sysdeps/mach/hurd/i386/trampoline.c

   1 /* Set thread_state for sighandler, and sigcontext to recover.  i386 version.
   2    Copyright (C) 1994,1995,1996,1997,1998,1999,2005,2008
   3         Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <hurd/signal.h>
  22 #include <hurd/userlink.h>
  23 #include <thread_state.h>
  24 #include <mach/machine/eflags.h>
  25 #include <assert.h>
  26 #include <errno.h>
  27 #include "hurdfault.h"
  28 #include <intr-msg.h>
  29
  30
  31 struct sigcontext *
  32 _hurd_setup_sighandler (struct hurd_sigstate *ss, __sighandler_t handler,
  33                         int signo, struct hurd_signal_detail *detail,
  34                         volatile int rpc_wait,
  35                         struct machine_thread_all_state *state)
  36 {
  37   void trampoline (void);
  38   void rpc_wait_trampoline (void);
  39   void firewall (void);
  40   extern const void _hurd_intr_rpc_msg_in_trap;
  41   extern const void _hurd_intr_rpc_msg_cx_sp;
  42   extern const void _hurd_intr_rpc_msg_sp_restored;
  43   void *volatile sigsp;
  44   struct sigcontext *scp;
  45   struct
  46     {
  47       int signo;
  48       long int sigcode;
  49       struct sigcontext *scp;   /* Points to ctx, below.  */
  50       void *sigreturn_addr;
  51       void *sigreturn_returns_here;
  52       struct sigcontext *return_scp; /* Same; arg to sigreturn.  */
  53       struct sigcontext ctx;
  54       struct hurd_userlink link;
  55     } *stackframe;
  56
  57   if (ss->context)
  58     {
  59       /* We have a previous sigcontext that sigreturn was about
  60          to restore when another signal arrived.  We will just base
  61          our setup on that.  */
  62       if (! _hurdsig_catch_memory_fault (ss->context))
  63         {
  64           memcpy (&state->basic, &ss->context->sc_i386_thread_state,
  65                   sizeof (state->basic));
  66           memcpy (&state->fpu, &ss->context->sc_i386_float_state,
  67                   sizeof (state->fpu));
  68           state->set |= (1 << i386_THREAD_STATE) | (1 << i386_FLOAT_STATE);
  69         }
  70     }
  71
  72   if (! machine_get_basic_state (ss->thread, state))
  73     return NULL;
  74
  75   /* Save the original SP in the gratuitous `esp' slot.
  76      We may need to reset the SP (the `uesp' slot) to avoid clobbering an
  77      interrupted RPC frame.  */
  78   state->basic.esp = state->basic.uesp;
  79
  80   if ((ss->actions[signo].sa_flags & SA_ONSTACK) &&
  81       !(ss->sigaltstack.ss_flags & (SS_DISABLE|SS_ONSTACK)))
  82     {
  83       sigsp = ss->sigaltstack.ss_sp + ss->sigaltstack.ss_size;
  84       ss->sigaltstack.ss_flags |= SS_ONSTACK;
  85       /* XXX need to set up base of new stack for
  86          per-thread variables, cthreads.  */
  87     }
  88   /* This code has intimate knowledge of the special mach_msg system call
  89      done in intr-msg.c; that code does (see intr-msg.h):
  90                                         movl %esp, %ecx
  91                                         leal ARGS, %esp
  92         _hurd_intr_rpc_msg_cx_sp:       movl $-25, %eax
  93         _hurd_intr_rpc_msg_do_trap:     lcall $7, $0
  94         _hurd_intr_rpc_msg_in_trap:     movl %ecx, %esp
  95         _hurd_intr_rpc_msg_sp_restored:
  96      We must check for the window during which %esp points at the
  97      mach_msg arguments.  The space below until %ecx is used by
  98      the _hurd_intr_rpc_mach_msg frame, and must not be clobbered.  */
  99   else if (state->basic.eip >= (int) &_hurd_intr_rpc_msg_cx_sp &&
 100            state->basic.eip < (int) &_hurd_intr_rpc_msg_sp_restored)
 101     /* The SP now points at the mach_msg args, but there is more stack
 102        space used below it.  The real SP is saved in %ecx; we must push the
 103        new frame below there, and restore that value as the SP on
 104        sigreturn.  */
 105     sigsp = (char *) (state->basic.uesp = state->basic.ecx);
 106   else
 107     sigsp = (char *) state->basic.uesp;
 108
 109   /* Push the arguments to call `trampoline' on the stack.  */
 110   sigsp -= sizeof (*stackframe);
 111   stackframe = sigsp;
 112
 113   if (_hurdsig_catch_memory_fault (stackframe))
 114     {
 115       /* We got a fault trying to write the stack frame.
