pjs/gc/boehm/os_dep.c

/*
 * Copyright (c) 1991-1995 by Xerox Corporation.  All rights reserved.
 * Copyright (c) 1996-1997 by Silicon Graphics.  All rights reserved.
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose,  provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 */

# include "gc_priv.h"

# if defined(LINUX) && !defined(POWERPC)
#   include <linux/version.h>
#   include <asm/sigcontext.h>
typedef char* caddr_t;
#   if (LINUX_VERSION_CODE <= 0x10400)
      /* Ugly hack to get struct sigcontext_struct definition.  Required      */
      /* for some early 1.3.X releases.  Will hopefully go away soon. */
      /* in some later Linux releases, asm/sigcontext.h may have to   */
      /* be included instead.                                         */
#     define __KERNEL__
#     include <asm/signal.h>
#     undef __KERNEL__
#   else
      /* Kernels prior to 2.1.1 defined struct sigcontext_struct instead of */
      /* struct sigcontext.  libc6 (glibc2) uses "struct sigcontext" in     */
      /* prototypes, so we have to include the top-level sigcontext.h to    */
      /* make sure the former gets defined to be the latter if appropriate. */
#     include <features.h>
#     if 2 <= __GLIBC__
#       if 0 == __GLIBC_MINOR__
	  /* glibc 2.1 no longer has sigcontext.h.  But signal.h	*/
	  /* has the right declaration for glibc 2.1.			*/
#         include <sigcontext.h>
#       endif /* 0 == __GLIBC_MINOR__ */
#     else /* not 2 <= __GLIBC__ */
        /* libc5 doesn't have <sigcontext.h>: go directly with the kernel   */
        /* one.  Check LINUX_VERSION_CODE to see which we should reference. */
#       include <asm/sigcontext.h>
#     endif /* 2 <= __GLIBC__ */
#   endif
# endif
# if !defined(OS2) && !defined(PCR) && !defined(AMIGA) && !defined(MACOS)
#   include <sys/types.h>
#   if !defined(MSWIN32) && !defined(SUNOS4)
#   	include <unistd.h>
#   endif
# endif

# include <stdio.h>
# include <signal.h>

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

# if !defined(THREADS) && !defined(STACKBOTTOM) && defined(HEURISTIC2)
#   define NEED_FIND_LIMIT
# endif

# if defined(IRIX_THREADS)
#   define NEED_FIND_LIMIT
# endif

# if (defined(SUNOS4) & defined(DYNAMIC_LOADING)) && !defined(PCR)
#   define NEED_FIND_LIMIT
# endif

# if (defined(SVR4) || defined(AUX) || defined(DGUX)) && !defined(PCR)
#   define NEED_FIND_LIMIT
# endif

# if defined(LINUX) && (defined(POWERPC) || defined(SPARC))
#   define NEED_FIND_LIMIT
# endif

#ifdef NEED_FIND_LIMIT
#   include <setjmp.h>
#endif

#ifdef FREEBSD
#  include <machine/trap.h>
#endif

#ifdef AMIGA
# include <proto/exec.h>
# include <proto/dos.h>
# include <dos/dosextens.h>
# include <workbench/startup.h>
#endif

#ifdef MSWIN32
# define WIN32_LEAN_AND_MEAN
# define NOSERVICE
# include <windows.h>
#endif

#ifdef MACOS
# include <Processes.h>
#endif

#ifdef IRIX5
# include <sys/uio.h>
# include <malloc.h>   /* for locking */
#endif
#ifdef USE_MMAP
# include <sys/types.h>
# include <sys/mman.h>
# include <sys/stat.h>
# include <fcntl.h>
#endif

#ifdef SUNOS5SIGS
# include <sys/siginfo.h>
# undef setjmp
# undef longjmp
# define setjmp(env) sigsetjmp(env, 1)
# define longjmp(env, val) siglongjmp(env, val)
# define jmp_buf sigjmp_buf
#endif

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

#ifdef PCR
# include "il/PCR_IL.h"
# include "th/PCR_ThCtl.h"
# include "mm/PCR_MM.h"
#endif

#if !defined(NO_EXECUTE_PERMISSION)
# define OPT_PROT_EXEC PROT_EXEC
#else
# define OPT_PROT_EXEC 0
#endif

#if defined(LINUX) && defined(POWERPC)
  ptr_t GC_data_start;

  void GC_init_linuxppc()
  {
    extern ptr_t GC_find_limit();
    extern char **_environ;
	/* This may need to be environ, without the underscore, for	*/
	/* some versions.						*/
    GC_data_start = GC_find_limit((ptr_t)&_environ, FALSE);
  }
#endif

#if defined(LINUX) && defined(SPARC)
  ptr_t GC_data_start;

  void GC_init_linuxsparc()
  {
    extern ptr_t GC_find_limit();
    extern char **_environ;
      /* This may need to be environ, without the underscore, for     */
      /* some versions.                                               */
    GC_data_start = GC_find_limit((ptr_t)&_environ, FALSE);
  }
#endif

# ifdef OS2

# include <stddef.h>

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

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

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

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

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

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

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

# else  /* IBM's compiler */

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

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

# endif  /* __IBMC__ */

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


/* Disable and enable signals during nontrivial allocations	*/

void GC_disable_signals(void)
{
    ULONG nest;
    
    DosEnterMustComplete(&nest);
    if (nest != 1) ABORT("nested GC_disable_signals");
}

void GC_enable_signals(void)
{
    ULONG nest;
    
    DosExitMustComplete(&nest);
    if (nest != 0) ABORT("GC_enable_signals");
}


# else

#  if !defined(PCR) && !defined(AMIGA) && !defined(MSWIN32) \
      && !defined(MACOS) && !defined(DJGPP) && !defined(DOS4GW)

#   if defined(sigmask) && !defined(UTS4)
	/* Use the traditional BSD interface */
#	define SIGSET_T int
#	define SIG_DEL(set, signal) (set) &= ~(sigmask(signal))
#	define SIG_FILL(set)  (set) = 0x7fffffff
    	  /* Setting the leading bit appears to provoke a bug in some	*/
    	  /* longjmp implementations.  Most systems appear not to have	*/
    	  /* a signal 32.						*/
#	define SIGSETMASK(old, new) (old) = sigsetmask(new)
#   else
	/* Use POSIX/SYSV interface	*/
#	define SIGSET_T sigset_t
#	define SIG_DEL(set, signal) sigdelset(&(set), (signal))
#	define SIG_FILL(set) sigfillset(&set)
#	define SIGSETMASK(old, new) sigprocmask(SIG_SETMASK, &(new), &(old))
#   endif

static GC_bool mask_initialized = FALSE;

static SIGSET_T new_mask;

static SIGSET_T old_mask;

static SIGSET_T dummy;

#if defined(PRINTSTATS) && !defined(THREADS)
# define CHECK_SIGNALS
  int GC_sig_disabled = 0;
#endif

void GC_disable_signals()
{
    if (!mask_initialized) {
    	SIG_FILL(new_mask);

	SIG_DEL(new_mask, SIGSEGV);
	SIG_DEL(new_mask, SIGILL);
	SIG_DEL(new_mask, SIGQUIT);
#	ifdef SIGBUS
	    SIG_DEL(new_mask, SIGBUS);
#	endif
#	ifdef SIGIOT
	    SIG_DEL(new_mask, SIGIOT);
#	endif
#	ifdef SIGEMT
	    SIG_DEL(new_mask, SIGEMT);
#	endif
#	ifdef SIGTRAP
	    SIG_DEL(new_mask, SIGTRAP);
#	endif 
	mask_initialized = TRUE;
    }
#   ifdef CHECK_SIGNALS
	if (GC_sig_disabled != 0) ABORT("Nested disables");
	GC_sig_disabled++;
#   endif
    SIGSETMASK(old_mask,new_mask);
}

void GC_enable_signals()
{
#   ifdef CHECK_SIGNALS
	if (GC_sig_disabled != 1) ABORT("Unmatched enable");
	GC_sig_disabled--;
#   endif
    SIGSETMASK(dummy,old_mask);
}

#  endif  /* !PCR */

# endif /*!OS/2 */

/* Ivan Demakov: simplest way (to me) */
#ifdef DOS4GW
  void GC_disable_signals() { }
  void GC_enable_signals() { }
#endif

/* Find the page size */
word GC_page_size;

# ifdef MSWIN32
  void GC_setpagesize()
  {
    SYSTEM_INFO sysinfo;
    
    GetSystemInfo(&sysinfo);
    GC_page_size = sysinfo.dwPageSize;
  }

# else
#   if defined(MPROTECT_VDB) || defined(PROC_VDB) || defined(USE_MMAP)
	void GC_setpagesize()
	{
	    GC_page_size = GETPAGESIZE();
	}
#   else
	/* It's acceptable to fake it. */
	void GC_setpagesize()
	{
	    GC_page_size = HBLKSIZE;
	}
#   endif
# endif

/* 
 * Find the base of the stack. 
 * Used only in single-threaded environment.
 * With threads, GC_mark_roots needs to know how to do this.
 * Called with allocator lock held.
 */
# ifdef MSWIN32 
# define is_writable(prot) ((prot) == PAGE_READWRITE \
			    || (prot) == PAGE_WRITECOPY \
			    || (prot) == PAGE_EXECUTE_READWRITE \
			    || (prot) == PAGE_EXECUTE_WRITECOPY)
/* Return the number of bytes that are writable starting at p.	*/
/* The pointer p is assumed to be page aligned.			*/
/* If base is not 0, *base becomes the beginning of the 	*/
/* allocation region containing p.				*/
word GC_get_writable_length(ptr_t p, ptr_t *base)
{
    MEMORY_BASIC_INFORMATION buf;
    word result;
    word protect;
    
    result = VirtualQuery(p, &buf, sizeof(buf));
    if (result != sizeof(buf)) ABORT("Weird VirtualQuery result");
    if (base != 0) *base = (ptr_t)(buf.AllocationBase);
    protect = (buf.Protect & ~(PAGE_GUARD | PAGE_NOCACHE));
    if (!is_writable(protect)) {
        return(0);
    }
    if (buf.State != MEM_COMMIT) return(0);
    return(buf.RegionSize);
}

ptr_t GC_get_stack_base()
{
    int dummy;
    ptr_t sp = (ptr_t)(&dummy);
    ptr_t trunc_sp = (ptr_t)((word)sp & ~(GC_page_size - 1));
    word size = GC_get_writable_length(trunc_sp, 0);
   
    return(trunc_sp + size);
}


# else

# ifdef OS2

ptr_t GC_get_stack_base()
{
    PTIB ptib;
    PPIB ppib;
    
    if (DosGetInfoBlocks(&ptib, &ppib) != NO_ERROR) {
    	GC_err_printf0("DosGetInfoBlocks failed\n");
    	ABORT("DosGetInfoBlocks failed\n");
    }
    return((ptr_t)(ptib -> tib_pstacklimit));
}

