| // 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 1-bit bitmaps in which 0 means uninteresting and 1 means live pointer |
| // to be visited during GC. The bits in each byte are consumed starting with |
| // the low bit: 1<<0, 1<<1, and so on. |
| // |
| // Heap bitmap |
| // |
| // The allocated heap comes from a subset of the memory in the range [start, used), |
| // where start == mheap_.arena_start and used == mheap_.arena_used. |
| // The heap bitmap comprises 2 bits for each pointer-sized word in that range, |
| // stored in bytes indexed backward in memory from start. |
| // That is, the byte at address start-1 holds the 2-bit entries for the four words |
| // start through start+3*ptrSize, the byte at start-2 holds the entries for |
| // start+4*ptrSize through start+7*ptrSize, and so on. |
| // |
| // In each 2-bit entry, the lower bit holds the same information as in the 1-bit |
| // bitmaps: 0 means uninteresting and 1 means live pointer to be visited during GC. |
| // The meaning of the high bit depends on the position of the word being described |
| // in its allocated object. In all words *except* the second word, the |
| // high bit indicates that the object is still being described. In |
| // these words, if a bit pair with a high bit 0 is encountered, the |
| // low bit can also be assumed to be 0, and the object description is |
| // over. This 00 is called the ``dead'' encoding: it signals that the |
| // rest of the words in the object are uninteresting to the garbage |
| // collector. |
| // |
| // In the second word, the high bit is the GC ``checkmarked'' bit (see below). |
| // |
| // The 2-bit entries are split when written into the byte, so that the top half |
| // of the byte contains 4 high 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 |
| // has no live pointer bit set and is (depending on position), not used, |
| // not checkmarked, and is the dead encoding. |
| // These properties 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. |
| // |
| // Checkmarks |
| // |
| // In a concurrent garbage collector, one worries about failing to mark |
| // a live object due to mutations without write barriers or bugs in the |
| // collector implementation. As a sanity check, the GC has a 'checkmark' |
| // mode that retraverses the object graph with the world stopped, to make |
| // sure that everything that should be marked is marked. |
| // In checkmark mode, in the heap bitmap, the high bit of the 2-bit entry |
| // for the second word of the object holds the checkmark bit. |
| // When not in checkmark mode, this bit is set to 1. |
| // |
| // The smallest possible allocation is 8 bytes. On a 32-bit machine, that |
| // means every allocated object has two words, so there is room for the |
| // checkmark bit. On a 64-bit machine, however, the 8-byte allocation is |
| // just one word, so the second bit pair is not available for encoding the |
| // checkmark. However, because non-pointer allocations are combined |
| // into larger 16-byte (maxTinySize) allocations, a plain 8-byte allocation |
| // must be a pointer, so the type bit in the first word is not actually needed. |
| // It is still used in general, except in checkmark the type bit is repurposed |
| // as the checkmark bit and then reinitialized (to 1) as the type bit when |
| // finished. |
| // |
| |
| 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 |
| heapBitmapScale = sys.PtrSize * (8 / 2) // number of data bytes described by one heap 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. |
| // subtractb is typically used when traversing the pointer tables referred to by hbits |
| // which are arranged in reverse order. |
| //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. |
| // subtract1 is typically used when traversing the pointer tables referred to by hbits |
| // which are arranged in reverse order. |
| //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)) |
| } |
| |
| // mapBits maps any additional bitmap memory needed for the new arena memory. |
| // |
| // Don't call this directly. Call mheap.setArenaUsed. |
| // |
| //go:nowritebarrier |
| func (h *mheap) mapBits(arena_used uintptr) { |
| // Caller has added extra mappings to the arena. |
| // Add extra mappings of bitmap words as needed. |
| // We allocate extra bitmap pieces in chunks of bitmapChunk. |
