text: /*
   * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
   * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
   * Copyright (c) 1996 by Silicon Graphics.  All rights reserved.
   * Copyright (c) 2000-2004 Hewlett-Packard Development Company, L.P.
   *
   * 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.
   */
  
  /*
   * This header is private to the gc.  It is almost always included from
   * gc_priv.h.  However it is possible to include it by itself if just the
   * configuration macros are needed.  In that
   * case, a few declarations relying on types declared in gc_priv.h will be
   * omitted.
   */
  
  #ifndef GCCONFIG_H
  #define GCCONFIG_H
  
  # ifndef GC_PRIVATE_H
      /* Fake ptr_t declaration, just to avoid compilation errors.        */
      /* This avoids many instances if "ifndef GC_PRIVATE_H" below.       */
      typedef struct GC_undefined_struct * ptr_t;
  #   include <stddef.h>  /* For size_t etc. */
  # endif
  
  /* Machine dependent parameters.  Some tuning parameters can be found   */
  /* near the top of gc_private.h.                                        */
  
  /* Machine specific parts contributed by various people.  See README file. */
  
  #if defined(__ANDROID__) && !defined(PLATFORM_ANDROID)
    /* __ANDROID__ macro is defined by Android NDK gcc.   */
  # define PLATFORM_ANDROID 1
  #endif
  
  #if defined(__SYMBIAN32__) && !defined(SYMBIAN)
  # define SYMBIAN
  # ifdef __WINS__
  #   pragma data_seg(".data2")
  # endif
  #endif
  
  /* First a unified test for Linux: */
  # if (defined(linux) || defined(__linux__) || defined(PLATFORM_ANDROID)) \
       && !defined(LINUX) && !defined(__native_client__)
  #   define LINUX
  # endif
  
  /* And one for QNX: */
  # if defined(__QNX__)
  #    define I386
  #    define OS_TYPE "QNX"
  #    define SA_RESTART 0
  #    define HEURISTIC1
       extern char etext[];
  #    define DATASTART ((ptr_t)(etext))
       extern int _end[];
  #    define DATAEND (_end)
  #    define mach_type_known
  # endif
  
  /* And one for NetBSD: */
  # if defined(__NetBSD__)
  #    define NETBSD
  # endif
  
  /* And one for OpenBSD: */
  # if defined(__OpenBSD__)
  #    define OPENBSD
  # endif
  
  /* And one for FreeBSD: */
  # if (defined(__FreeBSD__) || defined(__DragonFly__) \
        || defined(__FreeBSD_kernel__)) && !defined(FREEBSD)
  #    define FREEBSD
  # endif
  
  /* And one for Darwin: */
  # if defined(macosx) || (defined(__APPLE__) && defined(__MACH__))
  #   define DARWIN
  # endif
  
  /* Determine the machine type: */
  # if defined(__native_client__)
  #    define NACL
  #    define I386
  #    define mach_type_known
  # endif
  # if defined(__aarch64__)
  #    define AARCH64
  #    if !defined(LINUX) && !defined(DARWIN)
  #      define NOSYS
  #      define mach_type_known
  #    endif
  # endif
  # if defined(__arm) || defined(__arm__) || defined(__thumb__)
  #    define ARM32
  #    if !defined(LINUX) && !defined(NETBSD) && !defined(FREEBSD) \
          && !defined(OPENBSD) && !defined(DARWIN) \
          && !defined(_WIN32) && !defined(__CEGCC__) && !defined(SYMBIAN)
  #      define NOSYS
  #      define mach_type_known
  #    endif
  # endif
  # if defined(sun) && defined(mc68000)
  #    error SUNOS4 no longer supported
  # endif
  # if defined(hp9000s300)
  #    error M68K based HP machines no longer supported.
  # endif
  # if defined(OPENBSD) && defined(m68k)
       /* FIXME: Should we remove this case? */
  #    define M68K
  #    define mach_type_known
  # endif
  # if defined(OPENBSD) && defined(__sparc__)
  #    define SPARC
  #    define mach_type_known
  # endif
  # if defined(OPENBSD) && defined(__arm__)
  #    define ARM32
  #    define mach_type_known
  # endif
  # if defined(OPENBSD) && defined(__sh__)
  #    define SH
  #    define mach_type_known
  # endif
  # if defined(NETBSD) && (defined(m68k) || defined(__m68k__))
  #    define M68K
  #    define mach_type_known
  # endif
  # if defined(NETBSD) && defined(__powerpc__)
  #    define POWERPC
  #    define mach_type_known
  # endif
  # if defined(NETBSD) && (defined(__arm32__) || defined(__arm__))
  #    define ARM32
  #    define mach_type_known
  # endif
  # if defined(NETBSD) && defined(__sh__)
  #    define SH
  #    define mach_type_known
  # endif
  # if defined(vax) || defined(__vax__)
  #    define VAX
  #    ifdef ultrix
  #       define ULTRIX
  #    else
  #       define BSD
  #    endif
  #    define mach_type_known
  # endif
  # if defined(__NetBSD__) && defined(__vax__)
  #    define VAX
  #    define mach_type_known
  # endif
  # if defined(mips) || defined(__mips) || defined(_mips)
  #    define MIPS
  #    if defined(nec_ews) || defined(_nec_ews)
  #      define EWS4800
  #    endif
  #    if !defined(LINUX) && !defined(EWS4800) && !defined(NETBSD) \
          && !defined(OPENBSD)
  #      if defined(ultrix) || defined(__ultrix)
  #        define ULTRIX
  #      else
  #        define IRIX5   /* or IRIX 6.X */
  #      endif
  #    endif /* !LINUX */
  #    if defined(__NetBSD__) && defined(__MIPSEL__)
  #      undef ULTRIX
  #    endif
  #    define mach_type_known
  # endif
  # if defined(DGUX) && (defined(i386) || defined(__i386__))
  #    define I386
  #    ifndef _USING_DGUX
  #    define _USING_DGUX
  #    endif
  #    define mach_type_known
  # endif
  # if defined(sequent) && (defined(i386) || defined(__i386__))
  #    define I386
  #    define SEQUENT
  #    define mach_type_known
  # endif
  # if defined(sun) && (defined(i386) || defined(__i386__))
  #    define I386
  #    define SOLARIS
  #    define mach_type_known
  # endif
  # if defined(sun) && defined(__amd64)
  #    define X86_64
  #    define SOLARIS
  #    define mach_type_known
  # endif
  # if (defined(__OS2__) || defined(__EMX__)) && defined(__32BIT__)
  #    define I386
  #    define OS2
  #    define mach_type_known
  # endif
  # if defined(ibm032)
  #   error IBM PC/RT no longer supported.
  # endif
  # if defined(sun) && (defined(sparc) || defined(__sparc))
  #   define SPARC
      /* Test for SunOS 5.x */
  #     include <errno.h>
  #     define SOLARIS
  #   define mach_type_known
  # endif
  # if defined(sparc) && defined(unix) && !defined(sun) && !defined(linux) \
       && !defined(__OpenBSD__) && !defined(__NetBSD__) \
       && !defined(__FreeBSD__) && !defined(__DragonFly__)
  #   define SPARC
  #   define DRSNX
  #   define mach_type_known
  # endif
  # if defined(_IBMR2)
  #   define POWERPC
  #   define AIX
  #   define mach_type_known
  # endif
  # if defined(__NetBSD__) && defined(__sparc__)
  #   define SPARC
  #   define mach_type_known
  # endif
  # if defined(_M_XENIX) && defined(_M_SYSV) && defined(_M_I386)
          /* The above test may need refinement   */
  #   define I386
  #   if defined(_SCO_ELF)
  #     define SCO_ELF
  #   else
  #     define SCO
  #   endif
  #   define mach_type_known
  # endif
  # if defined(_AUX_SOURCE)
  #   error A/UX no longer supported
  # endif
  # if defined(_PA_RISC1_0) || defined(_PA_RISC1_1) || defined(_PA_RISC2_0) \
       || defined(hppa) || defined(__hppa__)
  #   define HP_PA
  #   if !defined(LINUX) && !defined(HPUX) && !defined(OPENBSD)
  #     define HPUX
  #   endif
  #   define mach_type_known
  # endif
  # if defined(__ia64) && (defined(_HPUX_SOURCE) || defined(__HP_aCC))
  #   define IA64
  #   ifndef HPUX
  #     define HPUX
  #   endif
  #   define mach_type_known
  # endif
  # if defined(__BEOS__) && defined(_X86_)
  #    define I386
  #    define BEOS
  #    define mach_type_known
  # endif
  # if defined(OPENBSD) && defined(__amd64__)
  #    define X86_64
  #    define mach_type_known
  # endif
  # if defined(LINUX) && (defined(i386) || defined(__i386__))
  #    define I386
  #    define mach_type_known
  # endif
  # if defined(LINUX) && defined(__x86_64__)
  #    define X86_64
  #    define mach_type_known
  # endif
  # if defined(LINUX) && (defined(__ia64__) || defined(__ia64))
  #    define IA64
  #    define mach_type_known
  # endif
  # if defined(LINUX) && defined(__aarch64__)
  #    define AARCH64
  #    define mach_type_known
  # endif
  # if defined(LINUX) && (defined(__arm) || defined(__arm__))
  #    define ARM32
  #    define mach_type_known
  # endif
  # if defined(LINUX) && defined(__cris__)
  #    ifndef CRIS
  #       define CRIS
  #    endif
  #    define mach_type_known
  # endif
  # if defined(LINUX) && (defined(powerpc) || defined(__powerpc__) \
                          || defined(powerpc64) || defined(__powerpc64__))
  #    define POWERPC
  #    define mach_type_known
  # endif
  # if defined(LINUX) && defined(__mc68000__)
  #    define M68K
  #    define mach_type_known
  # endif
  # if defined(LINUX) && (defined(sparc) || defined(__sparc__))
  #    define SPARC
  #    define mach_type_known
  # endif
  # if defined(LINUX) && defined(__sh__)
  #    define SH
  #    define mach_type_known
  # endif
  # if defined(LINUX) && defined(__avr32__)
  #    define AVR32
  #    define mach_type_known
  # endif
  # if defined(LINUX) && defined(__m32r__)
  #    define M32R
  #    define mach_type_known
  # endif
  # if defined(__alpha) || defined(__alpha__)
  #   define ALPHA
  #   if !defined(LINUX) && !defined(NETBSD) && !defined(OPENBSD) \
         && !defined(FREEBSD)
  #     define OSF1       /* a.k.a Digital Unix */
  #   endif
  #   define mach_type_known
  # endif
  # if defined(_AMIGA) && !defined(AMIGA)
  #   define AMIGA
  # endif
  # ifdef AMIGA
  #   define M68K
  #   define mach_type_known
  # endif
  # if defined(THINK_C) \
       || (defined(__MWERKS__) && !defined(__powerc) && !defined(SYMBIAN))
  #   define M68K
  #   define MACOS
  #   define mach_type_known
  # endif
  # if defined(__MWERKS__) && defined(__powerc) && !defined(__MACH__) \
       && !defined(SYMBIAN)
  #   define POWERPC
  #   define MACOS
  #   define mach_type_known
  # endif
  # if defined(__OpenBSD__) && defined(__powerpc__)
  #   define POWERPC
  #   define OPENBSD
  #   define mach_type_known
  # endif
  # if defined(DARWIN)
  #   if defined(__ppc__)  || defined(__ppc64__)
  #    define POWERPC
  #    define mach_type_known
  #   elif defined(__x86_64__) || defined(__x86_64)
  #    define X86_64
  #    define mach_type_known
  #   elif defined(__i386__)
  #    define I386
  #    define mach_type_known
  #   elif defined(__arm__)
  #    define ARM32
  #    define mach_type_known
  #    define DARWIN_DONT_PARSE_STACK
  #   elif defined(__aarch64__)
  #    define AARCH64
  #    define mach_type_known
  #    define DARWIN_DONT_PARSE_STACK
  #   endif
  # endif
  # if defined(__rtems__) && (defined(i386) || defined(__i386__))
  #   define I386
  #   define RTEMS
  #   define mach_type_known
  # endif
  # if defined(NeXT) && defined(mc68000)
  #   define M68K
  #   define NEXT
  #   define mach_type_known
  # endif
  # if defined(NeXT) && (defined(i386) || defined(__i386__))
  #   define I386
  #   define NEXT
  #   define mach_type_known
  # endif
  # if defined(__OpenBSD__) && (defined(i386) || defined(__i386__))
  #   define I386
  #   define OPENBSD
  #   define mach_type_known
  # endif
  # if defined(__NetBSD__) && (defined(i386) || defined(__i386__))
  #   define I386
  #   define mach_type_known
  # endif
  # if defined(__NetBSD__) && defined(__x86_64__)
  #    define X86_64
  #    define mach_type_known
  # endif
  # if defined(FREEBSD) && (defined(i386) || defined(__i386__))
  #   define I386
  #   define mach_type_known
  # endif
  # if defined(FREEBSD) && (defined(__amd64__) || defined(__x86_64__))
  #   define X86_64
  #   define mach_type_known
  # endif
  # if defined(FREEBSD) && defined(__ia64__)
  #   define IA64
  #   define mach_type_known
  # endif
  # if defined(FREEBSD) && defined(__sparc__)
  #   define SPARC
  #   define mach_type_known
  # endif
  # if defined(FREEBSD) && (defined(powerpc) || defined(__powerpc__))
  #   define POWERPC
  #   define mach_type_known
  # endif
  # if defined(FREEBSD) && defined(__arm__)
  #   define ARM32
  #   define mach_type_known
  # endif
  # if defined(bsdi) && (defined(i386) || defined(__i386__))
  #    define I386
  #    define BSDI
  #    define mach_type_known
  # endif
  # if !defined(mach_type_known) && defined(__386BSD__)
  #   define I386
  #   define THREE86BSD
  #   define mach_type_known
  # endif
  # if defined(_CX_UX) && defined(_M88K)
  #   define M88K
  #   define CX_UX
  #   define mach_type_known
  # endif
  # if defined(DGUX) && defined(m88k)
  #   define M88K
      /* DGUX defined */
  #   define mach_type_known
  # endif
  # if defined(_WIN32_WCE) || defined(__CEGCC__) || defined(__MINGW32CE__)
      /* SH3, SH4, MIPS already defined for corresponding architectures */
  #   if defined(SH3) || defined(SH4)
  #     define SH
  #   endif
  #   if defined(x86) || defined(__i386__)
  #     define I386
  #   endif
  #   if defined(_M_ARM) || defined(ARM) || defined(_ARM_)
  #     define ARM32
  #   endif
  #   define MSWINCE
  #   define mach_type_known
  # else
  #   if ((defined(_MSDOS) || defined(_MSC_VER)) && (_M_IX86 >= 300)) \
         || (defined(_WIN32) && !defined(__CYGWIN32__) && !defined(__CYGWIN__) \
             && !defined(SYMBIAN))
  #     if defined(__LP64__) || defined(_WIN64)
  #       define X86_64
  #     else
  #       define I386
  #     endif
  #     define MSWIN32    /* or Win64 */
  #     define mach_type_known
  #   endif
  #   if defined(_MSC_VER) && defined(_M_IA64)
  #     define IA64
  #     define MSWIN32    /* Really win64, but we don't treat 64-bit      */
                          /* variants as a different platform.            */
  #   endif
  # endif
  # if defined(__DJGPP__)
  #   define I386
  #   ifndef DJGPP
  #     define DJGPP  /* MSDOS running the DJGPP port of GCC */
  #   endif
  #   define mach_type_known
  # endif
  # if defined(__CYGWIN32__) || defined(__CYGWIN__)
  #   if defined(__LP64__)
  #     define X86_64
  #   else
  #     define I386
  #   endif
  #   define CYGWIN32
  #   define mach_type_known
  # endif
  # if defined(__MINGW32__) && !defined(mach_type_known)
  #   define I386
  #   define MSWIN32
  #   define mach_type_known
  # endif
  # if defined(__BORLANDC__)
  #   define I386
  #   define MSWIN32
  #   define mach_type_known
  # endif
  # if defined(_UTS) && !defined(mach_type_known)
  #   define S370
  #   define UTS4
  #   define mach_type_known
  # endif
  # if defined(__pj__)
  #   error PicoJava no longer supported
      /* The implementation had problems, and I haven't heard of users    */
      /* in ages.  If you want it resurrected, let me know.               */
  # endif
  # if defined(__embedded__) && defined(PPC)
  #   define POWERPC
  #   define NOSYS
  #   define mach_type_known
  # endif
  
