/* Purify.

   This code is based on public domain codes from CMUCL. It is placed
   in the public domain and is provided as-is.

   Stack direction changes, the x86/CGC stack scavenging, and static
   blue bag feature, by Paul Werkowski, 1995, 1996.
 
   Bug fixes, x86 code movement support, the scavenger hook support,
   and x86/GENCGC stack scavenging, by Douglas Crosher, 1996, 1997,
   1998.

   */
#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>
#include <string.h>

#include "lisp.h"
#include "arch.h"
#include "os.h"
#include "internals.h"
#include "globals.h"
#include "validate.h"
#include "interrupt.h"
#include "purify.h"
#include "interr.h"
#ifdef GENCGC
#include "gencgc.h"
#endif

#undef PRINTNOISE

#if (defined(i386) || defined(__x86_64))
static lispobj *current_dynamic_space_free_pointer;
#endif

#define gc_abort() lose("GC invariant lost!  File \"%s\", line %d\n", \
			__FILE__, __LINE__)

#if 1
#define gc_assert(ex) do { \
	if (!(ex)) gc_abort(); \
} while (0)
#else
#define gc_assert(ex)
#endif


#define assert_static_space_bounds(ptr) do { \
   if (!((lispobj*)STATIC_SPACE_START <= ptr && ptr < (lispobj*)(STATIC_SPACE_START + static_space_size))) \
      lose ("static-space overflow!  File \"%s\", line %d\n", \
			__FILE__, __LINE__); \
} while (0)

#define assert_readonly_space_bounds(ptr) do { \
   if (!((lispobj*)READ_ONLY_SPACE_START <= ptr && ptr < (lispobj*)(READ_ONLY_SPACE_START + read_only_space_size))) \
      lose ("readonly-space overflow!  File \"%s\", line %d\n", \
			__FILE__, __LINE__); \
} while (0)



/* These hold the original end of the read_only and static spaces so we can */
/* tell what are forwarding pointers. */

static lispobj *read_only_end, *static_end;

static lispobj *read_only_free, *static_free;
static lispobj *pscav(lispobj * addr, int nwords, boolean constant);

#define LATERBLOCKSIZE 1020
#define LATERMAXCOUNT 10

static struct later {
    struct later *next;
    union {
	lispobj *ptr;
	int count;
    } u[LATERBLOCKSIZE];
} *later_blocks = NULL;
static int later_count = 0;

#define CEILING(x,y) (((x) + ((y) - 1)) & (~((y) - 1)))
#define NWORDS(x,y) (CEILING((x),(y)) / (y))

#if defined(sparc) || (defined(DARWIN) && defined(__ppc__))
#define RAW_ADDR_OFFSET 0
#else
#define RAW_ADDR_OFFSET (6*sizeof(lispobj) - type_FunctionPointer)
#endif

static boolean
forwarding_pointer_p(lispobj obj)
{
    lispobj *ptr;

    ptr = (lispobj *) obj;

    return ((static_end <= ptr && ptr <= static_free) ||
	    (read_only_end <= ptr && ptr <= read_only_free));
}

static boolean
dynamic_pointer_p(lispobj ptr)
{
#if !(defined(i386) || defined(__x86_64))
    return (ptr >= (lispobj) dynamic_0_space);
#else
    /* Be more conservative, and remember, this is a maybe */
    return (ptr >= (lispobj) current_dynamic_space
	    && ptr < (lispobj) current_dynamic_space_free_pointer);
#endif
}


#if (defined(i386) || defined(__x86_64))

#ifdef WANT_CGC
/* Original x86/CGC stack scavenging code by Paul Werkowski */

static int
maybe_can_move_p(lispobj thing)
{
    lispobj *thingp, header;

    if (dynamic_pointer_p(thing)) {	/* in dynamic space */
	thingp = (lispobj *) PTR(thing);
	header = *thingp;
	if (Pointerp(header) && forwarding_pointer_p(header))
	    return -1;		/* must change it */
	if (LowtagOf(thing) == type_ListPointer)
	    return type_ListPointer;	/* can we check this somehow */
	else if (thing & 3) {	/* not fixnum */
	    int kind = TypeOf(header);

	    /* printf(" %x %x",header,kind); */
	    switch (kind) {	/* something with a header */
	      case type_Bignum:
	      case type_SingleFloat:
	      case type_DoubleFloat:
#ifdef type_LongFloat
	      case type_LongFloat:
#endif
#ifdef type_DoubleDoubleFloat
	      case type_DoubleDoubleFloat:
#endif
	      case type_Sap:
	      case type_SimpleVector:
	      case type_SimpleString:
	      case type_SimpleBitVector:
	      case type_SimpleArrayUnsignedByte2:
	      case type_SimpleArrayUnsignedByte4:
	      case type_SimpleArrayUnsignedByte8:
	      case type_SimpleArrayUnsignedByte16:
	      case type_SimpleArrayUnsignedByte32:
#ifdef type_SimpleArraySignedByte8
	      case type_SimpleArraySignedByte8:
#endif
#ifdef type_SimpleArraySignedByte16
	      case type_SimpleArraySignedByte16:
#endif
#ifdef type_SimpleArraySignedByte30
	      case type_SimpleArraySignedByte30:
#endif
#ifdef type_SimpleArraySignedByte32
	      case type_SimpleArraySignedByte32:
#endif
	      case type_SimpleArraySingleFloat:
	      case type_SimpleArrayDoubleFloat:
#ifdef type_SimpleArrayLongFloat
	      case type_SimpleArrayLongFloat:
#endif
#ifdef type_SimpleArrayDoubleDoubleFloat
	      case type_SimpleArrayDoubleDoubleFloat:
#endif
#ifdef type_SimpleArrayComplexSingleFloat
	      case type_SimpleArrayComplexSingleFloat:
#endif
#ifdef type_SimpleArrayComplexDoubleFloat
	      case type_SimpleArrayComplexDoubleFloat:
#endif
#ifdef type_SimpleArrayComplexLongFloat
	      case type_SimpleArrayComplexLongFloat:
#endif
#ifdef type_SimpleArrayComplexDoubleDoubleFloat
	      case type_SimpleArrayComplexDoubleDoubleFloat:
#endif
	      case type_CodeHeader:
	      case type_FunctionHeader:
	      case type_ClosureFunctionHeader:
	      case type_ReturnPcHeader:
	      case type_ClosureHeader:
	      case type_FuncallableInstanceHeader:
	      case type_InstanceHeader:
	      case type_ValueCellHeader:
	      case type_ByteCodeFunction:
	      case type_ByteCodeClosure:
#ifdef type_DylanFunctionHeader
	      case type_DylanFunctionHeader:
#endif
	      case type_WeakPointer:
	      case type_Fdefn:
#ifdef type_ScavengerHook
	      case type_ScavengerHook:
#endif
		  return kind;
		  break;
	      default:
		  return 0;
	    }
	}
    }
    return 0;
}

static int pverbose = 0;

#define PVERBOSE pverbose
static void
carefully_pscav_stack(lispobj * lowaddr, lispobj * base)
{
    lispobj *sp = lowaddr;

    while (sp < base) {
	int k;
	lispobj thing = *sp;

	if ((unsigned) thing & 0x3) {	/* may be pointer */
	    /* need to check for valid float/double? */
	    k = maybe_can_move_p(thing);
	    if (PVERBOSE)
		printf("%8x %8x %d\n", sp, thing, k);
	    if (k)
		pscav(sp, 1, FALSE);
	}
	sp++;
    }
}
#endif

