ptr_chck.c

/*
 * Copyright (c) 1991-1994 by Xerox Corporation.  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 "private/gc_pmark.h"

/*
 * These are checking routines calls to which could be inserted by a
 * preprocessor to validate C pointer arithmetic.
 */

STATIC void GC_CALLBACK GC_default_same_obj_print_proc(void * p, void * q)
{
    ABORT_ARG2("GC_same_obj test failed",
               ": %p and %p are not in the same object", p, q);
}

void (GC_CALLBACK *GC_same_obj_print_proc) (void *, void *)
                = GC_default_same_obj_print_proc;

/* Check that p and q point to the same object.  Call           */
/* *GC_same_obj_print_proc if they don't.                       */
/* Returns the first argument.  (Return value may be hard       */
/* to use due to typing issues.  But if we had a suitable       */
/* preprocessor...)                                             */
/* Succeeds if neither p nor q points to the heap.              */
/* We assume this is performance critical.  (It shouldn't       */
/* be called by production code, but this can easily make       */
/* debugging intolerably slow.)                                 */
GC_API void * GC_CALL GC_same_obj(void *p, void *q)
{
    struct hblk *h;
    hdr *hhdr;
    ptr_t base, limit;
    word sz;

    if (!EXPECT(GC_is_initialized, TRUE)) GC_init();
    hhdr = HDR((word)p);
    if (hhdr == 0) {
        if (divHBLKSZ((word)p) != divHBLKSZ((word)q)
            && HDR((word)q) != 0) {
            goto fail;
        }
        return(p);
    }
    /* If it's a pointer to the middle of a large object, move it       */
    /* to the beginning.                                                */
    if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
        h = HBLKPTR(p) - (word)hhdr;
        hhdr = HDR(h);
        while (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
           h = FORWARDED_ADDR(h, hhdr);
           hhdr = HDR(h);
        }
        limit = (ptr_t)h + hhdr -> hb_sz;
        if ((word)p >= (word)limit || (word)q >= (word)limit
            || (word)q < (word)h) {
            goto fail;
        }
        return(p);
    }
    sz = hhdr -> hb_sz;
    if (sz > MAXOBJBYTES) {
      base = (ptr_t)HBLKPTR(p);
      limit = base + sz;
      if ((word)p >= (word)limit) {
        goto fail;
      }
    } else {
      size_t offset;
      size_t pdispl = HBLKDISPL(p);

      offset = pdispl % sz;
      if (HBLKPTR(p) != HBLKPTR(q)) goto fail;
                /* W/o this check, we might miss an error if    */
                /* q points to the first object on a page, and  */
                /* points just before the page.                 */
      base = (ptr_t)p - offset;
      limit = base + sz;
    }
    /* [base, limit) delimits the object containing p, if any.  */
    /* If p is not inside a valid object, then either q is      */
    /* also outside any valid object, or it is outside          */
    /* [base, limit).                                           */
    if ((word)q >= (word)limit || (word)q < (word)base) {
        goto fail;
    }
    return(p);
fail:
    (*GC_same_obj_print_proc)((ptr_t)p, (ptr_t)q);
    return(p);
}

STATIC void GC_CALLBACK GC_default_is_valid_displacement_print_proc (void *p)
{
    ABORT_ARG1("GC_is_valid_displacement test failed", ": %p not valid", p);
}

void (GC_CALLBACK *GC_is_valid_displacement_print_proc)(void *) =
        GC_default_is_valid_displacement_print_proc;

/* Check that if p is a pointer to a heap page, then it points to       */
/* a valid displacement within a heap object.                           */
/* Uninteresting with GC_all_interior_pointers.                         */
/* Always returns its argument.                                         */
/* Note that we don't lock, since nothing relevant about the header     */
/* should change while we have a valid object pointer to the block.     */
GC_API void * GC_CALL GC_is_valid_displacement(void *p)
{
    hdr *hhdr;
    word pdispl;
    word offset;
    struct hblk *h;
    word sz;

    if (!EXPECT(GC_is_initialized, TRUE)) GC_init();
    hhdr = HDR((word)p);
    if (hhdr == 0) return(p);
    h = HBLKPTR(p);
    if (GC_all_interior_pointers) {
        while (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
           h = FORWARDED_ADDR(h, hhdr);
           hhdr = HDR(h);
        }
    } else if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) {
        goto fail;
    }
    sz = hhdr -> hb_sz;
    pdispl = HBLKDISPL(p);
    offset = pdispl % sz;
    if ((sz > MAXOBJBYTES && (word)p >= (word)h + sz)
        || !GC_valid_offsets[offset]
        || ((word)p + (sz - offset) > (word)(h + 1)
            && !IS_FORWARDING_ADDR_OR_NIL(HDR(h + 1)))) {
        goto fail;
    }
    return(p);
fail:
    (*GC_is_valid_displacement_print_proc)((ptr_t)p);
    return(p);
}

