mono/sgen/sgen-descriptor.h

   1 /*
   2  * sgen-descriptor.h: GC descriptors describe object layout.
   3
   4  * Copyright 2001-2003 Ximian, Inc
   5  * Copyright 2003-2010 Novell, Inc.
   6  * Copyright 2011 Xamarin Inc (http://www.xamarin.com)
   7  *
   8  * Copyright (C) 2012 Xamarin Inc
   9  *
  10  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
  11  */
  12 #ifndef __MONO_SGEN_DESCRIPTOR_H__
  13 #define __MONO_SGEN_DESCRIPTOR_H__
  14
  15 #include <mono/sgen/sgen-conf.h>
  16
  17 /*
  18  * ######################################################################
  19  * ########  GC descriptors
  20  * ######################################################################
  21  * Used to quickly get the info the GC needs about an object: size and
  22  * where the references are held.
  23  */
  24 #define OBJECT_HEADER_WORDS (SGEN_CLIENT_OBJECT_HEADER_SIZE / sizeof(gpointer))
  25 #define LOW_TYPE_BITS 3
  26 #define DESC_TYPE_MASK  ((1 << LOW_TYPE_BITS) - 1)
  27 #define MAX_RUNLEN_OBJECT_SIZE 0xFFFF
  28 #define VECTOR_INFO_SHIFT 14
  29 #define VECTOR_KIND_SHIFT 13
  30 #define VECTOR_ELSIZE_SHIFT 3
  31 #define VECTOR_BITMAP_SHIFT 16
  32 #define VECTOR_BITMAP_SIZE (GC_BITS_PER_WORD - VECTOR_BITMAP_SHIFT)
  33 #define BITMAP_NUM_BITS (GC_BITS_PER_WORD - LOW_TYPE_BITS)
  34 #define MAX_ELEMENT_SIZE 0x3ff
  35 #define VECTOR_SUBTYPE_PTRFREE (DESC_TYPE_V_PTRFREE << VECTOR_INFO_SHIFT)
  36 #define VECTOR_SUBTYPE_REFS    (DESC_TYPE_V_REFS << VECTOR_INFO_SHIFT)
  37 #define VECTOR_SUBTYPE_BITMAP  (DESC_TYPE_V_BITMAP << VECTOR_INFO_SHIFT)
  38
  39 #define VECTOR_KIND_SZARRAY  (DESC_TYPE_V_SZARRAY << VECTOR_KIND_SHIFT)
  40 #define VECTOR_KIND_ARRAY  (DESC_TYPE_V_ARRAY << VECTOR_KIND_SHIFT)
  41
  42 /*
  43  * Objects are aligned to 8 bytes boundaries.
  44  *
  45  * A descriptor is a pointer in GCVTable, so 32 or 64 bits of size.
  46  * The low 3 bits define the type of the descriptor. The other bits
  47  * depend on the type.
  48  *
  49  * It's important to be able to quickly identify two properties of classes from their
  50  * descriptors: whether they are small enough to live in the regular major heap (size <=
  51  * SGEN_MAX_SMALL_OBJ_SIZE), and whether they contain references.
  52  *
  53  * To that end we have three descriptor types that only apply to small classes: RUN_LENGTH,
  54  * BITMAP, and SMALL_PTRFREE.  We also have the type COMPLEX_PTRFREE, which applies to
  55  * classes that are either not small or of unknown size (those being strings and arrays).
  56  * The lowest two bits of the SMALL_PTRFREE and COMPLEX_PTRFREE tags are the same, so we can
  57  * quickly check for references.
  58  *
  59  * As a general rule the 13 remaining low bits define the size, either
  60  * of the whole object or of the elements in the arrays. While for objects
  61  * the size is already in bytes, for arrays we need to shift, because
  62  * array elements might be smaller than 8 bytes. In case of arrays, we
  63  * use two bits to describe what the additional high bits represents,
  64  * so the default behaviour can handle element sizes less than 2048 bytes.
  65  * The high 16 bits, if 0 it means the object is pointer-free.
  66  * This design should make it easy and fast to skip over ptr-free data.
  67  * The first 4 types should cover >95% of the objects.
  68  * Note that since the size of objects is limited to 64K, larger objects
  69  * will be allocated in the large object heap.
  70  * If we want 4-bytes alignment, we need to put vector and small bitmap
  71  * inside complex.
  72  *
  73  * We don't use 0 so that 0 isn't a valid GC descriptor.  No deep reason for this other than
  74  * to be able to identify a non-inited descriptor for debugging.