#if defined(GENCGC) && (defined(i386) || defined(__x86_64))
/*
 * Enhanced x86/GENCGC stack scavenging by Douglas Crosher.
 *
 * Scavenging the stack on the i386 is problematic due to conservative
 * roots and raw return addresses. Here it is handled in two passes:
 * the first pass runs before any objects are moved and tries to
 * identify valid pointers and return address on the stack, the second
 * pass scavenges these.
 */

static unsigned pointer_filter_verbose = 0;

static int
valid_dynamic_space_pointer(lispobj * pointer, lispobj * start_addr)
{
    /* If it's not a return address then it needs to be a valid lisp
       pointer. */
    if (!Pointerp((lispobj) pointer))
	return FALSE;

    /* Check that the object pointed to is consistent with the pointer
       low tag. */
    switch (LowtagOf((lispobj) pointer)) {
      case type_FunctionPointer:
	  /* Start_addr should be the enclosing code object, or a closure
	     header. */
	  switch (TypeOf(*start_addr)) {
	    case type_CodeHeader:
		/* This case is probably caught above. */
		break;
	    case type_ClosureHeader:
	    case type_FuncallableInstanceHeader:
	    case type_ByteCodeFunction:
	    case type_ByteCodeClosure:
#ifdef type_DylanFunctionHeader
	    case type_DylanFunctionHeader:
#endif
		if ((int) pointer != ((int) start_addr + type_FunctionPointer)) {
		    if (pointer_filter_verbose)
			fprintf(stderr, "*Wf2: %p %p %lx\n", pointer,
				start_addr, *start_addr);
		    return FALSE;
		}
		break;
	    default:
		if (pointer_filter_verbose)
		    fprintf(stderr, "*Wf3: %p %p %lx\n", pointer, start_addr,
			    *start_addr);
		return FALSE;
	  }
	  break;
      case type_ListPointer:
	  if ((int) pointer != ((int) start_addr + type_ListPointer)) {
	      if (pointer_filter_verbose)
		  fprintf(stderr, "*Wl1: %p %p %lx\n", pointer, start_addr,
			  *start_addr);
	      return FALSE;
	  }
	  /* Is it plausible cons? */
	  if ((Pointerp(start_addr[0])
	       || ((start_addr[0] & 3) == 0)	/* fixnum */
	       ||(TypeOf(start_addr[0]) == type_BaseChar)
	       || (TypeOf(start_addr[0]) == type_UnboundMarker))
	      && (Pointerp(start_addr[1])
		  || ((start_addr[1] & 3) == 0)	/* fixnum */
		  ||(TypeOf(start_addr[1]) == type_BaseChar)
		  || (TypeOf(start_addr[1]) == type_UnboundMarker)))
	      break;
	  else {
	      if (pointer_filter_verbose)
		  fprintf(stderr, "*Wl2: %p %p %lx\n", pointer, start_addr,
			  *start_addr);
	      return FALSE;
	  }
      case type_InstancePointer:
	  if ((int) pointer != ((int) start_addr + type_InstancePointer)) {
	      if (pointer_filter_verbose)
		  fprintf(stderr, "*Wi1: %p %p %lx\n", pointer, start_addr,
			  *start_addr);
	      return FALSE;
	  }
	  if (TypeOf(start_addr[0]) != type_InstanceHeader) {
	      if (pointer_filter_verbose)
		  fprintf(stderr, "*Wi2: %p %p %lx\n", pointer, start_addr,
			  *start_addr);
	      return FALSE;
	  }
	  break;
      case type_OtherPointer:
	  if ((int) pointer != ((int) start_addr + type_OtherPointer)) {
	      if (pointer_filter_verbose)
		  fprintf(stderr, "*Wo1: %p %p %lx\n", pointer, start_addr,
			  *start_addr);
	      return FALSE;
	  }
	  /* Is it plausible?  Not a cons. X should check the headers. */
	  if (Pointerp(start_addr[0]) || ((start_addr[0] & 3) == 0)) {
	      if (pointer_filter_verbose)
		  fprintf(stderr, "*Wo2: %p %p %lx\n", pointer, start_addr,
			  *start_addr);
	      return FALSE;
	  }
	  switch (TypeOf(start_addr[0])) {
	    case type_UnboundMarker:
	    case type_BaseChar:
		if (pointer_filter_verbose)
		    fprintf(stderr, "*Wo3: %p %p %lx\n", pointer, start_addr,
			    *start_addr);
		return FALSE;

		/* Only pointed to by function pointers? */
	    case type_ClosureHeader:
	    case type_FuncallableInstanceHeader:
	    case type_ByteCodeFunction:
	    case type_ByteCodeClosure:
#ifdef type_DylanFunctionHeader
	    case type_DylanFunctionHeader:
#endif
		if (pointer_filter_verbose)
		    fprintf(stderr, "*Wo4: %p %p %lx\n", pointer, start_addr,
			    *start_addr);
		return FALSE;

	    case type_InstanceHeader:
		if (pointer_filter_verbose)
		    fprintf(stderr, "*Wo5: %p %p %lx\n", pointer, start_addr,
			    *start_addr);
		return FALSE;

		/* The valid other immediate pointer objects */
	    case type_SimpleVector:
	    case type_Ratio:
	    case type_Complex:
#ifdef type_ComplexSingleFloat
	    case type_ComplexSingleFloat:
#endif
#ifdef type_ComplexDoubleFloat
	    case type_ComplexDoubleFloat:
#endif
#ifdef type_ComplexLongFloat
	    case type_ComplexLongFloat:
#endif
#ifdef type_ComplexDoubleDoubleFloat
	    case type_ComplexDoubleDoubleFloat:
#endif
	    case type_SimpleArray:
	    case type_ComplexString:
	    case type_ComplexBitVector:
	    case type_ComplexVector:
	    case type_ComplexArray:
	    case type_ValueCellHeader:
	    case type_SymbolHeader:
	    case type_Fdefn:
	    case type_CodeHeader:
	    case type_Bignum:
	    case type_SingleFloat:
	    case type_DoubleFloat:
#ifdef type_LongFloat
	    case type_LongFloat:
#endif
#ifdef type_DoubleDoubleFloat
	    case type_DoubleDoubleFloat:
#endif
	    case type_SimpleString:
	    case type_SimpleBitVector:
	    case type_SimpleArrayUnsignedByte2:
	    case type_SimpleArrayUnsignedByte4:
	    case type_SimpleArrayUnsignedByte8:
	    case type_SimpleArrayUnsignedByte16:
	    case type_SimpleArrayUnsignedByte32:
#ifdef type_SimpleArraySignedByte8
	    case type_SimpleArraySignedByte8:
#endif
#ifdef type_SimpleArraySignedByte16
	    case type_SimpleArraySignedByte16:
#endif
#ifdef type_SimpleArraySignedByte30
	    case type_SimpleArraySignedByte30:
#endif
#ifdef type_SimpleArraySignedByte32
	    case type_SimpleArraySignedByte32:
#endif
	    case type_SimpleArraySingleFloat:
	    case type_SimpleArrayDoubleFloat:
#ifdef type_SimpleArrayLongFloat
	    case type_SimpleArrayLongFloat:
#endif
#ifdef type_SimpleArrayDoubleDoubleFloat
	    case type_SimpleArrayDoubleDoubleFloat:
#endif
#ifdef type_SimpleArrayComplexSingleFloat
	    case type_SimpleArrayComplexSingleFloat:
#endif
#ifdef type_SimpleArrayComplexDoubleFloat
	    case type_SimpleArrayComplexDoubleFloat:
#endif
#ifdef type_SimpleArrayComplexLongFloat
	    case type_SimpleArrayComplexLongFloat:
#endif
#ifdef type_SimpleArrayComplexDoubleDoubleFloat
	    case type_SimpleArrayComplexDoubleDoubleFloat:
#endif
	    case type_Sap:
	    case type_WeakPointer:
	    case type_ScavengerHook:
		break;