| const bitmapChunk = 8192 |
| |
| n := (arena_used - mheap_.arena_start) / heapBitmapScale |
| n = round(n, bitmapChunk) |
| n = round(n, physPageSize) |
| if h.bitmap_mapped >= n { |
| return |
| } |
| |
| sysMap(unsafe.Pointer(h.bitmap-n), n-h.bitmap_mapped, h.arena_reserved, &memstats.gc_sys) |
| h.bitmap_mapped = n |
| } |
| |
| // 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 |
| } |
| |
| // 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} |
| } |
| |
| // refillaCache 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 returns whether the index'th object in s is unallocated. |
| 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 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. Some compilers |
| // are not able to inline atomic.Or8 function so if it appears as a hot spot consider |
| // inlining it manually. |
| 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) { |
| if base < mheap_.arena_start || base >= mheap_.arena_used { |
| throw("markBitsForSpan: base out of range") |
| } |
| 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 have already checked that addr is in the range [mheap_.arena_start, mheap_.arena_used). |
| // |
| // nosplit because it is used during write barriers and must not be preempted. |
| //go:nosplit |
| func heapBitsForAddr(addr uintptr) heapBits { |
| // 2 bits per work, 4 pairs per byte, and a mask is hard coded. |
| off := (addr - mheap_.arena_start) / sys.PtrSize |
| return heapBits{(*uint8)(unsafe.Pointer(mheap_.bitmap - off/4 - 1)), uint32(off & 3)} |
| } |
| |
| // heapBitsForSpan returns the heapBits for the span base address base. |
| func heapBitsForSpan(base uintptr) (hbits heapBits) { |
| if base < mheap_.arena_start || base >= mheap_.arena_used { |
| print("runtime: base ", hex(base), " not in range [", hex(mheap_.arena_start), ",", hex(mheap_.arena_used), ")\n") |
| throw("heapBitsForSpan: base out of range") |
| } |
| return heapBitsForAddr(base) |
| } |
| |
| // heapBitsForObject returns the base address for the heap object |
| // containing the address p, the heapBits for base, |
| // the object's span, and of the index of the object in s. |
| // If p does not point into a heap object, |
| // return base == 0 |
| // otherwise return the base of the object. |
| // |
| // 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. |
| func heapBitsForObject(p, refBase, refOff uintptr) (base uintptr, hbits heapBits, s *mspan, objIndex uintptr) { |
| arenaStart := mheap_.arena_start |
| if p < arenaStart || p >= mheap_.arena_used { |
| return |
| } |
| off := p - arenaStart |
| idx := off >> _PageShift |
| // p points into the heap, but possibly to the middle of an object. |
| // Consult the span table to find the block beginning. |
| s = mheap_.spans[idx] |
| if s == nil || p < s.base() || p >= s.limit || s.state != mSpanInUse { |
| if s == nil || s.state == _MSpanManual { |
| // 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. |
| // Pointers into stacks are also ok, the runtime manages these explicitly. |
| return |
| } |
| |
| // The following ensures that we are rigorous about what data |
| // structures hold valid pointers. |
| if debug.invalidptr != 0 { |
| // 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)) |
| if s.state != mSpanInUse { |
| print(" to unallocated span") |
| } else { |
| print(" to unused region of span") |
| } |
| print(" idx=", hex(idx), " span.base()=", hex(s.base()), " span.limit=", hex(s.limit), " span.state=", s.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?)") |
| } |
| 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 |
| } |
| } |
| // Now that we know the actual base, compute heapBits to return to caller. |
| hbits = heapBitsForAddr(base) |
| 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 { |
| return heapBits{h.bitp, h.shift + heapBitsShift} |
| } |
| return heapBits{subtract1(h.bitp), 0} |
| } |
| |
| // 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. |
| func (h heapBits) forward(n uintptr) heapBits { |
| n += uintptr(h.shift) / heapBitsShift |
| return heapBits{subtractb(h.bitp, n/4), uint32(n%4) * heapBitsShift} |
| } |
| |
| // 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. |
| 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 returns true if 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 |
| } |
| |
