macosx-nat-watchpoint.c   [plain text]

/* Mac OS X support for GDB, the GNU debugger.
   Copyright 1997, 1998, 1999, 2000, 2001, 2002
   Free Software Foundation, Inc.

   Contributed by Apple Computer, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include "defs.h"
#include "inferior.h"
#include "target.h"
#include "symfile.h"
#include "symtab.h"
#include "objfiles.h"
#include "gdbcmd.h"
#include "gdbcore.h"
#include "gdbthread.h"

#include "macosx-nat-watchpoint.h"
#include "macosx-nat-dyld.h"
#include "macosx-nat-inferior.h"
#include "macosx-nat-mutils.h"
#include "macosx-nat-sigthread.h"
#include "macosx-nat-threads.h"
#include "macosx-xdep.h"

#include <AvailabilityMacros.h>

#include <mach/mach_vm.h>

extern macosx_inferior_status *macosx_status;

/* Our implementation of hardware watchpoints involves making memory
   pages write-protected.  We must remember a page's original permissions,
   and we must also know when it is appropriate to restore a page's
   permissions to its original state.

   We use a "dictionary" of hardware-watched pages to do this.  Each
   hardware-watched page is recorded in the dictionary.  Each page's
   dictionary entry contains the original permissions and a reference
   count.  Pages are hashed into the dictionary by their start address.

   When hardware watchpoint is set on page X for the first time, page X
   is added to the dictionary with a reference count of 1.  If other
   hardware watchpoints are subsequently set on page X, its reference
   count is incremented.  When hardware watchpoints are removed from
   page X, its reference count is decremented.  If a page's reference
   count drops to 0, it's permissions are restored and the page's entry
   is thrown out of the dictionary.
 */
typedef struct memory_page
{
  CORE_ADDR page_start;
  int reference_count;
  int original_permissions;
  struct memory_page *next;
  struct memory_page *previous;
}
memory_page_t;

#define MEMORY_PAGE_DICTIONARY_BUCKET_COUNT  128

static struct
{
  LONGEST page_count;
  int page_size;
  int page_protections_allowed;
  /* These are just the heads of chains of actual page descriptors. */
  memory_page_t buckets[MEMORY_PAGE_DICTIONARY_BUCKET_COUNT];
}
memory_page_dictionary;

static memory_page_t *get_dictionary_entry_of_page (int pid,
                                                    CORE_ADDR page_start);

static void remove_dictionary_entry_of_page (int pid, memory_page_t * page);

static void
require_memory_page_dictionary (void)
{
  int i;

  /* Is the memory page dictionary ready for use?  If so, we're done. */
  if (memory_page_dictionary.page_count >= (LONGEST) 0)
    return;

  /* Else, initialize it. */
  memory_page_dictionary.page_count = (LONGEST) 0;
  memory_page_dictionary.page_size = 4096;

  for (i = 0; i < MEMORY_PAGE_DICTIONARY_BUCKET_COUNT; i++)
    {
      memory_page_dictionary.buckets[i].page_start = (CORE_ADDR) 0;
      memory_page_dictionary.buckets[i].reference_count = 0;
      memory_page_dictionary.buckets[i].next = NULL;
      memory_page_dictionary.buckets[i].previous = NULL;
    }
}

/* Write-protect the memory page that starts at this address.

   Returns the original permissions of the page.
 */
static int
write_protect_page (int pid, CORE_ADDR page_start)
{
  mach_vm_address_t r_start;
  mach_vm_size_t r_size;
  mach_port_t r_object_name;

  vm_region_basic_info_data_t r_data;
  mach_msg_type_number_t r_info_size;

  kern_return_t kret;

  r_start = page_start;
  r_info_size = VM_REGION_BASIC_INFO_COUNT_64;
  kret = mach_vm_region (macosx_status->task, &r_start, &r_size,
			 VM_REGION_BASIC_INFO_64,
			 (vm_region_info_t) & r_data, &r_info_size,
			 &r_object_name);
  if (kret != KERN_SUCCESS)
    return -1;
  if (r_start != page_start)
    return -1;

  if (memory_page_dictionary.page_protections_allowed)
    {

      kret =
        mach_vm_protect (macosx_status->task, r_start, 4096, 0,
			 r_data.protection & ~VM_PROT_WRITE);
      if (kret != KERN_SUCCESS)
        return -1;
    }

  return r_data.protection;
}

/* Unwrite-protect the memory page that starts at this address, restoring
   (what we must assume are) its original permissions.
 */
static void
unwrite_protect_page (int pid, CORE_ADDR page_start, int original_permissions)
{
  kern_return_t kret;
  kret =
    mach_vm_protect (macosx_status->task, page_start, 4096, 0,
                original_permissions);
}


/* Memory page-protections are used to implement "hardware" watchpoints
   on HP-UX.

