text: /*
   * 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.
   *
   * 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.
   */
  
  #ifdef SHENANGO_THREADS
  #include <runtime/runtime.h>
  #undef WARN
  #endif
  
  #include "private/gc_priv.h"
  
  #if !defined(OS2) && !defined(PCR) && !defined(AMIGA) && !defined(MACOS) \
      && !defined(MSWINCE) && !defined(SN_TARGET_ORBIS) \
      && !defined(SN_TARGET_PSP2) && !defined(__CC_ARM)
  # include <sys/types.h>
  # if !defined(MSWIN32) && !defined(MSWIN_XBOX1)
  #   include <unistd.h>
  # endif
  #endif
  
  #include <stdio.h>
  #if defined(MSWINCE) || defined(SN_TARGET_PS3)
  # define SIGSEGV 0 /* value is irrelevant */
  #else
  # include <signal.h>
  #endif
  
  #if defined(UNIX_LIKE) || defined(CYGWIN32) || defined(NACL) \
      || defined(SYMBIAN)
  # include <fcntl.h>
  #endif
  
  #if defined(LINUX) || defined(LINUX_STACKBOTTOM)
  # include <ctype.h>
  #endif
  
  /* Blatantly OS dependent routines, except for those that are related   */
  /* to dynamic loading.                                                  */
  
  #ifdef AMIGA
  # define GC_AMIGA_DEF
  # include "extra/AmigaOS.c"
  # undef GC_AMIGA_DEF
  #endif
  
  #if defined(MSWIN32) || defined(MSWINCE) || defined(CYGWIN32)
  # ifndef WIN32_LEAN_AND_MEAN
  #   define WIN32_LEAN_AND_MEAN 1
  # endif
  # define NOSERVICE
  # include <windows.h>
    /* It's not clear this is completely kosher under Cygwin.  But it     */
    /* allows us to get a working GC_get_stack_base.                      */
  #endif
  
  #ifdef MACOS
  # include <Processes.h>
  #endif
  
  #ifdef IRIX5
  # include <sys/uio.h>
  # include <malloc.h>   /* for locking */
  #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/types.h>
  # include <sys/mman.h>
  # include <sys/stat.h>
  # include <errno.h>
  #endif
  
  #ifdef DARWIN
    /* 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
  
  #ifdef PCR
  # include "il/PCR_IL.h"
  # include "th/PCR_ThCtl.h"
  # include "mm/PCR_MM.h"
  #endif
  
  #if defined(GC_DARWIN_THREADS) && defined(MPROTECT_VDB)
    /* Declare GC_mprotect_stop and GC_mprotect_resume as extern "C".     */
  # include "private/darwin_stop_world.h"
  #endif
  
  #if !defined(NO_EXECUTE_PERMISSION)
    STATIC GC_bool GC_pages_executable = TRUE;
  #else
    STATIC GC_bool GC_pages_executable = FALSE;
  #endif
  #define IGNORE_PAGES_EXECUTABLE 1
                          /* Undefined on GC_pages_executable real use.   */
  
  #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.                                                                */
  
  /* Repeatedly perform a read call until the buffer is filled or */
  /* we encounter EOF.                                            */
  STATIC ssize_t GC_repeat_read(int fd, char *buf, size_t count)
  {
  #   define READ read
      size_t num_read = 0;
  
      ASSERT_CANCEL_DISABLED();
      while (num_read < count) {
          ssize_t result = READ(fd, buf + num_read, count - num_read);
  
          if (result < 0) return result;
          if (result == 0) break;
          num_read += result;
      }
  #   undef READ
      return num_read;
  }
  
  #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.                              */
    STATIC size_t GC_get_file_len(int f)
    {
      size_t total = 0;
      ssize_t result;
  #   define GET_FILE_LEN_BUF_SZ 500
      char buf[GET_FILE_LEN_BUF_SZ];
  
      do {
          result = read(f, buf, GET_FILE_LEN_BUF_SZ);
          if (result == -1) return 0;
          total += result;
      } while (result > 0);
      return total;
    }
  
    STATIC size_t GC_get_maps_len(void)
    {
      int f = open("/proc/self/maps", O_RDONLY);
      size_t result;
      if (f < 0) return 0; /* treat missing file as empty */
      result = GC_get_file_len(f);
      close(f);
      return result;
    }
  #endif /* THREADS */
  
  /* Copy the contents of /proc/self/maps to a buffer in our address      */
  /* space.  Return the address of the buffer, or zero on failure.        */
  /* This code could be simplified if we could determine its size ahead   */
  /* of time.                                                             */
  GC_INNER 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/.../maps interface.                                */
      /* Since we expect the file can grow asynchronously in rare */
      /* cases, it should suffice to first determine              */
      /* the size (using lseek or 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.       */
          /* Note that lseek doesn't work, at least as of 2.6.15. */
          maps_size = GC_get_maps_len();
          if (0 == maps_size) return 0;
  #   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) {
                GC_scratch_recycle_no_gww(maps_buf, maps_buf_sz);
                /* 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);
  #             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) return 0;
  #             endif
                if (maps_buf == 0) return 0;
              }
              GC_ASSERT(maps_buf_sz >= maps_size + 1);
              f = open("/proc/self/maps", O_RDONLY);
              if (-1 == f) return 0;
  #           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)
                    break;
                  maps_size += result;
              } while ((size_t)result == maps_buf_sz-1);
              close(f);
              if (result <= 0)
                return 0;
  #           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_PRIdPTR " 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
   *  ^^^^^^^^ ^^^^^^^^ ^^^^          ^^
   *  start    end      prot          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 buf_ptr to (*start),      */
  /* (*end), (*prot), (*maj_dev) and (*mapping_name).  mapping_name may   */
  /* be NULL. (*prot) and (*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(REDIRECT_MALLOC)
    GC_INNER char *GC_parse_map_entry(char *buf_ptr, ptr_t *start, ptr_t *end,
                                      char **prot, unsigned int *maj_dev,
                                      char **mapping_name)
    {
      unsigned char *start_start, *end_start, *maj_dev_start;
      unsigned char *p;   /* unsigned for isspace, isxdigit */
  
      if (buf_ptr == NULL || *buf_ptr == '\0') {
          return NULL;
      }
  
      p = (unsigned char *)buf_ptr;
      while (isspace(*p)) ++p;
      start_start = p;
      GC_ASSERT(isxdigit(*start_start));
      *start = (ptr_t)strtoul((char *)start_start, (char **)&p, 16);
      GC_ASSERT(*p=='-');
  
      ++p;
      end_start = p;
      GC_ASSERT(isxdigit(*end_start));
      *end = (ptr_t)strtoul((char *)end_start, (char **)&p, 16);
      GC_ASSERT(isspace(*p));
  
      while (isspace(*p)) ++p;
      GC_ASSERT(*p == 'r' || *p == '-');
      *prot = (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));
      *maj_dev = strtoul((char *)maj_dev_start, NULL, 16);
  
      if (mapping_name == 0) {
        while (*p && *p++ != '\n');
      } else {
        while (*p && *p != '\n' && *p != '/' && *p != '[') p++;
        *mapping_name = (char *)p;
        while (*p && *p++ != '\n');
      }
      return (char *)p;
    }
  #endif /* REDIRECT_MALLOC || DYNAMIC_LOADING || IA64 || ... */
  
  #if defined(IA64) || defined(INCLUDE_LINUX_THREAD_DESCR)
    /* 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_mapping(ptr_t addr, ptr_t *startp,
                                          ptr_t *endp)
    {
      char *prot;
      ptr_t my_start, my_end;
      unsigned int maj_dev;
      char *maps = GC_get_maps();
      char *buf_ptr = maps;
  
      if (0 == maps) return(FALSE);
      for (;;) {
        buf_ptr = GC_parse_map_entry(buf_ptr, &my_start, &my_end,
                                     &prot, &maj_dev, 0);
  
        if (buf_ptr == NULL) return FALSE;
        if (prot[1] == 'w' && maj_dev == 0) {
            if ((word)my_end > (word)addr && (word)my_start <= (word)addr) {
              *startp = my_start;
              *endp = my_end;
              return TRUE;
            }
        }
      }
      return FALSE;
    }
  #endif /* IA64 || INCLUDE_LINUX_THREAD_DESCR */
  
  #if defined(REDIRECT_MALLOC)
    /* 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(char *nm, ptr_t *startp, ptr_t *endp)
    {
      size_t nm_len = strlen(nm);
      char *prot;
      char *map_path;
      ptr_t my_start, my_end;
      unsigned int maj_dev;
      char *maps = GC_get_maps();
      char *buf_ptr = maps;
  
      if (0 == maps) return(FALSE);
      for (;;) {
        buf_ptr = GC_parse_map_entry(buf_ptr, &my_start, &my_end,
                                     &prot, &maj_dev, &map_path);
  
        if (buf_ptr == NULL) return FALSE;
        if (prot[0] == 'r' && prot[1] == '-' && prot[2] == 'x') {
            char *p = map_path;
            /* Set p to point just past last slash, if any. */
              while (*p != '\0' && *p != '\n' && *p != ' ' && *p != '\t') ++p;
              while (*p != '/' && (word)p >= (word)map_path) --p;
              ++p;
            if (strncmp(nm, p, nm_len) == 0) {
              *startp = my_start;
              *endp = my_end;
              return TRUE;
            }
        }
      }
      return FALSE;
    }
  #endif /* REDIRECT_MALLOC */
  
  #ifdef IA64
    static ptr_t backing_store_base_from_proc(void)
    {
      ptr_t my_start, my_end;
      if (!GC_enclosing_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 I386 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
  # endif /* LINUX */
  
    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(IGNORE_PROG_DATA_START)
        /* Try the easy approaches first: */
        if (COVERT_DATAFLOW(__data_start) != 0) {
          GC_data_start = (ptr_t)(__data_start);
        } else {
          GC_data_start = (ptr_t)(data_start);
        }
        if (COVERT_DATAFLOW(GC_data_start) != 0) {
          if ((word)GC_data_start > (word)data_end)
            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;
      }
  
      GC_data_start = (ptr_t)GC_find_limit(data_end, FALSE);
    }
  #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 char *ecos_gc_brk = ecos_gc_memory;
  
    static void *tiny_sbrk(ptrdiff_t increment)
    {
      void *p = ecos_gc_brk;
      ecos_gc_brk += increment;
      if ((word)ecos_gc_brk > (word)(ecos_gc_memory + sizeof(ecos_gc_memory))) {
        ecos_gc_brk -= increment;
        return NULL;
      }
      return p;
    }
  # define sbrk tiny_sbrk
  #endif /* ECOS */
  
  #if defined(NETBSD) && defined(__ELF__)
    ptr_t GC_data_start = NULL;
  
    EXTERN_C_BEGIN
    extern char **environ;
    EXTERN_C_END
  
    GC_INNER void GC_init_netbsd_elf(void)
    {
          /* This may need to be environ, without the underscore, for     */
          /* some versions.                                               */
      GC_data_start = (ptr_t)GC_find_limit(&environ, FALSE);
    }
  #endif /* NETBSD */
  
  #if defined(ADDRESS_SANITIZER) && (defined(UNIX_LIKE) \
                      || defined(NEED_FIND_LIMIT) || defined(MPROTECT_VDB)) \
      && !defined(CUSTOM_ASAN_DEF_OPTIONS)
    /* 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;
  
  # ifdef THREADS
  #   include <sys/syscall.h>
      EXTERN_C_BEGIN
      extern sigset_t __syscall(quad_t, ...);
      EXTERN_C_END
  # endif
  
    /* Don't use GC_find_limit() because siglongjmp() outside of the      */
    /* signal handler by-passes our userland pthreads lib, leaving        */
    /* SIGSEGV and SIGPROF masked.  Instead, use this custom one that     */
    /* works-around the issues.                                           */
  
    STATIC void GC_fault_handler_openbsd(int sig GC_ATTR_UNUSED)
    {
       LONGJMP(GC_jmp_buf_openbsd, 1);
    }
  