# else

# ifdef AMIGA

ptr_t GC_get_stack_base()
{
    extern struct WBStartup *_WBenchMsg;
    extern long __base;
    extern long __stack;
    struct Task *task;
    struct Process *proc;
    struct CommandLineInterface *cli;
    long size;

    if ((task = FindTask(0)) == 0) {
	GC_err_puts("Cannot find own task structure\n");
	ABORT("task missing");
    }
    proc = (struct Process *)task;
    cli = BADDR(proc->pr_CLI);

    if (_WBenchMsg != 0 || cli == 0) {
	size = (char *)task->tc_SPUpper - (char *)task->tc_SPLower;
    } else {
	size = cli->cli_DefaultStack * 4;
    }
    return (ptr_t)(__base + GC_max(size, __stack));
}

# else



# ifdef NEED_FIND_LIMIT
  /* Some tools to implement HEURISTIC2	*/
#   define MIN_PAGE_SIZE 256	/* Smallest conceivable page size, bytes */
    /* static */ jmp_buf GC_jmp_buf;
    
    /*ARGSUSED*/
    void GC_fault_handler(sig)
    int sig;
    {
        longjmp(GC_jmp_buf, 1);
    }

#   ifdef __STDC__
	typedef void (*handler)(int);
#   else
	typedef void (*handler)();
#   endif

#   if defined(SUNOS5SIGS) || defined(IRIX5)
	static struct sigaction old_segv_act;
#	if defined(_sigargs) /* !Irix6.x */
	    static struct sigaction old_bus_act;
#	endif
#   else
        static handler old_segv_handler, old_bus_handler;
#   endif
    
    void GC_setup_temporary_fault_handler()
    {
#	if defined(SUNOS5SIGS) || defined(IRIX5)
	  struct sigaction	act;

	  act.sa_handler	= GC_fault_handler;
          act.sa_flags          = SA_RESTART | SA_NODEFER;
          /* The presence of SA_NODEFER represents yet another gross    */
          /* hack.  Under Solaris 2.3, siglongjmp doesn't appear to     */
          /* interact correctly with -lthread.  We hide the confusion   */
          /* by making sure that signal handling doesn't affect the     */
          /* signal mask.                                               */

	  (void) sigemptyset(&act.sa_mask);
#	  ifdef IRIX_THREADS
		/* Older versions have a bug related to retrieving and	*/
		/* and setting a handler at the same time.		*/
	        (void) sigaction(SIGSEGV, 0, &old_segv_act);
	        (void) sigaction(SIGSEGV, &act, 0);
#	  else
	        (void) sigaction(SIGSEGV, &act, &old_segv_act);
#		ifdef _sigargs	/* Irix 5.x, not 6.x */
		    /* Under 5.x, we may get SIGBUS.			*/
		    /* Pthreads doesn't exist under 5.x, so we don't	*/
		    /* have to worry in the threads case.		*/
		    (void) sigaction(SIGBUS, &act, &old_bus_act);
#		endif
#	  endif	/* IRIX_THREADS */
#	else
    	  old_segv_handler = signal(SIGSEGV, GC_fault_handler);
#	  ifdef SIGBUS
	    old_bus_handler = signal(SIGBUS, GC_fault_handler);
#	  endif
#	endif
    }
    
    void GC_reset_fault_handler()
    {
#       if defined(SUNOS5SIGS) || defined(IRIX5)
	  (void) sigaction(SIGSEGV, &old_segv_act, 0);
#	  ifdef _sigargs	/* Irix 5.x, not 6.x */
	      (void) sigaction(SIGBUS, &old_bus_act, 0);
#	  endif
#       else
  	  (void) signal(SIGSEGV, old_segv_handler);
#	  ifdef SIGBUS
	    (void) signal(SIGBUS, old_bus_handler);
#	  endif
#       endif
    }

    /* Return the first nonaddressible location > p (up) or 	*/
    /* the smallest location q s.t. [q,p] is addressible (!up).	*/
    ptr_t GC_find_limit(p, up)
    ptr_t p;
    GC_bool up;
    {
        static VOLATILE ptr_t result;
    		/* Needs to be static, since otherwise it may not be	*/
    		/* preserved across the longjmp.  Can safely be 	*/
    		/* static since it's only called once, with the		*/
    		/* allocation lock held.				*/


	GC_setup_temporary_fault_handler();
	if (setjmp(GC_jmp_buf) == 0) {
	    result = (ptr_t)(((word)(p))
			      & ~(MIN_PAGE_SIZE-1));
	    for (;;) {
 	        if (up) {
		    result += MIN_PAGE_SIZE;
 	        } else {
		    result -= MIN_PAGE_SIZE;
 	        }
		GC_noop1((word)(*result));
	    }
	}
	GC_reset_fault_handler();
 	if (!up) {
	    result += MIN_PAGE_SIZE;
 	}
	return(result);
    }
# endif


ptr_t GC_get_stack_base()
{
    word dummy;
    ptr_t result;

#   define STACKBOTTOM_ALIGNMENT_M1 ((word)STACK_GRAN - 1)

#   ifdef STACKBOTTOM
	return(STACKBOTTOM);
#   else
#	ifdef HEURISTIC1
#	   ifdef STACK_GROWS_DOWN
	     result = (ptr_t)((((word)(&dummy))
	     		       + STACKBOTTOM_ALIGNMENT_M1)
			      & ~STACKBOTTOM_ALIGNMENT_M1);
#	   else
	     result = (ptr_t)(((word)(&dummy))
			      & ~STACKBOTTOM_ALIGNMENT_M1);
#	   endif
#	endif /* HEURISTIC1 */
#	ifdef HEURISTIC2
#	    ifdef STACK_GROWS_DOWN
		result = GC_find_limit((ptr_t)(&dummy), TRUE);
#           	ifdef HEURISTIC2_LIMIT
		    if (result > HEURISTIC2_LIMIT
		        && (ptr_t)(&dummy) < HEURISTIC2_LIMIT) {
		            result = HEURISTIC2_LIMIT;
		    }
#	        endif
#	    else
		result = GC_find_limit((ptr_t)(&dummy), FALSE);
#           	ifdef HEURISTIC2_LIMIT
		    if (result < HEURISTIC2_LIMIT
		        && (ptr_t)(&dummy) > HEURISTIC2_LIMIT) {
		            result = HEURISTIC2_LIMIT;
		    }
#	        endif
#	    endif

#	endif /* HEURISTIC2 */
#	ifdef STACK_GROWS_DOWN
	    if (result == 0) result = (ptr_t)(signed_word)(-sizeof(ptr_t));
#	endif
    	return(result);
#   endif /* STACKBOTTOM */
}

# endif /* ! AMIGA */
# endif /* ! OS2 */
# endif /* ! MSWIN32 */

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

# ifdef OS2

void GC_register_data_segments()
{
    PTIB ptib;
    PPIB ppib;
    HMODULE module_handle;
#   define PBUFSIZ 512
    UCHAR path[PBUFSIZ];
    FILE * myexefile;
    struct exe_hdr hdrdos;	/* MSDOS header.	*/
    struct e32_exe hdr386;	/* Real header for my executable */
    struct o32_obj seg;	/* Currrent segment */
    int nsegs;
    
    
    if (DosGetInfoBlocks(&ptib, &ppib) != NO_ERROR) {
    	GC_err_printf0("DosGetInfoBlocks failed\n");
    	ABORT("DosGetInfoBlocks failed\n");
    }
    module_handle = ppib -> pib_hmte;
    if (DosQueryModuleName(module_handle, PBUFSIZ, path) != NO_ERROR) {
    	GC_err_printf0("DosQueryModuleName failed\n");
    	ABORT("DosGetInfoBlocks failed\n");
    }
    myexefile = fopen(path, "rb");
    if (myexefile == 0) {
        GC_err_puts("Couldn't open executable ");
        GC_err_puts(path); GC_err_puts("\n");
        ABORT("Failed to open executable\n");
    }
    if (fread((char *)(&hdrdos), 1, sizeof hdrdos, myexefile) < sizeof hdrdos) {
        GC_err_puts("Couldn't read MSDOS header from ");
        GC_err_puts(path); GC_err_puts("\n");
        ABORT("Couldn't read MSDOS header");
    }
    if (E_MAGIC(hdrdos) != EMAGIC) {
        GC_err_puts("Executable has wrong DOS magic number: ");
        GC_err_puts(path); GC_err_puts("\n");
        ABORT("Bad DOS magic number");
    }
    if (fseek(myexefile, E_LFANEW(hdrdos), SEEK_SET) != 0) {
        GC_err_puts("Seek to new header failed in ");
        GC_err_puts(path); GC_err_puts("\n");
        ABORT("Bad DOS magic number");
    }
    if (fread((char *)(&hdr386), 1, sizeof hdr386, myexefile) < sizeof hdr386) {
        GC_err_puts("Couldn't read MSDOS header from ");
        GC_err_puts(path); GC_err_puts("\n");
        ABORT("Couldn't read OS/2 header");
    }
    if (E32_MAGIC1(hdr386) != E32MAGIC1 || E32_MAGIC2(hdr386) != E32MAGIC2) {
        GC_err_puts("Executable has wrong OS/2 magic number:");
        GC_err_puts(path); GC_err_puts("\n");
        ABORT("Bad OS/2 magic number");
    }
    if ( E32_BORDER(hdr386) != E32LEBO || E32_WORDER(hdr386) != E32LEWO) {
        GC_err_puts("Executable %s has wrong byte order: ");
        GC_err_puts(path); GC_err_puts("\n");
        ABORT("Bad byte order");
    }
    if ( E32_CPU(hdr386) == E32CPU286) {
        GC_err_puts("GC can't handle 80286 executables: ");
        GC_err_puts(path); GC_err_puts("\n");
        EXIT();
    }
    if (fseek(myexefile, E_LFANEW(hdrdos) + E32_OBJTAB(hdr386),
    	      SEEK_SET) != 0) {
        GC_err_puts("Seek to object table failed: ");
        GC_err_puts(path); GC_err_puts("\n");
        ABORT("Seek to object table failed");
    }
    for (nsegs = E32_OBJCNT(hdr386); nsegs > 0; nsegs--) {
      int flags;
      if (fread((char *)(&seg), 1, sizeof seg, myexefile) < sizeof seg) {
        GC_err_puts("Couldn't read obj table entry from ");
        GC_err_puts(path); GC_err_puts("\n");
        ABORT("Couldn't read obj table entry");
      }
      flags = O32_FLAGS(seg);
      if (!(flags & OBJWRITE)) continue;
      if (!(flags & OBJREAD)) continue;
      if (flags & OBJINVALID) {
          GC_err_printf0("Object with invalid pages?\n");
          continue;
      } 
      GC_add_roots_inner(O32_BASE(seg), O32_BASE(seg)+O32_SIZE(seg), FALSE);
    }
}