   For every memory page that is currently being watched (i.e., that
   presently should be write-protected), write-protect it.
 */
void
macosx_enable_page_protection_events (int pid)
{
  int bucket;

  memory_page_dictionary.page_protections_allowed = 1;

  for (bucket = 0; bucket < MEMORY_PAGE_DICTIONARY_BUCKET_COUNT; bucket++)
    {
      memory_page_t *page;

      page = memory_page_dictionary.buckets[bucket].next;
      while (page != NULL)
        {
          page->original_permissions =
            write_protect_page (pid, page->page_start);
          page = page->next;
        }
    }
}

/* Memory page-protections are used to implement "hardware" watchpoints
   on HP-UX.

   For every memory page that is currently being watched (i.e., that
   presently is or should be write-protected), un-write-protect it.
 */
void
macosx_disable_page_protection_events (int pid)
{
  int bucket;

  for (bucket = 0; bucket < MEMORY_PAGE_DICTIONARY_BUCKET_COUNT; bucket++)
    {
      memory_page_t *page;

      page = memory_page_dictionary.buckets[bucket].next;
      while (page != NULL)
        {
          unwrite_protect_page (pid, page->page_start,
                                page->original_permissions);
          page = page->next;
        }
    }

  memory_page_dictionary.page_protections_allowed = 0;
}

/* The address range beginning with START and ending with START+LEN-1
   (inclusive) is to be watched via page-protection by a new watchpoint.
   Set protection for all pages that overlap that range.

   Note that our caller sets TYPE to:
   0 for a bp_hardware_watchpoint,
   1 for a bp_read_watchpoint,
   2 for a bp_access_watchpoint

   (Yes, this is intentionally (though lord only knows why) different
   from the TYPE that is passed to hppa_remove_hw_watchpoint.)
 */
static int
hppa_insert_hw_watchpoint (int pid, CORE_ADDR start, LONGEST len, int type)
{
  CORE_ADDR page_start;
  int dictionary_was_empty;
  int page_size;
  int page_id;
  LONGEST range_size_in_pages;

  if (type != 0)
    error ("read or access hardware watchpoints not supported on HP-UX");

  /* Examine all pages in the address range. */
  require_memory_page_dictionary ();

  dictionary_was_empty = (memory_page_dictionary.page_count == (LONGEST) 0);

  page_size = memory_page_dictionary.page_size;
  page_start = (start / page_size) * page_size;
  range_size_in_pages =
    ((LONGEST) len + (LONGEST) page_size - 1) / (LONGEST) page_size;

  for (page_id = 0; page_id < range_size_in_pages;
       page_id++, page_start += page_size)
    {
      memory_page_t *page;

      /* This gets the page entered into the dictionary if it was
         not already entered.
       */
      page = get_dictionary_entry_of_page (pid, page_start);
      page->reference_count++;
    }

  /* Our implementation depends on seeing calls to kernel code, for the
     following reason.  Here we ask to be notified of syscalls.

     When a protected page is accessed by user code, HP-UX raises a SIGBUS.
     Fine.

     But when kernel code accesses the page, it doesn't give a SIGBUS.
     Rather, the system call that touched the page fails, with errno=EFAULT.
     Not good for us.

     We could accomodate this "feature" by asking to be notified of syscall
     entries & exits; upon getting an entry event, disabling page-protections;
     upon getting an exit event, reenabling page-protections and then checking
     if any watchpoints triggered.

     However, this turns out to be a real performance loser.  syscalls are
     usually a frequent occurrence.  Having to unprotect-reprotect all watched
     pages, and also to then read all watched memory locations and compare for
     triggers, can be quite expensive.

     Instead, we'll only ask to be notified of syscall exits.  When we get
     one, we'll check whether errno is set.  If not, or if it's not EFAULT,
     we can just continue the inferior.

     If errno is set upon syscall exit to EFAULT, we must perform some fairly
     hackish stuff to determine whether the failure really was due to a
     page-protect trap on a watched location.
   */
#if 0
  if (dictionary_was_empty)
    hppa_enable_syscall_events (pid);
#endif

  return 1;
}


/* The address range beginning with START and ending with START+LEN-1
   (inclusive) was being watched via page-protection by a watchpoint
   which has been removed.  Remove protection for all pages that
   overlap that range, which are not also being watched by other
   watchpoints.
 */
static int
hppa_remove_hw_watchpoint (int pid, CORE_ADDR start, LONGEST len,
                           enum bptype type)
{
  CORE_ADDR page_start;
  int dictionary_is_empty;
  int page_size;
  int page_id;
  LONGEST range_size_in_pages;

  if (type != 0)
    error ("read or access hardware watchpoints not supported on HP-UX");

  /* Examine all pages in the address range. */
  require_memory_page_dictionary ();

  page_size = memory_page_dictionary.page_size;
  page_start = (start / page_size) * page_size;
  range_size_in_pages =
    ((LONGEST) len + (LONGEST) page_size - 1) / (LONGEST) page_size;

  for (page_id = 0; page_id < range_size_in_pages;
       page_id++, page_start += page_size)
    {
      memory_page_t *page;

      page = get_dictionary_entry_of_page (pid, page_start);
      page->reference_count--;

      /* Was this the last reference of this page?  If so, then we
         must scrub the entry from the dictionary, and also restore
         the page's original permissions.
       */
      if (page->reference_count == 0)
        remove_dictionary_entry_of_page (pid, page);
    }

  dictionary_is_empty = (memory_page_dictionary.page_count == (LONGEST) 0);

  /* If write protections are currently disallowed, then that implies that
     wait_for_inferior believes that the inferior is within a system call.
     Since we want to see both syscall entry and return, it's clearly not
     good to disable syscall events in this state!

