os_dep.c

/*
 * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
 * Copyright (c) 1991-1995 by Xerox Corporation.  All rights reserved.
 * Copyright (c) 1996-1999 by Silicon Graphics.  All rights reserved.
 * Copyright (c) 1999 by Hewlett-Packard Company.  All rights reserved.
 * Copyright (c) 2008-2022 Ivan Maidanski
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose, provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 */

#include "private/gc_priv.h"

#if (defined(MPROTECT_VDB) && !defined(MSWIN32) && !defined(MSWINCE)) \
    || (defined(SOLARIS) && defined(THREADS)) || defined(OPENBSD)
#  include <signal.h>
#endif

#if defined(UNIX_LIKE) || defined(CYGWIN32) || defined(NACL) \
    || defined(SYMBIAN)
#  include <fcntl.h>
#endif

#ifdef LINUX
#  include <ctype.h>
#endif

/* Blatantly OS dependent routines, except for those that are related   */
/* to dynamic loading.                                                  */

#ifdef IRIX5
#  include <malloc.h> /* for locking */
#  include <sys/uio.h>
#endif

#if defined(MMAP_SUPPORTED) || defined(ADD_HEAP_GUARD_PAGES)
#  if defined(USE_MUNMAP) && !defined(USE_MMAP) && !defined(CPPCHECK)
#    error Invalid config: USE_MUNMAP requires USE_MMAP
#  endif
#  include <sys/mman.h>
#  include <sys/stat.h>
#endif

#if defined(LINUX) && defined(SPECIFIC_MAIN_STACKBOTTOM)        \
    || defined(ADD_HEAP_GUARD_PAGES) || defined(MMAP_SUPPORTED) \
    || defined(NEED_PROC_MAPS)
#  include <errno.h>
#endif

#if defined(DARWIN) && !defined(DYNAMIC_LOADING) \
    && !defined(GC_DONT_REGISTER_MAIN_STATIC_DATA)
/* for get_etext and friends */
#  include <mach-o/getsect.h>
#endif

#ifdef DJGPP
/* Apparently necessary for djgpp 2.01.  May cause problems with      */
/* other versions.                                                    */
typedef long unsigned int caddr_t;
#endif

#if !defined(NO_EXECUTE_PERMISSION)
STATIC GC_bool GC_pages_executable = TRUE;
#else
STATIC GC_bool GC_pages_executable = FALSE;
#endif

/* Note: it is undefined later on GC_pages_executable real use. */
#define IGNORE_PAGES_EXECUTABLE 1

#if ((defined(LINUX) && defined(SPECIFIC_MAIN_STACKBOTTOM)                  \
      || defined(NEED_PROC_MAPS) || defined(PROC_VDB) || defined(SOFT_VDB)) \
     && !defined(PROC_READ))                                                \
    || defined(CPPCHECK)
/* Note: should probably call the real read, if read is wrapped.  */
#  define PROC_READ read
#endif

#if defined(LINUX) && defined(SPECIFIC_MAIN_STACKBOTTOM) \
    || defined(NEED_PROC_MAPS)
/* Repeatedly perform a read call until the buffer is filled  */
/* up, or we encounter EOF or an error.                       */
STATIC ssize_t
GC_repeat_read(int f, char *buf, size_t count)
{
  size_t num_read = 0;

  ASSERT_CANCEL_DISABLED();
  while (num_read < count) {
    ssize_t result = PROC_READ(f, buf + num_read, count - num_read);

    if (result < 0)
      return result;
    if (0 == result)
      break;
#  ifdef LINT2
    if ((size_t)result > count - num_read)
      ABORT("read() result cannot be bigger than requested length");
#  endif
    num_read += (size_t)result;
  }
  return num_read;
}
#endif /* LINUX && SPECIFIC_MAIN_STACKBOTTOM || NEED_PROC_MAPS */

#ifdef NEED_PROC_MAPS
/* We need to parse /proc/self/maps, either to find dynamic libraries,  */
/* and/or to find the register backing store base (IA64).  Do it once   */
/* here.                                                                */

#  ifdef THREADS
/* Determine the length of a file by incrementally reading it into a  */
/* buffer.  This would be silly to use it on a file supporting lseek, */
/* but Linux /proc files usually do not.                              */
/* As of Linux 4.15.0, lseek(SEEK_END) fails for /proc/self/maps.     */
STATIC size_t
GC_get_file_len(int f)
{
  size_t total = 0;
#    define GET_FILE_LEN_BUF_SZ 500
  char buf[GET_FILE_LEN_BUF_SZ];

  ASSERT_CANCEL_DISABLED();
  for (;;) {
    ssize_t result = PROC_READ(f, buf, sizeof(buf));

    if (result < 0) {
      /* An error has occurred.       */
      return 0;
    }
    if (0 == result)
      break;
#    ifdef LINT2
    if ((size_t)result >= GC_SIZE_MAX - total)
      ABORT("Too big file is passed to GC_get_file_len");
#    endif
    total += (size_t)result;
  }
  return total;
}

STATIC size_t
GC_get_maps_len(void)
{
  int f = open("/proc/self/maps", O_RDONLY);
  size_t result;

  if (f < 0) {
    /* Treat missing file as empty.   */
    return 0;
  }
  result = GC_get_file_len(f);
  close(f);
  return result;
}
#  endif /* THREADS */

/* Copy the content of /proc/self/maps to a buffer in our address       */
/* space.  Return the address of the buffer.                            */
GC_INNER const char *
GC_get_maps(void)
{
  ssize_t result;
  static char *maps_buf = NULL;
  static size_t maps_buf_sz = 1;
  size_t maps_size;
#  ifdef THREADS
  size_t old_maps_size = 0;
#  endif

  /* The buffer is essentially static, so there must be a single client. */
  GC_ASSERT(I_HOLD_LOCK());

  /* Note that in the presence of threads, the maps file can  */
  /* essentially shrink asynchronously and unexpectedly as    */
  /* threads that we already think of as dead release their   */
  /* stacks.  And there is no easy way to read the entire     */
  /* file atomically.  This is arguably a misfeature of the   */
  /* /proc/self/maps interface.                               */
  /* Since we expect the file can grow asynchronously in rare */
  /* cases, it should suffice to first determine              */
  /* the size (using read), and then to reread the file.      */
  /* If the size is inconsistent we have to retry.            */
  /* This only matters with threads enabled, and if we use    */
  /* this to locate roots (not the default).                  */

#  ifdef THREADS
  /* Determine the initial size of /proc/self/maps.       */
  maps_size = GC_get_maps_len();
  if (0 == maps_size)
    ABORT("Cannot determine length of /proc/self/maps");
#  else
  maps_size = 4000; /* Guess */
#  endif

  /* Read /proc/self/maps, growing maps_buf as necessary.     */
  /* Note that we may not allocate conventionally, and        */
  /* thus can't use stdio.                                    */
  do {
    int f;

    while (maps_size >= maps_buf_sz) {
#  ifdef LINT2
      /* Workaround passing tainted maps_buf to a tainted sink. */
      GC_noop1_ptr(maps_buf);
#  else
      GC_scratch_recycle_no_gww(maps_buf, maps_buf_sz);
#  endif
      /* Grow only by powers of 2, since we leak "too small" buffers.*/
      while (maps_size >= maps_buf_sz)
        maps_buf_sz *= 2;
      maps_buf = GC_scratch_alloc(maps_buf_sz);
      if (NULL == maps_buf)
        ABORT_ARG1("Insufficient space for /proc/self/maps buffer",
                   ", %lu bytes requested", (unsigned long)maps_buf_sz);
#  ifdef THREADS
      /* Recompute initial length, since we allocated.        */
      /* This can only happen a few times per program         */
      /* execution.                                           */
      maps_size = GC_get_maps_len();
      if (0 == maps_size)
        ABORT("Cannot determine length of /proc/self/maps");
#  endif
    }
    GC_ASSERT(maps_buf_sz >= maps_size + 1);
    f = open("/proc/self/maps", O_RDONLY);
    if (-1 == f)
      ABORT_ARG1("Cannot open /proc/self/maps", ": errno= %d", errno);
#  ifdef THREADS
    old_maps_size = maps_size;
#  endif
    maps_size = 0;
    do {
      result = GC_repeat_read(f, maps_buf, maps_buf_sz - 1);
      if (result < 0) {
        ABORT_ARG1("Failed to read /proc/self/maps", ": errno= %d", errno);
      }
      maps_size += (size_t)result;
    } while ((size_t)result == maps_buf_sz - 1);
    close(f);
    if (0 == maps_size)
      ABORT("Empty /proc/self/maps");
#  ifdef THREADS
    if (maps_size > old_maps_size) {
      /* This might be caused by e.g. thread creation. */
      WARN("Unexpected asynchronous /proc/self/maps growth"
           " (to %" WARN_PRIuPTR " bytes)\n",
           maps_size);
    }
#  endif
  } while (maps_size >= maps_buf_sz
#  ifdef THREADS
           || maps_size < old_maps_size
#  endif
  );
  maps_buf[maps_size] = '\0';
  return maps_buf;
}

/*
 *  GC_parse_map_entry parses an entry from /proc/self/maps so we can
 *  locate all writable data segments that belong to shared libraries.
 *  The format of one of these entries and the fields we care about
 *  is as follows:
 *  XXXXXXXX-XXXXXXXX r-xp 00000000 30:05 260537     name of mapping...\n
 *  ^^^^^^^^ ^^^^^^^^ ^^^^          ^^
 *  *p_start *p_end   *p_prot       *p_maj_dev
 *
 *  Note that since about august 2003 kernels, the columns no longer have
 *  fixed offsets on 64-bit kernels.  Hence we no longer rely on fixed offsets
 *  anywhere, which is safer anyway.
 */

/* Assign various fields of the first line in maps_ptr to *p_start,     */
/* *p_end, *p_prot, *p_maj_dev and *p_mapping_name.  p_mapping_name may */
/* be NULL. *p_prot and *p_mapping_name are assigned pointers into the  */
/* original buffer.                                                     */
#  if defined(DYNAMIC_LOADING) && defined(USE_PROC_FOR_LIBRARIES) \
      || defined(IA64) || defined(INCLUDE_LINUX_THREAD_DESCR)     \
      || (defined(CHECK_SOFT_VDB) && defined(MPROTECT_VDB))       \
      || defined(REDIR_MALLOC_AND_LINUXTHREADS)
GC_INNER const char *
GC_parse_map_entry(const char *maps_ptr, ptr_t *p_start, ptr_t *p_end,
                   const char **p_prot, unsigned *p_maj_dev,
                   const char **p_mapping_name)
{
  const unsigned char *start_start, *end_start, *maj_dev_start;
  const unsigned char *p; /* unsigned for isspace, isxdigit */

  if (maps_ptr == NULL || *maps_ptr == '\0') {
    return NULL;
  }

  p = (const unsigned char *)maps_ptr;
  while (isspace(*p))
    ++p;
  start_start = p;
  GC_ASSERT(isxdigit(*start_start));
  *p_start = (ptr_t)strtoul((const char *)start_start, (char **)&p, 16);
  GC_ASSERT(*p == '-');

  ++p;
  end_start = p;
  GC_ASSERT(isxdigit(*end_start));
  *p_end = (ptr_t)strtoul((const char *)end_start, (char **)&p, 16);
  GC_ASSERT(isspace(*p));

  while (isspace(*p))
    ++p;
  GC_ASSERT(*p == 'r' || *p == '-');
  *p_prot = (const char *)p;
  /* Skip past protection field to offset field.      */
  while (!isspace(*p))
    ++p;
  while (isspace(*p))
    p++;
  GC_ASSERT(isxdigit(*p));
  /* Skip past offset field, which we ignore.         */
  while (!isspace(*p))
    ++p;
  while (isspace(*p))
    p++;
  maj_dev_start = p;
  GC_ASSERT(isxdigit(*maj_dev_start));
  *p_maj_dev = strtoul((const char *)maj_dev_start, NULL, 16);

  if (p_mapping_name != NULL) {
    while (*p && *p != '\n' && *p != '/' && *p != '[')
      p++;
    *p_mapping_name = (const char *)p;
  }
  while (*p && *p++ != '\n') {
    /* Empty. */
  }
  return (const char *)p;
}
#  endif /* REDIRECT_MALLOC || DYNAMIC_LOADING || IA64 || ... */

#  if defined(IA64) || defined(INCLUDE_LINUX_THREAD_DESCR) \
      || (defined(CHECK_SOFT_VDB) && defined(MPROTECT_VDB))
/* Try to read the backing store base from /proc/self/maps.           */
/* Return the bounds of the writable mapping with a 0 major device,   */
/* which includes the address passed as data.                         */
/* Return FALSE if there is no such mapping.                          */
GC_INNER GC_bool
GC_enclosing_writable_mapping(ptr_t addr, ptr_t *startp, ptr_t *endp)
{
  const char *prot;
  ptr_t my_start, my_end;
  const char *maps_ptr;
  unsigned maj_dev;

  GC_ASSERT(I_HOLD_LOCK());
  maps_ptr = GC_get_maps();
  for (;;) {
    maps_ptr = GC_parse_map_entry(maps_ptr, &my_start, &my_end, &prot,
                                  &maj_dev, NULL);
    if (NULL == maps_ptr)
      break;

    if (ADDR_INSIDE(addr, my_start, my_end)) {
      if (prot[1] != 'w' || maj_dev != 0)
        break;
      *startp = my_start;
      *endp = my_end;
      return TRUE;
    }
  }
  return FALSE;
}
#  endif /* IA64 || INCLUDE_LINUX_THREAD_DESCR */

#  ifdef REDIR_MALLOC_AND_LINUXTHREADS
/* Find the text(code) mapping for the library whose name, after      */
/* stripping the directory part, starts with nm.                      */
GC_INNER GC_bool
GC_text_mapping(const char *nm, ptr_t *startp, ptr_t *endp)
{
  size_t nm_len;
  const char *prot, *map_path;
  ptr_t my_start, my_end;
  unsigned int maj_dev;
  const char *maps_ptr;

  GC_ASSERT(I_HOLD_LOCK());
  maps_ptr = GC_get_maps();
  nm_len = strlen(nm);
  for (;;) {
    maps_ptr = GC_parse_map_entry(maps_ptr, &my_start, &my_end, &prot,
                                  &maj_dev, &map_path);
    if (NULL == maps_ptr)
      break;

    if (prot[0] == 'r' && prot[1] == '-' && prot[2] == 'x') {
      const char *p = map_path;

      /* Set p to point just past last slash, if any.       */
      while (*p != '\0' && *p != '\n' && *p != ' ' && *p != '\t') {
        ++p;
      }
      while (ADDR_GE((ptr_t)p, (ptr_t)map_path) && *p != '/') {
        --p;
      }
      ++p;

      if (strncmp(nm, p, nm_len) == 0) {
        *startp = my_start;
        *endp = my_end;
        return TRUE;
      }
    }
  }
  return FALSE;
}
#  endif /* REDIR_MALLOC_AND_LINUXTHREADS */

#  ifdef IA64
static ptr_t
backing_store_base_from_proc(void)
{
  ptr_t my_start, my_end;

  GC_ASSERT(I_HOLD_LOCK());
  if (!GC_enclosing_writable_mapping(GC_save_regs_in_stack(), &my_start,
                                     &my_end)) {
    GC_COND_LOG_PRINTF("Failed to find backing store base from /proc\n");
    return 0;
  }
  return my_start;
}
#  endif

#endif /* NEED_PROC_MAPS */

#if defined(SEARCH_FOR_DATA_START)
/* The i686 case can be handled without a search.  The Alpha case     */
/* used to be handled differently as well, but the rules changed      */
/* for recent Linux versions.  This seems to be the easiest way to    */
/* cover all versions.                                                */

#  if defined(LINUX) || defined(HURD)
/* Some Linux distributions arrange to define __data_start.  Some   */
/* define data_start as a weak symbol.  The latter is technically   */
/* broken, since the user program may define data_start, in which   */
/* case we lose.  Nonetheless, we try both, preferring __data_start.*/
/* We assume gcc-compatible pragmas.                                */
EXTERN_C_BEGIN
#    pragma weak __data_start
#    pragma weak data_start
extern int __data_start[], data_start[];
EXTERN_C_END
#  elif defined(NETBSD)
EXTERN_C_BEGIN
extern char **environ;
EXTERN_C_END
#  endif

ptr_t GC_data_start = NULL;

GC_INNER void
GC_init_linux_data_start(void)
{
  ptr_t data_end = DATAEND;

#  if (defined(LINUX) || defined(HURD)) && defined(USE_PROG_DATA_START)
  /* Try the easy approaches first: */
  /* However, this may lead to wrong data start value if libgc  */
  /* code is put into a shared library (directly or indirectly) */
  /* which is linked with -Bsymbolic-functions option.  Thus,   */
  /* the following is not used by default.                      */
  if (COVERT_DATAFLOW(ADDR(__data_start)) != 0) {
    GC_data_start = (ptr_t)(__data_start);
  } else {
    GC_data_start = (ptr_t)(data_start);
  }
  if (COVERT_DATAFLOW(ADDR(GC_data_start)) != 0) {
    if (ADDR_LT(data_end, GC_data_start))
      ABORT_ARG2("Wrong __data_start/_end pair", ": %p .. %p",
                 (void *)GC_data_start, (void *)data_end);
    return;
  }
#    ifdef DEBUG_ADD_DEL_ROOTS
  GC_log_printf("__data_start not provided\n");
#    endif
#  endif /* LINUX */

  if (GC_no_dls) {
    /* Not needed, avoids the SIGSEGV caused by       */
    /* GC_find_limit which complicates debugging.     */
    GC_data_start = data_end; /* set data root size to 0 */
    return;
  }

#  ifdef NETBSD
  /* This may need to be environ, without the underscore, for       */
  /* some versions.                                                 */
  GC_data_start = (ptr_t)GC_find_limit(&environ, FALSE);
#  else
  GC_data_start = (ptr_t)GC_find_limit(data_end, FALSE);
#  endif
}
#endif /* SEARCH_FOR_DATA_START */

#ifdef ECOS

#  ifndef ECOS_GC_MEMORY_SIZE
#    define ECOS_GC_MEMORY_SIZE (448 * 1024)
#  endif /* ECOS_GC_MEMORY_SIZE */

/* TODO: This is a simple way of allocating memory which is           */
/* compatible with ECOS early releases.  Later releases use a more    */
/* sophisticated means of allocating memory than this simple static   */
/* allocator, but this method is at least bound to work.              */
static char ecos_gc_memory[ECOS_GC_MEMORY_SIZE];
static ptr_t ecos_gc_brk = ecos_gc_memory;

static void *
tiny_sbrk(ptrdiff_t increment)
{
  void *p = ecos_gc_brk;

  if (ADDR_LT((ptr_t)ecos_gc_memory + sizeof(ecos_gc_memory),
              (ptr_t)p + increment))
    return NULL;
  ecos_gc_brk += increment;
  return p;
}
#  define sbrk tiny_sbrk
#endif /* ECOS */

#if defined(ADDRESS_SANITIZER)                         \
    && (defined(UNIX_LIKE) || defined(NEED_FIND_LIMIT) \
        || defined(MPROTECT_VDB))                      \
    && !defined(CUSTOM_ASAN_DEF_OPTIONS)
EXTERN_C_BEGIN
GC_API const char *__asan_default_options(void);
EXTERN_C_END

/* To tell ASan to allow GC to use its own SIGBUS/SEGV handlers.      */
/* The function is exported just to be visible to ASan library.       */
GC_API const char *
__asan_default_options(void)
{
  return "allow_user_segv_handler=1";
}
#endif

#ifdef OPENBSD
static struct sigaction old_segv_act;
STATIC JMP_BUF GC_jmp_buf_openbsd;

STATIC void
GC_fault_handler_openbsd(int sig)
{
  UNUSED_ARG(sig);
  LONGJMP(GC_jmp_buf_openbsd, 1);
}

static volatile int firstpass;

/* Return first addressable location > p or bound.    */
STATIC ptr_t
GC_skip_hole_openbsd(ptr_t p, ptr_t bound)
{
  static volatile ptr_t result;
  struct sigaction act;
  size_t pgsz;

  GC_ASSERT(I_HOLD_LOCK());
  pgsz = (size_t)sysconf(_SC_PAGESIZE);
  GC_ASSERT(ADDR(bound) >= (word)pgsz);

  act.sa_handler = GC_fault_handler_openbsd;
  sigemptyset(&act.sa_mask);
  act.sa_flags = SA_NODEFER | SA_RESTART;
  /* act.sa_restorer is deprecated and should not be initialized. */
  sigaction(SIGSEGV, &act, &old_segv_act);

  firstpass = 1;
  result = PTR_ALIGN_DOWN(p, pgsz);
  if (SETJMP(GC_jmp_buf_openbsd) != 0 || firstpass) {
    firstpass = 0;
    if (ADDR_GE(result, bound - pgsz)) {
      result = bound;
    } else {
      /* Notes: no overflow is expected; do not use compound          */
      /* assignment with volatile-qualified left operand.             */
      result = result + pgsz;
      GC_noop1((word)(unsigned char)(*result));
    }
  }

  sigaction(SIGSEGV, &old_segv_act, 0);
  return result;
}
#endif /* OPENBSD */

#ifdef OS2

#  include <stddef.h>

#  if !defined(__IBMC__) && !defined(__WATCOMC__) /* e.g. EMX */

struct exe_hdr {
  unsigned short magic_number;
  unsigned short padding[29];
  long new_exe_offset;
};

#    define E_MAGIC(x) (x).magic_number
#    define EMAGIC 0x5A4D
#    define E_LFANEW(x) (x).new_exe_offset

struct e32_exe {
  unsigned char magic_number[2];
  unsigned char byte_order;
  unsigned char word_order;
  unsigned long exe_format_level;
  unsigned short cpu;
  unsigned short os;
  unsigned long padding1[13];
  unsigned long object_table_offset;
  unsigned long object_count;
  unsigned long padding2[31];
};

#    define E32_MAGIC1(x) (x).magic_number[0]
#    define E32MAGIC1 'L'
#    define E32_MAGIC2(x) (x).magic_number[1]
#    define E32MAGIC2 'X'
#    define E32_BORDER(x) (x).byte_order
#    define E32LEBO 0
#    define E32_WORDER(x) (x).word_order
#    define E32LEWO 0
#    define E32_CPU(x) (x).cpu
#    define E32CPU286 1
#    define E32_OBJTAB(x) (x).object_table_offset
#    define E32_OBJCNT(x) (x).object_count

struct o32_obj {
  unsigned long size;
  unsigned long base;
  unsigned long flags;
  unsigned long pagemap;
  unsigned long mapsize;
  unsigned long reserved;
};

#    define O32_FLAGS(x) (x).flags
#    define OBJREAD 0x0001L
#    define OBJWRITE 0x0002L
#    define OBJINVALID 0x0080L
#    define O32_SIZE(x) (x).size
#    define O32_BASE(x) (x).base

#  else /* IBM's compiler */

/* A kludge to get around what appears to be a header file bug.   */
#    ifndef WORD
#      define WORD unsigned short
#    endif
#    ifndef DWORD
#      define DWORD unsigned long
#    endif

#    define EXE386 1
#    include <exe386.h>
#    include <newexe.h>

#  endif /* __IBMC__ */

#  define INCL_DOSERRORS
#  define INCL_DOSEXCEPTIONS
#  define INCL_DOSFILEMGR
#  define INCL_DOSMEMMGR
#  define INCL_DOSMISC
#  define INCL_DOSMODULEMGR
#  define INCL_DOSPROCESS
#  include <os2.h>

#endif /* OS2 */

/* Find the page size.  */
GC_INNER size_t GC_page_size = 0;
#ifdef REAL_PAGESIZE_NEEDED
GC_INNER size_t GC_real_page_size = 0;
#endif

#ifdef SOFT_VDB
STATIC unsigned GC_log_pagesize = 0;
#endif

#ifdef ANY_MSWIN

#  ifndef VER_PLATFORM_WIN32_CE
#    define VER_PLATFORM_WIN32_CE 3
#  endif

#  if defined(MSWINCE) && defined(THREADS)
GC_INNER GC_bool GC_dont_query_stack_min = FALSE;
#  endif

GC_INNER SYSTEM_INFO GC_sysinfo;

#  ifndef CYGWIN32
#    define is_writable(prot)                               \
      ((prot) == PAGE_READWRITE || (prot) == PAGE_WRITECOPY \
       || (prot) == PAGE_EXECUTE_READWRITE                  \
       || (prot) == PAGE_EXECUTE_WRITECOPY)
/* Return the number of bytes that are writable starting at p.      */
/* The pointer p is assumed to be page aligned.                     */
/* If base is not 0, *base becomes the beginning of the             */
/* allocation region containing p.                                  */
STATIC word
GC_get_writable_length(ptr_t p, ptr_t *base)
{
  MEMORY_BASIC_INFORMATION buf;
  word result;
  word protect;

  result = VirtualQuery(p, &buf, sizeof(buf));
  if (result != sizeof(buf))
    ABORT("Weird VirtualQuery result");
  if (base != 0)
    *base = (ptr_t)(buf.AllocationBase);
  protect = buf.Protect & ~(word)(PAGE_GUARD | PAGE_NOCACHE);
  if (!is_writable(protect) || buf.State != MEM_COMMIT)
    return 0;
  return buf.RegionSize;
}

/* Fill in the GC_stack_base structure with the stack bottom for    */
/* this thread.  Should not acquire the allocator lock as the       */
/* function is used by GC_DllMain.                                  */
GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *sb)
{
  ptr_t trunc_sp;
  word size;

  /* Set page size if it is not ready (so client can use this       */
  /* function even before GC is initialized).                       */
  if (!GC_page_size)
    GC_setpagesize();

  trunc_sp = PTR_ALIGN_DOWN(GC_approx_sp(), GC_page_size);
  /* FIXME: This won't work if called from a deeply recursive       */
  /* client code (and the committed stack space has grown).         */
  size = GC_get_writable_length(trunc_sp, 0);
  GC_ASSERT(size != 0);
  sb->mem_base = trunc_sp + size;
  return GC_SUCCESS;
}
#  else /* CYGWIN32 */
/* An alternate version for Cygwin (adapted from Dave Korn's        */
/* gcc version of boehm-gc).                                        */
GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *sb)
{
#    ifdef X86_64
  sb->mem_base = ((NT_TIB *)NtCurrentTeb())->StackBase;
#    else
  void *_tlsbase;

  __asm__("movl %%fs:4, %0" : "=r"(_tlsbase));
  sb->mem_base = _tlsbase;
#    endif
  return GC_SUCCESS;
}
#  endif /* CYGWIN32 */
#  define HAVE_GET_STACK_BASE

