wait,
  45                         struct machine_thread_all_state *state)
  46 {
  47   __label__ trampoline, rpc_wait_trampoline, firewall;
  48   extern const void _hurd_intr_rpc_msg_in_trap;
  49   extern const void _hurd_intr_rpc_msg_cx_sp;
  50   extern const void _hurd_intr_rpc_msg_sp_restored;
  51   void *volatile sigsp;
  52   struct sigcontext *scp;
  53   struct
  54     {
  55       int signo;
  56       long int sigcode;
  57       struct sigcontext *scp;   /* Points to ctx, below.  */
  58       void *sigreturn_addr;
  59       void *sigreturn_returns_here;
  60       struct sigcontext *return_scp; /* Same; arg to sigreturn.  */
  61       struct sigcontext ctx;
  62       struct hurd_userlink link;
  63     } *stackframe;
  64
  65   if (ss->context)
  66     {
  67       /* We have a previous sigcontext that sigreturn was about
  68          to restore when another signal arrived.  We will just base
  69          our setup on that.  */
  70       if (_hurdsig_catch_fault (SIGSEGV))
  71         assert (_hurdsig_fault_sigcode >= (long int) ss->context &&
  72                 _hurdsig_fault_sigcode < (long int) (ss->context + 1));
  73       else
  74         {
  75           memcpy (&state->basic, &ss->context->sc_i386_thread_state,
  76                   sizeof (state->basic));
  77           memcpy (&state->fpu, &ss->context->sc_i386_float_state,
  78                   sizeof (state->fpu));
  79           state->set |= (1 << i386_THREAD_STATE) | (1 << i386_FLOAT_STATE);
  80         }
  81     }
  82
  83   if (! machine_get_basic_state (ss->thread, state))
  84     return NULL;
  85
  86   /* Save the original SP in the gratuitous `esp' slot.
  87      We may need to reset the SP (the `uesp' slot) to avoid clobbering an
  88      interrupted RPC frame.  */
  89   state->basic.esp = state->basic.uesp;
  90
  91   if ((ss->actions[signo].sa_flags & SA_ONSTACK) &&
  92       !(ss->sigaltstack.ss_flags & (SA_DISABLE|SA_ONSTACK)))
  93     {
  94       sigsp = ss->sigaltstack.ss_sp + ss->sigaltstack.ss_size;
  95       ss->sigaltstack.ss_flags |= SA_ONSTACK;
  96       /* XXX need to set up base of new stack for
  97          per-thread variables, cthreads.  */
  98     }
  99   /* This code has intimate knowledge of the special mach_msg system call
 100      done in intr-msg.c; that code does:
 101                                         movl %esp, %ecx
 102                                         leal ARGS, %esp
 103         _hurd_intr_rpc_msg_cx_sp:       movl $-25, %eax
 104         _hurd_intr_rpc_msg_do_trap:     lcall $7, $0
 105         _hurd_intr_rpc_msg_in_trap:     movl %ecx, %esp
 106         _hurd_intr_rpc_msg_sp_restored:
 107      We must check for the window during which %esp points at the
 108      mach_msg arguments.  The space below until %ecx is used by
 109      the _hurd_intr_rpc_mach_msg frame, and must not be clobbered.  */
 110   else if (state->basic.eip >= (int) &_hurd_intr_rpc_msg_cx_sp &&
 111            state->basic.eip < (int) &_hurd_intr_rpc_msg_sp_restored)
 112     /* The SP now points at the mach_msg args, but there is more stack
 113        space used below it.  The real SP is saved in %ecx; we must push the
 114        new frame below there, and restore that value as the SP on
 115        sigreturn.  */
 116     sigsp = (char *) (state->basic.uesp = state->basic.ecx);
 117   else
 118     sigsp = (char *) state->basic.uesp;
 119
 120   /* Push the arguments to call `trampoline' on the stack.  */
 121   sigsp -= sizeof (*stackframe);
 122   stackframe = sigsp;
 123
 124   if (_hurdsig_catch_fault (SIGSEGV))
 125     {
 126       assert (_hurdsig_fault_sigcode >= (long int) stackframe &&
 127               _hurdsig_fault_sigcode <= (long int) (stackframe + 1));
 128       /* We got a fault trying to write the stack frame.
 129          We cannot set up the signal handler.
 130          Returning NULL tells our caller, who will nuke us with a SIGILL.  */
 131       return NULL;
 132     }
 133   else
 134     {
 135       int ok;
 136
 137       extern void _hurdsig_longjmp_from_handler (void *, jmp_buf, int);
 138
 139       /* Add a link to the thread's active-resources list.  We mark this as
 140          the only user of the "resource", so the cleanup function will be
 141          called by any longjmp which is unwinding past the signal frame.