 116          We cannot set up the signal handler.
 117          Returning NULL tells our caller, who will nuke us with a SIGILL.  */
 118       return NULL;
 119     }
 120   else
 121     {
 122       int ok;
 123
 124       extern void _hurdsig_longjmp_from_handler (void *, jmp_buf, int);
 125
 126       /* Add a link to the thread's active-resources list.  We mark this as
 127          the only user of the "resource", so the cleanup function will be
 128          called by any longjmp which is unwinding past the signal frame.
 129          The cleanup function (in sigunwind.c) will make sure that all the
 130          appropriate cleanups done by sigreturn are taken care of.  */
 131       stackframe->link.cleanup = &_hurdsig_longjmp_from_handler;
 132       stackframe->link.cleanup_data = &stackframe->ctx;
 133       stackframe->link.resource.next = NULL;
 134       stackframe->link.resource.prevp = NULL;
 135       stackframe->link.thread.next = ss->active_resources;
 136       stackframe->link.thread.prevp = &ss->active_resources;
 137       if (stackframe->link.thread.next)
 138         stackframe->link.thread.next->thread.prevp
 139           = &stackframe->link.thread.next;
 140       ss->active_resources = &stackframe->link;
 141
 142       /* Set up the arguments for the signal handler.  */
 143       stackframe->signo = signo;
 144       stackframe->sigcode = detail->code;
 145       stackframe->scp = stackframe->return_scp = scp = &stackframe->ctx;
 146       stackframe->sigreturn_addr = &__sigreturn;
 147       stackframe->sigreturn_returns_here = firewall; /* Crash on return.  */
 148
 149       /* Set up the sigcontext from the current state of the thread.  */
 150
 151       scp->sc_onstack = ss->sigaltstack.ss_flags & SS_ONSTACK ? 1 : 0;
 152
 153       /* struct sigcontext is laid out so that starting at sc_gs mimics a
 154          struct i386_thread_state.  */
 155       memcpy (&scp->sc_i386_thread_state,
 156               &state->basic, sizeof (state->basic));
 157
 158       /* struct sigcontext is laid out so that starting at sc_fpkind mimics
 159          a struct i386_float_state.  */
 160       ok = machine_get_state (ss->thread, state, i386_FLOAT_STATE,
 161                               &state->fpu, &scp->sc_i386_float_state,
 162                               sizeof (state->fpu));
 163
 164       _hurdsig_end_catch_fault ();
 165
 166       if (! ok)
 167         return NULL;
 168     }
 169
 170   /* Modify the thread state to call the trampoline code on the new stack.  */
 171   if (rpc_wait)
 172     {
 173       /* The signalee thread was blocked in a mach_msg_trap system call,
 174          still waiting for a reply.  We will have it run the special
 175          trampoline code which retries the message receive before running
 176          the signal handler.