#elif defined(OS2)

static int
os2_getpagesize(void)
{
  ULONG result[1];

  if (DosQuerySysInfo(QSV_PAGE_SIZE, QSV_PAGE_SIZE, (void *)result,
                      sizeof(ULONG))
      != NO_ERROR) {
    WARN("DosQuerySysInfo failed\n", 0);
    result[0] = 4096;
  }
  return (int)result[0];
}

#endif /* !ANY_MSWIN && OS2 */

GC_INNER void
GC_setpagesize(void)
{
#ifdef ANY_MSWIN
  GetSystemInfo(&GC_sysinfo);
#  ifdef ALT_PAGESIZE_USED
  /* Allocations made with mmap() are aligned to the allocation     */
  /* granularity, which (at least on Win64) is not the same as the  */
  /* page size.  Probably we could distinguish the allocation       */
  /* granularity from the actual page size, but in practice there   */
  /* is no good reason to make allocations smaller than             */
  /* dwAllocationGranularity, so we just use it instead of the      */
  /* actual page size here (as Cygwin itself does in many cases).   */
  GC_page_size = (size_t)GC_sysinfo.dwAllocationGranularity;
#    ifdef REAL_PAGESIZE_NEEDED
  GC_real_page_size = (size_t)GC_sysinfo.dwPageSize;
  GC_ASSERT(GC_page_size >= GC_real_page_size);
#    endif
#  else
  GC_page_size = (size_t)GC_sysinfo.dwPageSize;
#  endif
#  if defined(MSWINCE) && !defined(_WIN32_WCE_EMULATION)
  {
    OSVERSIONINFO verInfo;
    /* Check the current WinCE version.     */
    verInfo.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
    if (!GetVersionEx(&verInfo))
      ABORT("GetVersionEx failed");
    if (verInfo.dwPlatformId == VER_PLATFORM_WIN32_CE
        && verInfo.dwMajorVersion < 6) {
      /* Only the first 32 MB of address space belongs to the       */
      /* current process (unless WinCE 6.0+ or emulation).          */
      GC_sysinfo.lpMaximumApplicationAddress = (LPVOID)((word)32 << 20);
#    ifdef THREADS
      /* On some old WinCE versions, it's observed that           */
      /* VirtualQuery calls don't work properly when used to      */
      /* get thread current stack committed minimum.              */
      if (verInfo.dwMajorVersion < 5)
        GC_dont_query_stack_min = TRUE;
#    endif
    }
  }
#  endif
#else
#  ifdef ALT_PAGESIZE_USED
#    ifdef REAL_PAGESIZE_NEEDED
  GC_real_page_size = (size_t)GETPAGESIZE();
#    endif
  /* It's acceptable to fake it.    */
  GC_page_size = HBLKSIZE;
#  else
  GC_page_size = (size_t)GETPAGESIZE();
#    if !defined(CPPCHECK)
  if (0 == GC_page_size)
    ABORT("getpagesize failed");
#    endif
#  endif
#endif /* !ANY_MSWIN */
#ifdef SOFT_VDB
  {
    size_t pgsize;
    unsigned log_pgsize = 0;

#  if !defined(CPPCHECK)
    if (((GC_page_size - 1) & GC_page_size) != 0) {
      /* Not a power of two.        */
      ABORT("Invalid page size");
    }
#  endif
    for (pgsize = GC_page_size; pgsize > 1; pgsize >>= 1)
      log_pgsize++;
    GC_log_pagesize = log_pgsize;
  }
#endif
}

#ifdef EMBOX
#  include <kernel/thread/thread_stack.h>
#  include <pthread.h>

GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *sb)
{
  pthread_t self = pthread_self();
  void *stack_addr = thread_stack_get(self);

  /* TODO: use pthread_getattr_np, pthread_attr_getstack alternatively */
#  ifdef STACK_GROWS_UP
  sb->mem_base = stack_addr;
#  else
  sb->mem_base = (ptr_t)stack_addr + thread_stack_get_size(self);
#  endif
  return GC_SUCCESS;
}
#  define HAVE_GET_STACK_BASE
#endif /* EMBOX */

#ifdef OS2
GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *sb)
{
  PTIB ptib; /* thread information block */
  PPIB ppib;

  if (DosGetInfoBlocks(&ptib, &ppib) != NO_ERROR) {
    WARN("DosGetInfoBlocks failed\n", 0);
    return GC_UNIMPLEMENTED;
  }
  sb->mem_base = ptib->tib_pstacklimit;
  return GC_SUCCESS;
}
#  define HAVE_GET_STACK_BASE
#endif /* OS2 */

#ifdef SERENITY
#  include <serenity.h>

GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *sb)
{
  uintptr_t base;
  size_t size;

  if (get_stack_bounds(&base, &size) < 0) {
    WARN("get_stack_bounds failed\n", 0);
    return GC_UNIMPLEMENTED;
  }
  sb->mem_base = base + size;
  return GC_SUCCESS;
}
#  define HAVE_GET_STACK_BASE
#endif /* SERENITY */

#if defined(NEED_FIND_LIMIT)                                 \
    || (defined(UNIX_LIKE) && !defined(NO_DEBUGGING))        \
    || (defined(USE_PROC_FOR_LIBRARIES) && defined(THREADS)) \
    || (defined(WRAP_MARK_SOME) && defined(NO_SEH_AVAILABLE))

#  include <signal.h>

#  ifdef USE_SEGV_SIGACT
#    ifndef OPENBSD
static struct sigaction old_segv_act;
#    endif
#    ifdef USE_BUS_SIGACT
static struct sigaction old_bus_act;
#    endif
#  else
static GC_fault_handler_t old_segv_hand;
#    ifdef HAVE_SIGBUS
static GC_fault_handler_t old_bus_hand;
#    endif
#  endif /* !USE_SEGV_SIGACT */

GC_INNER void
GC_set_and_save_fault_handler(GC_fault_handler_t h)
{
#  ifdef USE_SEGV_SIGACT
  struct sigaction act;

  act.sa_handler = h;
#    ifdef SIGACTION_FLAGS_NODEFER_HACK
  /* Was necessary for Solaris 2.3 and very temporary */
  /* NetBSD bugs.                                     */
  act.sa_flags = SA_RESTART | SA_NODEFER;
#    else
  act.sa_flags = SA_RESTART;
#    endif

  (void)sigemptyset(&act.sa_mask);
  /* act.sa_restorer is deprecated and should not be initialized. */
#    if defined(IRIX5) && defined(THREADS)
  /* Older versions have a bug related to retrieving and      */
  /* and setting a handler at the same time.                  */
  (void)sigaction(SIGSEGV, 0, &old_segv_act);
  (void)sigaction(SIGSEGV, &act, 0);
#    else
  (void)sigaction(SIGSEGV, &act, &old_segv_act);
#      ifdef USE_BUS_SIGACT
  /* Pthreads doesn't exist under Irix 5.x, so we   */
  /* don't have to worry in the threads case.       */
  (void)sigaction(SIGBUS, &act, &old_bus_act);
#      endif
#    endif /* !IRIX5 || !THREADS */
#  else
  old_segv_hand = signal(SIGSEGV, h);
#    ifdef HAVE_SIGBUS
  old_bus_hand = signal(SIGBUS, h);
#    endif
#  endif /* !USE_SEGV_SIGACT */
#  if defined(CPPCHECK) && defined(ADDRESS_SANITIZER)
  GC_noop1((word)(GC_funcptr_uint)(&__asan_default_options));
#  endif
}
#endif /* NEED_FIND_LIMIT || UNIX_LIKE || WRAP_MARK_SOME */

#if defined(NEED_FIND_LIMIT)                                 \
    || (defined(USE_PROC_FOR_LIBRARIES) && defined(THREADS)) \
    || (defined(WRAP_MARK_SOME) && defined(NO_SEH_AVAILABLE))
GC_INNER JMP_BUF GC_jmp_buf;

STATIC void
GC_fault_handler(int sig)
{
  UNUSED_ARG(sig);
  LONGJMP(GC_jmp_buf, 1);
}

GC_INNER void
GC_setup_temporary_fault_handler(void)
{
  /* Handler is process-wide, so this should only happen in one   */
  /* thread at a time.                                            */
  GC_ASSERT(I_HOLD_LOCK());
  GC_set_and_save_fault_handler(GC_fault_handler);
}

GC_INNER void
GC_reset_fault_handler(void)
{
#  ifdef USE_SEGV_SIGACT
  (void)sigaction(SIGSEGV, &old_segv_act, 0);
#    ifdef USE_BUS_SIGACT
  (void)sigaction(SIGBUS, &old_bus_act, 0);
#    endif
#  else
  (void)signal(SIGSEGV, old_segv_hand);
#    ifdef HAVE_SIGBUS
  (void)signal(SIGBUS, old_bus_hand);
#    endif
#  endif
}
#endif /* NEED_FIND_LIMIT || USE_PROC_FOR_LIBRARIES || WRAP_MARK_SOME */

#if defined(NEED_FIND_LIMIT) \
    || (defined(USE_PROC_FOR_LIBRARIES) && defined(THREADS))
#  define MIN_PAGE_SIZE 256 /* Smallest conceivable page size, in bytes. */

/* Return the first non-addressable location greater than p (if up) or  */
/* the smallest location q such that [q,p) is addressable (if not up).  */
/* We assume that p (if up) or p-1 (if not up) is addressable.          */
GC_ATTR_NO_SANITIZE_ADDR
STATIC ptr_t
GC_find_limit_with_bound(ptr_t p, GC_bool up, ptr_t bound)
{
  /* This is safer if static, since otherwise it may not be       */
  /* preserved across the longjmp.  Can safely be static since it */
  /* is only called with the allocator lock held.                 */
  static volatile ptr_t result;

  GC_ASSERT(up ? ADDR(bound) >= MIN_PAGE_SIZE
               : ADDR(bound) <= ~(word)MIN_PAGE_SIZE);
  GC_ASSERT(I_HOLD_LOCK());
  result = PTR_ALIGN_DOWN(p, MIN_PAGE_SIZE);
  GC_setup_temporary_fault_handler();
  if (SETJMP(GC_jmp_buf) == 0) {
    for (;;) {
      if (up) {
        if (ADDR_GE(result, bound - MIN_PAGE_SIZE)) {
          result = bound;
          break;
        }
        /* Notes: no overflow is expected; do not use       */
        /* compound assignment with volatile-qualified left */
        /* operand.                                         */
        result = result + MIN_PAGE_SIZE;
      } else {
        if (ADDR_GE(bound + MIN_PAGE_SIZE, result)) {
          /* This is to compensate further result increment */
          /* (we do not modify "up" variable since it might */
          /* be clobbered by setjmp otherwise).             */
          result = bound - MIN_PAGE_SIZE;
          break;
        }
        /* See the notes for the "up" case. */
        result = result - MIN_PAGE_SIZE;
      }
      GC_noop1((word)(unsigned char)(*result));
    }
  }
  GC_reset_fault_handler();
  return up ? result : result + MIN_PAGE_SIZE;
}

void *
GC_find_limit(void *p, int up)
{
  ptr_t bound;

#  ifdef CHERI_PURECAP
  bound = (ptr_t)cheri_address_set(p, cheri_base_get(p)
                                          + (up ? cheri_length_get(p) : 0));
#  else
  bound = up ? MAKE_CPTR(GC_WORD_MAX) : NULL;
#  endif
  return GC_find_limit_with_bound((ptr_t)p, (GC_bool)up, bound);
}
#endif /* NEED_FIND_LIMIT || USE_PROC_FOR_LIBRARIES */

#if defined(HPUX) && defined(IA64)
#  include <sys/param.h>
#  include <sys/pstat.h>

GC_INNER ptr_t
GC_get_register_stack_base(void)
{
  struct pst_vm_status vm_status;

  int i = 0;
  while (pstat_getprocvm(&vm_status, sizeof(vm_status), 0, i++) == 1) {
    if (vm_status.pst_type == PS_RSESTACK) {
      return (ptr_t)vm_status.pst_vaddr;
    }
  }

  /* Old way to get the register stack bottom.        */
  GC_ASSERT(GC_stackbottom != NULL);
  return PTR_ALIGN_DOWN(GC_stackbottom - BACKING_STORE_DISPLACEMENT - 1,
                        BACKING_STORE_ALIGNMENT);
}
#endif /* HPUX && IA64 */

#if defined(LINUX) && defined(IA64)
#  ifdef USE_LIBC_PRIVATES
EXTERN_C_BEGIN
#    pragma weak __libc_ia64_register_backing_store_base
extern ptr_t __libc_ia64_register_backing_store_base;
EXTERN_C_END
#  endif

GC_INNER ptr_t
GC_get_register_stack_base(void)
{
  ptr_t result;

  GC_ASSERT(I_HOLD_LOCK());
#  ifdef USE_LIBC_PRIVATES
  {
    ptr_t *p_libc_ia64_register_backing_store_base
        = &__libc_ia64_register_backing_store_base;

#    ifdef CPPCHECK
    /* Workaround a warning that the address of the global  */
    /* symbol (which is a weak one) cannot be null.         */
    GC_noop1_ptr(&p_libc_ia64_register_backing_store_base);
#    endif
    if (p_libc_ia64_register_backing_store_base != NULL
        && __libc_ia64_register_backing_store_base != NULL) {
      /* glibc 2.2.4 has a bug such that for dynamically linked   */
      /* executables __libc_ia64_register_backing_store_base is   */
      /* defined but uninitialized during constructor calls.      */
      /* Hence we check for both nonzero address and value.       */
      return __libc_ia64_register_backing_store_base;
    }
  }
#  endif
  result = backing_store_base_from_proc();
  if (0 == result) {
    /* This works better than a constant displacement heuristic.  */
    result = (ptr_t)GC_find_limit(GC_save_regs_in_stack(), FALSE);
  }
  return result;
}
#endif /* LINUX && IA64 */

#ifdef SPECIFIC_MAIN_STACKBOTTOM

#  ifdef HPUX
#    include <sys/param.h>
#    include <sys/pstat.h>

static ptr_t
os_main_stackbottom(void)
{
  struct pst_vm_status vm_status;
  int i = 0;

  while (pstat_getprocvm(&vm_status, sizeof(vm_status), 0, i++) == 1) {
    if (vm_status.pst_type == PS_STACK)
      return (ptr_t)vm_status.pst_vaddr;
  }

  /* Old way to get the stack bottom. */
#    ifdef STACK_GROWS_UP
  return (ptr_t)GC_find_limit(GC_approx_sp(), FALSE);
#    else
  return (ptr_t)GC_find_limit(GC_approx_sp(), TRUE /* up */);
#    endif
}

#  elif defined(LINUX)
#    include <sys/stat.h>

/* Number of fields preceding startstack one in /proc/self/stat.  */
#    define STAT_SKIP 27

#    ifdef USE_LIBC_PRIVATES
EXTERN_C_BEGIN
#      pragma weak __libc_stack_end
extern ptr_t __libc_stack_end;
EXTERN_C_END
#    endif

static ptr_t
os_main_stackbottom(void)
{
  /* We read the stack bottom value from /proc/self/stat.  We do this */
  /* using direct I/O system calls in order to avoid calling malloc   */
  /* in case REDIRECT_MALLOC is defined.                              */
#    define STAT_BUF_SIZE 4096
  unsigned char stat_buf[STAT_BUF_SIZE];
  int f;
  word addr;
  ssize_t i, buf_offset = 0, len;

  /* First try the easy way.  This should work for glibc 2.2. */
  /* This fails in a prelinked ("prelink" command) executable */
  /* since the correct value of __libc_stack_end never        */
  /* becomes visible to us.  The second test works around     */
  /* this.                                                    */
#    ifdef USE_LIBC_PRIVATES
  ptr_t *p_libc_stack_end = &__libc_stack_end;

#      ifdef CPPCHECK
  GC_noop1_ptr(&p_libc_stack_end);
#      endif
  if (p_libc_stack_end != NULL && __libc_stack_end != NULL) {
#      ifdef IA64
    /* Some versions of glibc set the address 16 bytes too        */
    /* low while the initialization code is running.              */
    if ((ADDR(__libc_stack_end) & 0xfff) + 0x10 < 0x1000) {
      return __libc_stack_end + 0x10;
    } else {
      /* It is not safe to add 16 bytes.  Thus, fallback to using /proc. */
    }
#      elif defined(SPARC)
    /* Older versions of glibc for 64-bit SPARC do not set this   */
    /* variable correctly, it gets set to either zero or one.     */
    if (ADDR(__libc_stack_end) != 1)
      return __libc_stack_end;
#      else
    return __libc_stack_end;
#      endif
  }
#    endif

  f = open("/proc/self/stat", O_RDONLY);
  if (-1 == f)
    ABORT_ARG1("Could not open /proc/self/stat", ": errno= %d", errno);
  len = GC_repeat_read(f, (char *)stat_buf, sizeof(stat_buf));
  if (len < 0)
    ABORT_ARG1("Failed to read /proc/self/stat", ": errno= %d", errno);
  close(f);

  /* Skip the required number of fields.  This number is hopefully    */
  /* constant across all Linux implementations.                       */
  for (i = 0; i < STAT_SKIP; ++i) {
    while (buf_offset < len && isspace(stat_buf[buf_offset++])) {
      /* empty */
    }
    while (buf_offset < len && !isspace(stat_buf[buf_offset++])) {
      /* empty */
    }
  }
  /* Skip spaces.     */
  while (buf_offset < len && isspace(stat_buf[buf_offset])) {
    buf_offset++;
  }
  /* Find the end of the number and cut the buffer there.     */
  for (i = 0; buf_offset + i < len; i++) {
    if (!isdigit(stat_buf[buf_offset + i]))
      break;
  }
  if (buf_offset + i >= len)
    ABORT("Could not parse /proc/self/stat");
  stat_buf[buf_offset + i] = '\0';

  addr = (word)STRTOULL((char *)stat_buf + buf_offset, NULL, 10);
  if (addr < 0x100000 || addr % ALIGNMENT != 0)
    ABORT_ARG1("Absurd stack bottom value", ": 0x%lx", (unsigned long)addr);
  return MAKE_CPTR(addr);
}

#  elif defined(QNX)
static ptr_t
os_main_stackbottom(void)
{
  /* TODO: this approach is not very exact but it works for the       */
  /* tests, at least, unlike other available heuristics.              */
  return (ptr_t)__builtin_frame_address(0);
}

#  elif defined(FREEBSD)
#    include <sys/sysctl.h>

/* This uses an undocumented sysctl call, but at least one expert     */
/* believes it will stay.                                             */
static ptr_t
os_main_stackbottom(void)
{
  int nm[2] = { CTL_KERN, KERN_USRSTACK };
  ptr_t base;
  size_t len = sizeof(ptr_t);
  int r = sysctl(nm, 2, &base, &len, NULL, 0);

  if (r != 0)
    ABORT("Error getting main stack base");
  return base;
}
#  endif

#endif /* SPECIFIC_MAIN_STACKBOTTOM */

#if defined(ECOS) || defined(NOSYS)
GC_INNER ptr_t
GC_get_main_stack_base(void)
{
  return STACKBOTTOM;
}
#  define GET_MAIN_STACKBASE_SPECIAL

#elif defined(SYMBIAN)
EXTERN_C_BEGIN
extern int GC_get_main_symbian_stack_base(void);
EXTERN_C_END

GC_INNER ptr_t
GC_get_main_stack_base(void)
{
  return (ptr_t)GC_get_main_symbian_stack_base();
}
#  define GET_MAIN_STACKBASE_SPECIAL

#elif defined(EMSCRIPTEN)
#  include <emscripten/stack.h>

GC_INNER ptr_t
GC_get_main_stack_base(void)
{
  return (ptr_t)emscripten_stack_get_base();
}
#  define GET_MAIN_STACKBASE_SPECIAL

#elif !defined(ANY_MSWIN) && !defined(EMBOX) && !defined(OS2)        \
    && !(defined(OPENBSD) && defined(THREADS)) && !defined(SERENITY) \
    && (!(defined(SOLARIS) && defined(THREADS)) || defined(_STRICT_STDC))

#  if (defined(HAVE_PTHREAD_ATTR_GET_NP) || defined(HAVE_PTHREAD_GETATTR_NP)) \
      && (defined(THREADS) || defined(USE_GET_STACKBASE_FOR_MAIN))
#    include <pthread.h>
#    ifdef HAVE_PTHREAD_NP_H
#      include <pthread_np.h> /* for pthread_attr_get_np() */
#    endif
#  elif defined(DARWIN) && !defined(NO_PTHREAD_GET_STACKADDR_NP)
/* We could use pthread_get_stackaddr_np even in case of a  */
/* single-threaded gclib (there is no -lpthread on Darwin). */
#    include <pthread.h>
#    undef STACKBOTTOM
#    define STACKBOTTOM (ptr_t) pthread_get_stackaddr_np(pthread_self())
#  endif

GC_INNER ptr_t
GC_get_main_stack_base(void)
{
  ptr_t result;
#  if (defined(HAVE_PTHREAD_ATTR_GET_NP) || defined(HAVE_PTHREAD_GETATTR_NP)) \
      && (defined(USE_GET_STACKBASE_FOR_MAIN)                                 \
          || (defined(THREADS) && !defined(REDIRECT_MALLOC)))
  pthread_attr_t attr;
  void *stackaddr;
  size_t size;

#    ifdef HAVE_PTHREAD_ATTR_GET_NP
  if (pthread_attr_init(&attr) == 0
      && (pthread_attr_get_np(pthread_self(), &attr) == 0
              ? TRUE
              : (pthread_attr_destroy(&attr), FALSE)))
#    else /* HAVE_PTHREAD_GETATTR_NP */
  if (pthread_getattr_np(pthread_self(), &attr) == 0)
#    endif
  {
    if (pthread_attr_getstack(&attr, &stackaddr, &size) == 0
        && stackaddr != NULL) {
      (void)pthread_attr_destroy(&attr);
#    ifndef STACK_GROWS_UP
      stackaddr = (char *)stackaddr + size;
#    endif
      return (ptr_t)stackaddr;
    }
    (void)pthread_attr_destroy(&attr);
  }
  WARN("pthread_getattr_np or pthread_attr_getstack failed"
       " for main thread\n",
       0);
#  endif
#  ifdef STACKBOTTOM
  result = STACKBOTTOM;
#  else
#    ifdef HEURISTIC1
#      define STACKBOTTOM_ALIGNMENT_M1 ((word)STACK_GRAN - 1)
#      ifdef STACK_GROWS_UP
  result = PTR_ALIGN_DOWN(GC_approx_sp(), STACKBOTTOM_ALIGNMENT_M1 + 1);
#      else
  result = PTR_ALIGN_UP(GC_approx_sp(), STACKBOTTOM_ALIGNMENT_M1 + 1);
#      endif
#    elif defined(SPECIFIC_MAIN_STACKBOTTOM)
  result = os_main_stackbottom();
#    elif defined(HEURISTIC2)
  {
    ptr_t sp = GC_approx_sp();

#      ifdef STACK_GROWS_UP
    result = (ptr_t)GC_find_limit(sp, FALSE);
#      else
    result = (ptr_t)GC_find_limit(sp, TRUE /* up */);
#      endif
#      if defined(HEURISTIC2_LIMIT) && !defined(CPPCHECK)
    if (HOTTER_THAN(HEURISTIC2_LIMIT, result)
        && HOTTER_THAN(sp, HEURISTIC2_LIMIT))
      result = HEURISTIC2_LIMIT;
#      endif
  }
#    elif defined(STACK_NOT_SCANNED) || defined(CPPCHECK)
  result = NULL;
#    else
#      error None of HEURISTIC* and *STACKBOTTOM defined!
#    endif
#    if !defined(STACK_GROWS_UP) && !defined(CPPCHECK)
  if (NULL == result)
    result = MAKE_CPTR((GC_signed_word)(-sizeof(ptr_t)));
#    endif
#  endif
#  if !defined(CPPCHECK)
  GC_ASSERT(HOTTER_THAN(GC_approx_sp(), result));
#  endif
  return result;
}
#  define GET_MAIN_STACKBASE_SPECIAL
#endif /* !ANY_MSWIN && !EMBOX && !OS2 && !SERENITY */

#if (defined(HAVE_PTHREAD_ATTR_GET_NP) || defined(HAVE_PTHREAD_GETATTR_NP)) \
    && defined(THREADS) && !defined(HAVE_GET_STACK_BASE)
#  include <pthread.h>
#  ifdef HAVE_PTHREAD_NP_H
#    include <pthread_np.h>
#  endif

GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *b)
{
  pthread_attr_t attr;
  size_t size;

#  ifdef HAVE_PTHREAD_ATTR_GET_NP
  if (pthread_attr_init(&attr) != 0)
    ABORT("pthread_attr_init failed");
  if (pthread_attr_get_np(pthread_self(), &attr) != 0) {
    WARN("pthread_attr_get_np failed\n", 0);
    (void)pthread_attr_destroy(&attr);
    return GC_UNIMPLEMENTED;
  }
#  else /* HAVE_PTHREAD_GETATTR_NP */
  if (pthread_getattr_np(pthread_self(), &attr) != 0) {
    WARN("pthread_getattr_np failed\n", 0);
    return GC_UNIMPLEMENTED;
  }
#  endif
  if (pthread_attr_getstack(&attr, &b->mem_base, &size) != 0) {
    ABORT("pthread_attr_getstack failed");
  }
  (void)pthread_attr_destroy(&attr);
#  ifndef STACK_GROWS_UP
  b->mem_base = (char *)b->mem_base + size;
#  endif
#  ifdef IA64
  /* We could try backing_store_base_from_proc, but that's safe     */
  /* only if no mappings are being asynchronously created.          */
  /* Subtracting the size from the stack base doesn't work for at   */
  /* least the main thread.                                         */
  LOCK();
  {
    IF_CANCEL(int cancel_state;)
    ptr_t bsp;
    ptr_t next_stack;

    DISABLE_CANCEL(cancel_state);
    bsp = GC_save_regs_in_stack();
    next_stack = GC_greatest_stack_base_below(bsp);
    if (NULL == next_stack) {
      b->reg_base = GC_find_limit(bsp, FALSE);
    } else {
      /* Avoid walking backwards into preceding memory stack and    */
      /* growing it.                                                */
      b->reg_base = GC_find_limit_with_bound(bsp, FALSE, next_stack);
    }
    RESTORE_CANCEL(cancel_state);
  }
  UNLOCK();
#  elif defined(E2K)
  b->reg_base = NULL;
#  endif
  return GC_SUCCESS;
}
#  define HAVE_GET_STACK_BASE
#endif /* THREADS && (HAVE_PTHREAD_ATTR_GET_NP || HAVE_PTHREAD_GETATTR_NP) */

#if defined(DARWIN) && defined(THREADS) \
    && !defined(NO_PTHREAD_GET_STACKADDR_NP)
#  include <pthread.h>

GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *b)
{
  /* pthread_get_stackaddr_np() should return stack bottom (highest   */
  /* stack address plus 1).                                           */
  b->mem_base = pthread_get_stackaddr_np(pthread_self());
  GC_ASSERT(HOTTER_THAN(GC_approx_sp(), (ptr_t)b->mem_base));
  return GC_SUCCESS;
}
#  define HAVE_GET_STACK_BASE
#endif /* DARWIN && THREADS && !NO_PTHREAD_GET_STACKADDR_NP */

#if defined(OPENBSD) && defined(THREADS)
#  include <pthread.h>
#  include <pthread_np.h>
#  include <sys/signal.h>

/* Find the stack using pthread_stackseg_np(). */
GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *sb)
{
  stack_t stack;
  if (pthread_stackseg_np(pthread_self(), &stack))
    ABORT("pthread_stackseg_np(self) failed");
  sb->mem_base = stack.ss_sp;
  return GC_SUCCESS;
}
#  define HAVE_GET_STACK_BASE
#endif /* OPENBSD && THREADS */

#if defined(SOLARIS) && defined(THREADS) && !defined(_STRICT_STDC)

#  include <pthread.h>
#  include <thread.h>

/* These variables are used to cache ss_sp value for the primordial   */
/* thread (it's better not to call thr_stksegment() twice for this    */
/* thread - see JDK bug #4352906).                                    */
/* Note: stackbase_main_self set to zero means stackbase_main_ss_sp   */
/* value is unset.                                                    */
static pthread_t stackbase_main_self = 0;
static void *stackbase_main_ss_sp = NULL;

#  ifdef CAN_HANDLE_FORK
GC_INNER void
GC_stackbase_info_update_after_fork(void)
{
  if (stackbase_main_self == GC_parent_pthread_self) {
    /* The primordial thread has forked the process. */
    stackbase_main_self = pthread_self();
  } else {
    stackbase_main_self = 0;
  }
}
#  endif

GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *b)
{
  stack_t s;
  pthread_t self = pthread_self();

  if (self == stackbase_main_self) {
    /* If the client calls GC_get_stack_base() from the main thread */
    /* then just return the cached value.                           */
    b->mem_base = stackbase_main_ss_sp;
    GC_ASSERT(b->mem_base != NULL);
    return GC_SUCCESS;
  }

  if (thr_stksegment(&s)) {
    /* According to the manual, the only failure error code returned  */
    /* is EAGAIN meaning "the information is not available due to the */
    /* thread is not yet completely initialized or it is an internal  */
    /* thread" - this shouldn't happen here.                          */
    ABORT("thr_stksegment failed");
  }
  /* s.ss_sp holds the pointer to the stack bottom. */
  GC_ASSERT(HOTTER_THAN(GC_approx_sp(), (ptr_t)s.ss_sp));

  if (!stackbase_main_self && thr_main() != 0) {
    /* Cache the stack bottom pointer for the primordial thread     */
    /* (this is done during GC_init, so there is no race).          */
    stackbase_main_ss_sp = s.ss_sp;
    stackbase_main_self = self;
  }

  b->mem_base = s.ss_sp;
  return GC_SUCCESS;
}
#  define HAVE_GET_STACK_BASE
#endif /* SOLARIS && THREADS */

#if defined(RTEMS) && defined(THREADS)
GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *sb)
{
  sb->mem_base = rtems_get_stack_bottom();
  return GC_SUCCESS;
}
#  define HAVE_GET_STACK_BASE
#endif /* RTEMS && THREADS */

#ifndef HAVE_GET_STACK_BASE

#  ifdef NEED_FIND_LIMIT
/* Retrieve the stack bottom.                                       */
/* Using the GC_find_limit version is risky.                        */
/* On IA64, for example, there is no guard page between the         */
/* stack of one thread and the register backing store of the        */
/* next.  Thus this is likely to identify way too large a           */
/* "stack" and thus at least result in disastrous performance.      */
/* TODO: Implement better strategies here. */
GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *b)
{
  IF_CANCEL(int cancel_state;)

  LOCK();
  /* TODO: DISABLE_CANCEL may be unnecessary? */
  DISABLE_CANCEL(cancel_state);
#    ifdef STACK_GROWS_UP
  b->mem_base = GC_find_limit(GC_approx_sp(), FALSE);
#    else
  b->mem_base = GC_find_limit(GC_approx_sp(), TRUE /* up */);
#    endif
#    ifdef IA64
  b->reg_base = GC_find_limit(GC_save_regs_in_stack(), FALSE);
#    elif defined(E2K)
  b->reg_base = NULL;
#    endif
  RESTORE_CANCEL(cancel_state);
  UNLOCK();
  return GC_SUCCESS;
}
#  else /* !NEED_FIND_LIMIT */
GC_API int GC_CALL
GC_get_stack_base(struct GC_stack_base *b)
{
#    if defined(GET_MAIN_STACKBASE_SPECIAL) && !defined(THREADS) \
        && !defined(IA64)
  b->mem_base = GC_get_main_stack_base();
  return GC_SUCCESS;
#    else
  UNUSED_ARG(b);
  return GC_UNIMPLEMENTED;
#    endif
}
#  endif

#endif /* !HAVE_GET_STACK_BASE */

#ifndef GET_MAIN_STACKBASE_SPECIAL
/* This is always called from the main thread.  Default implementation. */
GC_INNER ptr_t
GC_get_main_stack_base(void)
{
  struct GC_stack_base sb;

  if (GC_get_stack_base(&sb) != GC_SUCCESS)
    ABORT("GC_get_stack_base failed");
  GC_ASSERT(HOTTER_THAN(GC_approx_sp(), (ptr_t)sb.mem_base));
  return (ptr_t)sb.mem_base;
}
#endif /* !GET_MAIN_STACKBASE_SPECIAL */

/* Register static data segment(s) as roots.  If more data segments are */
/* added later then they need to be registered at that point (as we do  */
/* with SunOS dynamic loading), or GC_mark_roots needs to check for     */
/* them.                                                                */

#ifdef ANY_MSWIN

#  if defined(GWW_VDB)
#    ifndef MEM_WRITE_WATCH
#      define MEM_WRITE_WATCH 0x200000
#    endif
#    ifndef WRITE_WATCH_FLAG_RESET
#      define WRITE_WATCH_FLAG_RESET 1
#    endif

/* Since we can't easily check whether ULONG_PTR and SIZE_T are     */
/* defined in Win32 basetsd.h, we define own ULONG_PTR.             */
#    define GC_ULONG_PTR word

typedef UINT(WINAPI *GetWriteWatch_type)(DWORD, PVOID,
                                         GC_ULONG_PTR /* SIZE_T */, PVOID *,
                                         GC_ULONG_PTR *, PULONG);
static FARPROC GetWriteWatch_func;
static DWORD GetWriteWatch_alloc_flag;

#    define GC_GWW_AVAILABLE() (GetWriteWatch_func != 0)

static void
detect_GetWriteWatch(void)
{
  static GC_bool done;
  HMODULE hK32;
  if (done)
    return;

#    if defined(MPROTECT_VDB)
  {
    char *str = GETENV("GC_USE_GETWRITEWATCH");
#      if defined(GC_PREFER_MPROTECT_VDB)
    if (NULL == str || (*str == '0' && *(str + 1) == '\0')) {
      /* GC_USE_GETWRITEWATCH is unset or set to "0".           */
      /* Falling back to MPROTECT_VDB strategy.                 */
      done = TRUE;
      /* This should work as if GWW_VDB is undefined. */
      return;
    }
#      else
    if (str != NULL && *str == '0' && *(str + 1) == '\0') {
      /* GC_USE_GETWRITEWATCH is set "0".                       */
      /* Falling back to MPROTECT_VDB strategy.                 */
      done = TRUE;
      return;
    }
#      endif
  }
#    endif

#    if defined(MSWINRT_FLAVOR) && defined(FUNCPTR_IS_DATAPTR)
  {
    MEMORY_BASIC_INFORMATION memInfo;
    SIZE_T result = VirtualQuery(CAST_THRU_UINTPTR(void *, GetProcAddress),
                                 &memInfo, sizeof(memInfo));

    if (result != sizeof(memInfo))
      ABORT("Weird VirtualQuery result");
    hK32 = (HMODULE)memInfo.AllocationBase;
  }
#    else
  hK32 = GetModuleHandle(TEXT("kernel32.dll"));
#    endif
  if (hK32 != (HMODULE)0
      && (GetWriteWatch_func = GetProcAddress(hK32, "GetWriteWatch")) != 0) {
    void *page;

    GC_ASSERT(GC_page_size != 0);
    /* Also check whether VirtualAlloc accepts MEM_WRITE_WATCH, */
    /* as some versions of kernel32.dll have one but not the    */
    /* other, making the feature completely broken.             */
    page = VirtualAlloc(NULL, GC_page_size, MEM_WRITE_WATCH | MEM_RESERVE,
                        PAGE_READWRITE);
    if (page != NULL) {
      PVOID pages[16];
      GC_ULONG_PTR count = sizeof(pages) / sizeof(PVOID);
      DWORD page_size;
      /* Check that it actually works.  In spite of some        */
      /* documentation it actually seems to exist on Win2K.     */
      /* This test may be unnecessary, but ...                  */
      if ((*(GetWriteWatch_type)(GC_funcptr_uint)GetWriteWatch_func)(
              WRITE_WATCH_FLAG_RESET, page, GC_page_size, pages, &count,
              &page_size)
          != 0) {
        /* GetWriteWatch always fails. */
        GetWriteWatch_func = 0;
      } else {
        GetWriteWatch_alloc_flag = MEM_WRITE_WATCH;
      }
      VirtualFree(page, 0 /* dwSize */, MEM_RELEASE);
    } else {
      /* GetWriteWatch will be useless. */
      GetWriteWatch_func = 0;
    }
  }
  done = TRUE;
}

#  else
#    define GetWriteWatch_alloc_flag 0
#  endif /* !GWW_VDB */

#  ifdef MSWIN32
/* Unfortunately, we have to handle win32s very differently from    */
/* NT, since VirtualQuery has very different semantics.  In         */
/* particular, under win32s a VirtualQuery call on an unmapped page */
/* returns an invalid result.  Under NT, GC_register_data_segments  */
/* is a no-op and all real work is done by                          */
/* GC_register_dynamic_libraries().  Under win32s, we cannot find   */
/* the data segments associated with dll's.  We register the main   */
/* data segment here.                                               */

GC_INNER GC_bool GC_no_win32_dlls = FALSE;

/* This is a Windows NT derivative, i.e. NT, Win2K, XP or later.    */
GC_INNER GC_bool GC_wnt = FALSE;

GC_INNER void
GC_init_win32(void)
{
#    if defined(_WIN64) || (defined(_MSC_VER) && _MSC_VER >= 1800)
  /* MS Visual Studio 2013 deprecates GetVersion, but on the      */
  /* other hand it cannot be used to target pre-Win2K.            */
  GC_wnt = TRUE;
#    else
  /* Set GC_wnt.  If we're running under win32s, assume that no     */
  /* DLLs will be loaded.  I doubt anyone still runs win32s, but... */
  DWORD v = GetVersion();

  GC_wnt = !(v & (DWORD)0x80000000UL);
  GC_no_win32_dlls |= ((!GC_wnt) && (v & 0xff) <= 3);
#    endif
#    ifdef USE_MUNMAP
  if (GC_no_win32_dlls) {
    /* Turn off unmapping for safety (since may not work well     */
    /* with GlobalAlloc).                                         */
    GC_unmap_threshold = 0;
  }
#    endif
}

/* Return the smallest address p such that VirtualQuery returns     */
/* correct results for all addresses between p and start.  Assumes  */
/* VirtualQuery() returns correct information for start.            */
STATIC ptr_t
GC_least_described_address(ptr_t start)
{
  ptr_t limit = (ptr_t)GC_sysinfo.lpMinimumApplicationAddress;
  ptr_t p = PTR_ALIGN_DOWN(start, GC_page_size);

  GC_ASSERT(GC_page_size != 0);
  for (;;) {
    MEMORY_BASIC_INFORMATION buf;
    size_t result;
    ptr_t q;

    if (EXPECT(ADDR(p) <= (word)GC_page_size, FALSE)) {
      /* Avoid underflow.   */
      break;
    }
    q = p - GC_page_size;
    if (ADDR_LT(q, limit))
      break;

    result = VirtualQuery((LPVOID)q, &buf, sizeof(buf));
    if (result != sizeof(buf) || 0 == buf.AllocationBase)
      break;
    p = (ptr_t)buf.AllocationBase;
  }
  return p;
}

STATIC void
GC_register_root_section(ptr_t static_root)
{
  ptr_t p, base, limit;

  GC_ASSERT(I_HOLD_LOCK());
  if (!GC_no_win32_dlls)
    return;

  p = GC_least_described_address(static_root);
  base = limit = p;
  while (ADDR_LT(p, (ptr_t)GC_sysinfo.lpMaximumApplicationAddress)) {
    MEMORY_BASIC_INFORMATION buf;
    size_t result = VirtualQuery((LPVOID)p, &buf, sizeof(buf));

    if (result != sizeof(buf) || 0 == buf.AllocationBase
        || GC_is_heap_base(buf.AllocationBase))
      break;
    if (ADDR(p) > GC_WORD_MAX - buf.RegionSize) {
      /* Avoid overflow.    */
      break;
    }
    if (buf.State == MEM_COMMIT && is_writable(buf.Protect)) {
      if (p != limit) {
        if (base != limit)
          GC_add_roots_inner(base, limit, FALSE);
        base = p;
      }
      limit = p + buf.RegionSize;
    }
    p += buf.RegionSize;
  }
  if (base != limit)
    GC_add_roots_inner(base, limit, FALSE);
}
#  endif /* MSWIN32 */

#  if defined(USE_WINALLOC) && !defined(REDIRECT_MALLOC)
/* We maintain a linked list of AllocationBase values that we */
/* know correspond to malloc heap sections.  Currently this   */
/* is only called during a GC.  But there is some hope that   */
/* for long running programs we will eventually see most heap */
/* sections.                                                  */

/* In the long run, it would be more reliable to occasionally */
/* walk the malloc heap with HeapWalk on the default heap.    */
/* But that apparently works only for NT-based Windows.       */

/* Note: initialized to approximate largest root size.        */
STATIC size_t GC_max_root_size = 100000;

/* In the long run, a better data structure would also be nice... */
STATIC struct GC_malloc_heap_list {
  void *allocation_base;
  struct GC_malloc_heap_list *next;
} *GC_malloc_heap_l = 0;

/* Is p the base of one of the malloc heap sections we already    */
/* know about?                                                    */
STATIC GC_bool
GC_is_malloc_heap_base(const void *p)
{
  struct GC_malloc_heap_list *q;

  for (q = GC_malloc_heap_l; q != NULL; q = q->next) {
    if (q->allocation_base == p)
      return TRUE;
  }
  return FALSE;
}

STATIC void *
GC_get_allocation_base(void *p)
{
  MEMORY_BASIC_INFORMATION buf;
  size_t result = VirtualQuery(p, &buf, sizeof(buf));

  if (result != sizeof(buf)) {
    ABORT("Weird VirtualQuery result");
  }
  return buf.AllocationBase;
}

GC_INNER void
GC_add_current_malloc_heap(void)
{
  struct GC_malloc_heap_list *new_l = (struct GC_malloc_heap_list *)malloc(
      sizeof(struct GC_malloc_heap_list));
  void *candidate;

  if (NULL == new_l)
    return;
  /* Explicitly set to suppress maybe-uninitialized gcc warning.  */
  new_l->allocation_base = NULL;

  candidate = GC_get_allocation_base(new_l);
  if (GC_is_malloc_heap_base(candidate)) {
    /* Try a little harder to find malloc heap.   */
    size_t req_size = 10000;

    do {
      void *p = malloc(req_size);

      if (NULL == p) {
        free(new_l);
        return;
      }
      candidate = GC_get_allocation_base(p);
      free(p);
      req_size *= 2;
    } while (GC_is_malloc_heap_base(candidate)
             && req_size < GC_max_root_size / 10 && req_size < 500000);
    if (GC_is_malloc_heap_base(candidate)) {
      free(new_l);
      return;
    }
  }
  GC_COND_LOG_PRINTF("Found new system malloc AllocationBase at %p\n",
                     candidate);
  new_l->allocation_base = candidate;
  new_l->next = GC_malloc_heap_l;
  GC_malloc_heap_l = new_l;
}

/* Free all the linked list nodes.  Could be invoked at process   */
/* exit to avoid memory leak complains of a dynamic code analysis */
/* tool.                                                          */
STATIC void
GC_free_malloc_heap_list(void)
{
  struct GC_malloc_heap_list *q = GC_malloc_heap_l;

  GC_malloc_heap_l = NULL;
  while (q != NULL) {
    struct GC_malloc_heap_list *next = q->next;

    free(q);
    q = next;
  }
}
#  endif /* USE_WINALLOC && !REDIRECT_MALLOC */

/* Is p the start of either the malloc heap, or of one of our   */
/* heap sections?                                               */
GC_INNER GC_bool
GC_is_heap_base(const void *p)
{
  size_t i;

#  if defined(USE_WINALLOC) && !defined(REDIRECT_MALLOC)
  if (GC_root_size > GC_max_root_size)
    GC_max_root_size = GC_root_size;
  if (GC_is_malloc_heap_base(p))
    return TRUE;
#  endif
  for (i = 0; i < GC_n_heap_bases; i++) {
    if (GC_heap_bases[i] == p)
      return TRUE;
  }
  return FALSE;
}

GC_INNER void
GC_register_data_segments(void)
{
#  ifdef MSWIN32
  /* Note: any other GC global variable would fit too.    */
  GC_register_root_section((ptr_t)&GC_pages_executable);
#  endif
}

#endif /* ANY_MSWIN */

#ifdef DATASTART_USES_XGETDATASTART
#  ifdef CHERI_PURECAP
#    include <link.h>

/* The CheriBSD LLVM compiler declares etext, edata and end as typeless */
/* variables.  If libgc is statically linked with the executable, these */
/* capabilities are compiled with the read-only permissions and bounds  */
/* that span the .data and .bss sections.  If libgc is compiled as      */
/* a shared library, these symbols are compiled with zero bounds and    */
/* cannot be dereferenced; instead, the read-only capability returned   */
/* by the loader is used.                                               */

struct scan_bounds_s {
  word start_addr;
  word end_addr;
  ptr_t ld_cap;
};

static int
ld_cap_search(struct dl_phdr_info *info, size_t size, void *cd)
{
  struct scan_bounds_s *region = (struct scan_bounds_s *)cd;
  ptr_t load_ptr = (ptr_t)info->dlpi_addr;

  UNUSED_ARG(size);
  if (!SPANNING_CAPABILITY(load_ptr, region->start_addr, region->end_addr))
    return 0;

  region->ld_cap = (ptr_t)cheri_bounds_set(
      cheri_address_set(load_ptr, region->start_addr),
      region->end_addr - region->start_addr);
  return 1; /* stop */
}

static ptr_t
derive_cap_from_ldr(ptr_t range_start, ptr_t range_end)
{
  word scan_start = ADDR(range_start);
  word scan_end = ADDR(range_end);
  struct scan_bounds_s region;

  /* If symbols already span the required range, return one of them.    */
  if (SPANNING_CAPABILITY(range_start, scan_start, scan_end))
    return range_start;
  if (SPANNING_CAPABILITY(range_end, scan_start, scan_end))
    return range_end;

  /* Fall-back option: derive .data plus .bss end pointer from the      */
  /* read-only capability provided by loader.                           */
  region.start_addr = scan_start;
  region.end_addr = scan_end;
  region.ld_cap = NULL; /* prevent compiler warning */
  if (!dl_iterate_phdr(ld_cap_search, &region))
    ABORT("Cannot find static roots for capability system");
  GC_ASSERT(region.ld_cap != NULL);
  return region.ld_cap;
}
#  endif /* CHERI_PURECAP */

GC_INNER ptr_t
GC_SysVGetDataStart(size_t max_page_size, ptr_t etext_ptr)
{
  volatile ptr_t result;

  GC_ASSERT(max_page_size % ALIGNMENT == 0);
  result = PTR_ALIGN_UP(etext_ptr, ALIGNMENT);
#  ifdef CHERI_PURECAP
  result = derive_cap_from_ldr(result, DATAEND);
#  endif

  GC_setup_temporary_fault_handler();
  if (SETJMP(GC_jmp_buf) == 0) {
    /* Note that this is not equivalent to just adding max_page_size to */
    /* etext_ptr because the latter is not guaranteed to be multiple of */
    /* the page size.                                                   */
    ptr_t next_page = PTR_ALIGN_UP(result, max_page_size);

#  ifdef FREEBSD
    /* It's unclear whether this should be identical to the below, or   */
    /* whether it should apply to non-x86 architectures.  For now we    */
    /* do not assume that there is always an empty page after etext.    */
    /* But in some cases there actually seems to be slightly more.      */
    /* It also deals with holes between read-only and writable data.    */

    /* Try reading at the address.  This should happen before there is  */
    /* another thread.                                                  */
    for (; ADDR_LT(next_page, DATAEND); next_page += max_page_size) {
      GC_noop1((word)(*(volatile unsigned char *)next_page));
    }
#  else
    result = next_page + (ADDR(result) & ((word)max_page_size - 1));
    /* Try writing to the address. */
    {
#    ifdef AO_HAVE_fetch_and_add
      volatile AO_t zero = 0;

      (void)AO_fetch_and_add((volatile AO_t *)result, zero);
#    else
      /* Fallback to non-atomic fetch-and-store. */
      char v = *result;

#      ifdef CPPCHECK
      GC_noop1_ptr(&v);
#      endif
      *result = v;
#    endif
    }
#  endif
    GC_reset_fault_handler();
  } else {
    GC_reset_fault_handler();
    /* We got here via a longjmp.  The address is not readable.   */
    /* This is known to happen under Solaris 2.4 + gcc, which     */
    /* places string constants in the text segment, but after     */
    /* etext.  Use plan B.  Note that we now know there is a gap  */
    /* between text and data segments, so plan A brought us       */
    /* something.                                                 */
#  ifdef CHERI_PURECAP
    result = (ptr_t)GC_find_limit(cheri_address_set(result, ADDR(DATAEND)),
                                  FALSE);
#  else
    result = (ptr_t)GC_find_limit(DATAEND, FALSE);
#  endif
  }
  return (ptr_t)CAST_AWAY_VOLATILE_PVOID(result);
}
#endif /* DATASTART_USES_XGETDATASTART */

#if defined(OS2)
GC_INNER void
GC_register_data_segments(void)
{
  PTIB ptib;
  PPIB ppib;
  HMODULE module_handle;
#  define PBUFSIZ 512
  UCHAR path[PBUFSIZ];
  FILE *myexefile;
  struct exe_hdr hdrdos; /* MSDOS header */
  struct e32_exe hdr386; /* real header for my executable */
  struct o32_obj seg;    /* current segment */
  int nsegs;

#  if defined(CPPCHECK)
  hdrdos.padding[0] = 0; /* to prevent "field unused" warnings */
  hdr386.exe_format_level = 0;
  hdr386.os = 0;
  hdr386.padding1[0] = 0;
  hdr386.padding2[0] = 0;
  seg.pagemap = 0;
  seg.mapsize = 0;
  seg.reserved = 0;
#  endif
  if (DosGetInfoBlocks(&ptib, &ppib) != NO_ERROR) {
    ABORT("DosGetInfoBlocks failed");
  }
  module_handle = ppib->pib_hmte;
  if (DosQueryModuleName(module_handle, PBUFSIZ, path) != NO_ERROR) {
    ABORT("DosQueryModuleName failed");
  }
  myexefile = fopen(path, "rb");
  if (myexefile == 0) {
    ABORT_ARG1("Failed to open executable", ": %s", path);
  }
  if (fread((char *)&hdrdos, 1, sizeof(hdrdos), myexefile) < sizeof(hdrdos)) {
    ABORT_ARG1("Could not read MSDOS header", " from: %s", path);
  }
  if (E_MAGIC(hdrdos) != EMAGIC) {
    ABORT_ARG1("Bad DOS magic number", " in file: %s", path);
  }
  if (fseek(myexefile, E_LFANEW(hdrdos), SEEK_SET) != 0) {
    ABORT_ARG1("Bad DOS magic number", " in file: %s", path);
  }
  if (fread((char *)&hdr386, 1, sizeof(hdr386), myexefile) < sizeof(hdr386)) {
    ABORT_ARG1("Could not read OS/2 header", " from: %s", path);
  }
  if (E32_MAGIC1(hdr386) != E32MAGIC1 || E32_MAGIC2(hdr386) != E32MAGIC2) {
    ABORT_ARG1("Bad OS/2 magic number", " in file: %s", path);
  }
  if (E32_BORDER(hdr386) != E32LEBO || E32_WORDER(hdr386) != E32LEWO) {
    ABORT_ARG1("Bad byte order in executable", " file: %s", path);
  }
  if (E32_CPU(hdr386) == E32CPU286) {
    ABORT_ARG1("GC cannot handle 80286 executables", ": %s", path);
  }
  if (fseek(myexefile, E_LFANEW(hdrdos) + E32_OBJTAB(hdr386), SEEK_SET) != 0) {
    ABORT_ARG1("Seek to object table failed", " in file: %s", path);
  }
  for (nsegs = E32_OBJCNT(hdr386); nsegs > 0; nsegs--) {
    int flags;
    if (fread((char *)&seg, 1, sizeof(seg), myexefile) < sizeof(seg)) {
      ABORT_ARG1("Could not read obj table entry", " from file: %s", path);
    }
    flags = O32_FLAGS(seg);
    if (!(flags & OBJWRITE))
      continue;
    if (!(flags & OBJREAD))
      continue;
    if (flags & OBJINVALID) {
      GC_err_printf("Object with invalid pages?\n");
      continue;
    }
    GC_add_roots_inner((ptr_t)O32_BASE(seg),
                       (ptr_t)(O32_BASE(seg) + O32_SIZE(seg)), FALSE);
  }
  (void)fclose(myexefile);
}

#elif defined(OPENBSD)
/* Depending on arch alignment, there can be multiple holes       */
/* between DATASTART and DATAEND.  Scan in DATASTART .. DATAEND   */
/* and register each region.                                      */
GC_INNER void
GC_register_data_segments(void)
{
  ptr_t region_start = DATASTART;

  GC_ASSERT(I_HOLD_LOCK());
  if (ADDR(region_start) - 1U >= ADDR(DATAEND))
    ABORT_ARG2("Wrong DATASTART/END pair", ": %p .. %p", (void *)region_start,
               (void *)DATAEND);
  for (;;) {
    ptr_t region_end = GC_find_limit_with_bound(region_start, TRUE, DATAEND);

    GC_add_roots_inner(region_start, region_end, FALSE);
    if (ADDR_GE(region_end, DATAEND))
      break;
    region_start = GC_skip_hole_openbsd(region_end, DATAEND);
  }
}

