Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1 | // Copyright 2009 The Go Authors. All rights reserved. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | // Garbage collector: type and heap bitmaps. |
| 6 | // |
| 7 | // Stack, data, and bss bitmaps |
| 8 | // |
| 9 | // Stack frames and global variables in the data and bss sections are described |
| 10 | // by 1-bit bitmaps in which 0 means uninteresting and 1 means live pointer |
| 11 | // to be visited during GC. The bits in each byte are consumed starting with |
| 12 | // the low bit: 1<<0, 1<<1, and so on. |
| 13 | // |
| 14 | // Heap bitmap |
| 15 | // |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 16 | // The heap bitmap comprises 2 bits for each pointer-sized word in the heap, |
| 17 | // stored in the heapArena metadata backing each heap arena. |
| 18 | // That is, if ha is the heapArena for the arena starting a start, |
| 19 | // then ha.bitmap[0] holds the 2-bit entries for the four words start |
| 20 | // through start+3*ptrSize, ha.bitmap[1] holds the entries for |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 21 | // start+4*ptrSize through start+7*ptrSize, and so on. |
| 22 | // |
| 23 | // In each 2-bit entry, the lower bit holds the same information as in the 1-bit |
| 24 | // bitmaps: 0 means uninteresting and 1 means live pointer to be visited during GC. |
| 25 | // The meaning of the high bit depends on the position of the word being described |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 26 | // in its allocated object. In all words *except* the second word, the |
| 27 | // high bit indicates that the object is still being described. In |
| 28 | // these words, if a bit pair with a high bit 0 is encountered, the |
| 29 | // low bit can also be assumed to be 0, and the object description is |
| 30 | // over. This 00 is called the ``dead'' encoding: it signals that the |
| 31 | // rest of the words in the object are uninteresting to the garbage |
| 32 | // collector. |
| 33 | // |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 34 | // In the second word, the high bit is the GC ``checkmarked'' bit (see below). |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 35 | // |
| 36 | // The 2-bit entries are split when written into the byte, so that the top half |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 37 | // of the byte contains 4 high bits and the bottom half contains 4 low (pointer) |
| 38 | // bits. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 39 | // This form allows a copy from the 1-bit to the 4-bit form to keep the |
| 40 | // pointer bits contiguous, instead of having to space them out. |
| 41 | // |
| 42 | // The code makes use of the fact that the zero value for a heap bitmap |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 43 | // has no live pointer bit set and is (depending on position), not used, |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 44 | // not checkmarked, and is the dead encoding. |
| 45 | // These properties must be preserved when modifying the encoding. |
| 46 | // |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 47 | // The bitmap for noscan spans is not maintained. Code must ensure |
| 48 | // that an object is scannable before consulting its bitmap by |
| 49 | // checking either the noscan bit in the span or by consulting its |
| 50 | // type's information. |
| 51 | // |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 52 | // Checkmarks |
| 53 | // |
| 54 | // In a concurrent garbage collector, one worries about failing to mark |
| 55 | // a live object due to mutations without write barriers or bugs in the |
| 56 | // collector implementation. As a sanity check, the GC has a 'checkmark' |
| 57 | // mode that retraverses the object graph with the world stopped, to make |
| 58 | // sure that everything that should be marked is marked. |
| 59 | // In checkmark mode, in the heap bitmap, the high bit of the 2-bit entry |
| 60 | // for the second word of the object holds the checkmark bit. |
| 61 | // When not in checkmark mode, this bit is set to 1. |
| 62 | // |
| 63 | // The smallest possible allocation is 8 bytes. On a 32-bit machine, that |
| 64 | // means every allocated object has two words, so there is room for the |
| 65 | // checkmark bit. On a 64-bit machine, however, the 8-byte allocation is |
| 66 | // just one word, so the second bit pair is not available for encoding the |
| 67 | // checkmark. However, because non-pointer allocations are combined |
| 68 | // into larger 16-byte (maxTinySize) allocations, a plain 8-byte allocation |
| 69 | // must be a pointer, so the type bit in the first word is not actually needed. |
| 70 | // It is still used in general, except in checkmark the type bit is repurposed |
| 71 | // as the checkmark bit and then reinitialized (to 1) as the type bit when |
| 72 | // finished. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 73 | // |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 74 | |
| 75 | package runtime |
| 76 | |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 77 | import ( |
| 78 | "runtime/internal/atomic" |
| 79 | "runtime/internal/sys" |
| 80 | "unsafe" |
| 81 | ) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 82 | |
| 83 | const ( |
| 84 | bitPointer = 1 << 0 |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 85 | bitScan = 1 << 4 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 86 | |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 87 | heapBitsShift = 1 // shift offset between successive bitPointer or bitScan entries |
| 88 | wordsPerBitmapByte = 8 / 2 // heap words described by one bitmap byte |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 89 | |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 90 | // all scan/pointer bits in a byte |
| 91 | bitScanAll = bitScan | bitScan<<heapBitsShift | bitScan<<(2*heapBitsShift) | bitScan<<(3*heapBitsShift) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 92 | bitPointerAll = bitPointer | bitPointer<<heapBitsShift | bitPointer<<(2*heapBitsShift) | bitPointer<<(3*heapBitsShift) |
| 93 | ) |
| 94 | |
| 95 | // addb returns the byte pointer p+n. |
| 96 | //go:nowritebarrier |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 97 | //go:nosplit |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 98 | func addb(p *byte, n uintptr) *byte { |
| 99 | // Note: wrote out full expression instead of calling add(p, n) |
| 100 | // to reduce the number of temporaries generated by the |
| 101 | // compiler for this trivial expression during inlining. |
| 102 | return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + n)) |
| 103 | } |
| 104 | |
| 105 | // subtractb returns the byte pointer p-n. |
| 106 | //go:nowritebarrier |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 107 | //go:nosplit |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 108 | func subtractb(p *byte, n uintptr) *byte { |
| 109 | // Note: wrote out full expression instead of calling add(p, -n) |
| 110 | // to reduce the number of temporaries generated by the |
| 111 | // compiler for this trivial expression during inlining. |
| 112 | return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) - n)) |
| 113 | } |
| 114 | |
| 115 | // add1 returns the byte pointer p+1. |
| 116 | //go:nowritebarrier |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 117 | //go:nosplit |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 118 | func add1(p *byte) *byte { |
| 119 | // Note: wrote out full expression instead of calling addb(p, 1) |
| 120 | // to reduce the number of temporaries generated by the |
| 121 | // compiler for this trivial expression during inlining. |
| 122 | return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + 1)) |
| 123 | } |
| 124 | |
| 125 | // subtract1 returns the byte pointer p-1. |
| 126 | //go:nowritebarrier |
| 127 | // |
| 128 | // nosplit because it is used during write barriers and must not be preempted. |
| 129 | //go:nosplit |
| 130 | func subtract1(p *byte) *byte { |
| 131 | // Note: wrote out full expression instead of calling subtractb(p, 1) |
| 132 | // to reduce the number of temporaries generated by the |
| 133 | // compiler for this trivial expression during inlining. |
| 134 | return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) - 1)) |
| 135 | } |
| 136 | |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 137 | // heapBits provides access to the bitmap bits for a single heap word. |
| 138 | // The methods on heapBits take value receivers so that the compiler |
| 139 | // can more easily inline calls to those methods and registerize the |
| 140 | // struct fields independently. |
| 141 | type heapBits struct { |
| 142 | bitp *uint8 |
| 143 | shift uint32 |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 144 | arena uint32 // Index of heap arena containing bitp |
| 145 | last *uint8 // Last byte arena's bitmap |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 146 | } |
| 147 | |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 148 | // Make the compiler check that heapBits.arena is large enough to hold |
| 149 | // the maximum arena frame number. |
| 150 | var _ = heapBits{arena: (1<<heapAddrBits)/heapArenaBytes - 1} |
| 151 | |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 152 | // markBits provides access to the mark bit for an object in the heap. |
| 153 | // bytep points to the byte holding the mark bit. |
| 154 | // mask is a byte with a single bit set that can be &ed with *bytep |
| 155 | // to see if the bit has been set. |
| 156 | // *m.byte&m.mask != 0 indicates the mark bit is set. |
| 157 | // index can be used along with span information to generate |
| 158 | // the address of the object in the heap. |
| 159 | // We maintain one set of mark bits for allocation and one for |
| 160 | // marking purposes. |
| 161 | type markBits struct { |
| 162 | bytep *uint8 |
| 163 | mask uint8 |
| 164 | index uintptr |
| 165 | } |
| 166 | |
| 167 | //go:nosplit |
| 168 | func (s *mspan) allocBitsForIndex(allocBitIndex uintptr) markBits { |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 169 | bytep, mask := s.allocBits.bitp(allocBitIndex) |
| 170 | return markBits{bytep, mask, allocBitIndex} |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 171 | } |
| 172 | |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 173 | // refillAllocCache takes 8 bytes s.allocBits starting at whichByte |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 174 | // and negates them so that ctz (count trailing zeros) instructions |
| 175 | // can be used. It then places these 8 bytes into the cached 64 bit |
| 176 | // s.allocCache. |
| 177 | func (s *mspan) refillAllocCache(whichByte uintptr) { |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 178 | bytes := (*[8]uint8)(unsafe.Pointer(s.allocBits.bytep(whichByte))) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 179 | aCache := uint64(0) |
| 180 | aCache |= uint64(bytes[0]) |
| 181 | aCache |= uint64(bytes[1]) << (1 * 8) |
| 182 | aCache |= uint64(bytes[2]) << (2 * 8) |
| 183 | aCache |= uint64(bytes[3]) << (3 * 8) |
| 184 | aCache |= uint64(bytes[4]) << (4 * 8) |
| 185 | aCache |= uint64(bytes[5]) << (5 * 8) |
| 186 | aCache |= uint64(bytes[6]) << (6 * 8) |
| 187 | aCache |= uint64(bytes[7]) << (7 * 8) |
| 188 | s.allocCache = ^aCache |
| 189 | } |
| 190 | |
| 191 | // nextFreeIndex returns the index of the next free object in s at |
| 192 | // or after s.freeindex. |
| 193 | // There are hardware instructions that can be used to make this |
| 194 | // faster if profiling warrants it. |
| 195 | func (s *mspan) nextFreeIndex() uintptr { |
| 196 | sfreeindex := s.freeindex |
| 197 | snelems := s.nelems |
| 198 | if sfreeindex == snelems { |
| 199 | return sfreeindex |
| 200 | } |
| 201 | if sfreeindex > snelems { |
| 202 | throw("s.freeindex > s.nelems") |
| 203 | } |
| 204 | |
| 205 | aCache := s.allocCache |
| 206 | |
| 207 | bitIndex := sys.Ctz64(aCache) |
| 208 | for bitIndex == 64 { |
| 209 | // Move index to start of next cached bits. |
| 210 | sfreeindex = (sfreeindex + 64) &^ (64 - 1) |
| 211 | if sfreeindex >= snelems { |
| 212 | s.freeindex = snelems |
| 213 | return snelems |
| 214 | } |
| 215 | whichByte := sfreeindex / 8 |
| 216 | // Refill s.allocCache with the next 64 alloc bits. |
| 217 | s.refillAllocCache(whichByte) |
| 218 | aCache = s.allocCache |
| 219 | bitIndex = sys.Ctz64(aCache) |
| 220 | // nothing available in cached bits |
| 221 | // grab the next 8 bytes and try again. |
| 222 | } |
| 223 | result := sfreeindex + uintptr(bitIndex) |
| 224 | if result >= snelems { |
| 225 | s.freeindex = snelems |
| 226 | return snelems |
| 227 | } |
| 228 | |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 229 | s.allocCache >>= uint(bitIndex + 1) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 230 | sfreeindex = result + 1 |
| 231 | |
| 232 | if sfreeindex%64 == 0 && sfreeindex != snelems { |
| 233 | // We just incremented s.freeindex so it isn't 0. |
| 234 | // As each 1 in s.allocCache was encountered and used for allocation |
| 235 | // it was shifted away. At this point s.allocCache contains all 0s. |
| 236 | // Refill s.allocCache so that it corresponds |
| 237 | // to the bits at s.allocBits starting at s.freeindex. |
