src/runtime/x86-darwin-os.c

   1 #ifdef LISP_FEATURE_SB_THREAD
   2 #include <architecture/i386/table.h>
   3 #include <i386/user_ldt.h>
   4 #include <mach/mach_init.h>
   5 #endif
   6
   7 #include "thread.h"
   8 #include "validate.h"
   9 #include "runtime.h"
  10 #include "interrupt.h"
  11 #include "x86-darwin-os.h"
  12 #include "genesis/fdefn.h"
  13
  14 #include <mach/mach.h>
  15 #include <mach/mach_error.h>
  16 #include <mach/mach_types.h>
  17 #include <mach/sync_policy.h>
  18 #include <mach/vm_region.h>
  19 #include <mach/machine/thread_state.h>
  20 #include <mach/machine/thread_status.h>
  21 #include <sys/_types.h>
  22 #include <sys/ucontext.h>
  23 #include <pthread.h>
  24 #include <assert.h>
  25 #include <stdlib.h>
  26 #include <stdio.h>
  27
  28 #ifdef LISP_FEATURE_SB_THREAD
  29
  30 pthread_mutex_t modify_ldt_lock = PTHREAD_MUTEX_INITIALIZER;
  31
  32 void set_data_desc_size(data_desc_t* desc, unsigned long size)
  33 {
  34     desc->limit00 = (size - 1) & 0xffff;
  35     desc->limit16 = ((size - 1) >> 16) &0xf;
  36 }
  37
  38 void set_data_desc_addr(data_desc_t* desc, void* addr)
  39 {
  40     desc->base00 = (unsigned int)addr & 0xffff;
  41     desc->base16 = ((unsigned int)addr & 0xff0000) >> 16;
  42     desc->base24 = ((unsigned int)addr & 0xff000000) >> 24;
  43 }
  44
  45 #endif
  46
  47 #ifdef LISP_FEATURE_MACH_EXCEPTION_HANDLER
  48 kern_return_t mach_thread_init(mach_port_t thread_exception_port);
  49 #endif
  50
  51 int arch_os_thread_init(struct thread *thread) {
  52 #ifdef LISP_FEATURE_SB_THREAD
  53     int n;
  54     sel_t sel;
  55
  56     data_desc_t ldt_entry = { 0, 0, 0, DESC_DATA_WRITE,
  57                               3, 1, 0, DESC_DATA_32B, DESC_GRAN_BYTE, 0 };
  58
  59     set_data_desc_addr(&ldt_entry, thread);
  60     set_data_desc_size(&ldt_entry, dynamic_values_bytes);
  61
  62     thread_mutex_lock(&modify_ldt_lock);
  63     n = i386_set_ldt(LDT_AUTO_ALLOC, (union ldt_entry*) &ldt_entry, 1);
  64
  65     if (n < 0) {
  66         perror("i386_set_ldt");
  67         lose("unexpected i386_set_ldt(..) failure\n");
  68     }
  69     thread_mutex_unlock(&modify_ldt_lock);
  70
  71     FSHOW_SIGNAL((stderr, "/ TLS: Allocated LDT %x\n", n));
  72     sel.index = n;
  73     sel.rpl = USER_PRIV;
  74     sel.ti = SEL_LDT;
  75
  76     __asm__ __volatile__ ("mov %0, %%fs" : : "r"(sel));
  77
  78     thread->tls_cookie=n;
  79     pthread_setspecific(specials,thread);
  80 #endif
  81 #ifdef LISP_FEATURE_MACH_EXCEPTION_HANDLER
  82     mach_thread_init(THREAD_STRUCT_TO_EXCEPTION_PORT(thread));
  83 #endif
  84
  85 #ifdef LISP_FEATURE_C_STACK_IS_CONTROL_STACK
  86     stack_t sigstack;
  87
  88     /* Signal handlers are run on the control stack, so if it is exhausted
  89      * we had better use an alternate stack for whatever signal tells us
  90      * we've exhausted it */
  91     sigstack.ss_sp=((void *) thread)+dynamic_values_bytes;
  92     sigstack.ss_flags=0;
  93     sigstack.ss_size = 32*SIGSTKSZ;
  94     sigaltstack(&sigstack,0);
  95 #endif
  96     return 1;                  /* success */
  97 }
  98
  99 int arch_os_thread_cleanup(struct thread *thread) {
 100 #if defined(LISP_FEATURE_SB_THREAD)
 101     int n = thread->tls_cookie;
 102
 103     /* Set the %%fs register back to 0 and free the ldt by setting it
 104      * to NULL.