#elif !defined(ANY_MSWIN)
GC_INNER void
GC_register_data_segments(void)
{
  GC_ASSERT(I_HOLD_LOCK());
#  if !defined(DYNAMIC_LOADING) && defined(GC_DONT_REGISTER_MAIN_STATIC_DATA)
  /* Avoid even referencing DATASTART and DATAEND as they are   */
  /* unnecessary and cause linker errors when bitcode is        */
  /* enabled.  GC_register_data_segments is not called anyway.  */
#  elif defined(DYNAMIC_LOADING) && (defined(DARWIN) || defined(HAIKU))
  /* No-op.  GC_register_main_static_data() always returns false. */
#  elif defined(REDIRECT_MALLOC) && defined(SOLARIS) && defined(THREADS)
  /* As of Solaris 2.3, the Solaris threads implementation    */
  /* allocates the data structure for the initial thread with */
  /* sbrk at process startup.  It needs to be scanned, so     */
  /* that we don't lose some malloc allocated data structures */
  /* hanging from it.  We're on thin ice here...              */
  GC_ASSERT(DATASTART);
  {
    ptr_t p = (ptr_t)sbrk(0);

    if (ADDR_LT(DATASTART, p))
      GC_add_roots_inner(DATASTART, p, FALSE);
  }
#  else
  /* Note: subtract one to also check for NULL without        */
  /* a compiler warning.                                      */
  if (ADDR(DATASTART) - 1U >= ADDR(DATAEND)) {
    ABORT_ARG2("Wrong DATASTART/END pair", ": %p .. %p", (void *)DATASTART,
               (void *)DATAEND);
  }
  GC_add_roots_inner(DATASTART, DATAEND, FALSE);
#    ifdef GC_HAVE_DATAREGION2
  if (ADDR(DATASTART2) - 1U >= ADDR(DATAEND2))
    ABORT_ARG2("Wrong DATASTART/END2 pair", ": %p .. %p", (void *)DATASTART2,
               (void *)DATAEND2);
  GC_add_roots_inner(DATASTART2, DATAEND2, FALSE);
#    endif
#  endif
  /* Dynamic libraries are added at every collection, since they  */
  /* may change.                                                  */
}
#endif /* !ANY_MSWIN && !OPENBSD && !OS2 */

/* Auxiliary routines for obtaining memory from OS.     */

#ifdef NEED_UNIX_GET_MEM

#  define SBRK_ARG_T ptrdiff_t

#  if defined(MMAP_SUPPORTED)

#    ifdef USE_MMAP_FIXED
/* Seems to yield better performance on Solaris 2, but can be       */
/* unreliable if something is already mapped at the address.        */
#      define GC_MMAP_FLAGS MAP_FIXED | MAP_PRIVATE
#    else
#      define GC_MMAP_FLAGS MAP_PRIVATE
#    endif

#    ifdef USE_MMAP_ANON
#      define zero_fd -1
#      if defined(MAP_ANONYMOUS) && !defined(CPPCHECK)
#        define OPT_MAP_ANON MAP_ANONYMOUS
#      else
#        define OPT_MAP_ANON MAP_ANON
#      endif
#    else
static int zero_fd = -1;
#      define OPT_MAP_ANON 0
#    endif

#    ifndef MSWIN_XBOX1
#      if defined(SYMBIAN) && !defined(USE_MMAP_ANON)
EXTERN_C_BEGIN
extern char *GC_get_private_path_and_zero_file(void);
EXTERN_C_END
#      endif

STATIC void *
GC_unix_mmap_get_mem(size_t bytes)
{
  void *result;
  static word last_addr = HEAP_START;

#      ifndef USE_MMAP_ANON
  static GC_bool initialized = FALSE;

  if (!EXPECT(initialized, TRUE)) {
#        ifdef SYMBIAN
    char *path = GC_get_private_path_and_zero_file();
    if (path != NULL) {
      zero_fd = open(path, O_RDWR | O_CREAT, 0644);
      free(path);
    }
#        else
    zero_fd = open("/dev/zero", O_RDONLY);
#        endif
    if (zero_fd == -1)
      ABORT("Could not open /dev/zero");
    if (fcntl(zero_fd, F_SETFD, FD_CLOEXEC) == -1)
      WARN("Could not set FD_CLOEXEC for /dev/zero\n", 0);

    initialized = TRUE;
  }
#      endif

  GC_ASSERT(GC_page_size != 0);
  if (bytes & (GC_page_size - 1))
    ABORT("Bad GET_MEM arg");
  /* Note: it is essential for CHERI to have only address part in   */
  /* last_addr without metadata (thus the variable is of word type  */
  /* intentionally), otherwise mmap() fails setting errno to EPROT. */
  result
      = mmap(MAKE_CPTR(last_addr), bytes,
             (PROT_READ | PROT_WRITE) | (GC_pages_executable ? PROT_EXEC : 0),
             GC_MMAP_FLAGS | OPT_MAP_ANON, zero_fd, 0 /* offset */);
#      undef IGNORE_PAGES_EXECUTABLE

  if (EXPECT(MAP_FAILED == result, FALSE)) {
    if (HEAP_START == last_addr && GC_pages_executable
        && (EACCES == errno || EPERM == errno))
      ABORT("Cannot allocate executable pages");
    return NULL;
  }
#      ifdef LINUX
  GC_ASSERT(ADDR(result) <= ~(word)(GC_page_size - 1) - bytes);
  /* The following PTR_ALIGN_UP() cannot overflow.  */
#      else
  if (EXPECT(ADDR(result) > ~(word)(GC_page_size - 1) - bytes, FALSE)) {
    /* Oops.  We got the end of the address space.  This isn't      */
    /* usable by arbitrary C code, since one-past-end pointers      */
    /* do not work, so we discard it and try again.                 */
    /* Leave the last page mapped, so we can't repeat.              */
    (void)munmap(result, ~(GC_page_size - 1) - (size_t)ADDR(result));
    return GC_unix_mmap_get_mem(bytes);
  }
#      endif
  if ((ADDR(result) % HBLKSIZE) != 0)
    ABORT("Memory returned by mmap is not aligned to HBLKSIZE");
  last_addr = ADDR(result) + bytes;
  GC_ASSERT((last_addr & (GC_page_size - 1)) == 0);
  return result;
}
#    endif /* !MSWIN_XBOX1 */

#  endif /* MMAP_SUPPORTED */

#  if defined(USE_MMAP)

GC_INNER void *
GC_unix_get_mem(size_t bytes)
{
  return GC_unix_mmap_get_mem(bytes);
}

#  else /* !USE_MMAP */

STATIC void *
GC_unix_sbrk_get_mem(size_t bytes)
{
  void *result;

#    ifdef IRIX5
  /* Bare sbrk isn't thread safe.  Play by malloc rules.      */
  /* The equivalent may be needed on other systems as well.   */
  __LOCK_MALLOC();
#    endif
  {
    ptr_t cur_brk = (ptr_t)sbrk(0);
    SBRK_ARG_T lsbs = ADDR(cur_brk) & (GC_page_size - 1);

    GC_ASSERT(GC_page_size != 0);
    if (EXPECT((SBRK_ARG_T)bytes < 0, FALSE)) {
      /* Value of bytes is too big.   */
      result = NULL;
      goto out;
    }
    if (lsbs != 0) {
      if ((ptr_t)sbrk((SBRK_ARG_T)GC_page_size - lsbs) == (ptr_t)(-1)) {
        result = NULL;
        goto out;
      }
    }
#    ifdef ADD_HEAP_GUARD_PAGES
    /* This is useful for catching severe memory overwrite problems that */
    /* span heap sections.  It shouldn't otherwise be turned on.         */
    {
      ptr_t guard = (ptr_t)sbrk((SBRK_ARG_T)GC_page_size);
      if (mprotect(guard, GC_page_size, PROT_NONE) != 0)
        ABORT("ADD_HEAP_GUARD_PAGES: mprotect failed");
    }
#    endif
    result = sbrk((SBRK_ARG_T)bytes);
    if (EXPECT(ADDR(result) == GC_WORD_MAX, FALSE))
      result = NULL;
  }
out:
#    ifdef IRIX5
  __UNLOCK_MALLOC();
#    endif
  return result;
}

GC_INNER void *
GC_unix_get_mem(size_t bytes)
{
#    if defined(MMAP_SUPPORTED)
  /* By default, we try both sbrk and mmap, in that order.    */
  static GC_bool sbrk_failed = FALSE;
  void *result = NULL;

  if (GC_pages_executable) {
    /* If the allocated memory should have the execute permission   */
    /* then sbrk() cannot be used.                                  */
    return GC_unix_mmap_get_mem(bytes);
  }
  if (!sbrk_failed)
    result = GC_unix_sbrk_get_mem(bytes);
  if (NULL == result) {
    sbrk_failed = TRUE;
    result = GC_unix_mmap_get_mem(bytes);
    if (NULL == result) {
      /* Try sbrk again, in case sbrk memory became available.    */
      result = GC_unix_sbrk_get_mem(bytes);
    }
  }
  return result;
#    else /* !MMAP_SUPPORTED */
  return GC_unix_sbrk_get_mem(bytes);
#    endif
}

#  endif /* !USE_MMAP */

#endif /* NEED_UNIX_GET_MEM */

#if defined(OS2)
GC_INNER void *
GC_get_mem(size_t bytes)
{
  void *result = NULL;
  int retry;

  GC_ASSERT(GC_page_size != 0);
  bytes = SIZET_SAT_ADD(bytes, GC_page_size);
  for (retry = 0;; retry++) {
    if (DosAllocMem(&result, bytes,
                    (PAG_READ | PAG_WRITE | PAG_COMMIT)
                        | (GC_pages_executable ? PAG_EXECUTE : 0))
            == NO_ERROR
        && EXPECT(result != NULL, TRUE))
      break;
    /* TODO: Unclear the purpose of the retry.  (Probably, if           */
    /* DosAllocMem returns memory at 0 address then just retry once.)   */
    if (retry >= 1)
      return NULL;
  }
  return HBLKPTR((ptr_t)result + GC_page_size - 1);
}

#elif defined(MSWIN_XBOX1)
GC_INNER void *
GC_get_mem(size_t bytes)
{
  if (EXPECT(0 == bytes, FALSE))
    return NULL;
  return VirtualAlloc(NULL, bytes, MEM_COMMIT | MEM_TOP_DOWN, PAGE_READWRITE);
}

#elif defined(MSWINCE)
GC_INNER void *
GC_get_mem(size_t bytes)
{
  void *result = NULL; /* initialized to prevent warning */
  size_t i;

  GC_ASSERT(GC_page_size != 0);
  bytes = ROUNDUP_PAGESIZE(bytes);

  /* Try to find reserved, uncommitted pages. */
  for (i = 0; i < GC_n_heap_bases; i++) {
    if (((word)(-(GC_signed_word)GC_heap_lengths[i])
         & (GC_sysinfo.dwAllocationGranularity - 1))
        >= bytes) {
      result = GC_heap_bases[i] + GC_heap_lengths[i];
      break;
    }
  }

  if (i == GC_n_heap_bases) {
    /* Reserve more pages.  */
    size_t res_bytes
        = SIZET_SAT_ADD(bytes, (size_t)GC_sysinfo.dwAllocationGranularity - 1)
          & ~((size_t)GC_sysinfo.dwAllocationGranularity - 1);
    /* If we ever support MPROTECT_VDB here, we will probably need  */
    /* to ensure that res_bytes is greater (strictly) than bytes,   */
    /* so that VirtualProtect never spans regions.  It seems to be  */
    /* fine for a VirtualFree argument to span regions, so we       */
    /* should be OK for now.                                        */
    result = VirtualAlloc(NULL, res_bytes, MEM_RESERVE | MEM_TOP_DOWN,
                          GC_pages_executable ? PAGE_EXECUTE_READWRITE
                                              : PAGE_READWRITE);
    if (HBLKDISPL(result) != 0) {
      /* If I read the documentation correctly, this can only       */
      /* happen if HBLKSIZE > 64 KB or not a power of 2.            */
      ABORT("Bad VirtualAlloc result");
    }
    if (GC_n_heap_bases >= MAX_HEAP_SECTS)
      ABORT("Too many heap sections");
    if (EXPECT(NULL == result, FALSE))
      return NULL;
    GC_heap_bases[GC_n_heap_bases] = (ptr_t)result;
    GC_heap_lengths[GC_n_heap_bases] = 0;
    GC_n_heap_bases++;
  }

  /* Commit pages.    */
  result = VirtualAlloc(result, bytes, MEM_COMMIT,
                        GC_pages_executable ? PAGE_EXECUTE_READWRITE
                                            : PAGE_READWRITE);
#  undef IGNORE_PAGES_EXECUTABLE

  if (HBLKDISPL(result) != 0)
    ABORT("Bad VirtualAlloc result");
  if (EXPECT(result != NULL, TRUE))
    GC_heap_lengths[i] += bytes;
  return result;
}

#elif defined(CYGWIN32) || defined(MSWIN32)
#  ifdef USE_GLOBAL_ALLOC
#    define GLOBAL_ALLOC_TEST 1
#  else
#    define GLOBAL_ALLOC_TEST GC_no_win32_dlls
#  endif

#  if (defined(GC_USE_MEM_TOP_DOWN) && defined(USE_WINALLOC)) \
      || defined(CPPCHECK)
/* Use GC_USE_MEM_TOP_DOWN for better 64-bit testing.  Otherwise    */
/* all addresses tend to end up in the first 4 GB, hiding bugs.     */
DWORD GC_mem_top_down = MEM_TOP_DOWN;
#  else
#    define GC_mem_top_down 0
#  endif /* !GC_USE_MEM_TOP_DOWN */

GC_INNER void *
GC_get_mem(size_t bytes)
{
  void *result;

#  ifndef USE_WINALLOC
  result = GC_unix_get_mem(bytes);
#  else
#    if defined(MSWIN32) && !defined(MSWINRT_FLAVOR)
  if (GLOBAL_ALLOC_TEST) {
    /* VirtualAlloc doesn't like PAGE_EXECUTE_READWRITE.    */
    /* There are also unconfirmed rumors of other problems, */
    /* so we dodge the issue.                               */
    result = GlobalAlloc(0, SIZET_SAT_ADD(bytes, HBLKSIZE));
    /* Align it at HBLKSIZE boundary (NULL value remains unchanged). */
    result = PTR_ALIGN_UP((ptr_t)result, HBLKSIZE);
  } else
#    endif
  /* else */ {
    /* VirtualProtect only works on regions returned by a   */
    /* single VirtualAlloc call.  Thus we allocate one      */
    /* extra page, which will prevent merging of blocks     */
    /* in separate regions, and eliminate any temptation    */
    /* to call VirtualProtect on a range spanning regions.  */
    /* This wastes a small amount of memory, and risks      */
    /* increased fragmentation.  But better alternatives    */
    /* would require effort.                                */
#    ifdef MPROTECT_VDB
    /* We can't check for GC_incremental here (because    */
    /* GC_enable_incremental() might be called some time  */
    /* later after the GC initialization).                */
#      ifdef GWW_VDB
#        define VIRTUAL_ALLOC_PAD (GC_GWW_AVAILABLE() ? 0 : 1)
#      else
#        define VIRTUAL_ALLOC_PAD 1
#      endif
#    else
#      define VIRTUAL_ALLOC_PAD 0
#    endif
    /* Pass the MEM_WRITE_WATCH only if GetWriteWatch-based */
    /* VDBs are enabled and the GetWriteWatch function is   */
    /* available.  Otherwise we waste resources or possibly */
    /* cause VirtualAlloc to fail (observed in Windows 2000 */
    /* SP2).                                                */
    result = VirtualAlloc(
        NULL, SIZET_SAT_ADD(bytes, VIRTUAL_ALLOC_PAD),
        MEM_COMMIT | MEM_RESERVE | GetWriteWatch_alloc_flag | GC_mem_top_down,
        GC_pages_executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE);
#    undef IGNORE_PAGES_EXECUTABLE
  }
#  endif
  if (HBLKDISPL(result) != 0)
    ABORT("Bad VirtualAlloc result");
  if (GC_n_heap_bases >= MAX_HEAP_SECTS)
    ABORT("Too many heap sections");
  if (EXPECT(result != NULL, TRUE))
    GC_heap_bases[GC_n_heap_bases++] = (ptr_t)result;
  return result;
}
#endif /* CYGWIN32 || MSWIN32 */

#if defined(ANY_MSWIN) || defined(MSWIN_XBOX1)
GC_API void GC_CALL
GC_win32_free_heap(void)
{
#  if defined(USE_WINALLOC) && !defined(REDIRECT_MALLOC)
  GC_free_malloc_heap_list();
#  endif
#  if defined(CYGWIN32) || defined(MSWIN32)
#    ifndef MSWINRT_FLAVOR
#      ifdef MSWIN32
  if (GLOBAL_ALLOC_TEST)
#      endif
  {
    while (GC_n_heap_bases > 0) {
      GC_n_heap_bases--;
#      ifdef CYGWIN32
      /* FIXME: Is it OK to use non-GC free() here? */
#      else
      GlobalFree(GC_heap_bases[GC_n_heap_bases]);
#      endif
      GC_heap_bases[GC_n_heap_bases] = 0;
    }
    return;
  }
#    endif /* !MSWINRT_FLAVOR */
#    ifndef CYGWIN32
  /* Avoiding VirtualAlloc leak.  */
  while (GC_n_heap_bases > 0) {
    VirtualFree(GC_heap_bases[--GC_n_heap_bases], 0, MEM_RELEASE);
    GC_heap_bases[GC_n_heap_bases] = 0;
  }
#    endif
#  endif
}
#endif /* ANY_MSWIN || MSWIN_XBOX1 */

#if (defined(USE_MUNMAP) || defined(MPROTECT_VDB)) && !defined(USE_WINALLOC)
#  define ABORT_ON_REMAP_FAIL(C_msg_prefix, start_addr, len)             \
    ABORT_ARG3(C_msg_prefix " failed", " at %p (length %lu), errno= %d", \
               (void *)(start_addr), (unsigned long)(len), errno)
#endif

#ifdef USE_MUNMAP

#  if !defined(NN_PLATFORM_CTR) && !defined(MSWIN32) && !defined(MSWINCE) \
      && !defined(MSWIN_XBOX1)
#    ifdef SN_TARGET_PS3
#      include <sys/memory.h>
#    else
#      include <sys/mman.h>
#    endif
#    include <sys/stat.h>
#  endif

/* Compute a page aligned starting address for the unmap        */
/* operation on a block of size bytes starting at start.        */
/* Return 0 if the block is too small to make this feasible.    */
STATIC ptr_t
GC_unmap_start(ptr_t start, size_t bytes)
{
  ptr_t result;

  GC_ASSERT(GC_page_size != 0);
  result = PTR_ALIGN_UP(start, GC_page_size);
  if (ADDR_LT(start + bytes, result + GC_page_size))
    return NULL;

  return result;
}

/* We assume that GC_remap is called on exactly the same range  */
/* as a previous call to GC_unmap.  It is safe to consistently  */
/* round the endpoints in both places.                          */

static void
block_unmap_inner(ptr_t start_addr, size_t len)
{
  if (0 == start_addr)
    return;

#  ifdef USE_WINALLOC
  /* Under Win32/WinCE we commit (map) and decommit (unmap)         */
  /* memory using VirtualAlloc and VirtualFree.  These functions    */
  /* work on individual allocations of virtual memory, made         */
  /* previously using VirtualAlloc with the MEM_RESERVE flag.       */
  /* The ranges we need to (de)commit may span several of these     */
  /* allocations; therefore we use VirtualQuery to check            */
  /* allocation lengths, and split up the range as necessary.       */
  while (len != 0) {
    MEMORY_BASIC_INFORMATION mem_info;
    word free_len;

    if (VirtualQuery(start_addr, &mem_info, sizeof(mem_info))
        != sizeof(mem_info))
      ABORT("Weird VirtualQuery result");
    free_len = (len < mem_info.RegionSize) ? len : mem_info.RegionSize;
    if (!VirtualFree(start_addr, free_len, MEM_DECOMMIT))
      ABORT("VirtualFree failed");
    GC_unmapped_bytes += free_len;
    start_addr += free_len;
    len -= free_len;
  }
#  else
  if (len != 0) {
#    ifdef SN_TARGET_PS3
    ps3_free_mem(start_addr, len);
#    elif defined(AIX) || defined(COSMO) || defined(CYGWIN32) \
        || defined(HPUX)                                      \
        || (defined(LINUX) && !defined(PREFER_MMAP_PROT_NONE))
    /* On AIX, mmap(PROT_NONE) fails with ENOMEM unless the       */
    /* environment variable XPG_SUS_ENV is set to ON.             */
    /* On Cygwin, calling mmap() with the new protection flags on */
    /* an existing memory map with MAP_FIXED is broken.           */
    /* However, calling mprotect() on the given address range     */
    /* with PROT_NONE seems to work fine.                         */
    /* On Linux, low RLIMIT_AS value may lead to mmap failure.    */
#      if (defined(COSMO) || defined(LINUX)) \
          && !defined(FORCE_MPROTECT_BEFORE_MADVISE)
    /* On Linux, at least, madvise() should be sufficient.      */
#      else
    if (mprotect(start_addr, len, PROT_NONE))
      ABORT_ON_REMAP_FAIL("unmap: mprotect", start_addr, len);
#      endif
#      if !defined(CYGWIN32)
    /* On Linux (and some other platforms probably),    */
    /* mprotect(PROT_NONE) is just disabling access to  */
    /* the pages but not returning them to OS.          */
    if (madvise(start_addr, len, MADV_DONTNEED) == -1)
      ABORT_ON_REMAP_FAIL("unmap: madvise", start_addr, len);
#      endif
#    else
    /* We immediately remap it to prevent an intervening mmap()   */
    /* from accidentally grabbing the same address space.         */
    void *result = mmap(start_addr, len, PROT_NONE,
                        MAP_PRIVATE | MAP_FIXED | OPT_MAP_ANON, zero_fd,
                        0 /* offset */);

    if (EXPECT(MAP_FAILED == result, FALSE))
      ABORT_ON_REMAP_FAIL("unmap: mmap", start_addr, len);
    if (result != start_addr)
      ABORT("unmap: mmap() result differs from start_addr");
#      if defined(CPPCHECK) || defined(LINT2)
    /* Explicitly store the resource handle to a global variable. */
    GC_noop1_ptr(result);
#      endif
#    endif
    GC_unmapped_bytes += len;
  }
#  endif
}

/* Compute end address for an unmap operation on the indicated block.   */
GC_INLINE ptr_t
GC_unmap_end(ptr_t start, size_t bytes)
{
  return (ptr_t)HBLK_PAGE_ALIGNED(start + bytes);
}

GC_INNER void
GC_unmap(ptr_t start, size_t bytes)
{
  ptr_t start_addr = GC_unmap_start(start, bytes);
  ptr_t end_addr = GC_unmap_end(start, bytes);

  block_unmap_inner(start_addr, (size_t)(end_addr - start_addr));
}

GC_INNER void
GC_remap(ptr_t start, size_t bytes)
{
  ptr_t start_addr = GC_unmap_start(start, bytes);
  ptr_t end_addr = GC_unmap_end(start, bytes);
  word len = (word)(end_addr - start_addr);
  if (0 == start_addr)
    return;

    /* FIXME: Handle out-of-memory correctly (at least for Win32)       */
#  ifdef USE_WINALLOC
  while (len != 0) {
    MEMORY_BASIC_INFORMATION mem_info;
    word alloc_len;
    ptr_t result;

    if (VirtualQuery(start_addr, &mem_info, sizeof(mem_info))
        != sizeof(mem_info))
      ABORT("Weird VirtualQuery result");
    alloc_len = (len < mem_info.RegionSize) ? len : mem_info.RegionSize;
    result = (ptr_t)VirtualAlloc(start_addr, alloc_len, MEM_COMMIT,
                                 GC_pages_executable ? PAGE_EXECUTE_READWRITE
                                                     : PAGE_READWRITE);
    if (result != start_addr) {
      if (GetLastError() == ERROR_NOT_ENOUGH_MEMORY
          || GetLastError() == ERROR_OUTOFMEMORY) {
        ABORT("Not enough memory to process remapping");
      } else {
        ABORT("VirtualAlloc remapping failed");
      }
    }
#    ifdef LINT2
    GC_noop1_ptr(result);
#    endif
    GC_ASSERT(GC_unmapped_bytes >= alloc_len);
    GC_unmapped_bytes -= alloc_len;
    start_addr += alloc_len;
    len -= alloc_len;
  }
#    undef IGNORE_PAGES_EXECUTABLE
#  else
  /* It was already remapped with PROT_NONE. */
  {
#    if !defined(SN_TARGET_PS3) && !defined(FORCE_MPROTECT_BEFORE_MADVISE) \
        && (defined(LINUX) && !defined(PREFER_MMAP_PROT_NONE)              \
            || defined(COSMO))
    /* Nothing to unprotect as madvise() is just a hint.  */
#    elif defined(COSMO) || defined(NACL) || defined(NETBSD)
    /* NaCl does not expose mprotect, but mmap should work fine.  */
    /* In case of NetBSD, mprotect fails (unlike mmap) even       */
    /* without PROT_EXEC if PaX MPROTECT feature is enabled.      */
    void *result = mmap(
        start_addr, len,
        (PROT_READ | PROT_WRITE) | (GC_pages_executable ? PROT_EXEC : 0),
        MAP_PRIVATE | MAP_FIXED | OPT_MAP_ANON, zero_fd, 0 /* offset */);
    if (EXPECT(MAP_FAILED == result, FALSE))
      ABORT_ON_REMAP_FAIL("remap: mmap", start_addr, len);
    if (result != start_addr)
      ABORT("remap: mmap() result differs from start_addr");
#      if defined(CPPCHECK) || defined(LINT2)
    GC_noop1_ptr(result);
#      endif
#      undef IGNORE_PAGES_EXECUTABLE
#    else
    if (mprotect(start_addr, len,
                 (PROT_READ | PROT_WRITE)
                     | (GC_pages_executable ? PROT_EXEC : 0)))
      ABORT_ON_REMAP_FAIL("remap: mprotect", start_addr, len);
#      undef IGNORE_PAGES_EXECUTABLE
#    endif /* !NACL */
  }
  GC_ASSERT(GC_unmapped_bytes >= len);
  GC_unmapped_bytes -= len;
#  endif
}

/* Two adjacent blocks have already been unmapped and are about to      */
/* be merged.  Unmap the whole block.  This typically requires          */
/* that we unmap a small section in the middle that was not previously  */
/* unmapped due to alignment constraints.                               */
GC_INNER void
GC_unmap_gap(ptr_t start1, size_t bytes1, ptr_t start2, size_t bytes2)
{
  ptr_t start1_addr = GC_unmap_start(start1, bytes1);
  ptr_t end1_addr = GC_unmap_end(start1, bytes1);
  ptr_t start2_addr = GC_unmap_start(start2, bytes2);
  ptr_t start_addr = end1_addr;
  ptr_t end_addr = start2_addr;