  75  */
  76 enum {
  77         /* Keep in sync with `descriptor_types` in sgen-debug.c! */
  78         DESC_TYPE_RUN_LENGTH = 1,   /* 16 bits aligned byte size | 1-3 (offset, numptr) bytes tuples */
  79         DESC_TYPE_BITMAP = 2,       /* | 29-61 bitmap bits */
  80         DESC_TYPE_SMALL_PTRFREE = 3,
  81         DESC_TYPE_MAX_SMALL_OBJ = 3,
  82         DESC_TYPE_COMPLEX = 4,      /* index for bitmap into complex_descriptors */
  83         DESC_TYPE_VECTOR = 5,       /* 10 bits element size | 1 bit kind | 2 bits desc | element desc */
  84         DESC_TYPE_COMPLEX_ARR = 6,  /* index for bitmap into complex_descriptors */
  85         DESC_TYPE_COMPLEX_PTRFREE = 7, /* Nothing, used to encode large ptr objects and strings. */
  86         DESC_TYPE_MAX = 7,
  87
  88         DESC_TYPE_PTRFREE_MASK = 3,
  89         DESC_TYPE_PTRFREE_BITS = 3
  90 };
  91
  92 /* values for array kind */
  93 enum {
  94         DESC_TYPE_V_SZARRAY = 0, /*vector with no bounds data */
  95         DESC_TYPE_V_ARRAY = 1, /* array with bounds data */
  96 };
  97
  98 /* subtypes for arrays and vectors */
  99 enum {
 100         DESC_TYPE_V_PTRFREE = 0,/* there are no refs: keep first so it has a zero value  */
 101         DESC_TYPE_V_REFS,       /* all the array elements are refs */
 102         DESC_TYPE_V_RUN_LEN,    /* elements are run-length encoded as DESC_TYPE_RUN_LENGTH */
 103         DESC_TYPE_V_BITMAP      /* elements are as the bitmap in DESC_TYPE_SMALL_BITMAP */
 104 };
 105
 106 #define SGEN_DESC_STRING        (DESC_TYPE_COMPLEX_PTRFREE | (1 << LOW_TYPE_BITS))
 107
 108 /* Root bitmap descriptors are simpler: the lower three bits describe the type
 109  * and we either have 30/62 bitmap bits or nibble-based run-length,
 110  * or a complex descriptor, or a user defined marker function.
 111  */
 112 enum {
 113         ROOT_DESC_CONSERVATIVE, /* 0, so matches NULL value */
 114         ROOT_DESC_BITMAP,
 115         ROOT_DESC_RUN_LEN,
 116         ROOT_DESC_COMPLEX,
 117         ROOT_DESC_USER,
 118         ROOT_DESC_TYPE_MASK = 0x7,
 119         ROOT_DESC_TYPE_SHIFT = 3,
 120 };
 121
 122 typedef void (*SgenUserMarkFunc)     (GCObject **addr, void *gc_data);
 123 typedef void (*SgenUserRootMarkFunc) (void *addr, SgenUserMarkFunc mark_func, void *gc_data);
 124
 125 SgenDescriptor sgen_make_user_root_descriptor (SgenUserRootMarkFunc marker);
 126
 127 gsize* sgen_get_complex_descriptor (SgenDescriptor desc);
 128 void* sgen_get_complex_descriptor_bitmap (SgenDescriptor desc);
 129 SgenUserRootMarkFunc sgen_get_user_descriptor_func (SgenDescriptor desc);
 130
 131 void sgen_init_descriptors (void);
 132
 133 #ifdef HEAVY_STATISTICS
 134 void sgen_descriptor_count_scanned_object (SgenDescriptor desc);
 135 void sgen_descriptor_count_copied_object (SgenDescriptor desc);
 136 #endif
 137
 138 static inline gboolean
 139 sgen_gc_descr_has_references (SgenDescriptor desc)
 140 {
 141         /* This covers SMALL_PTRFREE and COMPLEX_PTRFREE */
 142         if ((desc & DESC_TYPE_PTRFREE_MASK) == DESC_TYPE_PTRFREE_BITS)
 143                 return FALSE;
 144
 145         /*The array is ptr-free*/
 146         if ((desc & 0xC007) == (DESC_TYPE_VECTOR | VECTOR_SUBTYPE_PTRFREE))
 147                 return FALSE;
 148
 149         return TRUE;
 150 }
 151
 152 #define SGEN_VTABLE_HAS_REFERENCES(vt)  (sgen_gc_descr_has_references (sgen_vtable_get_descriptor ((vt))))
 153 #define SGEN_OBJECT_HAS_REFERENCES(o)   (SGEN_VTABLE_HAS_REFERENCES (SGEN_LOAD_VTABLE ((o))))
 154
 155 /* helper macros to scan and traverse objects, macros because we resue them in many functions */
 156 #ifdef __GNUC__
 157 #define PREFETCH_READ(addr)     __builtin_prefetch ((addr), 0, 1)
 158 #define PREFETCH_WRITE(addr)    __builtin_prefetch ((addr), 1, 1)
 159 #else
 160 #define PREFETCH_READ(addr)
 161 #define PREFETCH_WRITE(addr)
 162 #endif
 163
 164 #if defined(__GNUC__) && SIZEOF_VOID_P==4
 165 #define GNUC_BUILTIN_CTZ(bmap)  __builtin_ctz(bmap)
 166 #elif defined(__GNUC__) && SIZEOF_VOID_P==8
 167 #define GNUC_BUILTIN_CTZ(bmap)  __builtin_ctzl(bmap)
 168 #endif
 169
 170 /* code using these macros must define a HANDLE_PTR(ptr) macro that does the work */
 171 #define OBJ_RUN_LEN_FOREACH_PTR(desc,obj)       do {    \
 172                 if ((desc) & 0xffff0000) {      \
 173                         /* there are pointers */        \
 174                         void **_objptr_end;     \
