factor/vm/mach_signal.cpp

// Fault handler information.  MacOSX version.
// Copyright (C) 1993-1999, 2002-2003  Bruno Haible <clisp.org at bruno>

// Copyright (C) 2003  Paolo Bonzini <gnu.org at bonzini>

// Used under BSD license with permission from Paolo Bonzini and Bruno Haible,
// 2005-03-10:

// http://sourceforge.net/mailarchive/message.php?msg_name=200503102200.32002.bruno%40clisp.org

// Modified for Factor by Slava Pestov

#include "master.hpp"

namespace factor {

// The exception port on which our thread listens.
mach_port_t our_exception_port;

// The following sources were used as a *reference* for this exception handling
// code:

// 1. Apple's mach/xnu documentation
// 2. Timothy J. Wood's "Mach Exception Handlers 101" post to the
//    omnigroup's macosx-dev list.
//    http://www.wodeveloper.com/omniLists/macosx-dev/2000/June/msg00137.html

// Modify a suspended thread's thread_state so that when the thread resumes
// executing, the call frame of the current C primitive (if any) is rewound, and
// the appropriate Factor error is thrown from the top-most Factor frame.
void factor_vm::call_fault_handler(exception_type_t exception,
                                   exception_data_type_t code,
                                   MACH_EXC_STATE_TYPE* exc_state,
                                   MACH_THREAD_STATE_TYPE* thread_state,
                                   MACH_FLOAT_STATE_TYPE* float_state) {
  cell handler = 0;

  if (exception == EXC_BAD_ACCESS) {
    set_memory_protection_error(MACH_EXC_STATE_FAULT(exc_state),
                                (cell)MACH_PROGRAM_COUNTER(thread_state));
    handler = (cell)factor::memory_signal_handler_impl;
  } else if (exception == EXC_ARITHMETIC && code != MACH_EXC_INTEGER_DIV) {
    signal_fpu_status = fpu_status(mach_fpu_status(float_state));
    mach_clear_fpu_status(float_state);
    handler = (cell)factor::fp_signal_handler_impl;
  } else {
    switch (exception) {
      case EXC_ARITHMETIC:
        signal_number = SIGFPE;
        break;
      case EXC_BAD_INSTRUCTION:
        signal_number = SIGILL;
        break;
      default:
        signal_number = SIGABRT;
        break;
    }

    handler = (cell)factor::synchronous_signal_handler_impl;
  }

  FACTOR_ASSERT(handler != 0);

  dispatch_signal_handler((cell*)&MACH_STACK_POINTER(thread_state),
                          (cell*)&MACH_PROGRAM_COUNTER(thread_state),
                          (cell)handler);
}

static void call_fault_handler(mach_port_t thread, exception_type_t exception,
                               exception_data_type_t code,
                               MACH_EXC_STATE_TYPE* exc_state,
                               MACH_THREAD_STATE_TYPE* thread_state,
                               MACH_FLOAT_STATE_TYPE* float_state) {
  // Look up the VM instance involved
  THREADHANDLE thread_id = pthread_from_mach_thread_np(thread);
  FACTOR_ASSERT(thread_id);
  std::map<THREADHANDLE, factor_vm*>::const_iterator vm =
      thread_vms.find(thread_id);

  // Handle the exception
  if (vm != thread_vms.end())
    vm->second->call_fault_handler(exception, code, exc_state, thread_state,
                                   float_state);
}

// Handle an exception by invoking the user's fault handler and/or forwarding
// the duty to the previously installed handlers.
extern "C" kern_return_t catch_exception_raise(
    mach_port_t exception_port, mach_port_t thread, mach_port_t task,
    exception_type_t exception, exception_data_t code,
    mach_msg_type_number_t code_count) {
  // 10.6 likes to report exceptions from child processes too. Ignore those
  if (task != mach_task_self())
    return KERN_FAILURE;

  // Get fault information and the faulting thread's register contents..
  // See http://web.mit.edu/darwin/src/modules/xnu/osfmk/man/thread_get_state.html.
  MACH_EXC_STATE_TYPE exc_state;
  mach_msg_type_number_t exc_state_count = MACH_EXC_STATE_COUNT;
  if (thread_get_state(thread, MACH_EXC_STATE_FLAVOR, (natural_t*)&exc_state,
                       &exc_state_count) !=
      KERN_SUCCESS) {
    // The thread is supposed to be suspended while the exception
    // handler is called. This shouldn't fail.
    return KERN_FAILURE;
  }