  # if defined(__WATCOMC__) && defined(__386__)
  #   define I386
  #   if !defined(OS2) && !defined(MSWIN32) && !defined(DOS4GW)
  #     if defined(__OS2__)
  #       define OS2
  #     else
  #       if defined(__WINDOWS_386__) || defined(__NT__)
  #         define MSWIN32
  #       else
  #         define DOS4GW
  #       endif
  #     endif
  #   endif
  #   define mach_type_known
  # endif
  # if defined(__s390__) && defined(LINUX)
  #    define S390
  #    define mach_type_known
  # endif
  # if defined(__GNU__)
  #   if defined(__i386__)
  /* The Debian Hurd running on generic PC */
  #     define  HURD
  #     define  I386
  #     define  mach_type_known
  #    endif
  # endif
  # if defined(__TANDEM)
      /* Nonstop S-series */
      /* FIXME: Should recognize Integrity series? */
  #   define MIPS
  #   define NONSTOP
  #   define mach_type_known
  # endif
  # if defined(__hexagon__) && defined(LINUX)
  #    define HEXAGON
  #    define mach_type_known
  # endif
  
  # if defined(SYMBIAN)
  #   define mach_type_known
  # endif
  
  /* Feel free to add more clauses here */
  
  /* Or manually define the machine type here.  A machine type is         */
  /* characterized by the architecture.  Some                             */
  /* machine types are further subdivided by OS.                          */
  /* Macros such as LINUX, FREEBSD, etc. distinguish them.                */
  /* SYSV on an M68K actually means A/UX.                                 */
  /* The distinction in these cases is usually the stack starting address */
  # ifndef mach_type_known
  #   error "The collector has not been ported to this machine/OS combination."
  # endif
                      /* Mapping is: M68K       ==> Motorola 680X0        */
                      /*             (NEXT, and SYSV (A/UX),              */
                      /*             MACOS and AMIGA variants)            */
                      /*             I386       ==> Intel 386             */
                      /*              (SEQUENT, OS2, SCO, LINUX, NETBSD,  */
                      /*               FREEBSD, THREE86BSD, MSWIN32,      */
                      /*               BSDI, SOLARIS, NEXT and others)    */
                      /*             NS32K      ==> Encore Multimax       */
                      /*             MIPS       ==> R2000 through R14K    */
                      /*                  (many variants)                 */
                      /*             VAX        ==> DEC VAX               */
                      /*                  (BSD, ULTRIX variants)          */
                      /*             HP_PA      ==> HP9000/700 & /800     */
                      /*                            HP/UX, LINUX          */
                      /*             SPARC      ==> SPARC v7/v8/v9        */
                      /*                  (SOLARIS, LINUX, DRSNX variants)        */
                      /*             ALPHA      ==> DEC Alpha             */
                      /*                  (OSF1 and LINUX variants)       */
                      /*             M88K       ==> Motorola 88XX0        */
                      /*                  (CX_UX and DGUX)                */
                      /*             S370       ==> 370-like machine      */
                      /*                  running Amdahl UTS4             */
                      /*             S390       ==> 390-like machine      */
                      /*                  running LINUX                   */
                      /*             AARCH64    ==> ARM AArch64           */
                      /*             ARM32      ==> Intel StrongARM       */
                      /*             IA64       ==> Intel IPF             */
                      /*                            (e.g. Itanium)        */
                      /*                  (LINUX and HPUX)                */
                      /*             SH         ==> Hitachi SuperH        */
                      /*                  (LINUX & MSWINCE)               */
                      /*             X86_64     ==> AMD x86-64            */
                      /*             POWERPC    ==> IBM/Apple PowerPC     */
                      /*                  (MACOS(<=9),DARWIN(incl.MACOSX),*/
                      /*                   LINUX, NETBSD, AIX, NOSYS      */
                      /*                   variants)                      */
                      /*                  Handles 32 and 64-bit variants. */
                      /*             CRIS       ==> Axis Etrax            */
                      /*             M32R       ==> Renesas M32R          */
                      /*             HEXAGON    ==> Qualcomm Hexagon      */
  
  
  /*
   * For each architecture and OS, the following need to be defined:
   *
   * CPP_WORDSZ is a simple integer constant representing the word size.
   * in bits.  We assume byte addressability, where a byte has 8 bits.
   * We also assume CPP_WORDSZ is either 32 or 64.
   * (We care about the length of pointers, not hardware
   * bus widths.  Thus a 64 bit processor with a C compiler that uses
   * 32 bit pointers should use CPP_WORDSZ of 32, not 64. Default is 32.)
   *
   * MACH_TYPE is a string representation of the machine type.
   * OS_TYPE is analogous for the OS.
   *
   * ALIGNMENT is the largest N, such that
   * all pointer are guaranteed to be aligned on N byte boundaries.
   * defining it to be 1 will always work, but perform poorly.
   *
   * DATASTART is the beginning of the data segment.
   * On some platforms SEARCH_FOR_DATA_START is defined.
   * SEARCH_FOR_DATASTART will cause GC_data_start to
   * be set to an address determined by accessing data backwards from _end
   * until an unmapped page is found.  DATASTART will be defined to be
   * GC_data_start.
   * On UNIX-like systems, the collector will scan the area between DATASTART
   * and DATAEND for root pointers.
   *
   * DATAEND, if not "end", where "end" is defined as "extern int end[]".
   * RTH suggests gaining access to linker script synth'd values with
   * this idiom instead of "&end", where "end" is defined as "extern int end".
   * Otherwise, "GCC will assume these are in .sdata/.sbss" and it will, e.g.,
   * cause failures on alpha*-*-* with -msmall-data or -fpic or mips-*-*
   * without any special options.
   *
   * STACKBOTTOM is the cool end of the stack, which is usually the
   * highest address in the stack.
   * Under PCR or OS/2, we have other ways of finding thread stacks.
   * For each machine, the following should:
   * 1) define STACK_GROWS_UP if the stack grows toward higher addresses, and
   * 2) define exactly one of
   *      STACKBOTTOM (should be defined to be an expression)
   *      LINUX_STACKBOTTOM
   *      HEURISTIC1
   *      HEURISTIC2
   * If STACKBOTTOM is defined, then it's value will be used directly as the
   * stack base.  If LINUX_STACKBOTTOM is defined, then it will be determined
   * with a method appropriate for most Linux systems.  Currently we look
   * first for __libc_stack_end (currently only if USE_LIBC_PRIVATES is
   * defined), and if that fails read it from /proc.  (If USE_LIBC_PRIVATES
   * is not defined and NO_PROC_STAT is defined, we revert to HEURISTIC2.)
   * If either of the last two macros are defined, then STACKBOTTOM is computed
   * during collector startup using one of the following two heuristics:
   * HEURISTIC1:  Take an address inside GC_init's frame, and round it up to
   *              the next multiple of STACK_GRAN.
   * HEURISTIC2:  Take an address inside GC_init's frame, increment it repeatedly
   *              in small steps (decrement if STACK_GROWS_UP), and read the value
   *              at each location.  Remember the value when the first
   *              Segmentation violation or Bus error is signaled.  Round that
   *              to the nearest plausible page boundary, and use that instead
   *              of STACKBOTTOM.
   *
   * Gustavo Rodriguez-Rivera points out that on most (all?) Unix machines,
   * the value of environ is a pointer that can serve as STACKBOTTOM.
   * I expect that HEURISTIC2 can be replaced by this approach, which
   * interferes far less with debugging.  However it has the disadvantage
   * that it's confused by a putenv call before the collector is initialized.
   * This could be dealt with by intercepting putenv ...
   *
   * If no expression for STACKBOTTOM can be found, and neither of the above
   * heuristics are usable, the collector can still be used with all of the above
   * undefined, provided one of the following is done:
   * 1) GC_mark_roots can be changed to somehow mark from the correct stack(s)
   *    without reference to STACKBOTTOM.  This is appropriate for use in
   *    conjunction with thread packages, since there will be multiple stacks.
   *    (Allocating thread stacks in the heap, and treating them as ordinary
   *    heap data objects is also possible as a last resort.  However, this is
   *    likely to introduce significant amounts of excess storage retention
   *    unless the dead parts of the thread stacks are periodically cleared.)
   * 2) Client code may set GC_stackbottom before calling any GC_ routines.
   *    If the author of the client code controls the main program, this is
   *    easily accomplished by introducing a new main program, setting
   *    GC_stackbottom to the address of a local variable, and then calling
   *    the original main program.  The new main program would read something
   *    like (provided real_main() is not inlined by the compiler):
   *
   *              # include "gc_private.h"
   *
   *              main(argc, argv, envp)
   *              int argc;
   *              char **argv, **envp;
   *              {
   *                  volatile int dummy;
   *
   *                  GC_stackbottom = (ptr_t)(&dummy);
   *                  return(real_main(argc, argv, envp));
   *              }
   *
   *
   * Each architecture may also define the style of virtual dirty bit
   * implementation to be used:
   *   MPROTECT_VDB: Write protect the heap and catch faults.
   *   GWW_VDB: Use win32 GetWriteWatch primitive.
   *   PROC_VDB: Use the SVR4 /proc primitives to read dirty bits.
   *
   * The first and second one may be combined, in which case a runtime
   * selection will be made, based on GetWriteWatch availability.
   *
   * An architecture may define DYNAMIC_LOADING if dyn_load.c
   * defined GC_register_dynamic_libraries() for the architecture.
   *
   * An architecture may define PREFETCH(x) to preload the cache with *x.
   * This defaults to GCC built-in operation (or a no-op for other compilers).
   *
   * PREFETCH_FOR_WRITE(x) is used if *x is about to be written.
   *
   * An architecture may also define CLEAR_DOUBLE(x) to be a fast way to
   * clear the two words at GC_malloc-aligned address x.  By default,
   * word stores of 0 are used instead.
   *
   * HEAP_START may be defined as the initial address hint for mmap-based
   * allocation.
   */
  
  /* If we are using a recent version of gcc, we can use                    */
  /* __builtin_unwind_init() to push the relevant registers onto the stack. */
  # if defined(__GNUC__) && ((__GNUC__ >= 3) \
                             || (__GNUC__ == 2 && __GNUC_MINOR__ >= 8)) \
       && !defined(__INTEL_COMPILER) && !defined(__PATHCC__) \
       && !defined(__FUJITSU) /* for FX10 system */ \
       && !(defined(POWERPC) && defined(DARWIN)) /* for MacOS X 10.3.9 */ \
       && !defined(RTEMS) \
       && !defined(__clang__) /* since no-op in clang (3.0) */
  #   define HAVE_BUILTIN_UNWIND_INIT
  # endif
  
  # ifdef SYMBIAN
  #   define MACH_TYPE "SYMBIAN"
  #   define OS_TYPE "SYMBIAN"
  #   define CPP_WORDSZ 32
  #   define ALIGNMENT 4
  #   define DATASTART NULL
  #   define DATAEND NULL
  # endif
  
  # define STACK_GRAN 0x1000000
  # ifdef M68K
  #   define MACH_TYPE "M68K"
  #   define ALIGNMENT 2
  #   ifdef OPENBSD
          /* FIXME: Should we remove this case? */
  #       define OS_TYPE "OPENBSD"
  #       define HEURISTIC2
  #       ifdef __ELF__
            extern ptr_t GC_data_start;
  #         define DATASTART GC_data_start
  #         define DYNAMIC_LOADING
  #       else
            extern char etext[];
  #         define DATASTART ((ptr_t)(etext))
  #       endif
  #   endif
  #   ifdef NETBSD
  #       define OS_TYPE "NETBSD"
  #       define HEURISTIC2
  #       ifdef __ELF__
            extern ptr_t GC_data_start;
  #         define DATASTART GC_data_start
  #         define DYNAMIC_LOADING
  #       else
            extern char etext[];
  #         define DATASTART ((ptr_t)(etext))
  #       endif
  #   endif
  #   ifdef LINUX
  #       define OS_TYPE "LINUX"
  #       define LINUX_STACKBOTTOM
  #       define MPROTECT_VDB
  #       ifdef __ELF__
  #            define DYNAMIC_LOADING
  #            include <features.h>
  #            if defined(__GLIBC__) && __GLIBC__ >= 2
  #              define SEARCH_FOR_DATA_START
  #            else /* !GLIBC2 */
  #              ifdef PLATFORM_ANDROID
  #                define __environ environ
  #              endif
                 extern char **__environ;
  #              define DATASTART ((ptr_t)(&__environ))
                               /* hideous kludge: __environ is the first */
                               /* word in crt0.o, and delimits the start */
                               /* of the data segment, no matter which   */
                               /* ld options were passed through.        */
                               /* We could use _etext instead, but that  */
                               /* would include .rodata, which may       */
                               /* contain large read-only data tables    */
                               /* that we'd rather not scan.             */
  #            endif /* !GLIBC2 */
               extern int _end[];
  #            define DATAEND (ptr_t)(_end)
  #       else
               extern int etext[];
  #            define DATASTART ((ptr_t)((((word) (etext)) + 0xfff) & ~0xfff))
  #       endif
  #   endif
  #   ifdef AMIGA
  #       define OS_TYPE "AMIGA"
                  /* STACKBOTTOM and DATASTART handled specially  */
                  /* in os_dep.c                                  */
  #       define DATAEND  /* not needed */
  #       define GETPAGESIZE() 4096
  #   endif
  #   ifdef MACOS
  #     ifndef __LOWMEM__
  #     include <LowMem.h>
  #     endif
  #     define OS_TYPE "MACOS"
                  /* see os_dep.c for details of global data segments. */
  #     define STACKBOTTOM ((ptr_t) LMGetCurStackBase())
  #     define DATAEND    /* not needed */
  #     define GETPAGESIZE() 4096
  #   endif
  #   ifdef NEXT
  #       define OS_TYPE "NEXT"
  #       define DATASTART ((ptr_t) get_etext())
  #       define DATASTART_IS_FUNC
  #       define STACKBOTTOM ((ptr_t) 0x4000000)
  #       define DATAEND  /* not needed */
  #   endif
  # endif
  