 175                         void **_objptr = (void**)(obj); \
 176                         _objptr += ((desc) >> 16) & 0xff;       \
 177                         _objptr_end = _objptr + (((desc) >> 24) & 0xff);        \
 178                         while (_objptr < _objptr_end) { \
 179                                 HANDLE_PTR ((GCObject**)_objptr, (obj)); \
 180                                 _objptr++;      \
 181                         };      \
 182                 }       \
 183         } while (0)
 184
 185 /* a bitmap desc means that there are pointer references or we'd have
 186  * choosen run-length, instead: add an assert to check.
 187  */
 188 #ifdef __GNUC__
 189 #define OBJ_BITMAP_FOREACH_PTR(desc,obj)        do {            \
 190                 /* there are pointers */                        \
 191                 void **_objptr = (void**)(obj);                 \
 192                 gsize _bmap = (desc) >> LOW_TYPE_BITS;          \
 193                 _objptr += OBJECT_HEADER_WORDS;                 \
 194                 do {                                            \
 195                         int _index = GNUC_BUILTIN_CTZ (_bmap);  \
 196                         _objptr += _index;                      \
 197                         _bmap >>= (_index + 1);                 \
 198                         HANDLE_PTR ((GCObject**)_objptr, (obj));        \
 199                         ++_objptr;                              \
 200                 } while (_bmap);                                \
 201         } while (0)
 202 #else
 203 #define OBJ_BITMAP_FOREACH_PTR(desc,obj)        do {    \
 204                 /* there are pointers */        \
 205                 void **_objptr = (void**)(obj); \
 206                 gsize _bmap = (desc) >> LOW_TYPE_BITS;  \
 207                 _objptr += OBJECT_HEADER_WORDS; \
 208                 do {    \
 209                         if ((_bmap & 1)) {      \
 210                                 HANDLE_PTR ((GCObject**)_objptr, (obj));        \
 211                         }       \
 212                         _bmap >>= 1;    \
 213                         ++_objptr;      \
 214                 } while (_bmap);        \
 215         } while (0)
 216 #endif
 217
 218 #define OBJ_COMPLEX_FOREACH_PTR(desc,obj)       do {    \
 219                 /* there are pointers */        \
 220                 void **_objptr = (void**)(obj); \
 221                 gsize *bitmap_data = sgen_get_complex_descriptor ((desc)); \
 222                 gsize bwords = (*bitmap_data) - 1;      \
 223                 void **start_run = _objptr;     \
 224                 bitmap_data++;  \
 225                 while (bwords-- > 0) {  \
 226                         gsize _bmap = *bitmap_data++;   \
 227                         _objptr = start_run;    \
 228                         /*g_print ("bitmap: 0x%x/%d at %p\n", _bmap, bwords, _objptr);*/        \
 229                         while (_bmap) { \
 230                                 if ((_bmap & 1)) {      \
 231                                         HANDLE_PTR ((GCObject**)_objptr, (obj));        \
 232                                 }       \
 233                                 _bmap >>= 1;    \
 234                                 ++_objptr;      \
 235                         }       \
 236                         start_run += GC_BITS_PER_WORD;  \
 237                 }       \
 238         } while (0)
 239
 240 /* this one is untested */
 241 #define OBJ_COMPLEX_ARR_FOREACH_PTR(desc,obj)   do {    \
 242                 /* there are pointers */        \
 243                 GCVTable vt = SGEN_LOAD_VTABLE (obj); \
 244                 gsize *mbitmap_data = sgen_get_complex_descriptor ((desc)); \
 245                 gsize mbwords = (*mbitmap_data++) - 1;  \
 246                 gsize el_size = sgen_client_array_element_size (vt);    \
 247                 char *e_start = sgen_client_array_data_start ((GCObject*)(obj));        \
 248                 char *e_end = e_start + el_size * sgen_client_array_length ((GCObject*)(obj));  \
 249                 while (e_start < e_end) {       \
 250                         void **_objptr = (void**)e_start;       \
 251                         gsize *bitmap_data = mbitmap_data;      \
 252                         gsize bwords = mbwords; \
 253                         while (bwords-- > 0) {  \
 254                                 gsize _bmap = *bitmap_data++;   \