| 238 | whichByte := sfreeindex / 8 |
| 239 | s.refillAllocCache(whichByte) |
| 240 | } |
| 241 | s.freeindex = sfreeindex |
| 242 | return result |
| 243 | } |
| 244 | |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 245 | // isFree returns whether the index'th object in s is unallocated. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 246 | func (s *mspan) isFree(index uintptr) bool { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 247 | if index < s.freeindex { |
| 248 | return false |
| 249 | } |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 250 | bytep, mask := s.allocBits.bitp(index) |
| 251 | return *bytep&mask == 0 |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 252 | } |
| 253 | |
| 254 | func (s *mspan) objIndex(p uintptr) uintptr { |
| 255 | byteOffset := p - s.base() |
| 256 | if byteOffset == 0 { |
| 257 | return 0 |
| 258 | } |
| 259 | if s.baseMask != 0 { |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 260 | // s.baseMask is non-0, elemsize is a power of two, so shift by s.divShift |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 261 | return byteOffset >> s.divShift |
| 262 | } |
| 263 | return uintptr(((uint64(byteOffset) >> s.divShift) * uint64(s.divMul)) >> s.divShift2) |
| 264 | } |
| 265 | |
| 266 | func markBitsForAddr(p uintptr) markBits { |
| 267 | s := spanOf(p) |
| 268 | objIndex := s.objIndex(p) |
| 269 | return s.markBitsForIndex(objIndex) |
| 270 | } |
| 271 | |
| 272 | func (s *mspan) markBitsForIndex(objIndex uintptr) markBits { |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 273 | bytep, mask := s.gcmarkBits.bitp(objIndex) |
| 274 | return markBits{bytep, mask, objIndex} |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 275 | } |
| 276 | |
| 277 | func (s *mspan) markBitsForBase() markBits { |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 278 | return markBits{(*uint8)(s.gcmarkBits), uint8(1), 0} |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 279 | } |
| 280 | |
| 281 | // isMarked reports whether mark bit m is set. |
| 282 | func (m markBits) isMarked() bool { |
| 283 | return *m.bytep&m.mask != 0 |
| 284 | } |
| 285 | |
| 286 | // setMarked sets the marked bit in the markbits, atomically. Some compilers |
| 287 | // are not able to inline atomic.Or8 function so if it appears as a hot spot consider |
| 288 | // inlining it manually. |
| 289 | func (m markBits) setMarked() { |
| 290 | // Might be racing with other updates, so use atomic update always. |
| 291 | // We used to be clever here and use a non-atomic update in certain |
| 292 | // cases, but it's not worth the risk. |
| 293 | atomic.Or8(m.bytep, m.mask) |
| 294 | } |
| 295 | |
| 296 | // setMarkedNonAtomic sets the marked bit in the markbits, non-atomically. |
| 297 | func (m markBits) setMarkedNonAtomic() { |
| 298 | *m.bytep |= m.mask |
| 299 | } |
| 300 | |
| 301 | // clearMarked clears the marked bit in the markbits, atomically. |
| 302 | func (m markBits) clearMarked() { |
| 303 | // Might be racing with other updates, so use atomic update always. |
| 304 | // We used to be clever here and use a non-atomic update in certain |
| 305 | // cases, but it's not worth the risk. |
| 306 | atomic.And8(m.bytep, ^m.mask) |
| 307 | } |
| 308 | |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 309 | // markBitsForSpan returns the markBits for the span base address base. |
| 310 | func markBitsForSpan(base uintptr) (mbits markBits) { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 311 | mbits = markBitsForAddr(base) |
| 312 | if mbits.mask != 1 { |
| 313 | throw("markBitsForSpan: unaligned start") |
| 314 | } |
| 315 | return mbits |
| 316 | } |
| 317 | |
| 318 | // advance advances the markBits to the next object in the span. |
| 319 | func (m *markBits) advance() { |
| 320 | if m.mask == 1<<7 { |
| 321 | m.bytep = (*uint8)(unsafe.Pointer(uintptr(unsafe.Pointer(m.bytep)) + 1)) |
| 322 | m.mask = 1 |
| 323 | } else { |
| 324 | m.mask = m.mask << 1 |
| 325 | } |
| 326 | m.index++ |
| 327 | } |
| 328 | |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 329 | // heapBitsForAddr returns the heapBits for the address addr. |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 330 | // The caller must ensure addr is in an allocated span. |
| 331 | // In particular, be careful not to point past the end of an object. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 332 | // |
| 333 | // nosplit because it is used during write barriers and must not be preempted. |
| 334 | //go:nosplit |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 335 | func heapBitsForAddr(addr uintptr) (h heapBits) { |
| 336 | // 2 bits per word, 4 pairs per byte, and a mask is hard coded. |
| 337 | arena := arenaIndex(addr) |
| 338 | ha := mheap_.arenas[arena.l1()][arena.l2()] |
| 339 | // The compiler uses a load for nil checking ha, but in this |
| 340 | // case we'll almost never hit that cache line again, so it |
| 341 | // makes more sense to do a value check. |
| 342 | if ha == nil { |
| 343 | // addr is not in the heap. Return nil heapBits, which |
| 344 | // we expect to crash in the caller. |
| 345 | return |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 346 | } |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 347 | h.bitp = &ha.bitmap[(addr/(sys.PtrSize*4))%heapArenaBitmapBytes] |
| 348 | h.shift = uint32((addr / sys.PtrSize) & 3) |
| 349 | h.arena = uint32(arena) |
| 350 | h.last = &ha.bitmap[len(ha.bitmap)-1] |
| 351 | return |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 352 | } |
| 353 | |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 354 | // findObject returns the base address for the heap object containing |
| 355 | // the address p, the object's span, and the index of the object in s. |
| 356 | // If p does not point into a heap object, it returns base == 0. |
| 357 | // |
| 358 | // If p points is an invalid heap pointer and debug.invalidptr != 0, |
| 359 | // findObject panics. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 360 | // |
| 361 | // refBase and refOff optionally give the base address of the object |
| 362 | // in which the pointer p was found and the byte offset at which it |
| 363 | // was found. These are used for error reporting. |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 364 | func findObject(p, refBase, refOff uintptr) (base uintptr, s *mspan, objIndex uintptr) { |
| 365 | s = spanOf(p) |
| 366 | // If p is a bad pointer, it may not be in s's bounds. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 367 | if s == nil || p < s.base() || p >= s.limit || s.state != mSpanInUse { |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 368 | if s == nil || s.state == _MSpanManual { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 369 | // If s is nil, the virtual address has never been part of the heap. |
| 370 | // This pointer may be to some mmap'd region, so we allow it. |
| 371 | // Pointers into stacks are also ok, the runtime manages these explicitly. |
| 372 | return |
| 373 | } |
| 374 | |
| 375 | // The following ensures that we are rigorous about what data |
| 376 | // structures hold valid pointers. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 377 | if debug.invalidptr != 0 { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 378 | // Typically this indicates an incorrect use |
| 379 | // of unsafe or cgo to store a bad pointer in |
| 380 | // the Go heap. It may also indicate a runtime |
| 381 | // bug. |
| 382 | // |
| 383 | // TODO(austin): We could be more aggressive |
| 384 | // and detect pointers to unallocated objects |
| 385 | // in allocated spans. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 386 | printlock() |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 387 | print("runtime: pointer ", hex(p)) |
| 388 | if s.state != mSpanInUse { |
| 389 | print(" to unallocated span") |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 390 | } else { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 391 | print(" to unused region of span") |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 392 | } |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 393 | print(" span.base()=", hex(s.base()), " span.limit=", hex(s.limit), " span.state=", s.state, "\n") |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 394 | if refBase != 0 { |
| 395 | print("runtime: found in object at *(", hex(refBase), "+", hex(refOff), ")\n") |
| 396 | gcDumpObject("object", refBase, refOff) |
| 397 | } |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 398 | getg().m.traceback = 2 |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 399 | throw("found bad pointer in Go heap (incorrect use of unsafe or cgo?)") |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 400 | } |
| 401 | return |
| 402 | } |
| 403 | // If this span holds object of a power of 2 size, just mask off the bits to |
| 404 | // the interior of the object. Otherwise use the size to get the base. |
| 405 | if s.baseMask != 0 { |
| 406 | // optimize for power of 2 sized objects. |
| 407 | base = s.base() |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 408 | base = base + (p-base)&uintptr(s.baseMask) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 409 | objIndex = (base - s.base()) >> s.divShift |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 410 | // base = p & s.baseMask is faster for small spans, |
| 411 | // but doesn't work for large spans. |
| 412 | // Overall, it's faster to use the more general computation above. |
| 413 | } else { |
| 414 | base = s.base() |
| 415 | if p-base >= s.elemsize { |
| 416 | // n := (p - base) / s.elemsize, using division by multiplication |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 417 | objIndex = uintptr(p-base) >> s.divShift * uintptr(s.divMul) >> s.divShift2 |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 418 | base += objIndex * s.elemsize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 419 | } |
| 420 | } |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 421 | return |
| 422 | } |
| 423 | |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 424 | // next returns the heapBits describing the next pointer-sized word in memory. |
| 425 | // That is, if h describes address p, h.next() describes p+ptrSize. |
| 426 | // Note that next does not modify h. The caller must record the result. |
| 427 | // |
| 428 | // nosplit because it is used during write barriers and must not be preempted. |
| 429 | //go:nosplit |
| 430 | func (h heapBits) next() heapBits { |
| 431 | if h.shift < 3*heapBitsShift { |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 432 | h.shift += heapBitsShift |
| 433 | } else if h.bitp != h.last { |
| 434 | h.bitp, h.shift = add1(h.bitp), 0 |
| 435 | } else { |
| 436 | // Move to the next arena. |
| 437 | return h.nextArena() |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 438 | } |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 439 | return h |
| 440 | } |
| 441 | |
| 442 | // nextArena advances h to the beginning of the next heap arena. |
| 443 | // |
| 444 | // This is a slow-path helper to next. gc's inliner knows that |
| 445 | // heapBits.next can be inlined even though it calls this. This is |
| 446 | // marked noinline so it doesn't get inlined into next and cause next |
| 447 | // to be too big to inline. |
| 448 | // |
| 449 | //go:nosplit |
| 450 | //go:noinline |
| 451 | func (h heapBits) nextArena() heapBits { |
| 452 | h.arena++ |
| 453 | ai := arenaIdx(h.arena) |
| 454 | l2 := mheap_.arenas[ai.l1()] |
| 455 | if l2 == nil { |
| 456 | // We just passed the end of the object, which |
| 457 | // was also the end of the heap. Poison h. It |
| 458 | // should never be dereferenced at this point. |
| 459 | return heapBits{} |
| 460 | } |
| 461 | ha := l2[ai.l2()] |
| 462 | if ha == nil { |
| 463 | return heapBits{} |
| 464 | } |
| 465 | h.bitp, h.shift = &ha.bitmap[0], 0 |
| 466 | h.last = &ha.bitmap[len(ha.bitmap)-1] |
| 467 | return h |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 468 | } |
| 469 | |
| 470 | // forward returns the heapBits describing n pointer-sized words ahead of h in memory. |
| 471 | // That is, if h describes address p, h.forward(n) describes p+n*ptrSize. |
| 472 | // h.forward(1) is equivalent to h.next(), just slower. |
| 473 | // Note that forward does not modify h. The caller must record the result. |
| 474 | // bits returns the heap bits for the current word. |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 475 | //go:nosplit |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 476 | func (h heapBits) forward(n uintptr) heapBits { |
| 477 | n += uintptr(h.shift) / heapBitsShift |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 478 | nbitp := uintptr(unsafe.Pointer(h.bitp)) + n/4 |
| 479 | h.shift = uint32(n%4) * heapBitsShift |
| 480 | if nbitp <= uintptr(unsafe.Pointer(h.last)) { |
| 481 | h.bitp = (*uint8)(unsafe.Pointer(nbitp)) |
| 482 | return h |
| 483 | } |
| 484 | |
| 485 | // We're in a new heap arena. |
| 486 | past := nbitp - (uintptr(unsafe.Pointer(h.last)) + 1) |
| 487 | h.arena += 1 + uint32(past/heapArenaBitmapBytes) |
| 488 | ai := arenaIdx(h.arena) |
| 489 | if l2 := mheap_.arenas[ai.l1()]; l2 != nil && l2[ai.l2()] != nil { |