    /* Return the first non-addressable location > p or bound.    */
    /* Requires the allocation lock.                              */
    STATIC ptr_t GC_find_limit_openbsd(ptr_t p, ptr_t bound)
    {
      static volatile ptr_t result;
               /* Safer if static, since otherwise it may not be  */
               /* preserved across the longjmp.  Can safely be    */
               /* static since it's only called with the          */
               /* allocation lock held.                           */
  
      struct sigaction act;
      word pgsz = (word)sysconf(_SC_PAGESIZE);
  
      GC_ASSERT((word)bound >= pgsz);
      GC_ASSERT(I_HOLD_LOCK());
  
      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);
  
      if (SETJMP(GC_jmp_buf_openbsd) == 0) {
        result = (ptr_t)((word)p & ~(pgsz-1));
        for (;;) {
          if ((word)result >= (word)bound - pgsz) {
            result = bound;
            break;
          }
          result += pgsz; /* no overflow expected */
          GC_noop1((word)(*result));
        }
      }
  
  #   ifdef THREADS
        /* Due to the siglongjump we need to manually unmask SIGPROF.     */
        __syscall(SYS_sigprocmask, SIG_UNBLOCK, sigmask(SIGPROF));
  #   endif
  
      sigaction(SIGSEGV, &old_segv_act, 0);
      return(result);
    }
  
    /* Return first addressable location > p or bound.    */
    /* Requires the allocation lock.                      */
    STATIC ptr_t GC_skip_hole_openbsd(ptr_t p, ptr_t bound)
    {
      static volatile ptr_t result;
      static volatile int firstpass;
  
      struct sigaction act;
      word pgsz = (word)sysconf(_SC_PAGESIZE);
  
      GC_ASSERT((word)bound >= pgsz);
      GC_ASSERT(I_HOLD_LOCK());
  
      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_t)((word)p & ~(pgsz-1));
      if (SETJMP(GC_jmp_buf_openbsd) != 0 || firstpass) {
        firstpass = 0;
        if ((word)result >= (word)bound - pgsz) {
          result = bound;
        } else {
          result += pgsz; /* no overflow expected */
          GC_noop1((word)(*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 <newexe.h>
  # include <exe386.h>
  
  # endif  /* __IBMC__ */
  
  # define INCL_DOSEXCEPTIONS
  # define INCL_DOSPROCESS
  # define INCL_DOSERRORS
  # define INCL_DOSMODULEMGR
  # define INCL_DOSMEMMGR
  # include <os2.h>
  
  # endif /* OS/2 */
  
  /* Find the page size */
  GC_INNER size_t GC_page_size = 0;
  
  #if defined(MSWIN32) || defined(MSWINCE) || defined(CYGWIN32)
  # 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;
  
    GC_INNER void GC_setpagesize(void)
    {
      GetSystemInfo(&GC_sysinfo);
  #   if defined(CYGWIN32) && defined(USE_MUNMAP)
        /* Allocations made with mmap() are aligned to the allocation     */
        /* granularity, which (at least on 64-bit Windows OS) is not the  */
        /* same as the page size.  Probably a separate variable could     */
        /* be added to 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;
        GC_ASSERT(GC_page_size >= (size_t)GC_sysinfo.dwPageSize);
  #   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
    }
  
  # 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 & ~(PAGE_GUARD | PAGE_NOCACHE));
        if (!is_writable(protect)) {
          return(0);
        }
        if (buf.State != MEM_COMMIT) return(0);
        return(buf.RegionSize);
      }
  
      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_t)((word)GC_approx_sp() & ~(GC_page_size - 1));
        /* 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
  
  #else /* !MSWIN32 */
    GC_INNER void GC_setpagesize(void)
    {
  #   if defined(MPROTECT_VDB) || defined(PROC_VDB) || defined(USE_MMAP)
        GC_page_size = (size_t)GETPAGESIZE();
  #     if !defined(CPPCHECK)
          if (0 == GC_page_size)
            ABORT("getpagesize failed");
  #     endif
  #   else
        /* It's acceptable to fake it.    */
        GC_page_size = HBLKSIZE;
  #   endif
    }
  #endif /* !MSWIN32 */
  
  #ifdef HAIKU
  # include <kernel/OS.h>
  
    GC_API int GC_CALL GC_get_stack_base(struct GC_stack_base *sb)
    {
      thread_info th;
      get_thread_info(find_thread(NULL),&th);
      sb->mem_base = th.stack_end;
      return GC_SUCCESS;
    }
  # define HAVE_GET_STACK_BASE
  #endif /* HAIKU */
  
  #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 AMIGA
  #   define GC_AMIGA_SB
  #   include "extra/AmigaOS.c"
  #   undef GC_AMIGA_SB
  #   define GET_MAIN_STACKBASE_SPECIAL
  # endif /* AMIGA */
  
  # if defined(NEED_FIND_LIMIT) || defined(UNIX_LIKE)
  
      typedef void (*GC_fault_handler_t)(int);
  
  #   if defined(SUNOS5SIGS) || defined(IRIX5) || defined(OSF1) \
         || defined(HAIKU) || defined(HURD) || defined(FREEBSD) \
         || defined(NETBSD)
          static struct sigaction old_segv_act;
  #       if defined(_sigargs) /* !Irix6.x */ \
             || defined(HURD) || defined(NETBSD) || defined(FREEBSD)
              static struct sigaction old_bus_act;
  #       endif
  #   else
        static GC_fault_handler_t old_segv_handler;
  #     ifdef HAVE_SIGBUS
          static GC_fault_handler_t old_bus_handler;
  #     endif
  #   endif
  
      GC_INNER void GC_set_and_save_fault_handler(GC_fault_handler_t h)
      {
  #       if defined(SUNOS5SIGS) || defined(IRIX5) || defined(OSF1) \
             || defined(HAIKU) || defined(HURD) || defined(FREEBSD) \
             || defined(NETBSD)
            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. */
  #         ifdef GC_IRIX_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);
  #           if defined(IRIX5) && defined(_sigargs) /* Irix 5.x, not 6.x */ \
                 || defined(HURD) || defined(NETBSD) || defined(FREEBSD)
                /* Under Irix 5.x or HP/UX, we may get SIGBUS.    */
                /* 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 /* !GC_IRIX_THREADS */
  #       else
            old_segv_handler = signal(SIGSEGV, h);
  #         ifdef HAVE_SIGBUS
              old_bus_handler = signal(SIGBUS, h);
  #         endif
  #       endif
  #       if defined(CPPCHECK) && defined(ADDRESS_SANITIZER)
            GC_noop1((word)&__asan_default_options);
  #       endif
      }
  # endif /* NEED_FIND_LIMIT || UNIX_LIKE */
  
  # if defined(NEED_FIND_LIMIT) \
       || (defined(USE_PROC_FOR_LIBRARIES) && defined(THREADS))
    /* Some tools to implement HEURISTIC2 */
  #   define MIN_PAGE_SIZE 256    /* Smallest conceivable page size, bytes */
  
      GC_INNER JMP_BUF GC_jmp_buf;
  
      STATIC void GC_fault_handler(int sig GC_ATTR_UNUSED)
      {
          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)
      {
  #       if defined(SUNOS5SIGS) || defined(IRIX5) || defined(OSF1) \
             || defined(HAIKU) || defined(HURD) || defined(FREEBSD) \
             || defined(NETBSD)
            (void) sigaction(SIGSEGV, &old_segv_act, 0);
  #         if defined(IRIX5) && defined(_sigargs) /* Irix 5.x, not 6.x */ \
               || defined(HURD) || defined(NETBSD)
                (void) sigaction(SIGBUS, &old_bus_act, 0);
  #         endif
  #       else
            (void) signal(SIGSEGV, old_segv_handler);
  #         ifdef HAVE_SIGBUS
              (void) signal(SIGBUS, old_bus_handler);
  #         endif
  #       endif
      }
  
      /* Return the first non-addressable location > p (up) or    */
      /* the smallest location q s.t. [q,p) is addressable (!up). */
      /* We assume that p (up) or p-1 (!up) is addressable.       */
      /* Requires allocation lock.                                */
      STATIC ptr_t GC_find_limit_with_bound(ptr_t p, GC_bool up, ptr_t bound)
      {
          static volatile ptr_t result;
                  /* Safer if static, since otherwise it may not be       */
                  /* preserved across the longjmp.  Can safely be         */
                  /* static since it's only called with the               */
                  /* allocation lock held.                                */
  
          GC_ASSERT(up ? (word)bound >= MIN_PAGE_SIZE
                       : (word)bound <= ~(word)MIN_PAGE_SIZE);
          GC_ASSERT(I_HOLD_LOCK());
          GC_setup_temporary_fault_handler();
          if (SETJMP(GC_jmp_buf) == 0) {
              result = (ptr_t)(((word)(p))
                                & ~(MIN_PAGE_SIZE-1));
              for (;;) {
                  if (up) {
                      if ((word)result >= (word)bound - MIN_PAGE_SIZE) {
                        result = bound;
                        break;
                      }
                      result += MIN_PAGE_SIZE; /* no overflow expected */
                  } else {
                      if ((word)result <= (word)bound + MIN_PAGE_SIZE) {
                        result = bound - MIN_PAGE_SIZE;
                                          /* This is to compensate        */
                                          /* further result increment (we */
                                          /* do not modify "up" variable  */
                                          /* since it might be clobbered  */
                                          /* by setjmp otherwise).        */
                        break;
                      }
                      result -= MIN_PAGE_SIZE; /* no underflow expected */
                  }
                  GC_noop1((word)(*result));
              }
          }
          GC_reset_fault_handler();
          if (!up) {
              result += MIN_PAGE_SIZE;
          }
          return(result);
      }
  
      void * GC_find_limit(void * p, int up)
      {
          return GC_find_limit_with_bound((ptr_t)p, (GC_bool)up,
                                          up ? (ptr_t)GC_WORD_MAX : 0);
      }
  # endif /* NEED_FIND_LIMIT || USE_PROC_FOR_LIBRARIES */
  
  #ifdef HPUX_STACKBOTTOM
  
  #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 stackbottom */
      return (ptr_t)(((word)GC_stackbottom - BACKING_STORE_DISPLACEMENT - 1)
                     & ~(BACKING_STORE_ALIGNMENT - 1));
    }
  
  #endif /* HPUX_STACK_BOTTOM */
  
  #ifdef LINUX_STACKBOTTOM
  
  # include <sys/types.h>
  # include <sys/stat.h>
  
  # define STAT_SKIP 27   /* Number of fields preceding startstack        */
                          /* field in /proc/self/stat                     */
  
  # ifdef USE_LIBC_PRIVATES
      EXTERN_C_BEGIN
  #   pragma weak __libc_stack_end
      extern ptr_t __libc_stack_end;
  #   ifdef IA64
  #     pragma weak __libc_ia64_register_backing_store_base
        extern ptr_t __libc_ia64_register_backing_store_base;
  #   endif
      EXTERN_C_END
  # endif
  
  # ifdef IA64
      GC_INNER ptr_t GC_get_register_stack_base(void)
      {
        ptr_t result;
  
  #     ifdef USE_LIBC_PRIVATES
          if (0 != &__libc_ia64_register_backing_store_base
              && 0 != __libc_ia64_register_backing_store_base) {
            /* 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) {
            result = (ptr_t)GC_find_limit(GC_save_regs_in_stack(), FALSE);
            /* Now seems to work better than constant displacement        */
            /* heuristic used in 6.X versions.  The latter seems to       */
            /* fail for 2.6 kernels.                                      */
        }
        return result;
      }
  # endif /* IA64 */
  