  GC_ASSERT(start1 + bytes1 == start2);
  if (0 == start1_addr)
    start_addr = GC_unmap_start(start1, bytes1 + bytes2);
  if (0 == start2_addr)
    end_addr = GC_unmap_end(start1, bytes1 + bytes2);
  block_unmap_inner(start_addr, (size_t)(end_addr - start_addr));
}

#endif /* USE_MUNMAP */

/* Routine for pushing any additional roots.  In the multi-threaded     */
/* environment, this is also responsible for marking from thread        */
/* stacks.                                                              */
#ifndef THREADS

#  if defined(EMSCRIPTEN) && defined(EMSCRIPTEN_ASYNCIFY)
#    include <emscripten.h>

static void
scan_regs_cb(void *begin, void *finish)
{
  GC_push_all_stack((ptr_t)begin, (ptr_t)finish);
}

STATIC void GC_CALLBACK
GC_default_push_other_roots(void)
{
  /* Note: this needs -sASYNCIFY linker flag. */
  emscripten_scan_registers(scan_regs_cb);
}

#  else
#    define GC_default_push_other_roots 0
#  endif

#else /* THREADS */

#  if defined(SN_TARGET_PS3)
STATIC void GC_CALLBACK
GC_default_push_other_roots(void)
{
  ABORT("GC_default_push_other_roots is not implemented");
}

GC_INNER void
GC_push_thread_structures(void)
{
  ABORT("GC_push_thread_structures is not implemented");
}

#  else /* GC_PTHREADS, etc. */
STATIC void GC_CALLBACK
GC_default_push_other_roots(void)
{
  GC_push_all_stacks();
}
#  endif

#endif /* THREADS */

GC_push_other_roots_proc GC_push_other_roots = GC_default_push_other_roots;

GC_API void GC_CALL
GC_set_push_other_roots(GC_push_other_roots_proc fn)
{
  GC_push_other_roots = fn;
}

GC_API GC_push_other_roots_proc GC_CALL
GC_get_push_other_roots(void)
{
  return GC_push_other_roots;
}

#if defined(SOFT_VDB) && !defined(NO_SOFT_VDB_LINUX_VER_RUNTIME_CHECK) \
    || (defined(GLIBC_2_19_TSX_BUG) && defined(GC_PTHREADS_PARAMARK))
GC_INNER int
GC_parse_version(int *pminor, const char *pverstr)
{
  char *endp;
  unsigned long value = strtoul(pverstr, &endp, 10);
  int major = (int)value;

  if (major < 0 || (char *)pverstr == endp || (unsigned)major != value) {
    /* Parse error.   */
    return -1;
  }
  if (*endp != '.') {
    /* No minor part. */
    *pminor = -1;
  } else {
    value = strtoul(endp + 1, &endp, 10);
    *pminor = (int)value;
    if (*pminor < 0 || (unsigned)(*pminor) != value) {
      return -1;
    }
  }
  return major;
}
#endif

/*
 * Routines for accessing dirty bits on virtual pages.
 * There are six ways to maintain this information:
 * DEFAULT_VDB: A simple dummy implementation that treats every page
 *              as possibly dirty.  This makes incremental collection
 *              useless, but the implementation is still correct.
 * Manual VDB:  Stacks and static data are always considered dirty.
 *              Heap pages are considered dirty if GC_dirty(p) has been
 *              called on some pointer p pointing to somewhere inside
 *              an object on that page.  A GC_dirty() call on a large
 *              object directly dirties only a single page, but for the
 *              manual VDB we are careful to treat an object with a dirty
 *              page as completely dirty.
 *              In order to avoid races, an object must be marked dirty
 *              after it is written, and a reference to the object
 *              must be kept on a stack or in a register in the interim.
 *              With threads enabled, an object directly reachable from the
 *              stack at the time of a collection is treated as dirty.
 *              In single-threaded mode, it suffices to ensure that no
 *              collection can take place between the pointer assignment
 *              and the GC_dirty() call.
 * PROC_VDB:    Use the /proc facility for reading dirty bits.  Only
 *              works under some SVR4 variants.  Even then, it may be
 *              too slow to be entirely satisfactory.  Requires reading
 *              dirty bits for entire address space.  Implementations tend
 *              to assume that the client is a (slow) debugger.
 * SOFT_VDB:    Use the /proc facility for reading soft-dirty PTEs.
 *              Works on Linux 3.18+ if the kernel is properly configured.
 *              The proposed implementation iterates over GC_heap_sects and
 *              GC_static_roots examining the soft-dirty bit of the words
 *              in /proc/self/pagemap corresponding to the pages of the
 *              sections; finally all soft-dirty bits of the process are
 *              cleared (by writing some special value to
 *              /proc/self/clear_refs file).  In case the soft-dirty bit is
 *              not supported by the kernel, MPROTECT_VDB may be defined as
 *              a fallback strategy.
 * MPROTECT_VDB:Protect pages and then catch the faults to keep track of
 *              dirtied pages.  The implementation (and implementability)
 *              is highly system dependent.  This usually fails when system
 *              calls write to a protected page.  We prevent the read system
 *              call from doing so.  It is the clients responsibility to
 *              make sure that other system calls are similarly protected
 *              or write only to the stack.
 * GWW_VDB:     Use the Win32 GetWriteWatch functions, if available, to
 *              read dirty bits.  In case it is not available (because we
 *              are running on Windows 95, Windows 2000 or earlier),
 *              MPROTECT_VDB may be defined as a fallback strategy.
 */

#if (defined(CHECKSUMS) && defined(GWW_VDB)) || defined(PROC_VDB)
/* Add all pages in pht2 to pht1.   */
STATIC void
GC_or_pages(page_hash_table pht1, const word *pht2)
{
  size_t i;

  for (i = 0; i < PHT_SIZE; i++)
    pht1[i] |= pht2[i];
}
#endif /* CHECKSUMS && GWW_VDB || PROC_VDB */

#ifdef GWW_VDB

#  define GC_GWW_BUF_LEN (MAXHINCR * HBLKSIZE / 4096 /* x86 page size */)
/* Still susceptible to overflow, if there are very large allocations, */
/* and everything is dirty.                                            */
static PVOID gww_buf[GC_GWW_BUF_LEN];

#  ifndef MPROTECT_VDB
#    define GC_gww_dirty_init GC_dirty_init
#  endif

GC_INNER GC_bool
GC_gww_dirty_init(void)
{
  /* No assumption about the allocator lock. */
  detect_GetWriteWatch();
  return GC_GWW_AVAILABLE();
}

GC_INLINE void
GC_gww_read_dirty(GC_bool output_unneeded)
{
  size_t i;

  GC_ASSERT(I_HOLD_LOCK());
  if (!output_unneeded)
    BZERO(GC_grungy_pages, sizeof(GC_grungy_pages));

  for (i = 0; i < GC_n_heap_sects; ++i) {
    GC_ULONG_PTR count;

    do {
      PVOID *pages = gww_buf;
      DWORD page_size;

      count = GC_GWW_BUF_LEN;
      /* GetWriteWatch is documented as returning non-zero when it    */
      /* fails, but the documentation doesn't explicitly say why it   */
      /* would fail or what its behavior will be if it fails.  It     */
      /* does appear to fail, at least on recent Win2K instances, if  */
      /* the underlying memory was not allocated with the appropriate */
      /* flag.  This is common if GC_enable_incremental is called     */
      /* shortly after GC initialization.  To avoid modifying the     */
      /* interface, we silently work around such a failure, it only   */
      /* affects the initial (small) heap allocation. If there are    */
      /* more dirty pages than will fit in the buffer, this is not    */
      /* treated as a failure; we must check the page count in the    */
      /* loop condition. Since each partial call will reset the       */
      /* status of some pages, this should eventually terminate even  */
      /* in the overflow case.                                        */
      if ((*(GetWriteWatch_type)(GC_funcptr_uint)GetWriteWatch_func)(
              WRITE_WATCH_FLAG_RESET, GC_heap_sects[i].hs_start,
              GC_heap_sects[i].hs_bytes, pages, &count, &page_size)
          != 0) {
        static int warn_count = 0;
        struct hblk *start = (struct hblk *)GC_heap_sects[i].hs_start;
        static const struct hblk *last_warned = NULL;
        size_t nblocks = divHBLKSZ(GC_heap_sects[i].hs_bytes);

        if (i != 0 && last_warned != start && warn_count++ < 5) {
          last_warned = start;
          WARN("GC_gww_read_dirty unexpectedly failed at %p:"
               " Falling back to marking all pages dirty\n",
               start);
        }
        if (!output_unneeded) {
          size_t j;

          for (j = 0; j < nblocks; ++j) {
            size_t index = PHT_HASH(start + j);

            set_pht_entry_from_index(GC_grungy_pages, index);
          }
        }
        /* Done with this section.    */
        count = 1;
      } else if (!output_unneeded) { /* succeeded */
        const PVOID *pages_end = pages + count;

        while (pages != pages_end) {
          struct hblk *h = (struct hblk *)(*pages++);
          ptr_t h_end = (ptr_t)h + page_size;

          do {
            set_pht_entry_from_index(GC_grungy_pages, PHT_HASH(h));
            h++;
          } while (ADDR_LT((ptr_t)h, h_end));
        }
      }
    } while (count == GC_GWW_BUF_LEN);
    /* FIXME: It's unclear from Microsoft's documentation if this loop */
    /* is useful.  We suspect the call just fails if the buffer fills  */
    /* up.  But that should still be handled correctly.                */
  }

#  ifdef CHECKSUMS
  GC_ASSERT(!output_unneeded);
  GC_or_pages(GC_written_pages, GC_grungy_pages);
#  endif
}

#elif defined(SOFT_VDB)
static int clear_refs_fd = -1;
#  define GC_GWW_AVAILABLE() (clear_refs_fd != -1)
#else
#  define GC_GWW_AVAILABLE() FALSE
#endif /* !GWW_VDB && !SOFT_VDB */

#ifdef DEFAULT_VDB
/* The client asserts that unallocated pages in the heap are never    */
/* written.                                                           */

/* Initialize virtual dirty bit implementation.       */
GC_INNER GC_bool
GC_dirty_init(void)
{
  GC_VERBOSE_LOG_PRINTF("Initializing DEFAULT_VDB...\n");
  /* GC_dirty_pages and GC_grungy_pages are already cleared.  */
  return TRUE;
}
#endif /* DEFAULT_VDB */

#if !defined(NO_MANUAL_VDB) || defined(MPROTECT_VDB)
#  if !defined(THREADS) || defined(HAVE_LOCKFREE_AO_OR)
#    ifdef MPROTECT_VDB
#      define async_set_pht_entry_from_index(db, index) \
        set_pht_entry_from_index_concurrent_volatile(db, index)
#    else
#      define async_set_pht_entry_from_index(db, index) \
        set_pht_entry_from_index_concurrent(db, index)
#    endif
#  elif defined(NEED_FAULT_HANDLER_LOCK)
/* We need to lock around the bitmap update (in the write fault     */
/* handler or GC_dirty) in order to avoid the risk of losing a bit. */
/* We do this with a test-and-set spin lock if possible.            */
static void
async_set_pht_entry_from_index(volatile page_hash_table db, size_t index)
{
  GC_acquire_dirty_lock();
  set_pht_entry_from_index(db, index);
  GC_release_dirty_lock();
}
#  else /* THREADS && !NEED_FAULT_HANDLER_LOCK */
#    error No test_and_set operation: Introduces a race.
#  endif
#endif /* !NO_MANUAL_VDB || MPROTECT_VDB */

#ifdef MPROTECT_VDB
/* This implementation maintains dirty bits itself by catching write  */
/* faults and keeping track of them.  We assume nobody else catches   */
/* SIGBUS or SIGSEGV.  We assume no write faults occur in system      */
/* calls.  This means that clients must ensure that system calls do   */
/* not write to the write-protected heap.  Probably the best way to   */
/* do this is to ensure that system calls write at most to            */
/* pointer-free objects in the heap, and do even that only if we are  */
/* on a platform on which those are not protected (or the collector   */
/* is built with DONT_PROTECT_PTRFREE defined).  We assume the page   */
/* size is a multiple of HBLKSIZE.                                    */

#  ifdef DARWIN
/* #define BROKEN_EXCEPTION_HANDLING */

/* Using vm_protect (mach syscall) over mprotect (BSD syscall)      */
/* seems to decrease the likelihood of some of the problems         */
/* described below.                                                 */
#    include <mach/vm_map.h>
STATIC mach_port_t GC_task_self = 0;
#    define PROTECT_INNER(addr, len, allow_write, C_msg_prefix)            \
      if (vm_protect(GC_task_self, (vm_address_t)(addr), (vm_size_t)(len), \
                     FALSE,                                                \
                     VM_PROT_READ | ((allow_write) ? VM_PROT_WRITE : 0)    \
                         | (GC_pages_executable ? VM_PROT_EXECUTE : 0))    \
          == KERN_SUCCESS) {                                               \
      } else                                                               \
        ABORT(C_msg_prefix "vm_protect() failed")

#  elif !defined(USE_WINALLOC)
#    include <sys/mman.h>
#    if !defined(AIX) && !defined(CYGWIN32) && !defined(HAIKU)
#      include <sys/syscall.h>
#    endif

#    define PROTECT_INNER(addr, len, allow_write, C_msg_prefix)           \
      if (mprotect((caddr_t)(addr), (size_t)(len),                        \
                   PROT_READ | ((allow_write) ? PROT_WRITE : 0)           \
                       | (GC_pages_executable ? PROT_EXEC : 0))           \
          >= 0) {                                                         \
      } else if (GC_pages_executable) {                                   \
        ABORT_ON_REMAP_FAIL(C_msg_prefix "mprotect vdb executable pages", \
                            addr, len);                                   \
      } else                                                              \
        ABORT_ON_REMAP_FAIL(C_msg_prefix "mprotect vdb", addr, len)
#    undef IGNORE_PAGES_EXECUTABLE

#  else /* USE_WINALLOC */
static DWORD protect_junk;
#    define PROTECT_INNER(addr, len, allow_write, C_msg_prefix)             \
      if (VirtualProtect(addr, len,                                         \
                         GC_pages_executable                                \
                             ? ((allow_write) ? PAGE_EXECUTE_READWRITE      \
                                              : PAGE_EXECUTE_READ)          \
                         : (allow_write) ? PAGE_READWRITE                   \
                                         : PAGE_READONLY,                   \
                         &protect_junk)) {                                  \
      } else                                                                \
        ABORT_ARG1(C_msg_prefix "VirtualProtect failed", ": errcode= 0x%X", \
                   (unsigned)GetLastError())
#  endif /* USE_WINALLOC */

#  define PROTECT(addr, len) PROTECT_INNER(addr, len, FALSE, "")
#  define UNPROTECT(addr, len) PROTECT_INNER(addr, len, TRUE, "un-")

#  if defined(MSWIN32)
typedef LPTOP_LEVEL_EXCEPTION_FILTER SIG_HNDLR_PTR;
#    undef SIG_DFL
#    define SIG_DFL ((LPTOP_LEVEL_EXCEPTION_FILTER)(~(GC_funcptr_uint)0))
#  elif defined(MSWINCE)
typedef LONG(WINAPI *SIG_HNDLR_PTR)(struct _EXCEPTION_POINTERS *);
#    undef SIG_DFL
#    define SIG_DFL ((SIG_HNDLR_PTR)(~(GC_funcptr_uint)0))
#  elif defined(DARWIN)
#    ifdef BROKEN_EXCEPTION_HANDLING
typedef void (*SIG_HNDLR_PTR)();
#    endif
#  else
typedef void (*SIG_HNDLR_PTR)(int, siginfo_t *, void *);
typedef void (*PLAIN_HNDLR_PTR)(int);
#  endif /* !DARWIN && !MSWIN32 && !MSWINCE */

#  ifndef DARWIN
/* Also old MSWIN32 ACCESS_VIOLATION filter.  */
STATIC SIG_HNDLR_PTR GC_old_segv_handler = 0;
#    ifdef USE_BUS_SIGACT
STATIC SIG_HNDLR_PTR GC_old_bus_handler = 0;
STATIC GC_bool GC_old_bus_handler_used_si = FALSE;
#    endif
#    if !defined(MSWIN32) && !defined(MSWINCE)
STATIC GC_bool GC_old_segv_handler_used_si = FALSE;
#    endif
#  endif /* !DARWIN */

#  ifdef THREADS
/* This function is used only by the fault handler.  Potential data   */
/* race between this function and GC_install_header, GC_remove_header */
/* should not be harmful because the added or removed header should   */
/* be already unprotected.                                            */
GC_ATTR_NO_SANITIZE_THREAD
static GC_bool
is_header_found_async(const void *p)
{
#    ifdef HASH_TL
  hdr *result;

  GET_HDR(p, result);
  return result != NULL;
#    else
  return HDR_INNER(p) != NULL;
#    endif
}
#  else
#    define is_header_found_async(p) (HDR(p) != NULL)
#  endif /* !THREADS */

#  ifndef DARWIN

#    if !defined(MSWIN32) && !defined(MSWINCE)
#      include <errno.h>
#      ifdef USE_BUS_SIGACT
#        define SIG_OK (sig == SIGBUS || sig == SIGSEGV)
#      else
/* Catch SIGSEGV but ignore SIGBUS.       */
#        define SIG_OK (sig == SIGSEGV)
#      endif
#      if defined(FREEBSD) || defined(OPENBSD)
#        ifndef SEGV_ACCERR
#          define SEGV_ACCERR 2
#        endif
#        if defined(AARCH64) || defined(ARM32) || defined(MIPS) \
            || (__FreeBSD__ >= 7 || defined(OPENBSD))
#          define CODE_OK (si->si_code == SEGV_ACCERR)
#        elif defined(POWERPC)
/* Pretend that we are AIM.     */
#          define AIM
#          include <machine/trap.h>
#          define CODE_OK \
            (si->si_code == EXC_DSI || si->si_code == SEGV_ACCERR)
#        else
#          define CODE_OK \
            (si->si_code == BUS_PAGE_FAULT || si->si_code == SEGV_ACCERR)
#        endif
#      elif defined(OSF1)
#        define CODE_OK (si->si_code == 2 /* experimentally determined */)
#      elif defined(IRIX5)
#        define CODE_OK (si->si_code == EACCES)
#      elif defined(AIX) || defined(COSMO) || defined(CYGWIN32) \
          || defined(HAIKU) || defined(HURD) || defined(LINUX)  \
          || defined(NETBSD)
/* Linux: Empirically c.trapno == 14, on IA32, but is that useful?      */
/* Should probably consider alignment issues on other architectures.    */
#        define CODE_OK TRUE
#      elif defined(HPUX)
#        define CODE_OK                                                 \
          (si->si_code == SEGV_ACCERR || si->si_code == BUS_ADRERR      \
           || si->si_code == BUS_UNKNOWN || si->si_code == SEGV_UNKNOWN \
           || si->si_code == BUS_OBJERR)
#      elif defined(SUNOS5SIGS)
#        define CODE_OK (si->si_code == SEGV_ACCERR)
#      endif
#      ifndef NO_GETCONTEXT
#        include <ucontext.h>
#      endif
STATIC void
GC_write_fault_handler(int sig, siginfo_t *si, void *raw_sc)
#    else /* MSWIN32 || MSWINCE */
#      define SIG_OK \
        (exc_info->ExceptionRecord->ExceptionCode == STATUS_ACCESS_VIOLATION)
#      define CODE_OK                                       \
        (exc_info->ExceptionRecord->ExceptionInformation[0] \
         == 1) /* write fault */
STATIC LONG WINAPI
GC_write_fault_handler(struct _EXCEPTION_POINTERS *exc_info)
#    endif
{
#    if !defined(MSWIN32) && !defined(MSWINCE)
  char *addr = (char *)si->si_addr;
#    else
  char *addr = (char *)exc_info->ExceptionRecord->ExceptionInformation[1];
#    endif

  if (SIG_OK && CODE_OK) {
    struct hblk *h = HBLK_PAGE_ALIGNED(addr);
    GC_bool in_allocd_block;
    size_t i;

    GC_ASSERT(GC_page_size != 0);
#    ifdef CHECKSUMS
    GC_record_fault(h);
#    endif
#    ifdef SUNOS5SIGS
    /* Address is only within the correct physical page.        */
    in_allocd_block = FALSE;
    for (i = 0; i < divHBLKSZ(GC_page_size); i++) {
      if (is_header_found_async(&h[i])) {
        in_allocd_block = TRUE;
        break;
      }
    }
#    else
    in_allocd_block = is_header_found_async(addr);
#    endif
    if (!in_allocd_block) {
      /* FIXME - We should make sure that we invoke the   */
      /* old handler with the appropriate calling         */
      /* sequence, which often depends on SA_SIGINFO.     */

      /* Heap blocks now begin and end on page boundaries.    */
      SIG_HNDLR_PTR old_handler;

#    if defined(MSWIN32) || defined(MSWINCE)
      old_handler = GC_old_segv_handler;
#    else
      GC_bool used_si;

#      ifdef USE_BUS_SIGACT
      if (sig == SIGBUS) {
        old_handler = GC_old_bus_handler;
        used_si = GC_old_bus_handler_used_si;
      } else
#      endif
      /* else */ {
        old_handler = GC_old_segv_handler;
        used_si = GC_old_segv_handler_used_si;
      }
#    endif

      if ((GC_funcptr_uint)old_handler == (GC_funcptr_uint)SIG_DFL) {
#    if !defined(MSWIN32) && !defined(MSWINCE)
        ABORT_ARG1("Unexpected segmentation fault outside heap", " at %p",
                   (void *)addr);
#    else
        return EXCEPTION_CONTINUE_SEARCH;
#    endif
      } else {
        /* FIXME: This code should probably check if the old    */
        /* signal handler used the traditional style and if so, */
        /* call it using that style.                            */
#    if defined(MSWIN32) || defined(MSWINCE)
        return (*old_handler)(exc_info);
#    else
        if (used_si)
          ((SIG_HNDLR_PTR)old_handler)(sig, si, raw_sc);
        else
          /* FIXME: should pass nonstandard args as well. */
          ((PLAIN_HNDLR_PTR)(GC_funcptr_uint)old_handler)(sig);
        return;
#    endif
      }
    }
    UNPROTECT(h, GC_page_size);
    /* We need to make sure that no collection occurs between       */
    /* the UNPROTECT and the setting of the dirty bit.  Otherwise   */
    /* a write by a third thread might go unnoticed.  Reversing     */
    /* the order is just as bad, since we would end up unprotecting */
    /* a page in a GC cycle during which it's not marked.           */
    /* Currently we do this by disabling the thread stopping        */
    /* signals while this handler is running.  An alternative might */
    /* be to record the fact that we're about to unprotect, or      */
    /* have just unprotected a page in the GC's thread structure,   */
    /* and then to have the thread stopping code set the dirty      */
    /* flag, if necessary.                                          */
    for (i = 0; i < divHBLKSZ(GC_page_size); i++) {
      size_t index = PHT_HASH(h + i);

      async_set_pht_entry_from_index(GC_dirty_pages, index);
    }
    /* The write() may not take place before dirty bits are read.   */
    /* But then we'll fault again ...                               */
#    if defined(MSWIN32) || defined(MSWINCE)
    return EXCEPTION_CONTINUE_EXECUTION;
#    else
    return;
#    endif
  }
#    if defined(MSWIN32) || defined(MSWINCE)
  return EXCEPTION_CONTINUE_SEARCH;
#    else
  ABORT_ARG1("Unexpected bus error or segmentation fault", " at %p",
             (void *)addr);
#    endif
}

#    if defined(GC_WIN32_THREADS) && !defined(CYGWIN32)
GC_INNER void
GC_set_write_fault_handler(void)
{
  SetUnhandledExceptionFilter(GC_write_fault_handler);
}
#    endif

#    ifdef SOFT_VDB
static GC_bool soft_dirty_init(void);
#    endif

GC_INNER GC_bool
GC_dirty_init(void)
{
#    if !defined(MSWIN32) && !defined(MSWINCE)
  struct sigaction act, oldact;
#    endif

  GC_ASSERT(I_HOLD_LOCK());
#    ifdef COUNT_PROTECTED_REGIONS
  GC_ASSERT(GC_page_size != 0);
  if ((GC_signed_word)(GC_heapsize / (word)GC_page_size)
      >= ((GC_signed_word)GC_UNMAPPED_REGIONS_SOFT_LIMIT
          - GC_num_unmapped_regions)
             * 2) {
    GC_COND_LOG_PRINTF("Cannot turn on GC incremental mode"
                       " as heap contains too many pages\n");
    return FALSE;
  }
#    endif
#    if !defined(MSWIN32) && !defined(MSWINCE)
  act.sa_flags = SA_RESTART | SA_SIGINFO;
  act.sa_sigaction = GC_write_fault_handler;
  (void)sigemptyset(&act.sa_mask);
#      ifdef SIGNAL_BASED_STOP_WORLD
  /* Arrange to postpone the signal while we are in a write fault */
  /* handler.  This effectively makes the handler atomic w.r.t.   */
  /* stopping the world for GC.                                   */
  (void)sigaddset(&act.sa_mask, GC_get_suspend_signal());
#      endif
#    endif /* !MSWIN32 */
  GC_VERBOSE_LOG_PRINTF(
      "Initializing mprotect virtual dirty bit implementation\n");
  if (GC_page_size % HBLKSIZE != 0) {
    ABORT("Page size not multiple of HBLKSIZE");
  }
#    ifdef GWW_VDB
  if (GC_gww_dirty_init()) {
    GC_COND_LOG_PRINTF("Using GetWriteWatch()\n");
    return TRUE;
  }
#    elif defined(SOFT_VDB)
#      ifdef CHECK_SOFT_VDB
  if (!soft_dirty_init())
    ABORT("Soft-dirty bit support is missing");
#      else
  if (soft_dirty_init()) {
    GC_COND_LOG_PRINTF("Using soft-dirty bit feature\n");
    return TRUE;
  }
#      endif
#    endif
#    ifdef MSWIN32
  GC_old_segv_handler = SetUnhandledExceptionFilter(GC_write_fault_handler);
  if (GC_old_segv_handler != NULL) {
    GC_COND_LOG_PRINTF("Replaced other UnhandledExceptionFilter\n");
  } else {
    GC_old_segv_handler = SIG_DFL;
  }
#    elif defined(MSWINCE)
    /* MPROTECT_VDB is unsupported for WinCE at present.      */
    /* FIXME: implement it (if possible). */
#    else
  /* act.sa_restorer is deprecated and should not be initialized. */
#      if defined(IRIX5) && defined(THREADS)
  sigaction(SIGSEGV, 0, &oldact);
  sigaction(SIGSEGV, &act, 0);
#      else
  {
    int res = sigaction(SIGSEGV, &act, &oldact);
    if (res != 0)
      ABORT("Sigaction failed");
  }
#      endif
  if (oldact.sa_flags & SA_SIGINFO) {
    GC_old_segv_handler = oldact.sa_sigaction;
    GC_old_segv_handler_used_si = TRUE;
  } else {
    GC_old_segv_handler = (SIG_HNDLR_PTR)(GC_funcptr_uint)oldact.sa_handler;
    GC_old_segv_handler_used_si = FALSE;
  }
  if ((GC_funcptr_uint)GC_old_segv_handler == (GC_funcptr_uint)SIG_IGN) {
    WARN("Previously ignored segmentation violation!?\n", 0);
    GC_old_segv_handler = (SIG_HNDLR_PTR)(GC_funcptr_uint)SIG_DFL;
  }
  if ((GC_funcptr_uint)GC_old_segv_handler != (GC_funcptr_uint)SIG_DFL) {
    GC_VERBOSE_LOG_PRINTF("Replaced other SIGSEGV handler\n");
  }
#      ifdef USE_BUS_SIGACT
  sigaction(SIGBUS, &act, &oldact);
  if ((oldact.sa_flags & SA_SIGINFO) != 0) {
    GC_old_bus_handler = oldact.sa_sigaction;
    GC_old_bus_handler_used_si = TRUE;
  } else {
    GC_old_bus_handler = (SIG_HNDLR_PTR)(GC_funcptr_uint)oldact.sa_handler;
  }
  if ((GC_funcptr_uint)GC_old_bus_handler == (GC_funcptr_uint)SIG_IGN) {
    WARN("Previously ignored bus error!?\n", 0);
    GC_old_bus_handler = (SIG_HNDLR_PTR)(GC_funcptr_uint)SIG_DFL;
  } else if ((GC_funcptr_uint)GC_old_bus_handler != (GC_funcptr_uint)SIG_DFL) {
    GC_VERBOSE_LOG_PRINTF("Replaced other SIGBUS handler\n");
  }
#      endif
#    endif /* !MSWIN32 && !MSWINCE */
#    if defined(CPPCHECK) && defined(ADDRESS_SANITIZER)
  GC_noop1((word)(GC_funcptr_uint)(&__asan_default_options));
#    endif
  return TRUE;
}
#  endif /* !DARWIN */