  # if defined(POWERPC)
  #   define MACH_TYPE "POWERPC"
  #   ifdef MACOS
  #     define ALIGNMENT 2  /* Still necessary?  Could it be 4?   */
  #     ifndef __LOWMEM__
  #     include <LowMem.h>
  #     endif
  #     define OS_TYPE "MACOS"
                          /* see os_dep.c for details of global data segments. */
  #     define STACKBOTTOM ((ptr_t) LMGetCurStackBase())
  #     define DATAEND  /* not needed */
  #   endif
  #   ifdef LINUX
  #     if defined(__powerpc64__)
  #       define ALIGNMENT 8
  #       define CPP_WORDSZ 64
  #       ifndef HBLKSIZE
  #         define HBLKSIZE 4096
  #       endif
  #     else
  #       define ALIGNMENT 4
  #     endif
  #     define OS_TYPE "LINUX"
        /* HEURISTIC1 has been reliably reported to fail for a 32-bit     */
        /* executable on a 64 bit kernel.                                 */
  #     if defined(__bg__)
          /* The Linux Compute Node Kernel (used on BlueGene systems)     */
          /* does not support LINUX_STACKBOTTOM way.                      */
  #       define HEURISTIC2
  #       define NO_PTHREAD_GETATTR_NP
  #     else
  #       define LINUX_STACKBOTTOM
  #     endif
  #     define DYNAMIC_LOADING
  #     define SEARCH_FOR_DATA_START
        extern int _end[];
  #     define DATAEND (ptr_t)(_end)
  #   endif
  #   ifdef DARWIN
  #     define OS_TYPE "DARWIN"
  #     define DYNAMIC_LOADING
  #     if defined(__ppc64__)
  #       define ALIGNMENT 8
  #       define CPP_WORDSZ 64
  #       define STACKBOTTOM ((ptr_t) 0x7fff5fc00000)
  #       define CACHE_LINE_SIZE 64
  #       ifndef HBLKSIZE
  #         define HBLKSIZE 4096
  #       endif
  #     else
  #       define ALIGNMENT 4
  #       define STACKBOTTOM ((ptr_t) 0xc0000000)
  #     endif
        /* XXX: see get_end(3), get_etext() and get_end() should not be used. */
        /* These aren't used when dyld support is enabled (it is by default). */
  #     define DATASTART ((ptr_t) get_etext())
  #     define DATAEND   ((ptr_t) get_end())
  #     ifndef USE_MMAP
  #       define USE_MMAP
  #     endif
  #     define USE_MMAP_ANON
  #     define MPROTECT_VDB
  #     include <unistd.h>
  #     define GETPAGESIZE() getpagesize()
  #     if defined(USE_PPC_PREFETCH) && defined(__GNUC__)
          /* The performance impact of prefetches is untested */
  #       define PREFETCH(x) \
            __asm__ __volatile__ ("dcbt 0,%0" : : "r" ((const void *) (x)))
  #       define PREFETCH_FOR_WRITE(x) \
            __asm__ __volatile__ ("dcbtst 0,%0" : : "r" ((const void *) (x)))
  #     endif
        /* There seems to be some issues with trylock hanging on darwin.  */
        /* This should be looked into some more.                          */
  #     define NO_PTHREAD_TRYLOCK
  #   endif
  #   ifdef OPENBSD
  #     define OS_TYPE "OPENBSD"
  #     define ALIGNMENT 4
  #     ifndef GC_OPENBSD_THREADS
  #       include <sys/param.h>
  #       include <uvm/uvm_extern.h>
  #       define STACKBOTTOM ((ptr_t) USRSTACK)
  #     endif
        extern int __data_start[];
  #     define DATASTART ((ptr_t)__data_start)
        extern char _end[];
  #     define DATAEND ((ptr_t)(&_end))
  #     define DYNAMIC_LOADING
  #   endif
  #   ifdef FREEBSD
  #       if defined(__powerpc64__)
  #           define ALIGNMENT 8
  #           define CPP_WORDSZ 64
  #           ifndef HBLKSIZE
  #               define HBLKSIZE 4096
  #           endif
  #       else
  #           define ALIGNMENT 4
  #       endif
  #       define OS_TYPE "FREEBSD"
  #       ifndef GC_FREEBSD_THREADS
  #           define MPROTECT_VDB
  #       endif
  #       define SIG_SUSPEND SIGUSR1
  #       define SIG_THR_RESTART SIGUSR2
  #       define FREEBSD_STACKBOTTOM
  #       ifdef __ELF__
  #           define DYNAMIC_LOADING
  #       endif
          extern char etext[];
          ptr_t GC_FreeBSDGetDataStart(size_t, ptr_t);
  #       define DATASTART GC_FreeBSDGetDataStart(0x1000, (ptr_t)etext)
  #       define DATASTART_IS_FUNC
  #   endif
  #   ifdef NETBSD
  #     define ALIGNMENT 4
  #     define OS_TYPE "NETBSD"
  #     define HEURISTIC2
        extern ptr_t GC_data_start;
  #     define DATASTART GC_data_start
  #     define DYNAMIC_LOADING
  #   endif
  #   ifdef SN_TARGET_PS3
  #     define NO_GETENV
  #     define CPP_WORDSZ 32
  #     define ALIGNMENT 4
        extern int _end [];
        extern int __bss_start;
  #     define DATAEND (ptr_t)(_end)
  #     define DATASTART (ptr_t)(__bss_start)
  #     define STACKBOTTOM ((ptr_t)ps3_get_stack_bottom())
  #     define NO_PTHREAD_TRYLOCK
                  /* Current GC LOCK() implementation for PS3 explicitly  */
                  /* use pthread_mutex_lock for some reason.              */
  #   endif
  #   ifdef AIX
  #     define OS_TYPE "AIX"
  #     undef ALIGNMENT /* in case it's defined   */
  #     undef IA64
        /* DOB: some AIX installs stupidly define IA64 in */
        /* /usr/include/sys/systemcfg.h                   */
  #     ifdef __64BIT__
  #       define ALIGNMENT 8
  #       define CPP_WORDSZ 64
  #       define STACKBOTTOM ((ptr_t)0x1000000000000000)
  #     else
  #       define ALIGNMENT 4
  #       define CPP_WORDSZ 32
  #       define STACKBOTTOM ((ptr_t)((ulong)&errno))
  #     endif
  #     ifndef USE_MMAP
  #       define USE_MMAP
  #     endif
  #     define USE_MMAP_ANON
          /* From AIX linker man page:
          _text Specifies the first location of the program.
          _etext Specifies the first location after the program.
          _data Specifies the first location of the data.
          _edata Specifies the first location after the initialized data
          _end or end Specifies the first location after all data.
          */
        extern int _data[], _end[];
  #     define DATASTART ((ptr_t)((ulong)_data))
  #     define DATAEND ((ptr_t)((ulong)_end))
        extern int errno;
  #     define DYNAMIC_LOADING
          /* For really old versions of AIX, this may have to be removed. */
  #   endif
  
  #   ifdef NOSYS
  #     define ALIGNMENT 4
  #     define OS_TYPE "NOSYS"
        extern void __end[], __dso_handle[];
  #     define DATASTART (__dso_handle)  /* OK, that's ugly.  */
  #     define DATAEND (ptr_t)(__end)
          /* Stack starts at 0xE0000000 for the simulator.  */
  #     undef STACK_GRAN
  #     define STACK_GRAN 0x10000000
  #     define HEURISTIC1
  #   endif
  # endif
  
  # ifdef VAX
  #   define MACH_TYPE "VAX"
  #   define ALIGNMENT 4  /* Pointers are longword aligned by 4.2 C compiler */
      extern char etext[];
  #   define DATASTART ((ptr_t)(etext))
  #   ifdef BSD
  #       define OS_TYPE "BSD"
  #       define HEURISTIC1
                          /* HEURISTIC2 may be OK, but it's hard to test. */
  #   endif
  #   ifdef ULTRIX
  #       define OS_TYPE "ULTRIX"
  #       define STACKBOTTOM ((ptr_t) 0x7fffc800)
  #   endif
  # endif
  
  # ifdef SPARC
  #   define MACH_TYPE "SPARC"
  #   if defined(__arch64__) || defined(__sparcv9)
  #     define ALIGNMENT 8
  #     define CPP_WORDSZ 64
  #     define ELF_CLASS ELFCLASS64
  #   else
  #     define ALIGNMENT 4        /* Required by hardware */
  #     define CPP_WORDSZ 32
  #   endif
      /* Don't define USE_ASM_PUSH_REGS.  We do use an asm helper, but    */
      /* not to push the registers on the mark stack.                     */
  #   ifdef SOLARIS
  #       define OS_TYPE "SOLARIS"
          extern int _etext[];
          extern int _end[];
          ptr_t GC_SysVGetDataStart(size_t, ptr_t);
  #       define DATASTART GC_SysVGetDataStart(0x10000, (ptr_t)_etext)
  #       define DATASTART_IS_FUNC
  #       define DATAEND (ptr_t)(_end)
  #       if !defined(USE_MMAP) && defined(REDIRECT_MALLOC)
  #         define USE_MMAP
              /* Otherwise we now use calloc.  Mmap may result in the     */
              /* heap interleaved with thread stacks, which can result in */
              /* excessive blacklisting.  Sbrk is unusable since it       */
              /* doesn't interact correctly with the system malloc.       */
  #       endif
  #       ifdef USE_MMAP
  #         define HEAP_START (ptr_t)0x40000000
  #       else
  #         define HEAP_START DATAEND
  #       endif
  #       define PROC_VDB
  /*      HEURISTIC1 reportedly no longer works under 2.7.                */
  /*      HEURISTIC2 probably works, but this appears to be preferable.   */
  /*      Apparently USRSTACK is defined to be USERLIMIT, but in some     */
  /*      installations that's undefined.  We work around this with a     */
  /*      gross hack:                                                     */
  #       include <sys/vmparam.h>
  #       ifdef USERLIMIT
            /* This should work everywhere, but doesn't.  */
  #         define STACKBOTTOM ((ptr_t) USRSTACK)
  #       else
  #         define HEURISTIC2
  #       endif
  #       include <unistd.h>
  #       define GETPAGESIZE()  sysconf(_SC_PAGESIZE)
                  /* getpagesize() appeared to be missing from at least one */
                  /* Solaris 5.4 installation.  Weird.                      */
  #       define DYNAMIC_LOADING
  #   endif
  #   ifdef DRSNX
  #       define OS_TYPE "DRSNX"
          ptr_t GC_SysVGetDataStart(size_t, ptr_t);
          extern int etext[];
  #       define DATASTART GC_SysVGetDataStart(0x10000, (ptr_t)etext)
  #       define DATASTART_IS_FUNC
  #       define MPROTECT_VDB
  #       define STACKBOTTOM ((ptr_t) 0xdfff0000)
  #       define DYNAMIC_LOADING
  #   endif
  #   ifdef LINUX
  #     define OS_TYPE "LINUX"
  #     ifdef __ELF__
  #       define DYNAMIC_LOADING
  #     else
  #       error --> Linux SPARC a.out not supported
  #     endif
        extern int _end[];
        extern int _etext[];
  #     define DATAEND (ptr_t)(_end)
  #     define SVR4
        ptr_t GC_SysVGetDataStart(size_t, ptr_t);
  #     ifdef __arch64__
  #       define DATASTART GC_SysVGetDataStart(0x100000, (ptr_t)_etext)
  #     else
  #       define DATASTART GC_SysVGetDataStart(0x10000, (ptr_t)_etext)
  #     endif
  #     define DATASTART_IS_FUNC
  #     define LINUX_STACKBOTTOM
  #   endif
  #   ifdef OPENBSD
  #     define OS_TYPE "OPENBSD"
  #     ifndef GC_OPENBSD_THREADS
  #       include <sys/param.h>
  #       include <uvm/uvm_extern.h>
  #       define STACKBOTTOM ((ptr_t) USRSTACK)
  #     endif
        extern int __data_start[];
  #     define DATASTART ((ptr_t)__data_start)
        extern char _end[];
  #     define DATAEND ((ptr_t)(&_end))
  #     define DYNAMIC_LOADING
  #   endif
  #   ifdef NETBSD
  #     define OS_TYPE "NETBSD"
  #     define HEURISTIC2
  #     ifdef __ELF__
          extern ptr_t GC_data_start;
  #       define DATASTART GC_data_start
  #       define DYNAMIC_LOADING
  #     else
          extern char etext[];
  #       define DATASTART ((ptr_t)(etext))
  #     endif
  #   endif
  #   ifdef FREEBSD
  #       define OS_TYPE "FREEBSD"
  #       define SIG_SUSPEND SIGUSR1
  #       define SIG_THR_RESTART SIGUSR2
  #       define FREEBSD_STACKBOTTOM
  #       ifdef __ELF__
  #           define DYNAMIC_LOADING
  #       endif
          extern char etext[];
          extern char edata[];
          extern char end[];
  #       define NEED_FIND_LIMIT
  #       define DATASTART ((ptr_t)(&etext))
          ptr_t GC_find_limit(ptr_t, GC_bool);
  #       define DATAEND (GC_find_limit (DATASTART, TRUE))
  #       define DATAEND_IS_FUNC
  #       define DATASTART2 ((ptr_t)(&edata))
  #       define DATAEND2 ((ptr_t)(&end))
  #   endif
  # endif
  