    STATIC ptr_t GC_linux_main_stack_base(void)
    {
      /* We read the stack base 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.                              */
  #   ifndef STAT_READ
        /* Also defined in pthread_support.c. */
  #     define STAT_BUF_SIZE 4096
  #     define STAT_READ read
  #   endif
            /* Should probably call the real read, if read is wrapped.    */
      char stat_buf[STAT_BUF_SIZE];
      int f;
      word result;
      int 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
        if (0 != &__libc_stack_end && 0 != __libc_stack_end ) {
  #       if defined(IA64)
            /* Some versions of glibc set the address 16 bytes too        */
            /* low while the initialization code is running.              */
            if (((word)__libc_stack_end & 0xfff) + 0x10 < 0x1000) {
              return __libc_stack_end + 0x10;
            } /* Otherwise it's not safe to add 16 bytes and we fall      */
              /* back 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 (__libc_stack_end != (ptr_t) (unsigned long)0x1)
              return __libc_stack_end;
  #       else
            return __libc_stack_end;
  #       endif
        }
  #   endif
      f = open("/proc/self/stat", O_RDONLY);
      if (f < 0)
        ABORT("Couldn't read /proc/self/stat");
      len = STAT_READ(f, stat_buf, STAT_BUF_SIZE);
      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';
  
      result = (word)STRTOULL(&stat_buf[buf_offset], NULL, 10);
      if (result < 0x100000 || (result & (sizeof(word) - 1)) != 0)
        ABORT("Absurd stack bottom value");
      return (ptr_t)result;
    }
  #endif /* LINUX_STACKBOTTOM */
  
  #ifdef FREEBSD_STACKBOTTOM
    /* This uses an undocumented sysctl call, but at least one expert     */
    /* believes it will stay.                                             */
  
  # include <unistd.h>
  # include <sys/types.h>
  # include <sys/sysctl.h>
  
    STATIC ptr_t GC_freebsd_main_stack_base(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) ABORT("Error getting main stack base");
      return base;
    }
  #endif /* FREEBSD_STACKBOTTOM */
  
  #if defined(ECOS) || defined(NOSYS)
    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
  
    ptr_t GC_get_main_stack_base(void)
    {
      return (ptr_t)GC_get_main_symbian_stack_base();
    }
  # define GET_MAIN_STACKBASE_SPECIAL
  #elif !defined(AMIGA) && !defined(HAIKU) && !defined(OS2) \
        && !defined(MSWIN32) && !defined(MSWINCE) && !defined(CYGWIN32) \
        && !defined(GC_OPENBSD_THREADS) \
        && (!defined(GC_SOLARIS_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
  
    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);
  #         ifdef STACK_GROWS_DOWN
              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
  #     define STACKBOTTOM_ALIGNMENT_M1 ((word)STACK_GRAN - 1)
  #     ifdef HEURISTIC1
  #       ifdef STACK_GROWS_DOWN
            result = (ptr_t)(((word)GC_approx_sp() + STACKBOTTOM_ALIGNMENT_M1)
                             & ~STACKBOTTOM_ALIGNMENT_M1);
  #       else
            result = (ptr_t)((word)GC_approx_sp() & ~STACKBOTTOM_ALIGNMENT_M1);
  #       endif
  #     elif defined(LINUX_STACKBOTTOM)
           result = GC_linux_main_stack_base();
  #     elif defined(FREEBSD_STACKBOTTOM)
           result = GC_freebsd_main_stack_base();
  #     elif defined(HEURISTIC2)
          {
            ptr_t sp = GC_approx_sp();
  #         ifdef STACK_GROWS_DOWN
              result = (ptr_t)GC_find_limit(sp, TRUE);
  #           if defined(HEURISTIC2_LIMIT) && !defined(CPPCHECK)
                if ((word)result > (word)HEURISTIC2_LIMIT
                    && (word)sp < (word)HEURISTIC2_LIMIT) {
                  result = HEURISTIC2_LIMIT;
                }
  #           endif
  #         else
              result = (ptr_t)GC_find_limit(sp, FALSE);
  #           if defined(HEURISTIC2_LIMIT) && !defined(CPPCHECK)
                if ((word)result < (word)HEURISTIC2_LIMIT
                    && (word)sp > (word)HEURISTIC2_LIMIT) {
                  result = HEURISTIC2_LIMIT;
                }
  #           endif
  #         endif
          }
  #     elif defined(STACK_NOT_SCANNED) || defined(CPPCHECK)
          result = NULL;
  #     else
  #       error None of HEURISTIC* and *STACKBOTTOM defined!
  #     endif
  #     if defined(STACK_GROWS_DOWN) && !defined(CPPCHECK)
          if (result == 0)
            result = (ptr_t)(signed_word)(-sizeof(ptr_t));
  #     endif
  #   endif
      GC_ASSERT((word)GC_approx_sp() HOTTER_THAN (word)result);
      return(result);
    }
  # define GET_MAIN_STACKBASE_SPECIAL
  #endif /* !AMIGA, !HAIKU, !OPENBSD, !OS2, !Windows */
  
  #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 IA64
        DCL_LOCK_STATE;
  #   endif
  
  #   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);
  #   ifdef STACK_GROWS_DOWN
          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 (0 == 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();
  #   endif
      return GC_SUCCESS;
    }
  # define HAVE_GET_STACK_BASE
  #endif /* THREADS && (HAVE_PTHREAD_ATTR_GET_NP || HAVE_PTHREAD_GETATTR_NP) */
  
  #if defined(GC_DARWIN_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((word)GC_approx_sp() HOTTER_THAN (word)b->mem_base);
      return GC_SUCCESS;
    }
  # define HAVE_GET_STACK_BASE
  #endif /* GC_DARWIN_THREADS */
  
  #ifdef GC_OPENBSD_THREADS
  # include <sys/signal.h>
  # include <pthread.h>
  # include <pthread_np.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 /* GC_OPENBSD_THREADS */
  
  #if defined(GC_SOLARIS_THREADS) && !defined(_STRICT_STDC)
  
  # include <thread.h>
  # include <signal.h>
  # include <pthread.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).                                    */
    static pthread_t stackbase_main_self = 0;
                          /* 0 means stackbase_main_ss_sp value is unset. */
    static void *stackbase_main_ss_sp = NULL;
  
    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((word)GC_approx_sp() HOTTER_THAN (word)s.ss_sp);
  
      if (!stackbase_main_self && thr_main() != 0)
        {
          /* Cache the stack base value 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 /* GC_SOLARIS_THREADS */
  
  #ifdef GC_RTEMS_PTHREADS
    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 /* GC_RTEMS_PTHREADS */
  
  #ifndef HAVE_GET_STACK_BASE
  # ifdef NEED_FIND_LIMIT
      /* Retrieve stack base.                                             */
      /* 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;)
        DCL_LOCK_STATE;
  
        LOCK();
        DISABLE_CANCEL(cancel_state);  /* May be unnecessary? */
  #     ifdef STACK_GROWS_DOWN
          b -> mem_base = GC_find_limit(GC_approx_sp(), TRUE);
  #       ifdef IA64
            b -> reg_base = GC_find_limit(GC_save_regs_in_stack(), FALSE);
  #       endif
  #     else
          b -> mem_base = GC_find_limit(GC_approx_sp(), FALSE);
  #     endif
        RESTORE_CANCEL(cancel_state);
        UNLOCK();
        return GC_SUCCESS;
      }
  # else
      GC_API int GC_CALL GC_get_stack_base(
                                  struct GC_stack_base *b GC_ATTR_UNUSED)
      {
  #     if defined(GET_MAIN_STACKBASE_SPECIAL) && !defined(THREADS) \
           && !defined(IA64)
          b->mem_base = GC_get_main_stack_base();
          return GC_SUCCESS;
  #     else
          return GC_UNIMPLEMENTED;
  #     endif
      }
  # endif /* !NEED_FIND_LIMIT */
  #endif /* !HAVE_GET_STACK_BASE */
  
  #ifndef GET_MAIN_STACKBASE_SPECIAL
    /* This is always called from the main thread.  Default implementation. */
    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((word)GC_approx_sp() HOTTER_THAN (word)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 (as we do with PCR).  Called with allocator lock held.          */
  # ifdef OS2
  
  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);
  }
  
  # else /* !OS2 */
  
  # 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 GetWriteWatch_type GetWriteWatch_func;
      static DWORD GetWriteWatch_alloc_flag;
  
  #   define GC_GWW_AVAILABLE() (GetWriteWatch_func != NULL)
  
      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 (str == NULL || (*str == '0' && *(str + 1) == '\0')) {
                /* GC_USE_GETWRITEWATCH is unset or set to "0".           */
                done = TRUE; /* falling back to MPROTECT_VDB strategy.    */
                /* 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".                       */
                done = TRUE; /* falling back to MPROTECT_VDB strategy.    */
                return;
              }
  #         endif
          }
  #     endif
  
  #     ifdef MSWINRT_FLAVOR
          {
            MEMORY_BASIC_INFORMATION memInfo;
            SIZE_T result = VirtualQuery(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 = (GetWriteWatch_type)GetProcAddress(hK32,
                                                  "GetWriteWatch")) != NULL) {
          /* 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.               */
          void * page = VirtualAlloc(NULL, GC_page_size,
                                      MEM_WRITE_WATCH | MEM_RESERVE,
                                      PAGE_READWRITE);
          if (page != NULL) {
            PVOID pages[16];
            GC_ULONG_PTR count = 16;
            DWORD page_size;
            /* Check that it actually works.  In spite of some            */
            /* documentation it actually seems to exist on W2K.           */
            /* This test may be unnecessary, but ...                      */
            if (GetWriteWatch_func(WRITE_WATCH_FLAG_RESET,
                                   page, GC_page_size,
                                   pages,
                                   &count,
                                   &page_size) != 0) {
              /* GetWriteWatch always fails. */
              GetWriteWatch_func = NULL;
            } else {
              GetWriteWatch_alloc_flag = MEM_WRITE_WATCH;
            }
            VirtualFree(page, 0 /* dwSize */, MEM_RELEASE);
          } else {
            /* GetWriteWatch will be useless. */
            GetWriteWatch_func = NULL;
          }
        }
  #     ifndef SMALL_CONFIG
          if (GetWriteWatch_func == NULL) {
            GC_COND_LOG_PRINTF("Did not find a usable GetWriteWatch()\n");
          } else {
            GC_COND_LOG_PRINTF("Using GetWriteWatch()\n");
          }
  #     endif
        done = TRUE;
      }
  
  # else
  #   define GetWriteWatch_alloc_flag 0
  # endif /* !GWW_VDB */
  
  # if defined(MSWIN32) || defined(MSWINCE) || defined(CYGWIN32)
  
  # 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 used to be set for gcc, to avoid dealing with           */
          /* the structured exception handling issues.  But we now have   */
          /* assembly code to do that right.                              */
  
    GC_INNER GC_bool GC_wnt = FALSE;
           /* This is a Windows NT derivative, i.e. NT, W2K, XP or later. */
  
    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 & 0x80000000);
        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 a such that VirtualQuery               */
    /* returns correct results for all addresses between a and start.     */
    /* Assumes VirtualQuery returns correct information for start.        */
    STATIC ptr_t GC_least_described_address(ptr_t start)
    {
      MEMORY_BASIC_INFORMATION buf;
      LPVOID limit;
      ptr_t p;
  
      limit = GC_sysinfo.lpMinimumApplicationAddress;
      p = (ptr_t)((word)start & ~(GC_page_size - 1));
      for (;;) {
          size_t result;
          LPVOID q = (LPVOID)(p - GC_page_size);
  
          if ((word)q > (word)p /* underflow */ || (word)q < (word)limit) break;
          result = VirtualQuery(q, &buf, sizeof(buf));
          if (result != sizeof(buf) || buf.AllocationBase == 0) break;
          p = (ptr_t)(buf.AllocationBase);
      }
      return p;
    }
  # endif /* MSWIN32 */
  
  # ifndef 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.                        */
  
    STATIC size_t GC_max_root_size = 100000; /* Appr. largest root size.  */
  
  # ifdef USE_WINALLOC
    /* 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(void *p)
    {
      struct GC_malloc_heap_list *q = GC_malloc_heap_l;
  
      while (0 != q) {
        if (q -> allocation_base == p) return TRUE;
        q = q -> next;
      }
      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;
      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 (0 == 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;
    }
  # endif /* USE_WINALLOC */
  