 142          The cleanup function (in sigunwind.c) will make sure that all the
 143          appropriate cleanups done by sigreturn are taken care of.  */
 144       stackframe->link.cleanup = &_hurdsig_longjmp_from_handler;
 145       stackframe->link.cleanup_data = &stackframe->ctx;
 146       stackframe->link.resource.next = NULL;
 147       stackframe->link.resource.prevp = NULL;
 148       stackframe->link.thread.next = ss->active_resources;
 149       stackframe->link.thread.prevp = &ss->active_resources;
 150       if (stackframe->link.thread.next)
 151         stackframe->link.thread.next->thread.prevp
 152           = &stackframe->link.thread.next;
 153       ss->active_resources = &stackframe->link;
 154
 155       /* Set up the arguments for the signal handler.  */
 156       stackframe->signo = signo;
 157       stackframe->sigcode = sigcode;
 158       stackframe->scp = stackframe->return_scp = scp = &stackframe->ctx;
 159       stackframe->sigreturn_addr = &__sigreturn;
 160       stackframe->sigreturn_returns_here = &&firewall; /* Crash on return.  */
 161
 162       /* Set up the sigcontext from the current state of the thread.  */
 163
 164       scp->sc_onstack = ss->sigaltstack.ss_flags & SA_ONSTACK ? 1 : 0;
 165
 166       /* struct sigcontext is laid out so that starting at sc_gs mimics a
 167          struct i386_thread_state.  */
 168       memcpy (&scp->sc_i386_thread_state,
 169               &state->basic, sizeof (state->basic));
 170
 171       /* struct sigcontext is laid out so that starting at sc_fpkind mimics
 172          a struct i386_float_state.  */
 173       ok = machine_get_state (ss->thread, state, i386_FLOAT_STATE,
 174                               &state->fpu, &scp->sc_i386_float_state,
 175                               sizeof (state->fpu));
 176
 177       _hurdsig_end_catch_fault ();
 178
 179       if (! ok)
 180         return NULL;
 181     }
 182
 183   /* Modify the thread state to call the trampoline code on the new stack.  */
 184   if (rpc_wait)
 185     {
 186       /* The signalee thread was blocked in a mach_msg_trap system call,
 187          still waiting for a reply.  We will have it run the special
 188          trampoline code which retries the message receive before running
 189          the signal handler.
 190
 191          To do this we change the OPTION argument on its stack to enable only
 192          message reception, since the request message has already been
 193          sent.  */
 194
 195       struct mach_msg_trap_args *args = (void *) state->basic.esp;
 196
 197       if (_hurdsig_catch_fault (SIGSEGV))
 198         {
 199           assert (_hurdsig_fault_sigcode >= (long int) args &&
 200                   _hurdsig_fault_sigcode < (long int) (args + 1));
 201           /* Faulted accessing ARGS.  Bomb.  */
 202           return NULL;
 203         }
 204
 205       assert (args->option & MACH_RCV_MSG);
 206       /* Disable the message-send, since it has already completed.  The
 207          calls we retry need only wait to receive the reply message.  */
 208       args->option &= ~MACH_SEND_MSG;
 209
 210       /* Limit the time to receive the reply message, in case the server
 211          claimed that `interrupt_operation' succeeded but in fact the RPC
 212          is hung.  */
 213       args->option |= MACH_RCV_TIMEOUT;
 214       args->timeout = _hurd_interrupted_rpc_timeout;
 215
 216       _hurdsig_end_catch_fault ();
 217
 218       state->basic.eip = (int) &&rpc_wait_trampoline;
 219       /* The reply-receiving trampoline code runs initially on the original
 220          user stack.  We pass it the signal stack pointer in %ebx.  */
 221       state->basic.uesp = state->basic.esp; /* Restore mach_msg syscall SP.  */
 222       state->basic.ebx = (int) sigsp;
 223       /* After doing the message receive, the trampoline code will need to
 224          update the %eax value to be restored by sigreturn.  To simplify
 225          the assembly code, we pass the address of its slot in SCP to the
 226          trampoline code in %ecx.  */
 227       state->basic.ecx = (int) &scp->sc_eax;
 228     }
 229   else
 230     {
 231       state->basic.eip = (int) &&trampoline;
 232       state->basic.uesp = (int) sigsp;
 233     }
 234   /* We pass the handler function to the trampoline code in %edx.  */
 235   state->basic.edx = (int) handler;
 236
 237   return scp;
 238
 239   /* The trampoline code follows.  This is not actually executed as part of
 240      this function, it is just convenient to write it that way.  */
 241
 242  rpc_wait_trampoline:
 243   /* This is the entry point when we have an RPC reply message to receive
 244      before running the handler.  The MACH_MSG_SEND bit has already been
 245      cleared in the OPTION argument on our stack.  The interrupted user
 246      stack pointer has not been changed, so the system call can find its
 247      arguments; the signal stack pointer is in %ebx.  For our convenience,
 248      %ecx points to the sc_eax member of the sigcontext.  */
 249   asm volatile
 250     (/* Retry the interrupted mach_msg system call.  */
 251      "movl $-25, %eax\n"        /* mach_msg_trap */
 252      "lcall $7, $0\n"
 253      /* When the sigcontext was saved, %eax was MACH_RCV_INTERRUPTED.  But
 254         now the message receive has completed and the original caller of
 255         the RPC (i.e. the code running when the signal arrived) needs to
 256         see the final return value of the message receive in %eax.  So
 257         store the new %eax value into the sc_eax member of the sigcontext
 258         (whose address is in %ecx to make this code simpler).  */
 259      "movl %eax, (%ecx)\n"
 260      /* Switch to the signal stack.  */
 261      "movl %ebx, %esp\n");
 262
 263  trampoline:
 264   /* Entry point for running the handler normally.  The arguments to the
 265      handler function are already on the top of the stack:
 266
 267        0(%esp)  SIGNO
 268        4(%esp)  SIGCODE
 269        8(%esp)  SCP
 270      */
 271   asm volatile
 272     ("call *%edx\n"             /* Call the handler function.  */
 273      "addl $12, %esp\n"         /* Pop its args.  */
 274      /* The word at the top of stack is &__sigreturn; following are a dummy
 275         word to fill the slot for the address for __sigreturn to return to,
 276         and a copy of SCP for __sigreturn's argument.  "Return" to calling
 277         __sigreturn (SCP); this call never returns.  */
 278      "ret");
 279
 280  firewall:
 281   asm volatile ("hlt");
 282
 283   /* NOTREACHED */
 284   return NULL;
 285 }