	    default:
		if (pointer_filter_verbose)
		    fprintf(stderr, "*Wo6: %p %p %lx\n", pointer, start_addr,
			    *start_addr);
		return FALSE;
	  }
	  break;
      default:
	  if (pointer_filter_verbose)
	      fprintf(stderr, "*W?: %p %p %lx\n", pointer, start_addr,
		      *start_addr);
	  return FALSE;
    }

    /* Looks good */
    return TRUE;
}

#define MAX_STACK_POINTERS 1024
lispobj *valid_stack_locations[MAX_STACK_POINTERS];
unsigned int num_valid_stack_locations;

#define MAX_STACK_RETURN_ADDRESSES 128
lispobj *valid_stack_ra_locations[MAX_STACK_RETURN_ADDRESSES];
lispobj *valid_stack_ra_code_objects[MAX_STACK_RETURN_ADDRESSES];
unsigned int num_valid_stack_ra_locations;

/*
 * Identify valid stack slots.
 */

static void
setup_i386_stack_scav(lispobj * lowaddr, lispobj * base)
{
    lispobj *sp = lowaddr;

    num_valid_stack_locations = 0;
    num_valid_stack_ra_locations = 0;

    for (sp = lowaddr; sp < base; sp++) {
	lispobj thing = *sp;
	lispobj *start_addr;

	/* Find the object start address */
	if ((start_addr = search_dynamic_space((void *) thing)) != NULL) {
	    /*
	     * Need to allow raw pointers into Code objects for return
	     * addresses. This will also pickup pointers to functions in code
	     * objects.
	     */
	    if (TypeOf(*start_addr) == type_CodeHeader) {
		gc_assert(num_valid_stack_ra_locations <
			  MAX_STACK_RETURN_ADDRESSES);
		valid_stack_ra_locations[num_valid_stack_ra_locations] = sp;
		valid_stack_ra_code_objects[num_valid_stack_ra_locations++] =
		    (lispobj *) ((int) start_addr + type_OtherPointer);
	    } else {
		if (valid_dynamic_space_pointer((void *) thing, start_addr)) {
		    gc_assert(num_valid_stack_locations < MAX_STACK_POINTERS);
		    valid_stack_locations[num_valid_stack_locations++] = sp;
		}
	    }
	}
    }
    if (pointer_filter_verbose) {
	fprintf(stderr, "Number of valid stack pointers = %d\n",
		num_valid_stack_locations);
	fprintf(stderr, "Number of stack return addresses = %d\n",
		num_valid_stack_ra_locations);
    }
}

static void
pscav_i386_stack(void)
{
    int i;

    for (i = 0; i < num_valid_stack_locations; i++)
	pscav(valid_stack_locations[i], 1, FALSE);

    for (i = 0; i < num_valid_stack_ra_locations; i++) {
	lispobj code_obj = (lispobj) (valid_stack_ra_code_objects[i]);

	pscav(&code_obj, 1, FALSE);
	if (pointer_filter_verbose)
	    fprintf(stderr,
		    "*C moved RA %lx to %x; for code object %p to %lx\n",
		    *valid_stack_ra_locations[i],
		    (int) (*valid_stack_ra_locations[i])
		    - ((int) valid_stack_ra_code_objects[i] - (int) code_obj),
		    valid_stack_ra_code_objects[i], code_obj);
	*valid_stack_ra_locations[i] =
	    (lispobj) ((int) (*valid_stack_ra_locations[i])
		       - ((int) valid_stack_ra_code_objects[i] -
			  (int) code_obj));
    }
}
#endif
#endif


static void
pscav_later(lispobj * where, int count)
{
    struct later *new;

    if (count > LATERMAXCOUNT) {
	while (count > LATERMAXCOUNT) {
	    pscav_later(where, LATERMAXCOUNT);
	    count -= LATERMAXCOUNT;
	    where += LATERMAXCOUNT;
	}
    } else {
	if (later_blocks == NULL || later_count == LATERBLOCKSIZE ||
	    (later_count == LATERBLOCKSIZE - 1 && count > 1)) {
	    new = (struct later *) malloc(sizeof(struct later));

	    new->next = later_blocks;
	    if (later_blocks && later_count < LATERBLOCKSIZE)
		later_blocks->u[later_count].ptr = NULL;
	    later_blocks = new;
	    later_count = 0;
	}

	if (count != 1)
	    later_blocks->u[later_count++].count = count;
	later_blocks->u[later_count++].ptr = where;
    }
}

static lispobj
ptrans_boxed(lispobj thing, lispobj header, boolean constant)
{
    int nwords;
    lispobj result, *new, *old;

    nwords = 1 + HeaderValue(header);

    /* Allocate it */
    old = (lispobj *) PTR(thing);
    if (constant) {
	new = read_only_free;
	read_only_free += CEILING(nwords, 2);
	assert_readonly_space_bounds(read_only_free);
    } else {
	new = static_free;
	static_free += CEILING(nwords, 2);
	assert_static_space_bounds(static_free);
    }

    /* Copy it. */
    memmove(new, old, nwords * sizeof(lispobj));

    /* Deposit forwarding pointer. */
    result = (lispobj) new | LowtagOf(thing);
    *old = result;

    /* Scavenge it. */
    pscav(new, nwords, constant);

    return result;
}

/* need to look at the layout to see if it is a pure structure class, and
   only then can we transport as constant.  If it is pure, we can
   ALWAYS transport as a constant */

static lispobj
ptrans_instance(lispobj thing, lispobj header, boolean constant)
{
    lispobj layout = ((struct instance *) PTR(thing))->slots[0];
    lispobj pure = ((struct instance *) PTR(layout))->slots[15];

    switch (pure) {
      case T:
	  return (ptrans_boxed(thing, header, 1));
      case NIL:
	  return (ptrans_boxed(thing, header, 0));
      case 0:{
	      /* Substructure: special case for the compact-info-envs, where
	         the instance may have a point to the dynamic space placed
	         into it (e.g. the cache-name slot), but the lists and arrays
	         at the time of a purify can be moved to the RO space. */
	      int nwords;
	      lispobj result, *new, *old;

	      nwords = 1 + HeaderValue(header);

	      /* Allocate it */
	      old = (lispobj *) PTR(thing);
	      new = static_free;
	      static_free += CEILING(nwords, 2);
	      assert_static_space_bounds(static_free);

	      /* Copy it. */
	      memmove(new, old, nwords * sizeof(lispobj));

	      /* Deposit forwarding pointer. */
	      result = (lispobj) new | LowtagOf(thing);
	      *old = result;