  # endif /* !REDIRECT_MALLOC */
  
    STATIC word GC_n_heap_bases = 0;      /* See GC_heap_bases.   */
  
    /* Is p the start of either the malloc heap, or of one of our */
    /* heap sections?                                             */
    GC_INNER GC_bool GC_is_heap_base(void *p)
    {
       unsigned i;
  #    ifndef REDIRECT_MALLOC
         if (GC_root_size > GC_max_root_size) GC_max_root_size = GC_root_size;
  #      ifdef USE_WINALLOC
           if (GC_is_malloc_heap_base(p)) return TRUE;
  #      endif
  #    endif
       for (i = 0; i < GC_n_heap_bases; i++) {
           if (GC_heap_bases[i] == p) return TRUE;
       }
       return FALSE;
    }
  
  #ifdef MSWIN32
    STATIC void GC_register_root_section(ptr_t static_root)
    {
        MEMORY_BASIC_INFORMATION buf;
        LPVOID p;
        char * base;
        char * limit;
  
        if (!GC_no_win32_dlls) return;
        p = base = limit = GC_least_described_address(static_root);
        while ((word)p < (word)GC_sysinfo.lpMaximumApplicationAddress) {
          size_t result = VirtualQuery(p, &buf, sizeof(buf));
          char * new_limit;
          DWORD protect;
  
          if (result != sizeof(buf) || buf.AllocationBase == 0
              || GC_is_heap_base(buf.AllocationBase)) break;
          new_limit = (char *)p + buf.RegionSize;
          protect = buf.Protect;
          if (buf.State == MEM_COMMIT
              && is_writable(protect)) {
              if ((char *)p == limit) {
                  limit = new_limit;
              } else {
                  if (base != limit) GC_add_roots_inner(base, limit, FALSE);
                  base = (char *)p;
                  limit = new_limit;
              }
          }
          if ((word)p > (word)new_limit /* overflow */) break;
          p = (LPVOID)new_limit;
        }
        if (base != limit) GC_add_roots_inner(base, limit, FALSE);
    }
  #endif /* MSWIN32 */
  
    void GC_register_data_segments(void)
    {
  #   ifdef MSWIN32
        GC_register_root_section((ptr_t)&GC_pages_executable);
                              /* any other GC global variable would fit too. */
  #   endif
    }
  
  # else /* !OS2 && !Windows */
  
  # if (defined(SVR4) || defined(AIX) || defined(DGUX) \
        || (defined(LINUX) && defined(SPARC))) && !defined(PCR)
    ptr_t GC_SysVGetDataStart(size_t max_page_size, ptr_t etext_addr)
    {
      word text_end = ((word)(etext_addr) + sizeof(word) - 1)
                      & ~(word)(sizeof(word) - 1);
          /* etext rounded to word boundary       */
      word next_page = ((text_end + (word)max_page_size - 1)
                        & ~((word)max_page_size - 1));
      word page_offset = (text_end & ((word)max_page_size - 1));
      volatile ptr_t result = (char *)(next_page + page_offset);
      /* Note that this isn't equivalent to just adding           */
      /* max_page_size to &etext if &etext is at a page boundary  */
  
      GC_setup_temporary_fault_handler();
      if (SETJMP(GC_jmp_buf) == 0) {
          /* 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;
  #         if defined(CPPCHECK)
              GC_noop1((word)&v);
  #         endif
            *result = v;
  #       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 place */
          /* 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.      */
          result = (char *)GC_find_limit(DATAEND, FALSE);
      }
      return (/* no volatile */ ptr_t)result;
    }
  # endif
  
  #ifdef DATASTART_USES_BSDGETDATASTART
  /* Its unclear whether this should be identical to the above, or        */
  /* whether it should apply to non-X86 architectures.                    */
  /* For now we don't assume that there is always an empty page after     */
  /* etext.  But in some cases there actually seems to be slightly more.  */
  /* This also deals with holes between read-only data and writable data. */
    GC_INNER ptr_t GC_FreeBSDGetDataStart(size_t max_page_size,
                                          ptr_t etext_addr)
    {
      word text_end = ((word)(etext_addr) + sizeof(word) - 1)
                       & ~(word)(sizeof(word) - 1);
          /* etext rounded to word boundary       */
      volatile word next_page = (text_end + (word)max_page_size - 1)
                                & ~((word)max_page_size - 1);
      volatile ptr_t result = (ptr_t)text_end;
      GC_setup_temporary_fault_handler();
      if (SETJMP(GC_jmp_buf) == 0) {
          /* Try reading at the address.                          */
          /* This should happen before there is another thread.   */
          for (; next_page < (word)DATAEND; next_page += (word)max_page_size)
              *(volatile char *)next_page;
          GC_reset_fault_handler();
      } else {
          GC_reset_fault_handler();
          /* As above, we go to plan B    */
          result = (ptr_t)GC_find_limit(DATAEND, FALSE);
      }
      return(result);
    }
  #endif /* DATASTART_USES_BSDGETDATASTART */
  
  #ifdef AMIGA
  
  #  define GC_AMIGA_DS
  #  include "extra/AmigaOS.c"
  #  undef GC_AMIGA_DS
  
  #elif defined(OPENBSD)
  
  /* Depending on arch alignment, there can be multiple holes     */
  /* between DATASTART and DATAEND.  Scan in DATASTART .. DATAEND */
  /* and register each region.                                    */
  void GC_register_data_segments(void)
  {
    ptr_t region_start = DATASTART;
  
    if ((word)region_start - 1U >= (word)DATAEND)
      ABORT_ARG2("Wrong DATASTART/END pair",
                 ": %p .. %p", (void *)region_start, (void *)DATAEND);
    for (;;) {
      ptr_t region_end = GC_find_limit_openbsd(region_start, DATAEND);
  
      GC_add_roots_inner(region_start, region_end, FALSE);
      if ((word)region_end >= (word)DATAEND)
        break;
      region_start = GC_skip_hole_openbsd(region_end, DATAEND);
    }
  }
  
  # else /* !OS2 && !Windows && !AMIGA && !OPENBSD */
  
  # if !defined(PCR) && !defined(MACOS) && defined(REDIRECT_MALLOC) \
       && defined(GC_SOLARIS_THREADS)
      EXTERN_C_BEGIN
      extern caddr_t sbrk(int);
      EXTERN_C_END
  # endif
  
    void GC_register_data_segments(void)
    {
  #   if !defined(PCR) && !defined(MACOS)
  #     if defined(REDIRECT_MALLOC) && defined(GC_SOLARIS_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 ((word)DATASTART < (word)p)
              GC_add_roots_inner(DATASTART, p, FALSE);
          }
  #     else
          if ((word)DATASTART - 1U >= (word)DATAEND) {
                                  /* Subtract one to check also for NULL  */
                                  /* without a compiler warning.          */
            ABORT_ARG2("Wrong DATASTART/END pair",
                       ": %p .. %p", (void *)DATASTART, (void *)DATAEND);
          }
          GC_add_roots_inner(DATASTART, DATAEND, FALSE);
  #       ifdef GC_HAVE_DATAREGION2
            if ((word)DATASTART2 - 1U >= (word)DATAEND2)
              ABORT_ARG2("Wrong DATASTART/END2 pair",
                         ": %p .. %p", (void *)DATASTART2, (void *)DATAEND2);
            GC_add_roots_inner(DATASTART2, DATAEND2, FALSE);
  #       endif
  #     endif
  #   endif
  #   if defined(MACOS)
      {
  #   if defined(THINK_C)
          extern void* GC_MacGetDataStart(void);
          /* globals begin above stack and end at a5. */
          GC_add_roots_inner((ptr_t)GC_MacGetDataStart(),
                             (ptr_t)LMGetCurrentA5(), FALSE);
  #   else
  #     if defined(__MWERKS__)
  #       if !__POWERPC__
            extern void* GC_MacGetDataStart(void);
            /* MATTHEW: Function to handle Far Globals (CW Pro 3) */
  #         if __option(far_data)
            extern void* GC_MacGetDataEnd(void);
  #         endif
            /* globals begin above stack and end at a5. */
            GC_add_roots_inner((ptr_t)GC_MacGetDataStart(),
                               (ptr_t)LMGetCurrentA5(), FALSE);
            /* MATTHEW: Handle Far Globals */
  #         if __option(far_data)
        /* Far globals follow he QD globals: */
            GC_add_roots_inner((ptr_t)LMGetCurrentA5(),
                               (ptr_t)GC_MacGetDataEnd(), FALSE);
  #         endif
  #       else
            extern char __data_start__[], __data_end__[];
            GC_add_roots_inner((ptr_t)&__data_start__,
                               (ptr_t)&__data_end__, FALSE);
  #       endif /* __POWERPC__ */
  #     endif /* __MWERKS__ */
  #   endif /* !THINK_C */
      }
  #   endif /* MACOS */
  
      /* Dynamic libraries are added at every collection, since they may  */
      /* change.                                                          */
    }
  
  # endif /* !AMIGA */
  # endif /* !MSWIN32 && !MSWINCE */
  # endif /* !OS2 */
  
  /*
   * Auxiliary routines for obtaining memory from OS.
   */
  
  # if !defined(OS2) && !defined(PCR) && !defined(AMIGA) \
       && !defined(USE_WINALLOC) && !defined(MACOS) && !defined(DOS4GW) \
       && !defined(NINTENDO_SWITCH) && !defined(NONSTOP) \
       && !defined(SN_TARGET_ORBIS) && !defined(SN_TARGET_PS3) \
       && !defined(SN_TARGET_PSP2) && !defined(RTEMS) && !defined(__CC_ARM)
  
  # define SBRK_ARG_T ptrdiff_t
  
  #if defined(MMAP_SUPPORTED)
  
  #ifdef USE_MMAP_FIXED
  #   define GC_MMAP_FLAGS MAP_FIXED | MAP_PRIVATE
          /* Seems to yield better performance on Solaris 2, but can      */
          /* be unreliable if something is already mapped at the address. */
  #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 ptr_t GC_unix_mmap_get_mem(size_t bytes)
    {
      void *result;
      static ptr_t 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
  
      if (bytes & (GC_page_size - 1)) ABORT("Bad GET_MEM arg");
      result = mmap(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)
          ABORT("Cannot allocate executable pages");
        return NULL;
      }
      last_addr = (ptr_t)(((word)result + bytes + GC_page_size - 1)
                          & ~(GC_page_size - 1));
  #   if !defined(LINUX)
        if (last_addr == 0) {
          /* Oops.  We got the end of the address space.  This isn't      */
          /* usable by arbitrary C code, since one-past-end pointers      */
          /* don't work, so we discard it and try again.                  */
          munmap(result, ~GC_page_size - (size_t)result + 1);
                          /* Leave last page mapped, so we can't repeat.  */
          return GC_unix_mmap_get_mem(bytes);
        }
  #   else
        GC_ASSERT(last_addr != 0);
  #   endif
      if (((word)result % HBLKSIZE) != 0)
        ABORT(
         "GC_unix_get_mem: Memory returned by mmap is not aligned to HBLKSIZE.");
      return((ptr_t)result);
    }
  # endif  /* !MSWIN_XBOX1 */
  
  #endif  /* MMAP_SUPPORTED */
  
  #if defined(USE_MMAP)
    ptr_t GC_unix_get_mem(size_t bytes)
    {
      return GC_unix_mmap_get_mem(bytes);
    }
  #else /* !USE_MMAP */
  
  STATIC ptr_t GC_unix_sbrk_get_mem(size_t bytes)
  {
    ptr_t 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 = (word)cur_brk & (GC_page_size-1);
  
      if ((SBRK_ARG_T)bytes < 0) {
          result = 0; /* too big */
          goto out;
      }
      if (lsbs != 0) {
          if((ptr_t)sbrk((SBRK_ARG_T)GC_page_size - lsbs) == (ptr_t)(-1)) {
              result = 0;
              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 /* ADD_HEAP_GUARD_PAGES */
      result = (ptr_t)sbrk((SBRK_ARG_T)bytes);
      if (result == (ptr_t)(-1)) result = 0;
    }
   out:
  # ifdef IRIX5
      __UNLOCK_MALLOC();
  # endif
    return(result);
  }
  
  ptr_t 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;
      ptr_t result = 0;
  
