| // Copyright 2009 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // Garbage collector: type and heap bitmaps. |
| // |
| // Stack, data, and bss bitmaps |
| // |
| // Stack frames and global variables in the data and bss sections are |
| // described by bitmaps with 1 bit per pointer-sized word. A "1" bit |
| // means the word is a live pointer to be visited by the GC (referred to |
| // as "pointer"). A "0" bit means the word should be ignored by GC |
| // (referred to as "scalar", though it could be a dead pointer value). |
| // |
| // Heap bitmap |
| // |
| // The heap bitmap comprises 2 bits for each pointer-sized word in the heap, |
| // stored in the heapArena metadata backing each heap arena. |
| // That is, if ha is the heapArena for the arena starting a start, |
| // then ha.bitmap[0] holds the 2-bit entries for the four words start |
| // through start+3*ptrSize, ha.bitmap[1] holds the entries for |
| // start+4*ptrSize through start+7*ptrSize, and so on. |
| // |
| // In each 2-bit entry, the lower bit is a pointer/scalar bit, just |
| // like in the stack/data bitmaps described above. The upper bit |
| // indicates scan/dead: a "1" value ("scan") indicates that there may |
| // be pointers in later words of the allocation, and a "0" value |
| // ("dead") indicates there are no more pointers in the allocation. If |
| // the upper bit is 0, the lower bit must also be 0, and this |
| // indicates scanning can ignore the rest of the allocation. |
| // |
| // The 2-bit entries are split when written into the byte, so that the top half |
| // of the byte contains 4 high (scan) bits and the bottom half contains 4 low |
| // (pointer) bits. This form allows a copy from the 1-bit to the 4-bit form to |
| // keep the pointer bits contiguous, instead of having to space them out. |
| // |
| // The code makes use of the fact that the zero value for a heap |
| // bitmap means scalar/dead. This property must be preserved when |
| // modifying the encoding. |
| // |
| // The bitmap for noscan spans is not maintained. Code must ensure |
| // that an object is scannable before consulting its bitmap by |
| // checking either the noscan bit in the span or by consulting its |
| // type's information. |
| |
| package runtime |
| |
| import ( |
| "runtime/internal/atomic" |
| "runtime/internal/sys" |
| "unsafe" |
| ) |
| |
| const ( |
| bitPointer = 1 << 0 |
| bitScan = 1 << 4 |
| |
| heapBitsShift = 1 // shift offset between successive bitPointer or bitScan entries |
| wordsPerBitmapByte = 8 / 2 // heap words described by one bitmap byte |
| |
| // all scan/pointer bits in a byte |
| bitScanAll = bitScan | bitScan<<heapBitsShift | bitScan<<(2*heapBitsShift) | bitScan<<(3*heapBitsShift) |
| bitPointerAll = bitPointer | bitPointer<<heapBitsShift | bitPointer<<(2*heapBitsShift) | bitPointer<<(3*heapBitsShift) |
| ) |
| |
| // addb returns the byte pointer p+n. |
| //go:nowritebarrier |
| //go:nosplit |
| func addb(p *byte, n uintptr) *byte { |
| // Note: wrote out full expression instead of calling add(p, n) |
| // to reduce the number of temporaries generated by the |
| // compiler for this trivial expression during inlining. |
| return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + n)) |
| } |
| |
| // subtractb returns the byte pointer p-n. |
| //go:nowritebarrier |
| //go:nosplit |
| func subtractb(p *byte, n uintptr) *byte { |
| // Note: wrote out full expression instead of calling add(p, -n) |
| // to reduce the number of temporaries generated by the |
| // compiler for this trivial expression during inlining. |
| return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) - n)) |
| } |
| |
| // add1 returns the byte pointer p+1. |
| //go:nowritebarrier |
| //go:nosplit |
| func add1(p *byte) *byte { |
| // Note: wrote out full expression instead of calling addb(p, 1) |
| // to reduce the number of temporaries generated by the |
| // compiler for this trivial expression during inlining. |
| return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + 1)) |
| } |
| |
| // subtract1 returns the byte pointer p-1. |
| //go:nowritebarrier |
| // |
| // nosplit because it is used during write barriers and must not be preempted. |
| //go:nosplit |
| func subtract1(p *byte) *byte { |
| // Note: wrote out full expression instead of calling subtractb(p, 1) |
| // to reduce the number of temporaries generated by the |
| // compiler for this trivial expression during inlining. |
| return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) - 1)) |
| } |
| |
| // heapBits provides access to the bitmap bits for a single heap word. |
| // The methods on heapBits take value receivers so that the compiler |
| // can more easily inline calls to those methods and registerize the |
| // struct fields independently. |
| type heapBits struct { |
| bitp *uint8 |
| shift uint32 |
| arena uint32 // Index of heap arena containing bitp |
| last *uint8 // Last byte arena's bitmap |
| } |
| |
| // Make the compiler check that heapBits.arena is large enough to hold |
| // the maximum arena frame number. |
| var _ = heapBits{arena: (1<<heapAddrBits)/heapArenaBytes - 1} |
| |
| // markBits provides access to the mark bit for an object in the heap. |
| // bytep points to the byte holding the mark bit. |
| // mask is a byte with a single bit set that can be &ed with *bytep |
| // to see if the bit has been set. |
| // *m.byte&m.mask != 0 indicates the mark bit is set. |
| // index can be used along with span information to generate |
| // the address of the object in the heap. |
| // We maintain one set of mark bits for allocation and one for |
| // marking purposes. |
| type markBits struct { |
| bytep *uint8 |
| mask uint8 |
| index uintptr |
| } |
| |
| //go:nosplit |
| func (s *mspan) allocBitsForIndex(allocBitIndex uintptr) markBits { |
| bytep, mask := s.allocBits.bitp(allocBitIndex) |
| return markBits{bytep, mask, allocBitIndex} |
| } |
| |
| // refillAllocCache takes 8 bytes s.allocBits starting at whichByte |
| // and negates them so that ctz (count trailing zeros) instructions |
| // can be used. It then places these 8 bytes into the cached 64 bit |
| // s.allocCache. |
| func (s *mspan) refillAllocCache(whichByte uintptr) { |
| bytes := (*[8]uint8)(unsafe.Pointer(s.allocBits.bytep(whichByte))) |
| aCache := uint64(0) |
| aCache |= uint64(bytes[0]) |
| aCache |= uint64(bytes[1]) << (1 * 8) |
| aCache |= uint64(bytes[2]) << (2 * 8) |
| aCache |= uint64(bytes[3]) << (3 * 8) |
| aCache |= uint64(bytes[4]) << (4 * 8) |
| aCache |= uint64(bytes[5]) << (5 * 8) |
| aCache |= uint64(bytes[6]) << (6 * 8) |
| aCache |= uint64(bytes[7]) << (7 * 8) |
| s.allocCache = ^aCache |
| } |
| |
| // nextFreeIndex returns the index of the next free object in s at |
| // or after s.freeindex. |
| // There are hardware instructions that can be used to make this |
| // faster if profiling warrants it. |
| func (s *mspan) nextFreeIndex() uintptr { |
| sfreeindex := s.freeindex |
| snelems := s.nelems |
| if sfreeindex == snelems { |
| return sfreeindex |
| } |
| if sfreeindex > snelems { |
| throw("s.freeindex > s.nelems") |
| } |
| |
| aCache := s.allocCache |
| |
| bitIndex := sys.Ctz64(aCache) |
| for bitIndex == 64 { |
| // Move index to start of next cached bits. |
| sfreeindex = (sfreeindex + 64) &^ (64 - 1) |
| if sfreeindex >= snelems { |
| s.freeindex = snelems |
| return snelems |
| } |
| whichByte := sfreeindex / 8 |
| // Refill s.allocCache with the next 64 alloc bits. |
| s.refillAllocCache(whichByte) |
| aCache = s.allocCache |
| bitIndex = sys.Ctz64(aCache) |
| // nothing available in cached bits |
| // grab the next 8 bytes and try again. |
| } |
| result := sfreeindex + uintptr(bitIndex) |
| if result >= snelems { |
| s.freeindex = snelems |
| return snelems |
| } |
| |
| s.allocCache >>= uint(bitIndex + 1) |
| sfreeindex = result + 1 |
| |
| if sfreeindex%64 == 0 && sfreeindex != snelems { |
| // We just incremented s.freeindex so it isn't 0. |
| // As each 1 in s.allocCache was encountered and used for allocation |
| // it was shifted away. At this point s.allocCache contains all 0s. |
| // Refill s.allocCache so that it corresponds |
| // to the bits at s.allocBits starting at s.freeindex. |
| whichByte := sfreeindex / 8 |
| s.refillAllocCache(whichByte) |
| } |
| s.freeindex = sfreeindex |
| return result |
| } |
| |
| // isFree reports whether the index'th object in s is unallocated. |
| // |
| // The caller must ensure s.state is mSpanInUse, and there must have |
| // been no preemption points since ensuring this (which could allow a |
| // GC transition, which would allow the state to change). |
| func (s *mspan) isFree(index uintptr) bool { |
| if index < s.freeindex { |
| return false |
| } |