| // isCheckmarked reports whether the heap bits have the checkmarked bit set. |
| // It must be told how large the object at h is, because the encoding of the |
| // checkmark bit varies by size. |
| // h must describe the initial word of the object. |
| func (h heapBits) isCheckmarked(size uintptr) bool { |
| if size == sys.PtrSize { |
| return (*h.bitp>>h.shift)&bitPointer != 0 |
| } |
| // All multiword objects are 2-word aligned, |
| // so we know that the initial word's 2-bit pair |
| // and the second word's 2-bit pair are in the |
| // same heap bitmap byte, *h.bitp. |
| return (*h.bitp>>(heapBitsShift+h.shift))&bitScan != 0 |
| } |
| |
| // setCheckmarked sets the checkmarked bit. |
| // It must be told how large the object at h is, because the encoding of the |
| // checkmark bit varies by size. |
| // h must describe the initial word of the object. |
| func (h heapBits) setCheckmarked(size uintptr) { |
| if size == sys.PtrSize { |
| atomic.Or8(h.bitp, bitPointer<<h.shift) |
| return |
| } |
| atomic.Or8(h.bitp, bitScan<<(heapBitsShift+h.shift)) |
| } |
| |
| // bulkBarrierPreWrite executes writebarrierptr_prewrite1 |
| // 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. |
| // |
| // 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.kind&kindNoPointers. |
| // |
| //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 !inheap(dst) { |
| gp := getg().m.curg |
| if gp != nil && gp.stack.lo <= dst && dst < gp.stack.hi { |
| // Destination is our own stack. No need for barriers. |
| return |
| } |
| |
| // If dst is a global, use the data or BSS bitmaps to |
| // execute write barriers. |
| for _, datap := range activeModules() { |
| if datap.data <= dst && dst < datap.edata { |
| bulkBarrierBitmap(dst, src, size, dst-datap.data, datap.gcdatamask.bytedata) |
| return |
| } |
| } |
| for _, datap := range activeModules() { |
| if datap.bss <= dst && dst < datap.ebss { |
| bulkBarrierBitmap(dst, src, size, dst-datap.bss, datap.gcbssmask.bytedata) |
| return |
| } |
| } |
| return |
| } |
| |
| h := heapBitsForAddr(dst) |
| if src == 0 { |
| for i := uintptr(0); i < size; i += sys.PtrSize { |
| if h.isPointer() { |
| dstx := (*uintptr)(unsafe.Pointer(dst + i)) |
| writebarrierptr_prewrite1(dstx, 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)) |
| writebarrierptr_prewrite1(dstx, *srcx) |
| } |
| 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) |
| |
| 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 { |
| writebarrierptr_prewrite1(dstx, 0) |
| } else { |
| srcx := (*uintptr)(unsafe.Pointer(src + i)) |
| writebarrierptr_prewrite1(dstx, *srcx) |
| } |
| } |
| mask <<= 1 |
| } |
| } |
| |
| // typeBitsBulkBarrier executes writebarrierptr_prewrite 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. |
| // |
| //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 |
| 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)) |
| writebarrierptr_prewrite(dstx, *srcx) |
| } |
| } |
| } |
| |
| // 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. |
| // It clears all checkmark bits. |
| // 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) { |
| size, n, total := s.layout() |
| |
| // Init the markbit structures |
| s.freeindex = 0 |
| s.allocCache = ^uint64(0) // all 1s indicating all free. |
| s.nelems = n |
| s.allocBits = nil |
| s.gcmarkBits = nil |
| s.gcmarkBits = newMarkBits(s.nelems) |
| s.allocBits = newAllocBits(s.nelems) |
| |
| // Clear bits corresponding to objects. |
| if total%heapBitmapScale != 0 { |
| throw("initSpan: unaligned length") |
| } |
| nbyte := total / heapBitmapScale |
| if sys.PtrSize == 8 && size == sys.PtrSize { |
| end := h.bitp |
| bitp := subtractb(end, nbyte-1) |
| for { |
| *bitp = bitPointerAll | bitScanAll |
| if bitp == end { |
| break |
| } |
| bitp = add1(bitp) |
| } |
| return |
| } |
| memclrNoHeapPointers(unsafe.Pointer(subtractb(h.bitp, nbyte-1)), nbyte) |
| } |
| |
| // initCheckmarkSpan initializes a span for being checkmarked. |
| // It clears the checkmark bits, which are set to 1 in normal operation. |
| func (h heapBits) initCheckmarkSpan(size, n, total uintptr) { |
| // The ptrSize == 8 is a compile-time constant false on 32-bit and eliminates this code entirely. |
| if sys.PtrSize == 8 && size == sys.PtrSize { |
| // Checkmark bit is type bit, bottom bit of every 2-bit entry. |
| // Only possible on 64-bit system, since minimum size is 8. |