      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 (0 == result) {
          sbrk_failed = TRUE;
          result = GC_unix_mmap_get_mem(bytes);
      }
      if (0 == 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 /* UN*X */
  
  # ifdef OS2
  
  void * os2_alloc(size_t bytes)
  {
      void * result;
  
      if (DosAllocMem(&result, bytes, (PAG_READ | PAG_WRITE | PAG_COMMIT)
                                      | (GC_pages_executable ? PAG_EXECUTE : 0))
                      != NO_ERROR) {
          return(0);
      }
      /* FIXME: What's the purpose of this recursion?  (Probably, if      */
      /* DosAllocMem returns memory at 0 address then just retry once.)   */
      if (result == 0) return(os2_alloc(bytes));
      return(result);
  }
  
  # endif /* OS2 */
  
  #ifdef MSWIN_XBOX1
      ptr_t GC_durango_get_mem(size_t bytes)
      {
        if (0 == bytes) return NULL;
        return (ptr_t)VirtualAlloc(NULL, bytes, MEM_COMMIT | MEM_TOP_DOWN,
                                   PAGE_READWRITE);
      }
  #elif defined(MSWINCE)
    ptr_t GC_wince_get_mem(size_t bytes)
    {
      ptr_t result = 0; /* initialized to prevent warning. */
      word i;
  
      bytes = ROUNDUP_PAGESIZE(bytes);
  
      /* Try to find reserved, uncommitted pages */
      for (i = 0; i < GC_n_heap_bases; i++) {
          if (((word)(-(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 strictly > bytes, so that VirtualProtect */
          /* never spans regions.  It seems to be OK for a VirtualFree         */
          /* argument to span regions, so we should be OK for now.             */
          result = (ptr_t) VirtualAlloc(NULL, res_bytes,
                                  MEM_RESERVE | MEM_TOP_DOWN,
                                  GC_pages_executable ? PAGE_EXECUTE_READWRITE :
                                                        PAGE_READWRITE);
          if (HBLKDISPL(result) != 0) ABORT("Bad VirtualAlloc result");
              /* If I read the documentation correctly, this can  */
              /* only happen if HBLKSIZE > 64k or not a power of 2.       */
          if (GC_n_heap_bases >= MAX_HEAP_SECTS) ABORT("Too many heap sections");
          if (result == NULL) return NULL;
          GC_heap_bases[GC_n_heap_bases] = result;
          GC_heap_lengths[GC_n_heap_bases] = 0;
          GC_n_heap_bases++;
      }
  
      /* Commit pages */
      result = (ptr_t) VirtualAlloc(result, bytes, MEM_COMMIT,
                                GC_pages_executable ? PAGE_EXECUTE_READWRITE :
                                                      PAGE_READWRITE);
  #   undef IGNORE_PAGES_EXECUTABLE
  
      if (result != NULL) {
          if (HBLKDISPL(result) != 0) ABORT("Bad VirtualAlloc result");
          GC_heap_lengths[i] += bytes;
      }
  
      return(result);
    }
  
  #elif (defined(USE_WINALLOC) && !defined(MSWIN_XBOX1)) || defined(CYGWIN32)
  
  # 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)
      DWORD GC_mem_top_down = MEM_TOP_DOWN;
                             /* Use GC_USE_MEM_TOP_DOWN for better 64-bit */
                             /* testing.  Otherwise all addresses tend to */
                             /* end up in first 4GB, hiding bugs.         */
  # else
  #   define GC_mem_top_down 0
  # endif /* !GC_USE_MEM_TOP_DOWN */
  
    ptr_t GC_win32_get_mem(size_t bytes)
    {
      ptr_t 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 = (ptr_t)GlobalAlloc(0, SIZET_SAT_ADD(bytes, HBLKSIZE));
          /* Align it at HBLKSIZE boundary.       */
          result = (ptr_t)(((word)result + HBLKSIZE - 1)
                           & ~(word)(HBLKSIZE - 1));
        } 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 = (ptr_t) VirtualAlloc(NULL,
                              SIZET_SAT_ADD(bytes, VIRTUAL_ALLOC_PAD),
                              GetWriteWatch_alloc_flag
                                  | (MEM_COMMIT | MEM_RESERVE)
                                  | GC_mem_top_down,
                              GC_pages_executable ? PAGE_EXECUTE_READWRITE :
                                                    PAGE_READWRITE);
  #       undef IGNORE_PAGES_EXECUTABLE
      }
  # endif /* USE_WINALLOC */
      if (HBLKDISPL(result) != 0) ABORT("Bad VirtualAlloc result");
          /* If I read the documentation correctly, this can      */
          /* only happen if HBLKSIZE > 64k or not a power of 2.   */
      if (GC_n_heap_bases >= MAX_HEAP_SECTS) ABORT("Too many heap sections");
      if (0 != result) GC_heap_bases[GC_n_heap_bases++] = result;
      return(result);
    }
  
    GC_API void GC_CALL GC_win32_free_heap(void)
    {
  #   ifndef MSWINRT_FLAVOR
  #     ifndef CYGWIN32
          if (GLOBAL_ALLOC_TEST)
  #     endif
        {
          while (GC_n_heap_bases-- > 0) {
  #         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
  #   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 /* USE_WINALLOC || CYGWIN32 */
  
  #ifdef AMIGA
  # define GC_AMIGA_AM
  # include "extra/AmigaOS.c"
  # undef GC_AMIGA_AM
  #endif
  
  #if defined(HAIKU)
  # include <stdlib.h>
    ptr_t GC_haiku_get_mem(size_t bytes)
    {
      void* mem;
  
      GC_ASSERT(GC_page_size != 0);
      if (posix_memalign(&mem, GC_page_size, bytes) == 0)
        return mem;
      return NULL;
    }
  #endif /* HAIKU */
  
  #ifdef USE_MUNMAP
  
  /* For now, this only works on Win32/WinCE and some Unix-like   */
  /* systems.  If you have something else, don't define           */
  /* USE_MUNMAP.                                                  */
  
  #if !defined(NN_PLATFORM_CTR) && !defined(MSWIN32) && !defined(MSWINCE) \
      && !defined(MSWIN_XBOX1)
  # include <unistd.h>
  # ifdef SN_TARGET_PS3
  #   include <sys/memory.h>
  # else
  #   include <sys/mman.h>
  # endif
  # include <sys/stat.h>
  # include <sys/types.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 = (ptr_t)(((word)start + GC_page_size - 1)
                              & ~(GC_page_size - 1));
  
      if ((word)(result + GC_page_size) > (word)(start + bytes)) return 0;
      return result;
  }
  
  /* Compute end address for an unmap operation on the indicated  */
  /* block.                                                       */
  STATIC ptr_t GC_unmap_end(ptr_t start, size_t bytes)
  {
      return (ptr_t)((word)(start + bytes) & ~(GC_page_size - 1));
  }
  
  /* 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.     */
  
  /* 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.                          */
  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);
      word len = end_addr - start_addr;
  
      if (0 == start_addr) return;
  #   ifdef USE_WINALLOC
        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;
        }
  #   elif defined(SN_TARGET_PS3)
        ps3_free_mem(start_addr, len);
  #   else
        /* We immediately remap it to prevent an intervening mmap from    */
        /* accidentally grabbing the same address space.                  */
        {
  #       ifdef CYGWIN32
            /* Calling mmap() with the new protection flags on an         */
            /* existing memory map with MAP_FIXED is broken on Cygwin.    */
            /* However, calling mprotect() on the given address range     */
            /* with PROT_NONE seems to work fine.                         */
            if (mprotect(start_addr, len, PROT_NONE))
              ABORT("mprotect(PROT_NONE) failed");
  #       else
            void * result = mmap(start_addr, len, PROT_NONE,
                                 MAP_PRIVATE | MAP_FIXED | OPT_MAP_ANON,
                                 zero_fd, 0/* offset */);
  
            if (result != (void *)start_addr)
              ABORT("mmap(PROT_NONE) failed");
  #         if defined(CPPCHECK) || defined(LINT2)
              /* Explicitly store the resource handle to a global variable. */
              GC_noop1((word)result);
  #         endif
  #       endif /* !CYGWIN32 */
        }
        GC_unmapped_bytes += len;
  #   endif
  }
  
  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 = 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((word)result);
  #         endif
            GC_unmapped_bytes -= alloc_len;
            start_addr += alloc_len;
            len -= alloc_len;
        }
  #   else
        /* It was already remapped with PROT_NONE. */
        {
  #       if 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 (result != (void *)start_addr)
              ABORT("mmap as mprotect failed");
  #         if defined(CPPCHECK) || defined(LINT2)
              GC_noop1((word)result);
  #         endif
  #       else
            if (mprotect(start_addr, len, (PROT_READ | PROT_WRITE)
                              | (GC_pages_executable ? PROT_EXEC : 0)) != 0) {
              ABORT_ARG3("mprotect remapping failed",
                         " at %p (length %lu), errcode= %d",
                         (void *)start_addr, (unsigned long)len, errno);
            }
  #       endif /* !NACL */
        }
  #     undef IGNORE_PAGES_EXECUTABLE
        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;
      size_t len;
  
      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);
      if (0 == start_addr) return;
      len = end_addr - start_addr;
  #   ifdef USE_WINALLOC
        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) {
          /* Immediately remap as above. */
  #       ifdef CYGWIN32
            if (mprotect(start_addr, len, PROT_NONE))
              ABORT("mprotect(PROT_NONE) failed");
  #       else
            void * result = mmap(start_addr, len, PROT_NONE,
                                 MAP_PRIVATE | MAP_FIXED | OPT_MAP_ANON,
                                 zero_fd, 0/* offset */);
  
            if (result != (void *)start_addr)
              ABORT("mmap(PROT_NONE) failed");
  #         if defined(CPPCHECK) || defined(LINT2)
              GC_noop1((word)result);
  #         endif
  #       endif /* !CYGWIN32 */
          GC_unmapped_bytes += len;
        }
  #   endif
  }
  
  #endif /* USE_MUNMAP */
  
  /* Routine for pushing any additional roots.  In THREADS        */
  /* environment, this is also responsible for marking from       */
  /* thread stacks.                                               */
  #ifndef THREADS
    GC_push_other_roots_proc GC_push_other_roots = 0;
  #else /* THREADS */
  
  # ifdef PCR
  PCR_ERes GC_push_thread_stack(PCR_Th_T *t, PCR_Any dummy)
  {
      struct PCR_ThCtl_TInfoRep info;
      PCR_ERes result;
  
      info.ti_stkLow = info.ti_stkHi = 0;
      result = PCR_ThCtl_GetInfo(t, &info);
      GC_push_all_stack((ptr_t)(info.ti_stkLow), (ptr_t)(info.ti_stkHi));
      return(result);
  }
  
  /* Push the contents of an old object. We treat this as stack   */
  /* data only because that makes it robust against mark stack    */
  /* overflow.                                                    */
  PCR_ERes GC_push_old_obj(void *p, size_t size, PCR_Any data)
  {
      GC_push_all_stack((ptr_t)p, (ptr_t)p + size);
      return(PCR_ERes_okay);
  }
  
  extern struct PCR_MM_ProcsRep * GC_old_allocator;
                                          /* defined in pcr_interface.c.  */
  
  STATIC void GC_CALLBACK GC_default_push_other_roots(void)
  {
      /* Traverse data allocated by previous memory managers.             */
            if ((*(GC_old_allocator->mmp_enumerate))(PCR_Bool_false,
                                                     GC_push_old_obj, 0)
                != PCR_ERes_okay) {
                ABORT("Old object enumeration failed");
            }
      /* Traverse all thread stacks. */
          if (PCR_ERes_IsErr(
                  PCR_ThCtl_ApplyToAllOtherThreads(GC_push_thread_stack,0))
              || PCR_ERes_IsErr(GC_push_thread_stack(PCR_Th_CurrThread(), 0))) {
            ABORT("Thread stack marking failed");
          }
  }
  