| bytep, mask := s.allocBits.bitp(index) |
| return *bytep&mask == 0 |
| } |
| |
| func (s *mspan) objIndex(p uintptr) uintptr { |
| byteOffset := p - s.base() |
| if byteOffset == 0 { |
| return 0 |
| } |
| if s.baseMask != 0 { |
| // s.baseMask is non-0, elemsize is a power of two, so shift by s.divShift |
| return byteOffset >> s.divShift |
| } |
| return uintptr(((uint64(byteOffset) >> s.divShift) * uint64(s.divMul)) >> s.divShift2) |
| } |
| |
| func markBitsForAddr(p uintptr) markBits { |
| s := spanOf(p) |
| objIndex := s.objIndex(p) |
| return s.markBitsForIndex(objIndex) |
| } |
| |
| func (s *mspan) markBitsForIndex(objIndex uintptr) markBits { |
| bytep, mask := s.gcmarkBits.bitp(objIndex) |
| return markBits{bytep, mask, objIndex} |
| } |
| |
| func (s *mspan) markBitsForBase() markBits { |
| return markBits{(*uint8)(s.gcmarkBits), uint8(1), 0} |
| } |
| |
| // isMarked reports whether mark bit m is set. |
| func (m markBits) isMarked() bool { |
| return *m.bytep&m.mask != 0 |
| } |
| |
| // setMarked sets the marked bit in the markbits, atomically. |
| func (m markBits) setMarked() { |
| // Might be racing with other updates, so use atomic update always. |
| // We used to be clever here and use a non-atomic update in certain |
| // cases, but it's not worth the risk. |
| atomic.Or8(m.bytep, m.mask) |
| } |
| |
| // setMarkedNonAtomic sets the marked bit in the markbits, non-atomically. |
| func (m markBits) setMarkedNonAtomic() { |
| *m.bytep |= m.mask |
| } |
| |
| // clearMarked clears the marked bit in the markbits, atomically. |
| func (m markBits) clearMarked() { |
| // Might be racing with other updates, so use atomic update always. |
| // We used to be clever here and use a non-atomic update in certain |
| // cases, but it's not worth the risk. |
| atomic.And8(m.bytep, ^m.mask) |
| } |
| |
| // markBitsForSpan returns the markBits for the span base address base. |
| func markBitsForSpan(base uintptr) (mbits markBits) { |
| mbits = markBitsForAddr(base) |
| if mbits.mask != 1 { |
| throw("markBitsForSpan: unaligned start") |
| } |
| return mbits |
| } |
| |
| // advance advances the markBits to the next object in the span. |
| func (m *markBits) advance() { |
| if m.mask == 1<<7 { |
| m.bytep = (*uint8)(unsafe.Pointer(uintptr(unsafe.Pointer(m.bytep)) + 1)) |
| m.mask = 1 |
| } else { |
| m.mask = m.mask << 1 |
| } |
| m.index++ |
| } |
| |
| // heapBitsForAddr returns the heapBits for the address addr. |
| // The caller must ensure addr is in an allocated span. |
| // In particular, be careful not to point past the end of an object. |
| // |
| // nosplit because it is used during write barriers and must not be preempted. |
| //go:nosplit |
| func heapBitsForAddr(addr uintptr) (h heapBits) { |
| // 2 bits per word, 4 pairs per byte, and a mask is hard coded. |
| arena := arenaIndex(addr) |
| ha := mheap_.arenas[arena.l1()][arena.l2()] |
| // The compiler uses a load for nil checking ha, but in this |
| // case we'll almost never hit that cache line again, so it |
| // makes more sense to do a value check. |
| if ha == nil { |
| // addr is not in the heap. Return nil heapBits, which |
| // we expect to crash in the caller. |
| return |
| } |
| h.bitp = &ha.bitmap[(addr/(sys.PtrSize*4))%heapArenaBitmapBytes] |
| h.shift = uint32((addr / sys.PtrSize) & 3) |
| h.arena = uint32(arena) |
| h.last = &ha.bitmap[len(ha.bitmap)-1] |
| return |
| } |
| |
| // badPointer throws bad pointer in heap panic. |
| func badPointer(s *mspan, p, refBase, refOff uintptr) { |
| // Typically this indicates an incorrect use |
| // of unsafe or cgo to store a bad pointer in |
| // the Go heap. It may also indicate a runtime |
| // bug. |
| // |
| // TODO(austin): We could be more aggressive |
| // and detect pointers to unallocated objects |
| // in allocated spans. |
| printlock() |
| print("runtime: pointer ", hex(p)) |
| state := s.state.get() |
| if state != mSpanInUse { |
| print(" to unallocated span") |
| } else { |
| print(" to unused region of span") |
| } |
| print(" span.base()=", hex(s.base()), " span.limit=", hex(s.limit), " span.state=", state, "\n") |
| if refBase != 0 { |
| print("runtime: found in object at *(", hex(refBase), "+", hex(refOff), ")\n") |
| gcDumpObject("object", refBase, refOff) |
| } |
| getg().m.traceback = 2 |
| throw("found bad pointer in Go heap (incorrect use of unsafe or cgo?)") |
| } |
| |
| // findObject returns the base address for the heap object containing |
| // the address p, the object's span, and the index of the object in s. |
| // If p does not point into a heap object, it returns base == 0. |
| // |
| // If p points is an invalid heap pointer and debug.invalidptr != 0, |
| // findObject panics. |
| // |
| // For gccgo, the forStack parameter is true if the value came from the stack. |
| // The stack is collected conservatively and may contain invalid pointers. |
| // |
| // refBase and refOff optionally give the base address of the object |
| // in which the pointer p was found and the byte offset at which it |
| // was found. These are used for error reporting. |
| // |
| // It is nosplit so it is safe for p to be a pointer to the current goroutine's stack. |
| // Since p is a uintptr, it would not be adjusted if the stack were to move. |
| //go:nosplit |
| func findObject(p, refBase, refOff uintptr, forStack bool) (base uintptr, s *mspan, objIndex uintptr) { |
| s = spanOf(p) |
| // If s is nil, the virtual address has never been part of the heap. |
| // This pointer may be to some mmap'd region, so we allow it. |
| if s == nil { |
| return |
| } |
| // If p is a bad pointer, it may not be in s's bounds. |
| // |
| // Check s.state to synchronize with span initialization |
| // before checking other fields. See also spanOfHeap. |
| if state := s.state.get(); state != mSpanInUse || p < s.base() || p >= s.limit { |
| // Pointers into stacks are also ok, the runtime manages these explicitly. |
| if state == mSpanManual || forStack { |
| return |
| } |
| // The following ensures that we are rigorous about what data |
| // structures hold valid pointers. |
| if debug.invalidptr != 0 { |
| badPointer(s, p, refBase, refOff) |
| } |
| return |
| } |
| |
| if forStack { |
| // A span can be entered in mheap_.spans, and be set |
| // to mSpanInUse, before it is fully initialized. |
| // All we need in practice is allocBits and gcmarkBits, |
| // so make sure they are set. |
| if s.allocBits == nil || s.gcmarkBits == nil { |
| return |
| } |
| } |
| |
| // If this span holds object of a power of 2 size, just mask off the bits to |
| // the interior of the object. Otherwise use the size to get the base. |
| if s.baseMask != 0 { |
| // optimize for power of 2 sized objects. |
| base = s.base() |
| base = base + (p-base)&uintptr(s.baseMask) |
| objIndex = (base - s.base()) >> s.divShift |
| // base = p & s.baseMask is faster for small spans, |
| // but doesn't work for large spans. |
| // Overall, it's faster to use the more general computation above. |
| } else { |
| base = s.base() |
| if p-base >= s.elemsize { |
| // n := (p - base) / s.elemsize, using division by multiplication |
| objIndex = uintptr(p-base) >> s.divShift * uintptr(s.divMul) >> s.divShift2 |
| base += objIndex * s.elemsize |
| } |
| } |
| return |
| } |
| |
| // next returns the heapBits describing the next pointer-sized word in memory. |
| // That is, if h describes address p, h.next() describes p+ptrSize. |
| // Note that next does not modify h. The caller must record the result. |
| // |
| // nosplit because it is used during write barriers and must not be preempted. |
| //go:nosplit |
| func (h heapBits) next() heapBits { |
| if h.shift < 3*heapBitsShift { |
| h.shift += heapBitsShift |
| } else if h.bitp != h.last { |
| h.bitp, h.shift = add1(h.bitp), 0 |
| } else { |
| // Move to the next arena. |
| return h.nextArena() |
| } |
| return h |
| } |
| |
| // nextArena advances h to the beginning of the next heap arena. |
| // |
| // This is a slow-path helper to next. gc's inliner knows that |
| // heapBits.next can be inlined even though it calls this. This is |
| // marked noinline so it doesn't get inlined into next and cause next |
| // to be too big to inline. |
| // |
| //go:nosplit |
| //go:noinline |
| func (h heapBits) nextArena() heapBits { |
| h.arena++ |
| ai := arenaIdx(h.arena) |
| l2 := mheap_.arenas[ai.l1()] |
| if l2 == nil { |
| // We just passed the end of the object, which |
| // was also the end of the heap. Poison h. It |
| // should never be dereferenced at this point. |
| return heapBits{} |
| } |
| ha := l2[ai.l2()] |
| if ha == nil { |
| return heapBits{} |
| } |
| h.bitp, h.shift = &ha.bitmap[0], 0 |
| h.last = &ha.bitmap[len(ha.bitmap)-1] |
| return h |
| } |
| |