| // Must clear type bit (checkmark bit) of every word. |
| // The type bit is the lower of every two-bit pair. |
| bitp := h.bitp |
| for i := uintptr(0); i < n; i += 4 { |
| *bitp &^= bitPointerAll |
| bitp = subtract1(bitp) |
| } |
| return |
| } |
| for i := uintptr(0); i < n; i++ { |
| *h.bitp &^= bitScan << (heapBitsShift + h.shift) |
| h = h.forward(size / sys.PtrSize) |
| } |
| } |
| |
| // clearCheckmarkSpan undoes all the checkmarking in a span. |
| // The actual checkmark bits are ignored, so the only work to do |
| // is to fix the pointer bits. (Pointer bits are ignored by scanobject |
| // but consulted by typedmemmove.) |
| func (h heapBits) clearCheckmarkSpan(size, n, total uintptr) { |
| // The ptrSize == 8 is a compile-time constant false on 32-bit and eliminates this code entirely. |
| if sys.PtrSize == 8 && size == sys.PtrSize { |
| // Checkmark bit is type bit, bottom bit of every 2-bit entry. |
| // Only possible on 64-bit system, since minimum size is 8. |
| // Must clear type bit (checkmark bit) of every word. |
| // The type bit is the lower of every two-bit pair. |
| bitp := h.bitp |
| for i := uintptr(0); i < n; i += 4 { |
| *bitp |= bitPointerAll |
| bitp = subtract1(bitp) |
| } |
| } |
| } |
| |
| // oneBitCount is indexed by byte and produces the |
| // number of 1 bits in that byte. For example 128 has 1 bit set |
| // and oneBitCount[128] will holds 1. |
| var oneBitCount = [256]uint8{ |
| 0, 1, 1, 2, 1, 2, 2, 3, |
| 1, 2, 2, 3, 2, 3, 3, 4, |
| 1, 2, 2, 3, 2, 3, 3, 4, |
| 2, 3, 3, 4, 3, 4, 4, 5, |
| 1, 2, 2, 3, 2, 3, 3, 4, |
| 2, 3, 3, 4, 3, 4, 4, 5, |
| 2, 3, 3, 4, 3, 4, 4, 5, |
| 3, 4, 4, 5, 4, 5, 5, 6, |
| 1, 2, 2, 3, 2, 3, 3, 4, |
| 2, 3, 3, 4, 3, 4, 4, 5, |
| 2, 3, 3, 4, 3, 4, 4, 5, |
| 3, 4, 4, 5, 4, 5, 5, 6, |
| 2, 3, 3, 4, 3, 4, 4, 5, |
| 3, 4, 4, 5, 4, 5, 5, 6, |
| 3, 4, 4, 5, 4, 5, 5, 6, |
| 4, 5, 5, 6, 5, 6, 6, 7, |
| 1, 2, 2, 3, 2, 3, 3, 4, |
| 2, 3, 3, 4, 3, 4, 4, 5, |
| 2, 3, 3, 4, 3, 4, 4, 5, |
| 3, 4, 4, 5, 4, 5, 5, 6, |
| 2, 3, 3, 4, 3, 4, 4, 5, |
| 3, 4, 4, 5, 4, 5, 5, 6, |
| 3, 4, 4, 5, 4, 5, 5, 6, |
| 4, 5, 5, 6, 5, 6, 6, 7, |
| 2, 3, 3, 4, 3, 4, 4, 5, |
| 3, 4, 4, 5, 4, 5, 5, 6, |
| 3, 4, 4, 5, 4, 5, 5, 6, |
| 4, 5, 5, 6, 5, 6, 6, 7, |
| 3, 4, 4, 5, 4, 5, 5, 6, |
| 4, 5, 5, 6, 5, 6, 6, 7, |
| 4, 5, 5, 6, 5, 6, 6, 7, |
| 5, 6, 6, 7, 6, 7, 7, 8} |
| |
| // countAlloc returns the number of objects allocated in span s by |
| // scanning the allocation bitmap. |
| // TODO:(rlh) Use popcount intrinsic. |
| func (s *mspan) countAlloc() int { |
| count := 0 |
| maxIndex := s.nelems / 8 |
| for i := uintptr(0); i < maxIndex; i++ { |
| mrkBits := *s.gcmarkBits.bytep(i) |
| count += int(oneBitCount[mrkBits]) |
| } |
| if bitsInLastByte := s.nelems % 8; bitsInLastByte != 0 { |
| mrkBits := *s.gcmarkBits.bytep(maxIndex) |
| mask := uint8((1 << bitsInLastByte) - 1) |
| bits := mrkBits & mask |
| count += int(oneBitCount[bits]) |
| } |
| 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 |
| |
| // 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) |
| |
| // Heap bitmap bits for 2-word object are only 4 bits, |
| // so also shared with objects next to it. |
| // This is called out as a special case primarily for 32-bit systems, |
| // so that on 32-bit systems the code below can assume all objects |
| // are 4-word aligned (because they're all 16-byte aligned). |
| 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 slice of pointer. |
| *h.bitp |= (bitPointer | bitScan | bitPointer<<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) | bitScan |
| // bitPointer == 1, bitScan is 1 << 4, heapBitsShift is 1. |
| // 110011 is shifted h.shift and complemented. |
| // This clears out the bits that are about to be |
| // ored into *h.hbitp in the next instructions. |
| *h.bitp &^= (bitPointer | bitScan | ((bitPointer | bitScan) << heapBitsShift)) << h.shift |
| *h.bitp |= uint8(hb << h.shift) |
| 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. |
| |
| 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 |
| } |
| return |
| } |
| |
| // 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 |
| } |
| if nw < 2 { |
| // Must write at least 2 words, because the "no scan" |
| // encoding doesn't take effect until the third word. |
| nw = 2 |
| } |
| |
| // Phase 1: Special case for leading byte (shift==0) or half-byte (shift==4). |