 105      */
 106     FSHOW_SIGNAL((stderr, "/ TLS: Freeing LDT %x\n", n));
 107
 108     __asm__ __volatile__ ("mov %0, %%fs" : : "r"(0));
 109     thread_mutex_lock(&modify_ldt_lock);
 110     i386_set_ldt(n, NULL, 1);
 111     thread_mutex_unlock(&modify_ldt_lock);
 112 #endif
 113     return 1;                  /* success */
 114 }
 115
 116 #ifdef LISP_FEATURE_MACH_EXCEPTION_HANDLER
 117
 118 void sigill_handler(int signal, siginfo_t *siginfo, os_context_t *context);
 119 void sigtrap_handler(int signal, siginfo_t *siginfo, os_context_t *context);
 120 void memory_fault_handler(int signal, siginfo_t *siginfo,
 121                           os_context_t *context);
 122
 123 /* exc_server handles mach exception messages from the kernel and
 124  * calls catch exception raise. We use the system-provided
 125  * mach_msg_server, which, I assume, calls exc_server in a loop.
 126  *
 127  */
 128 extern boolean_t exc_server();
 129
 130 /* This executes in the faulting thread as part of the signal
 131  * emulation.  It is passed a context with the uc_mcontext field
 132  * pointing to a valid block of memory. */
 133 void build_fake_signal_context(os_context_t *context,
 134                                x86_thread_state32_t *thread_state,
 135                                x86_float_state32_t *float_state) {
 136     pthread_sigmask(0, NULL, &context->uc_sigmask);
 137     context->uc_mcontext->SS = *thread_state;
 138     context->uc_mcontext->FS = *float_state;
 139 }
 140
 141 /* This executes in the faulting thread as part of the signal
 142  * emulation.  It is effectively the inverse operation from above. */
 143 void update_thread_state_from_context(x86_thread_state32_t *thread_state,
 144                                       x86_float_state32_t *float_state,
 145                                       os_context_t *context) {
 146     *thread_state = context->uc_mcontext->SS;
 147     *float_state = context->uc_mcontext->FS;
 148     pthread_sigmask(SIG_SETMASK, &context->uc_sigmask, NULL);
 149 }
 150
 151 /* Modify a context to push new data on its stack. */
 152 void push_context(u32 data, x86_thread_state32_t *thread_state)
 153 {
 154     u32 *stack_pointer;
 155
 156     stack_pointer = (u32*) thread_state->ESP;
 157     *(--stack_pointer) = data;
 158     thread_state->ESP = (unsigned int) stack_pointer;
 159 }
 160
 161 void align_context_stack(x86_thread_state32_t *thread_state)
 162 {
 163     /* 16byte align the stack (provided that the stack is, as it
 164      * should be, 4byte aligned. */
 165     while (thread_state->ESP & 15) push_context(0, thread_state);
 166 }
 167
 168 /* Stack allocation starts with a context that has a mod-4 ESP value
 169  * and needs to leave a context with a mod-16 ESP that will restore
 170  * the old ESP value and other register state when activated.  The
 171  * first part of this is the recovery trampoline, which loads ESP from
 172  * EBP, pops EBP, and returns. */
 173 asm("_stack_allocation_recover: movl %ebp, %esp; popl %ebp; ret;");
 174
 175 void open_stack_allocation(x86_thread_state32_t *thread_state)
 176 {
 177     void stack_allocation_recover(void);
 178
 179     push_context(thread_state->EIP, thread_state);
 180     push_context(thread_state->EBP, thread_state);
 181     thread_state->EBP = thread_state->ESP;
 182     thread_state->EIP = (unsigned int) stack_allocation_recover;
 183
 184     align_context_stack(thread_state);
 185 }
 186
 187 /* Stack allocation of data starts with a context with a mod-16 ESP
 188  * value and reserves some space on it by manipulating the ESP
 189  * register. */
 190 void *stack_allocate(x86_thread_state32_t *thread_state, size_t size)
 191 {
 192     /* round up size to 16byte multiple */
 193     size = (size + 15) & -16;
 194
 195     thread_state->ESP = ((u32)thread_state->ESP) - size;
 196
 197     return (void *)thread_state->ESP;
 198 }
 199
 200 /* Arranging to invoke a C function is tricky, as we have to assume
 201  * cdecl calling conventions (caller removes args) and x86/darwin
 202  * alignment requirements.  The simplest way to arrange this,
 203  * actually, is to open a new stack allocation.