| // forward returns the heapBits describing n pointer-sized words ahead of h in memory. |
| // That is, if h describes address p, h.forward(n) describes p+n*ptrSize. |
| // h.forward(1) is equivalent to h.next(), just slower. |
| // Note that forward does not modify h. The caller must record the result. |
| // bits returns the heap bits for the current word. |
| //go:nosplit |
| func (h heapBits) forward(n uintptr) heapBits { |
| n += uintptr(h.shift) / heapBitsShift |
| nbitp := uintptr(unsafe.Pointer(h.bitp)) + n/4 |
| h.shift = uint32(n%4) * heapBitsShift |
| if nbitp <= uintptr(unsafe.Pointer(h.last)) { |
| h.bitp = (*uint8)(unsafe.Pointer(nbitp)) |
| return h |
| } |
| |
| // We're in a new heap arena. |
| past := nbitp - (uintptr(unsafe.Pointer(h.last)) + 1) |
| h.arena += 1 + uint32(past/heapArenaBitmapBytes) |
| ai := arenaIdx(h.arena) |
| if l2 := mheap_.arenas[ai.l1()]; l2 != nil && l2[ai.l2()] != nil { |
| a := l2[ai.l2()] |
| h.bitp = &a.bitmap[past%heapArenaBitmapBytes] |
| h.last = &a.bitmap[len(a.bitmap)-1] |
| } else { |
| h.bitp, h.last = nil, nil |
| } |
| return h |
| } |
| |
| // forwardOrBoundary is like forward, but stops at boundaries between |
| // contiguous sections of the bitmap. It returns the number of words |
| // advanced over, which will be <= n. |
| func (h heapBits) forwardOrBoundary(n uintptr) (heapBits, uintptr) { |
| maxn := 4 * ((uintptr(unsafe.Pointer(h.last)) + 1) - uintptr(unsafe.Pointer(h.bitp))) |
| if n > maxn { |
| n = maxn |
| } |
| return h.forward(n), n |
| } |
| |
| // The caller can test morePointers and isPointer by &-ing with bitScan and bitPointer. |
| // The result includes in its higher bits the bits for subsequent words |
| // described by the same bitmap byte. |
| // |
| // nosplit because it is used during write barriers and must not be preempted. |
| //go:nosplit |
| func (h heapBits) bits() uint32 { |
| // The (shift & 31) eliminates a test and conditional branch |
| // from the generated code. |
| return uint32(*h.bitp) >> (h.shift & 31) |
| } |
| |
| // morePointers reports whether this word and all remaining words in this object |
| // are scalars. |
| // h must not describe the second word of the object. |
| func (h heapBits) morePointers() bool { |
| return h.bits()&bitScan != 0 |
| } |
| |
| // isPointer reports whether the heap bits describe a pointer word. |
| // |
| // nosplit because it is used during write barriers and must not be preempted. |
| //go:nosplit |
| func (h heapBits) isPointer() bool { |
| return h.bits()&bitPointer != 0 |
| } |
| |
| // bulkBarrierPreWrite executes a write barrier |
| // for every pointer slot in the memory range [src, src+size), |
| // using pointer/scalar information from [dst, dst+size). |
| // This executes the write barriers necessary before a memmove. |
| // src, dst, and size must be pointer-aligned. |
| // The range [dst, dst+size) must lie within a single object. |
| // It does not perform the actual writes. |
| // |
| // As a special case, src == 0 indicates that this is being used for a |
| // memclr. bulkBarrierPreWrite will pass 0 for the src of each write |
| // barrier. |
| // |
| // Callers should call bulkBarrierPreWrite immediately before |
| // calling memmove(dst, src, size). This function is marked nosplit |
| // to avoid being preempted; the GC must not stop the goroutine |
| // between the memmove and the execution of the barriers. |
| // The caller is also responsible for cgo pointer checks if this |
| // may be writing Go pointers into non-Go memory. |
| // |
| // The pointer bitmap is not maintained for allocations containing |
| // no pointers at all; any caller of bulkBarrierPreWrite must first |
| // make sure the underlying allocation contains pointers, usually |
| // by checking typ.ptrdata. |
| // |
| // Callers must perform cgo checks if writeBarrier.cgo. |
| // |
| //go:nosplit |
| func bulkBarrierPreWrite(dst, src, size uintptr) { |
| if (dst|src|size)&(sys.PtrSize-1) != 0 { |
| throw("bulkBarrierPreWrite: unaligned arguments") |
| } |
| if !writeBarrier.needed { |
| return |
| } |
| if s := spanOf(dst); s == nil { |
| // If dst is a global, use the data or BSS bitmaps to |
| // execute write barriers. |
| lo := 0 |
| hi := len(gcRootsIndex) |
| for lo < hi { |
| m := lo + (hi-lo)/2 |
| pr := gcRootsIndex[m] |
| addr := uintptr(pr.decl) |
| if addr <= dst && dst < addr+pr.size { |
| if dst < addr+pr.ptrdata { |
| bulkBarrierBitmap(dst, src, size, dst-addr, pr.gcdata) |
| } |
| return |
| } |
| if dst < addr { |
| hi = m |
| } else { |
| lo = m + 1 |
| } |
| } |
| return |
| } else if s.state.get() != mSpanInUse || dst < s.base() || s.limit <= dst { |
| // dst was heap memory at some point, but isn't now. |
| // It can't be a global. It must be either our stack, |
| // or in the case of direct channel sends, it could be |
| // another stack. Either way, no need for barriers. |
| // This will also catch if dst is in a freed span, |
| // though that should never have. |
| return |
| } |
| |
| buf := &getg().m.p.ptr().wbBuf |
| h := heapBitsForAddr(dst) |
| if src == 0 { |
| for i := uintptr(0); i < size; i += sys.PtrSize { |
| if h.isPointer() { |
| dstx := (*uintptr)(unsafe.Pointer(dst + i)) |
| if !buf.putFast(*dstx, 0) { |
| wbBufFlush(nil, 0) |
| } |
| } |
| h = h.next() |
| } |
| } else { |
| for i := uintptr(0); i < size; i += sys.PtrSize { |
| if h.isPointer() { |
| dstx := (*uintptr)(unsafe.Pointer(dst + i)) |
| srcx := (*uintptr)(unsafe.Pointer(src + i)) |
| if !buf.putFast(*dstx, *srcx) { |
| wbBufFlush(nil, 0) |
| } |
| } |
| h = h.next() |
| } |
| } |
| } |
| |
| // bulkBarrierPreWriteSrcOnly is like bulkBarrierPreWrite but |
| // does not execute write barriers for [dst, dst+size). |
| // |
| // In addition to the requirements of bulkBarrierPreWrite |
| // callers need to ensure [dst, dst+size) is zeroed. |
| // |
| // This is used for special cases where e.g. dst was just |
| // created and zeroed with malloc. |
| //go:nosplit |
| func bulkBarrierPreWriteSrcOnly(dst, src, size uintptr) { |
| if (dst|src|size)&(sys.PtrSize-1) != 0 { |
| throw("bulkBarrierPreWrite: unaligned arguments") |
| } |
| if !writeBarrier.needed { |
| return |
| } |
| buf := &getg().m.p.ptr().wbBuf |
| h := heapBitsForAddr(dst) |
| for i := uintptr(0); i < size; i += sys.PtrSize { |
| if h.isPointer() { |
| srcx := (*uintptr)(unsafe.Pointer(src + i)) |
| if !buf.putFast(0, *srcx) { |
| wbBufFlush(nil, 0) |
| } |
| } |
| h = h.next() |
| } |
| } |
| |
| // bulkBarrierBitmap executes write barriers for copying from [src, |
| // src+size) to [dst, dst+size) using a 1-bit pointer bitmap. src is |
| // assumed to start maskOffset bytes into the data covered by the |
| // bitmap in bits (which may not be a multiple of 8). |
| // |
| // This is used by bulkBarrierPreWrite for writes to data and BSS. |
| // |
| //go:nosplit |
| func bulkBarrierBitmap(dst, src, size, maskOffset uintptr, bits *uint8) { |
| word := maskOffset / sys.PtrSize |
| bits = addb(bits, word/8) |
| mask := uint8(1) << (word % 8) |
| |
| buf := &getg().m.p.ptr().wbBuf |
| for i := uintptr(0); i < size; i += sys.PtrSize { |
| if mask == 0 { |
| bits = addb(bits, 1) |
| if *bits == 0 { |
| // Skip 8 words. |
| i += 7 * sys.PtrSize |
| continue |
| } |
| mask = 1 |
| } |
| if *bits&mask != 0 { |
| dstx := (*uintptr)(unsafe.Pointer(dst + i)) |
| if src == 0 { |
| if !buf.putFast(*dstx, 0) { |
| wbBufFlush(nil, 0) |
| } |
| } else { |
| srcx := (*uintptr)(unsafe.Pointer(src + i)) |
| if !buf.putFast(*dstx, *srcx) { |
| wbBufFlush(nil, 0) |
| } |
| } |
| } |
| mask <<= 1 |
| } |
| } |
| |
| // typeBitsBulkBarrier executes a write barrier for every |
| // pointer that would be copied from [src, src+size) to [dst, |
| // dst+size) by a memmove using the type bitmap to locate those |
| // pointer slots. |
| // |
| // The type typ must correspond exactly to [src, src+size) and [dst, dst+size). |
| // dst, src, and size must be pointer-aligned. |
| // The type typ must have a plain bitmap, not a GC program. |
| // The only use of this function is in channel sends, and the |
| // 64 kB channel element limit takes care of this for us. |
| // |
| // Must not be preempted because it typically runs right before memmove, |
| // and the GC must observe them as an atomic action. |
| // |
| // Callers must perform cgo checks if writeBarrier.cgo. |
| // |
| //go:nosplit |
| func typeBitsBulkBarrier(typ *_type, dst, src, size uintptr) { |
| if typ == nil { |
| throw("runtime: typeBitsBulkBarrier without type") |
| } |
| if typ.size != size { |
| println("runtime: typeBitsBulkBarrier with type ", typ.string(), " of size ", typ.size, " but memory size", size) |
| throw("runtime: invalid typeBitsBulkBarrier") |
| } |
| if typ.kind&kindGCProg != 0 { |