  # endif /* PCR */
  
  # if defined(NN_PLATFORM_CTR) || defined(NINTENDO_SWITCH) \
       || defined(GC_PTHREADS) || defined(GC_WIN32_THREADS)
      STATIC void GC_CALLBACK GC_default_push_other_roots(void)
      {
        GC_push_all_stacks();
      }
  # endif
  
  # ifdef SN_TARGET_PS3
      STATIC void GC_CALLBACK GC_default_push_other_roots(void)
      {
        ABORT("GC_default_push_other_roots is not implemented");
      }
  
      void GC_push_thread_structures(void)
      {
        ABORT("GC_push_thread_structures is not implemented");
      }
  # endif /* SN_TARGET_PS3 */
  
    GC_push_other_roots_proc GC_push_other_roots = GC_default_push_other_roots;
  #endif /* THREADS */
  
  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;
  }
  
  /*
   * 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.
   * PCR_VDB:     Use PPCRs virtual dirty bit facility.
   * 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.
   * 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, page_hash_table pht2)
      {
        unsigned 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)
      {
        detect_GetWriteWatch();
        return GC_GWW_AVAILABLE();
      }
  
    GC_INLINE void GC_gww_read_dirty(GC_bool output_unneeded)
    {
      word i;
  
      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 behaviour will be if it fails.        */
          /* It does appear to fail, at least on recent W2K 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_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 struct hblk *last_warned = 0;
            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) {
              unsigned j;
  
              for (j = 0; j < nblocks; ++j) {
                word hash = PHT_HASH(start + j);
                set_pht_entry_from_index(GC_grungy_pages, hash);
              }
            }
            count = 1;  /* Done with this section. */
          } else /* succeeded */ if (!output_unneeded) {
            PVOID * pages_end = pages + count;
  
            while (pages != pages_end) {
              struct hblk * h = (struct hblk *) *pages++;
              struct hblk * h_end = (struct hblk *) ((char *) h + page_size);
              do {
                set_pht_entry_from_index(GC_grungy_pages, PHT_HASH(h));
              } while ((word)(++h) < (word)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
    }
  #else
  # define GC_GWW_AVAILABLE() FALSE
  #endif /* !GWW_VDB */
  
  #ifdef DEFAULT_VDB
    /* All of the following assume the allocation lock is held.   */
  
    /* 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 */
  
  #ifndef GC_DISABLE_INCREMENTAL
  # if !defined(THREADS) || defined(HAVE_LOCKFREE_AO_OR)
  #   define async_set_pht_entry_from_index(db, index) \
                          set_pht_entry_from_index_concurrent(db, index)
  # elif defined(AO_HAVE_test_and_set_acquire)
      /* 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.            */
      GC_INNER volatile AO_TS_t GC_fault_handler_lock = AO_TS_INITIALIZER;
  
      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
  #   error No test_and_set operation: Introduces a race.
  # endif /* THREADS && !AO_HAVE_test_and_set_acquire */
  #endif /* !GC_DISABLE_INCREMENTAL */
  
  #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 don't 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.  Another alternative is to wrap system calls
     * (see example for read below), but the current implementation holds
     * applications.
     * We assume the page size is a multiple of HBLKSIZE.
     * We prefer them to be the same.  We avoid protecting pointer-free
     * objects only if they are the same.
     */
  # ifdef DARWIN
      /* 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(addr,len) \
          if (vm_protect(GC_task_self, (vm_address_t)(addr), (vm_size_t)(len), \
                         FALSE, VM_PROT_READ \
                                | (GC_pages_executable ? VM_PROT_EXECUTE : 0)) \
                  == KERN_SUCCESS) {} else ABORT("vm_protect(PROTECT) failed")
  #   define UNPROTECT(addr,len) \
          if (vm_protect(GC_task_self, (vm_address_t)(addr), (vm_size_t)(len), \
                         FALSE, (VM_PROT_READ | VM_PROT_WRITE) \
                                | (GC_pages_executable ? VM_PROT_EXECUTE : 0)) \
                  == KERN_SUCCESS) {} else ABORT("vm_protect(UNPROTECT) failed")
  
  # elif !defined(USE_WINALLOC)
  #   include <sys/mman.h>
  #   include <signal.h>
  #   if !defined(CYGWIN32) && !defined(HAIKU)
  #     include <sys/syscall.h>
  #   endif
  
  #   define PROTECT(addr, len) \
          if (mprotect((caddr_t)(addr), (size_t)(len), \
                       PROT_READ \
                       | (GC_pages_executable ? PROT_EXEC : 0)) >= 0) { \
          } else ABORT("mprotect failed")
  #   define UNPROTECT(addr, len) \
          if (mprotect((caddr_t)(addr), (size_t)(len), \
                       (PROT_READ | PROT_WRITE) \
                       | (GC_pages_executable ? PROT_EXEC : 0)) >= 0) { \
          } else ABORT(GC_pages_executable ? \
                                  "un-mprotect executable page failed" \
                                      " (probably disabled by OS)" : \
                                  "un-mprotect failed")
  #   undef IGNORE_PAGES_EXECUTABLE
  
  # else /* USE_WINALLOC */
  #   ifndef MSWINCE
  #     include <signal.h>
  #   endif
  
      static DWORD protect_junk;
  #   define PROTECT(addr, len) \
          if (VirtualProtect((addr), (len), \
                             GC_pages_executable ? PAGE_EXECUTE_READ : \
                                                   PAGE_READONLY, \
                             &protect_junk)) { \
          } else ABORT_ARG1("VirtualProtect failed", \
                            ": errcode= 0x%X", (unsigned)GetLastError())
  #   define UNPROTECT(addr, len) \
          if (VirtualProtect((addr), (len), \
                             GC_pages_executable ? PAGE_EXECUTE_READWRITE : \
                                                   PAGE_READWRITE, \
                             &protect_junk)) { \
          } else ABORT("un-VirtualProtect failed")
  # endif /* USE_WINALLOC */
  
  # if defined(MSWIN32)
      typedef LPTOP_LEVEL_EXCEPTION_FILTER SIG_HNDLR_PTR;
  #   undef SIG_DFL
  #   define SIG_DFL (LPTOP_LEVEL_EXCEPTION_FILTER)((signed_word)-1)
  # elif defined(MSWINCE)
      typedef LONG (WINAPI *SIG_HNDLR_PTR)(struct _EXCEPTION_POINTERS *);
  #   undef SIG_DFL
  #   define SIG_DFL (SIG_HNDLR_PTR) (-1)
  # elif defined(DARWIN)
      typedef void (* SIG_HNDLR_PTR)();
  # else
      typedef void (* SIG_HNDLR_PTR)(int, siginfo_t *, void *);
      typedef void (* PLAIN_HNDLR_PTR)(int);
  # endif
  
  # if defined(__GLIBC__)
  #   if __GLIBC__ < 2 || __GLIBC__ == 2 && __GLIBC_MINOR__ < 2
  #       error glibc too old?
  #   endif
  # endif
  
  #ifndef DARWIN
    STATIC SIG_HNDLR_PTR GC_old_segv_handler = 0;
                          /* Also old MSWIN32 ACCESS_VIOLATION filter */
  # if !defined(MSWIN32) && !defined(MSWINCE)
      STATIC SIG_HNDLR_PTR GC_old_bus_handler = 0;
  #   if defined(FREEBSD) || defined(HURD) || defined(HPUX)
        STATIC GC_bool GC_old_bus_handler_used_si = FALSE;
  #   endif
      STATIC GC_bool GC_old_segv_handler_used_si = FALSE;
  # endif /* !MSWIN32 */
  #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(void *addr)
    {
  #   ifdef HASH_TL
        hdr *result;
        GET_HDR((ptr_t)addr, result);
        return result != NULL;
  #   else
        return HDR_INNER(addr) != NULL;
  #   endif
    }
  #else
  # define is_header_found_async(addr) (HDR(addr) != NULL)
  #endif /* !THREADS */
  
  #ifndef DARWIN
  
  # if !defined(MSWIN32) && !defined(MSWINCE)
  #   include <errno.h>
  #   if defined(FREEBSD) || defined(HURD) || defined(HPUX)
  #     define SIG_OK (sig == SIGBUS || sig == SIGSEGV)
  #   else
  #     define SIG_OK (sig == SIGSEGV)
                              /* Catch SIGSEGV but ignore SIGBUS. */
  #   endif
  #   if defined(FREEBSD)
  #     ifndef SEGV_ACCERR
  #       define SEGV_ACCERR 2
  #     endif
  #     if defined(AARCH64) || defined(ARM32) || defined(MIPS)
  #       define CODE_OK (si -> si_code == SEGV_ACCERR)
  #     elif defined(POWERPC)
  #       define AIM  /* Pretend that we're 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(CYGWIN32) || defined(HAIKU) || defined(HURD)
  #     define CODE_OK TRUE
  #   elif defined(LINUX)
  #     define CODE_OK TRUE
        /* Empirically c.trapno == 14, on IA32, but is that useful?       */
        /* Should probably consider alignment issues on other             */
        /* architectures.                                                 */
  #   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
  #   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 /* MSWIN32 || MSWINCE */
    {
  #   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 = (struct hblk *)((word)addr & ~(GC_page_size-1));
          GC_bool in_allocd_block;
          size_t i;
  
  #       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;
  
  #             if defined(FREEBSD) || defined(HURD) || defined(HPUX)
                  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 (old_handler == (SIG_HNDLR_PTR)(signed_word)SIG_DFL) {
  #               if !defined(MSWIN32) && !defined(MSWINCE)
                      ABORT_ARG1("Unexpected bus error or segmentation fault",
                                 " 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)(signed_word)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++) {
              word 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
  #endif /* !DARWIN */
  
  #ifdef USE_MUNMAP
    /* MPROTECT_VDB cannot deal with address space holes (for now),   */
    /* so if the collector is configured with both MPROTECT_VDB and   */
    /* USE_MUNMAP then, as a work around, select only one of them     */
    /* during GC_init or GC_enable_incremental.                       */
    GC_INNER GC_bool GC_dirty_init(void)
    {
      if (GC_unmap_threshold != 0) {
        if (GETENV("GC_UNMAP_THRESHOLD") != NULL
            || GETENV("GC_FORCE_UNMAP_ON_GCOLLECT") != NULL
            || GC_has_unmapped_memory()) {
          WARN("Can't maintain mprotect-based dirty bits"
               " in case of unmapping\n", 0);
          return FALSE;
        }
        GC_unmap_threshold = 0; /* in favor of incremental collection */
        WARN("Memory unmapping is disabled as incompatible"
             " with MPROTECT_VDB\n", 0);
      }
      return GC_mprotect_dirty_init();
    }
  #else
  # define GC_mprotect_dirty_init GC_dirty_init
  #endif /* !USE_MUNMAP */
  