  # ifdef I386
  #   define MACH_TYPE "I386"
  #   if defined(__LP64__) || defined(_WIN64)
  #     error This should be handled as X86_64
  #   else
  #     define CPP_WORDSZ 32
  #     define ALIGNMENT 4
                          /* Appears to hold for all "32 bit" compilers   */
                          /* except Borland.  The -a4 option fixes        */
                          /* Borland.  For Watcom the option is -zp4.     */
  #   endif
  #   ifdef SEQUENT
  #       define OS_TYPE "SEQUENT"
          extern int etext[];
  #       define DATASTART ((ptr_t)((((word) (etext)) + 0xfff) & ~0xfff))
  #       define STACKBOTTOM ((ptr_t) 0x3ffff000)
  #   endif
  #   ifdef BEOS
  #     define OS_TYPE "BEOS"
  #     include <OS.h>
  #     define GETPAGESIZE() B_PAGE_SIZE
        extern int etext[];
  #     define DATASTART ((ptr_t)((((word) (etext)) + 0xfff) & ~0xfff))
  #   endif
  #   ifdef SOLARIS
  #       define OS_TYPE "SOLARIS"
          extern int _etext[], _end[];
          ptr_t GC_SysVGetDataStart(size_t, ptr_t);
  #       define DATASTART GC_SysVGetDataStart(0x1000, (ptr_t)_etext)
  #       define DATASTART_IS_FUNC
  #       define DATAEND (ptr_t)(_end)
  /*      # define STACKBOTTOM ((ptr_t)(_start)) worked through 2.7,      */
  /*      but reportedly breaks under 2.8.  It appears that the stack     */
  /*      base is a property of the executable, so this should not break  */
  /*      old executables.                                                */
  /*      HEURISTIC2 probably works, but this appears to be preferable.   */
  #       include <sys/vm.h>
  #       define STACKBOTTOM ((ptr_t) USRSTACK)
  /* At least in Solaris 2.5, PROC_VDB gives wrong values for dirty bits. */
  /* It appears to be fixed in 2.8 and 2.9.                               */
  #       ifdef SOLARIS25_PROC_VDB_BUG_FIXED
  #         define PROC_VDB
  #       endif
  #       ifndef GC_THREADS
  #         define MPROTECT_VDB
  #       endif
  #       define DYNAMIC_LOADING
  #       if !defined(USE_MMAP) && defined(REDIRECT_MALLOC)
  #         define USE_MMAP
              /* Otherwise we now use calloc.  Mmap may result in the     */
              /* heap interleaved with thread stacks, which can result in */
              /* excessive blacklisting.  Sbrk is unusable since it       */
              /* doesn't interact correctly with the system malloc.       */
  #       endif
  #       ifdef USE_MMAP
  #         define HEAP_START (ptr_t)0x40000000
  #       else
  #         define HEAP_START DATAEND
  #       endif
  #   endif
  #   ifdef SCO
  #       define OS_TYPE "SCO"
          extern int etext[];
  #       define DATASTART ((ptr_t)((((word) (etext)) + 0x3fffff) \
                                    & ~0x3fffff) \
                                   +((word)etext & 0xfff))
  #       define STACKBOTTOM ((ptr_t) 0x7ffffffc)
  #   endif
  #   ifdef SCO_ELF
  #       define OS_TYPE "SCO_ELF"
          extern int etext[];
  #       define DATASTART ((ptr_t)(etext))
  #       define STACKBOTTOM ((ptr_t) 0x08048000)
  #       define DYNAMIC_LOADING
  #       define ELF_CLASS ELFCLASS32
  #   endif
  #   ifdef DGUX
  #       define OS_TYPE "DGUX"
          extern int _etext, _end;
          ptr_t GC_SysVGetDataStart(size_t, ptr_t);
  #       define DATASTART GC_SysVGetDataStart(0x1000, (ptr_t)(&_etext))
  #       define DATASTART_IS_FUNC
  #       define DATAEND (ptr_t)(&_end)
  #       define STACK_GROWS_DOWN
  #       define HEURISTIC2
  #       include <unistd.h>
  #       define GETPAGESIZE()  sysconf(_SC_PAGESIZE)
  #       define DYNAMIC_LOADING
  #       ifndef USE_MMAP
  #         define USE_MMAP
  #       endif
  #       define MAP_FAILED (void *) ((word)-1)
  #       ifdef USE_MMAP
  #         define HEAP_START (ptr_t)0x40000000
  #       else
  #         define HEAP_START DATAEND
  #       endif
  #   endif /* DGUX */
  
  #   ifdef NACL
  #      define OS_TYPE "NACL"
         extern int etext[];
  /* #define DATASTART ((ptr_t)((((word) (etext)) + 0xfff) & ~0xfff)) */
  #      define DATASTART ((ptr_t)0x10000000)
         extern int _end[];
  #      define DATAEND (_end)
  #      undef STACK_GRAN
  #      define STACK_GRAN 0x10000
  #      define HEURISTIC1
  #      define NO_PTHREAD_GETATTR_NP
  #      define GETPAGESIZE() 65536
  #      ifndef MAX_NACL_GC_THREADS
  #        define MAX_NACL_GC_THREADS 1024
  #      endif
  #   endif /* NACL */
  
  #   ifdef LINUX
  #       define OS_TYPE "LINUX"
  #       define LINUX_STACKBOTTOM
  #       if 0
  #         define HEURISTIC1
  #         undef STACK_GRAN
  #         define STACK_GRAN 0x10000000
            /* STACKBOTTOM is usually 0xc0000000, but this changes with   */
            /* different kernel configurations.  In particular, systems   */
            /* with 2GB physical memory will usually move the user        */
            /* address space limit, and hence initial SP to 0x80000000.   */
  #       endif
  #       if !defined(GC_LINUX_THREADS) || !defined(REDIRECT_MALLOC)
  #           define MPROTECT_VDB
  #       else
              /* We seem to get random errors in incremental mode,        */
              /* possibly because Linux threads is itself a malloc client */
              /* and can't deal with the signals.                         */
  #       endif
  #       define HEAP_START (ptr_t)0x1000
                  /* This encourages mmap to give us low addresses,       */
                  /* thus allowing the heap to grow to ~3GB               */
  #       ifdef __ELF__
  #            define DYNAMIC_LOADING
  #            ifdef UNDEFINED    /* includes ro data */
                 extern int _etext[];
  #              define DATASTART ((ptr_t)((((word) (_etext)) + 0xfff) & ~0xfff))
  #            endif
  #            include <features.h>
  #            if defined(__GLIBC__) && __GLIBC__ >= 2 \
                  || defined(PLATFORM_ANDROID)
  #                define SEARCH_FOR_DATA_START
  #            else
                   extern char **__environ;
  #                define DATASTART ((ptr_t)(&__environ))
                                /* hideous kludge: __environ is the first */
                                /* word in crt0.o, and delimits the start */
                                /* of the data segment, no matter which   */
                                /* ld options were passed through.        */
                                /* We could use _etext instead, but that  */
                                /* would include .rodata, which may       */
                                /* contain large read-only data tables    */
                                /* that we'd rather not scan.             */
  #            endif
               extern int _end[];
  #            define DATAEND (ptr_t)(_end)
  #            if defined(PLATFORM_ANDROID) && !defined(GC_NO_SIGSETJMP)
                 /* As of Android NDK r8b, _sigsetjmp is still missing    */
                 /* for x86 (setjmp is used instead to find data_start).  */
  #              define GC_NO_SIGSETJMP
  #            endif
  #       else
               extern int etext[];
  #            define DATASTART ((ptr_t)((((word) (etext)) + 0xfff) & ~0xfff))
  #       endif
  #       ifdef USE_I686_PREFETCH
  #         define PREFETCH(x) \
              __asm__ __volatile__ ("prefetchnta %0" : : "m"(*(char *)(x)))
              /* Empirically prefetcht0 is much more effective at reducing     */
              /* cache miss stalls for the targeted load instructions.  But it */
              /* seems to interfere enough with other cache traffic that the   */
              /* net result is worse than prefetchnta.                         */
  #         ifdef FORCE_WRITE_PREFETCH
              /* Using prefetches for write seems to have a slight negative    */
              /* impact on performance, at least for a PIII/500.               */
  #           define PREFETCH_FOR_WRITE(x) \
                __asm__ __volatile__ ("prefetcht0 %0" : : "m"(*(char *)(x)))
  #         else
  #           define NO_PREFETCH_FOR_WRITE
  #         endif
  #       elif defined(USE_3DNOW_PREFETCH)
  #         define PREFETCH(x) \
              __asm__ __volatile__ ("prefetch %0" : : "m"(*(char *)(x)))
  #         define PREFETCH_FOR_WRITE(x) \
              __asm__ __volatile__ ("prefetchw %0" : : "m"(*(char *)(x)))
  #       endif
  #   endif
  #   ifdef CYGWIN32
  #       define OS_TYPE "CYGWIN32"
  #       define DATASTART ((ptr_t)GC_DATASTART)  /* From gc.h */
  #       define DATAEND   ((ptr_t)GC_DATAEND)
  #       undef STACK_GRAN
  #       define STACK_GRAN 0x10000
  #       ifdef USE_MMAP
  #         define NEED_FIND_LIMIT
  #         define USE_MMAP_ANON
  #       endif
  #   endif
  #   ifdef OS2
  #       define OS_TYPE "OS2"
                  /* STACKBOTTOM and DATASTART are handled specially in   */
                  /* os_dep.c. OS2 actually has the right                 */
                  /* system call!                                         */
  #       define DATAEND  /* not needed */
  #   endif
  #   ifdef MSWIN32
  #       define OS_TYPE "MSWIN32"
                  /* STACKBOTTOM and DATASTART are handled specially in   */
                  /* os_dep.c.                                            */
  #       define MPROTECT_VDB
  #       define GWW_VDB
  #       define DATAEND  /* not needed */
  #   endif
  #   ifdef MSWINCE
  #       define OS_TYPE "MSWINCE"
  #       define DATAEND  /* not needed */
  #   endif
  #   ifdef DJGPP
  #       define OS_TYPE "DJGPP"
  #       include "stubinfo.h"
          extern int etext[];
          extern int _stklen;
          extern int __djgpp_stack_limit;
  #       define DATASTART ((ptr_t)((((word) (etext)) + 0x1ff) & ~0x1ff))
  /* #define STACKBOTTOM ((ptr_t)((word)_stubinfo+_stubinfo->size+_stklen)) */
  #       define STACKBOTTOM ((ptr_t)((word) __djgpp_stack_limit + _stklen))
                  /* This may not be right.  */
  #   endif
  #   ifdef OPENBSD
  #       define OS_TYPE "OPENBSD"
  #       ifndef GC_OPENBSD_THREADS
  #         include <sys/param.h>
  #         include <uvm/uvm_extern.h>
  #         define STACKBOTTOM ((ptr_t) USRSTACK)
  #       endif
          extern int __data_start[];
  #       define DATASTART ((ptr_t)__data_start)
          extern char _end[];
  #       define DATAEND ((ptr_t)(&_end))
  #       define DYNAMIC_LOADING
  #   endif
  #   ifdef FREEBSD
  #       define OS_TYPE "FREEBSD"
  #       ifndef GC_FREEBSD_THREADS
  #           define MPROTECT_VDB
  #       endif
  #       ifdef __GLIBC__
  #           define SIG_SUSPEND          (32+6)
  #           define SIG_THR_RESTART      (32+5)
              extern int _end[];
  #           define DATAEND (ptr_t)(_end)
  #       else
  #           define SIG_SUSPEND SIGUSR1
  #           define SIG_THR_RESTART SIGUSR2
                  /* SIGTSTP and SIGCONT could be used alternatively.     */
  #       endif
  #       define FREEBSD_STACKBOTTOM
  #       ifdef __ELF__
  #           define DYNAMIC_LOADING
  #       endif
          extern char etext[];
          char * GC_FreeBSDGetDataStart(size_t, ptr_t);
  #       define DATASTART GC_FreeBSDGetDataStart(0x1000, (ptr_t)etext)
  #       define DATASTART_IS_FUNC
  #   endif
  #   ifdef NETBSD
  #       define OS_TYPE "NETBSD"
  #       ifdef __ELF__
  #           define DYNAMIC_LOADING
  #       endif
  #   endif
  #   ifdef THREE86BSD
  #       define OS_TYPE "THREE86BSD"
  #   endif
  #   ifdef BSDI
  #       define OS_TYPE "BSDI"
  #   endif
  #   if defined(NETBSD) || defined(THREE86BSD) || defined(BSDI)
  #       define HEURISTIC2
          extern char etext[];
  #       define DATASTART ((ptr_t)(etext))
  #   endif
  #   ifdef NEXT
  #       define OS_TYPE "NEXT"
  #       define DATASTART ((ptr_t) get_etext())
  #       define DATASTART_IS_FUNC
  #       define STACKBOTTOM ((ptr_t)0xc0000000)
  #       define DATAEND  /* not needed */
  #   endif
  #   ifdef RTEMS
  #       define OS_TYPE "RTEMS"
  #       include <sys/unistd.h>
          extern int etext[];
          extern int end[];
          void *rtems_get_stack_bottom(void);
  #       define InitStackBottom rtems_get_stack_bottom()
  #       define DATASTART ((ptr_t)etext)
  #       define DATAEND ((ptr_t)end)
  #       define STACKBOTTOM ((ptr_t)InitStackBottom)
  #       define SIG_SUSPEND SIGUSR1
  #       define SIG_THR_RESTART SIGUSR2
  #   endif
  #   ifdef DOS4GW
  #     define OS_TYPE "DOS4GW"
        extern long __nullarea;
        extern char _end;
        extern char *_STACKTOP;
        /* Depending on calling conventions Watcom C either precedes      */
        /* or does not precedes with underscore names of C-variables.     */
        /* Make sure startup code variables always have the same names.   */
        #pragma aux __nullarea "*";
        #pragma aux _end "*";
  #     define STACKBOTTOM ((ptr_t) _STACKTOP)
                           /* confused? me too. */
  #     define DATASTART ((ptr_t) &__nullarea)
  #     define DATAEND ((ptr_t) &_end)
  #   endif
  #   ifdef HURD
  #     define OS_TYPE "HURD"
  #     define STACK_GROWS_DOWN
  #     define HEURISTIC2
  #     define SIG_SUSPEND SIGUSR1
  #     define SIG_THR_RESTART SIGUSR2
  #     define SEARCH_FOR_DATA_START
        extern int _end[];
  #     define DATAEND ((ptr_t) (_end))
  /* #     define MPROTECT_VDB  Not quite working yet? */
  #     define DYNAMIC_LOADING
  #   endif
  #   ifdef DARWIN
  #     define OS_TYPE "DARWIN"
  #     define DARWIN_DONT_PARSE_STACK
  #     define DYNAMIC_LOADING
        /* XXX: see get_end(3), get_etext() and get_end() should not be used. */
        /* These aren't used when dyld support is enabled (it is by default). */
  #     define DATASTART ((ptr_t) get_etext())
  #     define DATAEND   ((ptr_t) get_end())
  #     define STACKBOTTOM ((ptr_t) 0xc0000000)
  #     ifndef USE_MMAP
  #       define USE_MMAP
  #     endif
  #     define USE_MMAP_ANON
  #     define MPROTECT_VDB
  #     include <unistd.h>
  #     define GETPAGESIZE() getpagesize()
        /* There seems to be some issues with trylock hanging on darwin.  */
        /* This should be looked into some more.                          */
  #     define NO_PTHREAD_TRYLOCK
  #   endif /* DARWIN */
  # endif
  
  # ifdef NS32K
  #   define MACH_TYPE "NS32K"
  #   define ALIGNMENT 4
      extern char **environ;
  #   define DATASTART ((ptr_t)(&environ))
                                /* hideous kludge: environ is the first   */
                                /* word in crt0.o, and delimits the start */
                                /* of the data segment, no matter which   */
                                /* ld options were passed through.        */
  #   define STACKBOTTOM ((ptr_t) 0xfffff000) /* for Encore */
  # endif
  