	      /* Scavenge it. */
	      pscav(new, nwords, 1);

	      return result;
	  }
      default:
	  gc_abort();
	  return 0;		/* squelch stupid warning */
    }
}

static lispobj
ptrans_fdefn(lispobj thing, lispobj header)
{
    int nwords;
    lispobj result, *new, *old, oldfn;
    struct fdefn *fdefn;

    nwords = 1 + HeaderValue(header);

    /* Allocate it */
    old = (lispobj *) PTR(thing);
    new = static_free;
    static_free += CEILING(nwords, 2);
    assert_static_space_bounds(static_free);

    /* Copy it. */
    memmove(new, old, nwords * sizeof(lispobj));

    /* Deposit forwarding pointer. */
    result = (lispobj) new | LowtagOf(thing);
    *old = result;

    /* Scavenge the function. */
    fdefn = (struct fdefn *) new;
    oldfn = fdefn->function;
    pscav(&fdefn->function, 1, FALSE);
    if ((char *) oldfn + RAW_ADDR_OFFSET == fdefn->raw_addr)
	fdefn->raw_addr = (char *) fdefn->function + RAW_ADDR_OFFSET;

    return result;
}

static lispobj
ptrans_unboxed(lispobj thing, lispobj header)
{
    int nwords;
    lispobj result, *new, *old;

    nwords = 1 + HeaderValue(header);

    /* Allocate it */
    old = (lispobj *) PTR(thing);
    new = read_only_free;
    read_only_free += CEILING(nwords, 2);
    assert_readonly_space_bounds(read_only_free);

    /* Copy it. */
    memmove(new, old, nwords * sizeof(lispobj));

    /* Deposit forwarding pointer. */
    result = (lispobj) new | LowtagOf(thing);
    *old = result;

    return result;
}

static lispobj
ptrans_vector(lispobj thing, int bits, int extra,
	      boolean boxed, boolean constant)
{
    struct vector *vector;
    int nwords;
    lispobj result, *new;

    vector = (struct vector *) PTR(thing);
#ifdef __x86_64
    nwords =
	2 + (CEILING((fixnum_value(vector->length) + extra) * bits, 64) >> 6);
#else
    nwords =
	2 + (CEILING((fixnum_value(vector->length) + extra) * bits, 32) >> 5);
#endif

    if (boxed && !constant) {
	new = static_free;
	static_free += CEILING(nwords, 2);
	assert_static_space_bounds(static_free);
    } else {
	new = read_only_free;
	read_only_free += CEILING(nwords, 2);
	assert_readonly_space_bounds(read_only_free);
    }

    memmove(new, vector, nwords * sizeof(lispobj));

    result = (lispobj) new | LowtagOf(thing);
    vector->header = result;

    if (boxed)
	pscav(new, nwords, constant);

    return result;
}

#if (defined(i386) || defined(__x86_64))
static void
apply_code_fixups_during_purify(struct code *old_code, struct code *new_code)
{
    int nheader_words, ncode_words, nwords;
    void *code_start_addr;
    lispobj fixups = NIL;
    unsigned displacement = (unsigned) new_code - (unsigned) old_code;
    struct vector *fixups_vector;

    /* Byte compiled code has no fixups. The trace table offset will be
       a fixnum if it's x86 compiled code - check. */
    if (new_code->trace_table_offset & 0x3)
	return;

    /* Else it's x86 machine code. */
    ncode_words = fixnum_value(new_code->code_size);
    nheader_words = HeaderValue(*(lispobj *) new_code);
    nwords = ncode_words + nheader_words;

    code_start_addr = (void *) new_code + nheader_words * sizeof(lispobj);

    /* The first constant should be a pointer to the fixups for this
       code objects. Check. */
    fixups = new_code->constants[0];

    /* It will be 0 or the unbound-marker if there are no fixups, and
       will be an other-pointer to a vector if it is valid. */
    if ((fixups == 0) || (fixups == type_UnboundMarker) || !Pointerp(fixups)) {
#if defined(GENCGC) && (defined(i386) || defined(__x86_64))
	/* Check for a possible errors. */
	sniff_code_object(new_code, displacement);
#endif
	return;
    }

    fixups_vector = (struct vector *) PTR(fixups);

    /* Could be pointing to a forwarding pointer. */
    if (Pointerp(fixups) && (dynamic_pointer_p(fixups))
	&& forwarding_pointer_p(*(lispobj *) fixups_vector)) {
	/* If so then follow it. */
	fixups_vector = (struct vector *) PTR(*(lispobj *) fixups_vector);
    }

    if (TypeOf(fixups_vector->header) == type_SimpleArrayUnsignedByte32) {
	/* Got the fixups for the code block.  Now work through the vector,
	   and apply a fixup at each address. */
	int length = fixnum_value(fixups_vector->length);

	/* offset_vector still has 32-bit elements on amd64.
	   Eventually we will make this consistent with internals.h */
	unsigned int *offset_vector = (unsigned int *) fixups_vector->data;
	int i;

	for (i = 0; i < length; i++) {
	    unsigned offset = offset_vector[i];

	    /* Now check the current value of offset. */
	    unsigned old_value =

		*(unsigned *) ((unsigned) code_start_addr + offset);

	    /* If it's within the old_code object then it must be an
	       absolute fixup (relative ones are not saved) */
	    if ((old_value >= (unsigned) old_code)
		&& (old_value <
		    ((unsigned) old_code + nwords * sizeof(lispobj))))
		/* So add the dispacement. */
		*(unsigned *) ((unsigned) code_start_addr + offset) = old_value
		    + displacement;
	    else
		/* It is outside the old code object so it must be a relative
		   fixup (absolute fixups are not saved). So subtract the
		   displacement. */
		*(unsigned *) ((unsigned) code_start_addr + offset) = old_value
		    - displacement;
	}
    }

    /* No longer need the fixups. */
    new_code->constants[0] = 0;

#if defined(GENCGC) && (defined(i386) || defined(__x86_64))
    /* Check for possible errors. */
    sniff_code_object(new_code, displacement);
#endif
}
#endif

static lispobj
ptrans_code(lispobj thing)
{
    struct code *code, *new;
    int nwords;
    lispobj func, result;

    code = (struct code *) PTR(thing);
    nwords = HeaderValue(code->header) + fixnum_value(code->code_size);

    new = (struct code *) read_only_free;
    read_only_free += CEILING(nwords, 2);
    assert_readonly_space_bounds(read_only_free);

    memmove(new, code, nwords * sizeof(lispobj));

#if (defined(i386) || defined(__x86_64))
    apply_code_fixups_during_purify(code, new);
#endif

    result = (lispobj) new | type_OtherPointer;

    /* Stick in a forwarding pointer for the code object. */
    *(lispobj *) code = result;

    /* Put in forwarding pointers for all the functions. */
    for (func = code->entry_points;
	 func != NIL; func = ((struct function *) PTR(func))->next) {

	gc_assert(LowtagOf(func) == type_FunctionPointer);

	*(lispobj *) PTR(func) = result + (func - thing);
    }

    /* Arrange to scavenge the debug info later. */
    pscav_later(&new->debug_info, 1);

    if (new->trace_table_offset & 0x3)
#if 0
	pscav(&new->trace_table_offset, 1, FALSE);
#else
	new->trace_table_offset = NIL;	/* limit lifetime */
#endif