| 490 | a := l2[ai.l2()] |
| 491 | h.bitp = &a.bitmap[past%heapArenaBitmapBytes] |
| 492 | h.last = &a.bitmap[len(a.bitmap)-1] |
| 493 | } else { |
| 494 | h.bitp, h.last = nil, nil |
| 495 | } |
| 496 | return h |
| 497 | } |
| 498 | |
| 499 | // forwardOrBoundary is like forward, but stops at boundaries between |
| 500 | // contiguous sections of the bitmap. It returns the number of words |
| 501 | // advanced over, which will be <= n. |
| 502 | func (h heapBits) forwardOrBoundary(n uintptr) (heapBits, uintptr) { |
| 503 | maxn := 4 * ((uintptr(unsafe.Pointer(h.last)) + 1) - uintptr(unsafe.Pointer(h.bitp))) |
| 504 | if n > maxn { |
| 505 | n = maxn |
| 506 | } |
| 507 | return h.forward(n), n |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 508 | } |
| 509 | |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 510 | // The caller can test morePointers and isPointer by &-ing with bitScan and bitPointer. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 511 | // The result includes in its higher bits the bits for subsequent words |
| 512 | // described by the same bitmap byte. |
Dan Willemsen | a322328 | 2018-02-27 19:41:43 -0800 | [diff] [blame] | 513 | // |
| 514 | // nosplit because it is used during write barriers and must not be preempted. |
| 515 | //go:nosplit |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 516 | func (h heapBits) bits() uint32 { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 517 | // The (shift & 31) eliminates a test and conditional branch |
| 518 | // from the generated code. |
| 519 | return uint32(*h.bitp) >> (h.shift & 31) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 520 | } |
| 521 | |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 522 | // morePointers returns true if this word and all remaining words in this object |
| 523 | // are scalars. |
| 524 | // h must not describe the second word of the object. |
| 525 | func (h heapBits) morePointers() bool { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 526 | return h.bits()&bitScan != 0 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 527 | } |
| 528 | |
| 529 | // isPointer reports whether the heap bits describe a pointer word. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 530 | // |
| 531 | // nosplit because it is used during write barriers and must not be preempted. |
| 532 | //go:nosplit |
| 533 | func (h heapBits) isPointer() bool { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 534 | return h.bits()&bitPointer != 0 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 535 | } |
| 536 | |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 537 | // isCheckmarked reports whether the heap bits have the checkmarked bit set. |
| 538 | // It must be told how large the object at h is, because the encoding of the |
| 539 | // checkmark bit varies by size. |
| 540 | // h must describe the initial word of the object. |
| 541 | func (h heapBits) isCheckmarked(size uintptr) bool { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 542 | if size == sys.PtrSize { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 543 | return (*h.bitp>>h.shift)&bitPointer != 0 |
| 544 | } |
| 545 | // All multiword objects are 2-word aligned, |
| 546 | // so we know that the initial word's 2-bit pair |
| 547 | // and the second word's 2-bit pair are in the |
| 548 | // same heap bitmap byte, *h.bitp. |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 549 | return (*h.bitp>>(heapBitsShift+h.shift))&bitScan != 0 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 550 | } |
| 551 | |
| 552 | // setCheckmarked sets the checkmarked bit. |
| 553 | // It must be told how large the object at h is, because the encoding of the |
| 554 | // checkmark bit varies by size. |
| 555 | // h must describe the initial word of the object. |
| 556 | func (h heapBits) setCheckmarked(size uintptr) { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 557 | if size == sys.PtrSize { |
| 558 | atomic.Or8(h.bitp, bitPointer<<h.shift) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 559 | return |
| 560 | } |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 561 | atomic.Or8(h.bitp, bitScan<<(heapBitsShift+h.shift)) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 562 | } |
| 563 | |
Dan Willemsen | a322328 | 2018-02-27 19:41:43 -0800 | [diff] [blame] | 564 | // bulkBarrierPreWrite executes a write barrier |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 565 | // for every pointer slot in the memory range [src, src+size), |
| 566 | // using pointer/scalar information from [dst, dst+size). |
| 567 | // This executes the write barriers necessary before a memmove. |
| 568 | // src, dst, and size must be pointer-aligned. |
| 569 | // The range [dst, dst+size) must lie within a single object. |
Dan Willemsen | a322328 | 2018-02-27 19:41:43 -0800 | [diff] [blame] | 570 | // It does not perform the actual writes. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 571 | // |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 572 | // As a special case, src == 0 indicates that this is being used for a |
| 573 | // memclr. bulkBarrierPreWrite will pass 0 for the src of each write |
| 574 | // barrier. |
| 575 | // |
| 576 | // Callers should call bulkBarrierPreWrite immediately before |
| 577 | // calling memmove(dst, src, size). This function is marked nosplit |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 578 | // to avoid being preempted; the GC must not stop the goroutine |
| 579 | // between the memmove and the execution of the barriers. |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 580 | // The caller is also responsible for cgo pointer checks if this |
| 581 | // may be writing Go pointers into non-Go memory. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 582 | // |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 583 | // The pointer bitmap is not maintained for allocations containing |
| 584 | // no pointers at all; any caller of bulkBarrierPreWrite must first |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 585 | // make sure the underlying allocation contains pointers, usually |
| 586 | // by checking typ.kind&kindNoPointers. |
| 587 | // |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 588 | // Callers must perform cgo checks if writeBarrier.cgo. |
| 589 | // |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 590 | //go:nosplit |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 591 | func bulkBarrierPreWrite(dst, src, size uintptr) { |
| 592 | if (dst|src|size)&(sys.PtrSize-1) != 0 { |
| 593 | throw("bulkBarrierPreWrite: unaligned arguments") |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 594 | } |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 595 | if !writeBarrier.needed { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 596 | return |
| 597 | } |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 598 | if s := spanOf(dst); s == nil { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 599 | // If dst is a global, use the data or BSS bitmaps to |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 600 | // execute write barriers. |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 601 | for _, datap := range activeModules() { |
| 602 | if datap.data <= dst && dst < datap.edata { |
| 603 | bulkBarrierBitmap(dst, src, size, dst-datap.data, datap.gcdatamask.bytedata) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 604 | return |
| 605 | } |
| 606 | } |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 607 | for _, datap := range activeModules() { |
| 608 | if datap.bss <= dst && dst < datap.ebss { |
| 609 | bulkBarrierBitmap(dst, src, size, dst-datap.bss, datap.gcbssmask.bytedata) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 610 | return |
| 611 | } |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 612 | } |
| 613 | return |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 614 | } else if s.state != _MSpanInUse || dst < s.base() || s.limit <= dst { |
| 615 | // dst was heap memory at some point, but isn't now. |
| 616 | // It can't be a global. It must be either our stack, |
| 617 | // or in the case of direct channel sends, it could be |
| 618 | // another stack. Either way, no need for barriers. |
| 619 | // This will also catch if dst is in a freed span, |
| 620 | // though that should never have. |
| 621 | return |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 622 | } |
| 623 | |
Dan Willemsen | a322328 | 2018-02-27 19:41:43 -0800 | [diff] [blame] | 624 | buf := &getg().m.p.ptr().wbBuf |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 625 | h := heapBitsForAddr(dst) |
| 626 | if src == 0 { |
| 627 | for i := uintptr(0); i < size; i += sys.PtrSize { |
| 628 | if h.isPointer() { |
| 629 | dstx := (*uintptr)(unsafe.Pointer(dst + i)) |
Dan Willemsen | a322328 | 2018-02-27 19:41:43 -0800 | [diff] [blame] | 630 | if !buf.putFast(*dstx, 0) { |
| 631 | wbBufFlush(nil, 0) |
| 632 | } |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 633 | } |
| 634 | h = h.next() |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 635 | } |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 636 | } else { |
| 637 | for i := uintptr(0); i < size; i += sys.PtrSize { |
| 638 | if h.isPointer() { |
| 639 | dstx := (*uintptr)(unsafe.Pointer(dst + i)) |
| 640 | srcx := (*uintptr)(unsafe.Pointer(src + i)) |
Dan Willemsen | a322328 | 2018-02-27 19:41:43 -0800 | [diff] [blame] | 641 | if !buf.putFast(*dstx, *srcx) { |
| 642 | wbBufFlush(nil, 0) |
| 643 | } |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 644 | } |
| 645 | h = h.next() |
| 646 | } |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 647 | } |
| 648 | } |
| 649 | |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 650 | // bulkBarrierBitmap executes write barriers for copying from [src, |
| 651 | // src+size) to [dst, dst+size) using a 1-bit pointer bitmap. src is |
| 652 | // assumed to start maskOffset bytes into the data covered by the |
| 653 | // bitmap in bits (which may not be a multiple of 8). |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 654 | // |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 655 | // This is used by bulkBarrierPreWrite for writes to data and BSS. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 656 | // |
| 657 | //go:nosplit |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 658 | func bulkBarrierBitmap(dst, src, size, maskOffset uintptr, bits *uint8) { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 659 | word := maskOffset / sys.PtrSize |
| 660 | bits = addb(bits, word/8) |
| 661 | mask := uint8(1) << (word % 8) |
| 662 | |
Dan Willemsen | a322328 | 2018-02-27 19:41:43 -0800 | [diff] [blame] | 663 | buf := &getg().m.p.ptr().wbBuf |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 664 | for i := uintptr(0); i < size; i += sys.PtrSize { |
| 665 | if mask == 0 { |
| 666 | bits = addb(bits, 1) |
| 667 | if *bits == 0 { |
| 668 | // Skip 8 words. |
| 669 | i += 7 * sys.PtrSize |
| 670 | continue |
| 671 | } |
| 672 | mask = 1 |
| 673 | } |
| 674 | if *bits&mask != 0 { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 675 | dstx := (*uintptr)(unsafe.Pointer(dst + i)) |
| 676 | if src == 0 { |
Dan Willemsen | a322328 | 2018-02-27 19:41:43 -0800 | [diff] [blame] | 677 | if !buf.putFast(*dstx, 0) { |
| 678 | wbBufFlush(nil, 0) |
| 679 | } |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 680 | } else { |
| 681 | srcx := (*uintptr)(unsafe.Pointer(src + i)) |
Dan Willemsen | a322328 | 2018-02-27 19:41:43 -0800 | [diff] [blame] | 682 | if !buf.putFast(*dstx, *srcx) { |
| 683 | wbBufFlush(nil, 0) |
| 684 | } |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 685 | } |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 686 | } |
| 687 | mask <<= 1 |
| 688 | } |
| 689 | } |
| 690 | |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 691 | // typeBitsBulkBarrier executes a write barrier for every |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 692 | // pointer that would be copied from [src, src+size) to [dst, |
| 693 | // dst+size) by a memmove using the type bitmap to locate those |
| 694 | // pointer slots. |
| 695 | // |
| 696 | // The type typ must correspond exactly to [src, src+size) and [dst, dst+size). |
| 697 | // dst, src, and size must be pointer-aligned. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 698 | // The type typ must have a plain bitmap, not a GC program. |
| 699 | // The only use of this function is in channel sends, and the |
| 700 | // 64 kB channel element limit takes care of this for us. |
| 701 | // |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 702 | // Must not be preempted because it typically runs right before memmove, |
| 703 | // and the GC must observe them as an atomic action. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 704 | // |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 705 | // Callers must perform cgo checks if writeBarrier.cgo. |
| 706 | // |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 707 | //go:nosplit |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 708 | func typeBitsBulkBarrier(typ *_type, dst, src, size uintptr) { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 709 | if typ == nil { |
