2 * sgen-descriptor.h: GC descriptors describe object layout.
4 * Copyright 2001-2003 Ximian, Inc
5 * Copyright 2003-2010 Novell, Inc.
6 * Copyright 2011 Xamarin Inc (http://www.xamarin.com)
8 * Copyright (C) 2012 Xamarin Inc
10 * This library is free software; you can redistribute it and/or
11 * modify it under the terms of the GNU Library General Public
12 * License 2.0 as published by the Free Software Foundation;
14 * This library is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * Library General Public License for more details.
19 * You should have received a copy of the GNU Library General Public
20 * License 2.0 along with this library; if not, write to the Free
21 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
23 #ifndef __MONO_SGEN_DESCRIPTOR_H__
24 #define __MONO_SGEN_DESCRIPTOR_H__
26 #include <mono/metadata/gc-internal.h>
27 #include <mono/metadata/sgen-conf.h>
31 * ######################################################################
32 * ######## GC descriptors
33 * ######################################################################
34 * Used to quickly get the info the GC needs about an object: size and
35 * where the references are held.
37 #define OBJECT_HEADER_WORDS (sizeof(MonoObject)/sizeof(gpointer))
38 #define LOW_TYPE_BITS 3
39 #define MAX_RUNLEN_OBJECT_SIZE 0xFFFF
40 #define SMALL_BITMAP_SHIFT 16
41 #define SMALL_BITMAP_SIZE (GC_BITS_PER_WORD - SMALL_BITMAP_SHIFT)
42 #define VECTOR_INFO_SHIFT 14
43 #define VECTOR_KIND_SHIFT 13
44 #define VECTOR_ELSIZE_SHIFT 3
45 #define LARGE_BITMAP_SIZE (GC_BITS_PER_WORD - LOW_TYPE_BITS)
46 #define MAX_ELEMENT_SIZE 0x3ff
47 #define VECTOR_SUBTYPE_PTRFREE (DESC_TYPE_V_PTRFREE << VECTOR_INFO_SHIFT)
48 #define VECTOR_SUBTYPE_REFS (DESC_TYPE_V_REFS << VECTOR_INFO_SHIFT)
49 #define VECTOR_SUBTYPE_RUN_LEN (DESC_TYPE_V_RUN_LEN << VECTOR_INFO_SHIFT)
50 #define VECTOR_SUBTYPE_BITMAP (DESC_TYPE_V_BITMAP << VECTOR_INFO_SHIFT)
52 #define VECTOR_KIND_SZARRAY (DESC_TYPE_V_SZARRAY << VECTOR_KIND_SHIFT)
53 #define VECTOR_KIND_ARRAY (DESC_TYPE_V_ARRAY << VECTOR_KIND_SHIFT)
55 /* objects are aligned to 8 bytes boundaries
56 * A descriptor is a pointer in MonoVTable, so 32 or 64 bits of size.
57 * The low 3 bits define the type of the descriptor. The other bits
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
75 * We don't use 0 so that 0 isn't a valid GC descriptor. No
76 * deep reason for this other than to be able to identify a
77 * non-inited descriptor for debugging.
79 * If an object contains no references, its GC descriptor is
80 * always DESC_TYPE_RUN_LENGTH, without a size, no exceptions.
81 * This is so that we can quickly check for that in
82 * copy_object_no_checks(), without having to fetch the
85 DESC_TYPE_RUN_LENGTH = 1, /* 16 bits aligned byte size | 1-3 (offset, numptr) bytes tuples */
86 DESC_TYPE_SMALL_BITMAP, /* 16 bits aligned byte size | 16-48 bit bitmap */
87 DESC_TYPE_COMPLEX, /* index for bitmap into complex_descriptors */
88 DESC_TYPE_VECTOR, /* 10 bits element size | 1 bit kind | 2 bits desc | element desc */
89 DESC_TYPE_LARGE_BITMAP, /* | 29-61 bitmap bits */
90 DESC_TYPE_COMPLEX_ARR, /* index for bitmap into complex_descriptors */
91 DESC_TYPE_COMPLEX_PTRFREE, /*Nothing, used to encode large ptr objects. */
92 /* values for array kind */
93 DESC_TYPE_V_SZARRAY = 0, /*vector with no bounds data */
94 DESC_TYPE_V_ARRAY = 1, /* array with bounds data */
95 /* subtypes for arrays and vectors */
96 DESC_TYPE_V_PTRFREE = 0,/* there are no refs: keep first so it has a zero value */
97 DESC_TYPE_V_REFS, /* all the array elements are refs */
98 DESC_TYPE_V_RUN_LEN, /* elements are run-length encoded as DESC_TYPE_RUN_LENGTH */
99 DESC_TYPE_V_BITMAP /* elements are as the bitmap in DESC_TYPE_SMALL_BITMAP */
102 /* Root bitmap descriptors are simpler: the lower three bits describe the type
103 * and we either have 30/62 bitmap bits or nibble-based run-length,
104 * or a complex descriptor, or a user defined marker function.