| println("runtime: typeBitsBulkBarrier with type ", typ.string(), " with GC prog") |
| throw("runtime: invalid typeBitsBulkBarrier") |
| } |
| if !writeBarrier.needed { |
| return |
| } |
| ptrmask := typ.gcdata |
| buf := &getg().m.p.ptr().wbBuf |
| var bits uint32 |
| for i := uintptr(0); i < typ.ptrdata; i += sys.PtrSize { |
| if i&(sys.PtrSize*8-1) == 0 { |
| bits = uint32(*ptrmask) |
| ptrmask = addb(ptrmask, 1) |
| } else { |
| bits = bits >> 1 |
| } |
| if bits&1 != 0 { |
| dstx := (*uintptr)(unsafe.Pointer(dst + i)) |
| srcx := (*uintptr)(unsafe.Pointer(src + i)) |
| if !buf.putFast(*dstx, *srcx) { |
| wbBufFlush(nil, 0) |
| } |
| } |
| } |
| } |
| |
| // The methods operating on spans all require that h has been returned |
| // by heapBitsForSpan and that size, n, total are the span layout description |
| // returned by the mspan's layout method. |
| // If total > size*n, it means that there is extra leftover memory in the span, |
| // usually due to rounding. |
| // |
| // TODO(rsc): Perhaps introduce a different heapBitsSpan type. |
| |
| // initSpan initializes the heap bitmap for a span. |
| // If this is a span of pointer-sized objects, it initializes all |
| // words to pointer/scan. |
| // Otherwise, it initializes all words to scalar/dead. |
| func (h heapBits) initSpan(s *mspan) { |
| // Clear bits corresponding to objects. |
| nw := (s.npages << _PageShift) / sys.PtrSize |
| if nw%wordsPerBitmapByte != 0 { |
| throw("initSpan: unaligned length") |
| } |
| if h.shift != 0 { |
| throw("initSpan: unaligned base") |
| } |
| isPtrs := sys.PtrSize == 8 && s.elemsize == sys.PtrSize |
| for nw > 0 { |
| hNext, anw := h.forwardOrBoundary(nw) |
| nbyte := anw / wordsPerBitmapByte |
| if isPtrs { |
| bitp := h.bitp |
| for i := uintptr(0); i < nbyte; i++ { |
| *bitp = bitPointerAll | bitScanAll |
| bitp = add1(bitp) |
| } |
| } else { |
| memclrNoHeapPointers(unsafe.Pointer(h.bitp), nbyte) |
| } |
| h = hNext |
| nw -= anw |
| } |
| } |
| |
| // countAlloc returns the number of objects allocated in span s by |
| // scanning the allocation bitmap. |
| func (s *mspan) countAlloc() int { |
| count := 0 |
| bytes := divRoundUp(s.nelems, 8) |
| // Iterate over each 8-byte chunk and count allocations |
| // with an intrinsic. Note that newMarkBits guarantees that |
| // gcmarkBits will be 8-byte aligned, so we don't have to |
| // worry about edge cases, irrelevant bits will simply be zero. |
| for i := uintptr(0); i < bytes; i += 8 { |
| // Extract 64 bits from the byte pointer and get a OnesCount. |
| // Note that the unsafe cast here doesn't preserve endianness, |
| // but that's OK. We only care about how many bits are 1, not |
| // about the order we discover them in. |
| mrkBits := *(*uint64)(unsafe.Pointer(s.gcmarkBits.bytep(i))) |
| count += sys.OnesCount64(mrkBits) |
| } |
| return count |
| } |
| |
| // heapBitsSetType records that the new allocation [x, x+size) |
| // holds in [x, x+dataSize) one or more values of type typ. |
| // (The number of values is given by dataSize / typ.size.) |
| // If dataSize < size, the fragment [x+dataSize, x+size) is |
| // recorded as non-pointer data. |
| // It is known that the type has pointers somewhere; |
| // malloc does not call heapBitsSetType when there are no pointers, |
| // because all free objects are marked as noscan during |
| // heapBitsSweepSpan. |
| // |
| // There can only be one allocation from a given span active at a time, |
| // and the bitmap for a span always falls on byte boundaries, |
| // so there are no write-write races for access to the heap bitmap. |
| // Hence, heapBitsSetType can access the bitmap without atomics. |
| // |
| // There can be read-write races between heapBitsSetType and things |
| // that read the heap bitmap like scanobject. However, since |
| // heapBitsSetType is only used for objects that have not yet been |
| // made reachable, readers will ignore bits being modified by this |
| // function. This does mean this function cannot transiently modify |
| // bits that belong to neighboring objects. Also, on weakly-ordered |
| // machines, callers must execute a store/store (publication) barrier |
| // between calling this function and making the object reachable. |
| func heapBitsSetType(x, size, dataSize uintptr, typ *_type) { |
| const doubleCheck = false // slow but helpful; enable to test modifications to this code |
| |
| const ( |
| mask1 = bitPointer | bitScan // 00010001 |
| mask2 = bitPointer | bitScan | mask1<<heapBitsShift // 00110011 |
| mask3 = bitPointer | bitScan | mask2<<heapBitsShift // 01110111 |
| ) |
| |
| // dataSize is always size rounded up to the next malloc size class, |
| // except in the case of allocating a defer block, in which case |
| // size is sizeof(_defer{}) (at least 6 words) and dataSize may be |
| // arbitrarily larger. |
| // |
| // The checks for size == sys.PtrSize and size == 2*sys.PtrSize can therefore |
| // assume that dataSize == size without checking it explicitly. |
| |
| if sys.PtrSize == 8 && size == sys.PtrSize { |
| // It's one word and it has pointers, it must be a pointer. |
| // Since all allocated one-word objects are pointers |
| // (non-pointers are aggregated into tinySize allocations), |
| // initSpan sets the pointer bits for us. Nothing to do here. |
| if doubleCheck { |
| h := heapBitsForAddr(x) |
| if !h.isPointer() { |
| throw("heapBitsSetType: pointer bit missing") |
| } |
| if !h.morePointers() { |
| throw("heapBitsSetType: scan bit missing") |
| } |
| } |
| return |
| } |
| |
| h := heapBitsForAddr(x) |
| ptrmask := typ.gcdata // start of 1-bit pointer mask (or GC program, handled below) |
| |
| // 2-word objects only have 4 bitmap bits and 3-word objects only have 6 bitmap bits. |
| // Therefore, these objects share a heap bitmap byte with the objects next to them. |
| // These are called out as a special case primarily so the code below can assume all |
| // objects are at least 4 words long and that their bitmaps start either at the beginning |
| // of a bitmap byte, or half-way in (h.shift of 0 and 2 respectively). |
| |
| if size == 2*sys.PtrSize { |
| if typ.size == sys.PtrSize { |
| // We're allocating a block big enough to hold two pointers. |
| // On 64-bit, that means the actual object must be two pointers, |
| // or else we'd have used the one-pointer-sized block. |
| // On 32-bit, however, this is the 8-byte block, the smallest one. |
| // So it could be that we're allocating one pointer and this was |
| // just the smallest block available. Distinguish by checking dataSize. |
| // (In general the number of instances of typ being allocated is |
| // dataSize/typ.size.) |
| if sys.PtrSize == 4 && dataSize == sys.PtrSize { |
| // 1 pointer object. On 32-bit machines clear the bit for the |
| // unused second word. |
| *h.bitp &^= (bitPointer | bitScan | (bitPointer|bitScan)<<heapBitsShift) << h.shift |
| *h.bitp |= (bitPointer | bitScan) << h.shift |
| } else { |
| // 2-element array of pointer. |
| *h.bitp |= (bitPointer | bitScan | (bitPointer|bitScan)<<heapBitsShift) << h.shift |
| } |
| return |
| } |
| // Otherwise typ.size must be 2*sys.PtrSize, |
| // and typ.kind&kindGCProg == 0. |
| if doubleCheck { |
| if typ.size != 2*sys.PtrSize || typ.kind&kindGCProg != 0 { |
| print("runtime: heapBitsSetType size=", size, " but typ.size=", typ.size, " gcprog=", typ.kind&kindGCProg != 0, "\n") |
| throw("heapBitsSetType") |
| } |
| } |
| b := uint32(*ptrmask) |
| hb := b & 3 |
| hb |= bitScanAll & ((bitScan << (typ.ptrdata / sys.PtrSize)) - 1) |
| // Clear the bits for this object so we can set the |
| // appropriate ones. |
| *h.bitp &^= (bitPointer | bitScan | ((bitPointer | bitScan) << heapBitsShift)) << h.shift |
| *h.bitp |= uint8(hb << h.shift) |
| return |
| } else if size == 3*sys.PtrSize { |
| b := uint8(*ptrmask) |
| if doubleCheck { |
| if b == 0 { |
| println("runtime: invalid type ", typ.string()) |
| throw("heapBitsSetType: called with non-pointer type") |
| } |
| if sys.PtrSize != 8 { |
| throw("heapBitsSetType: unexpected 3 pointer wide size class on 32 bit") |
| } |
| if typ.kind&kindGCProg != 0 { |
| throw("heapBitsSetType: unexpected GC prog for 3 pointer wide size class") |
| } |
| if typ.size == 2*sys.PtrSize { |
| print("runtime: heapBitsSetType size=", size, " but typ.size=", typ.size, "\n") |
| throw("heapBitsSetType: inconsistent object sizes") |
| } |
| } |
| if typ.size == sys.PtrSize { |
| // The type contains a pointer otherwise heapBitsSetType wouldn't have been called. |
| // Since the type is only 1 pointer wide and contains a pointer, its gcdata must be exactly 1. |
| if doubleCheck && *typ.gcdata != 1 { |
| print("runtime: heapBitsSetType size=", size, " typ.size=", typ.size, "but *typ.gcdata", *typ.gcdata, "\n") |