    /* Scavenge the constants. */
    pscav(new->constants, HeaderValue(new->header) - 5, TRUE);

    /* Scavenge all the functions. */
    pscav(&new->entry_points, 1, TRUE);
    for (func = new->entry_points;
	 func != NIL; func = ((struct function *) PTR(func))->next) {
	gc_assert(LowtagOf(func) == type_FunctionPointer);
	gc_assert(!dynamic_pointer_p(func));

#if (defined(i386) || defined(__x86_64))
	/* Temporarily convert the self pointer to a real function
	   pointer. */
	((struct function *) PTR(func))->self -= RAW_ADDR_OFFSET;
#endif
	pscav(&((struct function *) PTR(func))->self, 2, TRUE);
#if (defined(i386) || defined(__x86_64))
	((struct function *) PTR(func))->self += RAW_ADDR_OFFSET;
#endif
	pscav_later(&((struct function *) PTR(func))->name, 3);
    }

    return result;
}

static lispobj
ptrans_func(lispobj thing, lispobj header)
{
    int nwords;
    lispobj code, *new, *old, result;
    struct function *function;

    /* THING can either be a function header, a closure function header, */
    /* a closure, or a funcallable-instance.  If it's a closure or a */
    /* funcallable-instance, we do the same as ptrans_boxed. */
    /* Otherwise we have to do something strange, 'cause it is buried inside */
    /* a code object. */

    if (TypeOf(header) == type_FunctionHeader ||
	TypeOf(header) == type_ClosureFunctionHeader) {

	/* We can only end up here if the code object has not been */
	/* scavenged, because if it had been scavenged, forwarding pointers */
	/* would have been left behind for all the entry points. */

	function = (struct function *) PTR(thing);
	code =
	    (PTR(thing) -
	     (HeaderValue(function->header) *
	      sizeof(lispobj))) | type_OtherPointer;

	/* This will cause the function's header to be replaced with a */
	/* forwarding pointer. */
	ptrans_code(code);

	/* So we can just return that. */
	return function->header;
    } else {
	/* It's some kind of closure-like thing. */
	nwords = 1 + HeaderValue(header);
	old = (lispobj *) PTR(thing);

	/* Allocate the new one. */
	if (TypeOf(header) == type_FuncallableInstanceHeader) {
	    /* FINs *must* not go in read_only space. */
	    new = static_free;
	    static_free += CEILING(nwords, 2);
	    assert_static_space_bounds(static_free);
	} else {
	    /* Closures can always go in read-only space, 'caues */
	    /* they never change. */

	    new = read_only_free;
	    read_only_free += CEILING(nwords, 2);
	    assert_readonly_space_bounds(read_only_free);
	}
	/* Copy it. */
	memmove(new, old, nwords * sizeof(lispobj));

	/* Deposit forwarding pointer. */
	result = (lispobj) new | LowtagOf(thing);
	*old = result;

	/* Scavenge it. */
	pscav(new, nwords, FALSE);

	return result;
    }
}

static lispobj
ptrans_returnpc(lispobj thing, lispobj header)
{
    lispobj code, new;

    /* Find the corresponding code object. */
    code = thing - HeaderValue(header) * sizeof(lispobj);

    /* Make sure it's been transported. */
    new = *(lispobj *) PTR(code);
    if (!forwarding_pointer_p(new))
	new = ptrans_code(code);

    /* Maintain the offset: */
    return new + (thing - code);
}

#define WORDS_PER_CONS CEILING(sizeof(struct cons) / sizeof(lispobj), 2)

static lispobj
ptrans_list(lispobj thing, boolean constant)
{
    struct cons *old, *new, *orig;
    int length;

    if (constant)
	orig = (struct cons *) read_only_free;
    else
	orig = (struct cons *) static_free;
    length = 0;

    do {
	/* Allocate a new cons cell. */
	old = (struct cons *) PTR(thing);
	if (constant) {
	    new = (struct cons *) read_only_free;
	    read_only_free += WORDS_PER_CONS;
	    assert_readonly_space_bounds(read_only_free);
	} else {
	    new = (struct cons *) static_free;
	    static_free += WORDS_PER_CONS;
	    assert_static_space_bounds(static_free);
	}

	/* Copy the cons cell and keep a pointer to the cdr. */
	new->car = old->car;
	thing = new->cdr = old->cdr;

	/* Set up the forwarding pointer. */
	*(lispobj *) old = ((lispobj) new) | type_ListPointer;

	/* And count this cell. */
	length++;
    } while (LowtagOf(thing) == type_ListPointer &&
	     dynamic_pointer_p(thing) &&
	     !(forwarding_pointer_p(*(lispobj *) PTR(thing))));

    /* Scavenge the list we just copied. */
    pscav((lispobj *) orig, length * WORDS_PER_CONS, constant);

    return ((lispobj) orig) | type_ListPointer;
}

static lispobj
ptrans_otherptr(lispobj thing, lispobj header, boolean constant)
{
    switch (TypeOf(header)) {
      case type_Bignum:
      case type_SingleFloat:
      case type_DoubleFloat:
#ifdef type_LongFloat
      case type_LongFloat:
#endif
#ifdef type_DoubleDoubleFloat
      case type_DoubleDoubleFloat:
#endif
#ifdef type_ComplexSingleFloat
      case type_ComplexSingleFloat:
#endif
#ifdef type_ComplexDoubleFloat
      case type_ComplexDoubleFloat:
#endif
#ifdef type_ComplexLongFloat
      case type_ComplexLongFloat:
#endif
#ifdef type_ComplexDoubleDoubleFloat
      case type_ComplexDoubleDoubleFloat:
#endif
      case type_Sap:
	  return ptrans_unboxed(thing, header);

      case type_Ratio:
      case type_Complex:
      case type_SimpleArray:
      case type_ComplexString:
      case type_ComplexVector:
      case type_ComplexArray:
	  return ptrans_boxed(thing, header, constant);

      case type_ValueCellHeader:
      case type_WeakPointer:
#ifdef type_ScavengerHook
      case type_ScavengerHook:
#endif
	  return ptrans_boxed(thing, header, FALSE);

      case type_SymbolHeader:
	  return ptrans_boxed(thing, header, FALSE);

      case type_SimpleString:
#ifndef UNICODE
	  return ptrans_vector(thing, 8, 1, FALSE, constant);
#else
	  return ptrans_vector(thing, 16, 1, FALSE, constant);
#endif
      case type_SimpleBitVector:
	  return ptrans_vector(thing, 1, 0, FALSE, constant);

      case type_SimpleVector:
#ifdef __x86_64
	  return ptrans_vector(thing, 64, 0, TRUE, constant);
#else
	  return ptrans_vector(thing, 32, 0, TRUE, constant);
#endif

      case type_SimpleArrayUnsignedByte2:
	  return ptrans_vector(thing, 2, 0, FALSE, constant);

      case type_SimpleArrayUnsignedByte4:
	  return ptrans_vector(thing, 4, 0, FALSE, constant);

      case type_SimpleArrayUnsignedByte8:
#ifdef type_SimpleArraySignedByte8
      case type_SimpleArraySignedByte8:
#endif
	  return ptrans_vector(thing, 8, 0, FALSE, constant);

      case type_SimpleArrayUnsignedByte16:
#ifdef type_SimpleArraySignedByte16
      case type_SimpleArraySignedByte16:
#endif
	  return ptrans_vector(thing, 16, 0, FALSE, constant);

      case type_SimpleArrayUnsignedByte32:
#ifdef type_SimpleArraySignedByte30
      case type_SimpleArraySignedByte30:
#endif
#ifdef type_SimpleArraySignedByte32
      case type_SimpleArraySignedByte32:
#endif
	  return ptrans_vector(thing, 32, 0, FALSE, constant);

      case type_SimpleArraySingleFloat:
	  return ptrans_vector(thing, 32, 0, FALSE, constant);

      case type_SimpleArrayDoubleFloat:
	  return ptrans_vector(thing, 64, 0, FALSE, constant);