| 710 | throw("runtime: typeBitsBulkBarrier without type") |
| 711 | } |
| 712 | if typ.size != size { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 713 | println("runtime: typeBitsBulkBarrier with type ", typ.string(), " of size ", typ.size, " but memory size", size) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 714 | throw("runtime: invalid typeBitsBulkBarrier") |
| 715 | } |
| 716 | if typ.kind&kindGCProg != 0 { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 717 | println("runtime: typeBitsBulkBarrier with type ", typ.string(), " with GC prog") |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 718 | throw("runtime: invalid typeBitsBulkBarrier") |
| 719 | } |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 720 | if !writeBarrier.needed { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 721 | return |
| 722 | } |
| 723 | ptrmask := typ.gcdata |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 724 | buf := &getg().m.p.ptr().wbBuf |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 725 | var bits uint32 |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 726 | for i := uintptr(0); i < typ.ptrdata; i += sys.PtrSize { |
| 727 | if i&(sys.PtrSize*8-1) == 0 { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 728 | bits = uint32(*ptrmask) |
| 729 | ptrmask = addb(ptrmask, 1) |
| 730 | } else { |
| 731 | bits = bits >> 1 |
| 732 | } |
| 733 | if bits&1 != 0 { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 734 | dstx := (*uintptr)(unsafe.Pointer(dst + i)) |
| 735 | srcx := (*uintptr)(unsafe.Pointer(src + i)) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 736 | if !buf.putFast(*dstx, *srcx) { |
| 737 | wbBufFlush(nil, 0) |
| 738 | } |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 739 | } |
| 740 | } |
| 741 | } |
| 742 | |
| 743 | // The methods operating on spans all require that h has been returned |
| 744 | // by heapBitsForSpan and that size, n, total are the span layout description |
| 745 | // returned by the mspan's layout method. |
| 746 | // If total > size*n, it means that there is extra leftover memory in the span, |
| 747 | // usually due to rounding. |
| 748 | // |
| 749 | // TODO(rsc): Perhaps introduce a different heapBitsSpan type. |
| 750 | |
| 751 | // initSpan initializes the heap bitmap for a span. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 752 | // It clears all checkmark bits. |
| 753 | // If this is a span of pointer-sized objects, it initializes all |
| 754 | // words to pointer/scan. |
| 755 | // Otherwise, it initializes all words to scalar/dead. |
| 756 | func (h heapBits) initSpan(s *mspan) { |
| 757 | size, n, total := s.layout() |
| 758 | |
| 759 | // Init the markbit structures |
| 760 | s.freeindex = 0 |
| 761 | s.allocCache = ^uint64(0) // all 1s indicating all free. |
| 762 | s.nelems = n |
| 763 | s.allocBits = nil |
| 764 | s.gcmarkBits = nil |
| 765 | s.gcmarkBits = newMarkBits(s.nelems) |
| 766 | s.allocBits = newAllocBits(s.nelems) |
| 767 | |
| 768 | // Clear bits corresponding to objects. |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 769 | nw := total / sys.PtrSize |
| 770 | if nw%wordsPerBitmapByte != 0 { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 771 | throw("initSpan: unaligned length") |
| 772 | } |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 773 | if h.shift != 0 { |
| 774 | throw("initSpan: unaligned base") |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 775 | } |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 776 | for nw > 0 { |
| 777 | hNext, anw := h.forwardOrBoundary(nw) |
| 778 | nbyte := anw / wordsPerBitmapByte |
| 779 | if sys.PtrSize == 8 && size == sys.PtrSize { |
| 780 | bitp := h.bitp |
| 781 | for i := uintptr(0); i < nbyte; i++ { |
| 782 | *bitp = bitPointerAll | bitScanAll |
| 783 | bitp = add1(bitp) |
| 784 | } |
| 785 | } else { |
| 786 | memclrNoHeapPointers(unsafe.Pointer(h.bitp), nbyte) |
| 787 | } |
| 788 | h = hNext |
| 789 | nw -= anw |
| 790 | } |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 791 | } |
| 792 | |
| 793 | // initCheckmarkSpan initializes a span for being checkmarked. |
| 794 | // It clears the checkmark bits, which are set to 1 in normal operation. |
| 795 | func (h heapBits) initCheckmarkSpan(size, n, total uintptr) { |
| 796 | // The ptrSize == 8 is a compile-time constant false on 32-bit and eliminates this code entirely. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 797 | if sys.PtrSize == 8 && size == sys.PtrSize { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 798 | // Checkmark bit is type bit, bottom bit of every 2-bit entry. |
| 799 | // Only possible on 64-bit system, since minimum size is 8. |
| 800 | // Must clear type bit (checkmark bit) of every word. |
| 801 | // The type bit is the lower of every two-bit pair. |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 802 | for i := uintptr(0); i < n; i += wordsPerBitmapByte { |
| 803 | *h.bitp &^= bitPointerAll |
| 804 | h = h.forward(wordsPerBitmapByte) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 805 | } |
| 806 | return |
| 807 | } |
| 808 | for i := uintptr(0); i < n; i++ { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 809 | *h.bitp &^= bitScan << (heapBitsShift + h.shift) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 810 | h = h.forward(size / sys.PtrSize) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 811 | } |
| 812 | } |
| 813 | |
| 814 | // clearCheckmarkSpan undoes all the checkmarking in a span. |
| 815 | // The actual checkmark bits are ignored, so the only work to do |
| 816 | // is to fix the pointer bits. (Pointer bits are ignored by scanobject |
| 817 | // but consulted by typedmemmove.) |
| 818 | func (h heapBits) clearCheckmarkSpan(size, n, total uintptr) { |
| 819 | // The ptrSize == 8 is a compile-time constant false on 32-bit and eliminates this code entirely. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 820 | if sys.PtrSize == 8 && size == sys.PtrSize { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 821 | // Checkmark bit is type bit, bottom bit of every 2-bit entry. |
| 822 | // Only possible on 64-bit system, since minimum size is 8. |
| 823 | // Must clear type bit (checkmark bit) of every word. |
| 824 | // The type bit is the lower of every two-bit pair. |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 825 | for i := uintptr(0); i < n; i += wordsPerBitmapByte { |
| 826 | *h.bitp |= bitPointerAll |
| 827 | h = h.forward(wordsPerBitmapByte) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 828 | } |
| 829 | } |
| 830 | } |
| 831 | |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 832 | // oneBitCount is indexed by byte and produces the |
| 833 | // number of 1 bits in that byte. For example 128 has 1 bit set |
| 834 | // and oneBitCount[128] will holds 1. |
| 835 | var oneBitCount = [256]uint8{ |
| 836 | 0, 1, 1, 2, 1, 2, 2, 3, |
| 837 | 1, 2, 2, 3, 2, 3, 3, 4, |
| 838 | 1, 2, 2, 3, 2, 3, 3, 4, |
| 839 | 2, 3, 3, 4, 3, 4, 4, 5, |
| 840 | 1, 2, 2, 3, 2, 3, 3, 4, |
| 841 | 2, 3, 3, 4, 3, 4, 4, 5, |
| 842 | 2, 3, 3, 4, 3, 4, 4, 5, |
| 843 | 3, 4, 4, 5, 4, 5, 5, 6, |
| 844 | 1, 2, 2, 3, 2, 3, 3, 4, |
| 845 | 2, 3, 3, 4, 3, 4, 4, 5, |
| 846 | 2, 3, 3, 4, 3, 4, 4, 5, |
| 847 | 3, 4, 4, 5, 4, 5, 5, 6, |
| 848 | 2, 3, 3, 4, 3, 4, 4, 5, |
| 849 | 3, 4, 4, 5, 4, 5, 5, 6, |
| 850 | 3, 4, 4, 5, 4, 5, 5, 6, |
| 851 | 4, 5, 5, 6, 5, 6, 6, 7, |
| 852 | 1, 2, 2, 3, 2, 3, 3, 4, |
| 853 | 2, 3, 3, 4, 3, 4, 4, 5, |
| 854 | 2, 3, 3, 4, 3, 4, 4, 5, |
| 855 | 3, 4, 4, 5, 4, 5, 5, 6, |
| 856 | 2, 3, 3, 4, 3, 4, 4, 5, |
| 857 | 3, 4, 4, 5, 4, 5, 5, 6, |
| 858 | 3, 4, 4, 5, 4, 5, 5, 6, |
| 859 | 4, 5, 5, 6, 5, 6, 6, 7, |
| 860 | 2, 3, 3, 4, 3, 4, 4, 5, |
| 861 | 3, 4, 4, 5, 4, 5, 5, 6, |
| 862 | 3, 4, 4, 5, 4, 5, 5, 6, |
| 863 | 4, 5, 5, 6, 5, 6, 6, 7, |
| 864 | 3, 4, 4, 5, 4, 5, 5, 6, |
| 865 | 4, 5, 5, 6, 5, 6, 6, 7, |
| 866 | 4, 5, 5, 6, 5, 6, 6, 7, |
| 867 | 5, 6, 6, 7, 6, 7, 7, 8} |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 868 | |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 869 | // countAlloc returns the number of objects allocated in span s by |
| 870 | // scanning the allocation bitmap. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 871 | // TODO:(rlh) Use popcount intrinsic. |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 872 | func (s *mspan) countAlloc() int { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 873 | count := 0 |
| 874 | maxIndex := s.nelems / 8 |
| 875 | for i := uintptr(0); i < maxIndex; i++ { |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 876 | mrkBits := *s.gcmarkBits.bytep(i) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 877 | count += int(oneBitCount[mrkBits]) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 878 | } |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 879 | if bitsInLastByte := s.nelems % 8; bitsInLastByte != 0 { |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 880 | mrkBits := *s.gcmarkBits.bytep(maxIndex) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 881 | mask := uint8((1 << bitsInLastByte) - 1) |
| 882 | bits := mrkBits & mask |
| 883 | count += int(oneBitCount[bits]) |
| 884 | } |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 885 | return count |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 886 | } |
| 887 | |
| 888 | // heapBitsSetType records that the new allocation [x, x+size) |
| 889 | // holds in [x, x+dataSize) one or more values of type typ. |
| 890 | // (The number of values is given by dataSize / typ.size.) |
| 891 | // If dataSize < size, the fragment [x+dataSize, x+size) is |
| 892 | // recorded as non-pointer data. |
| 893 | // It is known that the type has pointers somewhere; |
| 894 | // malloc does not call heapBitsSetType when there are no pointers, |
| 895 | // because all free objects are marked as noscan during |
| 896 | // heapBitsSweepSpan. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 897 | // |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 898 | // There can only be one allocation from a given span active at a time, |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 899 | // and the bitmap for a span always falls on byte boundaries, |
| 900 | // so there are no write-write races for access to the heap bitmap. |
| 901 | // Hence, heapBitsSetType can access the bitmap without atomics. |
| 902 | // |
| 903 | // There can be read-write races between heapBitsSetType and things |
| 904 | // that read the heap bitmap like scanobject. However, since |
| 905 | // heapBitsSetType is only used for objects that have not yet been |
| 906 | // made reachable, readers will ignore bits being modified by this |
| 907 | // function. This does mean this function cannot transiently modify |
| 908 | // bits that belong to neighboring objects. Also, on weakly-ordered |
| 909 | // machines, callers must execute a store/store (publication) barrier |
| 910 | // between calling this function and making the object reachable. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 911 | func heapBitsSetType(x, size, dataSize uintptr, typ *_type) { |
| 912 | const doubleCheck = false // slow but helpful; enable to test modifications to this code |
| 913 | |
| 914 | // dataSize is always size rounded up to the next malloc size class, |
| 915 | // except in the case of allocating a defer block, in which case |
| 916 | // size is sizeof(_defer{}) (at least 6 words) and dataSize may be |
| 917 | // arbitrarily larger. |
| 918 | // |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 919 | // The checks for size == sys.PtrSize and size == 2*sys.PtrSize can therefore |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 920 | // assume that dataSize == size without checking it explicitly. |
| 921 | |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 922 | if sys.PtrSize == 8 && size == sys.PtrSize { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 923 | // It's one word and it has pointers, it must be a pointer. |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 924 | // Since all allocated one-word objects are pointers |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 925 | // (non-pointers are aggregated into tinySize allocations), |
| 926 | // initSpan sets the pointer bits for us. Nothing to do here. |
| 927 | if doubleCheck { |
| 928 | h := heapBitsForAddr(x) |
| 929 | if !h.isPointer() { |
| 930 | throw("heapBitsSetType: pointer bit missing") |
| 931 | } |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 932 | if !h.morePointers() { |
| 933 | throw("heapBitsSetType: scan bit missing") |
| 934 | } |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 935 | } |
| 936 | return |
| 937 | } |
| 938 | |
| 939 | h := heapBitsForAddr(x) |
| 940 | ptrmask := typ.gcdata // start of 1-bit pointer mask (or GC program, handled below) |
| 941 | |
| 942 | // Heap bitmap bits for 2-word object are only 4 bits, |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 943 | // so also shared with objects next to it. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 944 | // This is called out as a special case primarily for 32-bit systems, |
| 945 | // so that on 32-bit systems the code below can assume all objects |
