sysdeps/mach/hurd/i386/trampoline.c

   1 /* Set thread_state for sighandler, and sigcontext to recover.  i386 version.
   2    Copyright (C) 1994-2014 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/signal.h>
  20 #include <hurd/userlink.h>
  21 #include <thread_state.h>
  22 #include <mach/machine/eflags.h>
  23 #include <assert.h>
  24 #include <errno.h>
  25 #include "hurdfault.h"
  26 #include <intr-msg.h>
  27
  28
  29 struct sigcontext *
  30 _hurd_setup_sighandler (struct hurd_sigstate *ss, __sighandler_t handler,
  31                         int signo, struct hurd_signal_detail *detail,
  32                         volatile int rpc_wait,
  33                         struct machine_thread_all_state *state)
  34 {
  35   void trampoline (void);
  36   void rpc_wait_trampoline (void);
  37   void firewall (void);
  38   extern const void _hurd_intr_rpc_msg_in_trap;
  39   extern const void _hurd_intr_rpc_msg_cx_sp;
  40   extern const void _hurd_intr_rpc_msg_sp_restored;
  41   void *volatile sigsp;
  42   struct sigcontext *scp;
  43   struct
  44     {
  45       int signo;
  46       long int sigcode;
  47       struct sigcontext *scp;   /* Points to ctx, below.  */
  48       void *sigreturn_addr;
  49       void *sigreturn_returns_here;
  50       struct sigcontext *return_scp; /* Same; arg to sigreturn.  */
  51       struct sigcontext ctx;
  52       struct hurd_userlink link;
  53     } *stackframe;
  54
  55   if (ss->context)
  56     {
  57       /* We have a previous sigcontext that sigreturn was about
  58          to restore when another signal arrived.  We will just base
  59          our setup on that.  */
  60       if (! _hurdsig_catch_memory_fault (ss->context))
  61         {
  62           memcpy (&state->basic, &ss->context->sc_i386_thread_state,
  63                   sizeof (state->basic));
  64           memcpy (&state->fpu, &ss->context->sc_i386_float_state,
  65                   sizeof (state->fpu));
  66           state->set |= (1 << i386_THREAD_STATE) | (1 << i386_FLOAT_STATE);
  67         }
  68     }
  69
  70   if (! machine_get_basic_state (ss->thread, state))
  71     return NULL;
  72
  73   /* Save the original SP in the gratuitous `esp' slot.
  74      We may need to reset the SP (the `uesp' slot) to avoid clobbering an
  75      interrupted RPC frame.  */
  76   state->basic.esp = state->basic.uesp;
  77
  78   if ((ss->actions[signo].sa_flags & SA_ONSTACK) &&
  79       !(ss->sigaltstack.ss_flags & (SS_DISABLE|SS_ONSTACK)))
  80     {
  81       sigsp = ss->sigaltstack.ss_sp + ss->sigaltstack.ss_size;
  82       ss->sigaltstack.ss_flags |= SS_ONSTACK;
  83       /* XXX need to set up base of new stack for
  84          per-thread variables, cthreads.  */
  85     }
  86   /* This code has intimate knowledge of the special mach_msg system call
  87      done in intr-msg.c; that code does (see intr-msg.h):
  88                                         movl %esp, %ecx
  89                                         leal ARGS, %esp
  90         _hurd_intr_rpc_msg_cx_sp:       movl $-25, %eax
  91         _hurd_intr_rpc_msg_do_trap:     lcall $7, $0
  92         _hurd_intr_rpc_msg_in_trap:     movl %ecx, %esp
  93         _hurd_intr_rpc_msg_sp_restored:
  94      We must check for the window during which %esp points at the
  95      mach_msg arguments.  The space below until %ecx is used by
  96      the _hurd_intr_rpc_mach_msg frame, and must not be clobbered.  */
  97   else if (state->basic.eip >= (int) &_hurd_intr_rpc_msg_cx_sp &&
  98            state->basic.eip < (int) &_hurd_intr_rpc_msg_sp_restored)
  99     /* The SP now points at the mach_msg args, but there is more stack
 100        space used below it.  The real SP is saved in %ecx; we must push the
 101        new frame below there, and restore that value as the SP on
 102        sigreturn.  */
 103     sigsp = (char *) (state->basic.uesp = state->basic.ecx);
 104   else
 105     sigsp = (char *) state->basic.uesp;
 106
 107   /* Push the arguments to call `trampoline' on the stack.  */
 108   sigsp -= sizeof (*stackframe);
 109   stackframe = sigsp;
 110
 111   if (_hurdsig_catch_memory_fault (stackframe))
 112     {
 113       /* We got a fault trying to write the stack frame.