#ifdef type_SimpleArrayLongFloat
      case type_SimpleArrayLongFloat:
#if (defined(i386) || defined(__x86_64))
	  return ptrans_vector(thing, 96, 0, FALSE, constant);
#endif
#ifdef sparc
	  return ptrans_vector(thing, 128, 0, FALSE, constant);
#endif
#endif

#ifdef type_SimpleArrayDoubleDoubleFloat
    case type_SimpleArrayDoubleDoubleFloat:
      return ptrans_vector(thing, 128, 0, FALSE, constant);
#endif
      
#ifdef type_SimpleArrayComplexSingleFloat
      case type_SimpleArrayComplexSingleFloat:
	  return ptrans_vector(thing, 64, 0, FALSE, constant);
#endif

#ifdef type_SimpleArrayComplexDoubleFloat
      case type_SimpleArrayComplexDoubleFloat:
	  return ptrans_vector(thing, 128, 0, FALSE, constant);
#endif

#ifdef type_SimpleArrayComplexLongFloat
      case type_SimpleArrayComplexLongFloat:
#if (defined(i386) || defined(__x86_64))
	  return ptrans_vector(thing, 192, 0, FALSE, constant);
#endif
#ifdef sparc
	  return ptrans_vector(thing, 256, 0, FALSE, constant);
#endif
#endif

#ifdef type_SimpleArrayComplexDoubleDoubleFloat
      case type_SimpleArrayComplexDoubleDoubleFloat:
	  return ptrans_vector(thing, 256, 0, FALSE, constant);
#endif

          
      case type_CodeHeader:
	  return ptrans_code(thing);

      case type_ReturnPcHeader:
	  return ptrans_returnpc(thing, header);

      case type_Fdefn:
	  return ptrans_fdefn(thing, header);

      default:
	  /* Should only come across other pointers to the above stuff. */
	  gc_abort();
	  return NIL;
    }
}

static int
pscav_fdefn(struct fdefn *fdefn)
{
    boolean fix_func;

    fix_func =
	((char *) (fdefn->function + RAW_ADDR_OFFSET) == fdefn->raw_addr);
    pscav(&fdefn->name, 1, TRUE);
    pscav(&fdefn->function, 1, FALSE);
    if (fix_func)
	fdefn->raw_addr = (char *) (fdefn->function + RAW_ADDR_OFFSET);
    return sizeof(struct fdefn) / sizeof(lispobj);
}

#if (defined(i386) || defined(__x86_64))
/* now putting code objects in static space */
static int
pscav_code(struct code *code)
{
    int nwords;
    lispobj func;

    nwords = HeaderValue(code->header) + fixnum_value(code->code_size);

    /* pw--The trace_table_offset slot can contain a list pointer. This
     * occurs when the code object is a top level form that initializes
     * a byte-compiled function. The fact that purify was ignoring this
     * slot may be a bug unrelated to the x86 port, except that TLF's
     * normally become unreachable after the loader calls them and 
     * won't be seen by purify at all!!
     */
    if (code->trace_table_offset & 0x3)
#if 0
	pscav(&code->trace_table_offset, 1, FALSE);
#else
	code->trace_table_offset = NIL;	/* limit lifetime */
#endif

    /* Arrange to scavenge the debug info later. */
    pscav_later(&code->debug_info, 1);

    /* Scavenge the constants. */
    pscav(code->constants, HeaderValue(code->header) - 5, TRUE);

    /* Scavenge all the functions. */
    pscav(&code->entry_points, 1, TRUE);
    for (func = code->entry_points;
	 func != NIL; func = ((struct function *) PTR(func))->next) {
	gc_assert(LowtagOf(func) == type_FunctionPointer);
	gc_assert(!dynamic_pointer_p(func));

	/* Temporarly convert the self pointer to a real function
	   pointer. */
	((struct function *) PTR(func))->self -= RAW_ADDR_OFFSET;
	pscav(&((struct function *) PTR(func))->self, 2, TRUE);
	((struct function *) PTR(func))->self += RAW_ADDR_OFFSET;
	pscav_later(&((struct function *) PTR(func))->name, 3);
    }

    return CEILING(nwords, 2);
}
#endif

#ifdef type_ScavengerHook
static struct scavenger_hook *scavenger_hooks = (void *) NIL;

static int
pscav_scavenger_hook(struct scavenger_hook *scav_hook)
{
    lispobj old_value = scav_hook->value;

    /* Scavenge the value */
    pscav((lispobj *) scav_hook + 1, 1, FALSE);

    /* Did the value object move? */
    if (scav_hook->value != old_value) {
	/* Check if this hook is already noted. */
	if (scav_hook->next == NULL) {
	    scav_hook->next = scavenger_hooks;
	    scavenger_hooks =
		(struct scavenger_hook *) ((unsigned long) scav_hook |
					   type_OtherPointer);
	}
    }

    /* Scavenge the function */
    pscav((lispobj *) scav_hook + 2, 1, FALSE);

    return 4;
}
#endif

static lispobj *
pscav(lispobj * addr, int nwords, boolean constant)
{
    lispobj thing, *thingp, header;
    int count = 0;
    struct vector *vector;

    while (nwords > 0) {
	thing = *addr;
	if (Pointerp(thing)) {
	    /* It's a pointer.  Is it something we might have to move? */
	    if (dynamic_pointer_p(thing)) {
		/* Maybe.  Have we already moved it? */
		thingp = (lispobj *) PTR(thing);
		header = *thingp;
		if (Pointerp(header) && forwarding_pointer_p(header))
		    /* Yep, so just copy the forwarding pointer. */
		    thing = header;
		else {
		    /* Nope, copy the object. */
		    switch (LowtagOf(thing)) {
		      case type_FunctionPointer:
			  thing = ptrans_func(thing, header);
			  break;

		      case type_ListPointer:
			  thing = ptrans_list(thing, constant);
			  break;

		      case type_InstancePointer:
			  thing = ptrans_instance(thing, header, constant);
			  break;

		      case type_OtherPointer:
			  thing = ptrans_otherptr(thing, header, constant);
			  break;

		      default:
			  /* It was a pointer, but not one of them? */
			  gc_abort();
		    }
		}
		*addr = thing;
	    }
	    count = 1;
	} else if (thing & 3) {
	    /* It's an other immediate.  Maybe the header for an unboxed */
	    /* object. */
	    switch (TypeOf(thing)) {
	      case type_Bignum:
	      case type_SingleFloat:
	      case type_DoubleFloat:
#ifdef type_LongFloat
	      case type_LongFloat:
#endif
#ifdef type_DoubleDoubleFloat
	      case type_DoubleDoubleFloat:
#endif
	      case type_Sap:
		  /* It's an unboxed simple object. */
		  count = HeaderValue(thing) + 1;
		  break;