| throw("heapBitsSetType: unexpected gcdata for 1 pointer wide type size in 3 pointer wide size class") |
| } |
| // 3 element array of pointers. Unrolling ptrmask 3 times into p yields 00000111. |
| b = 7 |
| } |
| |
| hb := b & 7 |
| // Set bitScan bits for all pointers. |
| hb |= hb << wordsPerBitmapByte |
| // First bitScan bit is always set since the type contains pointers. |
| hb |= bitScan |
| // Second bitScan bit needs to also be set if the third bitScan bit is set. |
| hb |= hb & (bitScan << (2 * heapBitsShift)) >> 1 |
| |
| // For h.shift > 1 heap bits cross a byte boundary and need to be written part |
| // to h.bitp and part to the next h.bitp. |
| switch h.shift { |
| case 0: |
| *h.bitp &^= mask3 << 0 |
| *h.bitp |= hb << 0 |
| case 1: |
| *h.bitp &^= mask3 << 1 |
| *h.bitp |= hb << 1 |
| case 2: |
| *h.bitp &^= mask2 << 2 |
| *h.bitp |= (hb & mask2) << 2 |
| // Two words written to the first byte. |
| // Advance two words to get to the next byte. |
| h = h.next().next() |
| *h.bitp &^= mask1 |
| *h.bitp |= (hb >> 2) & mask1 |
| case 3: |
| *h.bitp &^= mask1 << 3 |
| *h.bitp |= (hb & mask1) << 3 |
| // One word written to the first byte. |
| // Advance one word to get to the next byte. |
| h = h.next() |
| *h.bitp &^= mask2 |
| *h.bitp |= (hb >> 1) & mask2 |
| } |
| return |
| } |
| |
| // Copy from 1-bit ptrmask into 2-bit bitmap. |
| // The basic approach is to use a single uintptr as a bit buffer, |
| // alternating between reloading the buffer and writing bitmap bytes. |
| // In general, one load can supply two bitmap byte writes. |
| // This is a lot of lines of code, but it compiles into relatively few |
| // machine instructions. |
| |
| outOfPlace := false |
| if arenaIndex(x+size-1) != arenaIdx(h.arena) || (doubleCheck && fastrand()%2 == 0) { |
| // This object spans heap arenas, so the bitmap may be |
| // discontiguous. Unroll it into the object instead |
| // and then copy it out. |
| // |
| // In doubleCheck mode, we randomly do this anyway to |
| // stress test the bitmap copying path. |
| outOfPlace = true |
| h.bitp = (*uint8)(unsafe.Pointer(x)) |
| h.last = nil |
| } |
| |
| var ( |
| // Ptrmask input. |
| p *byte // last ptrmask byte read |
| b uintptr // ptrmask bits already loaded |
| nb uintptr // number of bits in b at next read |
| endp *byte // final ptrmask byte to read (then repeat) |
| endnb uintptr // number of valid bits in *endp |
| pbits uintptr // alternate source of bits |
| |
| // Heap bitmap output. |
| w uintptr // words processed |
| nw uintptr // number of words to process |
| hbitp *byte // next heap bitmap byte to write |
| hb uintptr // bits being prepared for *hbitp |
| ) |
| |
| hbitp = h.bitp |
| |
| // Handle GC program. Delayed until this part of the code |
| // so that we can use the same double-checking mechanism |
| // as the 1-bit case. Nothing above could have encountered |
| // GC programs: the cases were all too small. |
| if typ.kind&kindGCProg != 0 { |
| heapBitsSetTypeGCProg(h, typ.ptrdata, typ.size, dataSize, size, addb(typ.gcdata, 4)) |
| if doubleCheck { |
| // Double-check the heap bits written by GC program |
| // by running the GC program to create a 1-bit pointer mask |
| // and then jumping to the double-check code below. |
| // This doesn't catch bugs shared between the 1-bit and 4-bit |
| // GC program execution, but it does catch mistakes specific |
| // to just one of those and bugs in heapBitsSetTypeGCProg's |
| // implementation of arrays. |
| lock(&debugPtrmask.lock) |
| if debugPtrmask.data == nil { |
| debugPtrmask.data = (*byte)(persistentalloc(1<<20, 1, &memstats.other_sys)) |
| } |
| ptrmask = debugPtrmask.data |
| runGCProg(addb(typ.gcdata, 4), nil, ptrmask, 1) |
| } |
| goto Phase4 |
| } |
| |
| // Note about sizes: |
| // |
| // typ.size is the number of words in the object, |
| // and typ.ptrdata is the number of words in the prefix |
| // of the object that contains pointers. That is, the final |
| // typ.size - typ.ptrdata words contain no pointers. |
| // This allows optimization of a common pattern where |
| // an object has a small header followed by a large scalar |
| // buffer. If we know the pointers are over, we don't have |
| // to scan the buffer's heap bitmap at all. |
| // The 1-bit ptrmasks are sized to contain only bits for |
| // the typ.ptrdata prefix, zero padded out to a full byte |
| // of bitmap. This code sets nw (below) so that heap bitmap |
| // bits are only written for the typ.ptrdata prefix; if there is |
| // more room in the allocated object, the next heap bitmap |
| // entry is a 00, indicating that there are no more pointers |
| // to scan. So only the ptrmask for the ptrdata bytes is needed. |
| // |
| // Replicated copies are not as nice: if there is an array of |
| // objects with scalar tails, all but the last tail does have to |
| // be initialized, because there is no way to say "skip forward". |
| // However, because of the possibility of a repeated type with |
| // size not a multiple of 4 pointers (one heap bitmap byte), |
| // the code already must handle the last ptrmask byte specially |
| // by treating it as containing only the bits for endnb pointers, |
| // where endnb <= 4. We represent large scalar tails that must |
| // be expanded in the replication by setting endnb larger than 4. |
| // This will have the effect of reading many bits out of b, |
| // but once the real bits are shifted out, b will supply as many |
| // zero bits as we try to read, which is exactly what we need. |
| |
| p = ptrmask |
| if typ.size < dataSize { |
| // Filling in bits for an array of typ. |
| // Set up for repetition of ptrmask during main loop. |
| // Note that ptrmask describes only a prefix of |
| const maxBits = sys.PtrSize*8 - 7 |
| if typ.ptrdata/sys.PtrSize <= maxBits { |
| // Entire ptrmask fits in uintptr with room for a byte fragment. |
| // Load into pbits and never read from ptrmask again. |
| // This is especially important when the ptrmask has |
| // fewer than 8 bits in it; otherwise the reload in the middle |
| // of the Phase 2 loop would itself need to loop to gather |
| // at least 8 bits. |
| |
| // Accumulate ptrmask into b. |
| // ptrmask is sized to describe only typ.ptrdata, but we record |
| // it as describing typ.size bytes, since all the high bits are zero. |
| nb = typ.ptrdata / sys.PtrSize |
| for i := uintptr(0); i < nb; i += 8 { |
| b |= uintptr(*p) << i |
| p = add1(p) |
| } |
| nb = typ.size / sys.PtrSize |
| |
| // Replicate ptrmask to fill entire pbits uintptr. |
| // Doubling and truncating is fewer steps than |
| // iterating by nb each time. (nb could be 1.) |
| // Since we loaded typ.ptrdata/sys.PtrSize bits |
| // but are pretending to have typ.size/sys.PtrSize, |
| // there might be no replication necessary/possible. |
| pbits = b |
| endnb = nb |
| if nb+nb <= maxBits { |
| for endnb <= sys.PtrSize*8 { |
| pbits |= pbits << endnb |
| endnb += endnb |
| } |
| // Truncate to a multiple of original ptrmask. |
| // Because nb+nb <= maxBits, nb fits in a byte. |
| // Byte division is cheaper than uintptr division. |
| endnb = uintptr(maxBits/byte(nb)) * nb |
| pbits &= 1<<endnb - 1 |
| b = pbits |
| nb = endnb |
| } |
| |
| // Clear p and endp as sentinel for using pbits. |
| // Checked during Phase 2 loop. |
| p = nil |
| endp = nil |
| } else { |
| // Ptrmask is larger. Read it multiple times. |
| n := (typ.ptrdata/sys.PtrSize+7)/8 - 1 |
| endp = addb(ptrmask, n) |
| endnb = typ.size/sys.PtrSize - n*8 |
| } |
| } |
| if p != nil { |
| b = uintptr(*p) |
| p = add1(p) |
| nb = 8 |
| } |
| |
| if typ.size == dataSize { |
| // Single entry: can stop once we reach the non-pointer data. |
| nw = typ.ptrdata / sys.PtrSize |
| } else { |
| // Repeated instances of typ in an array. |
| // Have to process first N-1 entries in full, but can stop |
| // once we reach the non-pointer data in the final entry. |
| nw = ((dataSize/typ.size-1)*typ.size + typ.ptrdata) / sys.PtrSize |
| } |
| if nw == 0 { |
| // No pointers! Caller was supposed to check. |
| println("runtime: invalid type ", typ.string()) |
| throw("heapBitsSetType: called with non-pointer type") |
| return |
| } |
| |
| // Phase 1: Special case for leading byte (shift==0) or half-byte (shift==2). |
| // The leading byte is special because it contains the bits for word 1, |
| // which does not have the scan bit set. |
| // The leading half-byte is special because it's a half a byte, |
| // so we have to be careful with the bits already there. |
| switch { |
| default: |
| throw("heapBitsSetType: unexpected shift") |
| |
| case h.shift == 0: |
| // Ptrmask and heap bitmap are aligned. |
| // |
| // This is a fast path for small objects. |
| // |