  #if !defined(DARWIN)
    GC_INNER GC_bool GC_mprotect_dirty_init(void)
    {
      #ifdef SHENANGO_THREADS
      BUG();
      #else
  #   if !defined(MSWIN32) && !defined(MSWINCE)
        struct sigaction act, oldact;
        act.sa_flags = SA_RESTART | SA_SIGINFO;
        act.sa_sigaction = GC_write_fault_handler;
        (void)sigemptyset(&act.sa_mask);
  #     if defined(THREADS) && !defined(GC_OPENBSD_UTHREADS) \
           && !defined(GC_WIN32_THREADS) && !defined(NACL)
          /* 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");
      }
  #   if !defined(MSWIN32) && !defined(MSWINCE)
        /* act.sa_restorer is deprecated and should not be initialized. */
  #     if defined(GC_IRIX_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)(signed_word)oldact.sa_handler;
          GC_old_segv_handler_used_si = FALSE;
        }
        if (GC_old_segv_handler == (SIG_HNDLR_PTR)(signed_word)SIG_IGN) {
          WARN("Previously ignored segmentation violation!?\n", 0);
          GC_old_segv_handler = (SIG_HNDLR_PTR)(signed_word)SIG_DFL;
        }
        if (GC_old_segv_handler != (SIG_HNDLR_PTR)(signed_word)SIG_DFL) {
          GC_VERBOSE_LOG_PRINTF("Replaced other SIGSEGV handler\n");
        }
  #   if defined(HPUX) || defined(LINUX) || defined(HURD) \
         || (defined(FREEBSD) && (defined(__GLIBC__) || defined(SUNOS5SIGS)))
        sigaction(SIGBUS, &act, &oldact);
        if ((oldact.sa_flags & SA_SIGINFO) != 0) {
          GC_old_bus_handler = oldact.sa_sigaction;
  #       if !defined(LINUX)
            GC_old_bus_handler_used_si = TRUE;
  #       endif
        } else {
          GC_old_bus_handler = (SIG_HNDLR_PTR)(signed_word)oldact.sa_handler;
  #       if !defined(LINUX)
            GC_old_bus_handler_used_si = FALSE;
  #       endif
        }
        if (GC_old_bus_handler == (SIG_HNDLR_PTR)(signed_word)SIG_IGN) {
          WARN("Previously ignored bus error!?\n", 0);
  #       if !defined(LINUX)
            GC_old_bus_handler = (SIG_HNDLR_PTR)(signed_word)SIG_DFL;
  #       else
            /* GC_old_bus_handler is not used by GC_write_fault_handler.  */
  #       endif
        } else if (GC_old_bus_handler != (SIG_HNDLR_PTR)(signed_word)SIG_DFL) {
            GC_VERBOSE_LOG_PRINTF("Replaced other SIGBUS handler\n");
        }
  #   endif /* HPUX || LINUX || HURD || (FREEBSD && SUNOS5SIGS) */
  #   endif /* ! MS windows */
  #   if defined(GWW_VDB)
        if (GC_gww_dirty_init())
          return TRUE;
  #   endif
  #   if defined(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). */
  #   endif
  #   if defined(CPPCHECK) && defined(ADDRESS_SANITIZER)
        GC_noop1((word)&__asan_default_options);
  #   endif
      return TRUE;
      #endif
    }
  #endif /* !DARWIN */
  
  GC_API int GC_CALL GC_incremental_protection_needs(void)
  {
      GC_ASSERT(GC_is_initialized);
  
      if (GC_page_size == HBLKSIZE) {
          return GC_PROTECTS_POINTER_HEAP;
      } else {
          return GC_PROTECTS_POINTER_HEAP | GC_PROTECTS_PTRFREE_HEAP;
      }
  }
  #define HAVE_INCREMENTAL_PROTECTION_NEEDS
  
  #define IS_PTRFREE(hhdr) ((hhdr)->hb_descr == 0)
  #define PAGE_ALIGNED(x) !((word)(x) & (GC_page_size - 1))
  
  STATIC void GC_protect_heap(void)
  {
      unsigned i;
      GC_bool protect_all =
          (0 != (GC_incremental_protection_needs() & GC_PROTECTS_PTRFREE_HEAP));
  
      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;
  
          if (protect_all) {
            PROTECT(start, len);
          } else {
            struct hblk * current;
            struct hblk * current_start; /* Start of block to be protected. */
            struct hblk * limit;
  
            GC_ASSERT(PAGE_ALIGNED(len));
            GC_ASSERT(PAGE_ALIGNED(start));
            current_start = current = (struct hblk *)start;
            limit = (struct hblk *)(start + len);
            while ((word)current < (word)limit) {
              hdr * hhdr;
              word nhblks;
              GC_bool is_ptrfree;
  
              GC_ASSERT(PAGE_ALIGNED(current));
              GET_HDR(current, hhdr);
              if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
                /* This can happen only if we're 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(PAGE_ALIGNED(hhdr -> hb_sz));
                nhblks = divHBLKSZ(hhdr -> hb_sz);
                is_ptrfree = TRUE;        /* dirty on alloc */
              } else {
                nhblks = OBJ_SZ_TO_BLOCKS(hhdr -> hb_sz);
                is_ptrfree = IS_PTRFREE(hhdr);
              }
              if (is_ptrfree) {
                if ((word)current_start < (word)current) {
                  PROTECT(current_start, (ptr_t)current - (ptr_t)current_start);
                }
                current_start = (current += nhblks);
              } else {
                current += nhblks;
              }
            }
            if ((word)current_start < (word)current) {
              PROTECT(current_start, (ptr_t)current - (ptr_t)current_start);
            }
          }
      }
  }
  
  /*
   * Acquiring the allocation lock here is dangerous, since this
   * can be called from within GC_call_with_alloc_lock, and the cord
   * package does so.  On systems that allow nested lock acquisition, this
   * happens to work.
   */
  
  /* We no longer wrap read by default, since that was causing too many   */
  /* problems.  It is preferred that the client instead avoids writing    */
  /* to the write-protected heap with a system call.                      */
  #endif /* MPROTECT_VDB */
  
  #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/types.h>
  # include <sys/signal.h>
  # include <sys/syscall.h>
  # include <sys/stat.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 = 0;
  
  GC_INNER GC_bool GC_dirty_init(void)
  {
      char buf[40];
  
      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));
      }
  
      (void)snprintf(buf, sizeof(buf), "/proc/%ld/pagedata", (long)getpid());
      buf[sizeof(buf) - 1] = '\0';
      GC_proc_fd = open(buf, O_RDONLY);
      if (GC_proc_fd < 0) {
        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);
  
      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)
  {
  #   define READ read
      int nmaps;
      char * bufp = GC_proc_buf;
      int i;
  
      BZERO(GC_grungy_pages, sizeof(GC_grungy_pages));
      if (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: GC_proc_buf_size = %" WARN_PRIdPTR "\n",
               (signed_word)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 (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 = ((struct prpageheader *)bufp) -> pr_nmap;
  #   ifdef DEBUG_DIRTY_BITS
        GC_log_printf("Proc VDB read: pr_nmap= %u, pr_npage= %lu\n",
                      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 (; (word)vaddr < (word)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;
                       (word)h < (word)next_vaddr; h++) {
                      word index = PHT_HASH(h);
  
                      set_pht_entry_from_index(GC_grungy_pages, index);
                  }
              }
          }
          bufp = (char *)(((word)bufp + (sizeof(long)-1))
                          & ~(word)(sizeof(long)-1));
      }
  #   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);
  #   undef READ
  }
  
  #endif /* PROC_VDB */
  
  #ifdef PCR_VDB
  
  # include "vd/PCR_VD.h"
  
  # define NPAGES (32*1024)       /* 128 MB */
  
  PCR_VD_DB GC_grungy_bits[NPAGES];
  
  STATIC ptr_t GC_vd_base = NULL;
                          /* Address corresponding to GC_grungy_bits[0]   */
                          /* HBLKSIZE aligned.                            */
  
  GC_INNER GC_bool GC_dirty_init(void)
  {
      /* For the time being, we assume the heap generally grows up */
      GC_vd_base = GC_heap_sects[0].hs_start;
      if (GC_vd_base == 0) {
          ABORT("Bad initial heap segment");
      }
      if (PCR_VD_Start(HBLKSIZE, GC_vd_base, NPAGES*HBLKSIZE)
          != PCR_ERes_okay) {
          ABORT("Dirty bit initialization failed");
      }
      return TRUE;
  }
  #endif /* PCR_VDB */
  
  #ifndef GC_DISABLE_INCREMENTAL
    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)
    {
      word 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);
    }
  
    /* 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's happening (as in GC_enable_incremental).*/
    GC_INNER void GC_read_dirty(GC_bool output_unneeded)
    {
      if (GC_manual_vdb
  #       if defined(MPROTECT_VDB)
            || !GC_GWW_AVAILABLE()
  #       endif
          ) {
        if (!output_unneeded)
          BCOPY((/* no volatile */ void *)GC_dirty_pages, GC_grungy_pages,
                sizeof(GC_dirty_pages));
        BZERO((/* no volatile */ void *)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(PCR_VDB)
        /* lazily enable dirty bits on newly added heap sects */
        {
          static int onhs = 0;
          int nhs = GC_n_heap_sects;
          for (; onhs < nhs; onhs++) {
              PCR_VD_WriteProtectEnable(
                      GC_heap_sects[onhs].hs_start,
                      GC_heap_sects[onhs].hs_bytes);
          }
        }
        if (PCR_VD_Clear(GC_vd_base, NPAGES*HBLKSIZE, GC_grungy_bits)
            != PCR_ERes_okay) {
          ABORT("Dirty bit read failed");
        }
  #   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)
    {
  #   ifdef PCR_VDB
        if (!GC_manual_vdb) {
          if ((word)h < (word)GC_vd_base
              || (word)h >= (word)(GC_vd_base + NPAGES * HBLKSIZE)) {
            return TRUE;
          }
          return GC_grungy_bits[h-(struct hblk*)GC_vd_base] & PCR_VD_DB_dirtyBit;
        }
  #   elif defined(DEFAULT_VDB)
        if (!GC_manual_vdb)
          return TRUE;
  #   endif
      return NULL == HDR(h)
               || get_pht_entry_from_index(GC_grungy_pages, PHT_HASH(h));
    }
  
  # 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)
  #       ifdef MPROTECT_VDB
            if (!GC_GWW_AVAILABLE())
              return TRUE;
  #       endif
          return NULL == HDR(h)
                 || get_pht_entry_from_index(GC_written_pages, PHT_HASH(h));
  #     else
          /* TODO: implement me for MANUAL_VDB. */
          (void)h;
          return TRUE;
  #     endif
      }
  # endif /* CHECKSUMS || PROC_VDB */
  
    /* We expect block h to be written shortly.  Ensure that all pages    */
    /* containing any part of the n hblks starting at h are no longer     */
    /* protected.  If is_ptrfree is false, also ensure that they will     */
    /* subsequently appear to be dirty.  Not allowed to call GC_printf    */
    /* (and the friends) here, see Win32 GC_stop_world for the details.   */
    GC_INNER void GC_remove_protection(struct hblk *h, word nblocks,
                                       GC_bool is_ptrfree)
    {
  #   ifdef PCR_VDB
        (void)is_ptrfree;
        if (!GC_auto_incremental)
          return;
        PCR_VD_WriteProtectDisable(h, nblocks*HBLKSIZE);
        PCR_VD_WriteProtectEnable(h, nblocks*HBLKSIZE);
  #   elif defined(MPROTECT_VDB)
        struct hblk * h_trunc;    /* Truncated to page boundary */
        struct hblk * h_end;      /* Page boundary following block end */
        struct hblk * current;
  
        if (!GC_auto_incremental || GC_GWW_AVAILABLE())
          return;
        h_trunc = (struct hblk *)((word)h & ~(GC_page_size-1));
        h_end = (struct hblk *)(((word)(h + nblocks) + GC_page_size - 1)
                                & ~(GC_page_size - 1));
        if (h_end == h_trunc + 1 &&
          get_pht_entry_from_index(GC_dirty_pages, PHT_HASH(h_trunc))) {
          /* already marked dirty, and hence unprotected. */
          return;
        }
        for (current = h_trunc; (word)current < (word)h_end; ++current) {
          word index = PHT_HASH(current);
  
          if (!is_ptrfree || (word)current < (word)h
              || (word)current >= (word)(h + nblocks)) {
            async_set_pht_entry_from_index(GC_dirty_pages, index);
          }
        }
        UNPROTECT(h_trunc, (ptr_t)h_end - (ptr_t)h_trunc);
  #   else
        /* Ignore write hints.  They don't help us here.  */
        (void)h; (void)nblocks; (void)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. */
  
  /* #define BROKEN_EXCEPTION_HANDLING */
  
  #include <mach/mach.h>
  #include <mach/mach_error.h>
  #include <mach/exception.h>
  #include <mach/task.h>
  #include <pthread.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 GC_ATTR_UNUSED,
      int exception GC_ATTR_UNUSED, exception_data_t code GC_ATTR_UNUSED,
      mach_msg_type_number_t codeCnt GC_ATTR_UNUSED, int flavor GC_ATTR_UNUSED,
      thread_state_t old_state GC_ATTR_UNUSED, int old_stateCnt GC_ATTR_UNUSED,
      thread_state_t new_state GC_ATTR_UNUSED, int new_stateCnt GC_ATTR_UNUSED)
  {
    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 GC_ATTR_UNUSED,
      mach_port_t thread GC_ATTR_UNUSED, mach_port_t task GC_ATTR_UNUSED,
      int exception GC_ATTR_UNUSED, exception_data_t code GC_ATTR_UNUSED,
      mach_msg_type_number_t codeCnt GC_ATTR_UNUSED, int flavor GC_ATTR_UNUSED,
      thread_state_t old_state GC_ATTR_UNUSED, int old_stateCnt GC_ATTR_UNUSED,
      thread_state_t new_state GC_ATTR_UNUSED, int new_stateCnt GC_ATTR_UNUSED)
  {
    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);
    }
  