	      case type_SimpleVector:
		  if (HeaderValue(thing) == subtype_VectorValidHashing)
		      *addr = (subtype_VectorMustRehash << type_Bits) |
			  type_SimpleVector;
		  count = 1;
		  break;

	      case type_SimpleString:
		  vector = (struct vector *) addr;
#ifdef __x86_64
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length) + 1, 8) + 2,
			      2);
#else
		  count =
#ifndef UNICODE
		      CEILING(NWORDS(fixnum_value(vector->length) + 1, 4) + 2,
			      2);
#else
		      CEILING(NWORDS(fixnum_value(vector->length) + 1, 2) + 2,
			      2);
#endif
#endif
		  break;

	      case type_SimpleBitVector:
		  vector = (struct vector *) addr;
#ifdef __x86_64
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 64) + 2, 2);
#else
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 32) + 2, 2);
#endif
		  break;

	      case type_SimpleArrayUnsignedByte2:
		  vector = (struct vector *) addr;
#ifdef __x86_64
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 32) + 2, 2);
#else
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 16) + 2, 2);
#endif
		  break;

	      case type_SimpleArrayUnsignedByte4:
		  vector = (struct vector *) addr;
#ifdef __x86_64
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 16) + 2, 2);
#else
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 8) + 2, 2);
#endif
		  break;

	      case type_SimpleArrayUnsignedByte8:
#ifdef type_SimpleArraySignedByte8
	      case type_SimpleArraySignedByte8:
#endif
		  vector = (struct vector *) addr;
#ifdef __x86_64
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 8) + 2, 2);
#else
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 4) + 2, 2);
#endif
		  break;

	      case type_SimpleArrayUnsignedByte16:
#ifdef type_SimpleArraySignedByte16
	      case type_SimpleArraySignedByte16:
#endif
		  vector = (struct vector *) addr;
#ifdef __x86_64
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 4) + 2, 2);
#else
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 2) + 2, 2);
#endif
		  break;

	      case type_SimpleArrayUnsignedByte32:
#ifdef type_SimpleArraySignedByte30
	      case type_SimpleArraySignedByte30:
#endif
#ifdef type_SimpleArraySignedByte32
	      case type_SimpleArraySignedByte32:
#endif
		  vector = (struct vector *) addr;
#ifdef __x86_64
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 2) + 2, 2);
#else
		  count = CEILING(fixnum_value(vector->length) + 2, 2);
#endif
		  break;

	      case type_SimpleArraySingleFloat:
		  vector = (struct vector *) addr;
#ifdef __x86_64
		  count =
		      CEILING(NWORDS(fixnum_value(vector->length), 2) + 2, 2);
#else
		  count = CEILING(fixnum_value(vector->length) + 2, 2);
#endif
		  break;

	      case type_SimpleArrayDoubleFloat:
#ifdef type_SimpleArrayComplexSingleFloat
	      case type_SimpleArrayComplexSingleFloat:
#endif
		  vector = (struct vector *) addr;
#ifdef __x86_64
		  count = CEILING(fixnum_value(vector->length) + 2, 2);
#else
		  count = fixnum_value(vector->length) * 2 + 2;
#endif
		  break;

#ifdef type_SimpleArrayLongFloat
	      case type_SimpleArrayLongFloat:
		  vector = (struct vector *) addr;
#ifdef i386
		  count = fixnum_value(vector->length) * 3 + 2;
#endif
#ifdef __x86_64
		  count = fixnum_value(vector->length) * 2 + 2;
#endif
#ifdef sparc
		  count = fixnum_value(vector->length) * 4 + 2;
#endif
		  break;
#endif

#ifdef type_SimpleArrayComplexDoubleFloat
	      case type_SimpleArrayComplexDoubleFloat:
		  vector = (struct vector *) addr;
#ifdef __x86_64
		  count = fixnum_value(vector->length) * 2 + 2;
#else
		  count = fixnum_value(vector->length) * 4 + 2;
#endif
		  break;
#endif

#ifdef type_SimpleArrayComplexLongFloat
	      case type_SimpleArrayComplexLongFloat:
		  vector = (struct vector *) addr;
#ifdef i386
		  count = fixnum_value(vector->length) * 6 + 2;
#endif
#ifdef __x86_64
		  count = fixnum_value(vector->length) * 4 + 2;
#endif
#ifdef sparc
		  count = fixnum_value(vector->length) * 8 + 2;
#endif
		  break;
#endif

#ifdef type_SimpleArrayComplexDoubleDoubleFloat
	      case type_SimpleArrayComplexDoubleDoubleFloat:
		  vector = (struct vector *) addr;
		  count = fixnum_value(vector->length) * 8 + 2;
		  break;
#endif

	      case type_CodeHeader:
#if !(defined(i386) || defined(__x86_64))
		  gc_abort();	/* No code headers in static space */
#else
		  count = pscav_code((struct code *) addr);
#endif
		  break;

	      case type_FunctionHeader:
	      case type_ClosureFunctionHeader:
	      case type_ReturnPcHeader:
		  /* We should never hit any of these, 'cause they occur */
		  /* buried in the middle of code objects. */

		  gc_abort();


		  break;

#if (defined(i386) || defined(__x86_64))
	      case type_ClosureHeader:
	      case type_FuncallableInstanceHeader:
	      case type_ByteCodeFunction:
	      case type_ByteCodeClosure:
#ifdef type_DylanFunctionHeader
	      case type_DylanFunctionHeader:
#endif
		  /* The function self pointer needs special care on the
		     x86 because it is the real entry point. */
		  {
		      lispobj fun = ((struct closure *) addr)->function

			  - RAW_ADDR_OFFSET;
		      pscav(&fun, 1, constant);
		      ((struct closure *) addr)->function = fun + RAW_ADDR_OFFSET;
		  }
		  count = 2;
		  break;
#endif

	      case type_WeakPointer:
		  /* Weak pointers get preserved during purify, 'cause I don't */
		  /* feel like figuring out how to break them. */
		  pscav(addr + 1, 2, constant);
		  count = 4;
		  break;

	      case type_Fdefn:
		  /* We have to handle fdefn objects specially, so we can fix */
		  /* up the raw function address. */
		  count = pscav_fdefn((struct fdefn *) addr);
		  break;

#ifdef type_ScavengerHook
	      case type_ScavengerHook:
		  count = pscav_scavenger_hook((struct scavenger_hook *) addr);
		  break;
#endif

	      default:
		  count = 1;
		  break;
	    }
	} else {
	    /* It's a fixnum. */
	    count = 1;
	}

	addr += count;
	nwords -= count;
    }

    return addr;
}

int
purify(lispobj static_roots, lispobj read_only_roots)
{
    lispobj *clean;
    int count, i;
    struct later *laters, *next;

#ifdef PRINTNOISE
    printf("[Doing purification:");
    fflush(stdout);
#endif

    if (fixnum_value(SymbolValue(FREE_INTERRUPT_CONTEXT_INDEX)) != 0) {
	printf(" Ack! Can't purify interrupt contexts. ");
	fflush(stdout);
	return 0;
    }
#if defined(ibmrt) || defined(i386) || defined(__x86_64)
    current_dynamic_space_free_pointer =
	(lispobj *) SymbolValue(ALLOCATION_POINTER);
#endif

    read_only_end = read_only_free =
	(lispobj *) SymbolValue(READ_ONLY_SPACE_FREE_POINTER);
    static_end = static_free =
	(lispobj *) SymbolValue(STATIC_SPACE_FREE_POINTER);