 255                                 void **start_run = _objptr;     \
 256                                 /*g_print ("bitmap: 0x%x\n", _bmap);*/  \
 257                                 while (_bmap) { \
 258                                         if ((_bmap & 1)) {      \
 259                                                 HANDLE_PTR ((GCObject**)_objptr, (obj));        \
 260                                         }       \
 261                                         _bmap >>= 1;    \
 262                                         ++_objptr;      \
 263                                 }       \
 264                                 _objptr = start_run + GC_BITS_PER_WORD; \
 265                         }       \
 266                         e_start += el_size;     \
 267                 }       \
 268         } while (0)
 269
 270 #define OBJ_VECTOR_FOREACH_PTR(desc,obj)        do {    \
 271                 /* note: 0xffffc000 excludes DESC_TYPE_V_PTRFREE */     \
 272                 if ((desc) & 0xffffc000) {                              \
 273                         int el_size = ((desc) >> 3) & MAX_ELEMENT_SIZE; \
 274                         /* there are pointers */        \
 275                         int etype = (desc) & 0xc000;                    \
 276                         if (etype == (DESC_TYPE_V_REFS << 14)) {        \
 277                                 void **p = (void**)sgen_client_array_data_start ((GCObject*)(obj));     \
 278                                 void **end_refs = (void**)((char*)p + el_size * sgen_client_array_length ((GCObject*)(obj)));   \
 279                                 /* Note: this code can handle also arrays of struct with only references in them */     \
 280                                 while (p < end_refs) {  \
 281                                         HANDLE_PTR ((GCObject**)p, (obj));      \
 282                                         ++p;    \
 283                                 }       \
 284                         } else if (etype == DESC_TYPE_V_RUN_LEN << 14) {        \
 285                                 int offset = ((desc) >> 16) & 0xff;     \
 286                                 int num_refs = ((desc) >> 24) & 0xff;   \
 287                                 char *e_start = sgen_client_array_data_start ((GCObject*)(obj));        \
 288                                 char *e_end = e_start + el_size * sgen_client_array_length ((GCObject*)(obj));  \
 289                                 while (e_start < e_end) {       \
 290                                         void **p = (void**)e_start;     \
 291                                         int i;  \
 292                                         p += offset;    \
 293                                         for (i = 0; i < num_refs; ++i) {        \
 294                                                 HANDLE_PTR ((GCObject**)p + i, (obj));  \
 295                                         }       \
 296                                         e_start += el_size;     \
 297                                 }       \
 298                         } else if (etype == DESC_TYPE_V_BITMAP << 14) { \
 299                                 char *e_start = sgen_client_array_data_start ((GCObject*)(obj));        \
 300                                 char *e_end = e_start + el_size * sgen_client_array_length ((GCObject*)(obj));  \
 301                                 while (e_start < e_end) {       \
 302                                         void **p = (void**)e_start;     \
 303                                         gsize _bmap = (desc) >> 16;     \
 304                                         /* Note: there is no object header here to skip */      \
 305                                         while (_bmap) { \
 306                                                 if ((_bmap & 1)) {      \
 307                                                         HANDLE_PTR ((GCObject**)p, (obj));      \
 308                                                 }       \
 309                                                 _bmap >>= 1;    \
 310                                                 ++p;    \
 311                                         }       \
 312                                         e_start += el_size;     \
 313                                 }       \
 314                         }       \
 315                 }       \
 316         } while (0)
 317
 318
 319 #endif