STATIC void
GC_protect_heap(void)
{
  size_t i;

  GC_ASSERT(GC_page_size != 0);
  for (i = 0; i < GC_n_heap_sects; i++) {
    ptr_t start = GC_heap_sects[i].hs_start;
    size_t len = GC_heap_sects[i].hs_bytes;
    struct hblk *current;
    struct hblk *current_start; /* start of block to be protected */
    ptr_t limit;

    GC_ASSERT((ADDR(start) & (GC_page_size - 1)) == 0);
    GC_ASSERT((len & (GC_page_size - 1)) == 0);
#  ifndef DONT_PROTECT_PTRFREE
    /* We avoid protecting pointer-free objects unless the page   */
    /* size differs from HBLKSIZE.                                */
    if (GC_page_size != HBLKSIZE) {
      PROTECT(start, len);
      continue;
    }
#  endif

    current_start = (struct hblk *)start;
    limit = start + len;
    for (current = current_start;;) {
      size_t nblocks = 0;
      GC_bool is_ptrfree = TRUE;

      if (ADDR_LT((ptr_t)current, limit)) {
        hdr *hhdr;

        GET_HDR(current, hhdr);
        if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
          /* This can happen only if we are at the beginning of a heap  */
          /* segment, and a block spans heap segments.  We will handle  */
          /* that block as part of the preceding segment.               */
          GC_ASSERT(current_start == current);

          current_start = ++current;
          continue;
        }
        if (HBLK_IS_FREE(hhdr)) {
          GC_ASSERT(modHBLKSZ(hhdr->hb_sz) == 0);
          nblocks = divHBLKSZ(hhdr->hb_sz);
        } else {
          nblocks = OBJ_SZ_TO_BLOCKS(hhdr->hb_sz);
          is_ptrfree = IS_PTRFREE(hhdr);
        }
      }
      if (is_ptrfree) {
        if (ADDR_LT((ptr_t)current_start, (ptr_t)current)) {
#  ifdef DONT_PROTECT_PTRFREE
          ptr_t cur_aligned = PTR_ALIGN_UP((ptr_t)current, GC_page_size);

          current_start = HBLK_PAGE_ALIGNED(current_start);
          /* Adjacent free blocks might be protected too because  */
          /* of the alignment by the page size.                   */
          PROTECT(current_start, cur_aligned - (ptr_t)current_start);
#  else
          PROTECT(current_start, (ptr_t)current - (ptr_t)current_start);
#  endif
        }
        if (ADDR_GE((ptr_t)current, limit))
          break;
      }
      current += nblocks;
      if (is_ptrfree)
        current_start = current;
    }
  }
}

#  if defined(CAN_HANDLE_FORK) && defined(DARWIN) && defined(THREADS) \
      || defined(COUNT_PROTECTED_REGIONS)
/* Remove protection for the entire heap not updating GC_dirty_pages. */
STATIC void
GC_unprotect_all_heap(void)
{
  size_t i;

  GC_ASSERT(I_HOLD_LOCK());
  GC_ASSERT(GC_auto_incremental);
  for (i = 0; i < GC_n_heap_sects; i++) {
    UNPROTECT(GC_heap_sects[i].hs_start, GC_heap_sects[i].hs_bytes);
  }
}
#  endif

#  ifdef COUNT_PROTECTED_REGIONS
GC_INNER void
GC_handle_protected_regions_limit(void)
{
  GC_ASSERT(GC_page_size != 0);
  /* To prevent exceeding the limit of vm.max_map_count, the most */
  /* trivial (though highly restrictive) way is to turn off the   */
  /* incremental collection mode (based on mprotect) once the     */
  /* number of pages in the heap reaches that limit.              */
  if (GC_auto_incremental && !GC_GWW_AVAILABLE()
      && (GC_signed_word)(GC_heapsize / (word)GC_page_size)
             >= ((GC_signed_word)GC_UNMAPPED_REGIONS_SOFT_LIMIT
                 - GC_num_unmapped_regions)
                    * 2) {
    GC_unprotect_all_heap();
#    ifdef DARWIN
    GC_task_self = 0;
#    endif
    GC_incremental = FALSE;
    WARN("GC incremental mode is turned off"
         " to prevent hitting VM maps limit\n",
         0);
  }
}
#  endif /* COUNT_PROTECTED_REGIONS */

#endif /* MPROTECT_VDB */

#if !defined(THREADS) && (defined(PROC_VDB) || defined(SOFT_VDB))
static pid_t saved_proc_pid; /* pid used to compose /proc file names */
#endif

#ifdef PROC_VDB
/* This implementation assumes a Solaris 2.X like /proc               */
/* pseudo-file-system from which we can read page modified bits.      */
/* This facility is far from optimal (e.g. we would like to get the   */
/* info for only some of the address space), but it avoids            */
/* intercepting system calls.                                         */

#  include <errno.h>
#  include <sys/signal.h>
#  include <sys/stat.h>
#  include <sys/syscall.h>

#  ifdef GC_NO_SYS_FAULT_H
/* This exists only to check PROC_VDB code compilation (on Linux).  */
#    define PG_MODIFIED 1
struct prpageheader {
  int dummy[2]; /* pr_tstamp */
  unsigned long pr_nmap;
  unsigned long pr_npage;
};
struct prasmap {
  char *pr_vaddr;
  size_t pr_npage;
  char dummy1[64 + 8]; /* pr_mapname, pr_offset */
  unsigned pr_mflags;
  unsigned pr_pagesize;
  int dummy2[2];
};
#  else
#    include <sys/fault.h>
#    include <sys/procfs.h>
#  endif

#  define INITIAL_BUF_SZ 16384
STATIC size_t GC_proc_buf_size = INITIAL_BUF_SZ;
STATIC char *GC_proc_buf = NULL;
STATIC int GC_proc_fd = -1;

static GC_bool
proc_dirty_open_files(void)
{
  char buf[40];
  pid_t pid = getpid();

  (void)snprintf(buf, sizeof(buf), "/proc/%ld/pagedata", (long)pid);
  buf[sizeof(buf) - 1] = '\0';
  GC_proc_fd = open(buf, O_RDONLY);
  if (-1 == GC_proc_fd) {
    WARN("/proc open failed; cannot enable GC incremental mode\n", 0);
    return FALSE;
  }
  if (syscall(SYS_fcntl, GC_proc_fd, F_SETFD, FD_CLOEXEC) == -1)
    WARN("Could not set FD_CLOEXEC for /proc\n", 0);
#  ifndef THREADS
  /* Updated on success only.       */
  saved_proc_pid = pid;
#  endif
  return TRUE;
}

#  ifdef CAN_HANDLE_FORK
GC_INNER void
GC_dirty_update_child(void)
{
  GC_ASSERT(I_HOLD_LOCK());
  if (-1 == GC_proc_fd) {
    /* The GC incremental mode is off.      */
    return;
  }
  close(GC_proc_fd);
  if (!proc_dirty_open_files()) {
    /* Should be safe to turn it off.       */
    GC_incremental = FALSE;
  }
}
#  endif /* CAN_HANDLE_FORK */

GC_INNER GC_bool
GC_dirty_init(void)
{
  GC_ASSERT(I_HOLD_LOCK());
  if (GC_bytes_allocd != 0 || GC_bytes_allocd_before_gc != 0) {
    memset(GC_written_pages, 0xff, sizeof(page_hash_table));
    GC_VERBOSE_LOG_PRINTF(
        "Allocated %lu bytes: all pages may have been written\n",
        (unsigned long)(GC_bytes_allocd + GC_bytes_allocd_before_gc));
  }
  if (!proc_dirty_open_files())
    return FALSE;
  GC_proc_buf = GC_scratch_alloc(GC_proc_buf_size);
  if (GC_proc_buf == NULL)
    ABORT("Insufficient space for /proc read");
  return TRUE;
}

GC_INLINE void
GC_proc_read_dirty(GC_bool output_unneeded)
{
  size_t i, nmaps;
  char *bufp = GC_proc_buf;

  GC_ASSERT(I_HOLD_LOCK());
#  ifndef THREADS
  /* If the current pid differs from the saved one, then we are in  */
  /* the forked (child) process, the current /proc file should be   */
  /* closed, the new one should be opened with the updated path.    */
  /* Note, this is not needed for multi-threaded case because       */
  /* fork_child_proc() reopens the file right after fork.           */
  if (getpid() != saved_proc_pid
      && (-1 == GC_proc_fd /* no need to retry */
          || (close(GC_proc_fd), !proc_dirty_open_files()))) {
    /* Failed to reopen the file.  Punt!    */
    if (!output_unneeded)
      memset(GC_grungy_pages, 0xff, sizeof(page_hash_table));
    memset(GC_written_pages, 0xff, sizeof(page_hash_table));
    return;
  }
#  endif

  BZERO(GC_grungy_pages, sizeof(GC_grungy_pages));
  if (PROC_READ(GC_proc_fd, bufp, GC_proc_buf_size) <= 0) {
    /* Retry with larger buffer.    */
    size_t new_size = 2 * GC_proc_buf_size;
    char *new_buf;

    WARN("/proc read failed (buffer size is %" WARN_PRIuPTR " bytes)\n",
         GC_proc_buf_size);
    new_buf = GC_scratch_alloc(new_size);
    if (new_buf != 0) {
      GC_scratch_recycle_no_gww(bufp, GC_proc_buf_size);
      GC_proc_buf = bufp = new_buf;
      GC_proc_buf_size = new_size;
    }
    if (PROC_READ(GC_proc_fd, bufp, GC_proc_buf_size) <= 0) {
      WARN("Insufficient space for /proc read\n", 0);
      /* Punt:        */
      if (!output_unneeded)
        memset(GC_grungy_pages, 0xff, sizeof(page_hash_table));
      memset(GC_written_pages, 0xff, sizeof(page_hash_table));
      return;
    }
  }

  /* Copy dirty bits into GC_grungy_pages.    */
  nmaps = (size_t)(((struct prpageheader *)bufp)->pr_nmap);
#  ifdef DEBUG_DIRTY_BITS
  GC_log_printf("Proc VDB read: pr_nmap= %u, pr_npage= %lu\n", (unsigned)nmaps,
                ((struct prpageheader *)bufp)->pr_npage);
#  endif
#  if defined(GC_NO_SYS_FAULT_H) && defined(CPPCHECK)
  GC_noop1(((struct prpageheader *)bufp)->dummy[0]);
#  endif
  bufp += sizeof(struct prpageheader);
  for (i = 0; i < nmaps; i++) {
    struct prasmap *map = (struct prasmap *)bufp;
    ptr_t vaddr = (ptr_t)map->pr_vaddr;
    unsigned long npages = map->pr_npage;
    unsigned pagesize = map->pr_pagesize;
    ptr_t limit;

#  if defined(GC_NO_SYS_FAULT_H) && defined(CPPCHECK)
    GC_noop1(map->dummy1[0] + map->dummy2[0]);
#  endif
#  ifdef DEBUG_DIRTY_BITS
    GC_log_printf("pr_vaddr= %p, npage= %lu, mflags= 0x%x, pagesize= 0x%x\n",
                  (void *)vaddr, npages, map->pr_mflags, pagesize);
#  endif

    bufp += sizeof(struct prasmap);
    limit = vaddr + pagesize * npages;
    for (; ADDR_LT(vaddr, limit); vaddr += pagesize) {
      if ((*bufp++) & PG_MODIFIED) {
        struct hblk *h;
        ptr_t next_vaddr = vaddr + pagesize;

#  ifdef DEBUG_DIRTY_BITS
        GC_log_printf("dirty page at: %p\n", (void *)vaddr);
#  endif
        for (h = (struct hblk *)vaddr; ADDR_LT((ptr_t)h, next_vaddr); h++) {
          size_t index = PHT_HASH(h);

          set_pht_entry_from_index(GC_grungy_pages, index);
        }
      }
    }
    bufp = PTR_ALIGN_UP(bufp, sizeof(long));
  }
#  ifdef DEBUG_DIRTY_BITS
  GC_log_printf("Proc VDB read done\n");
#  endif

  /* Update GC_written_pages (even if output_unneeded).       */
  GC_or_pages(GC_written_pages, GC_grungy_pages);
}

#endif /* PROC_VDB */

#ifdef SOFT_VDB
#  ifndef VDB_BUF_SZ
#    define VDB_BUF_SZ 16384
#  endif

static int
open_proc_fd(pid_t pid, const char *proc_filename, int mode)
{
  int f;
  char buf[40];

  (void)snprintf(buf, sizeof(buf), "/proc/%ld/%s", (long)pid, proc_filename);
  buf[sizeof(buf) - 1] = '\0';
  f = open(buf, mode);
  if (-1 == f) {
    WARN("/proc/self/%s open failed; cannot enable GC incremental mode\n",
         proc_filename);
  } else if (fcntl(f, F_SETFD, FD_CLOEXEC) == -1) {
    WARN("Could not set FD_CLOEXEC for /proc\n", 0);
  }
  return f;
}

#  include <stdint.h> /* for uint64_t */

typedef uint64_t pagemap_elem_t;

static pagemap_elem_t *soft_vdb_buf;
static int pagemap_fd;

static GC_bool
soft_dirty_open_files(void)
{
  pid_t pid = getpid();

  clear_refs_fd = open_proc_fd(pid, "clear_refs", O_WRONLY);
  if (-1 == clear_refs_fd)
    return FALSE;
  pagemap_fd = open_proc_fd(pid, "pagemap", O_RDONLY);
  if (-1 == pagemap_fd) {
    close(clear_refs_fd);
    clear_refs_fd = -1;
    return FALSE;
  }
#  ifndef THREADS
  /* Updated on success only.       */
  saved_proc_pid = pid;
#  endif
  return TRUE;
}

#  ifdef CAN_HANDLE_FORK
GC_INNER void
GC_dirty_update_child(void)
{
  GC_ASSERT(I_HOLD_LOCK());
  if (-1 == clear_refs_fd) {
    /* The GC incremental mode is off.      */
    return;
  }
  close(clear_refs_fd);
  close(pagemap_fd);
  if (!soft_dirty_open_files())
    GC_incremental = FALSE;
}
#  endif /* CAN_HANDLE_FORK */

/* Clear soft-dirty bits from the task's PTEs.        */
static void
clear_soft_dirty_bits(void)
{
  ssize_t res = write(clear_refs_fd, "4\n", 2);

  if (res != 2)
    ABORT_ARG1("Failed to write to /proc/self/clear_refs", ": errno= %d",
               res < 0 ? errno : 0);
}

/* The bit 55 of the 64-bit qword of pagemap file is the soft-dirty one. */
#  define PM_SOFTDIRTY_MASK ((pagemap_elem_t)1 << 55)

static GC_bool
detect_soft_dirty_supported(ptr_t vaddr)
{
  off_t fpos;
  pagemap_elem_t buf[1];

  GC_ASSERT(GC_log_pagesize != 0);
  /* Make it dirty.   */
  *vaddr = 1;
  fpos = (off_t)((ADDR(vaddr) >> GC_log_pagesize) * sizeof(pagemap_elem_t));

  for (;;) {
    /* Read the relevant PTE from the pagemap file.   */
    if (lseek(pagemap_fd, fpos, SEEK_SET) == (off_t)(-1))
      return FALSE;
    if (PROC_READ(pagemap_fd, buf, sizeof(buf)) != (int)sizeof(buf))
      return FALSE;

    /* Is the soft-dirty bit unset?   */
    if ((buf[0] & PM_SOFTDIRTY_MASK) == 0)
      return FALSE;

    if (0 == *vaddr)
      break;
    /* Retry to check that writing to clear_refs works as expected.   */
    /* This malfunction of the soft-dirty bits implementation is      */
    /* observed on some Linux kernels on Power9 (e.g. in Fedora 36).  */
    clear_soft_dirty_bits();
    *vaddr = 0;
  }
  return TRUE; /* success */
}

#  ifndef NO_SOFT_VDB_LINUX_VER_RUNTIME_CHECK
#    include <string.h> /* for strcmp() */
#    include <sys/utsname.h>

/* Ensure the linux (kernel) major/minor version is as given or higher. */
static GC_bool
ensure_min_linux_ver(int major, int minor)
{
  struct utsname info;
  int actual_major;
  int actual_minor = -1;

  if (uname(&info) == -1) {
    /* uname() failed, should not happen actually.  */
    return FALSE;
  }
  if (strcmp(info.sysname, "Linux")) {
    WARN("Cannot ensure Linux version as running on other OS: %s\n",
         info.sysname);
    return FALSE;
  }
  actual_major = GC_parse_version(&actual_minor, info.release);
  return actual_major > major
         || (actual_major == major && actual_minor >= minor);
}
#  endif

#  ifdef MPROTECT_VDB
static GC_bool
soft_dirty_init(void)
#  else
GC_INNER GC_bool
GC_dirty_init(void)
#  endif
{
#  if defined(MPROTECT_VDB) && !defined(CHECK_SOFT_VDB)
  char *str = GETENV("GC_USE_GETWRITEWATCH");
#    ifdef GC_PREFER_MPROTECT_VDB
  if (NULL == str || (*str == '0' && *(str + 1) == '\0')) {
    /* The environment variable is unset or set to "0".   */
    return FALSE;
  }
#    else
  if (str != NULL && *str == '0' && *(str + 1) == '\0') {
    /* The environment variable is set "0".       */
    return FALSE;
  }
#    endif
#  endif
  GC_ASSERT(I_HOLD_LOCK());
  GC_ASSERT(NULL == soft_vdb_buf);
#  ifndef NO_SOFT_VDB_LINUX_VER_RUNTIME_CHECK
  if (!ensure_min_linux_ver(3, 18)) {
    GC_COND_LOG_PRINTF(
        "Running on old kernel lacking correct soft-dirty bit support\n");
    return FALSE;
  }
#  endif
  if (!soft_dirty_open_files())
    return FALSE;
  soft_vdb_buf = (pagemap_elem_t *)GC_scratch_alloc(VDB_BUF_SZ);
  if (NULL == soft_vdb_buf)
    ABORT("Insufficient space for /proc pagemap buffer");
  if (!detect_soft_dirty_supported((ptr_t)soft_vdb_buf)) {
    GC_COND_LOG_PRINTF("Soft-dirty bit is not supported by kernel\n");
    /* Release the resources. */
    GC_scratch_recycle_no_gww(soft_vdb_buf, VDB_BUF_SZ);
    soft_vdb_buf = NULL;
    close(clear_refs_fd);
    clear_refs_fd = -1;
    close(pagemap_fd);
    return FALSE;
  }
  return TRUE;
}

static off_t pagemap_buf_fpos; /* valid only if pagemap_buf_len > 0 */

static size_t pagemap_buf_len;

/* Read bytes from /proc/self/pagemap at given file position.         */
/* len - the maximum number of bytes to read; (*pres) - amount of     */
/* bytes actually read, always bigger than 0 but never exceeds len;   */
/* next_fpos_hint - the file position of the next bytes block to read */
/* ahead if possible (0 means no information provided).               */
static const pagemap_elem_t *
pagemap_buffered_read(size_t *pres, off_t fpos, size_t len,
                      off_t next_fpos_hint)
{
  ssize_t res;
  size_t ofs;

  GC_ASSERT(GC_page_size != 0);
  GC_ASSERT(len > 0);
  if (pagemap_buf_fpos <= fpos
      && fpos < pagemap_buf_fpos + (off_t)pagemap_buf_len) {
    /* The requested data is already in the buffer.   */
    ofs = (size_t)(fpos - pagemap_buf_fpos);
    res = (ssize_t)(pagemap_buf_fpos + pagemap_buf_len - fpos);
  } else {
    off_t aligned_pos = fpos
                        & ~(off_t)(GC_page_size < VDB_BUF_SZ ? GC_page_size - 1
                                                             : VDB_BUF_SZ - 1);

    for (;;) {
      size_t count;

      if ((0 == pagemap_buf_len
           || pagemap_buf_fpos + (off_t)pagemap_buf_len != aligned_pos)
          && lseek(pagemap_fd, aligned_pos, SEEK_SET) == (off_t)(-1))
        ABORT_ARG2("Failed to lseek /proc/self/pagemap",
                   ": offset= %lu, errno= %d", (unsigned long)fpos, errno);

      /* How much to read at once?    */
      ofs = (size_t)(fpos - aligned_pos);
      GC_ASSERT(ofs < VDB_BUF_SZ);
      if (next_fpos_hint > aligned_pos
          && next_fpos_hint - aligned_pos < VDB_BUF_SZ) {
        count = VDB_BUF_SZ;
      } else {
        count = len + ofs;
        if (count > VDB_BUF_SZ)
          count = VDB_BUF_SZ;
      }

      GC_ASSERT(count % sizeof(pagemap_elem_t) == 0);
      res = PROC_READ(pagemap_fd, soft_vdb_buf, count);
      if (res > (ssize_t)ofs)
        break;
      if (res <= 0)
        ABORT_ARG1("Failed to read /proc/self/pagemap", ": errno= %d",
                   res < 0 ? errno : 0);
      /* Retry (once) w/o page-alignment.     */
      aligned_pos = fpos;
    }

    /* Save the buffer (file window) position and size.       */
    pagemap_buf_fpos = aligned_pos;
    pagemap_buf_len = (size_t)res;
    res -= (ssize_t)ofs;
  }

  GC_ASSERT(ofs % sizeof(pagemap_elem_t) == 0);
  *pres = (size_t)res < len ? (size_t)res : len;
  return &soft_vdb_buf[ofs / sizeof(pagemap_elem_t)];
}

static void
soft_set_grungy_pages(ptr_t start, ptr_t limit, ptr_t next_start_hint,
                      GC_bool is_static_root)
{
  ptr_t vaddr = (ptr_t)HBLK_PAGE_ALIGNED(start);
  off_t next_fpos_hint = (off_t)((ADDR(next_start_hint) >> GC_log_pagesize)
                                 * sizeof(pagemap_elem_t));

  GC_ASSERT(I_HOLD_LOCK());
  GC_ASSERT(modHBLKSZ(ADDR(start)) == 0);
  GC_ASSERT(GC_log_pagesize != 0);
  while (ADDR_LT(vaddr, limit)) {
    size_t res;
    ptr_t limit_buf;
    word vlen_p = ADDR(limit) - ADDR(vaddr) + GC_page_size - 1;
    const pagemap_elem_t *bufp = pagemap_buffered_read(
        &res,
        (off_t)((ADDR(vaddr) >> GC_log_pagesize) * sizeof(pagemap_elem_t)),
        (size_t)((vlen_p >> GC_log_pagesize) * sizeof(pagemap_elem_t)),
        next_fpos_hint);

    if (res % sizeof(pagemap_elem_t) != 0) {
      /* Punt: */
      memset(GC_grungy_pages, 0xff, sizeof(page_hash_table));
      WARN("Incomplete read of pagemap, not multiple of entry size\n", 0);
      break;
    }

    limit_buf = vaddr + ((res / sizeof(pagemap_elem_t)) << GC_log_pagesize);
    for (; ADDR_LT(vaddr, limit_buf); vaddr += GC_page_size, bufp++) {
      if ((*bufp & PM_SOFTDIRTY_MASK) != 0) {
        struct hblk *h;
        ptr_t next_vaddr = vaddr + GC_page_size;

        if (EXPECT(ADDR_LT(limit, next_vaddr), FALSE))
          next_vaddr = limit;
          /* If the bit is set, the respective PTE was written to       */
          /* since clearing the soft-dirty bits.                        */
#  ifdef DEBUG_DIRTY_BITS
        if (is_static_root)
          GC_log_printf("static root dirty page at: %p\n", (void *)vaddr);
#  endif
        h = (struct hblk *)vaddr;
        if (EXPECT(ADDR_LT(vaddr, start), FALSE))
          h = (struct hblk *)start;
        for (; ADDR_LT((ptr_t)h, next_vaddr); h++) {
          size_t index = PHT_HASH(h);

          /* Filter out the blocks without pointers.  It might worth  */
          /* for the case when the heap is large enough for the hash  */
          /* collisions to occur frequently.  Thus, off by default.   */
#  if defined(FILTER_PTRFREE_HBLKS_IN_SOFT_VDB) || defined(CHECKSUMS) \
      || defined(DEBUG_DIRTY_BITS)
          if (!is_static_root) {
            hdr *hhdr;

#    ifdef CHECKSUMS
            set_pht_entry_from_index(GC_written_pages, index);
#    endif
            GET_HDR(h, hhdr);
            if (NULL == hhdr)
              continue;

