sysdeps/mach/hurd/i386/trampoline.c

   1 /* Set thread_state for sighandler, and sigcontext to recover.  i386 version.
   2    Copyright (C) 1994-2018 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_cx_sp;
  39   extern const void _hurd_intr_rpc_msg_sp_restored;
  40   void *volatile sigsp;
  41   struct sigcontext *scp;
  42   struct
  43     {
  44       int signo;
  45       long int sigcode;
  46       struct sigcontext *scp;   /* Points to ctx, below.  */
  47       void *sigreturn_addr;
  48       void *sigreturn_returns_here;
  49       struct sigcontext *return_scp; /* Same; arg to sigreturn.  */
  50       struct sigcontext ctx;
  51       struct hurd_userlink link;
  52     } *stackframe;
  53
  54   if (ss->context)
  55     {
  56       /* We have a previous sigcontext that sigreturn was about
  57          to restore when another signal arrived.  We will just base
  58          our setup on that.  */
  59       if (! _hurdsig_catch_memory_fault (ss->context))
  60         {
  61           memcpy (&state->basic, &ss->context->sc_i386_thread_state,
  62                   sizeof (state->basic));
  63           memcpy (&state->fpu, &ss->context->sc_i386_float_state,
  64                   sizeof (state->fpu));
  65           state->set |= (1 << i386_REGS_SEGS_STATE) | (1 << i386_FLOAT_STATE);
  66         }
  67     }
  68
  69   if (! machine_get_basic_state (ss->thread, state))
  70     return NULL;
  71
  72   /* Save the original SP in the gratuitous `esp' slot.
  73      We may need to reset the SP (the `uesp' slot) to avoid clobbering an
  74      interrupted RPC frame.  */
  75   state->basic.esp = state->basic.uesp;
  76
  77   if ((ss->actions[signo].sa_flags & SA_ONSTACK) &&
  78       !(ss->sigaltstack.ss_flags & (SS_DISABLE|SS_ONSTACK)))
  79     {
  80       sigsp = ss->sigaltstack.ss_sp + ss->sigaltstack.ss_size;
  81       ss->sigaltstack.ss_flags |= SS_ONSTACK;
  82     }
  83   /* This code has intimate knowledge of the special mach_msg system call
  84      done in intr-msg.c; that code does (see intr-msg.h):
  85                                         movl %esp, %ecx
  86                                         leal ARGS, %esp
  87         _hurd_intr_rpc_msg_cx_sp:       movl $-25, %eax
  88         _hurd_intr_rpc_msg_do_trap:     lcall $7, $0
  89         _hurd_intr_rpc_msg_in_trap:     movl %ecx, %esp
  90         _hurd_intr_rpc_msg_sp_restored:
  91      We must check for the window during which %esp points at the
  92      mach_msg arguments.  The space below until %ecx is used by
  93      the _hurd_intr_rpc_mach_msg frame, and must not be clobbered.  */
  94   else if (state->basic.eip >= (int) &_hurd_intr_rpc_msg_cx_sp &&
  95            state->basic.eip < (int) &_hurd_intr_rpc_msg_sp_restored)
  96     /* The SP now points at the mach_msg args, but there is more stack
  97        space used below it.  The real SP is saved in %ecx; we must push the
  98        new frame below there, and restore that value as the SP on
  99        sigreturn.  */
 100     sigsp = (char *) (state->basic.uesp = state->basic.ecx);
 101   else
 102     sigsp = (char *) state->basic.uesp;
 103
 104   /* Push the arguments to call `trampoline' on the stack.  */
 105   sigsp -= sizeof (*stackframe);
 106   stackframe = sigsp;
 107
 108   if (_hurdsig_catch_memory_fault (stackframe))
 109     {
 110       /* We got a fault trying to write the stack frame.
 111          We cannot set up the signal handler.
 112          Returning NULL tells our caller, who will nuke us with a SIGILL.  */
 113       return NULL;
 114     }
 115   else
 116     {
 117       int ok;
 118
 119       extern void _hurdsig_longjmp_from_handler (void *, jmp_buf, int);
 120
 121       /* Add a link to the thread's active-resources list.  We mark this as
 122          the only user of the "resource", so the cleanup function will be
 123          called by any longjmp which is unwinding past the signal frame.
