boehm-gc/include/private/gc_hdrs.h

   1 /*
   2  * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
   3  * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
   4  *
   5  * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
   6  * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
   7  *
   8  * Permission is hereby granted to use or copy this program
   9  * for any purpose,  provided the above notices are retained on all copies.
  10  * Permission to modify the code and to distribute modified code is granted,
  11  * provided the above notices are retained, and a notice that the code was
  12  * modified is included with the above copyright notice.
  13  */
  14 /* Boehm, July 11, 1995 11:54 am PDT */
  15 # ifndef GC_HEADERS_H
  16 # define GC_HEADERS_H
  17 typedef struct hblkhdr hdr;
  18
  19 # if CPP_WORDSZ != 32 && CPP_WORDSZ < 36
  20         --> Get a real machine.
  21 # endif
  22
  23 /*
  24  * The 2 level tree data structure that is used to find block headers.
  25  * If there are more than 32 bits in a pointer, the top level is a hash
  26  * table.
  27  *
  28  * This defines HDR, GET_HDR, and SET_HDR, the main macros used to
  29  * retrieve and set object headers.
  30  *
  31  * Since 5.0 alpha 5, we can also take advantage of a header lookup
  32  * cache.  This is a locally declared direct mapped cache, used inside
  33  * the marker.  The HC_GET_HDR macro uses and maintains this
  34  * cache.  Assuming we get reasonable hit rates, this shaves a few
  35  * memory references from each pointer validation.
  36  */
  37
  38 # if CPP_WORDSZ > 32
  39 #   define HASH_TL
  40 # endif
  41
  42 /* Define appropriate out-degrees for each of the two tree levels       */
  43 # ifdef SMALL_CONFIG
  44 #   define LOG_BOTTOM_SZ 11
  45         /* Keep top index size reasonable with smaller blocks. */
  46 # else
  47 #   define LOG_BOTTOM_SZ 10
  48 # endif
  49 # ifndef HASH_TL
  50 #   define LOG_TOP_SZ (WORDSZ - LOG_BOTTOM_SZ - LOG_HBLKSIZE)
  51 # else
  52 #   define LOG_TOP_SZ 11
  53 # endif
  54 # define TOP_SZ (1 << LOG_TOP_SZ)
  55 # define BOTTOM_SZ (1 << LOG_BOTTOM_SZ)
  56
  57 #ifndef SMALL_CONFIG
  58 # define USE_HDR_CACHE
  59 #endif
  60
  61 /* #define COUNT_HDR_CACHE_HITS  */
  62
  63 extern hdr * GC_invalid_header; /* header for an imaginary block        */
  64                                 /* containing no objects.               */
  65
  66
  67 /* Check whether p and corresponding hhdr point to long or invalid      */
  68 /* object.  If so, advance hhdr to                                      */
  69 /* beginning of block, or set hhdr to GC_invalid_header.                */
  70 #define ADVANCE(p, hhdr, source) \
  71             { \
  72               hdr * new_hdr = GC_invalid_header; \
  73               p = GC_find_start(p, hhdr, &new_hdr); \
  74               hhdr = new_hdr; \
  75             }
  76
  77 #ifdef USE_HDR_CACHE
  78
  79 # ifdef COUNT_HDR_CACHE_HITS
  80     extern word GC_hdr_cache_hits;
  81     extern word GC_hdr_cache_misses;
  82 #   define HC_HIT() ++GC_hdr_cache_hits
  83 #   define HC_MISS() ++GC_hdr_cache_misses
  84 # else
  85 #   define HC_HIT()
  86 #   define HC_MISS()
  87 # endif
  88
  89   typedef struct hce {
  90     word block_addr;    /* right shifted by LOG_HBLKSIZE */
  91     hdr * hce_hdr;
  92   } hdr_cache_entry;
  93
  94 # define HDR_CACHE_SIZE 8  /* power of 2 */
  95
  96 # define DECLARE_HDR_CACHE \
  97         hdr_cache_entry hdr_cache[HDR_CACHE_SIZE]
  98
  99 # define INIT_HDR_CACHE BZERO(hdr_cache, sizeof(hdr_cache));
 100
 101 # define HCE(h) hdr_cache + (((word)(h) >> LOG_HBLKSIZE) & (HDR_CACHE_SIZE-1))
 102
 103 # define HCE_VALID_FOR(hce,h) ((hce) -> block_addr == \
 104                                 ((word)(h) >> LOG_HBLKSIZE))
 105
 106 # define HCE_HDR(h) ((hce) -> hce_hdr)
 107
 108
 109 /* Analogous to GET_HDR, except that in the case of large objects, it   */
 110 /* Returns the header for the object beginning, and updates p.          */
 111 /* Returns &GC_bad_header instead of 0.  All of this saves a branch     */
 112 /* in the fast path.                                                    */
 113 # define HC_GET_HDR(p, hhdr, source) \
 114         { \
 115           hdr_cache_entry * hce = HCE(p); \
 116           if (HCE_VALID_FOR(hce, p)) { \
 117             HC_HIT(); \
 118             hhdr = hce -> hce_hdr; \
 119           } else { \
 120             HC_MISS(); \
 121             GET_HDR(p, hhdr); \
 122             if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) { \
 123               ADVANCE(p, hhdr, source); \
 124             } else { \
 125               hce -> block_addr = (word)(p) >> LOG_HBLKSIZE; \
 126               hce -> hce_hdr = hhdr; \
 127             } \
 128           } \
 129         }
 130
 131 #else /* !USE_HDR_CACHE */
 132
 133 # define DECLARE_HDR_CACHE
 134
 135 # define INIT_HDR_CACHE
 136
 137 # define HC_GET_HDR(p, hhdr, source) \
 138         { \
 139           GET_HDR(p, hhdr); \
 140           if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) { \
 141             ADVANCE(p, hhdr, source); \
 142           } \
 143         }
 144 #endif
 145
 146 typedef struct bi {
 147     hdr * index[BOTTOM_SZ];
 148         /*
 149          * The bottom level index contains one of three kinds of values:
 150          * 0 means we're not responsible for this block,
 151          *   or this is a block other than the first one in a free block.