  MACH_THREAD_STATE_TYPE thread_state;
  mach_msg_type_number_t thread_state_count = MACH_THREAD_STATE_COUNT;
  if (thread_get_state(thread, MACH_THREAD_STATE_FLAVOR,
                       (natural_t*)&thread_state, &thread_state_count) !=
      KERN_SUCCESS) {
    // The thread is supposed to be suspended while the exception
    // handler is called. This shouldn't fail.
    return KERN_FAILURE;
  }

  MACH_FLOAT_STATE_TYPE float_state;
  mach_msg_type_number_t float_state_count = MACH_FLOAT_STATE_COUNT;
  if (thread_get_state(thread, MACH_FLOAT_STATE_FLAVOR,
                       (natural_t*)&float_state, &float_state_count) !=
      KERN_SUCCESS) {
    // The thread is supposed to be suspended while the exception
    // handler is called. This shouldn't fail.
    return KERN_FAILURE;
  }

  // Modify registers so to have the thread resume executing the
  // fault handler
  call_fault_handler(thread, exception, code[0], &exc_state, &thread_state,
                     &float_state);

  // Set the faulting thread's register contents..
  // See http://web.mit.edu/darwin/src/modules/xnu/osfmk/man/thread_set_state.html.
  if (thread_set_state(thread, MACH_FLOAT_STATE_FLAVOR,
                       (natural_t*)&float_state, float_state_count) !=
      KERN_SUCCESS) {
    return KERN_FAILURE;
  }

  if (thread_set_state(thread, MACH_THREAD_STATE_FLAVOR,
                       (natural_t*)&thread_state, thread_state_count) !=
      KERN_SUCCESS) {
    return KERN_FAILURE;
  }

  return KERN_SUCCESS;
}

// The main function of the thread listening for exceptions.
static void* mach_exception_thread(void* arg) {
  for (;;) {
    // These two structures contain some private kernel data. We don't need
    // to access any of it so we don't bother defining a proper struct. The
    // correct definitions are in the xnu source code.
    // Buffer for a message to be received.
    struct {
      mach_msg_header_t head;
      mach_msg_body_t msgh_body;
      char data[1024];
    } msg;
    // Buffer for a reply message.
    struct {
      mach_msg_header_t head;
      char data[1024];
    } reply;

    // Wait for a message on the exception port.
    if (mach_msg(&msg.head, MACH_RCV_MSG | MACH_RCV_LARGE, 0, sizeof(msg),
                 our_exception_port, MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL) !=
        MACH_MSG_SUCCESS) {
      abort();
    }

    // Handle the message: Call exc_server, which will call
    // catch_exception_raise and produce a reply message.
    exc_server(&msg.head, &reply.head);

    // Send the reply.
    if (mach_msg(&reply.head, MACH_SEND_MSG, reply.head.msgh_size, 0,
                 MACH_PORT_NULL, MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL) !=
        MACH_MSG_SUCCESS) {
      abort();
    }
  }
  return NULL;  // quiet warning
}

// Initialize the Mach exception handler thread.
void mach_initialize() {
  mach_port_t self;
  exception_mask_t mask;

  self = mach_task_self();

  // Allocate a port on which the thread shall listen for exceptions.
  if (mach_port_allocate(self, MACH_PORT_RIGHT_RECEIVE, &our_exception_port) !=
      KERN_SUCCESS)
    fatal_error("mach_port_allocate() failed", 0);

  // See
  // http://web.mit.edu/darwin/src/modules/xnu/osfmk/man/mach_port_insert_right.html.

  if (mach_port_insert_right(self, our_exception_port, our_exception_port,
                             MACH_MSG_TYPE_MAKE_SEND) !=
      KERN_SUCCESS)
    fatal_error("mach_port_insert_right() failed", 0);

  // The exceptions we want to catch.
  mask = EXC_MASK_BAD_ACCESS | EXC_MASK_BAD_INSTRUCTION | EXC_MASK_ARITHMETIC;

  // Create the thread listening on the exception port.
  start_thread(mach_exception_thread, NULL);

  // Replace the exception port info for these exceptions with our own.
  // Note that we replace the exception port for the entire task, not only
  // for a particular thread. This has the effect that when our exception
  // port gets the message, the thread specific exception port has already
  // been asked, and we don't need to bother about it. See
  // http://web.mit.edu/darwin/src/modules/xnu/osfmk/man/task_set_exception_ports.html.
  if (task_set_exception_ports(self, mask, our_exception_port,
                               EXCEPTION_DEFAULT, MACHINE_THREAD_STATE) !=
      KERN_SUCCESS)
    fatal_error("task_set_exception_ports() failed", 0);
}

}