# else

# ifdef MSWIN32
  /* Unfortunately, we have to handle win32s very differently from NT, 	*/
  /* Since VirtualQuery has very different semantics.  In particular,	*/
  /* under win32s a VirtualQuery call on an unmapped page returns an	*/
  /* invalid result.  Under GC_register_data_segments is a noop and	*/
  /* all real work is done by GC_register_dynamic_libraries.  Under	*/
  /* win32s, we cannot find the data segments associated with dll's.	*/
  /* We rgister the main data segment here.				*/
  GC_bool GC_win32s = FALSE;	/* We're running under win32s.	*/
  
  GC_bool GC_is_win32s()
  {
      DWORD v = GetVersion();
      
      /* Check that this is not NT, and Windows major version <= 3	*/
      return ((v & 0x80000000) && (v & 0xff) <= 3);
  }
  
  void GC_init_win32()
  {
      GC_win32s = GC_is_win32s();
  }
  
  /* Return the smallest address a such that VirtualQuery		*/
  /* returns correct results for all addresses between a and start.	*/
  /* Assumes VirtualQuery returns correct information for start.	*/
  ptr_t GC_least_described_address(ptr_t start)
  {  
    MEMORY_BASIC_INFORMATION buf;
    SYSTEM_INFO sysinfo;
    DWORD result;
    LPVOID limit;
    ptr_t p;
    LPVOID q;
    
    GetSystemInfo(&sysinfo);
    limit = sysinfo.lpMinimumApplicationAddress;
    p = (ptr_t)((word)start & ~(GC_page_size - 1));
    for (;;) {
    	q = (LPVOID)(p - GC_page_size);
    	if ((ptr_t)q > (ptr_t)p /* underflow */ || q < limit) break;
    	result = VirtualQuery(q, &buf, sizeof(buf));
    	if (result != sizeof(buf) || buf.AllocationBase == 0) break;
    	p = (ptr_t)(buf.AllocationBase);
    }
    return(p);
  }
  
  /* Is p the start of either the malloc heap, or of one of our */
  /* heap sections?						*/
  GC_bool GC_is_heap_base (ptr_t p)
  {
     
     register unsigned i;
     
#    ifndef REDIRECT_MALLOC
       static ptr_t malloc_heap_pointer = 0;
     
       if (0 == malloc_heap_pointer) {
         MEMORY_BASIC_INFORMATION buf;
         register DWORD result = VirtualQuery(malloc(1), &buf, sizeof(buf));
         
         if (result != sizeof(buf)) {
             ABORT("Weird VirtualQuery result");
         }
         malloc_heap_pointer = (ptr_t)(buf.AllocationBase);
       }
       if (p == malloc_heap_pointer) return(TRUE);
#    endif
     for (i = 0; i < GC_n_heap_bases; i++) {
         if (GC_heap_bases[i] == p) return(TRUE);
     }
     return(FALSE);
  }
  
  void GC_register_root_section(ptr_t static_root)
  {
      MEMORY_BASIC_INFORMATION buf;
      SYSTEM_INFO sysinfo;
      DWORD result;
      DWORD protect;
      LPVOID p;
      char * base;
      char * limit, * new_limit;
    
      if (!GC_win32s) return;
      p = base = limit = GC_least_described_address(static_root);
      GetSystemInfo(&sysinfo);
      while (p < sysinfo.lpMaximumApplicationAddress) {
        result = VirtualQuery(p, &buf, sizeof(buf));
        if (result != sizeof(buf) || buf.AllocationBase == 0
            || GC_is_heap_base(buf.AllocationBase)) break;
        new_limit = (char *)p + buf.RegionSize;
        protect = buf.Protect;
        if (buf.State == MEM_COMMIT
            && is_writable(protect)) {
            if ((char *)p == limit) {
                limit = new_limit;
            } else {
                if (base != limit) GC_add_roots_inner(base, limit, FALSE);
                base = p;
                limit = new_limit;
            }
        }
        if (p > (LPVOID)new_limit /* overflow */) break;
        p = (LPVOID)new_limit;
      }
      if (base != limit) GC_add_roots_inner(base, limit, FALSE);
  }
  
  void GC_register_data_segments()
  {
      static char dummy;
      
      GC_register_root_section((ptr_t)(&dummy));
  }
# else
# ifdef AMIGA

  void GC_register_data_segments()
  {
    extern struct WBStartup *_WBenchMsg;
    struct Process	*proc;
    struct CommandLineInterface *cli;
    BPTR myseglist;
    ULONG *data;

    if ( _WBenchMsg != 0 ) {
	if ((myseglist = _WBenchMsg->sm_Segment) == 0) {
	    GC_err_puts("No seglist from workbench\n");
	    return;
	}
    } else {
	if ((proc = (struct Process *)FindTask(0)) == 0) {
	    GC_err_puts("Cannot find process structure\n");
	    return;
	}
	if ((cli = BADDR(proc->pr_CLI)) == 0) {
	    GC_err_puts("No CLI\n");
	    return;
	}
	if ((myseglist = cli->cli_Module) == 0) {
	    GC_err_puts("No seglist from CLI\n");
	    return;
	}
    }

    for (data = (ULONG *)BADDR(myseglist); data != 0;
         data = (ULONG *)BADDR(data[0])) {
#        ifdef AMIGA_SKIP_SEG
           if (((ULONG) GC_register_data_segments < (ULONG) &data[1]) ||
           ((ULONG) GC_register_data_segments > (ULONG) &data[1] + data[-1])) {
#	 else
      	   {
#	 endif /* AMIGA_SKIP_SEG */
          GC_add_roots_inner((char *)&data[1],
          		     ((char *)&data[1]) + data[-1], FALSE);
         }
    }
  }


# else

# if (defined(SVR4) || defined(AUX) || defined(DGUX)) && !defined(PCR)
char * GC_SysVGetDataStart(max_page_size, etext_addr)
int max_page_size;
int * etext_addr;
{
    word text_end = ((word)(etext_addr) + sizeof(word) - 1)
    		    & ~(sizeof(word) - 1);
    	/* etext rounded to word boundary	*/
    word next_page = ((text_end + (word)max_page_size - 1)
    		      & ~((word)max_page_size - 1));
    word page_offset = (text_end & ((word)max_page_size - 1));
    VOLATILE char * result = (char *)(next_page + page_offset);
    /* Note that this isnt equivalent to just adding		*/
    /* max_page_size to &etext if &etext is at a page boundary	*/
    
    GC_setup_temporary_fault_handler();
    if (setjmp(GC_jmp_buf) == 0) {
    	/* Try writing to the address.	*/
    	*result = *result;
        GC_reset_fault_handler();
    } else {
        GC_reset_fault_handler();
    	/* We got here via a longjmp.  The address is not readable.	*/
    	/* This is known to happen under Solaris 2.4 + gcc, which place	*/
    	/* string constants in the text segment, but after etext.	*/
    	/* Use plan B.  Note that we now know there is a gap between	*/
    	/* text and data segments, so plan A bought us something.	*/
    	result = (char *)GC_find_limit((ptr_t)(DATAEND) - MIN_PAGE_SIZE, FALSE);
    }
    return((char *)result);
}
# endif


void GC_register_data_segments()
{
#   if !defined(PCR) && !defined(SRC_M3) && !defined(NEXT) && !defined(MACOS)
#     if defined(REDIRECT_MALLOC) && defined(SOLARIS_THREADS)
	/* As of Solaris 2.3, the Solaris threads implementation	*/
	/* allocates the data structure for the initial thread with	*/
	/* sbrk at process startup.  It needs to be scanned, so that	*/
	/* we don't lose some malloc allocated data structures		*/
	/* hanging from it.  We're on thin ice here ...			*/
        extern caddr_t sbrk();

	GC_add_roots_inner(DATASTART, (char *)sbrk(0), FALSE);
#     else
	GC_add_roots_inner(DATASTART, (char *)(DATAEND), FALSE);
#     endif
#   endif
#   if !defined(PCR) && defined(NEXT)
      GC_add_roots_inner(DATASTART, (char *) get_end(), FALSE);
#   endif
#   if defined(MACOS)
    {
#   if defined(THINK_C)
	extern void* GC_MacGetDataStart(void);
	/* globals begin above stack and end at a5. */
	GC_add_roots_inner((ptr_t)GC_MacGetDataStart(),
			   (ptr_t)LMGetCurrentA5(), FALSE);
#   else
#     if defined(__MWERKS__)
#       if !__POWERPC__
	  extern void* GC_MacGetDataStart(void);
	  /* MATTHEW: Function to handle Far Globals (CW Pro 3) */
#         if __option(far_data)
	  extern void* GC_MacGetDataEnd(void);
#         endif
	  /* globals begin above stack and end at a5. */
	  GC_add_roots_inner((ptr_t)GC_MacGetDataStart(),
          		     (ptr_t)LMGetCurrentA5(), FALSE);
	  /* MATTHEW: Handle Far Globals */          		     
#         if __option(far_data)
      /* Far globals follow he QD globals: */
	  GC_add_roots_inner((ptr_t)LMGetCurrentA5(),
          		     (ptr_t)GC_MacGetDataEnd(), FALSE);
#         endif
#       else
	  extern char __data_start__[], __data_end__[];
	  GC_add_roots_inner((ptr_t)&__data_start__,
	  		     (ptr_t)&__data_end__, FALSE);
#       endif /* __POWERPC__ */
#     endif /* __MWERKS__ */
#   endif /* !THINK_C */
    }
#   endif /* MACOS */