| 946 | // are 4-word aligned (because they're all 16-byte aligned). |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 947 | if size == 2*sys.PtrSize { |
| 948 | if typ.size == sys.PtrSize { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 949 | // We're allocating a block big enough to hold two pointers. |
| 950 | // On 64-bit, that means the actual object must be two pointers, |
| 951 | // or else we'd have used the one-pointer-sized block. |
| 952 | // On 32-bit, however, this is the 8-byte block, the smallest one. |
| 953 | // So it could be that we're allocating one pointer and this was |
| 954 | // just the smallest block available. Distinguish by checking dataSize. |
| 955 | // (In general the number of instances of typ being allocated is |
| 956 | // dataSize/typ.size.) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 957 | if sys.PtrSize == 4 && dataSize == sys.PtrSize { |
| 958 | // 1 pointer object. On 32-bit machines clear the bit for the |
| 959 | // unused second word. |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 960 | *h.bitp &^= (bitPointer | bitScan | ((bitPointer | bitScan) << heapBitsShift)) << h.shift |
| 961 | *h.bitp |= (bitPointer | bitScan) << h.shift |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 962 | } else { |
| 963 | // 2-element slice of pointer. |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 964 | *h.bitp |= (bitPointer | bitScan | bitPointer<<heapBitsShift) << h.shift |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 965 | } |
| 966 | return |
| 967 | } |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 968 | // Otherwise typ.size must be 2*sys.PtrSize, |
| 969 | // and typ.kind&kindGCProg == 0. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 970 | if doubleCheck { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 971 | if typ.size != 2*sys.PtrSize || typ.kind&kindGCProg != 0 { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 972 | print("runtime: heapBitsSetType size=", size, " but typ.size=", typ.size, " gcprog=", typ.kind&kindGCProg != 0, "\n") |
| 973 | throw("heapBitsSetType") |
| 974 | } |
| 975 | } |
| 976 | b := uint32(*ptrmask) |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 977 | hb := (b & 3) | bitScan |
| 978 | // bitPointer == 1, bitScan is 1 << 4, heapBitsShift is 1. |
| 979 | // 110011 is shifted h.shift and complemented. |
| 980 | // This clears out the bits that are about to be |
| 981 | // ored into *h.hbitp in the next instructions. |
| 982 | *h.bitp &^= (bitPointer | bitScan | ((bitPointer | bitScan) << heapBitsShift)) << h.shift |
| 983 | *h.bitp |= uint8(hb << h.shift) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 984 | return |
| 985 | } |
| 986 | |
| 987 | // Copy from 1-bit ptrmask into 2-bit bitmap. |
| 988 | // The basic approach is to use a single uintptr as a bit buffer, |
| 989 | // alternating between reloading the buffer and writing bitmap bytes. |
| 990 | // In general, one load can supply two bitmap byte writes. |
| 991 | // This is a lot of lines of code, but it compiles into relatively few |
| 992 | // machine instructions. |
| 993 | |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 994 | outOfPlace := false |
| 995 | if arenaIndex(x+size-1) != arenaIdx(h.arena) || (doubleCheck && fastrand()%2 == 0) { |
| 996 | // This object spans heap arenas, so the bitmap may be |
| 997 | // discontiguous. Unroll it into the object instead |
| 998 | // and then copy it out. |
| 999 | // |
| 1000 | // In doubleCheck mode, we randomly do this anyway to |
| 1001 | // stress test the bitmap copying path. |
| 1002 | outOfPlace = true |
| 1003 | h.bitp = (*uint8)(unsafe.Pointer(x)) |
| 1004 | h.last = nil |
| 1005 | } |
| 1006 | |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1007 | var ( |
| 1008 | // Ptrmask input. |
| 1009 | p *byte // last ptrmask byte read |
| 1010 | b uintptr // ptrmask bits already loaded |
| 1011 | nb uintptr // number of bits in b at next read |
| 1012 | endp *byte // final ptrmask byte to read (then repeat) |
| 1013 | endnb uintptr // number of valid bits in *endp |
| 1014 | pbits uintptr // alternate source of bits |
| 1015 | |
| 1016 | // Heap bitmap output. |
| 1017 | w uintptr // words processed |
| 1018 | nw uintptr // number of words to process |
| 1019 | hbitp *byte // next heap bitmap byte to write |
| 1020 | hb uintptr // bits being prepared for *hbitp |
| 1021 | ) |
| 1022 | |
| 1023 | hbitp = h.bitp |
| 1024 | |
| 1025 | // Handle GC program. Delayed until this part of the code |
| 1026 | // so that we can use the same double-checking mechanism |
| 1027 | // as the 1-bit case. Nothing above could have encountered |
| 1028 | // GC programs: the cases were all too small. |
| 1029 | if typ.kind&kindGCProg != 0 { |
| 1030 | heapBitsSetTypeGCProg(h, typ.ptrdata, typ.size, dataSize, size, addb(typ.gcdata, 4)) |
| 1031 | if doubleCheck { |
| 1032 | // Double-check the heap bits written by GC program |
| 1033 | // by running the GC program to create a 1-bit pointer mask |
| 1034 | // and then jumping to the double-check code below. |
| 1035 | // This doesn't catch bugs shared between the 1-bit and 4-bit |
| 1036 | // GC program execution, but it does catch mistakes specific |
| 1037 | // to just one of those and bugs in heapBitsSetTypeGCProg's |
| 1038 | // implementation of arrays. |
| 1039 | lock(&debugPtrmask.lock) |
| 1040 | if debugPtrmask.data == nil { |
| 1041 | debugPtrmask.data = (*byte)(persistentalloc(1<<20, 1, &memstats.other_sys)) |
| 1042 | } |
| 1043 | ptrmask = debugPtrmask.data |
| 1044 | runGCProg(addb(typ.gcdata, 4), nil, ptrmask, 1) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1045 | } |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1046 | goto Phase4 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1047 | } |
| 1048 | |
| 1049 | // Note about sizes: |
| 1050 | // |
| 1051 | // typ.size is the number of words in the object, |
| 1052 | // and typ.ptrdata is the number of words in the prefix |
| 1053 | // of the object that contains pointers. That is, the final |
| 1054 | // typ.size - typ.ptrdata words contain no pointers. |
| 1055 | // This allows optimization of a common pattern where |
| 1056 | // an object has a small header followed by a large scalar |
| 1057 | // buffer. If we know the pointers are over, we don't have |
| 1058 | // to scan the buffer's heap bitmap at all. |
| 1059 | // The 1-bit ptrmasks are sized to contain only bits for |
| 1060 | // the typ.ptrdata prefix, zero padded out to a full byte |
| 1061 | // of bitmap. This code sets nw (below) so that heap bitmap |
| 1062 | // bits are only written for the typ.ptrdata prefix; if there is |
| 1063 | // more room in the allocated object, the next heap bitmap |
| 1064 | // entry is a 00, indicating that there are no more pointers |
| 1065 | // to scan. So only the ptrmask for the ptrdata bytes is needed. |
| 1066 | // |
| 1067 | // Replicated copies are not as nice: if there is an array of |
| 1068 | // objects with scalar tails, all but the last tail does have to |
| 1069 | // be initialized, because there is no way to say "skip forward". |
| 1070 | // However, because of the possibility of a repeated type with |
| 1071 | // size not a multiple of 4 pointers (one heap bitmap byte), |
| 1072 | // the code already must handle the last ptrmask byte specially |
| 1073 | // by treating it as containing only the bits for endnb pointers, |
| 1074 | // where endnb <= 4. We represent large scalar tails that must |
| 1075 | // be expanded in the replication by setting endnb larger than 4. |
| 1076 | // This will have the effect of reading many bits out of b, |
| 1077 | // but once the real bits are shifted out, b will supply as many |
| 1078 | // zero bits as we try to read, which is exactly what we need. |
| 1079 | |
| 1080 | p = ptrmask |
| 1081 | if typ.size < dataSize { |
| 1082 | // Filling in bits for an array of typ. |
| 1083 | // Set up for repetition of ptrmask during main loop. |
| 1084 | // Note that ptrmask describes only a prefix of |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1085 | const maxBits = sys.PtrSize*8 - 7 |
| 1086 | if typ.ptrdata/sys.PtrSize <= maxBits { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1087 | // Entire ptrmask fits in uintptr with room for a byte fragment. |
| 1088 | // Load into pbits and never read from ptrmask again. |
| 1089 | // This is especially important when the ptrmask has |
| 1090 | // fewer than 8 bits in it; otherwise the reload in the middle |
| 1091 | // of the Phase 2 loop would itself need to loop to gather |
| 1092 | // at least 8 bits. |
| 1093 | |
| 1094 | // Accumulate ptrmask into b. |
| 1095 | // ptrmask is sized to describe only typ.ptrdata, but we record |
| 1096 | // it as describing typ.size bytes, since all the high bits are zero. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1097 | nb = typ.ptrdata / sys.PtrSize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1098 | for i := uintptr(0); i < nb; i += 8 { |
| 1099 | b |= uintptr(*p) << i |
| 1100 | p = add1(p) |
| 1101 | } |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1102 | nb = typ.size / sys.PtrSize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1103 | |
| 1104 | // Replicate ptrmask to fill entire pbits uintptr. |
| 1105 | // Doubling and truncating is fewer steps than |
| 1106 | // iterating by nb each time. (nb could be 1.) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1107 | // Since we loaded typ.ptrdata/sys.PtrSize bits |
| 1108 | // but are pretending to have typ.size/sys.PtrSize, |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1109 | // there might be no replication necessary/possible. |
| 1110 | pbits = b |
| 1111 | endnb = nb |
| 1112 | if nb+nb <= maxBits { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1113 | for endnb <= sys.PtrSize*8 { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1114 | pbits |= pbits << endnb |
| 1115 | endnb += endnb |
| 1116 | } |
| 1117 | // Truncate to a multiple of original ptrmask. |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 1118 | // Because nb+nb <= maxBits, nb fits in a byte. |
| 1119 | // Byte division is cheaper than uintptr division. |
| 1120 | endnb = uintptr(maxBits/byte(nb)) * nb |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1121 | pbits &= 1<<endnb - 1 |
| 1122 | b = pbits |
| 1123 | nb = endnb |
| 1124 | } |
| 1125 | |
| 1126 | // Clear p and endp as sentinel for using pbits. |
| 1127 | // Checked during Phase 2 loop. |
| 1128 | p = nil |
| 1129 | endp = nil |
| 1130 | } else { |
| 1131 | // Ptrmask is larger. Read it multiple times. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1132 | n := (typ.ptrdata/sys.PtrSize+7)/8 - 1 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1133 | endp = addb(ptrmask, n) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1134 | endnb = typ.size/sys.PtrSize - n*8 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1135 | } |
| 1136 | } |
| 1137 | if p != nil { |
| 1138 | b = uintptr(*p) |
| 1139 | p = add1(p) |
| 1140 | nb = 8 |
| 1141 | } |
| 1142 | |
| 1143 | if typ.size == dataSize { |
| 1144 | // Single entry: can stop once we reach the non-pointer data. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1145 | nw = typ.ptrdata / sys.PtrSize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1146 | } else { |
| 1147 | // Repeated instances of typ in an array. |
| 1148 | // Have to process first N-1 entries in full, but can stop |
| 1149 | // once we reach the non-pointer data in the final entry. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1150 | nw = ((dataSize/typ.size-1)*typ.size + typ.ptrdata) / sys.PtrSize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1151 | } |
| 1152 | if nw == 0 { |
| 1153 | // No pointers! Caller was supposed to check. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1154 | println("runtime: invalid type ", typ.string()) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1155 | throw("heapBitsSetType: called with non-pointer type") |
| 1156 | return |
| 1157 | } |
| 1158 | if nw < 2 { |
| 1159 | // Must write at least 2 words, because the "no scan" |
| 1160 | // encoding doesn't take effect until the third word. |
| 1161 | nw = 2 |
| 1162 | } |
| 1163 | |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1164 | // Phase 1: Special case for leading byte (shift==0) or half-byte (shift==2). |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1165 | // The leading byte is special because it contains the bits for word 1, |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1166 | // which does not have the scan bit set. |
| 1167 | // The leading half-byte is special because it's a half a byte, |
| 1168 | // so we have to be careful with the bits already there. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1169 | switch { |
| 1170 | default: |
| 1171 | throw("heapBitsSetType: unexpected shift") |
| 1172 | |
| 1173 | case h.shift == 0: |
| 1174 | // Ptrmask and heap bitmap are aligned. |
| 1175 | // Handle first byte of bitmap specially. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1176 | // |
| 1177 | // The first byte we write out covers the first four |
| 1178 | // words of the object. The scan/dead bit on the first |
| 1179 | // word must be set to scan since there are pointers |