 124          The cleanup function (in sigunwind.c) will make sure that all the
 125          appropriate cleanups done by sigreturn are taken care of.  */
 126       stackframe->link.cleanup = &_hurdsig_longjmp_from_handler;
 127       stackframe->link.cleanup_data = &stackframe->ctx;
 128       stackframe->link.resource.next = NULL;
 129       stackframe->link.resource.prevp = NULL;
 130       stackframe->link.thread.next = ss->active_resources;
 131       stackframe->link.thread.prevp = &ss->active_resources;
 132       if (stackframe->link.thread.next)
 133         stackframe->link.thread.next->thread.prevp
 134           = &stackframe->link.thread.next;
 135       ss->active_resources = &stackframe->link;
 136
 137       /* Set up the arguments for the signal handler.  */
 138       stackframe->signo = signo;
 139       stackframe->sigcode = detail->code;
 140       stackframe->scp = stackframe->return_scp = scp = &stackframe->ctx;
 141       stackframe->sigreturn_addr = &__sigreturn;
 142       stackframe->sigreturn_returns_here = firewall; /* Crash on return.  */
 143
 144       /* Set up the sigcontext from the current state of the thread.  */
 145
 146       scp->sc_onstack = ss->sigaltstack.ss_flags & SS_ONSTACK ? 1 : 0;
 147
 148       /* struct sigcontext is laid out so that starting at sc_gs mimics a
 149          struct i386_thread_state.  */
 150       memcpy (&scp->sc_i386_thread_state,
 151               &state->basic, sizeof (state->basic));
 152
 153       /* struct sigcontext is laid out so that starting at sc_fpkind mimics
 154          a struct i386_float_state.  */
 155       ok = machine_get_state (ss->thread, state, i386_FLOAT_STATE,
 156                               &state->fpu, &scp->sc_i386_float_state,
 157                               sizeof (state->fpu));
 158
 159       _hurdsig_end_catch_fault ();
 160
 161       if (! ok)
 162         return NULL;
 163     }
 164
 165   /* Modify the thread state to call the trampoline code on the new stack.  */
 166   if (rpc_wait)
 167     {
 168       /* The signalee thread was blocked in a mach_msg_trap system call,
 169          still waiting for a reply.  We will have it run the special
 170          trampoline code which retries the message receive before running
 171          the signal handler.
 172
 173          To do this we change the OPTION argument on its stack to enable only
 174          message reception, since the request message has already been
 175          sent.  */
 176
 177       struct mach_msg_trap_args *args = (void *) state->basic.esp;
 178
 179       if (_hurdsig_catch_memory_fault (args))
 180         {
 181           /* Faulted accessing ARGS.  Bomb.  */
 182           return NULL;
 183         }
 184
 185       assert (args->option & MACH_RCV_MSG);
 186       /* Disable the message-send, since it has already completed.  The
 187          calls we retry need only wait to receive the reply message.  */
 188       args->option &= ~MACH_SEND_MSG;
 189
 190       /* Limit the time to receive the reply message, in case the server
 191          claimed that `interrupt_operation' succeeded but in fact the RPC
 192          is hung.  */
 193       args->option |= MACH_RCV_TIMEOUT;
 194       args->timeout = _hurd_interrupted_rpc_timeout;
 195
 196       _hurdsig_end_catch_fault ();
 197
 198       state->basic.eip = (int) rpc_wait_trampoline;
 199       /* The reply-receiving trampoline code runs initially on the original
 200          user stack.  We pass it the signal stack pointer in %ebx.  */
 201       state->basic.uesp = state->basic.esp; /* Restore mach_msg syscall SP.  */
 202       state->basic.ebx = (int) sigsp;
 203       /* After doing the message receive, the trampoline code will need to
 204          update the %eax value to be restored by sigreturn.  To simplify
 205          the assembly code, we pass the address of its slot in SCP to the
 206          trampoline code in %ecx.  */
 207       state->basic.ecx = (int) &scp->sc_eax;
 208     }
 209   else
 210     {
 211       state->basic.eip = (int) trampoline;
 212       state->basic.uesp = (int) sigsp;
 213     }
 214   /* We pass the handler function to the trampoline code in %edx.  */
 215   state->basic.edx = (int) handler;
 216
 217   /* The x86 ABI says the DF bit is clear on entry to any function.  */
 218   state->basic.efl &= ~EFL_DF;
 219
 220   return scp;
 221 }
 222
 223 /* The trampoline code follows.  This used to be located inside
 224    _hurd_setup_sighandler, but was optimized away by gcc 2.95.  */
 225
 226 asm ("rpc_wait_trampoline:\n");
 227   /* This is the entry point when we have an RPC reply message to receive
 228      before running the handler.  The MACH_MSG_SEND bit has already been
 229      cleared in the OPTION argument on our stack.  The interrupted user
 230      stack pointer has not been changed, so the system call can find its
 231      arguments; the signal stack pointer is in %ebx.  For our convenience,
 232      %ecx points to the sc_eax member of the sigcontext.  */
 233 asm (/* Retry the interrupted mach_msg system call.  */
 234      "movl $-25, %eax\n"        /* mach_msg_trap */
 235      "lcall $7, $0\n"
 236      /* When the sigcontext was saved, %eax was MACH_RCV_INTERRUPTED.  But
 237         now the message receive has completed and the original caller of
 238         the RPC (i.e. the code running when the signal arrived) needs to
 239         see the final return value of the message receive in %eax.  So
 240         store the new %eax value into the sc_eax member of the sigcontext
 241         (whose address is in %ecx to make this code simpler).  */
 242      "movl %eax, (%ecx)\n"
 243      /* Switch to the signal stack.  */
 244      "movl %ebx, %esp\n");
 245
 246  asm ("trampoline:\n");
 247   /* Entry point for running the handler normally.  The arguments to the
 248      handler function are already on the top of the stack:
 249
 250        0(%esp)  SIGNO
 251        4(%esp)  SIGCODE
 252        8(%esp)  SCP
 253      */
 254 asm ("call *%edx\n"             /* Call the handler function.  */
 255      "addl $12, %esp\n"         /* Pop its args.  */
 256      /* The word at the top of stack is &__sigreturn; following are a dummy
 257         word to fill the slot for the address for __sigreturn to return to,
 258         and a copy of SCP for __sigreturn's argument.  "Return" to calling
 259         __sigreturn (SCP); this call never returns.  */
 260      "ret");
 261
 262 asm ("firewall:\n"
 263      "hlt");