    /* Dynamic libraries are added at every collection, since they may  */
    /* change.								*/
}

# endif  /* ! AMIGA */
# endif  /* ! MSWIN32 */
# endif  /* ! OS2 */

/*
 * Auxiliary routines for obtaining memory from OS.
 */
 
# if !defined(OS2) && !defined(PCR) && !defined(AMIGA) \
	&& !defined(MSWIN32) && !defined(MACOS) && !defined(DOS4GW)

# ifdef SUNOS4
    extern caddr_t sbrk();
# endif
# ifdef __STDC__
#   define SBRK_ARG_T ptrdiff_t
# else
#   define SBRK_ARG_T int
# endif

# ifdef RS6000
/* The compiler seems to generate speculative reads one past the end of	*/
/* an allocated object.  Hence we need to make sure that the page 	*/
/* following the last heap page is also mapped.				*/
ptr_t GC_unix_get_mem(bytes)
word bytes;
{
    caddr_t cur_brk = (caddr_t)sbrk(0);
    caddr_t result;
    SBRK_ARG_T lsbs = (word)cur_brk & (GC_page_size-1);
    static caddr_t my_brk_val = 0;
    
    if ((SBRK_ARG_T)bytes < 0) return(0); /* too big */
    if (lsbs != 0) {
        if((caddr_t)(sbrk(GC_page_size - lsbs)) == (caddr_t)(-1)) return(0);
    }
    if (cur_brk == my_brk_val) {
    	/* Use the extra block we allocated last time. */
        result = (ptr_t)sbrk((SBRK_ARG_T)bytes);
        if (result == (caddr_t)(-1)) return(0);
        result -= GC_page_size;
    } else {
        result = (ptr_t)sbrk(GC_page_size + (SBRK_ARG_T)bytes);
        if (result == (caddr_t)(-1)) return(0);
    }
    my_brk_val = result + bytes + GC_page_size;	/* Always page aligned */
    return((ptr_t)result);
}

#else  /* Not RS6000 */

#if defined(USE_MMAP)
/* Tested only under IRIX5 and Solaris 2 */

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

ptr_t GC_unix_get_mem(bytes)
word bytes;
{
    static GC_bool initialized = FALSE;
    static int fd;
    void *result;
    static ptr_t last_addr = HEAP_START;

    if (!initialized) {
	fd = open("/dev/zero", O_RDONLY);
	initialized = TRUE;
    }
    if (bytes & (GC_page_size -1)) ABORT("Bad GET_MEM arg");
    result = mmap(last_addr, bytes, PROT_READ | PROT_WRITE | OPT_PROT_EXEC,
		  GC_MMAP_FLAGS, fd, 0/* offset */);
    if (result == MAP_FAILED) return(0);
    last_addr = (ptr_t)result + bytes + GC_page_size - 1;
    last_addr = (ptr_t)((word)last_addr & ~(GC_page_size - 1));
    return((ptr_t)result);
}

#else /* Not RS6000, not USE_MMAP */
ptr_t GC_unix_get_mem(bytes)
word bytes;
{
  ptr_t result;
# ifdef IRIX5
    /* Bare sbrk isn't thread safe.  Play by malloc rules.	*/
    /* The equivalent may be needed on other systems as well. 	*/
    __LOCK_MALLOC();
# endif
  {
    ptr_t cur_brk = (ptr_t)sbrk(0);
    SBRK_ARG_T lsbs = (word)cur_brk & (GC_page_size-1);
    
    if ((SBRK_ARG_T)bytes < 0) return(0); /* too big */
    if (lsbs != 0) {
        if((ptr_t)sbrk(GC_page_size - lsbs) == (ptr_t)(-1)) return(0);
    }
    result = (ptr_t)sbrk((SBRK_ARG_T)bytes);
    if (result == (ptr_t)(-1)) result = 0;
  }
# ifdef IRIX5
    __UNLOCK_MALLOC();
# endif
  return(result);
}

#endif /* Not USE_MMAP */
#endif /* Not RS6000 */

# endif /* UN*X */

# ifdef OS2

void * os2_alloc(size_t bytes)
{
    void * result;

    if (DosAllocMem(&result, bytes, PAG_EXECUTE | PAG_READ |
    				    PAG_WRITE | PAG_COMMIT)
		    != NO_ERROR) {
	return(0);
    }
    if (result == 0) return(os2_alloc(bytes));
    return(result);
}

# endif /* OS2 */


# ifdef MSWIN32
word GC_n_heap_bases = 0;

ptr_t GC_win32_get_mem(bytes)
word bytes;
{
    ptr_t result;
    
    if (GC_win32s) {
    	/* VirtualAlloc doesn't like PAGE_EXECUTE_READWRITE.	*/
    	/* There are also unconfirmed rumors of other		*/
    	/* problems, so we dodge the issue.			*/
        result = (ptr_t) GlobalAlloc(0, bytes + HBLKSIZE);
        result = (ptr_t)(((word)result + HBLKSIZE) & ~(HBLKSIZE-1));
    } else {
        result = (ptr_t) VirtualAlloc(NULL, bytes,
    				      MEM_COMMIT | MEM_RESERVE,
    				      PAGE_EXECUTE_READWRITE);
    }
    if (HBLKDISPL(result) != 0) ABORT("Bad VirtualAlloc result");
    	/* If I read the documentation correctly, this can	*/
    	/* only happen if HBLKSIZE > 64k or not a power of 2.	*/
    if (GC_n_heap_bases >= MAX_HEAP_SECTS) ABORT("Too many heap sections");
    GC_heap_bases[GC_n_heap_bases++] = result;
    return(result);			  
}

void GC_win32_free_heap ()
{
    if (GC_win32s) {
 	while (GC_n_heap_bases > 0) {
 	    GlobalFree (GC_heap_bases[--GC_n_heap_bases]);
 	    GC_heap_bases[GC_n_heap_bases] = 0;
 	}
    }
}


# endif

/* Routine for pushing any additional roots.  In THREADS 	*/
/* environment, this is also responsible for marking from 	*/
/* thread stacks.  In the SRC_M3 case, it also handles		*/
/* global variables.						*/
#ifndef THREADS
void (*GC_push_other_roots)() = 0;
#else /* THREADS */

# ifdef PCR
PCR_ERes GC_push_thread_stack(PCR_Th_T *t, PCR_Any dummy)
{
    struct PCR_ThCtl_TInfoRep info;
    PCR_ERes result;
    
    info.ti_stkLow = info.ti_stkHi = 0;
    result = PCR_ThCtl_GetInfo(t, &info);
    GC_push_all_stack((ptr_t)(info.ti_stkLow), (ptr_t)(info.ti_stkHi));
    return(result);
}

/* Push the contents of an old object. We treat this as stack	*/
/* data only becasue that makes it robust against mark stack	*/
/* overflow.							*/
PCR_ERes GC_push_old_obj(void *p, size_t size, PCR_Any data)
{
    GC_push_all_stack((ptr_t)p, (ptr_t)p + size);
    return(PCR_ERes_okay);
}


void GC_default_push_other_roots()
{
    /* Traverse data allocated by previous memory managers.		*/
	{
	  extern struct PCR_MM_ProcsRep * GC_old_allocator;
	  
	  if ((*(GC_old_allocator->mmp_enumerate))(PCR_Bool_false,
	  					   GC_push_old_obj, 0)
	      != PCR_ERes_okay) {
	      ABORT("Old object enumeration failed");
	  }
	}
    /* Traverse all thread stacks. */
	if (PCR_ERes_IsErr(
                PCR_ThCtl_ApplyToAllOtherThreads(GC_push_thread_stack,0))
              || PCR_ERes_IsErr(GC_push_thread_stack(PCR_Th_CurrThread(), 0))) {
              ABORT("Thread stack marking failed\n");
	}
}

# endif /* PCR */

# ifdef SRC_M3

# ifdef ALL_INTERIOR_POINTERS
    --> misconfigured
# endif


extern void ThreadF__ProcessStacks();

void GC_push_thread_stack(start, stop)
word start, stop;
{
   GC_push_all_stack((ptr_t)start, (ptr_t)stop + sizeof(word));
}

/* Push routine with M3 specific calling convention. */
GC_m3_push_root(dummy1, p, dummy2, dummy3)
word *p;
ptr_t dummy1, dummy2;
int dummy3;
{
    word q = *p;
    
    if ((ptr_t)(q) >= GC_least_plausible_heap_addr
	 && (ptr_t)(q) < GC_greatest_plausible_heap_addr) {
	 GC_push_one_checked(q,FALSE);
    }
}

/* M3 set equivalent to RTHeap.TracedRefTypes */
typedef struct { int elts[1]; }  RefTypeSet;
RefTypeSet GC_TracedRefTypes = {{0x1}};

/* From finalize.c */
extern void GC_push_finalizer_structures();

/* From stubborn.c: */
# ifdef STUBBORN_ALLOC
    extern GC_PTR * GC_changing_list_start;
# endif


void GC_default_push_other_roots()
{
    /* Use the M3 provided routine for finding static roots.	*/
    /* This is a bit dubious, since it presumes no C roots.	*/
    /* We handle the collector roots explicitly.		*/
       {
# 	 ifdef STUBBORN_ALLOC
           GC_push_one(GC_changing_list_start);
#	 endif
      	 GC_push_finalizer_structures();
      	 RTMain__GlobalMapProc(GC_m3_push_root, 0, GC_TracedRefTypes);
       }
	if (GC_words_allocd > 0) {
	    ThreadF__ProcessStacks(GC_push_thread_stack);
	}
	/* Otherwise this isn't absolutely necessary, and we have	*/
	/* startup ordering problems.					*/
}