STATIC void GC_CALLBACK GC_default_is_visible_print_proc(void * p)
{
    ABORT_ARG1("GC_is_visible test failed", ": %p not GC-visible", p);
}

void (GC_CALLBACK *GC_is_visible_print_proc)(void * p) =
                GC_default_is_visible_print_proc;

#ifndef THREADS
/* Could p be a stack address? */
   STATIC GC_bool GC_on_stack(void *p)
   {
#    ifdef STACK_GROWS_DOWN
       if ((word)p >= (word)GC_approx_sp()
           && (word)p < (word)GC_stackbottom) {
         return(TRUE);
       }
#    else
       if ((word)p <= (word)GC_approx_sp()
           && (word)p > (word)GC_stackbottom) {
         return(TRUE);
       }
#    endif
     return(FALSE);
   }
#endif

/* Check that p is visible                                              */
/* to the collector as a possibly pointer containing location.          */
/* If it isn't, invoke *GC_is_visible_print_proc.                       */
/* Returns the argument in all cases.  May erroneously succeed          */
/* in hard cases.  (This is intended for debugging use with             */
/* untyped allocations.  The idea is that it should be possible, though */
/* slow, to add such a call to all indirect pointer stores.)            */
/* Currently useless for the multi-threaded worlds.                     */
GC_API void * GC_CALL GC_is_visible(void *p)
{
    hdr *hhdr;

    if ((word)p & (ALIGNMENT - 1)) goto fail;
    if (!EXPECT(GC_is_initialized, TRUE)) GC_init();
#   ifdef THREADS
        hhdr = HDR((word)p);
        if (hhdr != 0 && GC_base(p) == 0) {
            goto fail;
        } else {
            /* May be inside thread stack.  We can't do much. */
            return(p);
        }
#   else
        /* Check stack first: */
          if (GC_on_stack(p)) return(p);
        hhdr = HDR((word)p);
        if (hhdr == 0) {
            if (GC_is_static_root(p)) return(p);
            /* Else do it again correctly:      */
#           if defined(DYNAMIC_LOADING) || defined(MSWIN32) \
                || defined(MSWINCE) || defined(CYGWIN32) || defined(PCR)
              GC_register_dynamic_libraries();
              if (GC_is_static_root(p))
                return(p);
#           endif
            goto fail;
        } else {
            /* p points to the heap. */
            word descr;
            ptr_t base = (ptr_t)GC_base(p);
                        /* TODO: should GC_base be manually inlined? */

            if (NULL == base) goto fail;
            if (HBLKPTR(base) != HBLKPTR(p))
                hhdr = HDR(base);
            descr = hhdr -> hb_descr;
    retry:
            switch(descr & GC_DS_TAGS) {
                case GC_DS_LENGTH:
                    if ((word)p - (word)base > descr) goto fail;
                    break;
                case GC_DS_BITMAP:
                    if ((word)p - (word)base >= WORDS_TO_BYTES(BITMAP_BITS)
                        || ((word)p & (sizeof(word) - 1))) goto fail;
                    if (!(((word)1 << (WORDSZ - ((ptr_t)p - (ptr_t)base) - 1))
                          & descr)) goto fail;
                    break;
                case GC_DS_PROC:
                    /* We could try to decipher this partially.         */
                    /* For now we just punt.                            */
                    break;
                case GC_DS_PER_OBJECT:
                    if ((signed_word)descr >= 0) {
                      descr = *(word *)((ptr_t)base + (descr & ~GC_DS_TAGS));
                    } else {
                      ptr_t type_descr = *(ptr_t *)base;
                      descr = *(word *)(type_descr
                                        - (descr - (word)(GC_DS_PER_OBJECT
                                           - GC_INDIR_PER_OBJ_BIAS)));
                    }
                    goto retry;
            }
            return(p);
        }
#   endif
fail:
    (*GC_is_visible_print_proc)((ptr_t)p);
    return(p);
}

GC_API void * GC_CALL GC_pre_incr (void **p, ptrdiff_t how_much)
{
    void * initial = *p;
    void * result = GC_same_obj((void *)((ptr_t)initial + how_much), initial);

    if (!GC_all_interior_pointers) {
        (void) GC_is_valid_displacement(result);
    }
    return (*p = result);
}

GC_API void * GC_CALL GC_post_incr (void **p, ptrdiff_t how_much)
{
    void * initial = *p;
    void * result = GC_same_obj((void *)((ptr_t)initial + how_much), initial);

    if (!GC_all_interior_pointers) {
        (void) GC_is_valid_displacement(result);
    }
    *p = result;
    return(initial);
}