            (void)GC_find_starting_hblk(h, &hhdr);
            if (HBLK_IS_FREE(hhdr) || IS_PTRFREE(hhdr))
              continue;
#    ifdef DEBUG_DIRTY_BITS
            GC_log_printf("dirty page (hblk) at: %p\n", (void *)h);
#    endif
          }
#  else
          UNUSED_ARG(is_static_root);
#  endif
          set_pht_entry_from_index(GC_grungy_pages, index);
        }
      } else {
#  if defined(CHECK_SOFT_VDB) /* && MPROTECT_VDB */
        /* Ensure that each clean page according to the soft-dirty  */
        /* VDB is also identified such by the mprotect-based one.   */
        if (!is_static_root
            && get_pht_entry_from_index(GC_dirty_pages, PHT_HASH(vaddr))) {
          ptr_t my_start, my_end; /* the values are not used */

          /* There could be a hash collision, thus we need to       */
          /* verify the page is clean using slow GC_get_maps().     */
          if (GC_enclosing_writable_mapping(vaddr, &my_start, &my_end)) {
            ABORT("Inconsistent soft-dirty against mprotect dirty bits");
          }
        }
#  endif
      }
    }
    /* Read the next portion of pagemap file if incomplete.   */
  }
}

GC_INLINE void
GC_soft_read_dirty(GC_bool output_unneeded)
{
  GC_ASSERT(I_HOLD_LOCK());
#  ifndef THREADS
  /* Similar as for GC_proc_read_dirty.     */
  if (getpid() != saved_proc_pid
      && (-1 == clear_refs_fd /* no need to retry */
          || (close(clear_refs_fd), close(pagemap_fd),
              !soft_dirty_open_files()))) {
    /* Failed to reopen the files.  */
    if (!output_unneeded) {
      /* Punt: */
      memset(GC_grungy_pages, 0xff, sizeof(page_hash_table));
#    ifdef CHECKSUMS
      memset(GC_written_pages, 0xff, sizeof(page_hash_table));
#    endif
    }
    return;
  }
#  endif

  if (!output_unneeded) {
    size_t i;

    BZERO(GC_grungy_pages, sizeof(GC_grungy_pages));
    pagemap_buf_len = 0; /* invalidate soft_vdb_buf */

    for (i = 0; i < GC_n_heap_sects; ++i) {
      ptr_t start = GC_heap_sects[i].hs_start;

      soft_set_grungy_pages(
          start, start + GC_heap_sects[i].hs_bytes,
          i + 1 < GC_n_heap_sects ? GC_heap_sects[i + 1].hs_start : NULL,
          FALSE);
    }

#  ifndef NO_VDB_FOR_STATIC_ROOTS
    for (i = 0; i < n_root_sets; ++i) {
      soft_set_grungy_pages(
          (ptr_t)HBLKPTR(GC_static_roots[i].r_start), GC_static_roots[i].r_end,
          i + 1 < n_root_sets ? GC_static_roots[i + 1].r_start : NULL, TRUE);
    }
#  endif
  }

  clear_soft_dirty_bits();
}
#endif /* SOFT_VDB */

#ifndef NO_MANUAL_VDB
GC_INNER GC_bool GC_manual_vdb = FALSE;

/* Manually mark the page containing p as dirty.  Logically, this     */
/* dirties the entire object.                                         */
GC_INNER void
GC_dirty_inner(const void *p)
{
  size_t index = PHT_HASH(p);

#  if defined(MPROTECT_VDB)
  /* Do not update GC_dirty_pages if it should be followed by the   */
  /* page unprotection.                                             */
  GC_ASSERT(GC_manual_vdb);
#  endif
  async_set_pht_entry_from_index(GC_dirty_pages, index);
}
#endif /* !NO_MANUAL_VDB */

#ifndef GC_DISABLE_INCREMENTAL
/* Retrieve system dirty bits for the heap to a local buffer (unless  */
/* output_unneeded).  Restore the systems notion of which pages are   */
/* dirty.  We assume that either the world is stopped or it is OK to  */
/* lose dirty bits while it is happening (GC_enable_incremental is    */
/* the caller and output_unneeded is TRUE at least if multi-threading */
/* support is on).                                                    */
GC_INNER void
GC_read_dirty(GC_bool output_unneeded)
{
  GC_ASSERT(I_HOLD_LOCK());
#  ifdef DEBUG_DIRTY_BITS
  GC_log_printf("read dirty begin\n");
#  endif
  if (GC_manual_vdb
#  if defined(MPROTECT_VDB)
      || !GC_GWW_AVAILABLE()
#  endif
  ) {
    if (!output_unneeded)
      BCOPY(CAST_AWAY_VOLATILE_PVOID(GC_dirty_pages), GC_grungy_pages,
            sizeof(GC_dirty_pages));
    BZERO(CAST_AWAY_VOLATILE_PVOID(GC_dirty_pages), sizeof(GC_dirty_pages));
#  ifdef MPROTECT_VDB
    if (!GC_manual_vdb)
      GC_protect_heap();
#  endif
    return;
  }

#  ifdef GWW_VDB
  GC_gww_read_dirty(output_unneeded);
#  elif defined(PROC_VDB)
  GC_proc_read_dirty(output_unneeded);
#  elif defined(SOFT_VDB)
  GC_soft_read_dirty(output_unneeded);
#  endif
#  if defined(CHECK_SOFT_VDB) /* && MPROTECT_VDB */
  BZERO(CAST_AWAY_VOLATILE_PVOID(GC_dirty_pages), sizeof(GC_dirty_pages));
  GC_protect_heap();
#  endif
}

#  if !defined(NO_VDB_FOR_STATIC_ROOTS) && !defined(PROC_VDB)
GC_INNER GC_bool
GC_is_vdb_for_static_roots(void)
{
  if (GC_manual_vdb)
    return FALSE;
#    if defined(MPROTECT_VDB)
  /* Currently used only in conjunction with SOFT_VDB.    */
  return GC_GWW_AVAILABLE();
#    else
#      ifndef LINT2
  GC_ASSERT(GC_incremental);
#      endif
  return TRUE;
#    endif
}
#  endif

/* Is the HBLKSIZE sized page at h marked dirty in the local buffer?  */
/* If the actual page size is different, this returns TRUE if any     */
/* of the pages overlapping h are dirty.  This routine may err on the */
/* side of labeling pages as dirty (and this implementation does).    */
GC_INNER GC_bool
GC_page_was_dirty(struct hblk *h)
{
  size_t index;

#  ifdef DEFAULT_VDB
  if (!GC_manual_vdb)
    return TRUE;
#  elif defined(PROC_VDB)
  /* Unless manual VDB is on, the bitmap covers all process memory. */
  if (GC_manual_vdb)
#  endif
  {
    if (NULL == HDR(h))
      return TRUE;
  }
  index = PHT_HASH(h);
  return get_pht_entry_from_index(GC_grungy_pages, index);
}

#  if defined(CHECKSUMS) || defined(PROC_VDB)
/* Could any valid GC heap pointer ever have been written to this page? */
GC_INNER GC_bool
GC_page_was_ever_dirty(struct hblk *h)
{
#    if defined(GWW_VDB) || defined(PROC_VDB) || defined(SOFT_VDB)
  size_t index;

#      ifdef MPROTECT_VDB
  if (!GC_GWW_AVAILABLE())
    return TRUE;
#      endif
#      if defined(PROC_VDB)
  if (GC_manual_vdb)
#      endif
  {
    if (NULL == HDR(h))
      return TRUE;
  }
  index = PHT_HASH(h);
  return get_pht_entry_from_index(GC_written_pages, index);
#    else
  /* TODO: implement me for MANUAL_VDB. */
  UNUSED_ARG(h);
  return TRUE;
#    endif
}
#  endif /* CHECKSUMS || PROC_VDB */

GC_INNER void
GC_remove_protection(struct hblk *h, size_t nblocks, GC_bool is_ptrfree)
{
#  ifdef MPROTECT_VDB
  struct hblk *current;
  struct hblk *h_trunc; /* truncated to page boundary */
  ptr_t h_end;          /* page boundary following the block end */
#  endif

#  ifndef PARALLEL_MARK
  GC_ASSERT(I_HOLD_LOCK());
#  endif
#  ifdef MPROTECT_VDB
  /* Note it is not allowed to call GC_printf (and the friends) */
  /* in this function, see Win32 GC_stop_world for the details. */
#    ifdef DONT_PROTECT_PTRFREE
  if (is_ptrfree)
    return;
#    endif
  if (!GC_auto_incremental || GC_GWW_AVAILABLE())
    return;
  GC_ASSERT(GC_page_size != 0);
  h_trunc = HBLK_PAGE_ALIGNED(h);
  h_end = PTR_ALIGN_UP((ptr_t)(h + nblocks), GC_page_size);
  /* Note that we cannot examine GC_dirty_pages to check    */
  /* whether the page at h_trunc has already been marked    */
  /* dirty as there could be a hash collision.              */
  for (current = h_trunc; ADDR_LT((ptr_t)current, h_end); ++current) {
    size_t index = PHT_HASH(current);

#    ifndef DONT_PROTECT_PTRFREE
    if (!is_ptrfree
        || !ADDR_INSIDE((ptr_t)current, (ptr_t)h, (ptr_t)(h + nblocks)))
#    endif
    {
      async_set_pht_entry_from_index(GC_dirty_pages, index);
    }
  }
  UNPROTECT(h_trunc, h_end - (ptr_t)h_trunc);
#  else
  /* Ignore write hints.  They don't help us here.  */
  UNUSED_ARG(h);
  UNUSED_ARG(nblocks);
  UNUSED_ARG(is_ptrfree);
#  endif
}
#endif /* !GC_DISABLE_INCREMENTAL */

#if defined(MPROTECT_VDB) && defined(DARWIN)
/* 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.
         www.omnigroup.com/mailman/archive/macosx-dev/2000-June/014178.html
      3. macosx-nat.c from Apple's GDB source code.
*/

/* The bug that caused all this trouble should now be fixed.            */
/* This should eventually be removed if all goes well.                  */

#  include <mach/exception.h>
#  include <mach/mach.h>
#  include <mach/mach_error.h>
#  include <mach/task.h>

EXTERN_C_BEGIN

/* Some of the following prototypes are missing in any header, although */
/* they are documented.  Some are in mach/exc.h file.                   */
extern boolean_t exc_server(mach_msg_header_t *, mach_msg_header_t *);

extern kern_return_t exception_raise(mach_port_t, mach_port_t, mach_port_t,
                                     exception_type_t, exception_data_t,
                                     mach_msg_type_number_t);

extern kern_return_t exception_raise_state(
    mach_port_t, mach_port_t, mach_port_t, exception_type_t, exception_data_t,
    mach_msg_type_number_t, thread_state_flavor_t *, thread_state_t,
    mach_msg_type_number_t, thread_state_t, mach_msg_type_number_t *);

extern kern_return_t exception_raise_state_identity(
    mach_port_t, mach_port_t, mach_port_t, exception_type_t, exception_data_t,
    mach_msg_type_number_t, thread_state_flavor_t *, thread_state_t,
    mach_msg_type_number_t, thread_state_t, mach_msg_type_number_t *);

GC_API_OSCALL 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);

GC_API_OSCALL kern_return_t catch_exception_raise_state(
    mach_port_name_t exception_port, int exception, exception_data_t code,
    mach_msg_type_number_t codeCnt, int flavor, thread_state_t old_state,
    int old_stateCnt, thread_state_t new_state, int new_stateCnt);

GC_API_OSCALL kern_return_t catch_exception_raise_state_identity(
    mach_port_name_t exception_port, mach_port_t thread, mach_port_t task,
    int exception, exception_data_t code, mach_msg_type_number_t codeCnt,
    int flavor, thread_state_t old_state, int old_stateCnt,
    thread_state_t new_state, int new_stateCnt);

EXTERN_C_END

/* These should never be called, but just in case...  */
GC_API_OSCALL kern_return_t
catch_exception_raise_state(mach_port_name_t exception_port, int exception,
                            exception_data_t code,
                            mach_msg_type_number_t codeCnt, int flavor,
                            thread_state_t old_state, int old_stateCnt,
                            thread_state_t new_state, int new_stateCnt)
{
  UNUSED_ARG(exception_port);
  UNUSED_ARG(exception);
  UNUSED_ARG(code);
  UNUSED_ARG(codeCnt);
  UNUSED_ARG(flavor);
  UNUSED_ARG(old_state);
  UNUSED_ARG(old_stateCnt);
  UNUSED_ARG(new_state);
  UNUSED_ARG(new_stateCnt);
  ABORT_RET("Unexpected catch_exception_raise_state invocation");
  return KERN_INVALID_ARGUMENT;
}

GC_API_OSCALL kern_return_t
catch_exception_raise_state_identity(
    mach_port_name_t exception_port, mach_port_t thread, mach_port_t task,
    int exception, exception_data_t code, mach_msg_type_number_t codeCnt,
    int flavor, thread_state_t old_state, int old_stateCnt,
    thread_state_t new_state, int new_stateCnt)
{
  UNUSED_ARG(exception_port);
  UNUSED_ARG(thread);
  UNUSED_ARG(task);
  UNUSED_ARG(exception);
  UNUSED_ARG(code);
  UNUSED_ARG(codeCnt);
  UNUSED_ARG(flavor);
  UNUSED_ARG(old_state);
  UNUSED_ARG(old_stateCnt);
  UNUSED_ARG(new_state);
  UNUSED_ARG(new_stateCnt);
  ABORT_RET("Unexpected catch_exception_raise_state_identity invocation");
  return KERN_INVALID_ARGUMENT;
}

#  define MAX_EXCEPTION_PORTS 16

static struct {
  mach_msg_type_number_t count;
  exception_mask_t masks[MAX_EXCEPTION_PORTS];
  exception_handler_t ports[MAX_EXCEPTION_PORTS];
  exception_behavior_t behaviors[MAX_EXCEPTION_PORTS];
  thread_state_flavor_t flavors[MAX_EXCEPTION_PORTS];
} GC_old_exc_ports;

STATIC struct ports_s {
  void (*volatile os_callback[3])(void);
  mach_port_t exception;
#  if defined(THREADS)
  mach_port_t reply;
#  endif
} GC_ports = { { /* This is to prevent stripping these routines as dead.     */
                 (void (*)(void))catch_exception_raise,
                 (void (*)(void))catch_exception_raise_state,
                 (void (*)(void))catch_exception_raise_state_identity },
#  ifdef THREADS
               0, /* for 'exception' */
#  endif
               0 };

typedef struct {
  mach_msg_header_t head;
} GC_msg_t;

typedef enum {
  GC_MP_NORMAL,
  GC_MP_DISCARDING,
  GC_MP_STOPPED
} GC_mprotect_state_t;

#  ifdef THREADS
/* FIXME: 1 and 2 seem to be safe to use in the msgh_id field, but it */
/* is not documented.  Use the source and see if they should be OK.   */
#    define ID_STOP 1
#    define ID_RESUME 2

/* This value is only used on the reply port. */
#    define ID_ACK 3

STATIC GC_mprotect_state_t GC_mprotect_state = GC_MP_NORMAL;

/* The following should ONLY be called when the world is stopped.     */
STATIC void
GC_mprotect_thread_notify(mach_msg_id_t id)
{
  struct buf_s {
    GC_msg_t msg;
    mach_msg_trailer_t trailer;
  } buf;
  mach_msg_return_t r;

  /* remote, local */
  buf.msg.head.msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_MAKE_SEND, 0);
  buf.msg.head.msgh_size = sizeof(buf.msg);
  buf.msg.head.msgh_remote_port = GC_ports.exception;
  buf.msg.head.msgh_local_port = MACH_PORT_NULL;
  buf.msg.head.msgh_id = id;

  r = mach_msg(&buf.msg.head, MACH_SEND_MSG | MACH_RCV_MSG | MACH_RCV_LARGE,
               sizeof(buf.msg), sizeof(buf), GC_ports.reply,
               MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL);
  if (r != MACH_MSG_SUCCESS)
    ABORT("mach_msg failed in GC_mprotect_thread_notify");
  if (buf.msg.head.msgh_id != ID_ACK)
    ABORT("Invalid ack in GC_mprotect_thread_notify");
}

/* Should only be called by the mprotect thread.      */
STATIC void
GC_mprotect_thread_reply(void)
{
  GC_msg_t msg;
  mach_msg_return_t r;

  /* remote, local */
  msg.head.msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_MAKE_SEND, 0);
  msg.head.msgh_size = sizeof(msg);
  msg.head.msgh_remote_port = GC_ports.reply;
  msg.head.msgh_local_port = MACH_PORT_NULL;
  msg.head.msgh_id = ID_ACK;

  r = mach_msg(&msg.head, MACH_SEND_MSG, sizeof(msg), 0, MACH_PORT_NULL,
               MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL);
  if (r != MACH_MSG_SUCCESS)
    ABORT("mach_msg failed in GC_mprotect_thread_reply");
}

GC_INNER void
GC_mprotect_stop(void)
{
  GC_mprotect_thread_notify(ID_STOP);
}

GC_INNER void
GC_mprotect_resume(void)
{
  GC_mprotect_thread_notify(ID_RESUME);
}

#    ifdef CAN_HANDLE_FORK
GC_INNER void
GC_dirty_update_child(void)
{
  GC_ASSERT(I_HOLD_LOCK());
  if (0 == GC_task_self) {
    /* The GC incremental mode is off.      */
    return;
  }

  GC_ASSERT(GC_mprotect_state == GC_MP_NORMAL);
  GC_task_self = mach_task_self(); /* needed by UNPROTECT() */
  GC_unprotect_all_heap();

  /* Restore the old task exception ports.  */
  /* TODO: Should we do it in fork_prepare/parent_proc? */
  if (GC_old_exc_ports.count > 0) {
    /* TODO: Should we check GC_old_exc_ports.count<=1? */
    if (task_set_exception_ports(
            GC_task_self, GC_old_exc_ports.masks[0], GC_old_exc_ports.ports[0],
            GC_old_exc_ports.behaviors[0], GC_old_exc_ports.flavors[0])
        != KERN_SUCCESS)
      ABORT("task_set_exception_ports failed (in child)");
  }

  /* TODO: Re-enable incremental mode in child. */
  GC_task_self = 0;
  GC_incremental = FALSE;
}
#    endif /* CAN_HANDLE_FORK */

#  else
/* The compiler should optimize away any GC_mprotect_state computations. */
#    define GC_mprotect_state GC_MP_NORMAL
#  endif /* !THREADS */

struct mp_reply_s {
  mach_msg_header_t head;
  char data[256];
};

struct mp_msg_s {
  mach_msg_header_t head;
  mach_msg_body_t msgh_body;
  char data[1024];
};

STATIC void *
GC_mprotect_thread(void *arg)
{
  mach_msg_return_t r;
  /* 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.       */
  struct mp_reply_s reply;
  struct mp_msg_s msg;
  mach_msg_id_t id;

  if (ADDR(arg) == GC_WORD_MAX)
    return 0; /* to prevent a compiler warning */
#  if defined(CPPCHECK)
  reply.data[0] = 0; /* to prevent "field unused" warnings */
  msg.data[0] = 0;
#  endif

#  if defined(HAVE_PTHREAD_SETNAME_NP_WITHOUT_TID)
  (void)pthread_setname_np("GC-mprotect");
#  endif
#  if defined(THREADS) && !defined(GC_NO_THREADS_DISCOVERY)
  GC_darwin_register_self_mach_handler();
#  endif

  for (;;) {
    r = mach_msg(
        &msg.head,
        MACH_RCV_MSG | MACH_RCV_LARGE
            | (GC_mprotect_state == GC_MP_DISCARDING ? MACH_RCV_TIMEOUT : 0),
        0, sizeof(msg), GC_ports.exception,
        GC_mprotect_state == GC_MP_DISCARDING ? 0 : MACH_MSG_TIMEOUT_NONE,
        MACH_PORT_NULL);
    id = r == MACH_MSG_SUCCESS ? msg.head.msgh_id : -1;

#  if defined(THREADS)
    if (GC_mprotect_state == GC_MP_DISCARDING) {
      if (r == MACH_RCV_TIMED_OUT) {
        GC_mprotect_state = GC_MP_STOPPED;
        GC_mprotect_thread_reply();
        continue;
      }
      if (r == MACH_MSG_SUCCESS && (id == ID_STOP || id == ID_RESUME))
        ABORT("Out of order mprotect thread request");
    }
#  endif /* THREADS */

    if (r != MACH_MSG_SUCCESS) {
      ABORT_ARG2("mach_msg failed", ": errcode= %d (%s)", (int)r,
                 mach_error_string(r));
    }

    switch (id) {
#  if defined(THREADS)
    case ID_STOP:
      if (GC_mprotect_state != GC_MP_NORMAL)
        ABORT("Called mprotect_stop when state wasn't normal");
      GC_mprotect_state = GC_MP_DISCARDING;
      break;
    case ID_RESUME:
      if (GC_mprotect_state != GC_MP_STOPPED)
        ABORT("Called mprotect_resume when state wasn't stopped");
      GC_mprotect_state = GC_MP_NORMAL;
      GC_mprotect_thread_reply();
      break;
#  endif /* THREADS */
    default:
      /* Handle the message (calls catch_exception_raise).  */
      if (!exc_server(&msg.head, &reply.head))
        ABORT("exc_server failed");
      /* Send the reply.    */
      r = mach_msg(&reply.head, MACH_SEND_MSG, reply.head.msgh_size, 0,
                   MACH_PORT_NULL, MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL);
      if (r != MACH_MSG_SUCCESS) {
        /* This will fail if the thread dies, but the thread should */
        /* not die...                                               */
#  ifdef BROKEN_EXCEPTION_HANDLING
        GC_err_printf("mach_msg failed with %d %s while sending "
                      "exc reply\n",
                      (int)r, mach_error_string(r));
#  else
        ABORT("mach_msg failed while sending exception reply");
#  endif
      }
    } /* switch */
  }
}

/* All this SIGBUS code should not be necessary.  All protection faults */
/* should be going through the mach exception handler.  However, it     */
/* seems a SIGBUS is occasionally sent for some unknown reason.  Even   */
/* more odd, it seems to be meaningless and safe to ignore.             */
#  ifdef BROKEN_EXCEPTION_HANDLING

/* Updates to this aren't atomic, but the SIGBUS'es seem pretty rare.    */
/* Even if this doesn't get updated property, it isn't really a problem. */
STATIC int GC_sigbus_count = 0;

STATIC void
GC_darwin_sigbus(int num, siginfo_t *sip, void *context)
{
  if (num != SIGBUS)
    ABORT("Got a non-sigbus signal in the sigbus handler");

  /* Ugh... some seem safe to ignore, but too many in a row probably  */
  /* means trouble.  GC_sigbus_count is reset for each mach exception */
  /* that is handled.                                                 */
  if (GC_sigbus_count >= 8)
    ABORT("Got many SIGBUS signals in a row!");
  GC_sigbus_count++;
  WARN("Ignoring SIGBUS\n", 0);
}
#  endif /* BROKEN_EXCEPTION_HANDLING */

GC_INNER GC_bool
GC_dirty_init(void)
{
  kern_return_t r;
  mach_port_t me;
  pthread_t thread;
  pthread_attr_t attr;
  exception_mask_t mask;

  GC_ASSERT(I_HOLD_LOCK());
#  if defined(CAN_HANDLE_FORK) && !defined(THREADS)
  if (GC_handle_fork) {
    /* To both support GC incremental mode and GC functions usage in  */
    /* the forked child, pthread_atfork should be used to install     */
    /* handlers that switch off GC_incremental in the child           */
    /* gracefully (unprotecting all pages and clearing                */
    /* GC_mach_handler_thread).  For now, we just disable incremental */
    /* mode if fork() handling is requested by the client.            */
    WARN("Can't turn on GC incremental mode as fork()"
         " handling requested\n",
         0);
    return FALSE;
  }
#  endif

  GC_VERBOSE_LOG_PRINTF("Initializing mach/darwin mprotect"
                        " virtual dirty bit implementation\n");
#  ifdef BROKEN_EXCEPTION_HANDLING
  WARN("Enabling workarounds for various darwin exception handling bugs\n", 0);
#  endif
  if (GC_page_size % HBLKSIZE != 0) {
    ABORT("Page size not multiple of HBLKSIZE");
  }

  GC_task_self = me = mach_task_self();
  GC_ASSERT(me != 0);

  r = mach_port_allocate(me, MACH_PORT_RIGHT_RECEIVE, &GC_ports.exception);
  /* TODO: WARN and return FALSE in case of a failure. */
  if (r != KERN_SUCCESS)
    ABORT("mach_port_allocate failed (exception port)");

  r = mach_port_insert_right(me, GC_ports.exception, GC_ports.exception,
                             MACH_MSG_TYPE_MAKE_SEND);
  if (r != KERN_SUCCESS)
    ABORT("mach_port_insert_right failed (exception port)");

#  if defined(THREADS)
  r = mach_port_allocate(me, MACH_PORT_RIGHT_RECEIVE, &GC_ports.reply);
  if (r != KERN_SUCCESS)
    ABORT("mach_port_allocate failed (reply port)");
#  endif

  /* The exceptions we want to catch. */
  mask = EXC_MASK_BAD_ACCESS;
  r = task_get_exception_ports(me, mask, GC_old_exc_ports.masks,
                               &GC_old_exc_ports.count, GC_old_exc_ports.ports,
                               GC_old_exc_ports.behaviors,
                               GC_old_exc_ports.flavors);
  if (r != KERN_SUCCESS)
    ABORT("task_get_exception_ports failed");

  r = task_set_exception_ports(me, mask, GC_ports.exception, EXCEPTION_DEFAULT,
                               GC_MACH_THREAD_STATE);
  if (r != KERN_SUCCESS)
    ABORT("task_set_exception_ports failed");

  if (pthread_attr_init(&attr) != 0)
    ABORT("pthread_attr_init failed");
  if (pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED) != 0)
    ABORT("pthread_attr_setdetachedstate failed");
  /* This will call the real pthread function, not our wrapper. */
  if (GC_inner_pthread_create(&thread, &attr, GC_mprotect_thread, NULL) != 0)
    ABORT("pthread_create failed");
  (void)pthread_attr_destroy(&attr);

  /* Setup the sigbus handler for ignoring the meaningless SIGBUS signals. */
#  ifdef BROKEN_EXCEPTION_HANDLING
  {
    struct sigaction sa, oldsa;
    sa.sa_handler = (SIG_HNDLR_PTR)GC_darwin_sigbus;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART | SA_SIGINFO;
    /* sa.sa_restorer is deprecated and should not be initialized. */
    if (sigaction(SIGBUS, &sa, &oldsa) < 0)
      ABORT("sigaction failed");
    if ((GC_funcptr_uint)oldsa.sa_handler != (GC_funcptr_uint)SIG_DFL) {
      GC_VERBOSE_LOG_PRINTF("Replaced other SIGBUS handler\n");
    }
  }
#  endif /* BROKEN_EXCEPTION_HANDLING  */
#  if defined(CPPCHECK)
  GC_noop1((word)(GC_funcptr_uint)GC_ports.os_callback[0]);
#  endif
  return TRUE;
}