  # ifdef MIPS
  #   define MACH_TYPE "MIPS"
  #   ifdef LINUX
  #     define OS_TYPE "LINUX"
  #     define DYNAMIC_LOADING
        extern int _end[];
  #     define DATAEND (ptr_t)(_end)
  #     pragma weak __data_start
        extern int __data_start[];
  #     define DATASTART ((ptr_t)(__data_start))
  #     ifdef _MIPS_SZPTR
  #       define CPP_WORDSZ _MIPS_SZPTR
  #       define ALIGNMENT (_MIPS_SZPTR/8)
  #     else
  #       define ALIGNMENT 4
  #     endif
  #     ifndef HBLKSIZE
  #       define HBLKSIZE 4096
  #     endif
  #     if __GLIBC__ == 2 && __GLIBC_MINOR__ >= 2 || __GLIBC__ > 2
  #       define LINUX_STACKBOTTOM
  #     else
  #       define STACKBOTTOM ((ptr_t)0x7fff8000)
  #     endif
  #   endif /* Linux */
  #   ifdef EWS4800
  #      define HEURISTIC2
  #      if defined(_MIPS_SZPTR) && (_MIPS_SZPTR == 64)
           extern int _fdata[], _end[];
  #        define DATASTART ((ptr_t)_fdata)
  #        define DATAEND ((ptr_t)_end)
  #        define CPP_WORDSZ _MIPS_SZPTR
  #        define ALIGNMENT (_MIPS_SZPTR/8)
  #      else
           extern int etext[], edata[], end[];
           extern int _DYNAMIC_LINKING[], _gp[];
  #        define DATASTART ((ptr_t)((((word)etext + 0x3ffff) & ~0x3ffff) \
                 + ((word)etext & 0xffff)))
  #        define DATAEND (ptr_t)(edata)
  #        define DATASTART2 (_DYNAMIC_LINKING \
                 ? (ptr_t)(((word)_gp + 0x8000 + 0x3ffff) & ~0x3ffff) \
                 : (ptr_t)edata)
  #        define DATAEND2 (ptr_t)(end)
  #        define ALIGNMENT 4
  #      endif
  #      define OS_TYPE "EWS4800"
  #   endif
  #   ifdef ULTRIX
  #       define HEURISTIC2
  #       define DATASTART (ptr_t)0x10000000
                                /* Could probably be slightly higher since */
                                /* startup code allocates lots of stuff.   */
  #       define OS_TYPE "ULTRIX"
  #       define ALIGNMENT 4
  #   endif
  #   ifdef IRIX5
  #       define HEURISTIC2
          extern int _fdata[];
  #       define DATASTART ((ptr_t)(_fdata))
  #       ifdef USE_MMAP
  #         define HEAP_START (ptr_t)0x30000000
  #       else
  #         define HEAP_START DATASTART
  #       endif
                                /* Lowest plausible heap address.         */
                                /* In the MMAP case, we map there.        */
                                /* In either case it is used to identify  */
                                /* heap sections so they're not           */
                                /* considered as roots.                   */
  #       define OS_TYPE "IRIX5"
  /*#       define MPROTECT_VDB DOB: this should work, but there is evidence */
  /*              of recent breakage.                                        */
  #       ifdef _MIPS_SZPTR
  #         define CPP_WORDSZ _MIPS_SZPTR
  #         define ALIGNMENT (_MIPS_SZPTR/8)
  #       else
  #         define ALIGNMENT 4
  #       endif
  #       define DYNAMIC_LOADING
  #   endif
  #   ifdef MSWINCE
  #       define OS_TYPE "MSWINCE"
  #       define ALIGNMENT 4
  #       define DATAEND /* not needed */
  #   endif
  #   if defined(NETBSD)
  #     define OS_TYPE "NETBSD"
  #     define ALIGNMENT 4
  #     define HEURISTIC2
  #     ifdef __ELF__
          extern ptr_t GC_data_start;
  #       define DATASTART GC_data_start
  #       define NEED_FIND_LIMIT
  #       define DYNAMIC_LOADING
  #     else
  #       define DATASTART ((ptr_t) 0x10000000)
  #       define STACKBOTTOM ((ptr_t) 0x7ffff000)
  #     endif /* _ELF_ */
  #  endif
  #  ifdef OPENBSD
  #    define OS_TYPE "OPENBSD"
  #    define ALIGNMENT 4
  #     ifndef GC_OPENBSD_THREADS
  #      include <sys/param.h>
  #      include <uvm/uvm_extern.h>
  #      define STACKBOTTOM ((ptr_t) USRSTACK)
  #    endif
       extern int _fdata[];
  #    define DATASTART ((ptr_t)_fdata)
       extern char _end[];
  #    define DATAEND ((ptr_t)(&_end))
  #    define DYNAMIC_LOADING
  #  endif
  #  if defined(NONSTOP)
  #    define CPP_WORDSZ 32
  #    define OS_TYPE "NONSTOP"
  #    define ALIGNMENT 4
  #    define DATASTART ((ptr_t) 0x08000000)
       extern char **environ;
  #    define DATAEND ((ptr_t)(environ - 0x10))
  #    define STACKBOTTOM ((ptr_t) 0x4fffffff)
  #   endif
  # endif
  
  # ifdef HP_PA
  #   define MACH_TYPE "HP_PA"
  #   ifdef __LP64__
  #     define CPP_WORDSZ 64
  #     define ALIGNMENT 8
  #   else
  #     define CPP_WORDSZ 32
  #     define ALIGNMENT 4
  #   endif
  #   if !defined(GC_HPUX_THREADS) && !defined(GC_LINUX_THREADS) \
         && !defined(OPENBSD) && !defined(LINUX) /* For now. */
  #     define MPROTECT_VDB
  #   endif
  #   define STACK_GROWS_UP
  #   ifdef HPUX
  #     define OS_TYPE "HPUX"
        extern int __data_start[];
  #     define DATASTART ((ptr_t)(__data_start))
  #     ifdef USE_HPUX_FIXED_STACKBOTTOM
          /* The following appears to work for 7xx systems running HP/UX  */
          /* 9.xx.  Furthermore, it might result in much faster           */
          /* collections than HEURISTIC2, which may involve scanning      */
          /* segments that directly precede the stack.  It is not the     */
          /* default, since it may not work on older machine/OS           */
          /* combinations. (Thanks to Raymond X.T. Nijssen for uncovering */
          /* this.)                                                       */
  #       define STACKBOTTOM ((ptr_t) 0x7b033000)  /* from /etc/conf/h/param.h */
  #     else
          /* Gustavo Rodriguez-Rivera suggested changing HEURISTIC2       */
          /* to this.  Note that the GC must be initialized before the    */
          /* first putenv call.                                           */
          extern char ** environ;
  #       define STACKBOTTOM ((ptr_t)environ)
  #     endif
  #     define DYNAMIC_LOADING
  #     include <unistd.h>
  #     define GETPAGESIZE() sysconf(_SC_PAGE_SIZE)
  #     ifndef __GNUC__
  #       define PREFETCH(x)  do { \
                                register long addr = (long)(x); \
                                (void) _asm ("LDW", 0, 0, addr, 0); \
                              } while (0)
  #     endif
  #   endif /* HPUX */
  #   ifdef LINUX
  #     define OS_TYPE "LINUX"
  #     define LINUX_STACKBOTTOM
  #     define DYNAMIC_LOADING
  #     define SEARCH_FOR_DATA_START
        extern int _end[];
  #     define DATAEND (ptr_t)(&_end)
  #   endif /* LINUX */
  #  ifdef OPENBSD
  #     define OS_TYPE "OPENBSD"
  #     ifndef GC_OPENBSD_THREADS
  #       include <sys/param.h>
  #       include <uvm/uvm_extern.h>
  #       define STACKBOTTOM ((ptr_t) USRSTACK)
  #     endif
        extern int __data_start[];
  #     define DATASTART ((ptr_t)__data_start)
        extern char _end[];
  #     define DATAEND ((ptr_t)(&_end))
  #     define DYNAMIC_LOADING
  #  endif
  # endif /* HP_PA */
  
  # ifdef ALPHA
  #   define MACH_TYPE "ALPHA"
  #   define ALIGNMENT 8
  #   define CPP_WORDSZ 64
  #   ifdef NETBSD
  #       define OS_TYPE "NETBSD"
  #       define HEURISTIC2
          extern ptr_t GC_data_start;
  #       define DATASTART GC_data_start
  #       define ELFCLASS32 32
  #       define ELFCLASS64 64
  #       define ELF_CLASS ELFCLASS64
  #       define DYNAMIC_LOADING
  #   endif
  #   ifdef OPENBSD
  #       define OS_TYPE "OPENBSD"
  #       define ELF_CLASS ELFCLASS64
  #       ifndef GC_OPENBSD_THREADS
  #         include <sys/param.h>
  #         include <uvm/uvm_extern.h>
  #         define STACKBOTTOM ((ptr_t) USRSTACK)
  #       endif
          extern int __data_start[];
  #       define DATASTART ((ptr_t)__data_start)
          extern char _end[];
  #       define DATAEND ((ptr_t)(&_end))
  #       define DYNAMIC_LOADING
  #   endif
  #   ifdef FREEBSD
  #       define OS_TYPE "FREEBSD"
  /* MPROTECT_VDB is not yet supported at all on FreeBSD/alpha. */
  #       define SIG_SUSPEND SIGUSR1
  #       define SIG_THR_RESTART SIGUSR2
                  /* SIGTSTP and SIGCONT could be used alternatively.     */
  #       define FREEBSD_STACKBOTTOM
  #       ifdef __ELF__
  #           define DYNAMIC_LOADING
  #       endif
  /* Handle unmapped hole alpha*-*-freebsd[45]* puts between etext and edata. */
          extern char etext[];
          extern char edata[];
          extern char end[];
  #       define NEED_FIND_LIMIT
  #       define DATASTART ((ptr_t)(&etext))
          ptr_t GC_find_limit(ptr_t, GC_bool);
  #       define DATAEND (GC_find_limit (DATASTART, TRUE))
  #       define DATAEND_IS_FUNC
  #       define DATASTART2 ((ptr_t)(&edata))
  #       define DATAEND2 ((ptr_t)(&end))
  #   endif
  #   ifdef OSF1
  #       define OS_TYPE "OSF1"
  #       define DATASTART ((ptr_t) 0x140000000)
          extern int _end[];
  #       define DATAEND ((ptr_t) &_end)
          extern char ** environ;
          /* round up from the value of environ to the nearest page boundary */
          /* Probably breaks if putenv is called before collector            */
          /* initialization.                                                 */
  #       define STACKBOTTOM ((ptr_t)(((word)(environ) | (getpagesize()-1))+1))
  /* #    define HEURISTIC2 */
          /* Normally HEURISTIC2 is too conservative, since               */
          /* the text segment immediately follows the stack.              */
          /* Hence we give an upper pound.                                */
          /* This is currently unused, since we disabled HEURISTIC2       */
          extern int __start[];
  #       define HEURISTIC2_LIMIT ((ptr_t)((word)(__start) & ~(getpagesize()-1)))
  #       ifndef GC_OSF1_THREADS
            /* Unresolved signal issues with threads.     */
  #         define MPROTECT_VDB
  #       endif
  #       define DYNAMIC_LOADING
  #   endif
  #   ifdef LINUX
  #       define OS_TYPE "LINUX"
  #       define LINUX_STACKBOTTOM
  #       ifdef __ELF__
  #         define SEARCH_FOR_DATA_START
  #         define DYNAMIC_LOADING
  #       else
  #           define DATASTART ((ptr_t) 0x140000000)
  #       endif
          extern int _end[];
  #       define DATAEND (ptr_t)(_end)
  #       define MPROTECT_VDB
                  /* Has only been superficially tested.  May not */
                  /* work on all versions.                        */
  #   endif
  # endif
  
  # ifdef IA64
  #   define MACH_TYPE "IA64"
  #   ifdef HPUX
  #       ifdef _ILP32
  #         define CPP_WORDSZ 32
              /* Requires 8 byte alignment for malloc */
  #         define ALIGNMENT 4
  #       else
  #         ifndef _LP64
  #           error --> unknown ABI
  #         endif
  #         define CPP_WORDSZ 64
              /* Requires 16 byte alignment for malloc */
  #         define ALIGNMENT 8
  #       endif
  #       define OS_TYPE "HPUX"
          extern int __data_start[];
  #       define DATASTART ((ptr_t)(__data_start))
          /* Gustavo Rodriguez-Rivera suggested changing HEURISTIC2       */
          /* to this.  Note that the GC must be initialized before the    */
          /* first putenv call.                                           */
          extern char ** environ;
  #       define STACKBOTTOM ((ptr_t)environ)
  #       define HPUX_STACKBOTTOM
  #       define DYNAMIC_LOADING
  #       include <unistd.h>
  #       define GETPAGESIZE() sysconf(_SC_PAGE_SIZE)
          /* The following was empirically determined, and is probably    */
          /* not very robust.                                             */
          /* Note that the backing store base seems to be at a nice       */
          /* address minus one page.                                      */
  #       define BACKING_STORE_DISPLACEMENT 0x1000000
  #       define BACKING_STORE_ALIGNMENT 0x1000
          extern ptr_t GC_register_stackbottom;
  #       define BACKING_STORE_BASE GC_register_stackbottom
          /* Known to be wrong for recent HP/UX versions!!!       */
  #   endif
  #   ifdef LINUX
  #       define CPP_WORDSZ 64
  #       define ALIGNMENT 8
  #       define OS_TYPE "LINUX"
          /* The following works on NUE and older kernels:        */
  /* #       define STACKBOTTOM ((ptr_t) 0xa000000000000000l)     */
          /* This does not work on NUE:                           */
  #       define LINUX_STACKBOTTOM
          /* We also need the base address of the register stack  */
          /* backing store.  This is computed in                  */
          /* GC_linux_register_stack_base based on the following  */
          /* constants:                                           */
  #       define BACKING_STORE_ALIGNMENT 0x100000
  #       define BACKING_STORE_DISPLACEMENT 0x80000000
          extern ptr_t GC_register_stackbottom;
  #       define BACKING_STORE_BASE GC_register_stackbottom
  #       define SEARCH_FOR_DATA_START
  #       ifdef __GNUC__
  #         define DYNAMIC_LOADING
  #       else
            /* In the Intel compiler environment, we seem to end up with  */
            /* statically linked executables and an undefined reference   */
            /* to _DYNAMIC                                                */
  #       endif
  #       define MPROTECT_VDB
                  /* Requires Linux 2.3.47 or later.      */
          extern int _end[];
  #       define DATAEND (ptr_t)(_end)
  #       ifdef __GNUC__
  #         ifndef __INTEL_COMPILER
  #           define PREFETCH(x) \
                __asm__ ("        lfetch  [%0]": : "r"(x))
  #           define PREFETCH_FOR_WRITE(x) \
                __asm__ ("        lfetch.excl     [%0]": : "r"(x))
  #           define CLEAR_DOUBLE(x) \
                __asm__ ("        stf.spill       [%0]=f0": : "r"((void *)(x)))
  #         else
  #           include <ia64intrin.h>
  #           define PREFETCH(x) __lfetch(__lfhint_none, (x))
  #           define PREFETCH_FOR_WRITE(x) __lfetch(__lfhint_nta, (x))
  #           define CLEAR_DOUBLE(x) __stf_spill((void *)(x), 0)
  #         endif /* __INTEL_COMPILER */
  #       endif
  #   endif
  #   ifdef CYGWIN32
  #       define OS_TYPE "CYGWIN32"
  #       define DATASTART ((ptr_t)GC_DATASTART)  /* From gc.h */
  #       define DATAEND   ((ptr_t)GC_DATAEND)
  #       undef STACK_GRAN
  #       define STACK_GRAN 0x10000
  #       ifdef USE_MMAP
  #         define NEED_FIND_LIMIT
  #         define USE_MMAP_ANON
  #       endif
  #   endif
  #   ifdef MSWIN32
        /* FIXME: This is a very partial guess.  There is no port, yet.   */
  #     define OS_TYPE "MSWIN32"
                  /* STACKBOTTOM and DATASTART are handled specially in   */
                  /* os_dep.c.                                            */
  #     define DATAEND  /* not needed */
  #     if defined(_WIN64)
  #       define CPP_WORDSZ 64
  #     else
  #       define CPP_WORDSZ 32   /* Is this possible?     */
  #     endif
  #     define ALIGNMENT 8
  #   endif
  # endif
  