# endif /* SRC_M3 */

# if defined(SOLARIS_THREADS) || defined(WIN32_THREADS) \
     || defined(IRIX_THREADS) || defined(LINUX_THREADS) \
     || defined(IRIX_PCR_THREADS) || defined(GENERIC_THREADS)

extern void GC_push_all_stacks();

void GC_default_push_other_roots()
{
    GC_push_all_stacks();
}

# endif /* SOLARIS_THREADS || ... */

void (*GC_push_other_roots)() = GC_default_push_other_roots;

#endif

/*
 * Routines for accessing dirty  bits on virtual pages.
 * We plan to eventaually implement four strategies for doing so:
 * DEFAULT_VDB:	A simple dummy implementation that treats every page
 *		as possibly dirty.  This makes incremental collection
 *		useless, but the implementation is still correct.
 * PCR_VDB:	Use PPCRs virtual dirty bit facility.
 * PROC_VDB:	Use the /proc facility for reading dirty bits.  Only
 *		works under some SVR4 variants.  Even then, it may be
 *		too slow to be entirely satisfactory.  Requires reading
 *		dirty bits for entire address space.  Implementations tend
 *		to assume that the client is a (slow) debugger.
 * MPROTECT_VDB:Protect pages and then catch the faults to keep track of
 *		dirtied pages.  The implementation (and implementability)
 *		is highly system dependent.  This usually fails when system
 *		calls write to a protected page.  We prevent the read system
 *		call from doing so.  It is the clients responsibility to
 *		make sure that other system calls are similarly protected
 *		or write only to the stack.
 */
 
GC_bool GC_dirty_maintained = FALSE;

# ifdef DEFAULT_VDB

/* All of the following assume the allocation lock is held, and	*/
/* signals are disabled.					*/

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

/* Initialize virtual dirty bit implementation.			*/
void GC_dirty_init()
{
    GC_dirty_maintained = TRUE;
}

/* Retrieve system dirty bits for heap to a local buffer.	*/
/* Restore the systems notion of which pages are dirty.		*/
void GC_read_dirty()
{}

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

/*
 * The following two routines are typically less crucial.  They matter
 * most with large dynamic libraries, or if we can't accurately identify
 * stacks, e.g. under Solaris 2.X.  Otherwise the following default
 * versions are adequate.
 */
 
/* Could any valid GC heap pointer ever have been written to this page?	*/
/*ARGSUSED*/
GC_bool GC_page_was_ever_dirty(h)
struct hblk *h;
{
    return(TRUE);
}

/* Reset the n pages starting at h to "was never dirty" status.	*/
void GC_is_fresh(h, n)
struct hblk *h;
word n;
{
}

/* A call hints that h is about to be written.	*/
/* May speed up some dirty bit implementations.	*/
/*ARGSUSED*/
void GC_write_hint(h)
struct hblk *h;
{
}

# endif /* DEFAULT_VDB */


# ifdef MPROTECT_VDB

/*
 * See DEFAULT_VDB for interface descriptions.
 */

/*
 * This implementation maintains dirty bits itself by catching write
 * faults and keeping track of them.  We assume nobody else catches
 * SIGBUS or SIGSEGV.  We assume no write faults occur in system calls
 * except as a result of a read system call.  This means clients must
 * either ensure that system calls do not touch the heap, or must
 * provide their own wrappers analogous to the one for read.
 * We assume the page size is a multiple of HBLKSIZE.
 * This implementation is currently SunOS 4.X and IRIX 5.X specific, though we
 * tried to use portable code where easily possible.  It is known
 * not to work under a number of other systems.
 */

# ifndef MSWIN32

#   include <sys/mman.h>
#   include <signal.h>
#   include <sys/syscall.h>

#   define PROTECT(addr, len) \
    	  if (mprotect((caddr_t)(addr), (int)(len), \
    	      	       PROT_READ | OPT_PROT_EXEC) < 0) { \
    	    ABORT("mprotect failed"); \
    	  }
#   define UNPROTECT(addr, len) \
    	  if (mprotect((caddr_t)(addr), (int)(len), \
    	  	       PROT_WRITE | PROT_READ | OPT_PROT_EXEC ) < 0) { \
    	    ABORT("un-mprotect failed"); \
    	  }
    	  
# else

#   include <signal.h>

    static DWORD protect_junk;
#   define PROTECT(addr, len) \
	  if (!VirtualProtect((addr), (len), PAGE_EXECUTE_READ, \
	  		      &protect_junk)) { \
	    DWORD last_error = GetLastError(); \
	    GC_printf1("Last error code: %lx\n", last_error); \
	    ABORT("VirtualProtect failed"); \
	  }
#   define UNPROTECT(addr, len) \
	  if (!VirtualProtect((addr), (len), PAGE_EXECUTE_READWRITE, \
	  		      &protect_junk)) { \
	    ABORT("un-VirtualProtect failed"); \
	  }
	  
# endif

#if defined(SUNOS4) || defined(FREEBSD)
    typedef void (* SIG_PF)();
#endif
#if defined(SUNOS5SIGS) || defined(OSF1) || defined(LINUX)
    typedef void (* SIG_PF)(int);
#endif
#if defined(MSWIN32)
    typedef LPTOP_LEVEL_EXCEPTION_FILTER SIG_PF;
#   undef SIG_DFL
#   define SIG_DFL (LPTOP_LEVEL_EXCEPTION_FILTER) (-1)
#endif

#if defined(IRIX5) || defined(OSF1)
    typedef void (* REAL_SIG_PF)(int, int, struct sigcontext *);
#endif
#if defined(SUNOS5SIGS)
    typedef void (* REAL_SIG_PF)(int, struct siginfo *, void *);
#endif
#if defined(LINUX)
#   include <linux/version.h>
#   if (LINUX_VERSION_CODE >= 0x20100) && !defined(M68K) || defined(ALPHA)
      typedef struct sigcontext s_c;
#   else
      typedef struct sigcontext_struct s_c;
#   endif
#   ifdef ALPHA
    typedef void (* REAL_SIG_PF)(int, int, s_c *);
    /* Retrieve fault address from sigcontext structure by decoding	*/
    /* instruction.							*/
    char * get_fault_addr(s_c *sc) {
        unsigned instr;
	word faultaddr;

	instr = *((unsigned *)(sc->sc_pc));
	faultaddr = sc->sc_regs[(instr >> 16) & 0x1f];
	faultaddr += (word) (((int)instr << 16) >> 16);
	return (char *)faultaddr;
    }
#   else /* !ALPHA */
    typedef void (* REAL_SIG_PF)(int, s_c);
#   endif /* !ALPHA */
# endif

SIG_PF GC_old_bus_handler;
SIG_PF GC_old_segv_handler;	/* Also old MSWIN32 ACCESS_VIOLATION filter */

/*ARGSUSED*/
# if defined (SUNOS4) || defined(FREEBSD)
    void GC_write_fault_handler(sig, code, scp, addr)
    int sig, code;
    struct sigcontext *scp;
    char * addr;
#   ifdef SUNOS4
#     define SIG_OK (sig == SIGSEGV || sig == SIGBUS)
#     define CODE_OK (FC_CODE(code) == FC_PROT \
              	    || (FC_CODE(code) == FC_OBJERR \
              	       && FC_ERRNO(code) == FC_PROT))
#   endif
#   ifdef FREEBSD
#     define SIG_OK (sig == SIGBUS)
#     define CODE_OK (code == BUS_PAGE_FAULT)
#   endif
# endif
# if defined(IRIX5) || defined(OSF1)
#   include <errno.h>
    void GC_write_fault_handler(int sig, int code, struct sigcontext *scp)
#   define SIG_OK (sig == SIGSEGV)
#   ifdef OSF1
#     define CODE_OK (code == 2 /* experimentally determined */)
#   endif
#   ifdef IRIX5
#     define CODE_OK (code == EACCES)
#   endif
# endif
# if defined(LINUX)
#   ifdef ALPHA
      void GC_write_fault_handler(int sig, int code, s_c * sc)
#   else
      void GC_write_fault_handler(int sig, s_c sc)
#   endif
#   define SIG_OK (sig == SIGSEGV)
#   define CODE_OK TRUE
	/* Empirically c.trapno == 14, but is that useful?      */
	/* We assume Intel architecture, so alignment		*/
	/* faults are not possible.				*/
# endif
# if defined(SUNOS5SIGS)
    void GC_write_fault_handler(int sig, struct siginfo *scp, void * context)
#   define SIG_OK (sig == SIGSEGV)
#   define CODE_OK (scp -> si_code == SEGV_ACCERR)
# endif
# if defined(MSWIN32)
    LONG WINAPI GC_write_fault_handler(struct _EXCEPTION_POINTERS *exc_info)
#   define SIG_OK (exc_info -> ExceptionRecord -> ExceptionCode == \
			EXCEPTION_ACCESS_VIOLATION)
#   define CODE_OK (exc_info -> ExceptionRecord -> ExceptionInformation[0] == 1)
			/* Write fault */
# endif
{
    register unsigned i;
#   ifdef IRIX5
	char * addr = (char *) (size_t) (scp -> sc_badvaddr);
#   endif
#   if defined(OSF1) && defined(ALPHA)
	char * addr = (char *) (scp -> sc_traparg_a0);
#   endif
#   ifdef SUNOS5SIGS
	char * addr = (char *) (scp -> si_addr);
#   endif
#   ifdef LINUX
#     ifdef I386
	char * addr = (char *) (sc.cr2);
#     else
#	if defined(M68K)
          char * addr = NULL;

	  struct sigcontext *scp = (struct sigcontext *)(&sc);

	  int format = (scp->sc_formatvec >> 12) & 0xf;
	  unsigned long *framedata = (unsigned long *)(scp + 1); 
	  unsigned long ea;

	  if (format == 0xa || format == 0xb) {
	  	/* 68020/030 */
	  	ea = framedata[2];
	  } else if (format == 7) {
	  	/* 68040 */
	  	ea = framedata[3];
	  } else if (format == 4) {
	  	/* 68060 */
	  	ea = framedata[0];
	  	if (framedata[1] & 0x08000000) {
	  		/* correct addr on misaligned access */
	  		ea = (ea+4095)&(~4095);
	  	}
	  }	
	  addr = (char *)ea;
#	else
#	  ifdef ALPHA
            char * addr = get_fault_addr(sc);
#	  else
		--> architecture not supported
#	  endif
#	endif
#     endif
#   endif
#   if defined(MSWIN32)
	char * addr = (char *) (exc_info -> ExceptionRecord
				-> ExceptionInformation[1]);
#	define sig SIGSEGV
#   endif
    
    if (SIG_OK && CODE_OK) {
        register struct hblk * h =
        		(struct hblk *)((word)addr & ~(GC_page_size-1));
        GC_bool in_allocd_block;
        