  #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 ((word)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(THREADS) && !defined(GC_NO_THREADS_DISCOVERY)
      GC_darwin_register_mach_handler_thread(mach_thread_self());
  # 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 */
              /* shouldn't 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 */
    } /* for(;;) */
  }
  
  /* All this SIGBUS code shouldn't 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 more than 8 SIGBUSs in a row!");
      } else {
        GC_sigbus_count++;
        WARN("Ignoring SIGBUS\n", 0);
      }
    }
  #endif /* BROKEN_EXCEPTION_HANDLING */
  
  GC_INNER GC_bool GC_mprotect_dirty_init(void)
  {
    #ifdef SHENANGO_THREADS
    BUG();
  #else
    kern_return_t r;
    mach_port_t me;
    pthread_t thread;
    pthread_attr_t attr;
    exception_mask_t mask;
  
  # ifdef CAN_HANDLE_FORK
      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();
  
    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");
  
  # undef pthread_create
    /* This will call the real pthread function, not our wrapper */
    if (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 SIGBUSs */
  # 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 (oldsa.sa_handler != (SIG_HNDLR_PTR)(signed_word)SIG_DFL) {
          GC_VERBOSE_LOG_PRINTF("Replaced other SIGBUS handler\n");
        }
      }
  # endif /* BROKEN_EXCEPTION_HANDLING  */
    return TRUE;
    #endif
  }
  
  /* 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)
  {
    unsigned int 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 < GC_old_exc_ports.count; i++)
      if (GC_old_exc_ports.masks[i] & (1 << exception))
        break;
    if (i == 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 32-bit x86.      */
  #     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 GC_ATTR_UNUSED,
                        mach_port_t thread, mach_port_t task GC_ATTR_UNUSED,
                        exception_type_t exception, exception_data_t code,
                        mach_msg_type_number_t code_count GC_ATTR_UNUSED)
  {
    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;
  
    if (exception != EXC_BAD_ACCESS || code[0] != KERN_PROTECTION_FAILURE) {
  #   ifdef DEBUG_EXCEPTION_HANDLING
        /* We aren't 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);
  #   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 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 /* BROKEN_EXCEPTION_HANDLING */
        /* 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 SIGBUSs */
      GC_sigbus_count = 0;
  # endif
  
    if (GC_mprotect_state == GC_MP_NORMAL) { /* common case */
      struct hblk * h = (struct hblk*)((word)addr & ~(GC_page_size-1));
      size_t i;
  
      UNPROTECT(h, GC_page_size);
      for (i = 0; i < divHBLKSZ(GC_page_size); i++) {
        word 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're just going to PROTECT() it again later. The thread
         will just fault again once it resumes */
    } else {
      /* Shouldn't 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 */
  
  #ifndef HAVE_INCREMENTAL_PROTECTION_NEEDS
    GC_API int GC_CALL GC_incremental_protection_needs(void)
    {
      return GC_PROTECTS_NONE;
    }
  #endif /* !HAVE_INCREMENTAL_PROTECTION_NEEDS */
  
  #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.                        */
  
  /* I suspect the following works for most X86 *nix variants, so         */
  /* long as the frame pointer is explicitly stored.  In the case of gcc, */
  /* compiler flags (e.g. -fomit-frame-pointer) determine whether it is.  */
  #if defined(I386) && defined(LINUX) && defined(SAVE_CALL_CHAIN)
  #   include <features.h>
  
      struct frame {
          struct frame *fr_savfp;
          long    fr_savpc;
  #       if NARGS > 0
            long  fr_arg[NARGS];  /* All the arguments go here.   */
  #       endif
      };
  #endif
  
  #if defined(SPARC)
  #  if defined(LINUX)
  #    include <features.h>
  
  #   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 */
  
  #ifdef NEED_CALLINFO
  /* Fill in the pc and argument information for up to NFRAMES of my      */
  /* callers.  Ignore my frame and my callers frame.                      */
  
  #ifdef LINUX
  #   include <unistd.h>
  #endif
  
  #endif /* NEED_CALLINFO */
  
  #if defined(GC_HAVE_BUILTIN_BACKTRACE)
  # ifdef _MSC_VER
  #  include "private/msvc_dbg.h"
  # else
  #  include <execinfo.h>
  # endif
  #endif
  
  #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.                        */
  # ifdef THREADS
      __thread    /* If your compiler doesn't understand this             */
                  /* you could use something like pthread_getspecific.    */
  # endif
      GC_bool GC_in_save_callers = FALSE;
  #endif
  
  GC_INNER void GC_save_callers(struct callinfo info[NFRAMES])
  {
    void * tmp_info[NFRAMES + 1];
    int npcs, i;
  # define IGNORE_FRAMES 1
  
    /* We retrieve NFRAMES+1 pc values, but discard the first, since it   */
    /* points to our own frame.                                           */
  # ifdef REDIRECT_MALLOC
      if (GC_in_save_callers) {
        info[0].ci_pc = (word)(&GC_save_callers);
        for (i = 1; i < NFRAMES; ++i) info[i].ci_pc = 0;
        return;
      }
      GC_in_save_callers = TRUE;
  # endif
  
    GC_ASSERT(I_HOLD_LOCK());
                  /* 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_STATIC_ASSERT(sizeof(struct callinfo) == sizeof(void *));
    npcs = backtrace((void **)tmp_info, NFRAMES + IGNORE_FRAMES);
    if (npcs > IGNORE_FRAMES)
      BCOPY(&tmp_info[IGNORE_FRAMES], info,
            (npcs - IGNORE_FRAMES) * sizeof(void *));
    for (i = npcs - IGNORE_FRAMES; i < NFRAMES; ++i) info[i].ci_pc = 0;
  # ifdef REDIRECT_MALLOC
      GC_in_save_callers = FALSE;
  # endif
  }
  
  #else /* No builtin backtrace; do it ourselves */
  
  #if (defined(OPENBSD) || defined(NETBSD) || defined(FREEBSD)) && 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
      frame = (struct frame *)GC_save_regs_in_stack();
      fp = (struct frame *)((long) frame -> FR_SAVFP + BIAS);
  #endif
  
     for (; !((word)fp HOTTER_THAN (word)frame)
            && !((word)GC_stackbottom HOTTER_THAN (word)fp)
            && nframes < NFRAMES;
          fp = (struct frame *)((long) fp -> FR_SAVFP + BIAS), nframes++) {
  #     if NARGS > 0
          int i;
  #     endif
  
        info[nframes].ci_pc = fp->FR_SAVPC;
  #     if NARGS > 0
          for (i = 0; i < NARGS; i++) {
            info[nframes].ci_arg[i] = ~(fp->fr_arg[i]);
          }
  #     endif /* NARGS > 0 */
    }
    if (nframes < NFRAMES) info[nframes].ci_pc = 0;
  }
  
  #endif /* No builtin backtrace */
  
  #endif /* SAVE_CALL_CHAIN */
  
  #ifdef NEED_CALLINFO
  
  /* Print info to stderr.  We do NOT hold the allocation lock */
  GC_INNER void GC_print_callers(struct callinfo info[NFRAMES])
  {
      int i;
      static int reentry_count = 0;
      GC_bool stop = FALSE;
      DCL_LOCK_STATE;
  
      /* FIXME: This should probably use a different lock, so that we     */
      /* become callable with or without the allocation lock.             */
      LOCK();
        ++reentry_count;
      UNLOCK();
  
  #   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 && !stop; i++) {
          if (info[i].ci_pc == 0) break;
  #       if NARGS > 0
          {
            int j;
  
            GC_err_printf("\t\targs: ");
            for (j = 0; j < NARGS; j++) {
              if (j != 0) GC_err_printf(", ");
              GC_err_printf("%d (0x%X)", ~(info[i].ci_arg[j]),
                                          ~(info[i].ci_arg[j]));
            }
            GC_err_printf("\n");
          }
  #       endif
          if (reentry_count > 1) {
              /* We were called during an allocation during       */
              /* a previous GC_print_callers call; punt.          */
              GC_err_printf("\t\t##PC##= 0x%lx\n",
                            (unsigned long)info[i].ci_pc);
              continue;
          }
          {
            char buf[40];
            char *name;
  #         if defined(GC_HAVE_BUILTIN_BACKTRACE) \
               && !defined(GC_BACKTRACE_SYMBOLS_BROKEN)
              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)info[i].ci_pc);
              buf[sizeof(buf) - 1] = '\0';
              name = buf;
            }
  #         if defined(LINUX) && !defined(SMALL_CONFIG)
              /* Try for a line number. */
              {
                  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;
                  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;
                  int ret_code;
                  /* Try to get it via a hairy and expensive scheme.      */
                  /* First we get the name of the executable:             */
                  if (will_fail) goto out;
                  if (!found_exe_name) {
                    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. */
                      goto out;
                    }
                    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)info[i].ci_pc);
                  cmd_buf[sizeof(cmd_buf) - 1] = '\0';
                  old_preload = GETENV("LD_PRELOAD");
                  if (0 != old_preload) {
                    size_t old_len = strlen(old_preload);
                    if (old_len >= PRELOAD_SZ) {
                      will_fail = TRUE;
                      goto out;
                    }
                    BCOPY(old_preload, preload_buf, old_len + 1);
                    unsetenv ("LD_PRELOAD");
                  }
                  pipe = popen(cmd_buf, "r");
                  if (0 != old_preload
                      && 0 != setenv ("LD_PRELOAD", preload_buf, 0)) {
                    WARN("Failed to reset LD_PRELOAD\n", 0);
                  }
                  if (pipe == NULL
                      || (result_len = fread(result_buf, 1,
                                             RESULT_SZ - 1, pipe)) == 0) {
                    if (pipe != NULL) pclose(pipe);
                    will_fail = TRUE;
                    goto out;
                  }
                  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')) {
                      pclose(pipe);
                      goto out;
                  }
                  /* Get rid of embedded newline, if any.  Test for "main" */
                  {
                    char * nl = strchr(result_buf, '\n');
                    if (nl != NULL
                        && (word)nl < (word)(result_buf + result_len)) {
                      *nl = ':';
                    }
                    if (strncmp(result_buf, "main",
                                nl != NULL ? (size_t)(nl - result_buf)
                                           : result_len) == 0) {
                      stop = TRUE;
                    }
                  }
                  if (result_len < RESULT_SZ - 25) {
                    /* Add in hex address */
                    (void)snprintf(&result_buf[result_len],
                                   sizeof(result_buf) - result_len,
                                   " [0x%lx]", (unsigned long)info[i].ci_pc);
                    result_buf[sizeof(result_buf) - 1] = '\0';
                  }
                  name = result_buf;
                  pclose(pipe);
                  out:;
              }
  #         endif /* LINUX */
            GC_err_printf("\t\t%s\n", name);
  #         if defined(GC_HAVE_BUILTIN_BACKTRACE) \
               && !defined(GC_BACKTRACE_SYMBOLS_BROKEN)
              if (sym_name != NULL)
                free(sym_name);   /* May call GC_[debug_]free; that's OK  */
  #         endif
          }
      }
      LOCK();
        --reentry_count;
      UNLOCK();
  }
  
  #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)
    {
      char *maps;
  
      GC_err_printf("---------- Begin address map ----------\n");
      maps = GC_get_maps();
      GC_err_puts(maps != NULL ? maps : "Failed to get map!\n");
      GC_err_printf("---------- End address map ----------\n");
    }
  #endif /* LINUX && ELF */
  