  # ifdef M88K
  #   define MACH_TYPE "M88K"
  #   define ALIGNMENT 4
      extern int etext[];
  #   ifdef CX_UX
  #       define OS_TYPE "CX_UX"
  #       define DATASTART ((((word)etext + 0x3fffff) & ~0x3fffff) + 0x10000)
  #   endif
  #   ifdef  DGUX
  #       define OS_TYPE "DGUX"
          ptr_t GC_SysVGetDataStart(size_t, ptr_t);
  #       define DATASTART GC_SysVGetDataStart(0x10000, (ptr_t)etext)
  #       define DATASTART_IS_FUNC
  #   endif
  #   define STACKBOTTOM ((char*)0xf0000000) /* determined empirically */
  # endif
  
  # ifdef S370
      /* If this still works, and if anyone cares, this should probably   */
      /* be moved to the S390 category.                                   */
  #   define MACH_TYPE "S370"
  #   define ALIGNMENT 4  /* Required by hardware */
  #   ifdef UTS4
  #       define OS_TYPE "UTS4"
          extern int etext[];
          extern int _etext[];
          extern int _end[];
          ptr_t GC_SysVGetDataStart(size_t, ptr_t);
  #       define DATASTART GC_SysVGetDataStart(0x10000, (ptr_t)_etext)
  #       define DATASTART_IS_FUNC
  #       define DATAEND (ptr_t)(_end)
  #       define HEURISTIC2
  #   endif
  # endif
  
  # ifdef S390
  #   define MACH_TYPE "S390"
  #   ifndef __s390x__
  #   define ALIGNMENT 4
  #   define CPP_WORDSZ 32
  #   else
  #   define ALIGNMENT 8
  #   define CPP_WORDSZ 64
  #   ifndef HBLKSIZE
  #     define HBLKSIZE 4096
  #   endif
  #   endif
  #   ifdef LINUX
  #       define OS_TYPE "LINUX"
  #       define LINUX_STACKBOTTOM
  #       define DYNAMIC_LOADING
          extern int __data_start[] __attribute__((__weak__));
  #       define DATASTART ((ptr_t)(__data_start))
          extern int _end[] __attribute__((__weak__));
  #       define DATAEND (ptr_t)(_end)
  #       define CACHE_LINE_SIZE 256
  #       define GETPAGESIZE() 4096
  #   endif
  # endif
  
  # ifdef AARCH64
  #   define CPP_WORDSZ 64
  #   define MACH_TYPE "AARCH64"
  #   define ALIGNMENT 8
  #   ifndef HBLKSIZE
  #     define HBLKSIZE 4096
  #   endif
  #   ifdef LINUX
  #     define OS_TYPE "LINUX"
  #     define LINUX_STACKBOTTOM
  #     define DYNAMIC_LOADING
        extern int __data_start[];
  #     define DATASTART ((ptr_t)__data_start)
        extern char _end[];
  #     define DATAEND ((ptr_t)(&_end))
  #   endif
  #   ifdef DARWIN
        /* iOS */
  #     define OS_TYPE "DARWIN"
  #     ifndef GC_DONT_REGISTER_MAIN_STATIC_DATA
  #       define DYNAMIC_LOADING
  #     endif
  #     define DATASTART ((ptr_t) get_etext())
  #     define DATAEND   ((ptr_t) get_end())
  #     define STACKBOTTOM ((ptr_t) 0x16fdfffff)
  #     ifndef USE_MMAP
  #       define USE_MMAP
  #     endif
  #     define USE_MMAP_ANON
  #     define MPROTECT_VDB
  #     include <unistd.h>
  #     define GETPAGESIZE() getpagesize()
        /* FIXME: There seems to be some issues with trylock hanging on   */
        /* darwin. This should be looked into some more.                  */
  #     define NO_PTHREAD_TRYLOCK
  #     ifndef NO_DYLD_BIND_FULLY_IMAGE
  #       define NO_DYLD_BIND_FULLY_IMAGE
  #     endif
  #   endif
  #   ifdef NOSYS
        /* __data_start is usually defined in the target linker script.   */
        extern int __data_start[];
  #     define DATASTART ((ptr_t)__data_start)
        extern void *__stack_base__;
  #     define STACKBOTTOM ((ptr_t)__stack_base__)
  #   endif
  # endif
  
  # ifdef ARM32
  #   define CPP_WORDSZ 32
  #   define MACH_TYPE "ARM32"
  #   define ALIGNMENT 4
  #   ifdef NETBSD
  #       define OS_TYPE "NETBSD"
  #       define HEURISTIC2
  #       ifdef __ELF__
             extern ptr_t GC_data_start;
  #          define DATASTART GC_data_start
  #          define DYNAMIC_LOADING
  #       else
             extern char etext[];
  #          define DATASTART ((ptr_t)(etext))
  #       endif
  #   endif
  #   ifdef LINUX
  #       define OS_TYPE "LINUX"
  #       define LINUX_STACKBOTTOM
  #       undef STACK_GRAN
  #       define STACK_GRAN 0x10000000
  #       ifdef __ELF__
  #            define DYNAMIC_LOADING
  #            include <features.h>
  #            if defined(__GLIBC__) && __GLIBC__ >= 2 \
                  || defined(PLATFORM_ANDROID)
  #                define SEARCH_FOR_DATA_START
  #            else
                   extern char **__environ;
  #                define DATASTART ((ptr_t)(&__environ))
                                /* hideous kludge: __environ is the first */
                                /* word in crt0.o, and delimits the start */
                                /* of the data segment, no matter which   */
                                /* ld options were passed through.        */
                                /* We could use _etext instead, but that  */
                                /* would include .rodata, which may       */
                                /* contain large read-only data tables    */
                                /* that we'd rather not scan.             */
  #            endif
               extern int _end[];
  #            define DATAEND (ptr_t)(_end)
  #       else
               extern int etext[];
  #            define DATASTART ((ptr_t)((((word) (etext)) + 0xfff) & ~0xfff))
  #       endif
  #   endif
  #   ifdef MSWINCE
  #     define OS_TYPE "MSWINCE"
  #     define DATAEND /* not needed */
  #   endif
  #   ifdef FREEBSD
        /* FreeBSD/arm */
  #     define ALIGNMENT 4
  #     define OS_TYPE "FREEBSD"
  #     ifdef __ELF__
  #       define DYNAMIC_LOADING
  #     endif
  #     define HEURISTIC2
        extern char etext[];
  #     define SEARCH_FOR_DATA_START
  #   endif
  #   ifdef DARWIN
        /* iPhone */
  #     define OS_TYPE "DARWIN"
  #     ifndef GC_DONT_REGISTER_MAIN_STATIC_DATA
  #       define DYNAMIC_LOADING
  #     endif
  #     define DATASTART ((ptr_t) get_etext())
  #     define DATAEND   ((ptr_t) get_end())
  #     define STACKBOTTOM ((ptr_t) 0x30000000)
  #     ifndef USE_MMAP
  #       define USE_MMAP
  #     endif
  #     define USE_MMAP_ANON
  #     define MPROTECT_VDB
  #     include <unistd.h>
  #     define GETPAGESIZE() getpagesize()
        /* FIXME: There seems to be some issues with trylock hanging on   */
        /* darwin. This should be looked into some more.                  */
  #     define NO_PTHREAD_TRYLOCK
  #     ifndef NO_DYLD_BIND_FULLY_IMAGE
  #       define NO_DYLD_BIND_FULLY_IMAGE
  #     endif
  #   endif
  #   ifdef OPENBSD
  #     define ALIGNMENT 4
  #     define OS_TYPE "OPENBSD"
  #     ifndef GC_OPENBSD_THREADS
  #       include <sys/param.h>
  #       include <uvm/uvm_extern.h>
  #       define STACKBOTTOM ((ptr_t) USRSTACK)
  #     endif
        extern int __data_start[];
  #     define DATASTART ((ptr_t)__data_start)
        extern char _end[];
  #     define DATAEND ((ptr_t)(&_end))
  #     define DYNAMIC_LOADING
  #   endif
  #   ifdef NOSYS
        /* __data_start is usually defined in the target linker script.  */
        extern int __data_start[];
  #     define DATASTART (ptr_t)(__data_start)
        /* __stack_base__ is set in newlib/libc/sys/arm/crt0.S  */
        extern void *__stack_base__;
  #     define STACKBOTTOM ((ptr_t) (__stack_base__))
  #   endif
  #endif
  
  # ifdef CRIS
  #   define MACH_TYPE "CRIS"
  #   define CPP_WORDSZ 32
  #   define ALIGNMENT 1
  #   define OS_TYPE "LINUX"
  #   define DYNAMIC_LOADING
  #   define LINUX_STACKBOTTOM
  #   define SEARCH_FOR_DATA_START
        extern int _end[];
  #   define DATAEND (ptr_t)(_end)
  # endif
  
  # if defined(SH) && !defined(SH4)
  #   define MACH_TYPE "SH"
  #   define ALIGNMENT 4
  #   ifdef MSWINCE
  #     define OS_TYPE "MSWINCE"
  #     define DATAEND /* not needed */
  #   endif
  #   ifdef LINUX
  #     define OS_TYPE "LINUX"
  #     define LINUX_STACKBOTTOM
  #     define DYNAMIC_LOADING
  #     define SEARCH_FOR_DATA_START
        extern int _end[];
  #     define DATAEND (ptr_t)(_end)
  #   endif
  #   ifdef NETBSD
  #      define OS_TYPE "NETBSD"
  #      define HEURISTIC2
         extern ptr_t GC_data_start;
  #      define DATASTART GC_data_start
  #      define DYNAMIC_LOADING
  #   endif
  #   ifdef OPENBSD
  #      define OS_TYPE "OPENBSD"
  #      ifndef GC_OPENBSD_THREADS
  #        include <sys/param.h>
  #        include <uvm/uvm_extern.h>
  #        define STACKBOTTOM ((ptr_t) USRSTACK)
  #      endif
         extern int __data_start[];
  #      define DATASTART ((ptr_t)__data_start)
         extern char _end[];
  #      define DATAEND ((ptr_t)(&_end))
  #      define DYNAMIC_LOADING
  #   endif
  # endif
  
  # ifdef SH4
  #   define MACH_TYPE "SH4"
  #   define OS_TYPE "MSWINCE"
  #   define ALIGNMENT 4
  #   define DATAEND /* not needed */
  # endif
  
  # ifdef AVR32
  #   define MACH_TYPE "AVR32"
  #   define CPP_WORDSZ 32
  #   define ALIGNMENT 4
  #   define OS_TYPE "LINUX"
  #   define DYNAMIC_LOADING
  #   define LINUX_STACKBOTTOM
  #   define SEARCH_FOR_DATA_START
      extern int _end[];
  #   define DATAEND (_end)
  # endif
  
  # ifdef M32R
  #   define CPP_WORDSZ 32
  #   define MACH_TYPE "M32R"
  #   define ALIGNMENT 4
  #   ifdef LINUX
  #     define OS_TYPE "LINUX"
  #     define LINUX_STACKBOTTOM
  #     undef STACK_GRAN
  #     define STACK_GRAN 0x10000000
  #     define DYNAMIC_LOADING
  #     define SEARCH_FOR_DATA_START
        extern int _end[];
  #     define DATAEND (ptr_t)(_end)
  #   endif
  # endif
  