 177
 178          To do this we change the OPTION argument on its stack to enable only
 179          message reception, since the request message has already been
 180          sent.  */
 181
 182       struct mach_msg_trap_args *args = (void *) state->basic.esp;
 183
 184       if (_hurdsig_catch_memory_fault (args))
 185         {
 186           /* Faulted accessing ARGS.  Bomb.  */
 187           return NULL;
 188         }
 189
 190       assert (args->option & MACH_RCV_MSG);
 191       /* Disable the message-send, since it has already completed.  The
 192          calls we retry need only wait to receive the reply message.  */
 193       args->option &= ~MACH_SEND_MSG;
 194
 195       /* Limit the time to receive the reply message, in case the server
 196          claimed that `interrupt_operation' succeeded but in fact the RPC
 197          is hung.  */
 198       args->option |= MACH_RCV_TIMEOUT;
 199       args->timeout = _hurd_interrupted_rpc_timeout;
 200
 201       _hurdsig_end_catch_fault ();
 202
 203       state->basic.eip = (int) rpc_wait_trampoline;
 204       /* The reply-receiving trampoline code runs initially on the original
 205          user stack.  We pass it the signal stack pointer in %ebx.  */
 206       state->basic.uesp = state->basic.esp; /* Restore mach_msg syscall SP.  */
 207       state->basic.ebx = (int) sigsp;
 208       /* After doing the message receive, the trampoline code will need to
 209          update the %eax value to be restored by sigreturn.  To simplify
 210          the assembly code, we pass the address of its slot in SCP to the
 211          trampoline code in %ecx.  */
 212       state->basic.ecx = (int) &scp->sc_eax;
 213     }
 214   else
 215     {
 216       state->basic.eip = (int) trampoline;
 217       state->basic.uesp = (int) sigsp;
 218     }
 219   /* We pass the handler function to the trampoline code in %edx.  */
 220   state->basic.edx = (int) handler;
 221
 222   /* The x86 ABI says the DF bit is clear on entry to any function.  */
 223   state->basic.efl &= ~EFL_DF;
 224
 225   return scp;
 226 }
 227
 228 /* The trampoline code follows.  This used to be located inside
 229    _hurd_setup_sighandler, but was optimized away by gcc 2.95.  */
 230
 231 asm ("rpc_wait_trampoline:\n");
 232   /* This is the entry point when we have an RPC reply message to receive
 233      before running the handler.  The MACH_MSG_SEND bit has already been
 234      cleared in the OPTION argument on our stack.  The interrupted user
 235      stack pointer has not been changed, so the system call can find its
 236      arguments; the signal stack pointer is in %ebx.  For our convenience,
 237      %ecx points to the sc_eax member of the sigcontext.  */
 238 asm (/* Retry the interrupted mach_msg system call.  */
 239      "movl $-25, %eax\n"        /* mach_msg_trap */
 240      "lcall $7, $0\n"
 241      /* When the sigcontext was saved, %eax was MACH_RCV_INTERRUPTED.  But
 242         now the message receive has completed and the original caller of
 243         the RPC (i.e. the code running when the signal arrived) needs to
 244         see the final return value of the message receive in %eax.  So
 245         store the new %eax value into the sc_eax member of the sigcontext
 246         (whose address is in %ecx to make this code simpler).  */
 247      "movl %eax, (%ecx)\n"
 248      /* Switch to the signal stack.  */
 249      "movl %ebx, %esp\n");
 250
 251  asm ("trampoline:\n");
 252   /* Entry point for running the handler normally.  The arguments to the
 253      handler function are already on the top of the stack:
 254
 255        0(%esp)  SIGNO
 256        4(%esp)  SIGCODE
 257        8(%esp)  SCP
 258      */
 259 asm ("call *%edx\n"             /* Call the handler function.  */
 260      "addl $12, %esp\n"         /* Pop its args.  */
 261      /* The word at the top of stack is &__sigreturn; following are a dummy
 262         word to fill the slot for the address for __sigreturn to return to,
 263         and a copy of SCP for __sigreturn's argument.  "Return" to calling
 264         __sigreturn (SCP); this call never returns.  */
 265      "ret");
 266
 267 asm ("firewall:\n"
 268      "hlt");