     ??rehrauer: Yeah, it'd be better if we had a specific flag that said,
     "inferior is between syscall events now".  Oh well.
   */
#if 0
  if (dictionary_is_empty && memory_page_dictionary.page_protections_allowed)
    hppa_disable_syscall_events (pid);
#endif

  return 1;
}


/* Could we implement a watchpoint of this type via our available
   hardware support?

   This query does not consider whether a particular address range
   could be so watched, but just whether support is generally available
   for such things.  See hppa_range_profitable_for_hw_watchpoint for a
   query that answers whether a particular range should be watched via
   hardware support.
 */
int
macosx_can_use_hw_watchpoint (int type, int cnt, int ot)
{
  return (type == bp_hardware_watchpoint);
}

int
macosx_region_ok_for_hw_watchpoint (CORE_ADDR start, LONGEST len)
{
  return 1;
}

/* Given the starting address of a memory page, hash it to a bucket in
   the memory page dictionary. */

static int
get_dictionary_bucket_of_page (CORE_ADDR page_start)
{
  CORE_ADDR hash;

  hash = (page_start / memory_page_dictionary.page_size);
  hash = hash % MEMORY_PAGE_DICTIONARY_BUCKET_COUNT;

  return hash;
}

/* Given a memory page's starting address, get (i.e., find an existing
   or create a new) dictionary entry for the page.  The page will be
   write-protected when this function returns, but may have a reference
   count of 0 (if the page was newly-added to the dictionary).  */

static memory_page_t *
get_dictionary_entry_of_page (int pid, CORE_ADDR page_start)
{
  int bucket;
  memory_page_t *page = NULL;
  memory_page_t *previous_page = NULL;

  /* We're going to be using the dictionary now, than-kew. */
  require_memory_page_dictionary ();

  /* Try to find an existing dictionary entry for this page.  Hash
     on the page's starting address. */

  bucket = get_dictionary_bucket_of_page (page_start);
  page = &memory_page_dictionary.buckets[bucket];
  while (page != NULL)
    {
      if (page->page_start == page_start)
        break;
      previous_page = page;
      page = page->next;
    }

  /* Did we find a dictionary entry for this page?  If not, then
     add it to the dictionary now. */

  if (page == NULL)
    {
      /* Create a new entry. */
      page = (memory_page_t *) xmalloc (sizeof (memory_page_t));
      page->page_start = page_start;
      page->reference_count = 0;
      page->next = NULL;
      page->previous = NULL;

      /* We'll write-protect the page now, if that's allowed. */
      page->original_permissions = write_protect_page (pid, page_start);

      /* Add the new entry to the dictionary. */
      page->previous = previous_page;
      previous_page->next = page;

      memory_page_dictionary.page_count++;
    }

  return page;
}

static void
remove_dictionary_entry_of_page (int pid, memory_page_t * page)
{
  /* Restore the page's original permissions. */
  unwrite_protect_page (pid, page->page_start, page->original_permissions);

  /* Kick the page out of the dictionary. */
  if (page->previous != NULL)
    page->previous->next = page->next;
  if (page->next != NULL)
    page->next->previous = page->previous;

  /* Just in case someone retains a handle to this after it's freed. */
  page->page_start = (CORE_ADDR) 0;

  memory_page_dictionary.page_count--;

  xfree (page);
}

int
macosx_insert_watchpoint (CORE_ADDR addr, size_t len, int type)
{
  return hppa_insert_hw_watchpoint (PIDGET (inferior_ptid), addr, len, type);
}

int
macosx_remove_watchpoint (CORE_ADDR addr, size_t len, int type)
{
  return hppa_remove_hw_watchpoint (PIDGET (inferior_ptid), addr, len, type);
}

int macosx_stopped_by_watchpoint
  (struct target_waitstatus *w, int stop_signal,
   int stepped_after_stopped_by_watchpoint)
{
  return
    ((w->kind == TARGET_WAITKIND_STOPPED)
     && (stop_signal == TARGET_EXC_BAD_ACCESS)
     && (!stepped_after_stopped_by_watchpoint)
     && bpstat_have_active_hw_watchpoints ());
}

void
_initialize_macosx_nat_watchpoint (void)
{
  memory_page_dictionary.page_count = (LONGEST) - 1;
  memory_page_dictionary.page_protections_allowed = 1;
}