/* The source code for Apple's GDB was used as a reference for the      */
/* exception forwarding code.  This code is similar to be GDB code only */
/* because there is only one way to do it.                              */
STATIC kern_return_t
GC_forward_exception(mach_port_t thread, mach_port_t task,
                     exception_type_t exception, exception_data_t data,
                     mach_msg_type_number_t data_count)
{
  size_t i;
  kern_return_t r;
  mach_port_t port;
  exception_behavior_t behavior;
  thread_state_flavor_t flavor;

  thread_state_data_t thread_state;
  mach_msg_type_number_t thread_state_count = THREAD_STATE_MAX;

  for (i = 0; i < (size_t)GC_old_exc_ports.count; i++) {
    if ((GC_old_exc_ports.masks[i] & ((exception_mask_t)1 << exception)) != 0)
      break;
  }
  if (i == (size_t)GC_old_exc_ports.count)
    ABORT("No handler for exception!");

  port = GC_old_exc_ports.ports[i];
  behavior = GC_old_exc_ports.behaviors[i];
  flavor = GC_old_exc_ports.flavors[i];

  if (behavior == EXCEPTION_STATE || behavior == EXCEPTION_STATE_IDENTITY) {
    r = thread_get_state(thread, flavor, thread_state, &thread_state_count);
    if (r != KERN_SUCCESS)
      ABORT("thread_get_state failed in forward_exception");
  }

  switch (behavior) {
  case EXCEPTION_STATE:
    r = exception_raise_state(port, thread, task, exception, data, data_count,
                              &flavor, thread_state, thread_state_count,
                              thread_state, &thread_state_count);
    break;
  case EXCEPTION_STATE_IDENTITY:
    r = exception_raise_state_identity(
        port, thread, task, exception, data, data_count, &flavor, thread_state,
        thread_state_count, thread_state, &thread_state_count);
    break;
  /* case EXCEPTION_DEFAULT: */ /* default signal handlers */
  default:                      /* user-supplied signal handlers */
    r = exception_raise(port, thread, task, exception, data, data_count);
  }

  if (behavior == EXCEPTION_STATE || behavior == EXCEPTION_STATE_IDENTITY) {
    r = thread_set_state(thread, flavor, thread_state, thread_state_count);
    if (r != KERN_SUCCESS)
      ABORT("thread_set_state failed in forward_exception");
  }
  return r;
}

#  define FWD() GC_forward_exception(thread, task, exception, code, code_count)

#  ifdef ARM32
#    define DARWIN_EXC_STATE ARM_EXCEPTION_STATE
#    define DARWIN_EXC_STATE_COUNT ARM_EXCEPTION_STATE_COUNT
#    define DARWIN_EXC_STATE_T arm_exception_state_t
#    define DARWIN_EXC_STATE_DAR THREAD_FLD_NAME(far)
#  elif defined(AARCH64)
#    define DARWIN_EXC_STATE ARM_EXCEPTION_STATE64
#    define DARWIN_EXC_STATE_COUNT ARM_EXCEPTION_STATE64_COUNT
#    define DARWIN_EXC_STATE_T arm_exception_state64_t
#    define DARWIN_EXC_STATE_DAR THREAD_FLD_NAME(far)
#  elif defined(POWERPC)
#    if CPP_WORDSZ == 32
#      define DARWIN_EXC_STATE PPC_EXCEPTION_STATE
#      define DARWIN_EXC_STATE_COUNT PPC_EXCEPTION_STATE_COUNT
#      define DARWIN_EXC_STATE_T ppc_exception_state_t
#    else
#      define DARWIN_EXC_STATE PPC_EXCEPTION_STATE64
#      define DARWIN_EXC_STATE_COUNT PPC_EXCEPTION_STATE64_COUNT
#      define DARWIN_EXC_STATE_T ppc_exception_state64_t
#    endif
#    define DARWIN_EXC_STATE_DAR THREAD_FLD_NAME(dar)
#  elif defined(I386) || defined(X86_64)
#    if CPP_WORDSZ == 32
#      if defined(i386_EXCEPTION_STATE_COUNT) \
          && !defined(x86_EXCEPTION_STATE32_COUNT)
/* Use old naming convention for i686.    */
#        define DARWIN_EXC_STATE i386_EXCEPTION_STATE
#        define DARWIN_EXC_STATE_COUNT i386_EXCEPTION_STATE_COUNT
#        define DARWIN_EXC_STATE_T i386_exception_state_t
#      else
#        define DARWIN_EXC_STATE x86_EXCEPTION_STATE32
#        define DARWIN_EXC_STATE_COUNT x86_EXCEPTION_STATE32_COUNT
#        define DARWIN_EXC_STATE_T x86_exception_state32_t
#      endif
#    else
#      define DARWIN_EXC_STATE x86_EXCEPTION_STATE64
#      define DARWIN_EXC_STATE_COUNT x86_EXCEPTION_STATE64_COUNT
#      define DARWIN_EXC_STATE_T x86_exception_state64_t
#    endif
#    define DARWIN_EXC_STATE_DAR THREAD_FLD_NAME(faultvaddr)
#  elif !defined(CPPCHECK)
#    error FIXME for non-arm/ppc/x86 darwin
#  endif

/* This violates the namespace rules but there isn't anything that can  */
/* be done about it.  The exception handling stuff is hard coded to     */
/* call this.  catch_exception_raise, catch_exception_raise_state and   */
/* and catch_exception_raise_state_identity are called from OS.         */
GC_API_OSCALL 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)
{
  kern_return_t r;
  char *addr;
  thread_state_flavor_t flavor = DARWIN_EXC_STATE;
  mach_msg_type_number_t exc_state_count = DARWIN_EXC_STATE_COUNT;
  DARWIN_EXC_STATE_T exc_state;

  UNUSED_ARG(exception_port);
  UNUSED_ARG(task);
  if (exception != EXC_BAD_ACCESS || code[0] != KERN_PROTECTION_FAILURE) {
#  ifdef DEBUG_EXCEPTION_HANDLING
    /* We are not interested, pass it on to the old handler.  */
    GC_log_printf("Exception: 0x%x Code: 0x%x 0x%x in catch...\n", exception,
                  code_count > 0 ? code[0] : -1,
                  code_count > 1 ? code[1] : -1);
#  else
    UNUSED_ARG(code_count);
#  endif
    return FWD();
  }

  r = thread_get_state(thread, flavor, (natural_t *)&exc_state,
                       &exc_state_count);
  if (r != KERN_SUCCESS) {
    /* The thread is supposed to be suspended while the exception       */
    /* handler is called.  This shouldn't fail.                         */
#  ifdef BROKEN_EXCEPTION_HANDLING
    GC_err_printf("thread_get_state failed in catch_exception_raise\n");
    return KERN_SUCCESS;
#  else
    ABORT("thread_get_state failed in catch_exception_raise");
#  endif
  }

  /* This is the address that caused the fault. */
  addr = (char *)exc_state.DARWIN_EXC_STATE_DAR;
  if (!is_header_found_async(addr)) {
    /* Ugh... just like the SIGBUS problem above, it seems we get       */
    /* a bogus KERN_PROTECTION_FAILURE every once and a while.  We wait */
    /* till we get a bunch in a row before doing anything about it.     */
    /* If a "real" fault ever occurs it'll just keep faulting over and  */
    /* over and we'll hit the limit pretty quickly.                     */
#  ifdef BROKEN_EXCEPTION_HANDLING
    static const char *last_fault;
    static int last_fault_count;

    if (addr != last_fault) {
      last_fault = addr;
      last_fault_count = 0;
    }
    if (++last_fault_count < 32) {
      if (last_fault_count == 1)
        WARN("Ignoring KERN_PROTECTION_FAILURE at %p\n", addr);
      return KERN_SUCCESS;
    }

    GC_err_printf("Unexpected KERN_PROTECTION_FAILURE at %p; aborting...\n",
                  (void *)addr);
    /* Can't pass it along to the signal handler because that is      */
    /* ignoring SIGBUS signals.  We also shouldn't call ABORT here as */
    /* signals don't always work too well from the exception handler. */
    EXIT();
#  else
    /* Pass it along to the next exception handler (which should call */
    /* SIGBUS/SIGSEGV).                                               */
    return FWD();
#  endif /* !BROKEN_EXCEPTION_HANDLING */
  }

#  ifdef BROKEN_EXCEPTION_HANDLING
  /* Reset the number of consecutive SIGBUS signals.  */
  GC_sigbus_count = 0;
#  endif

  GC_ASSERT(GC_page_size != 0);
  if (GC_mprotect_state == GC_MP_NORMAL) {
    /* The common case. */
    struct hblk *h = HBLK_PAGE_ALIGNED(addr);
    size_t i;

#  ifdef CHECKSUMS
    GC_record_fault(h);
#  endif
    UNPROTECT(h, GC_page_size);
    for (i = 0; i < divHBLKSZ(GC_page_size); i++) {
      size_t index = PHT_HASH(h + i);

      async_set_pht_entry_from_index(GC_dirty_pages, index);
    }
  } else if (GC_mprotect_state == GC_MP_DISCARDING) {
    /* Lie to the thread for now.  No sense UNPROTECT()'ing the memory  */
    /* when we are just going to PROTECT() it again later.  The thread  */
    /* will just fault again once it resumes.                           */
  } else {
    /* Should not happen, I don't think. */
    GC_err_printf("KERN_PROTECTION_FAILURE while world is stopped\n");
    return FWD();
  }
  return KERN_SUCCESS;
}
#  undef FWD

#  ifndef NO_DESC_CATCH_EXCEPTION_RAISE
/* These symbols should have REFERENCED_DYNAMICALLY (0x10) bit set to */
/* let strip know they are not to be stripped.                        */
__asm__(".desc _catch_exception_raise, 0x10");
__asm__(".desc _catch_exception_raise_state, 0x10");
__asm__(".desc _catch_exception_raise_state_identity, 0x10");
#  endif

#endif /* DARWIN && MPROTECT_VDB */

GC_API int GC_CALL
GC_incremental_protection_needs(void)
{
  GC_ASSERT(GC_is_initialized);
#ifdef MPROTECT_VDB
#  if defined(GWW_VDB) || (defined(SOFT_VDB) && !defined(CHECK_SOFT_VDB))
  /* Only if the incremental mode is already switched on.   */
  if (GC_GWW_AVAILABLE())
    return GC_PROTECTS_NONE;
#  endif
#  ifndef DONT_PROTECT_PTRFREE
  if (GC_page_size != HBLKSIZE)
    return GC_PROTECTS_POINTER_HEAP | GC_PROTECTS_PTRFREE_HEAP;
#  endif
  return GC_PROTECTS_POINTER_HEAP;
#else
  return GC_PROTECTS_NONE;
#endif
}

GC_API unsigned GC_CALL
GC_get_actual_vdb(void)
{
#ifndef GC_DISABLE_INCREMENTAL
  if (GC_incremental) {
#  ifndef NO_MANUAL_VDB
    if (GC_manual_vdb)
      return GC_VDB_MANUAL;
#  endif
#  ifdef MPROTECT_VDB
#    ifdef GWW_VDB
    if (GC_GWW_AVAILABLE())
      return GC_VDB_GWW;
#    endif
#    ifdef SOFT_VDB
    if (GC_GWW_AVAILABLE())
      return GC_VDB_SOFT;
#    endif
    return GC_VDB_MPROTECT;
#  elif defined(GWW_VDB)
    return GC_VDB_GWW;
#  elif defined(SOFT_VDB)
    return GC_VDB_SOFT;
#  elif defined(PROC_VDB)
    return GC_VDB_PROC;
#  else /* DEFAULT_VDB */
    return GC_VDB_DEFAULT;
#  endif
  }
#endif
  return GC_VDB_NONE;
}

#ifdef ECOS
/* Undo sbrk() redirection. */
#  undef sbrk
#endif

/* If value is non-zero then allocate executable memory.        */
GC_API void GC_CALL
GC_set_pages_executable(int value)
{
  GC_ASSERT(!GC_is_initialized);
  /* Even if IGNORE_PAGES_EXECUTABLE is defined, GC_pages_executable is */
  /* touched here to prevent a compiler warning.                        */
  GC_pages_executable = (GC_bool)(value != 0);
}

/* Returns non-zero if the GC-allocated memory is executable.   */
/* GC_get_pages_executable is defined after all the places      */
/* where GC_get_pages_executable is undefined.                  */
GC_API int GC_CALL
GC_get_pages_executable(void)
{
#ifdef IGNORE_PAGES_EXECUTABLE
  return 1; /* Always allocate executable memory. */
#else
  return (int)GC_pages_executable;
#endif
}

/* Call stack save code for debugging.  Should probably be in           */
/* mach_dep.c, but that requires reorganization.                        */
#ifdef NEED_CALLINFO

/* I suspect the following works for most *nix i686 variants, so long */
/* as the frame pointer is explicitly stored.  In the case of gcc,    */
/* the client code should not be compiled with -fomit-frame-pointer.  */
#  if defined(I386) && defined(LINUX) && defined(SAVE_CALL_CHAIN)
struct frame {
  struct frame *fr_savfp;
  long fr_savpc;
#    if NARGS > 0
  /* All the arguments go here. */
  long fr_arg[NARGS];
#    endif
};
#  endif

#  if defined(SPARC)
#    if defined(LINUX)
#      if defined(SAVE_CALL_CHAIN)
struct frame {
  long fr_local[8];
  long fr_arg[6];
  struct frame *fr_savfp;
  long fr_savpc;
#        ifndef __arch64__
  char *fr_stret;
#        endif
  long fr_argd[6];
  long fr_argx[0];
};
#      endif
#    elif defined(DRSNX)
#      include <sys/sparc/frame.h>
#    elif defined(OPENBSD)
#      include <frame.h>
#    elif defined(FREEBSD) || defined(NETBSD)
#      include <machine/frame.h>
#    else
#      include <sys/frame.h>
#    endif
#    if NARGS > 6
#      error We only know how to get the first 6 arguments
#    endif
#  endif /* SPARC */

/* Fill in the pc and argument information for up to NFRAMES of my    */
/* callers.  Ignore my frame and my callers frame.                    */

#  if defined(GC_HAVE_BUILTIN_BACKTRACE)
#    ifdef _MSC_VER
EXTERN_C_BEGIN
int backtrace(void *addresses[], int count);
char **backtrace_symbols(void *const addresses[], int count);
EXTERN_C_END
#    else
#      include <execinfo.h>
#    endif
#  endif /* GC_HAVE_BUILTIN_BACKTRACE */

#  ifdef SAVE_CALL_CHAIN

#    if NARGS == 0 && NFRAMES % 2 == 0 /* No padding */ \
        && defined(GC_HAVE_BUILTIN_BACKTRACE)

#      ifdef REDIRECT_MALLOC
/* Deal with possible malloc calls in backtrace by omitting */
/* the infinitely recursing backtrace.                      */
STATIC GC_bool GC_in_save_callers = FALSE;

#        if defined(THREADS) && defined(DBG_HDRS_ALL)
#          include "private/dbg_mlc.h"

/* A dummy version of GC_save_callers() which does not call   */
/* backtrace().                                               */
GC_INNER void
GC_save_callers_no_unlock(struct callinfo info[NFRAMES])
{
  GC_ASSERT(I_HOLD_LOCK());
  info[0].ci_pc
      = CAST_THRU_UINTPTR(GC_return_addr_t, GC_save_callers_no_unlock);
  BZERO(&info[1], sizeof(void *) * (NFRAMES - 1));
}
#        endif
#      endif /* REDIRECT_MALLOC */

GC_INNER void
GC_save_callers(struct callinfo info[NFRAMES])
{
  void *tmp_info[NFRAMES + 1];
  int npcs, i;

  /* backtrace() may call dl_iterate_phdr which is also used by   */
  /* GC_register_dynamic_libraries(), and dl_iterate_phdr is not  */
  /* guaranteed to be reentrant.                                  */
  GC_ASSERT(I_HOLD_LOCK());

  GC_STATIC_ASSERT(sizeof(struct callinfo) == sizeof(void *));
#      ifdef REDIRECT_MALLOC
  if (GC_in_save_callers) {
    info[0].ci_pc = CAST_THRU_UINTPTR(GC_return_addr_t, GC_save_callers);
    BZERO(&info[1], sizeof(void *) * (NFRAMES - 1));
    return;
  }
  GC_in_save_callers = TRUE;
  /* backtrace() might call a redirected malloc. */
  UNLOCK();
  npcs = backtrace((void **)tmp_info, NFRAMES + 1);
  LOCK();
#      else
  npcs = backtrace((void **)tmp_info, NFRAMES + 1);
#      endif
  /* We retrieve NFRAMES+1 pc values, but discard the first one,  */
  /* since it points to our own frame.                            */
  i = 0;
  if (npcs > 1) {
    i = npcs - 1;
    BCOPY(&tmp_info[1], info, (unsigned)i * sizeof(void *));
  }
  BZERO(&info[i], sizeof(void *) * (unsigned)(NFRAMES - i));
#      ifdef REDIRECT_MALLOC
  GC_in_save_callers = FALSE;
#      endif
}

#    elif defined(I386) || defined(SPARC)

#      if defined(ANY_BSD) && defined(SPARC)
#        define FR_SAVFP fr_fp
#        define FR_SAVPC fr_pc
#      else
#        define FR_SAVFP fr_savfp
#        define FR_SAVPC fr_savpc
#      endif

#      if defined(SPARC) && (defined(__arch64__) || defined(__sparcv9))
#        define BIAS 2047
#      else
#        define BIAS 0
#      endif

GC_INNER void
GC_save_callers(struct callinfo info[NFRAMES])
{
  struct frame *frame;
  struct frame *fp;
  int nframes = 0;
#      ifdef I386
  /* We assume this is turned on only with gcc as the compiler. */
  asm("movl %%ebp,%0" : "=r"(frame));
  fp = frame;
#      else /* SPARC */
  frame = (struct frame *)GC_save_regs_in_stack();
  fp = (struct frame *)((ptr_t)frame->FR_SAVFP + BIAS);
#      endif

  for (; !HOTTER_THAN((ptr_t)fp, (ptr_t)frame)
#      ifndef THREADS
         && !HOTTER_THAN(GC_stackbottom, (ptr_t)fp)
#      elif defined(STACK_GROWS_UP)
         && fp != NULL
#      endif
         && nframes < NFRAMES;
       fp = (struct frame *)((ptr_t)fp->FR_SAVFP + BIAS), nframes++) {
#      if NARGS > 0
    int i;
#      endif

    info[nframes].ci_pc = (GC_return_addr_t)fp->FR_SAVPC;
#      if NARGS > 0
    for (i = 0; i < NARGS; i++) {
      info[nframes].ci_arg[i] = GC_HIDE_NZ_POINTER(MAKE_CPTR(fp->fr_arg[i]));
    }
#      endif
  }
  if (nframes < NFRAMES)
    info[nframes].ci_pc = 0;
}

#    endif /* !GC_HAVE_BUILTIN_BACKTRACE */

#  endif /* SAVE_CALL_CHAIN */

/* Print info to stderr.  We do not hold the allocator lock.  */
GC_INNER void
GC_print_callers(struct callinfo info[NFRAMES])
{
  int i, reent_cnt;
#  if defined(AO_HAVE_fetch_and_add1) && defined(AO_HAVE_fetch_and_sub1)
  static volatile AO_t reentry_count = 0;

  /* Note: alternatively, if available, we may use a thread-local   */
  /* storage, thus, enabling concurrent usage of GC_print_callers;  */
  /* but practically this has little sense because printing is done */
  /* into a single output stream.                                   */
  GC_ASSERT(I_DONT_HOLD_LOCK());
  reent_cnt = (int)(GC_signed_word)AO_fetch_and_add1(&reentry_count);
#  else
  static int reentry_count = 0;

  /* Note: this could use a different lock. */
  LOCK();
  reent_cnt = reentry_count++;
  UNLOCK();
#  endif
#  if NFRAMES == 1
  GC_err_printf("\tCaller at allocation:\n");
#  else
  GC_err_printf("\tCall chain at allocation:\n");
#  endif
  for (i = 0; i < NFRAMES; i++) {
#  if defined(LINUX) && !defined(SMALL_CONFIG)
    GC_bool stop = FALSE;
#  endif

    if (0 == info[i].ci_pc)
      break;
#  if NARGS > 0
    {
      int j;

      GC_err_printf("\t\targs: ");
      for (j = 0; j < NARGS; j++) {
        void *p = GC_REVEAL_NZ_POINTER(info[i].ci_arg[j]);

        if (j != 0)
          GC_err_printf(", ");
        GC_err_printf("%ld (%p)", (long)(GC_signed_word)ADDR(p), p);
      }
      GC_err_printf("\n");
    }
#  endif
    if (reent_cnt > 0) {
      /* We were called either concurrently or during an allocation */
      /* by backtrace_symbols() called from GC_print_callers; punt. */
      GC_err_printf("\t\t##PC##= 0x%lx\n", (unsigned long)ADDR(info[i].ci_pc));
      continue;
    }

    {
      char buf[40];
      char *name;
#  if defined(GC_HAVE_BUILTIN_BACKTRACE) \
      && !defined(GC_BACKTRACE_SYMBOLS_BROKEN) && defined(FUNCPTR_IS_DATAPTR)
      char **sym_name = backtrace_symbols((void **)&info[i].ci_pc, 1);
      if (sym_name != NULL) {
        name = sym_name[0];
      } else
#  endif
      /* else */ {
        (void)snprintf(buf, sizeof(buf), "##PC##= 0x%lx",
                       (unsigned long)ADDR(info[i].ci_pc));
        buf[sizeof(buf) - 1] = '\0';
        name = buf;
      }
#  if defined(LINUX) && !defined(SMALL_CONFIG)
      /* Try for a line number. */
      do {
        FILE *pipe;
#    define EXE_SZ 100
        static char exe_name[EXE_SZ];
#    define CMD_SZ 200
        char cmd_buf[CMD_SZ];
#    define RESULT_SZ 200
        static char result_buf[RESULT_SZ];
        size_t result_len;
        const char *old_preload;
#    define PRELOAD_SZ 200
        char preload_buf[PRELOAD_SZ];
        static GC_bool found_exe_name = FALSE;
        static GC_bool will_fail = FALSE;

        /* Try to get it via a hairy and expensive scheme.      */
        /* First we get the name of the executable:             */
        if (will_fail)
          break;
        if (!found_exe_name) {
          int ret_code = readlink("/proc/self/exe", exe_name, EXE_SZ);

          if (ret_code < 0 || ret_code >= EXE_SZ || exe_name[0] != '/') {
            will_fail = TRUE; /* Don't try again. */
            break;
          }
          exe_name[ret_code] = '\0';
          found_exe_name = TRUE;
        }
        /* Then we use popen to start addr2line -e <exe> <addr> */
        /* There are faster ways to do this, but hopefully this */
        /* isn't time critical.                                 */
        (void)snprintf(cmd_buf, sizeof(cmd_buf),
                       "/usr/bin/addr2line -f -e %s 0x%lx", exe_name,
                       (unsigned long)ADDR(info[i].ci_pc));
        cmd_buf[sizeof(cmd_buf) - 1] = '\0';
        old_preload = GETENV("LD_PRELOAD");
        if (old_preload != NULL) {
          size_t old_len = strlen(old_preload);
          if (old_len >= PRELOAD_SZ) {
            will_fail = TRUE;
            break;
          }
          BCOPY(old_preload, preload_buf, old_len + 1);
          unsetenv("LD_PRELOAD");
        }
        pipe = popen(cmd_buf, "r");
        if (old_preload != NULL
            && setenv("LD_PRELOAD", preload_buf, 0 /* overwrite */) == -1) {
          WARN("Failed to reset LD_PRELOAD\n", 0);
        }
        if (NULL == pipe) {
          will_fail = TRUE;
          break;
        }
        result_len = fread(result_buf, 1, RESULT_SZ - 1, pipe);
        (void)pclose(pipe);
        if (0 == result_len) {
          will_fail = TRUE;
          break;
        }
        if (result_buf[result_len - 1] == '\n')
          --result_len;
        result_buf[result_len] = 0;
        if (result_buf[0] == '?'
            || (result_buf[result_len - 2] == ':'
                && result_buf[result_len - 1] == '0'))
          break;
        /* Get rid of embedded newline, if any.  Test for "main". */
        {
          char *nl = strchr(result_buf, '\n');
          if (nl != NULL && ADDR_LT(nl, result_buf + result_len)) {
            *nl = ':';
          }
          if (strncmp(result_buf, "main",
                      nl != NULL
                          ? (size_t)(ADDR(nl) /* a cppcheck workaround */
                                     - COVERT_DATAFLOW(ADDR(result_buf)))
                          : result_len)
              == 0) {
            stop = TRUE;
          }
        }
        if (result_len < RESULT_SZ - 25) {
          /* Add address in the hex format.     */
          (void)snprintf(&result_buf[result_len],
                         sizeof(result_buf) - result_len, " [0x%lx]",
                         (unsigned long)ADDR(info[i].ci_pc));
          result_buf[sizeof(result_buf) - 1] = '\0';
        }
#    if defined(CPPCHECK)
        GC_noop1((unsigned char)name[0]);
        /* The value of name computed previously is discarded. */
#    endif
        name = result_buf;
      } while (0);
#  endif /* LINUX */
      GC_err_printf("\t\t%s\n", name);
#  if defined(GC_HAVE_BUILTIN_BACKTRACE) \
      && !defined(GC_BACKTRACE_SYMBOLS_BROKEN) && defined(FUNCPTR_IS_DATAPTR)
      if (sym_name != NULL) {
        /* May call GC_[debug_]free; that's OK.   */
        free(sym_name);
      }
#  endif
    }
#  if defined(LINUX) && !defined(SMALL_CONFIG)
    if (stop)
      break;
#  endif
  }
#  if defined(AO_HAVE_fetch_and_add1) && defined(AO_HAVE_fetch_and_sub1)
  (void)AO_fetch_and_sub1(&reentry_count);
#  else
  LOCK();
  --reentry_count;
  UNLOCK();
#  endif
}

#endif /* NEED_CALLINFO */

#if defined(LINUX) && defined(__ELF__) && !defined(SMALL_CONFIG)
/* Dump /proc/self/maps to GC_stderr, to enable looking up names for  */
/* addresses in FIND_LEAK output.                                     */
void
GC_print_address_map(void)
{
  const char *maps_ptr;

  GC_ASSERT(I_HOLD_LOCK());
  maps_ptr = GC_get_maps();
  GC_err_printf("---------- Begin address map ----------\n");
  GC_err_puts(maps_ptr);
  GC_err_printf("---------- End address map ----------\n");
}
#endif /* LINUX && ELF */