| // The first byte we write out covers the first four |
| // words of the object. The scan/dead bit on the first |
| // word must be set to scan since there are pointers |
| // somewhere in the object. |
| // In all following words, we set the scan/dead |
| // appropriately to indicate that the object continues |
| // to the next 2-bit entry in the bitmap. |
| // |
| // We set four bits at a time here, but if the object |
| // is fewer than four words, phase 3 will clear |
| // unnecessary bits. |
| hb = b & bitPointerAll |
| hb |= bitScanAll |
| if w += 4; w >= nw { |
| goto Phase3 |
| } |
| *hbitp = uint8(hb) |
| hbitp = add1(hbitp) |
| b >>= 4 |
| nb -= 4 |
| |
| case h.shift == 2: |
| // Ptrmask and heap bitmap are misaligned. |
| // |
| // On 32 bit architectures only the 6-word object that corresponds |
| // to a 24 bytes size class can start with h.shift of 2 here since |
| // all other non 16 byte aligned size classes have been handled by |
| // special code paths at the beginning of heapBitsSetType on 32 bit. |
| // |
| // Many size classes are only 16 byte aligned. On 64 bit architectures |
| // this results in a heap bitmap position starting with a h.shift of 2. |
| // |
| // The bits for the first two words are in a byte shared |
| // with another object, so we must be careful with the bits |
| // already there. |
| // |
| // We took care of 1-word, 2-word, and 3-word objects above, |
| // so this is at least a 6-word object. |
| hb = (b & (bitPointer | bitPointer<<heapBitsShift)) << (2 * heapBitsShift) |
| hb |= bitScan << (2 * heapBitsShift) |
| if nw > 1 { |
| hb |= bitScan << (3 * heapBitsShift) |
| } |
| b >>= 2 |
| nb -= 2 |
| *hbitp &^= uint8((bitPointer | bitScan | ((bitPointer | bitScan) << heapBitsShift)) << (2 * heapBitsShift)) |
| *hbitp |= uint8(hb) |
| hbitp = add1(hbitp) |
| if w += 2; w >= nw { |
| // We know that there is more data, because we handled 2-word and 3-word objects above. |
| // This must be at least a 6-word object. If we're out of pointer words, |
| // mark no scan in next bitmap byte and finish. |
| hb = 0 |
| w += 4 |
| goto Phase3 |
| } |
| } |
| |
| // Phase 2: Full bytes in bitmap, up to but not including write to last byte (full or partial) in bitmap. |
| // The loop computes the bits for that last write but does not execute the write; |
| // it leaves the bits in hb for processing by phase 3. |
| // To avoid repeated adjustment of nb, we subtract out the 4 bits we're going to |
| // use in the first half of the loop right now, and then we only adjust nb explicitly |
| // if the 8 bits used by each iteration isn't balanced by 8 bits loaded mid-loop. |
| nb -= 4 |
| for { |
| // Emit bitmap byte. |
| // b has at least nb+4 bits, with one exception: |
| // if w+4 >= nw, then b has only nw-w bits, |
| // but we'll stop at the break and then truncate |
| // appropriately in Phase 3. |
| hb = b & bitPointerAll |
| hb |= bitScanAll |
| if w += 4; w >= nw { |
| break |
| } |
| *hbitp = uint8(hb) |
| hbitp = add1(hbitp) |
| b >>= 4 |
| |
| // Load more bits. b has nb right now. |
| if p != endp { |
| // Fast path: keep reading from ptrmask. |
| // nb unmodified: we just loaded 8 bits, |
| // and the next iteration will consume 8 bits, |
| // leaving us with the same nb the next time we're here. |
| if nb < 8 { |
| b |= uintptr(*p) << nb |
| p = add1(p) |
| } else { |
| // Reduce the number of bits in b. |
| // This is important if we skipped |
| // over a scalar tail, since nb could |
| // be larger than the bit width of b. |
| nb -= 8 |
| } |
| } else if p == nil { |
| // Almost as fast path: track bit count and refill from pbits. |
| // For short repetitions. |
| if nb < 8 { |
| b |= pbits << nb |
| nb += endnb |
| } |
| nb -= 8 // for next iteration |
| } else { |
| // Slow path: reached end of ptrmask. |
| // Process final partial byte and rewind to start. |
| b |= uintptr(*p) << nb |
| nb += endnb |
| if nb < 8 { |
| b |= uintptr(*ptrmask) << nb |
| p = add1(ptrmask) |
| } else { |
| nb -= 8 |
| p = ptrmask |
| } |
| } |
| |
| // Emit bitmap byte. |
| hb = b & bitPointerAll |
| hb |= bitScanAll |
| if w += 4; w >= nw { |
| break |
| } |
| *hbitp = uint8(hb) |
| hbitp = add1(hbitp) |
| b >>= 4 |
| } |
| |
| Phase3: |
| // Phase 3: Write last byte or partial byte and zero the rest of the bitmap entries. |
| if w > nw { |
| // Counting the 4 entries in hb not yet written to memory, |
| // there are more entries than possible pointer slots. |
| // Discard the excess entries (can't be more than 3). |
| mask := uintptr(1)<<(4-(w-nw)) - 1 |
| hb &= mask | mask<<4 // apply mask to both pointer bits and scan bits |
| } |
| |
| // Change nw from counting possibly-pointer words to total words in allocation. |
| nw = size / sys.PtrSize |
| |
| // Write whole bitmap bytes. |
| // The first is hb, the rest are zero. |
| if w <= nw { |
| *hbitp = uint8(hb) |
| hbitp = add1(hbitp) |
| hb = 0 // for possible final half-byte below |
| for w += 4; w <= nw; w += 4 { |
| *hbitp = 0 |
| hbitp = add1(hbitp) |
| } |
| } |
| |
| // Write final partial bitmap byte if any. |
| // We know w > nw, or else we'd still be in the loop above. |
| // It can be bigger only due to the 4 entries in hb that it counts. |
| // If w == nw+4 then there's nothing left to do: we wrote all nw entries |
| // and can discard the 4 sitting in hb. |
| // But if w == nw+2, we need to write first two in hb. |
| // The byte is shared with the next object, so be careful with |
| // existing bits. |
| if w == nw+2 { |
| *hbitp = *hbitp&^(bitPointer|bitScan|(bitPointer|bitScan)<<heapBitsShift) | uint8(hb) |
| } |
| |
| Phase4: |
| // Phase 4: Copy unrolled bitmap to per-arena bitmaps, if necessary. |
| if outOfPlace { |
| // TODO: We could probably make this faster by |
| // handling [x+dataSize, x+size) specially. |
| h := heapBitsForAddr(x) |
| // cnw is the number of heap words, or bit pairs |
| // remaining (like nw above). |
| cnw := size / sys.PtrSize |
| src := (*uint8)(unsafe.Pointer(x)) |
| // We know the first and last byte of the bitmap are |
| // not the same, but it's still possible for small |
| // objects span arenas, so it may share bitmap bytes |
| // with neighboring objects. |
| // |
| // Handle the first byte specially if it's shared. See |
| // Phase 1 for why this is the only special case we need. |
| if doubleCheck { |
| if !(h.shift == 0 || h.shift == 2) { |
| print("x=", x, " size=", size, " cnw=", h.shift, "\n") |
| throw("bad start shift") |
| } |
| } |
| if h.shift == 2 { |
| *h.bitp = *h.bitp&^((bitPointer|bitScan|(bitPointer|bitScan)<<heapBitsShift)<<(2*heapBitsShift)) | *src |
| h = h.next().next() |
| cnw -= 2 |
| src = addb(src, 1) |
| } |
| // We're now byte aligned. Copy out to per-arena |
| // bitmaps until the last byte (which may again be |
| // partial). |
| for cnw >= 4 { |
| // This loop processes four words at a time, |
| // so round cnw down accordingly. |
| hNext, words := h.forwardOrBoundary(cnw / 4 * 4) |
| |
| // n is the number of bitmap bytes to copy. |
| n := words / 4 |
| memmove(unsafe.Pointer(h.bitp), unsafe.Pointer(src), n) |
| cnw -= words |
| h = hNext |
| src = addb(src, n) |
| } |
| if doubleCheck && h.shift != 0 { |
| print("cnw=", cnw, " h.shift=", h.shift, "\n") |
| throw("bad shift after block copy") |
| } |
| // Handle the last byte if it's shared. |
| if cnw == 2 { |
| *h.bitp = *h.bitp&^(bitPointer|bitScan|(bitPointer|bitScan)<<heapBitsShift) | *src |
| src = addb(src, 1) |
| h = h.next().next() |
| } |
| if doubleCheck { |
| if uintptr(unsafe.Pointer(src)) > x+size { |
| throw("copy exceeded object size") |
| } |
| if !(cnw == 0 || cnw == 2) { |
| print("x=", x, " size=", size, " cnw=", cnw, "\n") |
| throw("bad number of remaining words") |
| } |
| // Set up hbitp so doubleCheck code below can check it. |
| hbitp = h.bitp |
| } |
| // Zero the object where we wrote the bitmap. |
| memclrNoHeapPointers(unsafe.Pointer(x), uintptr(unsafe.Pointer(src))-x) |
| } |
| |
| // Double check the whole bitmap. |
| if doubleCheck { |
| // x+size may not point to the heap, so back up one |
| // word and then advance it the way we do above. |
| end := heapBitsForAddr(x + size - sys.PtrSize) |
| if outOfPlace { |
| // In out-of-place copying, we just advance |
| // using next. |
| end = end.next() |
| } else { |
| // Don't use next because that may advance to |
| // the next arena and the in-place logic |
| // doesn't do that. |
| end.shift += heapBitsShift |
| if end.shift == 4*heapBitsShift { |
| end.bitp, end.shift = add1(end.bitp), 0 |
| } |
| } |
| if typ.kind&kindGCProg == 0 && (hbitp != end.bitp || (w == nw+2) != (end.shift == 2)) { |
| println("ended at wrong bitmap byte for", typ.string(), "x", dataSize/typ.size) |