#	ifdef SUNOS5SIGS
	    /* Address is only within the correct physical page.	*/
	    in_allocd_block = FALSE;
            for (i = 0; i < divHBLKSZ(GC_page_size); i++) {
              if (HDR(h+i) != 0) {
                in_allocd_block = TRUE;
              }
            }
#	else
	    in_allocd_block = (HDR(addr) != 0);
#	endif
        if (!in_allocd_block) {
	    /* Heap blocks now begin and end on page boundaries */
            SIG_PF old_handler;
            
            if (sig == SIGSEGV) {
            	old_handler = GC_old_segv_handler;
            } else {
                old_handler = GC_old_bus_handler;
            }
            if (old_handler == SIG_DFL) {
#		ifndef MSWIN32
		    GC_err_printf1("Segfault at 0x%lx\n", addr);
                    ABORT("Unexpected bus error or segmentation fault");
#		else
		    return(EXCEPTION_CONTINUE_SEARCH);
#		endif
            } else {
#		if defined (SUNOS4) || defined(FREEBSD)
		    (*old_handler) (sig, code, scp, addr);
		    return;
#		endif
#		if defined (SUNOS5SIGS)
		    (*(REAL_SIG_PF)old_handler) (sig, scp, context);
		    return;
#		endif
#		if defined (LINUX)
#		    ifdef ALPHA
		        (*(REAL_SIG_PF)old_handler) (sig, code, sc);
#		    else 
		        (*(REAL_SIG_PF)old_handler) (sig, sc);
#		    endif
		    return;
#		endif
#		if defined (IRIX5) || defined(OSF1)
		    (*(REAL_SIG_PF)old_handler) (sig, code, scp);
		    return;
#		endif
#		ifdef MSWIN32
		    return((*old_handler)(exc_info));
#		endif
            }
        }
        for (i = 0; i < divHBLKSZ(GC_page_size); i++) {
            register int index = PHT_HASH(h+i);
            
            set_pht_entry_from_index(GC_dirty_pages, index);
        }
        UNPROTECT(h, GC_page_size);
#	if defined(OSF1) || defined(LINUX)
	    /* These reset the signal handler each time by default. */
	    signal(SIGSEGV, (SIG_PF) GC_write_fault_handler);
#	endif
    	/* The write may not take place before dirty bits are read.	*/
    	/* But then we'll fault again ...				*/
#	ifdef MSWIN32
	    return(EXCEPTION_CONTINUE_EXECUTION);
#	else
	    return;
#	endif
    }
#ifdef MSWIN32
    return EXCEPTION_CONTINUE_SEARCH;
#else
    GC_err_printf1("Segfault at 0x%lx\n", addr);
    ABORT("Unexpected bus error or segmentation fault");
#endif
}

/*
 * We hold the allocation lock.  We expect block h to be written
 * shortly.
 */
void GC_write_hint(h)
struct hblk *h;
{
    register struct hblk * h_trunc;
    register unsigned i;
    register GC_bool found_clean;
    
    if (!GC_dirty_maintained) return;
    h_trunc = (struct hblk *)((word)h & ~(GC_page_size-1));
    found_clean = FALSE;
    for (i = 0; i < divHBLKSZ(GC_page_size); i++) {
        register int index = PHT_HASH(h_trunc+i);
            
        if (!get_pht_entry_from_index(GC_dirty_pages, index)) {
            found_clean = TRUE;
            set_pht_entry_from_index(GC_dirty_pages, index);
        }
    }
    if (found_clean) {
    	UNPROTECT(h_trunc, GC_page_size);
    }
}

void GC_dirty_init()
{
#if defined(SUNOS5SIGS) || defined(IRIX5)
    struct sigaction	act, oldact;
#   ifdef IRIX5
    	act.sa_flags	= SA_RESTART;
        act.sa_handler  = GC_write_fault_handler;
#   else
    	act.sa_flags	= SA_RESTART | SA_SIGINFO;
        act.sa_sigaction = GC_write_fault_handler;
#   endif
    (void)sigemptyset(&act.sa_mask); 
#endif
#   ifdef PRINTSTATS
	GC_printf0("Inititalizing mprotect virtual dirty bit implementation\n");
#   endif
    GC_dirty_maintained = TRUE;
    if (GC_page_size % HBLKSIZE != 0) {
        GC_err_printf0("Page size not multiple of HBLKSIZE\n");
        ABORT("Page size not multiple of HBLKSIZE");
    }
#   if defined(SUNOS4) || defined(FREEBSD)
      GC_old_bus_handler = signal(SIGBUS, GC_write_fault_handler);
      if (GC_old_bus_handler == SIG_IGN) {
        GC_err_printf0("Previously ignored bus error!?");
        GC_old_bus_handler = SIG_DFL;
      }
      if (GC_old_bus_handler != SIG_DFL) {
#	ifdef PRINTSTATS
          GC_err_printf0("Replaced other SIGBUS handler\n");
#	endif
      }
#   endif
#   if defined(OSF1) || defined(SUNOS4) || defined(LINUX)
      GC_old_segv_handler = signal(SIGSEGV, (SIG_PF)GC_write_fault_handler);
      if (GC_old_segv_handler == SIG_IGN) {
        GC_err_printf0("Previously ignored segmentation violation!?");
        GC_old_segv_handler = SIG_DFL;
      }
      if (GC_old_segv_handler != SIG_DFL) {
#	ifdef PRINTSTATS
          GC_err_printf0("Replaced other SIGSEGV handler\n");
#	endif
      }
#   endif
#   if defined(SUNOS5SIGS) || defined(IRIX5)
#     if defined(IRIX_THREADS) || defined(IRIX_PCR_THREADS)
      	sigaction(SIGSEGV, 0, &oldact);
      	sigaction(SIGSEGV, &act, 0);
#     else
      	sigaction(SIGSEGV, &act, &oldact);
#     endif
#     if defined(_sigargs)
	/* This is Irix 5.x, not 6.x.  Irix 5.x does not have	*/
	/* sa_sigaction.					*/
	GC_old_segv_handler = oldact.sa_handler;
#     else /* Irix 6.x or SUNOS5SIGS */
        if (oldact.sa_flags & SA_SIGINFO) {
          GC_old_segv_handler = (SIG_PF)(oldact.sa_sigaction);
        } else {
          GC_old_segv_handler = oldact.sa_handler;
        }
#     endif
      if (GC_old_segv_handler == SIG_IGN) {
	     GC_err_printf0("Previously ignored segmentation violation!?");
	     GC_old_segv_handler = SIG_DFL;
      }
      if (GC_old_segv_handler != SIG_DFL) {
#       ifdef PRINTSTATS
	  GC_err_printf0("Replaced other SIGSEGV handler\n");
#       endif
      }
#    endif
#   if defined(MSWIN32)
      GC_old_segv_handler = SetUnhandledExceptionFilter(GC_write_fault_handler);
      if (GC_old_segv_handler != NULL) {
#	ifdef PRINTSTATS
          GC_err_printf0("Replaced other UnhandledExceptionFilter\n");
#	endif
      } else {
          GC_old_segv_handler = SIG_DFL;
      }
#   endif
}



void GC_protect_heap()
{
    ptr_t start;
    word len;
    unsigned i;
    
    for (i = 0; i < GC_n_heap_sects; i++) {
        start = GC_heap_sects[i].hs_start;
        len = GC_heap_sects[i].hs_bytes;
        PROTECT(start, len);
    }
}

/* We assume that either the world is stopped or its OK to lose dirty	*/
/* bits while this is happenning (as in GC_enable_incremental).		*/
void GC_read_dirty()
{
    BCOPY((word *)GC_dirty_pages, GC_grungy_pages,
          (sizeof GC_dirty_pages));
    BZERO((word *)GC_dirty_pages, (sizeof GC_dirty_pages));
    GC_protect_heap();
}

GC_bool GC_page_was_dirty(h)
struct hblk * h;
{
    register word index = PHT_HASH(h);
    
    return(HDR(h) == 0 || get_pht_entry_from_index(GC_grungy_pages, index));
}

/*
 * Acquiring the allocation lock here is dangerous, since this
 * can be called from within GC_call_with_alloc_lock, and the cord
 * package does so.  On systems that allow nested lock acquisition, this
 * happens to work.
 * On other systems, SET_LOCK_HOLDER and friends must be suitably defined.
 */
 
void GC_begin_syscall()
{
    if (!I_HOLD_LOCK()) LOCK();
}

void GC_end_syscall()
{
    if (!I_HOLD_LOCK()) UNLOCK();
}

void GC_unprotect_range(addr, len)
ptr_t addr;
word len;
{
    struct hblk * start_block;
    struct hblk * end_block;
    register struct hblk *h;
    ptr_t obj_start;
    
    if (!GC_incremental) return;
    obj_start = GC_base(addr);
    if (obj_start == 0) return;
    if (GC_base(addr + len - 1) != obj_start) {
        ABORT("GC_unprotect_range(range bigger than object)");
    }
    start_block = (struct hblk *)((word)addr & ~(GC_page_size - 1));
    end_block = (struct hblk *)((word)(addr + len - 1) & ~(GC_page_size - 1));
    end_block += GC_page_size/HBLKSIZE - 1;
    for (h = start_block; h <= end_block; h++) {
        register word index = PHT_HASH(h);
        
        set_pht_entry_from_index(GC_dirty_pages, index);
    }
    UNPROTECT(start_block,
    	      ((ptr_t)end_block - (ptr_t)start_block) + HBLKSIZE);
}