 204  * WARNING!!! THIS DOES NOT PRESERVE REGISTERS! */
 205 void call_c_function_in_context(x86_thread_state32_t *thread_state,
 206                                 void *function,
 207                                 int nargs,
 208                                 ...)
 209 {
 210     va_list ap;
 211     int i;
 212     u32 *stack_pointer;
 213
 214     /* Set up to restore stack on exit. */
 215     open_stack_allocation(thread_state);
 216
 217     /* Have to keep stack 16byte aligned on x86/darwin. */
 218     for (i = (3 & -nargs); i; i--) {
 219         push_context(0, thread_state);
 220     }
 221
 222     thread_state->ESP = ((u32)thread_state->ESP) - nargs * 4;
 223     stack_pointer = (u32 *)thread_state->ESP;
 224
 225     va_start(ap, nargs);
 226     for (i = 0; i < nargs; i++) {
 227         //push_context(va_arg(ap, u32), thread_state);
 228         stack_pointer[i] = va_arg(ap, u32);
 229     }
 230     va_end(ap);
 231
 232     push_context(thread_state->EIP, thread_state);
 233     thread_state->EIP = (unsigned int) function;
 234 }
 235
 236 void signal_emulation_wrapper(x86_thread_state32_t *thread_state,
 237                               x86_float_state32_t *float_state,
 238                               int signal,
 239                               siginfo_t *siginfo,
 240                               void (*handler)(int, siginfo_t *, void *))
 241 {
 242
 243     /* CLH: FIXME **NOTE: HACK ALERT!** Ideally, we would allocate
 244      * context and regs on the stack as local variables, but this
 245      * causes problems for the lisp debugger. When it walks the stack
 246      * for a back trace, it sees the 1) address of the local variable
 247      * on the stack and thinks that is a frame pointer to a lisp
 248      * frame, and, 2) the address of the sap that we alloc'ed in
 249      * dynamic space and thinks that is a return address, so it,
 250      * heuristicly (and wrongly), chooses that this should be
 251      * interpreted as a lisp frame instead of as a C frame.
 252      * We can work around this in this case by os_validating the
 253      * context (and regs just for symmetry).
 254      */
 255
 256     os_context_t *context;
 257     mcontext_t *regs;
 258
 259     context = (os_context_t*) os_validate(0, sizeof(os_context_t));
 260     regs = (mcontext_t*) os_validate(0, sizeof(mcontext_t));
 261     context->uc_mcontext = regs;
 262
 263     /* when BSD signals are fired, they mask they signals in sa_mask
 264        which always seem to be the blockable_sigset, for us, so we
 265        need to:
 266        1) save the current sigmask
 267        2) block blockable signals
 268        3) call the signal handler
 269        4) restore the sigmask */
 270
 271     build_fake_signal_context(context, thread_state, float_state);
 272
 273     block_blockable_signals(0, 0);
 274
 275     handler(signal, siginfo, context);
 276
 277     update_thread_state_from_context(thread_state, float_state, context);
 278
 279     os_invalidate((os_vm_address_t)context, sizeof(os_context_t));
 280     os_invalidate((os_vm_address_t)regs, sizeof(mcontext_t));
 281
 282     /* Trap to restore the signal context. */
 283     asm volatile ("movl %0, %%eax; movl %1, %%ebx; .long 0xffff0b0f"
 284                   : : "r" (thread_state), "r" (float_state));
 285 }
 286
 287 /* Convenience wrapper for the above */
 288 void call_handler_on_thread(mach_port_t thread,
 289                             x86_thread_state32_t *thread_state,
 290                             int signal,
 291                             siginfo_t *siginfo,
 292                             void (*handler)(int, siginfo_t *, void *))
 293 {
 294     x86_thread_state32_t new_state;
 295     x86_thread_state32_t *save_thread_state;
 296     x86_float_state32_t *save_float_state;
 297     mach_msg_type_number_t state_count;
 298     siginfo_t *save_siginfo;
 299     kern_return_t ret;
 300     /* Initialize the new state */
 301     new_state = *thread_state;
 302     open_stack_allocation(&new_state);
 303     stack_allocate(&new_state, 256);
 304     /* Save old state */
 305     save_thread_state = (x86_thread_state32_t *)stack_allocate(&new_state, sizeof(*save_thread_state));