| 1180 | // somewhere in the object. The scan/dead bit on the |
| 1181 | // second word is the checkmark, so we don't set it. |
| 1182 | // In all following words, we set the scan/dead |
| 1183 | // appropriately to indicate that the object contains |
| 1184 | // to the next 2-bit entry in the bitmap. |
| 1185 | // |
| 1186 | // TODO: It doesn't matter if we set the checkmark, so |
| 1187 | // maybe this case isn't needed any more. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1188 | hb = b & bitPointerAll |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1189 | hb |= bitScan | bitScan<<(2*heapBitsShift) | bitScan<<(3*heapBitsShift) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1190 | if w += 4; w >= nw { |
| 1191 | goto Phase3 |
| 1192 | } |
| 1193 | *hbitp = uint8(hb) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1194 | hbitp = add1(hbitp) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1195 | b >>= 4 |
| 1196 | nb -= 4 |
| 1197 | |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1198 | case sys.PtrSize == 8 && h.shift == 2: |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1199 | // Ptrmask and heap bitmap are misaligned. |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1200 | // The bits for the first two words are in a byte shared |
| 1201 | // with another object, so we must be careful with the bits |
| 1202 | // already there. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1203 | // We took care of 1-word and 2-word objects above, |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1204 | // so this is at least a 6-word object. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1205 | hb = (b & (bitPointer | bitPointer<<heapBitsShift)) << (2 * heapBitsShift) |
| 1206 | // This is not noscan, so set the scan bit in the |
| 1207 | // first word. |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1208 | hb |= bitScan << (2 * heapBitsShift) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1209 | b >>= 2 |
| 1210 | nb -= 2 |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1211 | // Note: no bitScan for second word because that's |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1212 | // the checkmark. |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1213 | *hbitp &^= uint8((bitPointer | bitScan | (bitPointer << heapBitsShift)) << (2 * heapBitsShift)) |
| 1214 | *hbitp |= uint8(hb) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1215 | hbitp = add1(hbitp) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1216 | if w += 2; w >= nw { |
| 1217 | // We know that there is more data, because we handled 2-word objects above. |
| 1218 | // This must be at least a 6-word object. If we're out of pointer words, |
| 1219 | // mark no scan in next bitmap byte and finish. |
| 1220 | hb = 0 |
| 1221 | w += 4 |
| 1222 | goto Phase3 |
| 1223 | } |
| 1224 | } |
| 1225 | |
| 1226 | // Phase 2: Full bytes in bitmap, up to but not including write to last byte (full or partial) in bitmap. |
| 1227 | // The loop computes the bits for that last write but does not execute the write; |
| 1228 | // it leaves the bits in hb for processing by phase 3. |
| 1229 | // To avoid repeated adjustment of nb, we subtract out the 4 bits we're going to |
| 1230 | // use in the first half of the loop right now, and then we only adjust nb explicitly |
| 1231 | // if the 8 bits used by each iteration isn't balanced by 8 bits loaded mid-loop. |
| 1232 | nb -= 4 |
| 1233 | for { |
| 1234 | // Emit bitmap byte. |
| 1235 | // b has at least nb+4 bits, with one exception: |
| 1236 | // if w+4 >= nw, then b has only nw-w bits, |
| 1237 | // but we'll stop at the break and then truncate |
| 1238 | // appropriately in Phase 3. |
| 1239 | hb = b & bitPointerAll |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1240 | hb |= bitScanAll |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1241 | if w += 4; w >= nw { |
| 1242 | break |
| 1243 | } |
| 1244 | *hbitp = uint8(hb) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1245 | hbitp = add1(hbitp) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1246 | b >>= 4 |
| 1247 | |
| 1248 | // Load more bits. b has nb right now. |
| 1249 | if p != endp { |
| 1250 | // Fast path: keep reading from ptrmask. |
| 1251 | // nb unmodified: we just loaded 8 bits, |
| 1252 | // and the next iteration will consume 8 bits, |
| 1253 | // leaving us with the same nb the next time we're here. |
| 1254 | if nb < 8 { |
| 1255 | b |= uintptr(*p) << nb |
| 1256 | p = add1(p) |
| 1257 | } else { |
| 1258 | // Reduce the number of bits in b. |
| 1259 | // This is important if we skipped |
| 1260 | // over a scalar tail, since nb could |
| 1261 | // be larger than the bit width of b. |
| 1262 | nb -= 8 |
| 1263 | } |
| 1264 | } else if p == nil { |
| 1265 | // Almost as fast path: track bit count and refill from pbits. |
| 1266 | // For short repetitions. |
| 1267 | if nb < 8 { |
| 1268 | b |= pbits << nb |
| 1269 | nb += endnb |
| 1270 | } |
| 1271 | nb -= 8 // for next iteration |
| 1272 | } else { |
| 1273 | // Slow path: reached end of ptrmask. |
| 1274 | // Process final partial byte and rewind to start. |
| 1275 | b |= uintptr(*p) << nb |
| 1276 | nb += endnb |
| 1277 | if nb < 8 { |
| 1278 | b |= uintptr(*ptrmask) << nb |
| 1279 | p = add1(ptrmask) |
| 1280 | } else { |
| 1281 | nb -= 8 |
| 1282 | p = ptrmask |
| 1283 | } |
| 1284 | } |
| 1285 | |
| 1286 | // Emit bitmap byte. |
| 1287 | hb = b & bitPointerAll |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1288 | hb |= bitScanAll |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1289 | if w += 4; w >= nw { |
| 1290 | break |
| 1291 | } |
| 1292 | *hbitp = uint8(hb) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1293 | hbitp = add1(hbitp) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1294 | b >>= 4 |
| 1295 | } |
| 1296 | |
| 1297 | Phase3: |
| 1298 | // Phase 3: Write last byte or partial byte and zero the rest of the bitmap entries. |
| 1299 | if w > nw { |
| 1300 | // Counting the 4 entries in hb not yet written to memory, |
| 1301 | // there are more entries than possible pointer slots. |
| 1302 | // Discard the excess entries (can't be more than 3). |
| 1303 | mask := uintptr(1)<<(4-(w-nw)) - 1 |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1304 | hb &= mask | mask<<4 // apply mask to both pointer bits and scan bits |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1305 | } |
| 1306 | |
| 1307 | // Change nw from counting possibly-pointer words to total words in allocation. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1308 | nw = size / sys.PtrSize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1309 | |
| 1310 | // Write whole bitmap bytes. |
| 1311 | // The first is hb, the rest are zero. |
| 1312 | if w <= nw { |
| 1313 | *hbitp = uint8(hb) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1314 | hbitp = add1(hbitp) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1315 | hb = 0 // for possible final half-byte below |
| 1316 | for w += 4; w <= nw; w += 4 { |
| 1317 | *hbitp = 0 |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1318 | hbitp = add1(hbitp) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1319 | } |
| 1320 | } |
| 1321 | |
| 1322 | // Write final partial bitmap byte if any. |
| 1323 | // We know w > nw, or else we'd still be in the loop above. |
| 1324 | // It can be bigger only due to the 4 entries in hb that it counts. |
| 1325 | // If w == nw+4 then there's nothing left to do: we wrote all nw entries |
| 1326 | // and can discard the 4 sitting in hb. |
| 1327 | // But if w == nw+2, we need to write first two in hb. |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1328 | // The byte is shared with the next object, so be careful with |
| 1329 | // existing bits. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1330 | if w == nw+2 { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1331 | *hbitp = *hbitp&^(bitPointer|bitScan|(bitPointer|bitScan)<<heapBitsShift) | uint8(hb) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1332 | } |
| 1333 | |
| 1334 | Phase4: |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1335 | // Phase 4: Copy unrolled bitmap to per-arena bitmaps, if necessary. |
| 1336 | if outOfPlace { |
| 1337 | // TODO: We could probably make this faster by |
| 1338 | // handling [x+dataSize, x+size) specially. |
| 1339 | h := heapBitsForAddr(x) |
| 1340 | // cnw is the number of heap words, or bit pairs |
| 1341 | // remaining (like nw above). |
| 1342 | cnw := size / sys.PtrSize |
| 1343 | src := (*uint8)(unsafe.Pointer(x)) |
| 1344 | // We know the first and last byte of the bitmap are |
| 1345 | // not the same, but it's still possible for small |
| 1346 | // objects span arenas, so it may share bitmap bytes |
| 1347 | // with neighboring objects. |
| 1348 | // |
| 1349 | // Handle the first byte specially if it's shared. See |
| 1350 | // Phase 1 for why this is the only special case we need. |
| 1351 | if doubleCheck { |
| 1352 | if !(h.shift == 0 || (sys.PtrSize == 8 && h.shift == 2)) { |
| 1353 | print("x=", x, " size=", size, " cnw=", h.shift, "\n") |
| 1354 | throw("bad start shift") |
| 1355 | } |
| 1356 | } |
| 1357 | if sys.PtrSize == 8 && h.shift == 2 { |
| 1358 | *h.bitp = *h.bitp&^((bitPointer|bitScan|(bitPointer|bitScan)<<heapBitsShift)<<(2*heapBitsShift)) | *src |
| 1359 | h = h.next().next() |
| 1360 | cnw -= 2 |
| 1361 | src = addb(src, 1) |
| 1362 | } |
| 1363 | // We're now byte aligned. Copy out to per-arena |
| 1364 | // bitmaps until the last byte (which may again be |
| 1365 | // partial). |
| 1366 | for cnw >= 4 { |
| 1367 | // This loop processes four words at a time, |
| 1368 | // so round cnw down accordingly. |
| 1369 | hNext, words := h.forwardOrBoundary(cnw / 4 * 4) |
| 1370 | |
| 1371 | // n is the number of bitmap bytes to copy. |
| 1372 | n := words / 4 |
| 1373 | memmove(unsafe.Pointer(h.bitp), unsafe.Pointer(src), n) |
| 1374 | cnw -= words |
| 1375 | h = hNext |
| 1376 | src = addb(src, n) |
| 1377 | } |
| 1378 | if doubleCheck && h.shift != 0 { |
| 1379 | print("cnw=", cnw, " h.shift=", h.shift, "\n") |
| 1380 | throw("bad shift after block copy") |
| 1381 | } |
| 1382 | // Handle the last byte if it's shared. |
| 1383 | if cnw == 2 { |
| 1384 | *h.bitp = *h.bitp&^(bitPointer|bitScan|(bitPointer|bitScan)<<heapBitsShift) | *src |
| 1385 | src = addb(src, 1) |
| 1386 | h = h.next().next() |
| 1387 | } |
| 1388 | if doubleCheck { |
| 1389 | if uintptr(unsafe.Pointer(src)) > x+size { |
| 1390 | throw("copy exceeded object size") |
| 1391 | } |
| 1392 | if !(cnw == 0 || cnw == 2) { |
| 1393 | print("x=", x, " size=", size, " cnw=", cnw, "\n") |
| 1394 | throw("bad number of remaining words") |
| 1395 | } |
| 1396 | // Set up hbitp so doubleCheck code below can check it. |
| 1397 | hbitp = h.bitp |
| 1398 | } |
| 1399 | // Zero the object where we wrote the bitmap. |
| 1400 | memclrNoHeapPointers(unsafe.Pointer(x), uintptr(unsafe.Pointer(src))-x) |
| 1401 | } |
| 1402 | |
| 1403 | // Double check the whole bitmap. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1404 | if doubleCheck { |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1405 | // x+size may not point to the heap, so back up one |
| 1406 | // word and then call next(). |
| 1407 | end := heapBitsForAddr(x + size - sys.PtrSize).next() |
| 1408 | endAI := arenaIdx(end.arena) |
| 1409 | if !outOfPlace && (end.bitp == nil || (end.shift == 0 && end.bitp == &mheap_.arenas[endAI.l1()][endAI.l2()].bitmap[0])) { |
| 1410 | // The unrolling code above walks hbitp just |
| 1411 | // past the bitmap without moving to the next |
| 1412 | // arena. Synthesize this for end.bitp. |
| 1413 | end.arena-- |
| 1414 | endAI = arenaIdx(end.arena) |
| 1415 | end.bitp = addb(&mheap_.arenas[endAI.l1()][endAI.l2()].bitmap[0], heapArenaBitmapBytes) |
| 1416 | end.last = nil |
| 1417 | } |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1418 | if typ.kind&kindGCProg == 0 && (hbitp != end.bitp || (w == nw+2) != (end.shift == 2)) { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1419 | println("ended at wrong bitmap byte for", typ.string(), "x", dataSize/typ.size) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1420 | print("typ.size=", typ.size, " typ.ptrdata=", typ.ptrdata, " dataSize=", dataSize, " size=", size, "\n") |
| 1421 | print("w=", w, " nw=", nw, " b=", hex(b), " nb=", nb, " hb=", hex(hb), "\n") |
| 1422 | h0 := heapBitsForAddr(x) |
| 1423 | print("initial bits h0.bitp=", h0.bitp, " h0.shift=", h0.shift, "\n") |
| 1424 | print("ended at hbitp=", hbitp, " but next starts at bitp=", end.bitp, " shift=", end.shift, "\n") |
| 1425 | throw("bad heapBitsSetType") |
| 1426 | } |
| 1427 | |
| 1428 | // Double-check that bits to be written were written correctly. |
| 1429 | // Does not check that other bits were not written, unfortunately. |
| 1430 | h := heapBitsForAddr(x) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1431 | nptr := typ.ptrdata / sys.PtrSize |
| 1432 | ndata := typ.size / sys.PtrSize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1433 | count := dataSize / typ.size |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1434 | totalptr := ((count-1)*typ.size + typ.ptrdata) / sys.PtrSize |