| print("typ.size=", typ.size, " typ.ptrdata=", typ.ptrdata, " dataSize=", dataSize, " size=", size, "\n") |
| print("w=", w, " nw=", nw, " b=", hex(b), " nb=", nb, " hb=", hex(hb), "\n") |
| h0 := heapBitsForAddr(x) |
| print("initial bits h0.bitp=", h0.bitp, " h0.shift=", h0.shift, "\n") |
| print("ended at hbitp=", hbitp, " but next starts at bitp=", end.bitp, " shift=", end.shift, "\n") |
| throw("bad heapBitsSetType") |
| } |
| |
| // Double-check that bits to be written were written correctly. |
| // Does not check that other bits were not written, unfortunately. |
| h := heapBitsForAddr(x) |
| nptr := typ.ptrdata / sys.PtrSize |
| ndata := typ.size / sys.PtrSize |
| count := dataSize / typ.size |
| totalptr := ((count-1)*typ.size + typ.ptrdata) / sys.PtrSize |
| for i := uintptr(0); i < size/sys.PtrSize; i++ { |
| j := i % ndata |
| var have, want uint8 |
| have = (*h.bitp >> h.shift) & (bitPointer | bitScan) |
| if i >= totalptr { |
| if typ.kind&kindGCProg != 0 && i < (totalptr+3)/4*4 { |
| // heapBitsSetTypeGCProg always fills |
| // in full nibbles of bitScan. |
| want = bitScan |
| } |
| } else { |
| if j < nptr && (*addb(ptrmask, j/8)>>(j%8))&1 != 0 { |
| want |= bitPointer |
| } |
| want |= bitScan |
| } |
| if have != want { |
| println("mismatch writing bits for", typ.string(), "x", dataSize/typ.size) |
| print("typ.size=", typ.size, " typ.ptrdata=", typ.ptrdata, " dataSize=", dataSize, " size=", size, "\n") |
| print("kindGCProg=", typ.kind&kindGCProg != 0, " outOfPlace=", outOfPlace, "\n") |
| print("w=", w, " nw=", nw, " b=", hex(b), " nb=", nb, " hb=", hex(hb), "\n") |
| h0 := heapBitsForAddr(x) |
| print("initial bits h0.bitp=", h0.bitp, " h0.shift=", h0.shift, "\n") |
| print("current bits h.bitp=", h.bitp, " h.shift=", h.shift, " *h.bitp=", hex(*h.bitp), "\n") |
| print("ptrmask=", ptrmask, " p=", p, " endp=", endp, " endnb=", endnb, " pbits=", hex(pbits), " b=", hex(b), " nb=", nb, "\n") |
| println("at word", i, "offset", i*sys.PtrSize, "have", hex(have), "want", hex(want)) |
| if typ.kind&kindGCProg != 0 { |
| println("GC program:") |
| dumpGCProg(addb(typ.gcdata, 4)) |
| } |
| throw("bad heapBitsSetType") |
| } |
| h = h.next() |
| } |
| if ptrmask == debugPtrmask.data { |
| unlock(&debugPtrmask.lock) |
| } |
| } |
| } |
| |
| var debugPtrmask struct { |
| lock mutex |
| data *byte |
| } |
| |
| // heapBitsSetTypeGCProg implements heapBitsSetType using a GC program. |
| // progSize is the size of the memory described by the program. |
| // elemSize is the size of the element that the GC program describes (a prefix of). |
| // dataSize is the total size of the intended data, a multiple of elemSize. |
| // allocSize is the total size of the allocated memory. |
| // |
| // GC programs are only used for large allocations. |
| // heapBitsSetType requires that allocSize is a multiple of 4 words, |
| // so that the relevant bitmap bytes are not shared with surrounding |
| // objects. |
| func heapBitsSetTypeGCProg(h heapBits, progSize, elemSize, dataSize, allocSize uintptr, prog *byte) { |
| if sys.PtrSize == 8 && allocSize%(4*sys.PtrSize) != 0 { |
| // Alignment will be wrong. |
| throw("heapBitsSetTypeGCProg: small allocation") |
| } |
| var totalBits uintptr |
| if elemSize == dataSize { |
| totalBits = runGCProg(prog, nil, h.bitp, 2) |
| if totalBits*sys.PtrSize != progSize { |
| println("runtime: heapBitsSetTypeGCProg: total bits", totalBits, "but progSize", progSize) |
| throw("heapBitsSetTypeGCProg: unexpected bit count") |
| } |
| } else { |
| count := dataSize / elemSize |
| |
| // Piece together program trailer to run after prog that does: |
| // literal(0) |
| // repeat(1, elemSize-progSize-1) // zeros to fill element size |
| // repeat(elemSize, count-1) // repeat that element for count |
| // This zero-pads the data remaining in the first element and then |
| // repeats that first element to fill the array. |
| var trailer [40]byte // 3 varints (max 10 each) + some bytes |
| i := 0 |
| if n := elemSize/sys.PtrSize - progSize/sys.PtrSize; n > 0 { |
| // literal(0) |
| trailer[i] = 0x01 |
| i++ |
| trailer[i] = 0 |
| i++ |
| if n > 1 { |
| // repeat(1, n-1) |
| trailer[i] = 0x81 |
| i++ |
| n-- |
| for ; n >= 0x80; n >>= 7 { |
| trailer[i] = byte(n | 0x80) |
| i++ |
| } |
| trailer[i] = byte(n) |
| i++ |
| } |
| } |
| // repeat(elemSize/ptrSize, count-1) |
| trailer[i] = 0x80 |
| i++ |
| n := elemSize / sys.PtrSize |
| for ; n >= 0x80; n >>= 7 { |
| trailer[i] = byte(n | 0x80) |
| i++ |
| } |
| trailer[i] = byte(n) |
| i++ |
| n = count - 1 |
| for ; n >= 0x80; n >>= 7 { |
| trailer[i] = byte(n | 0x80) |
| i++ |
| } |
| trailer[i] = byte(n) |
| i++ |
| trailer[i] = 0 |
| i++ |
| |
| runGCProg(prog, &trailer[0], h.bitp, 2) |
| |
| // Even though we filled in the full array just now, |
| // record that we only filled in up to the ptrdata of the |
| // last element. This will cause the code below to |
| // memclr the dead section of the final array element, |
| // so that scanobject can stop early in the final element. |
| totalBits = (elemSize*(count-1) + progSize) / sys.PtrSize |
| } |
| endProg := unsafe.Pointer(addb(h.bitp, (totalBits+3)/4)) |
| endAlloc := unsafe.Pointer(addb(h.bitp, allocSize/sys.PtrSize/wordsPerBitmapByte)) |
| memclrNoHeapPointers(endProg, uintptr(endAlloc)-uintptr(endProg)) |
| } |
| |
| // progToPointerMask returns the 1-bit pointer mask output by the GC program prog. |
| // size the size of the region described by prog, in bytes. |
| // The resulting bitvector will have no more than size/sys.PtrSize bits. |
| func progToPointerMask(prog *byte, size uintptr) bitvector { |
| n := (size/sys.PtrSize + 7) / 8 |
| x := (*[1 << 30]byte)(persistentalloc(n+1, 1, &memstats.buckhash_sys))[:n+1] |
| x[len(x)-1] = 0xa1 // overflow check sentinel |
| n = runGCProg(prog, nil, &x[0], 1) |
| if x[len(x)-1] != 0xa1 { |
| throw("progToPointerMask: overflow") |
| } |
| return bitvector{int32(n), &x[0]} |
| } |
| |
| // Packed GC pointer bitmaps, aka GC programs. |
| // |
| // For large types containing arrays, the type information has a |
| // natural repetition that can be encoded to save space in the |
| // binary and in the memory representation of the type information. |
| // |
| // The encoding is a simple Lempel-Ziv style bytecode machine |
| // with the following instructions: |
| // |
| // 00000000: stop |
| // 0nnnnnnn: emit n bits copied from the next (n+7)/8 bytes |
| // 10000000 n c: repeat the previous n bits c times; n, c are varints |
| // 1nnnnnnn c: repeat the previous n bits c times; c is a varint |
| |
| // runGCProg executes the GC program prog, and then trailer if non-nil, |
| // writing to dst with entries of the given size. |
| // If size == 1, dst is a 1-bit pointer mask laid out moving forward from dst. |
| // If size == 2, dst is the 2-bit heap bitmap, and writes move backward |
| // starting at dst (because the heap bitmap does). In this case, the caller guarantees |
| // that only whole bytes in dst need to be written. |
| // |
| // runGCProg returns the number of 1- or 2-bit entries written to memory. |
| func runGCProg(prog, trailer, dst *byte, size int) uintptr { |
| dstStart := dst |
| |
| // Bits waiting to be written to memory. |
| var bits uintptr |
| var nbits uintptr |
| |
| p := prog |
| Run: |
| for { |
| // Flush accumulated full bytes. |
| // The rest of the loop assumes that nbits <= 7. |
| for ; nbits >= 8; nbits -= 8 { |
| if size == 1 { |
| *dst = uint8(bits) |
| dst = add1(dst) |
| bits >>= 8 |
| } else { |
| v := bits&bitPointerAll | bitScanAll |
| *dst = uint8(v) |
| dst = add1(dst) |
| bits >>= 4 |
| v = bits&bitPointerAll | bitScanAll |
| *dst = uint8(v) |
| dst = add1(dst) |
| bits >>= 4 |
| } |
| } |
| |
| // Process one instruction. |
| inst := uintptr(*p) |
| p = add1(p) |
| n := inst & 0x7F |
| if inst&0x80 == 0 { |
| // Literal bits; n == 0 means end of program. |
| if n == 0 { |
| // Program is over; continue in trailer if present. |
| if trailer != nil { |
| p = trailer |
| trailer = nil |
| continue |
| } |
| break Run |
| } |
| nbyte := n / 8 |
| for i := uintptr(0); i < nbyte; i++ { |
| bits |= uintptr(*p) << nbits |
| p = add1(p) |
| if size == 1 { |
| *dst = uint8(bits) |
| dst = add1(dst) |
| bits >>= 8 |
| } else { |
| v := bits&0xf | bitScanAll |
| *dst = uint8(v) |
| dst = add1(dst) |
| bits >>= 4 |
| v = bits&0xf | bitScanAll |
| *dst = uint8(v) |
| dst = add1(dst) |
| bits >>= 4 |
| } |
| } |
| if n %= 8; n > 0 { |
| bits |= uintptr(*p) << nbits |
| p = add1(p) |
| nbits += n |
| } |
| continue Run |
| } |
| |
| // Repeat. If n == 0, it is encoded in a varint in the next bytes. |
| if n == 0 { |
| for off := uint(0); ; off += 7 { |
| x := uintptr(*p) |
| p = add1(p) |
| n |= (x & 0x7F) << off |
| if x&0x80 == 0 { |
| break |
| } |
| } |