 306     *save_thread_state = *thread_state;
 307     /* Save float state */
 308     save_float_state = (x86_float_state32_t *)stack_allocate(&new_state, sizeof(*save_float_state));
 309     state_count = x86_FLOAT_STATE32_COUNT;
 310     if ((ret = thread_get_state(thread,
 311                                 x86_FLOAT_STATE32,
 312                                 (thread_state_t)save_float_state,
 313                                 &state_count)) != KERN_SUCCESS)
 314         lose("thread_get_state (x86_THREAD_STATE32) failed %d\n", ret);
 315     /* Set up siginfo */
 316     save_siginfo = stack_allocate(&new_state, sizeof(*siginfo));
 317     if (siginfo == NULL)
 318         save_siginfo = siginfo;
 319     else
 320         *save_siginfo = *siginfo;
 321     /* Prepare to call */
 322     call_c_function_in_context(&new_state,
 323                                signal_emulation_wrapper,
 324                                5,
 325                                save_thread_state,
 326                                save_float_state,
 327                                signal,
 328                                save_siginfo,
 329                                handler);
 330     /* Update the thread state */
 331     state_count = x86_THREAD_STATE32_COUNT;
 332     if ((ret = thread_set_state(thread,
 333                                 x86_THREAD_STATE32,
 334                                 (thread_state_t)&new_state,
 335                                 state_count)) != KERN_SUCCESS)
 336         lose("thread_set_state (x86_FLOAT_STATE32) failed %d\n", ret);
 337
 338 }
 339
 340 #if defined DUMP_CONTEXT
 341 void dump_context(x86_thread_state32_t *thread_state)
 342 {
 343     int i;
 344     u32 *stack_pointer;
 345
 346     printf("eax: %08lx  ecx: %08lx  edx: %08lx  ebx: %08lx\n",
 347            thread_state->EAX, thread_state->ECX, thread_state->EDX, thread_state->EAX);
 348     printf("esp: %08lx  ebp: %08lx  esi: %08lx  edi: %08lx\n",
 349            thread_state->ESP, thread_state->EBP, thread_state->ESI, thread_state->EDI);
 350     printf("eip: %08lx  eflags: %08lx\n",
 351            thread_state->EIP, thread_state->EFLAGS);
 352     printf("cs: %04hx  ds: %04hx  es: %04hx  "
 353            "ss: %04hx  fs: %04hx  gs: %04hx\n",
 354            thread_state->CS,
 355            thread_state->DS,
 356            thread_state->ES,
 357            thread_state->SS,
 358            thread_state->FS,
 359            thread_state->GS);
 360
 361     stack_pointer = (u32 *)thread_state->ESP;
 362     for (i = 0; i < 48; i+=4) {
 363         printf("%08x:  %08x %08x %08x %08x\n",
 364                thread_state->ESP + (i * 4),
 365                stack_pointer[i],
 366                stack_pointer[i+1],
 367                stack_pointer[i+2],
 368                stack_pointer[i+3]);
 369     }
 370 }
 371 #endif
 372
 373 void
 374 control_stack_exhausted_handler(int signal, siginfo_t *siginfo,
 375                                 os_context_t *context) {
 376
 377     unblock_signals_in_context_and_maybe_warn(context);
 378     arrange_return_to_lisp_function
 379         (context, StaticSymbolFunction(CONTROL_STACK_EXHAUSTED_ERROR));
 380 }
 381
 382 void
 383 undefined_alien_handler(int signal, siginfo_t *siginfo, os_context_t *context) {
 384     arrange_return_to_lisp_function
 385         (context, StaticSymbolFunction(UNDEFINED_ALIEN_VARIABLE_ERROR));
 386 }
 387
 388 kern_return_t
 389 catch_exception_raise(mach_port_t exception_port,
 390                       mach_port_t thread,
 391                       mach_port_t task,
 392                       exception_type_t exception,
 393                       exception_data_t code_vector,
 394                       mach_msg_type_number_t code_count)
 395 {
 396     struct thread *th = (struct thread*) exception_port;
 397     x86_thread_state32_t thread_state;
 398     mach_msg_type_number_t state_count;
 399     vm_address_t region_addr;
 400     vm_size_t region_size;
 401     vm_region_basic_info_data_t region_info;
 402     mach_msg_type_number_t info_count;
 403     mach_port_t region_name;
 404     void *addr = NULL;
 405     int signal = 0;
 406     void (*handler)(int, siginfo_t *, void *) = NULL;