107 ROOT_DESC_CONSERVATIVE, /* 0, so matches NULL value */
112 ROOT_DESC_TYPE_MASK = 0x7,
113 ROOT_DESC_TYPE_SHIFT = 3,
116 gsize* sgen_get_complex_descriptor (mword desc) MONO_INTERNAL;
117 void* sgen_get_complex_descriptor_bitmap (mword desc) MONO_INTERNAL;
118 MonoGCRootMarkFunc sgen_get_user_descriptor_func (mword desc) MONO_INTERNAL;
121 static inline gboolean
122 sgen_gc_descr_has_references (mword desc)
124 /*Both string and fixed size objects are encoded using a zero run RUN_LEN*/
125 if ((desc & 0xffff0007) == DESC_TYPE_RUN_LENGTH)
128 /*The array is ptr-free*/
129 if ((desc & 0xC007) == (DESC_TYPE_VECTOR | VECTOR_SUBTYPE_PTRFREE))
132 if ((desc & 0x7) == DESC_TYPE_COMPLEX_PTRFREE)
138 #define SGEN_VTABLE_HAS_REFERENCES(vt) (sgen_gc_descr_has_references ((mword)((MonoVTable*)(vt))->gc_descr))
139 #define SGEN_CLASS_HAS_REFERENCES(c) (sgen_gc_descr_has_references ((mword)(c)->gc_descr))
140 #define SGEN_OBJECT_HAS_REFERENCES(o) (SGEN_VTABLE_HAS_REFERENCES (SGEN_LOAD_VTABLE ((o))))
142 /* helper macros to scan and traverse objects, macros because we resue them in many functions */
143 #define OBJ_RUN_LEN_SIZE(size,desc,obj) do { \
144 (size) = ((desc) & 0xfff8); \
147 #define OBJ_BITMAP_SIZE(size,desc,obj) do { \
148 (size) = ((desc) & 0xfff8); \
152 #define PREFETCH(addr) __builtin_prefetch ((addr))
154 #define PREFETCH(addr)
157 #if defined(__GNUC__) && SIZEOF_VOID_P==4
158 #define GNUC_BUILTIN_CTZ(bmap) __builtin_ctz(bmap)
159 #elif defined(__GNUC__) && SIZEOF_VOID_P==8
160 #define GNUC_BUILTIN_CTZ(bmap) __builtin_ctzl(bmap)
163 /* code using these macros must define a HANDLE_PTR(ptr) macro that does the work */
164 #define OBJ_RUN_LEN_FOREACH_PTR(desc,obj) do { \
165 if ((desc) & 0xffff0000) { \
166 /* there are pointers */ \
167 void **_objptr_end; \
168 void **_objptr = (void**)(obj); \
169 _objptr += ((desc) >> 16) & 0xff; \
170 _objptr_end = _objptr + (((desc) >> 24) & 0xff); \
171 HANDLE_PTR (_objptr, (obj)); \
173 while (_objptr < _objptr_end) { \
174 HANDLE_PTR (_objptr, (obj)); \
180 #if defined(__GNUC__)
181 #define OBJ_BITMAP_FOREACH_PTR(desc,obj) do { \
182 /* there are pointers */ \
183 void **_objptr = (void**)(obj); \
184 gsize _bmap = (desc) >> 16; \
185 _objptr += OBJECT_HEADER_WORDS; \
187 int _index = GNUC_BUILTIN_CTZ (_bmap); \
189 _bmap >>= (_index + 1); \
190 HANDLE_PTR (_objptr, (obj)); \
194 int _index = GNUC_BUILTIN_CTZ (_bmap); \
196 _bmap >>= (_index + 1); \
197 HANDLE_PTR (_objptr, (obj)); \
202 #define OBJ_BITMAP_FOREACH_PTR(desc,obj) do { \
203 /* there are pointers */ \
204 void **_objptr = (void**)(obj); \
205 gsize _bmap = (desc) >> 16; \
206 _objptr += OBJECT_HEADER_WORDS; \
209 HANDLE_PTR (_objptr, (obj)); \
217 /* a bitmap desc means that there are pointer references or we'd have
218 * choosen run-length, instead: add an assert to check.