| 1435 | for i := uintptr(0); i < size/sys.PtrSize; i++ { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1436 | j := i % ndata |
| 1437 | var have, want uint8 |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1438 | have = (*h.bitp >> h.shift) & (bitPointer | bitScan) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1439 | if i >= totalptr { |
| 1440 | want = 0 // deadmarker |
| 1441 | if typ.kind&kindGCProg != 0 && i < (totalptr+3)/4*4 { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1442 | want = bitScan |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1443 | } |
| 1444 | } else { |
| 1445 | if j < nptr && (*addb(ptrmask, j/8)>>(j%8))&1 != 0 { |
| 1446 | want |= bitPointer |
| 1447 | } |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1448 | if i != 1 { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1449 | want |= bitScan |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1450 | } else { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1451 | have &^= bitScan |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1452 | } |
| 1453 | } |
| 1454 | if have != want { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1455 | println("mismatch writing bits for", typ.string(), "x", dataSize/typ.size) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1456 | print("typ.size=", typ.size, " typ.ptrdata=", typ.ptrdata, " dataSize=", dataSize, " size=", size, "\n") |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1457 | print("kindGCProg=", typ.kind&kindGCProg != 0, " outOfPlace=", outOfPlace, "\n") |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1458 | print("w=", w, " nw=", nw, " b=", hex(b), " nb=", nb, " hb=", hex(hb), "\n") |
| 1459 | h0 := heapBitsForAddr(x) |
| 1460 | print("initial bits h0.bitp=", h0.bitp, " h0.shift=", h0.shift, "\n") |
| 1461 | print("current bits h.bitp=", h.bitp, " h.shift=", h.shift, " *h.bitp=", hex(*h.bitp), "\n") |
| 1462 | print("ptrmask=", ptrmask, " p=", p, " endp=", endp, " endnb=", endnb, " pbits=", hex(pbits), " b=", hex(b), " nb=", nb, "\n") |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1463 | println("at word", i, "offset", i*sys.PtrSize, "have", hex(have), "want", hex(want)) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1464 | if typ.kind&kindGCProg != 0 { |
| 1465 | println("GC program:") |
| 1466 | dumpGCProg(addb(typ.gcdata, 4)) |
| 1467 | } |
| 1468 | throw("bad heapBitsSetType") |
| 1469 | } |
| 1470 | h = h.next() |
| 1471 | } |
| 1472 | if ptrmask == debugPtrmask.data { |
| 1473 | unlock(&debugPtrmask.lock) |
| 1474 | } |
| 1475 | } |
| 1476 | } |
| 1477 | |
| 1478 | var debugPtrmask struct { |
| 1479 | lock mutex |
| 1480 | data *byte |
| 1481 | } |
| 1482 | |
| 1483 | // heapBitsSetTypeGCProg implements heapBitsSetType using a GC program. |
| 1484 | // progSize is the size of the memory described by the program. |
| 1485 | // elemSize is the size of the element that the GC program describes (a prefix of). |
| 1486 | // dataSize is the total size of the intended data, a multiple of elemSize. |
| 1487 | // allocSize is the total size of the allocated memory. |
| 1488 | // |
| 1489 | // GC programs are only used for large allocations. |
| 1490 | // heapBitsSetType requires that allocSize is a multiple of 4 words, |
| 1491 | // so that the relevant bitmap bytes are not shared with surrounding |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1492 | // objects. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1493 | func heapBitsSetTypeGCProg(h heapBits, progSize, elemSize, dataSize, allocSize uintptr, prog *byte) { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1494 | if sys.PtrSize == 8 && allocSize%(4*sys.PtrSize) != 0 { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1495 | // Alignment will be wrong. |
| 1496 | throw("heapBitsSetTypeGCProg: small allocation") |
| 1497 | } |
| 1498 | var totalBits uintptr |
| 1499 | if elemSize == dataSize { |
| 1500 | totalBits = runGCProg(prog, nil, h.bitp, 2) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1501 | if totalBits*sys.PtrSize != progSize { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1502 | println("runtime: heapBitsSetTypeGCProg: total bits", totalBits, "but progSize", progSize) |
| 1503 | throw("heapBitsSetTypeGCProg: unexpected bit count") |
| 1504 | } |
| 1505 | } else { |
| 1506 | count := dataSize / elemSize |
| 1507 | |
| 1508 | // Piece together program trailer to run after prog that does: |
| 1509 | // literal(0) |
| 1510 | // repeat(1, elemSize-progSize-1) // zeros to fill element size |
| 1511 | // repeat(elemSize, count-1) // repeat that element for count |
| 1512 | // This zero-pads the data remaining in the first element and then |
| 1513 | // repeats that first element to fill the array. |
| 1514 | var trailer [40]byte // 3 varints (max 10 each) + some bytes |
| 1515 | i := 0 |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1516 | if n := elemSize/sys.PtrSize - progSize/sys.PtrSize; n > 0 { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1517 | // literal(0) |
| 1518 | trailer[i] = 0x01 |
| 1519 | i++ |
| 1520 | trailer[i] = 0 |
| 1521 | i++ |
| 1522 | if n > 1 { |
| 1523 | // repeat(1, n-1) |
| 1524 | trailer[i] = 0x81 |
| 1525 | i++ |
| 1526 | n-- |
| 1527 | for ; n >= 0x80; n >>= 7 { |
| 1528 | trailer[i] = byte(n | 0x80) |
| 1529 | i++ |
| 1530 | } |
| 1531 | trailer[i] = byte(n) |
| 1532 | i++ |
| 1533 | } |
| 1534 | } |
| 1535 | // repeat(elemSize/ptrSize, count-1) |
| 1536 | trailer[i] = 0x80 |
| 1537 | i++ |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1538 | n := elemSize / sys.PtrSize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1539 | for ; n >= 0x80; n >>= 7 { |
| 1540 | trailer[i] = byte(n | 0x80) |
| 1541 | i++ |
| 1542 | } |
| 1543 | trailer[i] = byte(n) |
| 1544 | i++ |
| 1545 | n = count - 1 |
| 1546 | for ; n >= 0x80; n >>= 7 { |
| 1547 | trailer[i] = byte(n | 0x80) |
| 1548 | i++ |
| 1549 | } |
| 1550 | trailer[i] = byte(n) |
| 1551 | i++ |
| 1552 | trailer[i] = 0 |
| 1553 | i++ |
| 1554 | |
| 1555 | runGCProg(prog, &trailer[0], h.bitp, 2) |
| 1556 | |
| 1557 | // Even though we filled in the full array just now, |
| 1558 | // record that we only filled in up to the ptrdata of the |
| 1559 | // last element. This will cause the code below to |
| 1560 | // memclr the dead section of the final array element, |
| 1561 | // so that scanobject can stop early in the final element. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1562 | totalBits = (elemSize*(count-1) + progSize) / sys.PtrSize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1563 | } |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1564 | endProg := unsafe.Pointer(addb(h.bitp, (totalBits+3)/4)) |
| 1565 | endAlloc := unsafe.Pointer(addb(h.bitp, allocSize/sys.PtrSize/wordsPerBitmapByte)) |
| 1566 | memclrNoHeapPointers(endProg, uintptr(endAlloc)-uintptr(endProg)) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1567 | } |
| 1568 | |
| 1569 | // progToPointerMask returns the 1-bit pointer mask output by the GC program prog. |
| 1570 | // size the size of the region described by prog, in bytes. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1571 | // The resulting bitvector will have no more than size/sys.PtrSize bits. |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1572 | func progToPointerMask(prog *byte, size uintptr) bitvector { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1573 | n := (size/sys.PtrSize + 7) / 8 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1574 | x := (*[1 << 30]byte)(persistentalloc(n+1, 1, &memstats.buckhash_sys))[:n+1] |
| 1575 | x[len(x)-1] = 0xa1 // overflow check sentinel |
| 1576 | n = runGCProg(prog, nil, &x[0], 1) |
| 1577 | if x[len(x)-1] != 0xa1 { |
| 1578 | throw("progToPointerMask: overflow") |
| 1579 | } |
| 1580 | return bitvector{int32(n), &x[0]} |
| 1581 | } |
| 1582 | |
| 1583 | // Packed GC pointer bitmaps, aka GC programs. |
| 1584 | // |
| 1585 | // For large types containing arrays, the type information has a |
| 1586 | // natural repetition that can be encoded to save space in the |
| 1587 | // binary and in the memory representation of the type information. |
| 1588 | // |
| 1589 | // The encoding is a simple Lempel-Ziv style bytecode machine |
| 1590 | // with the following instructions: |
| 1591 | // |
| 1592 | // 00000000: stop |
| 1593 | // 0nnnnnnn: emit n bits copied from the next (n+7)/8 bytes |
| 1594 | // 10000000 n c: repeat the previous n bits c times; n, c are varints |
| 1595 | // 1nnnnnnn c: repeat the previous n bits c times; c is a varint |
| 1596 | |
| 1597 | // runGCProg executes the GC program prog, and then trailer if non-nil, |
| 1598 | // writing to dst with entries of the given size. |
| 1599 | // If size == 1, dst is a 1-bit pointer mask laid out moving forward from dst. |
| 1600 | // If size == 2, dst is the 2-bit heap bitmap, and writes move backward |
| 1601 | // starting at dst (because the heap bitmap does). In this case, the caller guarantees |
| 1602 | // that only whole bytes in dst need to be written. |
| 1603 | // |
| 1604 | // runGCProg returns the number of 1- or 2-bit entries written to memory. |
| 1605 | func runGCProg(prog, trailer, dst *byte, size int) uintptr { |
| 1606 | dstStart := dst |
| 1607 | |
| 1608 | // Bits waiting to be written to memory. |
| 1609 | var bits uintptr |
| 1610 | var nbits uintptr |
| 1611 | |
| 1612 | p := prog |
| 1613 | Run: |
| 1614 | for { |
| 1615 | // Flush accumulated full bytes. |
| 1616 | // The rest of the loop assumes that nbits <= 7. |
| 1617 | for ; nbits >= 8; nbits -= 8 { |
| 1618 | if size == 1 { |
| 1619 | *dst = uint8(bits) |
| 1620 | dst = add1(dst) |
| 1621 | bits >>= 8 |
| 1622 | } else { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1623 | v := bits&bitPointerAll | bitScanAll |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1624 | *dst = uint8(v) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1625 | dst = add1(dst) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1626 | bits >>= 4 |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1627 | v = bits&bitPointerAll | bitScanAll |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1628 | *dst = uint8(v) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1629 | dst = add1(dst) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1630 | bits >>= 4 |
| 1631 | } |
| 1632 | } |
| 1633 | |
| 1634 | // Process one instruction. |
| 1635 | inst := uintptr(*p) |
| 1636 | p = add1(p) |
| 1637 | n := inst & 0x7F |
| 1638 | if inst&0x80 == 0 { |
| 1639 | // Literal bits; n == 0 means end of program. |
| 1640 | if n == 0 { |
| 1641 | // Program is over; continue in trailer if present. |
| 1642 | if trailer != nil { |
| 1643 | //println("trailer") |
| 1644 | p = trailer |
| 1645 | trailer = nil |
| 1646 | continue |
| 1647 | } |
| 1648 | //println("done") |
| 1649 | break Run |
| 1650 | } |
| 1651 | //println("lit", n, dst) |
| 1652 | nbyte := n / 8 |
| 1653 | for i := uintptr(0); i < nbyte; i++ { |
| 1654 | bits |= uintptr(*p) << nbits |
| 1655 | p = add1(p) |
| 1656 | if size == 1 { |
| 1657 | *dst = uint8(bits) |
| 1658 | dst = add1(dst) |
| 1659 | bits >>= 8 |
| 1660 | } else { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1661 | v := bits&0xf | bitScanAll |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1662 | *dst = uint8(v) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1663 | dst = add1(dst) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1664 | bits >>= 4 |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1665 | v = bits&0xf | bitScanAll |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1666 | *dst = uint8(v) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1667 | dst = add1(dst) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1668 | bits >>= 4 |
| 1669 | } |
| 1670 | } |
| 1671 | if n %= 8; n > 0 { |
| 1672 | bits |= uintptr(*p) << nbits |
| 1673 | p = add1(p) |
| 1674 | nbits += n |
| 1675 | } |
| 1676 | continue Run |
| 1677 | } |
| 1678 | |
| 1679 | // Repeat. If n == 0, it is encoded in a varint in the next bytes. |
| 1680 | if n == 0 { |
| 1681 | for off := uint(0); ; off += 7 { |
| 1682 | x := uintptr(*p) |
| 1683 | p = add1(p) |
| 1684 | n |= (x & 0x7F) << off |
| 1685 | if x&0x80 == 0 { |
| 1686 | break |
| 1687 | } |
| 1688 | } |
| 1689 | } |
| 1690 | |
| 1691 | // Count is encoded in a varint in the next bytes. |
| 1692 | c := uintptr(0) |
| 1693 | for off := uint(0); ; off += 7 { |
| 1694 | x := uintptr(*p) |
| 1695 | p = add1(p) |
| 1696 | c |= (x & 0x7F) << off |
| 1697 | if x&0x80 == 0 { |
| 1698 | break |
| 1699 | } |
| 1700 | } |
| 1701 | c *= n // now total number of bits to copy |
| 1702 | |
| 1703 | // If the number of bits being repeated is small, load them |
| 1704 | // into a register and use that register for the entire loop |
| 1705 | // instead of repeatedly reading from memory. |
| 1706 | // Handling fewer than 8 bits here makes the general loop simpler. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1707 | // The cutoff is sys.PtrSize*8 - 7 to guarantee that when we add |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1708 | // the pattern to a bit buffer holding at most 7 bits (a partial byte) |
| 1709 | // it will not overflow. |