 407     siginfo_t siginfo;
 408     kern_return_t ret;
 409
 410     /* Get state and info */
 411     state_count = x86_THREAD_STATE32_COUNT;
 412     if ((ret = thread_get_state(thread,
 413                                 x86_THREAD_STATE32,
 414                                 (thread_state_t)&thread_state,
 415                                 &state_count)) != KERN_SUCCESS)
 416         lose("thread_get_state (x86_THREAD_STATE32) failed %d\n", ret);
 417     switch (exception) {
 418     case EXC_BAD_ACCESS:
 419         signal = SIGBUS;
 420         /* Check if write protection fault */
 421         if ((code_vector[0] & OS_VM_PROT_ALL) == 0) {
 422             ret = KERN_INVALID_RIGHT;
 423             break;
 424         }
 425         addr = (void*)code_vector[1];
 426         /* Undefined alien */
 427         if (os_trunc_to_page(addr) == undefined_alien_address) {
 428             handler = undefined_alien_handler;
 429             break;
 430         }
 431         /* At stack guard */
 432         if (os_trunc_to_page(addr) == CONTROL_STACK_GUARD_PAGE(th)) {
 433             lower_thread_control_stack_guard_page(th);
 434             handler = control_stack_exhausted_handler;
 435             break;
 436         }
 437         /* Return from stack guard */
 438         if (os_trunc_to_page(addr) == CONTROL_STACK_RETURN_GUARD_PAGE(th)) {
 439             reset_thread_control_stack_guard_page(th);
 440             break;
 441         }
 442         /* Regular memory fault */
 443         handler = memory_fault_handler;
 444         break;
 445     case EXC_BAD_INSTRUCTION:
 446         signal = SIGTRAP;
 447         /* Check if illegal instruction trap */
 448         if (code_vector[0] != EXC_I386_INVOP) {
 449             ret = KERN_INVALID_RIGHT;
 450             break;
 451         }
 452         /* Check if UD2 instruction */
 453         if (*(unsigned short *)thread_state.EIP != 0x0b0f) {
 454             /* KLUDGE: There are two ways we could get here:
 455              * 1) We're executing data and we've hit some truly
 456              *    illegal opcode, of which there are a few, see
 457              *    Intel 64 and IA-32 Architectures
 458              *    Sofware Developer's Manual
 459              *    Volume 3A page 5-34)
 460              * 2) The kernel started an unrelated signal handler
 461              *    before we got a chance to run. The context that
 462              *    caused the exception is saved in a stack frame
 463              *    somewhere down below.
 464              * In either case we rely on the exception to retrigger,
 465              * eventually bailing out if we're spinning on case 2).
 466              */
 467             static mach_port_t last_thread;
 468             static unsigned int last_eip;
 469             if (last_thread == thread && last_eip == thread_state.EIP)
 470                 ret = KERN_INVALID_RIGHT;
 471             else
 472                 ret = KERN_SUCCESS;
 473             last_thread = thread;
 474             last_eip = thread_state.EIP;
 475             break;
 476         }
 477         /* Skip the trap code */
 478         thread_state.EIP += 2;
 479         /* Return from handler? */
 480         if (*(unsigned short *)thread_state.EIP == 0xffff) {
 481             if ((ret = thread_set_state(thread,
 482                                         x86_THREAD_STATE32,
 483                                         (thread_state_t)thread_state.EAX,
 484                                         x86_THREAD_STATE32_COUNT)) != KERN_SUCCESS)
 485                 lose("thread_set_state (x86_THREAD_STATE32) failed %d\n", ret);
 486             if ((ret = thread_set_state(thread,
 487                                         x86_FLOAT_STATE32,
 488                                         (thread_state_t)thread_state.EBX,
 489                                         x86_FLOAT_STATE32_COUNT)) != KERN_SUCCESS)
 490                 lose("thread_set_state (x86_FLOAT_STATE32) failed %d\n", ret);
 491             break;
 492         }
 493         /* Trap call */
 494         handler = sigtrap_handler;
 495         break;
 496     default:
 497         ret = KERN_INVALID_RIGHT;
 498     }
 499     /* Call handler */