#if 0
#ifndef MSWIN32
/* Replacement for UNIX system call.	 */
/* Other calls that write to the heap	 */
/* should be handled similarly.		 */
# if defined(__STDC__) && !defined(SUNOS4)
#   include <unistd.h>
    ssize_t read(int fd, void *buf, size_t nbyte)
# else
#   ifndef LINT
      int read(fd, buf, nbyte)
#   else
      int GC_read(fd, buf, nbyte)
#   endif
    int fd;
    char *buf;
    int nbyte;
# endif
{
    int result;
    
    GC_begin_syscall();
    GC_unprotect_range(buf, (word)nbyte);
#   ifdef IRIX5
	/* Indirect system call may not always be easily available.	*/
	/* We could call _read, but that would interfere with the	*/
	/* libpthread interception of read.				*/
	{
	    struct iovec iov;

	    iov.iov_base = buf;
	    iov.iov_len = nbyte;
	    result = readv(fd, &iov, 1);
	}
#   else
    	result = syscall(SYS_read, fd, buf, nbyte);
#   endif
    GC_end_syscall();
    return(result);
}
#endif /* !MSWIN32 */
#endif


/*ARGSUSED*/
GC_bool GC_page_was_ever_dirty(h)
struct hblk *h;
{
    return(TRUE);
}

/* Reset the n pages starting at h to "was never dirty" status.	*/
/*ARGSUSED*/
void GC_is_fresh(h, n)
struct hblk *h;
word n;
{
}

# endif /* MPROTECT_VDB */

# ifdef PROC_VDB

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

#include <errno.h>
#include <sys/types.h>
#include <sys/signal.h>
#include <sys/fault.h>
#include <sys/syscall.h>
#include <sys/procfs.h>
#include <sys/stat.h>
#include <fcntl.h>

#define INITIAL_BUF_SZ 4096
word GC_proc_buf_size = INITIAL_BUF_SZ;
char *GC_proc_buf;

#ifdef SOLARIS_THREADS
/* We don't have exact sp values for threads.  So we count on	*/
/* occasionally declaring stack pages to be fresh.  Thus we 	*/
/* need a real implementation of GC_is_fresh.  We can't clear	*/
/* entries in GC_written_pages, since that would declare all	*/
/* pages with the given hash address to be fresh.		*/
#   define MAX_FRESH_PAGES 8*1024	/* Must be power of 2 */
    struct hblk ** GC_fresh_pages;	/* A direct mapped cache.	*/
    					/* Collisions are dropped.	*/

#   define FRESH_PAGE_SLOT(h) (divHBLKSZ((word)(h)) & (MAX_FRESH_PAGES-1))
#   define ADD_FRESH_PAGE(h) \
	GC_fresh_pages[FRESH_PAGE_SLOT(h)] = (h)
#   define PAGE_IS_FRESH(h) \
	(GC_fresh_pages[FRESH_PAGE_SLOT(h)] == (h) && (h) != 0)
#endif

/* Add all pages in pht2 to pht1 */
void GC_or_pages(pht1, pht2)
page_hash_table pht1, pht2;
{
    register int i;
    
    for (i = 0; i < PHT_SIZE; i++) pht1[i] |= pht2[i];
}

int GC_proc_fd;

void GC_dirty_init()
{
    int fd;
    char buf[30];

    GC_dirty_maintained = TRUE;
    if (GC_words_allocd != 0 || GC_words_allocd_before_gc != 0) {
    	register int i;
    
        for (i = 0; i < PHT_SIZE; i++) GC_written_pages[i] = (word)(-1);
#       ifdef PRINTSTATS
	    GC_printf1("Allocated words:%lu:all pages may have been written\n",
	    	       (unsigned long)
	    	      		(GC_words_allocd + GC_words_allocd_before_gc));
#	endif       
    }
    sprintf(buf, "/proc/%d", getpid());
    fd = open(buf, O_RDONLY);
    if (fd < 0) {
    	ABORT("/proc open failed");
    }
    GC_proc_fd = syscall(SYS_ioctl, fd, PIOCOPENPD, 0);
    close(fd);
    if (GC_proc_fd < 0) {
    	ABORT("/proc ioctl failed");
    }
    GC_proc_buf = GC_scratch_alloc(GC_proc_buf_size);
#   ifdef SOLARIS_THREADS
	GC_fresh_pages = (struct hblk **)
	  GC_scratch_alloc(MAX_FRESH_PAGES * sizeof (struct hblk *));
	if (GC_fresh_pages == 0) {
	    GC_err_printf0("No space for fresh pages\n");
	    EXIT();
	}
	BZERO(GC_fresh_pages, MAX_FRESH_PAGES * sizeof (struct hblk *));
#   endif
}

/* Ignore write hints. They don't help us here.	*/
/*ARGSUSED*/
void GC_write_hint(h)
struct hblk *h;
{
}

#ifdef SOLARIS_THREADS
#   define READ(fd,buf,nbytes) syscall(SYS_read, fd, buf, nbytes)
#else
#   define READ(fd,buf,nbytes) read(fd, buf, nbytes)
#endif

void GC_read_dirty()
{
    unsigned long ps, np;
    int nmaps;
    ptr_t vaddr;
    struct prasmap * map;
    char * bufp;
    ptr_t current_addr, limit;
    int i;
int dummy;

    BZERO(GC_grungy_pages, (sizeof GC_grungy_pages));
    
    bufp = GC_proc_buf;
    if (READ(GC_proc_fd, bufp, GC_proc_buf_size) <= 0) {
#	ifdef PRINTSTATS
            GC_printf1("/proc read failed: GC_proc_buf_size = %lu\n",
            	       GC_proc_buf_size);
#	endif       
        {
            /* Retry with larger buffer. */
            word new_size = 2 * GC_proc_buf_size;
            char * new_buf = GC_scratch_alloc(new_size);
            
            if (new_buf != 0) {
                GC_proc_buf = bufp = new_buf;
                GC_proc_buf_size = new_size;
            }
            if (syscall(SYS_read, GC_proc_fd, bufp, GC_proc_buf_size) <= 0) {
                WARN("Insufficient space for /proc read\n", 0);
                /* Punt:	*/
        	memset(GC_grungy_pages, 0xff, sizeof (page_hash_table));
		memset(GC_written_pages, 0xff, sizeof(page_hash_table));
#		ifdef SOLARIS_THREADS
		    BZERO(GC_fresh_pages,
		    	  MAX_FRESH_PAGES * sizeof (struct hblk *)); 
#		endif
		return;
            }
        }
    }
    /* Copy dirty bits into GC_grungy_pages */
    	nmaps = ((struct prpageheader *)bufp) -> pr_nmap;
	/* printf( "nmaps = %d, PG_REFERENCED = %d, PG_MODIFIED = %d\n",
		     nmaps, PG_REFERENCED, PG_MODIFIED); */
	bufp = bufp + sizeof(struct prpageheader);
	for (i = 0; i < nmaps; i++) {
	    map = (struct prasmap *)bufp;
	    vaddr = (ptr_t)(map -> pr_vaddr);
	    ps = map -> pr_pagesize;
	    np = map -> pr_npage;
	    /* printf("vaddr = 0x%X, ps = 0x%X, np = 0x%X\n", vaddr, ps, np); */
	    limit = vaddr + ps * np;
	    bufp += sizeof (struct prasmap);
	    for (current_addr = vaddr;
	         current_addr < limit; current_addr += ps){
	        if ((*bufp++) & PG_MODIFIED) {
	            register struct hblk * h = (struct hblk *) current_addr;
	            
	            while ((ptr_t)h < current_addr + ps) {
	                register word index = PHT_HASH(h);
	                
	                set_pht_entry_from_index(GC_grungy_pages, index);
#			ifdef SOLARIS_THREADS
			  {
			    register int slot = FRESH_PAGE_SLOT(h);
			    
			    if (GC_fresh_pages[slot] == h) {
			        GC_fresh_pages[slot] = 0;
			    }
			  }
#			endif
	                h++;
	            }
	        }
	    }
	    bufp += sizeof(long) - 1;
	    bufp = (char *)((unsigned long)bufp & ~(sizeof(long)-1));
	}
    /* Update GC_written_pages. */
        GC_or_pages(GC_written_pages, GC_grungy_pages);
#   ifdef SOLARIS_THREADS
      /* Make sure that old stacks are considered completely clean	*/
      /* unless written again.						*/
	GC_old_stacks_are_fresh();
#   endif
}

#undef READ

GC_bool GC_page_was_dirty(h)
struct hblk *h;
{
    register word index = PHT_HASH(h);
    register GC_bool result;
    
    result = get_pht_entry_from_index(GC_grungy_pages, index);
#   ifdef SOLARIS_THREADS
	if (result && PAGE_IS_FRESH(h)) result = FALSE;
	/* This happens only if page was declared fresh since	*/
	/* the read_dirty call, e.g. because it's in an unused  */
	/* thread stack.  It's OK to treat it as clean, in	*/
	/* that case.  And it's consistent with 		*/
	/* GC_page_was_ever_dirty.				*/
#   endif
    return(result);
}

GC_bool GC_page_was_ever_dirty(h)
struct hblk *h;
{
    register word index = PHT_HASH(h);
    register GC_bool result;
    
    result = get_pht_entry_from_index(GC_written_pages, index);
#   ifdef SOLARIS_THREADS
	if (result && PAGE_IS_FRESH(h)) result = FALSE;
#   endif
    return(result);
}

/* Caller holds allocation lock.	*/
void GC_is_fresh(h, n)
struct hblk *h;
word n;
{

    register word index;
    
#   ifdef SOLARIS_THREADS
      register word i;
      
      if (GC_fresh_pages != 0) {
        for (i = 0; i < n; i++) {
          ADD_FRESH_PAGE(h + i);
        }
      }
#   endif
}