#ifdef PRINTNOISE
    printf(" roots");
    fflush(stdout);
#endif

#ifdef GENCGC
#if (defined(i386) || defined(__x86_64))
    gc_assert(control_stack_end > ((&read_only_roots) + 1));
    setup_i386_stack_scav(((&static_roots) - 2), control_stack_end);
#elif defined(sparc)
#endif
#endif

    pscav(&static_roots, 1, FALSE);
    pscav(&read_only_roots, 1, TRUE);

#ifdef PRINTNOISE
    printf(" handlers");
    fflush(stdout);
#endif
    pscav((lispobj *) interrupt_handlers,
	  sizeof(interrupt_handlers) / sizeof(lispobj), FALSE);

#ifdef PRINTNOISE
    printf(" stack");
    fflush(stdout);
#endif
#if !(defined(i386) || defined(__x86_64))
    pscav(control_stack, current_control_stack_pointer - control_stack, FALSE);
#else
#ifdef GENCGC
    pscav_i386_stack();
#endif
#ifdef WANT_CGC
    gc_assert(control_stack_end > ((&read_only_roots) + 1));
    carefully_pscav_stack(((&read_only_roots) + 1), control_stack_end);
#endif
#endif

#ifdef PRINTNOISE
    printf(" bindings");
    fflush(stdout);
#endif
#if !defined(BINDING_STACK_POINTER)
    pscav(binding_stack, current_binding_stack_pointer - binding_stack, FALSE);
#else
    pscav(binding_stack,
	  (lispobj *) SymbolValue(BINDING_STACK_POINTER) - binding_stack,
	  FALSE);
#endif

#ifdef SCAVENGE_READ_ONLY_SPACE
    if (SymbolValue(SCAVENGE_READ_ONLY_SPACE) != type_UnboundMarker
	&& SymbolValue(SCAVENGE_READ_ONLY_SPACE) != NIL) {
	unsigned read_only_space_size =
	    (lispobj *) SymbolValue(READ_ONLY_SPACE_FREE_POINTER) -

	    read_only_space;
	fprintf(stderr, "Scavenge read only space: %lu bytes\n",
		(unsigned long) (read_only_space_size * sizeof(lispobj)));
	pscav(read_only_space, read_only_space_size, FALSE);
    }
#endif

#ifdef PRINTNOISE
    printf(" static");
    fflush(stdout);
#endif
    clean = static_space;
    do {
	while (clean < static_free)
          clean = pscav(clean, static_free - clean, FALSE);
        if (clean != static_free) {
            fprintf(stderr, "*** clean (%p) != static_free (%p)\n",
                    clean, static_free);
            fprintf(stderr, "    Possible heap corruption?\n");
        }
        
	laters = later_blocks;
	count = later_count;
	later_blocks = NULL;
	later_count = 0;
	while (laters != NULL) {
	    for (i = 0; i < count; i++) {
		if (laters->u[i].count == 0);
		else if (laters->u[i].count <= LATERMAXCOUNT) {
		    pscav(laters->u[i + 1].ptr, laters->u[i].count, TRUE);
		    i++;
		} else
		    pscav(laters->u[i].ptr, 1, TRUE);
	    }
	    next = laters->next;
	    free(laters);
	    laters = next;
	    count = LATERBLOCKSIZE;
	}
    } while (clean < static_free || later_blocks != NULL);

    if (clean != static_free) {
        fprintf(stderr, "*** clean (%p) != static_free (%p)\n",
                clean, static_free);
        fprintf(stderr, "    Possible heap corruption?\n");
    }
        


#ifdef PRINTNOISE
    printf(" cleanup");
    fflush(stdout);
#endif

#if defined(WANT_CGC) && defined(X86_CGC_ACTIVE_P)
    if (SymbolValue(X86_CGC_ACTIVE_P) != T)
	os_zero((os_vm_address_t) current_dynamic_space,
		(os_vm_size_t) dynamic_space_size);
#else
#if !defined(GENCGC)
    os_zero((os_vm_address_t) current_dynamic_space,
	    (os_vm_size_t) dynamic_space_size);
#endif
#endif

    /*
     * Zero stack. Note the stack is also zeroed by sub-gc calling
     * scrub-control-stack - this zeros the stack on the x86.
     */
#if !(defined(i386) || defined(__x86_64))
    os_zero((os_vm_address_t) current_control_stack_pointer,
	    (os_vm_size_t) (control_stack_size -
			    ((current_control_stack_pointer - control_stack) *
			     sizeof(lispobj))));
#endif

#if defined(WANT_CGC) && defined(STATIC_BLUE_BAG)
    {
	lispobj bag = SymbolValue(STATIC_BLUE_BAG);
	struct cons *cons = (struct cons *) static_free;
	struct cons *pair = cons + 1;

	static_free += 2 * WORDS_PER_CONS;
	if (bag == type_UnboundMarker)
	    bag = NIL;
	cons->cdr = bag;
	cons->car = (lispobj) pair | type_ListPointer;
	pair->car = (lispobj) static_end;
	pair->cdr = (lispobj) static_free;
	bag = (lispobj) cons | type_ListPointer;
	SetSymbolValue(STATIC_BLUE_BAG, bag);
    }
#endif

    /*
     * It helps to update the heap free pointers so that free_heap can
     * verify after it's done.
     */
    SetSymbolValue(READ_ONLY_SPACE_FREE_POINTER, (lispobj) read_only_free);
    SetSymbolValue(STATIC_SPACE_FREE_POINTER, (lispobj) static_free);

#if 0
    /*
     * Test the static space for validity.  This was useful in
     * catching some corruption problems on x86.  Should we enable
     * this all the time?
     */
    verify_space((lispobj *) static_space, static_free - static_space);
#endif
    
#if !defined(ALLOCATION_POINTER)
    current_dynamic_space_free_pointer = current_dynamic_space;
#else
#if defined(WANT_CGC) && defined(X86_CGC_ACTIVE_P)
    /* X86 using CGC */
    if (SymbolValue(X86_CGC_ACTIVE_P) != T)
	SetSymbolValue(ALLOCATION_POINTER, (lispobj) current_dynamic_space);
    else
	cgc_free_heap();
#else
#ifdef GENCGC
    gc_free_heap();
#else
    /* ibmrt using GC */
    SetSymbolValue(ALLOCATION_POINTER, (lispobj) current_dynamic_space);
#endif
#endif
#endif

#ifdef type_ScavengerHook
    /* Call the scavenger hook functions */
    {
	struct scavenger_hook *sh;

	for (sh = (struct scavenger_hook *) PTR((int) scavenger_hooks);
	     (lispobj) sh != PTR(NIL);) {
	    struct scavenger_hook *sh_next =
		(struct scavenger_hook *) PTR((unsigned long) sh->next);

	    funcall0(sh->function);
	    sh->next = NULL;
	    sh = sh_next;
	}
	scavenger_hooks = (struct scavenger_hook *) NIL;
    }
#endif

#ifdef PRINTNOISE
    printf(" Done.]\n");
    fflush(stdout);
#endif

    return 0;
}