 500     if (handler != 0) {
 501       siginfo.si_signo = signal;
 502       siginfo.si_addr = addr;
 503       call_handler_on_thread(thread, &thread_state, signal, &siginfo, handler);
 504     }
 505     return ret;
 506 }
 507
 508 void *
 509 mach_exception_handler(void *port)
 510 {
 511   mach_msg_server(exc_server, 2048, (mach_port_t) port, 0);
 512   /* mach_msg_server should never return, but it should dispatch mach
 513    * exceptions to our catch_exception_raise function
 514    */
 515   lose("mach_msg_server returned");
 516 }
 517
 518 #endif
 519
 520 #ifdef LISP_FEATURE_MACH_EXCEPTION_HANDLER
 521
 522 /* Sets up the thread that will listen for mach exceptions. note that
 523    the exception handlers will be run on this thread. This is
 524    different from the BSD-style signal handling situation in which the
 525    signal handlers run in the relevant thread directly. */
 526
 527 mach_port_t mach_exception_handler_port_set = MACH_PORT_NULL;
 528
 529 pthread_t
 530 setup_mach_exception_handling_thread()
 531 {
 532     kern_return_t ret;
 533     pthread_t mach_exception_handling_thread = NULL;
 534     pthread_attr_t attr;
 535
 536     /* allocate a mach_port for this process */
 537     ret = mach_port_allocate(mach_task_self(),
 538                              MACH_PORT_RIGHT_PORT_SET,
 539                              &mach_exception_handler_port_set);
 540
 541     /* create the thread that will receive the mach exceptions */
 542
 543     FSHOW((stderr, "Creating mach_exception_handler thread!\n"));
 544
 545     pthread_attr_init(&attr);
 546     pthread_create(&mach_exception_handling_thread,
 547                    &attr,
 548                    mach_exception_handler,
 549                    (void*) mach_exception_handler_port_set);
 550     pthread_attr_destroy(&attr);
 551
 552     return mach_exception_handling_thread;
 553 }
 554
 555 /* tell the kernel that we want EXC_BAD_ACCESS exceptions sent to the
 556    exception port (which is being listened to do by the mach
 557    exception handling thread). */
 558 kern_return_t
 559 mach_thread_init(mach_port_t thread_exception_port)
 560 {
 561     kern_return_t ret;
 562     /* allocate a named port for the thread */
 563
 564     FSHOW((stderr, "Allocating mach port %x\n", thread_exception_port));
 565
 566     ret = mach_port_allocate_name(mach_task_self(),
 567                                   MACH_PORT_RIGHT_RECEIVE,
 568                                   thread_exception_port);
 569     if (ret) {
 570         lose("mach_port_allocate_name failed with return_code %d\n", ret);
 571     }
 572
 573     /* establish the right for the thread_exception_port to send messages */
 574     ret = mach_port_insert_right(mach_task_self(),
 575                                  thread_exception_port,
 576                                  thread_exception_port,
 577                                  MACH_MSG_TYPE_MAKE_SEND);
 578     if (ret) {
 579         lose("mach_port_insert_right failed with return_code %d\n", ret);
 580     }
 581
 582     ret = thread_set_exception_ports(mach_thread_self(),
 583                                      EXC_MASK_BAD_ACCESS | EXC_MASK_BAD_INSTRUCTION,
 584                                      thread_exception_port,
 585                                      EXCEPTION_DEFAULT,
 586                                      THREAD_STATE_NONE);
 587     if (ret) {
 588         lose("thread_set_exception_port failed with return_code %d\n", ret);
 589     }
 590
 591     ret = mach_port_move_member(mach_task_self(),
 592                                 thread_exception_port,
 593                                 mach_exception_handler_port_set);
 594     if (ret) {
 595         lose("mach_port_ failed with return_code %d\n", ret);
 596     }
 597
 598     return ret;
 599 }
 600
 601 void
 602 setup_mach_exceptions() {
 603     setup_mach_exception_handling_thread();
 604     mach_thread_init(THREAD_STRUCT_TO_EXCEPTION_PORT(all_threads));
 605 }
 606
 607 pid_t
 608 mach_fork() {
 609     pid_t pid = fork();
 610     if (pid == 0) {
 611         setup_mach_exceptions();
 612         return pid;
 613     } else {
 614         return pid;
 615     }
 616 }
 617
 618 #endif