 114          We cannot set up the signal handler.
 115          Returning NULL tells our caller, who will nuke us with a SIGILL.  */
 116       return NULL;
 117     }
 118   else
 119     {
 120       int ok;
 121
 122       extern void _hurdsig_longjmp_from_handler (void *, jmp_buf, int);
 123
 124       /* Add a link to the thread's active-resources list.  We mark this as
 125          the only user of the "resource", so the cleanup function will be
 126          called by any longjmp which is unwinding past the signal frame.
 127          The cleanup function (in sigunwind.c) will make sure that all the
 128          appropriate cleanups done by sigreturn are taken care of.  */
 129       stackframe->link.cleanup = &_hurdsig_longjmp_from_handler;
 130       stackframe->link.cleanup_data = &stackframe->ctx;
 131       stackframe->link.resource.next = NULL;
 132       stackframe->link.resource.prevp = NULL;
 133       stackframe->link.thread.next = ss->active_resources;
 134       stackframe->link.thread.prevp = &ss->active_resources;
 135       if (stackframe->link.thread.next)
 136         stackframe->link.thread.next->thread.prevp
 137           = &stackframe->link.thread.next;
 138       ss->active_resources = &stackframe->link;
 139
 140       /* Set up the arguments for the signal handler.  */
 141       stackframe->signo = signo;
 142       stackframe->sigcode = detail->code;
 143       stackframe->scp = stackframe->return_scp = scp = &stackframe->ctx;
 144       stackframe->sigreturn_addr = &__sigreturn;
 145       stackframe->sigreturn_returns_here = firewall; /* Crash on return.  */
 146
 147       /* Set up the sigcontext from the current state of the thread.  */
 148
 149       scp->sc_onstack = ss->sigaltstack.ss_flags & SS_ONSTACK ? 1 : 0;
 150
 151       /* struct sigcontext is laid out so that starting at sc_gs mimics a
 152          struct i386_thread_state.  */
 153       memcpy (&scp->sc_i386_thread_state,
 154               &state->basic, sizeof (state->basic));
 155
 156       /* struct sigcontext is laid out so that starting at sc_fpkind mimics
 157          a struct i386_float_state.  */
 158       ok = machine_get_state (ss->thread, state, i386_FLOAT_STATE,
 159                               &state->fpu, &scp->sc_i386_float_state,
 160                               sizeof (state->fpu));
 161
 162       _hurdsig_end_catch_fault ();
 163
 164       if (! ok)
 165         return NULL;
 166     }
 167
 168   /* Modify the thread state to call the trampoline code on the new stack.  */
 169   if (rpc_wait)
 170     {
 171       /* The signalee thread was blocked in a mach_msg_trap system call,
 172          still waiting for a reply.  We will have it run the special
 173          trampoline code which retries the message receive before running
 174          the signal handler.