 152          * 1 < (long)X <= MAX_JUMP means the block starts at least
 153          *        X * HBLKSIZE bytes before the current address.
 154          * A valid pointer points to a hdr structure. (The above can't be
 155          * valid pointers due to the GET_MEM return convention.)
 156          */
 157     struct bi * asc_link;       /* All indices are linked in    */
 158                                 /* ascending order...           */
 159     struct bi * desc_link;      /* ... and in descending order. */
 160     word key;                   /* high order address bits.     */
 161 # ifdef HASH_TL
 162     struct bi * hash_link;      /* Hash chain link.             */
 163 # endif
 164 } bottom_index;
 165
 166 /* extern bottom_index GC_all_nils; - really part of GC_arrays */
 167
 168 /* extern bottom_index * GC_top_index []; - really part of GC_arrays */
 169                                 /* Each entry points to a bottom_index. */
 170                                 /* On a 32 bit machine, it points to    */
 171                                 /* the index for a set of high order    */
 172                                 /* bits equal to the index.  For longer */
 173                                 /* addresses, we hash the high order    */
 174                                 /* bits to compute the index in         */
 175                                 /* GC_top_index, and each entry points  */
 176                                 /* to a hash chain.                     */
 177                                 /* The last entry in each chain is      */
 178                                 /* GC_all_nils.                         */
 179
 180
 181 # define MAX_JUMP (HBLKSIZE - 1)
 182
 183 # define HDR_FROM_BI(bi, p) \
 184                 ((bi)->index[((word)(p) >> LOG_HBLKSIZE) & (BOTTOM_SZ - 1)])
 185 # ifndef HASH_TL
 186 #   define BI(p) (GC_top_index \
 187                 [(word)(p) >> (LOG_BOTTOM_SZ + LOG_HBLKSIZE)])
 188 #   define HDR_INNER(p) HDR_FROM_BI(BI(p),p)
 189 #   ifdef SMALL_CONFIG
 190 #       define HDR(p) GC_find_header((ptr_t)(p))
 191 #   else
 192 #       define HDR(p) HDR_INNER(p)
 193 #   endif
 194 #   define GET_BI(p, bottom_indx) (bottom_indx) = BI(p)
 195 #   define GET_HDR(p, hhdr) (hhdr) = HDR(p)
 196 #   define SET_HDR(p, hhdr) HDR_INNER(p) = (hhdr)
 197 #   define GET_HDR_ADDR(p, ha) (ha) = &(HDR_INNER(p))
 198 # else /* hash */
 199 /*  Hash function for tree top level */
 200 #   define TL_HASH(hi) ((hi) & (TOP_SZ - 1))
 201 /*  Set bottom_indx to point to the bottom index for address p */
 202 #   define GET_BI(p, bottom_indx) \
 203         { \
 204             register word hi = \
 205                 (word)(p) >> (LOG_BOTTOM_SZ + LOG_HBLKSIZE); \
 206             register bottom_index * _bi = GC_top_index[TL_HASH(hi)]; \
 207             \
 208             while (_bi -> key != hi && _bi != GC_all_nils) \
 209                 _bi = _bi -> hash_link; \
 210             (bottom_indx) = _bi; \
 211         }
 212 #   define GET_HDR_ADDR(p, ha) \
 213         { \
 214             register bottom_index * bi; \
 215             \
 216             GET_BI(p, bi);      \
 217             (ha) = &(HDR_FROM_BI(bi, p)); \
 218         }
 219 #   define GET_HDR(p, hhdr) { register hdr ** _ha; GET_HDR_ADDR(p, _ha); \
 220                               (hhdr) = *_ha; }
 221 #   define SET_HDR(p, hhdr) { register hdr ** _ha; GET_HDR_ADDR(p, _ha); \
 222                               *_ha = (hhdr); }
 223 #   define HDR(p) GC_find_header((ptr_t)(p))
 224 # endif
 225
 226 /* Is the result a forwarding address to someplace closer to the        */
 227 /* beginning of the block or NIL?                                       */
 228 # define IS_FORWARDING_ADDR_OR_NIL(hhdr) ((unsigned long) (hhdr) <= MAX_JUMP)
 229
 230 /* Get an HBLKSIZE aligned address closer to the beginning of the block */
 231 /* h.  Assumes hhdr == HDR(h) and IS_FORWARDING_ADDR(hhdr).             */
 232 # define FORWARDED_ADDR(h, hhdr) ((struct hblk *)(h) - (unsigned long)(hhdr))
 233 # endif /*  GC_HEADERS_H */