# endif /* PROC_VDB */


# ifdef PCR_VDB

# include "vd/PCR_VD.h"

# define NPAGES (32*1024)	/* 128 MB */

PCR_VD_DB  GC_grungy_bits[NPAGES];

ptr_t GC_vd_base;	/* Address corresponding to GC_grungy_bits[0]	*/
			/* HBLKSIZE aligned.				*/

void GC_dirty_init()
{
    GC_dirty_maintained = TRUE;
    /* For the time being, we assume the heap generally grows up */
    GC_vd_base = GC_heap_sects[0].hs_start;
    if (GC_vd_base == 0) {
   	ABORT("Bad initial heap segment");
    }
    if (PCR_VD_Start(HBLKSIZE, GC_vd_base, NPAGES*HBLKSIZE)
	!= PCR_ERes_okay) {
	ABORT("dirty bit initialization failed");
    }
}

void GC_read_dirty()
{
    /* lazily enable dirty bits on newly added heap sects */
    {
        static int onhs = 0;
        int nhs = GC_n_heap_sects;
        for( ; onhs < nhs; onhs++ ) {
            PCR_VD_WriteProtectEnable(
                    GC_heap_sects[onhs].hs_start,
                    GC_heap_sects[onhs].hs_bytes );
        }
    }


    if (PCR_VD_Clear(GC_vd_base, NPAGES*HBLKSIZE, GC_grungy_bits)
        != PCR_ERes_okay) {
	ABORT("dirty bit read failed");
    }
}

GC_bool GC_page_was_dirty(h)
struct hblk *h;
{
    if((ptr_t)h < GC_vd_base || (ptr_t)h >= GC_vd_base + NPAGES*HBLKSIZE) {
	return(TRUE);
    }
    return(GC_grungy_bits[h - (struct hblk *)GC_vd_base] & PCR_VD_DB_dirtyBit);
}

/*ARGSUSED*/
void GC_write_hint(h)
struct hblk *h;
{
    PCR_VD_WriteProtectDisable(h, HBLKSIZE);
    PCR_VD_WriteProtectEnable(h, HBLKSIZE);
}

# endif /* PCR_VDB */

/*
 * Call stack save code for debugging.
 * Should probably be in mach_dep.c, but that requires reorganization.
 */
#if defined(SPARC) && !defined(LINUX)
#   if defined(SUNOS4)
#     include <machine/frame.h>
#   else
#     if defined (DRSNX)
#	include <sys/sparc/frame.h>
#     else
#       include <sys/frame.h>
#     endif
#   endif
#   if NARGS > 6
	--> We only know how to to get the first 6 arguments
#   endif

#ifdef SAVE_CALL_CHAIN
/* Fill in the pc and argument information for up to NFRAMES of my	*/
/* callers.  Ignore my frame and my callers frame.			*/
void GC_save_callers (info) 
struct callinfo info[NFRAMES];
{
  struct frame *frame;
  struct frame *fp;
  int nframes = 0;
  word GC_save_regs_in_stack();

  frame = (struct frame *) GC_save_regs_in_stack ();
  
  for (fp = frame -> fr_savfp; fp != 0 && nframes < NFRAMES;
       fp = fp -> fr_savfp, nframes++) {
      register int i;
      
      info[nframes].ci_pc = fp->fr_savpc;
#     if NARGS > 0
      for (i = 0; i < NARGS; i++) {
	info[nframes].ci_arg[i] = ~(fp->fr_arg[i]);
      }
#     endif
  }
  if (nframes < NFRAMES) info[nframes].ci_pc = 0;
}

#endif /* SAVE_CALL_CHAIN */
#endif /* SPARC */


#if defined(SAVE_CALL_CHAIN) && defined(POWERPC) && defined(MACOS)

#if (NFRAMES > 2)

/* traditional, fixed-size call chain buffer. */

static asm void *GetSP() 
{
	mr		r3, sp
	blr
}

void GC_save_callers(struct callinfo info[NFRAMES]) 
{
	int	i;
	void* currentSP;
	
	currentSP = GetSP();				// GC_save_callers's frame.
	currentSP = *((void **)currentSP);	// GC_debug_malloc's frame.
	currentSP = *((void **)currentSP);	// GC_debug_malloc's caller's frame.
	
	for (i = 0; i < NFRAMES; i++) {
		word* linkageArea = (word *)currentSP;
		// LR saved at 8(SP) in each frame. subtract 4 to get address of calling instruction.
		info[i].ci_pc = linkageArea[2] - sizeof(word);
		currentSP = *((void **)currentSP);
		// the bottom-most frame is marked as pointing to NULL.
		if (currentSP == NULL || (word)currentSP & 0x1)
			break;
	}
}

#else

/* new and improved store all call chains in a tree, which lets us track arbitrarily deep chains. */ 
/* use GC_scratch_alloc() to allocate the tree nodes. */

#include "call_tree.h"

typedef struct stack_frame stack_frame;

struct stack_frame {
	stack_frame*	next;				// savedSP
	void*			savedCR;
	void*			savedLR;
	void*			reserved0;
	void*			reserved1;
	void*			savedTOC;
};

asm stack_frame* getStackFrame()
{
	mr		r3, sp
	blr
}

static call_tree* find_tree(stack_frame* frame)
{
    /* primordial root of the call tree. */
    static call_tree root = { 0, 0, 0, 0, 0 };

    /* ensure frame is non-NULL and 4-byte aligned. */
    if ((frame == NULL) || ((word)frame & 0x3))
        return &root;
    else {
        call_tree* parent = find_tree(frame->next);
        if (parent != NULL) {
            call_tree** link = &parent->children;
            call_tree* tree = *link;
            while (tree != NULL) {
                if (tree->pc == frame->savedLR)
                    break;
                link = &tree->siblings;
                tree = *link;
            }
            if (tree == NULL) {
                /* no tree exists for this frame, so we create one. */
                tree = (call_tree*) GC_scratch_alloc(sizeof(call_tree));
                if (tree != NULL) {
                    tree->pc = frame->savedLR;
                    tree->id = 0;
                    tree->parent = parent;
                    tree->siblings = parent->children;
                    parent->children = tree;
                    tree->children = NULL;
                }
            } else {
                if (parent->children != tree) {
                    /* splay tree to front of list. */
                    *link = tree->siblings;
                    tree->siblings = parent->children;
                    parent->children = tree;
                }
            }
            return tree;
        }
        return NULL;
    }
}

static int fix_stack(stack_frame* frame)
{
    // only fix the REAL stack.
    if (! GC_base(frame)) {
        Ptr stackBase = LMGetCurStackBase();
        while (frame) {
            // if we find a bogus frame in the stack, we clear it out.
            if (frame->next < frame || (Ptr)frame->next > stackBase) {
                frame->next = NULL;
                return 1;
            }
            frame = frame->next;
        }
    }
    return 0;
}

void GC_save_callers(struct callinfo info[NFRAMES]) 
{
	int	i;
	stack_frame* currentFrame;
	call_tree* currentTree = NULL;
	
	currentFrame = getStackFrame();		// GC_save_callers's frame.
	currentFrame = currentFrame->next;	// GC_debug_malloc's frame.
	currentFrame = currentFrame->next;	// GC_debug_malloc's caller's frame.

	if (info != GC_last_stack) {
    	currentTree = find_tree(currentFrame);
    } else {
        static int fixed_stack = 0;
        if (!fixed_stack)
            fixed_stack = fix_stack(currentFrame);
    }
    
	info[0].ci_pc = (word) currentTree;
	info[1].ci_pc = 0;
}

#endif

#endif /* POWERPC && MACOS */

#if defined(SAVE_CALL_CHAIN) && defined(LINUX)

#include "call_tree.h"

typedef struct stack_frame stack_frame;

#if defined(__i386) 
struct stack_frame {
  stack_frame* next;
  void* pc;
};

static stack_frame* getStackFrame()
{
  stack_frame* currentFrame;
#if defined(__i386) 
  __asm__( "movl %%ebp, %0" : "=g"(currentFrame));
#elif defined(__x86_64__)
  __asm__( "movq %%rbp, %0" : "=g"(currentFrame));
#else
  /*
   * It would be nice if this worked uniformly, but at least on i386 and
   * x86_64, it stopped working with gcc 4.1, because it points to the
   * end of the saved registers instead of the start.
   */
  currentFrame = (stack_frame*)__builtin_frame_address(0);
#endif
  currentFrame = currentFrame->next;
  return currentFrame;
}
#endif /* __i386 */

static call_tree* find_tree(stack_frame* frame)
{
    /* primordial root of the call tree. */
    static call_tree root = { 0, 0, 0, 0, 0 };

    long pc = (long)frame->pc;

    if ((pc < 0x08000000) || (pc > 0x7fffffff) || (frame->next < frame)) {
        return &root;
    } else {
        call_tree* parent = find_tree(frame->next);
        if (parent != NULL) {
            call_tree** link = &parent->children;
            call_tree* tree = *link;
            while (tree != NULL) {
                if (tree->pc == frame->pc)
                    break;
                link = &tree->siblings;
                tree = *link;
            }
            if (tree == NULL) {
                /* no tree exists for this frame, so we create one. */
                tree = (call_tree*) GC_scratch_alloc(sizeof(call_tree));
                if (tree != NULL) {
                    tree->pc = frame->pc;
                    tree->id = 0;
                    tree->parent = parent;
                    tree->siblings = parent->children;
                    parent->children = tree;
                    tree->children = NULL;
                }
            } else {
                if (parent->children != tree) {
                    /* splay tree to front of list. */
                    *link = tree->siblings;
                    tree->siblings = parent->children;
                    parent->children = tree;
                }
            }
            return tree;
        }
        return NULL;
    }
}

void GC_save_callers(struct callinfo info[NFRAMES]) 
{
  stack_frame* currentFrame;
  call_tree* currentTree;
	
  currentFrame = getStackFrame();	// GC_save_callers's frame.
  currentFrame = currentFrame->next;	// GC_debug_malloc's frame.
  currentFrame = currentFrame->next;	// GC_debug_malloc's caller's frame.
	
  currentTree = find_tree(currentFrame);
	
  info[0].ci_pc = (word) currentTree;
  info[1].ci_pc = 0;
}

#endif /* defined(SAVE_CALL_CHAIN) && defined(LINUX) */