 175
 176          To do this we change the OPTION argument on its stack to enable only
 177          message reception, since the request message has already been
 178          sent.  */
 179
 180       struct mach_msg_trap_args *args = (void *) state->basic.esp;
 181
 182       if (_hurdsig_catch_memory_fault (args))
 183         {
 184           /* Faulted accessing ARGS.  Bomb.  */
 185           return NULL;
 186         }
 187
 188       assert (args->option & MACH_RCV_MSG);
 189       /* Disable the message-send, since it has already completed.  The
 190          calls we retry need only wait to receive the reply message.  */
 191       args->option &= ~MACH_SEND_MSG;
 192
 193       /* Limit the time to receive the reply message, in case the server
 194          claimed that `interrupt_operation' succeeded but in fact the RPC
 195          is hung.  */
 196       args->option |= MACH_RCV_TIMEOUT;
 197       args->timeout = _hurd_interrupted_rpc_timeout;
 198
 199       _hurdsig_end_catch_fault ();
 200
 201       state->basic.eip = (int) rpc_wait_trampoline;
 202       /* The reply-receiving trampoline code runs initially on the original
 203          user stack.  We pass it the signal stack pointer in %ebx.  */
 204       state->basic.uesp = state->basic.esp; /* Restore mach_msg syscall SP.  */
 205       state->basic.ebx = (int) sigsp;
 206       /* After doing the message receive, the trampoline code will need to
 207          update the %eax value to be restored by sigreturn.  To simplify
 208          the assembly code, we pass the address of its slot in SCP to the
 209          trampoline code in %ecx.  */
 210       state->basic.ecx = (int) &scp->sc_eax;
 211     }
 212   else
 213     {
 214       state->basic.eip = (int) trampoline;
 215       state->basic.uesp = (int) sigsp;
 216     }
 217   /* We pass the handler function to the trampoline code in %edx.  */
 218   state->basic.edx = (int) handler;
 219
 220   /* The x86 ABI says the DF bit is clear on entry to any function.  */
 221   state->basic.efl &= ~EFL_DF;
 222
 223   return scp;
 224 }
 225
 226 /* The trampoline code follows.  This used to be located inside
 227    _hurd_setup_sighandler, but was optimized away by gcc 2.95.  */
 228
 229 asm ("rpc_wait_trampoline:\n");
 230   /* This is the entry point when we have an RPC reply message to receive
 231      before running the handler.  The MACH_MSG_SEND bit has already been
 232      cleared in the OPTION argument on our stack.  The interrupted user
 233      stack pointer has not been changed, so the system call can find its
 234      arguments; the signal stack pointer is in %ebx.  For our convenience,
 235      %ecx points to the sc_eax member of the sigcontext.  */
 236 asm (/* Retry the interrupted mach_msg system call.  */
 237      "movl $-25, %eax\n"        /* mach_msg_trap */
 238      "lcall $7, $0\n"
 239      /* When the sigcontext was saved, %eax was MACH_RCV_INTERRUPTED.  But
 240         now the message receive has completed and the original caller of
 241         the RPC (i.e. the code running when the signal arrived) needs to
 242         see the final return value of the message receive in %eax.  So
 243         store the new %eax value into the sc_eax member of the sigcontext
 244         (whose address is in %ecx to make this code simpler).  */
 245      "movl %eax, (%ecx)\n"
 246      /* Switch to the signal stack.  */
 247      "movl %ebx, %esp\n");
 248
 249  asm ("trampoline:\n");
 250   /* Entry point for running the handler normally.  The arguments to the
 251      handler function are already on the top of the stack:
 252
 253        0(%esp)  SIGNO
 254        4(%esp)  SIGCODE
 255        8(%esp)  SCP
 256      */
 257 asm ("call *%edx\n"             /* Call the handler function.  */
 258      "addl $12, %esp\n"         /* Pop its args.  */
 259      /* The word at the top of stack is &__sigreturn; following are a dummy
 260         word to fill the slot for the address for __sigreturn to return to,
 261         and a copy of SCP for __sigreturn's argument.  "Return" to calling
 262         __sigreturn (SCP); this call never returns.  */
 263      "ret");
 264
 265 asm ("firewall:\n"
 266      "hlt");