  # ifdef X86_64
  #   define MACH_TYPE "X86_64"
  #   ifdef __ILP32__
  #     define ALIGNMENT 4
  #     define CPP_WORDSZ 32
  #   else
  #     define ALIGNMENT 8
  #     define CPP_WORDSZ 64
  #   endif
  #   ifndef HBLKSIZE
  #     define HBLKSIZE 4096
  #   endif
  #   define CACHE_LINE_SIZE 64
  #   ifdef OPENBSD
  #       define OS_TYPE "OPENBSD"
  #       define ELF_CLASS ELFCLASS64
  #       ifndef GC_OPENBSD_THREADS
  #         include <sys/param.h>
  #         include <uvm/uvm_extern.h>
  #         define STACKBOTTOM ((ptr_t) USRSTACK)
  #       endif
          extern int __data_start[];
  #       define DATASTART ((ptr_t)__data_start)
          extern char _end[];
  #       define DATAEND ((ptr_t)(&_end))
  #       define DYNAMIC_LOADING
  #   endif
  #   ifdef LINUX
  #       define OS_TYPE "LINUX"
  #       define LINUX_STACKBOTTOM
  #       if !defined(GC_LINUX_THREADS) || !defined(REDIRECT_MALLOC)
  #           define MPROTECT_VDB
  #       else
              /* We seem to get random errors in incremental mode,        */
              /* possibly because Linux threads is itself a malloc client */
              /* and can't deal with the signals.                         */
  #       endif
  #       ifdef __ELF__
  #            define DYNAMIC_LOADING
  #            ifdef UNDEFINED    /* includes ro data */
                 extern int _etext[];
  #              define DATASTART ((ptr_t)((((word) (_etext)) + 0xfff) & ~0xfff))
  #            endif
  #            include <features.h>
  #            define SEARCH_FOR_DATA_START
               extern int _end[];
  #            define DATAEND (ptr_t)(_end)
  #       else
               extern int etext[];
  #            define DATASTART ((ptr_t)((((word) (etext)) + 0xfff) & ~0xfff))
  #       endif
  #       if defined(__GLIBC__) && !defined(__UCLIBC__)
            /* At present, there's a bug in GLibc getcontext() on         */
            /* Linux/x64 (it clears FPU exception mask).  We define this  */
            /* macro to workaround it.                                    */
            /* FIXME: This seems to be fixed in GLibc v2.14.              */
  #         define GETCONTEXT_FPU_EXCMASK_BUG
  #       endif
  #   endif
  #   ifdef DARWIN
  #     define OS_TYPE "DARWIN"
  #     define DARWIN_DONT_PARSE_STACK
  #     define DYNAMIC_LOADING
        /* XXX: see get_end(3), get_etext() and get_end() should not be used. */
        /* These aren't used when dyld support is enabled (it is by default)  */
  #     define DATASTART ((ptr_t) get_etext())
  #     define DATAEND   ((ptr_t) get_end())
  #     define STACKBOTTOM ((ptr_t) 0x7fff5fc00000)
  #     ifndef USE_MMAP
  #       define USE_MMAP
  #     endif
  #     define USE_MMAP_ANON
  #     define MPROTECT_VDB
  #     include <unistd.h>
  #     define GETPAGESIZE() getpagesize()
        /* There seems to be some issues with trylock hanging on darwin.  */
        /* This should be looked into some more.                          */
  #     define NO_PTHREAD_TRYLOCK
  #   endif
  #   ifdef FREEBSD
  #       define OS_TYPE "FREEBSD"
  #       ifndef GC_FREEBSD_THREADS
  #           define MPROTECT_VDB
  #       endif
  #       ifdef __GLIBC__
  #           define SIG_SUSPEND          (32+6)
  #           define SIG_THR_RESTART      (32+5)
              extern int _end[];
  #           define DATAEND (ptr_t)(_end)
  #       else
  #           define SIG_SUSPEND SIGUSR1
  #           define SIG_THR_RESTART SIGUSR2
                  /* SIGTSTP and SIGCONT could be used alternatively.     */
  #       endif
  #       define FREEBSD_STACKBOTTOM
  #       ifdef __ELF__
  #           define DYNAMIC_LOADING
  #       endif
          extern char etext[];
          ptr_t GC_FreeBSDGetDataStart(size_t, ptr_t);
  #       define DATASTART GC_FreeBSDGetDataStart(0x1000, (ptr_t)etext)
  #       define DATASTART_IS_FUNC
  #   endif
  #   ifdef NETBSD
  #       define OS_TYPE "NETBSD"
  #       define HEURISTIC2
  #       ifdef __ELF__
              extern ptr_t GC_data_start;
  #           define DATASTART GC_data_start
  #           define DYNAMIC_LOADING
  #       else
  #           define SEARCH_FOR_DATA_START
  #       endif
  #   endif
  #   ifdef SOLARIS
  #       define OS_TYPE "SOLARIS"
  #       define ELF_CLASS ELFCLASS64
          extern int _etext[], _end[];
          ptr_t GC_SysVGetDataStart(size_t, ptr_t);
  #       define DATASTART GC_SysVGetDataStart(0x1000, (ptr_t)_etext)
  #       define DATASTART_IS_FUNC
  #       define DATAEND (ptr_t)(_end)
  /*      # define STACKBOTTOM ((ptr_t)(_start)) worked through 2.7,      */
  /*      but reportedly breaks under 2.8.  It appears that the stack     */
  /*      base is a property of the executable, so this should not break  */
  /*      old executables.                                                */
  /*      HEURISTIC2 probably works, but this appears to be preferable.   */
  /*      Apparently USRSTACK is defined to be USERLIMIT, but in some     */
  /*      installations that's undefined.  We work around this with a     */
  /*      gross hack:                                                     */
  #       include <sys/vmparam.h>
  #       ifdef USERLIMIT
            /* This should work everywhere, but doesn't.  */
  #         define STACKBOTTOM ((ptr_t) USRSTACK)
  #       else
  #         define HEURISTIC2
  #       endif
  /* At least in Solaris 2.5, PROC_VDB gives wrong values for dirty bits. */
  /* It appears to be fixed in 2.8 and 2.9.                               */
  #       ifdef SOLARIS25_PROC_VDB_BUG_FIXED
  #         define PROC_VDB
  #       endif
  #       ifndef GC_THREADS
  #         define MPROTECT_VDB
  #       endif
  #       define DYNAMIC_LOADING
  #       if !defined(USE_MMAP) && defined(REDIRECT_MALLOC)
  #         define USE_MMAP
              /* Otherwise we now use calloc.  Mmap may result in the     */
              /* heap interleaved with thread stacks, which can result in */
              /* excessive blacklisting.  Sbrk is unusable since it       */
              /* doesn't interact correctly with the system malloc.       */
  #       endif
  #       ifdef USE_MMAP
  #         define HEAP_START (ptr_t)0x40000000
  #       else
  #         define HEAP_START DATAEND
  #       endif
  #   endif
  #   ifdef MSWIN32
  #       define OS_TYPE "MSWIN32"
                  /* STACKBOTTOM and DATASTART are handled specially in   */
                  /* os_dep.c.                                            */
  #       if !defined(__GNUC__) || defined(__INTEL_COMPILER)
            /* GCC does not currently support SetUnhandledExceptionFilter */
            /* (does not generate SEH unwinding information) on x64.      */
  #         define MPROTECT_VDB
  #       endif
  #       define GWW_VDB
  #       define DATAEND  /* not needed */
  #   endif
  # endif /* X86_64 */
  
  # ifdef HEXAGON
  #   define CPP_WORDSZ 32
  #   define MACH_TYPE "HEXAGON"
  #   define ALIGNMENT 4
  #   ifdef LINUX
  #       define OS_TYPE "LINUX"
  #       define LINUX_STACKBOTTOM
  #       define MPROTECT_VDB
  #       ifdef __ELF__
  #            define DYNAMIC_LOADING
  #            include <features.h>
  #            if defined(__GLIBC__) && __GLIBC__ >= 2
  #                define SEARCH_FOR_DATA_START
  #            else
  #                error --> unknown Hexagon libc configuration
  #            endif
               extern int _end[];
  #            define DATAEND (ptr_t)(_end)
  #       else
  #            error --> bad Hexagon Linux configuration
  #       endif
  #   else
  #       error --> unknown Hexagon OS configuration
  #   endif
  # endif
  
  #if defined(__GLIBC__) && !defined(DONT_USE_LIBC_PRIVATES)
    /* Use glibc's stack-end marker. */
  # define USE_LIBC_PRIVATES
  #endif
  
  #if defined(LINUX_STACKBOTTOM) && defined(NO_PROC_STAT) \
      && !defined(USE_LIBC_PRIVATES)
      /* This combination will fail, since we have no way to get  */
      /* the stack base.  Use HEURISTIC2 instead.                 */
  #   undef LINUX_STACKBOTTOM
  #   define HEURISTIC2
      /* This may still fail on some architectures like IA64.     */
      /* We tried ...                                             */
  #endif
  
  #if defined(LINUX) && defined(USE_MMAP)
      /* The kernel may do a somewhat better job merging mappings etc.    */
      /* with anonymous mappings.                                         */
  #   define USE_MMAP_ANON
  #endif
  
  #if defined(GC_LINUX_THREADS) && defined(REDIRECT_MALLOC) \
      && !defined(USE_PROC_FOR_LIBRARIES)
      /* Nptl allocates thread stacks with mmap, which is fine.  But it   */
      /* keeps a cache of thread stacks.  Thread stacks contain the       */
      /* thread control blocks.  These in turn contain a pointer to       */
      /* (sizeof (void *) from the beginning of) the dtv for thread-local */
      /* storage, which is calloc allocated.  If we don't scan the cached */
      /* thread stacks, we appear to lose the dtv.  This tends to         */
      /* result in something that looks like a bogus dtv count, which     */
      /* tends to result in a memset call on a block that is way too      */
      /* large.  Sometimes we're lucky and the process just dies ...      */
      /* There seems to be a similar issue with some other memory         */
      /* allocated by the dynamic loader.                                 */
      /* This should be avoidable by either:                              */
      /* - Defining USE_PROC_FOR_LIBRARIES here.                          */
      /*   That performs very poorly, precisely because we end up         */
      /*   scanning cached stacks.                                        */
      /* - Have calloc look at its callers.                               */
      /*   In spite of the fact that it is gross and disgusting.          */
      /* In fact neither seems to suffice, probably in part because       */
      /* even with USE_PROC_FOR_LIBRARIES, we don't scan parts of stack   */
      /* segments that appear to be out of bounds.  Thus we actually      */
      /* do both, which seems to yield the best results.                  */
  
  #   define USE_PROC_FOR_LIBRARIES
  #endif
  
  #ifndef STACK_GROWS_UP
  # define STACK_GROWS_DOWN
  #endif
  
  #ifndef CPP_WORDSZ
  # define CPP_WORDSZ 32
  #endif
  
  #ifndef OS_TYPE
  # define OS_TYPE ""
  #endif
  
  #ifndef DATAEND
    extern int end[];
  # define DATAEND (ptr_t)(end)
  #endif
  
  #if defined(PLATFORM_ANDROID) && !defined(THREADS) \
      && !defined(USE_GET_STACKBASE_FOR_MAIN)
    /* Always use pthread_attr_getstack on Android ("-lpthread" option is  */
    /* not needed to be specified manually) since GC_linux_main_stack_base */
    /* causes app crash if invoked inside Dalvik VM.                       */
  # define USE_GET_STACKBASE_FOR_MAIN
  #endif
  
  #if (defined(SVR4) || defined(PLATFORM_ANDROID)) && !defined(GETPAGESIZE)
  # include <unistd.h>
  # define GETPAGESIZE()  sysconf(_SC_PAGESIZE)
  #endif
  
  #ifndef GETPAGESIZE
  # if defined(SOLARIS) || defined(IRIX5) || defined(LINUX) \
       || defined(NETBSD) || defined(FREEBSD) || defined(HPUX)
  #   include <unistd.h>
  # endif
  # define GETPAGESIZE() getpagesize()
  #endif
  
  #if defined(SOLARIS) || defined(DRSNX) || defined(UTS4)
          /* OS has SVR4 generic features.        */
          /* Probably others also qualify.        */
  # define SVR4
  #endif
  
  #if defined(SOLARIS) || defined(DRSNX)
          /* OS has SOLARIS style semi-undocumented interface     */
          /* to dynamic loader.                                   */
  # define SOLARISDL
          /* OS has SOLARIS style signal handlers.        */
  # define SUNOS5SIGS
  #endif
  
  #if defined(HPUX)
  # define SUNOS5SIGS
  #endif
  
  #if defined(FREEBSD) && (defined(__DragonFly__) || __FreeBSD__ >= 4 \
                           || (__FreeBSD_kernel__ >= 4))
  # define SUNOS5SIGS
  #endif
  
  #if !defined(GC_EXPLICIT_SIGNALS_UNBLOCK) && defined(SUNOS5SIGS) \
      && !defined(GC_NO_PTHREAD_SIGMASK)
  # define GC_EXPLICIT_SIGNALS_UNBLOCK
  #endif
  
  #if !defined(NO_MARKER_SPECIAL_SIGMASK) \
      && (defined(NACL) || defined(GC_WIN32_PTHREADS))
    /* Either there is no pthread_sigmask(), or GC marker thread cannot   */
    /* steal and drop user signal calls.                                  */
  # define NO_MARKER_SPECIAL_SIGMASK
  #endif
  
  #ifdef GC_NETBSD_THREADS
  # define SIGRTMIN 33
  # define SIGRTMAX 63
  #endif
  
  #ifdef GC_OPENBSD_THREADS
  # include <sys/param.h>
    /* Prior to 5.2 release, OpenBSD had user threads and required        */
    /* special handling.                                                  */
  # if OpenBSD < 201211
  #   define GC_OPENBSD_UTHREADS 1
  # endif
  #endif /* GC_OPENBSD_THREADS */
  
  #if defined(SVR4) || defined(LINUX) || defined(IRIX5) || defined(HPUX) \
      || defined(OPENBSD) || defined(NETBSD) || defined(FREEBSD) \
      || defined(DGUX) || defined(BSD) || defined(HURD) \
      || defined(AIX) || defined(DARWIN) || defined(OSF1)
  # define UNIX_LIKE      /* Basic Unix-like system calls work.   */
  #endif
  
  #if CPP_WORDSZ != 32 && CPP_WORDSZ != 64
  # error --> bad word size
  #endif
  
  #ifndef ALIGNMENT
  # error --> undefined ALIGNMENT
  #endif
  
  #ifdef PCR
  # undef DYNAMIC_LOADING
  # undef STACKBOTTOM
  # undef HEURISTIC1
  # undef HEURISTIC2
  # undef PROC_VDB
  # undef MPROTECT_VDB
  # define PCR_VDB
  #endif
  
  #if !defined(STACKBOTTOM) && (defined(ECOS) || defined(NOSYS))
  # error --> undefined STACKBOTTOM
  #endif
  
  #ifdef IGNORE_DYNAMIC_LOADING
  # undef DYNAMIC_LOADING
  #endif
  
  #if defined(SMALL_CONFIG) && !defined(GC_DISABLE_INCREMENTAL)
    /* Presumably not worth the space it takes.   */
  # define GC_DISABLE_INCREMENTAL
  #endif
  
  #if (defined(MSWIN32) || defined(MSWINCE)) && !defined(USE_WINALLOC)
    /* USE_WINALLOC is only an option for Cygwin. */
  # define USE_WINALLOC
  #endif
  
  #ifdef USE_WINALLOC
  # undef USE_MMAP
  #endif
  
  #if defined(LINUX) || defined(FREEBSD) || defined(SOLARIS) || defined(IRIX5) \
      || ((defined(USE_MMAP) || defined(USE_MUNMAP)) && !defined(USE_WINALLOC))
  # define MMAP_SUPPORTED
  #endif
  
  #if defined(GC_DISABLE_INCREMENTAL) || defined(MANUAL_VDB)
  # undef GWW_VDB
  # undef MPROTECT_VDB
  # undef PCR_VDB
  # undef PROC_VDB
  #endif
  
  #ifdef GC_DISABLE_INCREMENTAL
  # undef CHECKSUMS
  #endif
  
  #ifdef USE_GLOBAL_ALLOC
    /* Cannot pass MEM_WRITE_WATCH to GlobalAlloc().      */
  # undef GWW_VDB
  #endif
  
  #ifdef USE_MUNMAP
    /* FIXME: Remove this undef if possible.      */
  # undef MPROTECT_VDB  /* Can't deal with address space holes.   */
  #endif
  
  /* PARALLEL_MARK does not cause undef MPROTECT_VDB any longer.  */
  
  #if defined(MPROTECT_VDB) && defined(GC_PREFER_MPROTECT_VDB)
    /* Choose MPROTECT_VDB manually (if multiple strategies available).   */
  # undef PCR_VDB
  # undef PROC_VDB
    /* #undef GWW_VDB - handled in os_dep.c       */
  #endif
  
  #ifdef PROC_VDB
    /* Multi-VDB mode is not implemented. */
  # undef MPROTECT_VDB
  #endif
  
  #if !defined(PCR_VDB) && !defined(PROC_VDB) && !defined(MPROTECT_VDB) \
      && !defined(GWW_VDB) && !defined(MANUAL_VDB) \
      && !defined(GC_DISABLE_INCREMENTAL)
  # define DEFAULT_VDB
  #endif
  
  #if ((defined(UNIX_LIKE) && (defined(DARWIN) || defined(HURD) \
                               || defined(OPENBSD) || defined(ARM32) \
                               || defined(MIPS) || defined(AVR32))) \
       || (defined(LINUX) && (defined(SPARC) || defined(M68K))) \
       || ((defined(RTEMS) || defined(PLATFORM_ANDROID)) && defined(I386))) \
      && !defined(NO_GETCONTEXT)
  # define NO_GETCONTEXT
  #endif
  
  #ifndef PREFETCH
  # if defined(__GNUC__) && __GNUC__ >= 3 && !defined(NO_PREFETCH)
  #   define PREFETCH(x) __builtin_prefetch((x), 0, 0)
  # else
  #   define PREFETCH(x) (void)0
  # endif
  #endif
  
  #ifndef PREFETCH_FOR_WRITE
  # if defined(__GNUC__) && __GNUC__ >= 3 && !defined(NO_PREFETCH_FOR_WRITE)
  #   define PREFETCH_FOR_WRITE(x) __builtin_prefetch((x), 1)
  # else
  #   define PREFETCH_FOR_WRITE(x) (void)0
  # endif
  #endif
  