220 #define OBJ_LARGE_BITMAP_FOREACH_PTR(desc,obj) do { \
221 /* there are pointers */ \
222 void **_objptr = (void**)(obj); \
223 gsize _bmap = (desc) >> LOW_TYPE_BITS; \
224 _objptr += OBJECT_HEADER_WORDS; \
227 HANDLE_PTR (_objptr, (obj)); \
234 #define OBJ_COMPLEX_FOREACH_PTR(vt,obj) do { \
235 /* there are pointers */ \
236 void **_objptr = (void**)(obj); \
237 gsize *bitmap_data = sgen_get_complex_descriptor ((desc)); \
238 int bwords = (*bitmap_data) - 1; \
239 void **start_run = _objptr; \
242 MonoObject *myobj = (MonoObject*)obj; \
243 g_print ("found %d at %p (0x%zx): %s.%s\n", bwords, (obj), (desc), myobj->vtable->klass->name_space, myobj->vtable->klass->name); \
245 while (bwords-- > 0) { \
246 gsize _bmap = *bitmap_data++; \
247 _objptr = start_run; \
248 /*g_print ("bitmap: 0x%x/%d at %p\n", _bmap, bwords, _objptr);*/ \
251 HANDLE_PTR (_objptr, (obj)); \
256 start_run += GC_BITS_PER_WORD; \
260 /* this one is untested */
261 #define OBJ_COMPLEX_ARR_FOREACH_PTR(vt,obj) do { \
262 /* there are pointers */ \
263 gsize *mbitmap_data = sgen_get_complex_descriptor ((vt)->desc); \
264 int mbwords = (*mbitmap_data++) - 1; \
265 int el_size = mono_array_element_size (vt->klass); \
266 char *e_start = (char*)(obj) + G_STRUCT_OFFSET (MonoArray, vector); \
267 char *e_end = e_start + el_size * mono_array_length_fast ((MonoArray*)(obj)); \
269 g_print ("found %d at %p (0x%zx): %s.%s\n", mbwords, (obj), (vt)->desc, vt->klass->name_space, vt->klass->name); \
270 while (e_start < e_end) { \
271 void **_objptr = (void**)e_start; \
272 gsize *bitmap_data = mbitmap_data; \
273 unsigned int bwords = mbwords; \
274 while (bwords-- > 0) { \
275 gsize _bmap = *bitmap_data++; \
276 void **start_run = _objptr; \
277 /*g_print ("bitmap: 0x%x\n", _bmap);*/ \
280 HANDLE_PTR (_objptr, (obj)); \
285 _objptr = start_run + GC_BITS_PER_WORD; \
287 e_start += el_size; \
291 #define OBJ_VECTOR_FOREACH_PTR(desc,obj) do { \
292 /* note: 0xffffc000 excludes DESC_TYPE_V_PTRFREE */ \
293 if ((desc) & 0xffffc000) { \
294 int el_size = ((desc) >> 3) & MAX_ELEMENT_SIZE; \
295 /* there are pointers */ \
296 int etype = (desc) & 0xc000; \
297 if (etype == (DESC_TYPE_V_REFS << 14)) { \
298 void **p = (void**)((char*)(obj) + G_STRUCT_OFFSET (MonoArray, vector)); \
299 void **end_refs = (void**)((char*)p + el_size * mono_array_length_fast ((MonoArray*)(obj))); \
300 /* Note: this code can handle also arrays of struct with only references in them */ \
301 while (p < end_refs) { \
302 HANDLE_PTR (p, (obj)); \
305 } else if (etype == DESC_TYPE_V_RUN_LEN << 14) { \
306 int offset = ((desc) >> 16) & 0xff; \
307 int num_refs = ((desc) >> 24) & 0xff; \
308 char *e_start = (char*)(obj) + G_STRUCT_OFFSET (MonoArray, vector); \
309 char *e_end = e_start + el_size * mono_array_length_fast ((MonoArray*)(obj)); \
310 while (e_start < e_end) { \
311 void **p = (void**)e_start; \
314 for (i = 0; i < num_refs; ++i) { \
315 HANDLE_PTR (p + i, (obj)); \
317 e_start += el_size; \
319 } else if (etype == DESC_TYPE_V_BITMAP << 14) { \
320 char *e_start = (char*)(obj) + G_STRUCT_OFFSET (MonoArray, vector); \
321 char *e_end = e_start + el_size * mono_array_length_fast ((MonoArray*)(obj)); \
322 while (e_start < e_end) { \
323 void **p = (void**)e_start; \
324 gsize _bmap = (desc) >> 16; \
325 /* Note: there is no object header here to skip */ \
328 HANDLE_PTR (p, (obj)); \
333 e_start += el_size; \