| } |
| |
| // Count is encoded in a varint in the next bytes. |
| c := uintptr(0) |
| for off := uint(0); ; off += 7 { |
| x := uintptr(*p) |
| p = add1(p) |
| c |= (x & 0x7F) << off |
| if x&0x80 == 0 { |
| break |
| } |
| } |
| c *= n // now total number of bits to copy |
| |
| // If the number of bits being repeated is small, load them |
| // into a register and use that register for the entire loop |
| // instead of repeatedly reading from memory. |
| // Handling fewer than 8 bits here makes the general loop simpler. |
| // The cutoff is sys.PtrSize*8 - 7 to guarantee that when we add |
| // the pattern to a bit buffer holding at most 7 bits (a partial byte) |
| // it will not overflow. |
| src := dst |
| const maxBits = sys.PtrSize*8 - 7 |
| if n <= maxBits { |
| // Start with bits in output buffer. |
| pattern := bits |
| npattern := nbits |
| |
| // If we need more bits, fetch them from memory. |
| if size == 1 { |
| src = subtract1(src) |
| for npattern < n { |
| pattern <<= 8 |
| pattern |= uintptr(*src) |
| src = subtract1(src) |
| npattern += 8 |
| } |
| } else { |
| src = subtract1(src) |
| for npattern < n { |
| pattern <<= 4 |
| pattern |= uintptr(*src) & 0xf |
| src = subtract1(src) |
| npattern += 4 |
| } |
| } |
| |
| // We started with the whole bit output buffer, |
| // and then we loaded bits from whole bytes. |
| // Either way, we might now have too many instead of too few. |
| // Discard the extra. |
| if npattern > n { |
| pattern >>= npattern - n |
| npattern = n |
| } |
| |
| // Replicate pattern to at most maxBits. |
| if npattern == 1 { |
| // One bit being repeated. |
| // If the bit is 1, make the pattern all 1s. |
| // If the bit is 0, the pattern is already all 0s, |
| // but we can claim that the number of bits |
| // in the word is equal to the number we need (c), |
| // because right shift of bits will zero fill. |
| if pattern == 1 { |
| pattern = 1<<maxBits - 1 |
| npattern = maxBits |
| } else { |
| npattern = c |
| } |
| } else { |
| b := pattern |
| nb := npattern |
| if nb+nb <= maxBits { |
| // Double pattern until the whole uintptr is filled. |
| for nb <= sys.PtrSize*8 { |
| b |= b << nb |
| nb += nb |
| } |
| // Trim away incomplete copy of original pattern in high bits. |
| // TODO(rsc): Replace with table lookup or loop on systems without divide? |
| nb = maxBits / npattern * npattern |
| b &= 1<<nb - 1 |
| pattern = b |
| npattern = nb |
| } |
| } |
| |
| // Add pattern to bit buffer and flush bit buffer, c/npattern times. |
| // Since pattern contains >8 bits, there will be full bytes to flush |
| // on each iteration. |
| for ; c >= npattern; c -= npattern { |
| bits |= pattern << nbits |
| nbits += npattern |
| if size == 1 { |
| for nbits >= 8 { |
| *dst = uint8(bits) |
| dst = add1(dst) |
| bits >>= 8 |
| nbits -= 8 |
| } |
| } else { |
| for nbits >= 4 { |
| *dst = uint8(bits&0xf | bitScanAll) |
| dst = add1(dst) |
| bits >>= 4 |
| nbits -= 4 |
| } |
| } |
| } |
| |
| // Add final fragment to bit buffer. |
| if c > 0 { |
| pattern &= 1<<c - 1 |
| bits |= pattern << nbits |
| nbits += c |
| } |
| continue Run |
| } |
| |
| // Repeat; n too large to fit in a register. |
| // Since nbits <= 7, we know the first few bytes of repeated data |
| // are already written to memory. |
| off := n - nbits // n > nbits because n > maxBits and nbits <= 7 |
| if size == 1 { |
| // Leading src fragment. |
| src = subtractb(src, (off+7)/8) |
| if frag := off & 7; frag != 0 { |
| bits |= uintptr(*src) >> (8 - frag) << nbits |
| src = add1(src) |
| nbits += frag |
| c -= frag |
| } |
| // Main loop: load one byte, write another. |
| // The bits are rotating through the bit buffer. |
| for i := c / 8; i > 0; i-- { |
| bits |= uintptr(*src) << nbits |
| src = add1(src) |
| *dst = uint8(bits) |
| dst = add1(dst) |
| bits >>= 8 |
| } |
| // Final src fragment. |
| if c %= 8; c > 0 { |
| bits |= (uintptr(*src) & (1<<c - 1)) << nbits |
| nbits += c |
| } |
| } else { |
| // Leading src fragment. |
| src = subtractb(src, (off+3)/4) |
| if frag := off & 3; frag != 0 { |
| bits |= (uintptr(*src) & 0xf) >> (4 - frag) << nbits |
| src = add1(src) |
| nbits += frag |
| c -= frag |
| } |
| // Main loop: load one byte, write another. |
| // The bits are rotating through the bit buffer. |
| for i := c / 4; i > 0; i-- { |
| bits |= (uintptr(*src) & 0xf) << nbits |
| src = add1(src) |
| *dst = uint8(bits&0xf | bitScanAll) |
| dst = add1(dst) |
| bits >>= 4 |
| } |
| // Final src fragment. |
| if c %= 4; c > 0 { |
| bits |= (uintptr(*src) & (1<<c - 1)) << nbits |
| nbits += c |
| } |
| } |
| } |
| |
| // Write any final bits out, using full-byte writes, even for the final byte. |
| var totalBits uintptr |
| if size == 1 { |
| totalBits = (uintptr(unsafe.Pointer(dst))-uintptr(unsafe.Pointer(dstStart)))*8 + nbits |
| nbits += -nbits & 7 |
| for ; nbits > 0; nbits -= 8 { |
| *dst = uint8(bits) |
| dst = add1(dst) |
| bits >>= 8 |
| } |
| } else { |
| totalBits = (uintptr(unsafe.Pointer(dst))-uintptr(unsafe.Pointer(dstStart)))*4 + nbits |
| nbits += -nbits & 3 |
| for ; nbits > 0; nbits -= 4 { |
| v := bits&0xf | bitScanAll |
| *dst = uint8(v) |
| dst = add1(dst) |
| bits >>= 4 |
| } |
| } |
| return totalBits |
| } |
| |
| // materializeGCProg allocates space for the (1-bit) pointer bitmask |
| // for an object of size ptrdata. Then it fills that space with the |
| // pointer bitmask specified by the program prog. |
| // The bitmask starts at s.startAddr. |
| // The result must be deallocated with dematerializeGCProg. |
| func materializeGCProg(ptrdata uintptr, prog *byte) *mspan { |
| // Each word of ptrdata needs one bit in the bitmap. |
| bitmapBytes := divRoundUp(ptrdata, 8*sys.PtrSize) |
| // Compute the number of pages needed for bitmapBytes. |
| pages := divRoundUp(bitmapBytes, pageSize) |
| s := mheap_.allocManual(pages, spanAllocPtrScalarBits) |
| runGCProg(addb(prog, 4), nil, (*byte)(unsafe.Pointer(s.startAddr)), 1) |
| return s |
| } |
| func dematerializeGCProg(s *mspan) { |
| mheap_.freeManual(s, spanAllocPtrScalarBits) |
| } |
| |
| func dumpGCProg(p *byte) { |
| nptr := 0 |
| for { |
| x := *p |
| p = add1(p) |
| if x == 0 { |
| print("\t", nptr, " end\n") |
| break |
| } |
| if x&0x80 == 0 { |
| print("\t", nptr, " lit ", x, ":") |
| n := int(x+7) / 8 |
| for i := 0; i < n; i++ { |
| print(" ", hex(*p)) |
| p = add1(p) |
| } |
| print("\n") |
| nptr += int(x) |
| } else { |
| nbit := int(x &^ 0x80) |
| if nbit == 0 { |
| for nb := uint(0); ; nb += 7 { |
| x := *p |
| p = add1(p) |
| nbit |= int(x&0x7f) << nb |
| if x&0x80 == 0 { |
| break |
| } |
| } |
| } |
| count := 0 |
| for nb := uint(0); ; nb += 7 { |
| x := *p |
| p = add1(p) |
| count |= int(x&0x7f) << nb |
| if x&0x80 == 0 { |
| break |
| } |
| } |
| print("\t", nptr, " repeat ", nbit, " × ", count, "\n") |
| nptr += nbit * count |
| } |
| } |
| } |
| |
| // Testing. |
| |
| // gcbits returns the GC type info for x, for testing. |
| // The result is the bitmap entries (0 or 1), one entry per byte. |
| //go:linkname reflect_gcbits reflect.gcbits |
| func reflect_gcbits(x interface{}) []byte { |
| ret := getgcmask(x) |
| typ := (*ptrtype)(unsafe.Pointer(efaceOf(&x)._type)).elem |
| nptr := typ.ptrdata / sys.PtrSize |
| for uintptr(len(ret)) > nptr && ret[len(ret)-1] == 0 { |
| ret = ret[:len(ret)-1] |
| } |
| return ret |
| } |
| |
| // Returns GC type info for the pointer stored in ep for testing. |
| // If ep points to the stack, only static live information will be returned |
| // (i.e. not for objects which are only dynamically live stack objects). |
| func getgcmask(ep interface{}) (mask []byte) { |
| e := *efaceOf(&ep) |
| p := e.data |
| t := e._type |
| // data or bss |
| roots := gcRoots |
| for roots != nil { |
| for i := 0; i < roots.count; i++ { |
| pr := roots.roots[i] |
| addr := uintptr(pr.decl) |
| if addr <= uintptr(p) && uintptr(p) < addr+pr.size { |
| n := (*ptrtype)(unsafe.Pointer(t)).elem.size |
| mask = make([]byte, n/sys.PtrSize) |
| copy(mask, (*[1 << 29]uint8)(unsafe.Pointer(pr.gcdata))[:pr.ptrdata]) |
| } |
| return |
| } |
| roots = roots.next |
| } |
| |
| // heap |
| if base, s, _ := findObject(uintptr(p), 0, 0, false); base != 0 { |
| hbits := heapBitsForAddr(base) |
| n := s.elemsize |
| mask = make([]byte, n/sys.PtrSize) |
| for i := uintptr(0); i < n; i += sys.PtrSize { |
| if hbits.isPointer() { |
| mask[i/sys.PtrSize] = 1 |
| } |
| if !hbits.morePointers() { |
| mask = mask[:i/sys.PtrSize] |
| break |
| } |
| hbits = hbits.next() |
| } |
| return |
| } |
| |
| // otherwise, not something the GC knows about. |
| // possibly read-only data, like malloc(0). |
| // must not have pointers |
| // For gccgo, may live on the stack, which is collected conservatively. |
| return |
| } |