| 1710 | src := dst |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1711 | const maxBits = sys.PtrSize*8 - 7 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1712 | if n <= maxBits { |
| 1713 | // Start with bits in output buffer. |
| 1714 | pattern := bits |
| 1715 | npattern := nbits |
| 1716 | |
| 1717 | // If we need more bits, fetch them from memory. |
| 1718 | if size == 1 { |
| 1719 | src = subtract1(src) |
| 1720 | for npattern < n { |
| 1721 | pattern <<= 8 |
| 1722 | pattern |= uintptr(*src) |
| 1723 | src = subtract1(src) |
| 1724 | npattern += 8 |
| 1725 | } |
| 1726 | } else { |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1727 | src = subtract1(src) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1728 | for npattern < n { |
| 1729 | pattern <<= 4 |
| 1730 | pattern |= uintptr(*src) & 0xf |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1731 | src = subtract1(src) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1732 | npattern += 4 |
| 1733 | } |
| 1734 | } |
| 1735 | |
| 1736 | // We started with the whole bit output buffer, |
| 1737 | // and then we loaded bits from whole bytes. |
| 1738 | // Either way, we might now have too many instead of too few. |
| 1739 | // Discard the extra. |
| 1740 | if npattern > n { |
| 1741 | pattern >>= npattern - n |
| 1742 | npattern = n |
| 1743 | } |
| 1744 | |
| 1745 | // Replicate pattern to at most maxBits. |
| 1746 | if npattern == 1 { |
| 1747 | // One bit being repeated. |
| 1748 | // If the bit is 1, make the pattern all 1s. |
| 1749 | // If the bit is 0, the pattern is already all 0s, |
| 1750 | // but we can claim that the number of bits |
| 1751 | // in the word is equal to the number we need (c), |
| 1752 | // because right shift of bits will zero fill. |
| 1753 | if pattern == 1 { |
| 1754 | pattern = 1<<maxBits - 1 |
| 1755 | npattern = maxBits |
| 1756 | } else { |
| 1757 | npattern = c |
| 1758 | } |
| 1759 | } else { |
| 1760 | b := pattern |
| 1761 | nb := npattern |
| 1762 | if nb+nb <= maxBits { |
| 1763 | // Double pattern until the whole uintptr is filled. |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1764 | for nb <= sys.PtrSize*8 { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1765 | b |= b << nb |
| 1766 | nb += nb |
| 1767 | } |
| 1768 | // Trim away incomplete copy of original pattern in high bits. |
| 1769 | // TODO(rsc): Replace with table lookup or loop on systems without divide? |
| 1770 | nb = maxBits / npattern * npattern |
| 1771 | b &= 1<<nb - 1 |
| 1772 | pattern = b |
| 1773 | npattern = nb |
| 1774 | } |
| 1775 | } |
| 1776 | |
| 1777 | // Add pattern to bit buffer and flush bit buffer, c/npattern times. |
| 1778 | // Since pattern contains >8 bits, there will be full bytes to flush |
| 1779 | // on each iteration. |
| 1780 | for ; c >= npattern; c -= npattern { |
| 1781 | bits |= pattern << nbits |
| 1782 | nbits += npattern |
| 1783 | if size == 1 { |
| 1784 | for nbits >= 8 { |
| 1785 | *dst = uint8(bits) |
| 1786 | dst = add1(dst) |
| 1787 | bits >>= 8 |
| 1788 | nbits -= 8 |
| 1789 | } |
| 1790 | } else { |
| 1791 | for nbits >= 4 { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1792 | *dst = uint8(bits&0xf | bitScanAll) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1793 | dst = add1(dst) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1794 | bits >>= 4 |
| 1795 | nbits -= 4 |
| 1796 | } |
| 1797 | } |
| 1798 | } |
| 1799 | |
| 1800 | // Add final fragment to bit buffer. |
| 1801 | if c > 0 { |
| 1802 | pattern &= 1<<c - 1 |
| 1803 | bits |= pattern << nbits |
| 1804 | nbits += c |
| 1805 | } |
| 1806 | continue Run |
| 1807 | } |
| 1808 | |
| 1809 | // Repeat; n too large to fit in a register. |
| 1810 | // Since nbits <= 7, we know the first few bytes of repeated data |
| 1811 | // are already written to memory. |
| 1812 | off := n - nbits // n > nbits because n > maxBits and nbits <= 7 |
| 1813 | if size == 1 { |
| 1814 | // Leading src fragment. |
| 1815 | src = subtractb(src, (off+7)/8) |
| 1816 | if frag := off & 7; frag != 0 { |
| 1817 | bits |= uintptr(*src) >> (8 - frag) << nbits |
| 1818 | src = add1(src) |
| 1819 | nbits += frag |
| 1820 | c -= frag |
| 1821 | } |
| 1822 | // Main loop: load one byte, write another. |
| 1823 | // The bits are rotating through the bit buffer. |
| 1824 | for i := c / 8; i > 0; i-- { |
| 1825 | bits |= uintptr(*src) << nbits |
| 1826 | src = add1(src) |
| 1827 | *dst = uint8(bits) |
| 1828 | dst = add1(dst) |
| 1829 | bits >>= 8 |
| 1830 | } |
| 1831 | // Final src fragment. |
| 1832 | if c %= 8; c > 0 { |
| 1833 | bits |= (uintptr(*src) & (1<<c - 1)) << nbits |
| 1834 | nbits += c |
| 1835 | } |
| 1836 | } else { |
| 1837 | // Leading src fragment. |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1838 | src = subtractb(src, (off+3)/4) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1839 | if frag := off & 3; frag != 0 { |
| 1840 | bits |= (uintptr(*src) & 0xf) >> (4 - frag) << nbits |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1841 | src = add1(src) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1842 | nbits += frag |
| 1843 | c -= frag |
| 1844 | } |
| 1845 | // Main loop: load one byte, write another. |
| 1846 | // The bits are rotating through the bit buffer. |
| 1847 | for i := c / 4; i > 0; i-- { |
| 1848 | bits |= (uintptr(*src) & 0xf) << nbits |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1849 | src = add1(src) |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1850 | *dst = uint8(bits&0xf | bitScanAll) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1851 | dst = add1(dst) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1852 | bits >>= 4 |
| 1853 | } |
| 1854 | // Final src fragment. |
| 1855 | if c %= 4; c > 0 { |
| 1856 | bits |= (uintptr(*src) & (1<<c - 1)) << nbits |
| 1857 | nbits += c |
| 1858 | } |
| 1859 | } |
| 1860 | } |
| 1861 | |
| 1862 | // Write any final bits out, using full-byte writes, even for the final byte. |
| 1863 | var totalBits uintptr |
| 1864 | if size == 1 { |
| 1865 | totalBits = (uintptr(unsafe.Pointer(dst))-uintptr(unsafe.Pointer(dstStart)))*8 + nbits |
| 1866 | nbits += -nbits & 7 |
| 1867 | for ; nbits > 0; nbits -= 8 { |
| 1868 | *dst = uint8(bits) |
| 1869 | dst = add1(dst) |
| 1870 | bits >>= 8 |
| 1871 | } |
| 1872 | } else { |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1873 | totalBits = (uintptr(unsafe.Pointer(dst))-uintptr(unsafe.Pointer(dstStart)))*4 + nbits |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1874 | nbits += -nbits & 3 |
| 1875 | for ; nbits > 0; nbits -= 4 { |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1876 | v := bits&0xf | bitScanAll |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1877 | *dst = uint8(v) |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1878 | dst = add1(dst) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1879 | bits >>= 4 |
| 1880 | } |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1881 | } |
| 1882 | return totalBits |
| 1883 | } |
| 1884 | |
| 1885 | func dumpGCProg(p *byte) { |
| 1886 | nptr := 0 |
| 1887 | for { |
| 1888 | x := *p |
| 1889 | p = add1(p) |
| 1890 | if x == 0 { |
| 1891 | print("\t", nptr, " end\n") |
| 1892 | break |
| 1893 | } |
| 1894 | if x&0x80 == 0 { |
| 1895 | print("\t", nptr, " lit ", x, ":") |
| 1896 | n := int(x+7) / 8 |
| 1897 | for i := 0; i < n; i++ { |
| 1898 | print(" ", hex(*p)) |
| 1899 | p = add1(p) |
| 1900 | } |
| 1901 | print("\n") |
| 1902 | nptr += int(x) |
| 1903 | } else { |
| 1904 | nbit := int(x &^ 0x80) |
| 1905 | if nbit == 0 { |
| 1906 | for nb := uint(0); ; nb += 7 { |
| 1907 | x := *p |
| 1908 | p = add1(p) |
| 1909 | nbit |= int(x&0x7f) << nb |
| 1910 | if x&0x80 == 0 { |
| 1911 | break |
| 1912 | } |
| 1913 | } |
| 1914 | } |
| 1915 | count := 0 |
| 1916 | for nb := uint(0); ; nb += 7 { |
| 1917 | x := *p |
| 1918 | p = add1(p) |
| 1919 | count |= int(x&0x7f) << nb |
| 1920 | if x&0x80 == 0 { |
| 1921 | break |
| 1922 | } |
| 1923 | } |
| 1924 | print("\t", nptr, " repeat ", nbit, " × ", count, "\n") |
| 1925 | nptr += nbit * count |
| 1926 | } |
| 1927 | } |
| 1928 | } |
| 1929 | |
| 1930 | // Testing. |
| 1931 | |
| 1932 | func getgcmaskcb(frame *stkframe, ctxt unsafe.Pointer) bool { |
| 1933 | target := (*stkframe)(ctxt) |
| 1934 | if frame.sp <= target.sp && target.sp < frame.varp { |
| 1935 | *target = *frame |
| 1936 | return false |
| 1937 | } |
| 1938 | return true |
| 1939 | } |
| 1940 | |
| 1941 | // gcbits returns the GC type info for x, for testing. |
| 1942 | // The result is the bitmap entries (0 or 1), one entry per byte. |
| 1943 | //go:linkname reflect_gcbits reflect.gcbits |
| 1944 | func reflect_gcbits(x interface{}) []byte { |
| 1945 | ret := getgcmask(x) |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1946 | typ := (*ptrtype)(unsafe.Pointer(efaceOf(&x)._type)).elem |
| 1947 | nptr := typ.ptrdata / sys.PtrSize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1948 | for uintptr(len(ret)) > nptr && ret[len(ret)-1] == 0 { |
| 1949 | ret = ret[:len(ret)-1] |
| 1950 | } |
| 1951 | return ret |
| 1952 | } |
| 1953 | |
| 1954 | // Returns GC type info for object p for testing. |
| 1955 | func getgcmask(ep interface{}) (mask []byte) { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1956 | e := *efaceOf(&ep) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1957 | p := e.data |
| 1958 | t := e._type |
| 1959 | // data or bss |
Dan Willemsen | ebae302 | 2017-01-13 23:01:08 -0800 | [diff] [blame] | 1960 | for _, datap := range activeModules() { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1961 | // data |
| 1962 | if datap.data <= uintptr(p) && uintptr(p) < datap.edata { |
| 1963 | bitmap := datap.gcdatamask.bytedata |
| 1964 | n := (*ptrtype)(unsafe.Pointer(t)).elem.size |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1965 | mask = make([]byte, n/sys.PtrSize) |
| 1966 | for i := uintptr(0); i < n; i += sys.PtrSize { |
| 1967 | off := (uintptr(p) + i - datap.data) / sys.PtrSize |
| 1968 | mask[i/sys.PtrSize] = (*addb(bitmap, off/8) >> (off % 8)) & 1 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1969 | } |
| 1970 | return |
| 1971 | } |
| 1972 | |
| 1973 | // bss |
| 1974 | if datap.bss <= uintptr(p) && uintptr(p) < datap.ebss { |
| 1975 | bitmap := datap.gcbssmask.bytedata |
| 1976 | n := (*ptrtype)(unsafe.Pointer(t)).elem.size |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1977 | mask = make([]byte, n/sys.PtrSize) |
| 1978 | for i := uintptr(0); i < n; i += sys.PtrSize { |
| 1979 | off := (uintptr(p) + i - datap.bss) / sys.PtrSize |
| 1980 | mask[i/sys.PtrSize] = (*addb(bitmap, off/8) >> (off % 8)) & 1 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1981 | } |
| 1982 | return |
| 1983 | } |
| 1984 | } |
| 1985 | |
| 1986 | // heap |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1987 | if base, s, _ := findObject(uintptr(p), 0, 0); base != 0 { |
| 1988 | hbits := heapBitsForAddr(base) |
| 1989 | n := s.elemsize |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1990 | mask = make([]byte, n/sys.PtrSize) |
| 1991 | for i := uintptr(0); i < n; i += sys.PtrSize { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1992 | if hbits.isPointer() { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1993 | mask[i/sys.PtrSize] = 1 |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1994 | } |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1995 | if i != 1*sys.PtrSize && !hbits.morePointers() { |
| 1996 | mask = mask[:i/sys.PtrSize] |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 1997 | break |
| 1998 | } |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 1999 | hbits = hbits.next() |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 2000 | } |
| 2001 | return |
| 2002 | } |
| 2003 | |
| 2004 | // stack |
| 2005 | if _g_ := getg(); _g_.m.curg.stack.lo <= uintptr(p) && uintptr(p) < _g_.m.curg.stack.hi { |
| 2006 | var frame stkframe |
| 2007 | frame.sp = uintptr(p) |
| 2008 | _g_ := getg() |
| 2009 | gentraceback(_g_.m.curg.sched.pc, _g_.m.curg.sched.sp, 0, _g_.m.curg, 0, nil, 1000, getgcmaskcb, noescape(unsafe.Pointer(&frame)), 0) |
Dan Willemsen | d279748 | 2017-07-26 13:13:13 -0700 | [diff] [blame] | 2010 | if frame.fn.valid() { |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 2011 | locals, _ := getStackMap(&frame, nil, false) |
| 2012 | if locals.n == 0 { |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 2013 | return |
| 2014 | } |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 2015 | size := uintptr(locals.n) * sys.PtrSize |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 2016 | n := (*ptrtype)(unsafe.Pointer(t)).elem.size |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 2017 | mask = make([]byte, n/sys.PtrSize) |
| 2018 | for i := uintptr(0); i < n; i += sys.PtrSize { |
Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 2019 | off := (uintptr(p) + i - frame.varp + size) / sys.PtrSize |
Dan Willemsen | c741332 | 2018-08-27 23:21:26 -0700 | [diff] [blame^] | 2020 | mask[i/sys.PtrSize] = locals.ptrbit(off) |
Dan Willemsen | 09eb3b1 | 2015-09-16 14:34:17 -0700 | [diff] [blame] | 2021 | } |
| 2022 | } |
| 2023 | return |
| 2024 | } |
| 2025 | |
| 2026 | // otherwise, not something the GC knows about. |
| 2027 | // possibly read-only data, like malloc(0). |
| 2028 | // must not have pointers |
| 2029 | return |
| 2030 | } |