  #ifndef CACHE_LINE_SIZE
  # define CACHE_LINE_SIZE 32     /* Wild guess   */
  #endif
  
  #ifndef STATIC
  # ifndef NO_DEBUGGING
  #   define STATIC /* ignore to aid profiling and possibly debugging     */
  # else
  #   define STATIC static
  # endif
  #endif
  
  #if defined(LINUX) && (defined(USE_PROC_FOR_LIBRARIES) || defined(IA64) \
                         || !defined(SMALL_CONFIG))
  # define NEED_PROC_MAPS
  #endif
  
  #if defined(LINUX) || defined(HURD) || defined(__GLIBC__)
  # define REGISTER_LIBRARIES_EARLY
    /* We sometimes use dl_iterate_phdr, which may acquire an internal    */
    /* lock.  This isn't safe after the world has stopped.  So we must    */
    /* call GC_register_dynamic_libraries before stopping the world.      */
    /* For performance reasons, this may be beneficial on other           */
    /* platforms as well, though it should be avoided in win32.           */
  #endif /* LINUX */
  
  #if defined(SEARCH_FOR_DATA_START)
    extern ptr_t GC_data_start;
  # define DATASTART GC_data_start
  #endif
  
  #ifndef CLEAR_DOUBLE
  # define CLEAR_DOUBLE(x) (((word*)(x))[0] = 0, ((word*)(x))[1] = 0)
  #endif
  
  #if defined(GC_LINUX_THREADS) && defined(REDIRECT_MALLOC) \
      && !defined(INCLUDE_LINUX_THREAD_DESCR)
    /* Will not work, since libc and the dynamic loader use thread        */
    /* locals, sometimes as the only reference.                           */
  # define INCLUDE_LINUX_THREAD_DESCR
  #endif
  
  #if defined(GC_IRIX_THREADS) && !defined(IRIX5)
  # error --> inconsistent configuration
  #endif
  #if defined(GC_LINUX_THREADS) && !defined(LINUX) && !defined(NACL)
  # error --> inconsistent configuration
  #endif
  #if defined(GC_NETBSD_THREADS) && !defined(NETBSD)
  # error --> inconsistent configuration
  #endif
  #if defined(GC_FREEBSD_THREADS) && !defined(FREEBSD)
  # error --> inconsistent configuration
  #endif
  #if defined(GC_SOLARIS_THREADS) && !defined(SOLARIS)
  # error --> inconsistent configuration
  #endif
  #if defined(GC_HPUX_THREADS) && !defined(HPUX)
  # error --> inconsistent configuration
  #endif
  #if defined(GC_AIX_THREADS) && !defined(_AIX)
  # error --> inconsistent configuration
  #endif
  #if defined(GC_GNU_THREADS) && !defined(HURD)
  # error --> inconsistent configuration
  #endif
  #if defined(GC_WIN32_THREADS) && !defined(MSWIN32) && !defined(CYGWIN32) \
      && !defined(MSWINCE)
  # error --> inconsistent configuration
  #endif
  
  #if defined(PCR) || defined(GC_WIN32_THREADS) || defined(GC_PTHREADS) \
      || defined(SN_TARGET_PS3)
  # define THREADS
  #endif
  
  #if defined(PARALLEL_MARK) && !defined(THREADS)
  # error "invalid config - PARALLEL_MARK requires GC_THREADS"
  #endif
  
  #if defined(UNIX_LIKE) && defined(THREADS) && !defined(NO_CANCEL_SAFE) \
      && !defined(PLATFORM_ANDROID)
    /* Make the code cancellation-safe.  This basically means that we     */
    /* ensure that cancellation requests are ignored while we are in      */
    /* the collector.  This applies only to Posix deferred cancellation;  */
    /* we don't handle Posix asynchronous cancellation.                   */
    /* Note that this only works if pthread_setcancelstate is             */
    /* async-signal-safe, at least in the absence of asynchronous         */
    /* cancellation.  This appears to be true for the glibc version,      */
    /* though it is not documented.  Without that assumption, there       */
    /* seems to be no way to safely wait in a signal handler, which       */
    /* we need to do for thread suspension.                               */
    /* Also note that little other code appears to be cancellation-safe.  */
    /* Hence it may make sense to turn this off for performance.          */
  # define CANCEL_SAFE
  #endif
  
  #ifdef CANCEL_SAFE
  # define IF_CANCEL(x) x
  #else
  # define IF_CANCEL(x) /* empty */
  #endif
  
  #if !defined(CAN_HANDLE_FORK) && !defined(NO_HANDLE_FORK) \
      && !defined(HAVE_NO_FORK) \
      && ((defined(GC_PTHREADS) && !defined(NACL) \
           && !defined(GC_WIN32_PTHREADS) && !defined(USE_WINALLOC)) \
          || (defined(DARWIN) && defined(MPROTECT_VDB)) || defined(HANDLE_FORK))
    /* Attempts (where supported and requested) to make GC_malloc work in */
    /* a child process fork'ed from a multi-threaded parent.              */
  # define CAN_HANDLE_FORK
  #endif
  
  #if defined(CAN_HANDLE_FORK) && !defined(CAN_CALL_ATFORK) \
      && !defined(HURD) && !defined(PLATFORM_ANDROID)
    /* Have working pthread_atfork().     */
  # define CAN_CALL_ATFORK
  #endif
  
  #if !defined(CAN_HANDLE_FORK) && !defined(HAVE_NO_FORK) \
      && (defined(MSWIN32) || defined(MSWINCE) || defined(DOS4GW) \
          || defined(OS2) || defined(SYMBIAN) /* and probably others ... */)
  # define HAVE_NO_FORK
  #endif
  
  #if !defined(USE_MARK_BITS) && !defined(USE_MARK_BYTES) \
      && defined(PARALLEL_MARK)
     /* Minimize compare-and-swap usage.  */
  #  define USE_MARK_BYTES
  #endif
  
  #if defined(MSWINCE) && !defined(__CEGCC__) && !defined(NO_GETENV)
  # define NO_GETENV
  #endif
  
  #if (defined(NO_GETENV) || defined(MSWINCE)) && !defined(NO_GETENV_WIN32)
  # define NO_GETENV_WIN32
  #endif
  
  #ifndef STRTOULL
  # if defined(_WIN64) && !defined(__GNUC__)
  #   define STRTOULL _strtoui64
  # elif defined(_LLP64) || defined(__LLP64__) || defined(_WIN64)
  #   define STRTOULL strtoull
  # else
      /* strtoul() fits since sizeof(long) >= sizeof(word).       */
  #   define STRTOULL strtoul
  # endif
  #endif /* !STRTOULL */
  
  #ifndef GC_WORD_C
  # if defined(_WIN64) && !defined(__GNUC__)
  #   define GC_WORD_C(val) val##ui64
  # elif defined(_LLP64) || defined(__LLP64__) || defined(_WIN64)
  #   define GC_WORD_C(val) val##ULL
  # else
  #   define GC_WORD_C(val) ((word)val##UL)
  # endif
  #endif /* !GC_WORD_C */
  
  #if defined(SPARC)
  # define ASM_CLEAR_CODE /* Stack clearing is crucial, and we    */
                          /* include assembly code to do it well. */
  #endif
  
  /* Can we save call chain in objects for debugging?                     */
  /* SET NFRAMES (# of saved frames) and NARGS (#of args for each         */
  /* frame) to reasonable values for the platform.                        */
  /* Set SAVE_CALL_CHAIN if we can.  SAVE_CALL_COUNT can be specified     */
  /* at build time, though we feel free to adjust it slightly.            */
  /* Define NEED_CALLINFO if we either save the call stack or             */
  /* GC_ADD_CALLER is defined.                                            */
  /* GC_CAN_SAVE_CALL_STACKS is set in gc.h.                              */
  #if defined(SPARC)
  # define CAN_SAVE_CALL_ARGS
  #endif
  #if (defined(I386) || defined(X86_64)) \
      && (defined(LINUX) || defined(__GLIBC__))
    /* SAVE_CALL_CHAIN is supported if the code is compiled to save       */
    /* frame pointers by default, i.e. no -fomit-frame-pointer flag.      */
  # define CAN_SAVE_CALL_ARGS
  #endif
  
  #if defined(SAVE_CALL_COUNT) && !defined(GC_ADD_CALLER) \
      && defined(GC_CAN_SAVE_CALL_STACKS)
  # define SAVE_CALL_CHAIN
  #endif
  #ifdef SAVE_CALL_CHAIN
  # if defined(SAVE_CALL_NARGS) && defined(CAN_SAVE_CALL_ARGS)
  #   define NARGS SAVE_CALL_NARGS
  # else
  #   define NARGS 0      /* Number of arguments to save for each call.   */
  # endif
  #endif
  #ifdef SAVE_CALL_CHAIN
  # ifndef SAVE_CALL_COUNT
  #   define NFRAMES 6    /* Number of frames to save. Even for   */
                          /* alignment reasons.                   */
  # else
  #   define NFRAMES ((SAVE_CALL_COUNT + 1) & ~1)
  # endif
  # define NEED_CALLINFO
  #endif /* SAVE_CALL_CHAIN */
  #ifdef GC_ADD_CALLER
  # define NFRAMES 1
  # define NARGS 0
  # define NEED_CALLINFO
  #endif
  
  #if (defined(FREEBSD) || (defined(DARWIN) && !defined(_POSIX_C_SOURCE)) \
          || (defined(SOLARIS) && (!defined(_XOPEN_SOURCE) \
                                   || defined(__EXTENSIONS__))) \
          || defined(LINUX)) && !defined(HAVE_DLADDR)
  # define HAVE_DLADDR
  #endif
  
  #if defined(MAKE_BACK_GRAPH) && !defined(DBG_HDRS_ALL)
  # define DBG_HDRS_ALL
  #endif
  
  #if defined(POINTER_MASK) && !defined(POINTER_SHIFT)
  # define POINTER_SHIFT 0
  #endif
  
  #if defined(POINTER_SHIFT) && !defined(POINTER_MASK)
  # define POINTER_MASK ((GC_word)(-1))
  #endif
  
  #if !defined(FIXUP_POINTER) && defined(POINTER_MASK)
  # define FIXUP_POINTER(p) (p = ((p) & POINTER_MASK) << POINTER_SHIFT)
  #endif
  
  #if defined(FIXUP_POINTER)
  # define NEED_FIXUP_POINTER 1
  #else
  # define NEED_FIXUP_POINTER 0
  # define FIXUP_POINTER(p)
  #endif
  
  #if !defined(MARK_BIT_PER_GRANULE) && !defined(MARK_BIT_PER_OBJ)
  # define MARK_BIT_PER_GRANULE   /* Usually faster       */
  #endif
  
  /* Some static sanity tests.    */
  #if defined(MARK_BIT_PER_GRANULE) && defined(MARK_BIT_PER_OBJ)
  # error Define only one of MARK_BIT_PER_GRANULE and MARK_BIT_PER_OBJ.
  #endif
  
  #if defined(STACK_GROWS_UP) && defined(STACK_GROWS_DOWN)
  # error "Only one of STACK_GROWS_UP and STACK_GROWS_DOWN should be defd."
  #endif
  #if !defined(STACK_GROWS_UP) && !defined(STACK_GROWS_DOWN)
  # error "One of STACK_GROWS_UP and STACK_GROWS_DOWN should be defd."
  #endif
  
  #if defined(REDIRECT_MALLOC) && defined(THREADS) && !defined(LINUX)
  # error "REDIRECT_MALLOC with THREADS works at most on Linux."
  #endif
  
  #ifdef GC_PRIVATE_H
          /* This relies on some type definitions from gc_priv.h, from    */
          /* where it's normally included.                                */
          /*                                                              */
          /* How to get heap memory from the OS:                          */
          /* Note that sbrk()-like allocation is preferred, since it      */
          /* usually makes it possible to merge consecutively allocated   */
          /* chunks.  It also avoids unintended recursion with            */
          /* REDIRECT_MALLOC macro defined.                               */
          /* GET_MEM() returns a HLKSIZE aligned chunk.                   */
          /* 0 is taken to mean failure.                                  */
          /* In case of MMAP_SUPPORTED, the argument must also be         */
          /* a multiple of a physical page size.                          */
          /* GET_MEM is currently not assumed to retrieve 0 filled space, */
          /* though we should perhaps take advantage of the case in which */
          /* does.                                                        */
          struct hblk;    /* See gc_priv.h.       */
  # if defined(PCR)
      char * real_malloc(size_t bytes);
  #   define GET_MEM(bytes) HBLKPTR(real_malloc((size_t)(bytes) + GC_page_size) \
                                            + GC_page_size-1)
  # elif defined(OS2)
      void * os2_alloc(size_t bytes);
  #   define GET_MEM(bytes) HBLKPTR((ptr_t)os2_alloc((size_t)(bytes) \
                                              + GC_page_size) + GC_page_size-1)
  # elif defined(NEXT) || defined(DOS4GW) || defined(NONSTOP) \
          || (defined(AMIGA) && !defined(GC_AMIGA_FASTALLOC)) \
          || (defined(SOLARIS) && !defined(USE_MMAP)) || defined(RTEMS) \
          || defined(__CC_ARM)
  #   define GET_MEM(bytes) HBLKPTR((size_t)calloc(1, \
                                              (size_t)(bytes) + GC_page_size) \
                                    + GC_page_size - 1)
  # elif defined(MSWIN32) || defined(CYGWIN32)
      ptr_t GC_win32_get_mem(GC_word bytes);
  #   define GET_MEM(bytes) (struct hblk *)GC_win32_get_mem(bytes)
  # elif defined(MACOS)
  #   if defined(USE_TEMPORARY_MEMORY)
        Ptr GC_MacTemporaryNewPtr(size_t size, Boolean clearMemory);
  #     define GET_MEM(bytes) HBLKPTR( \
                          GC_MacTemporaryNewPtr((bytes) + GC_page_size, true) \
                          + GC_page_size-1)
  #   else
  #     define GET_MEM(bytes) HBLKPTR(NewPtrClear((bytes) + GC_page_size) \
                                      + GC_page_size-1)
  #   endif
  # elif defined(MSWINCE)
      ptr_t GC_wince_get_mem(GC_word bytes);
  #   define GET_MEM(bytes) (struct hblk *)GC_wince_get_mem(bytes)
  # elif defined(AMIGA) && defined(GC_AMIGA_FASTALLOC)
      void *GC_amiga_get_mem(size_t size);
  #   define GET_MEM(bytes) HBLKPTR((size_t) \
                            GC_amiga_get_mem((size_t)(bytes) + GC_page_size) \
                            + GC_page_size-1)
  # elif defined(SN_TARGET_PS3)
      void *ps3_get_mem(size_t size);
  #   define GET_MEM(bytes) (struct hblk*)ps3_get_mem(bytes)
  # else
      ptr_t GC_unix_get_mem(GC_word bytes);
  #   define GET_MEM(bytes) (struct hblk *)GC_unix_get_mem(bytes)
  # endif
  #endif /* GC_PRIVATE_H */
  
  #endif /* GCCONFIG_H */
  