| // 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. |
| // Handle first byte of bitmap specially. |
| // |
| // 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. The scan/dead bit on the |
| // second word is the checkmark, so we don't set it. |
| // In all following words, we set the scan/dead |
| // appropriately to indicate that the object contains |
| // to the next 2-bit entry in the bitmap. |
| // |
| // TODO: It doesn't matter if we set the checkmark, so |
| // maybe this case isn't needed any more. |
| hb = b & bitPointerAll |
| hb |= bitScan | bitScan<<(2*heapBitsShift) | bitScan<<(3*heapBitsShift) |
| if w += 4; w >= nw { |
| goto Phase3 |
| } |
| *hbitp = uint8(hb) |
| hbitp = subtract1(hbitp) |
| b >>= 4 |
| nb -= 4 |
| |
| case sys.PtrSize == 8 && h.shift == 2: |
| // Ptrmask and heap bitmap are misaligned. |
| // 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 and 2-word objects above, |
| // so this is at least a 6-word object. |
| hb = (b & (bitPointer | bitPointer<<heapBitsShift)) << (2 * heapBitsShift) |
| // This is not noscan, so set the scan bit in the |
| // first word. |
| hb |= bitScan << (2 * heapBitsShift) |
| b >>= 2 |
| nb -= 2 |
| // Note: no bitScan for second word because that's |
| // the checkmark. |
| *hbitp &^= uint8((bitPointer | bitScan | (bitPointer << heapBitsShift)) << (2 * heapBitsShift)) |
| *hbitp |= uint8(hb) |
| hbitp = subtract1(hbitp) |
| if w += 2; w >= nw { |
| // We know that there is more data, because we handled 2-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 = subtract1(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 = subtract1(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 = subtract1(hbitp) |
| hb = 0 // for possible final half-byte below |
| for w += 4; w <= nw; w += 4 { |
| *hbitp = 0 |
| hbitp = subtract1(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: all done, but perhaps double check. |
| if doubleCheck { |
| end := heapBitsForAddr(x + size) |
| 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 { |
| want = 0 // deadmarker |
| if typ.kind&kindGCProg != 0 && i < (totalptr+3)/4*4 { |
| want = bitScan |
| } |
| } else { |
| if j < nptr && (*addb(ptrmask, j/8)>>(j%8))&1 != 0 { |
| want |= bitPointer |
| } |
| if i != 1 { |
| want |= bitScan |
| } else { |
| have &^= 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, "\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", have, "want", 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(subtractb(h.bitp, (totalBits+3)/4)) |
| endAlloc := unsafe.Pointer(subtractb(h.bitp, allocSize/heapBitmapScale)) |
| memclrNoHeapPointers(add(endAlloc, 1), uintptr(endProg)-uintptr(endAlloc)) |
| } |
| |
| // 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 = subtract1(dst) |
| bits >>= 4 |
| v = bits&bitPointerAll | bitScanAll |
| *dst = uint8(v) |
| dst = subtract1(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 { |
| //println("trailer") |
| p = trailer |
| trailer = nil |
| continue |
| } |
| //println("done") |
| break Run |
| } |
| //println("lit", n, dst) |
| 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 = subtract1(dst) |
| bits >>= 4 |
| v = bits&0xf | bitScanAll |
| *dst = uint8(v) |
| dst = subtract1(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 = add1(src) |
| for npattern < n { |
| pattern <<= 4 |
| pattern |= uintptr(*src) & 0xf |
| src = add1(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 = subtract1(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 = addb(src, (off+3)/4) |
| if frag := off & 3; frag != 0 { |
| bits |= (uintptr(*src) & 0xf) >> (4 - frag) << nbits |
| src = subtract1(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 = subtract1(src) |
| *dst = uint8(bits&0xf | bitScanAll) |
| dst = subtract1(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(dstStart))-uintptr(unsafe.Pointer(dst)))*4 + nbits |
| nbits += -nbits & 3 |
| for ; nbits > 0; nbits -= 4 { |
| v := bits&0xf | bitScanAll |
| *dst = uint8(v) |
| dst = subtract1(dst) |
| bits >>= 4 |
| } |
| } |
| return totalBits |
| } |
| |
| 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. |
| |
| func getgcmaskcb(frame *stkframe, ctxt unsafe.Pointer) bool { |
| target := (*stkframe)(ctxt) |
| if frame.sp <= target.sp && target.sp < frame.varp { |
| *target = *frame |
| return false |
| } |
| return true |
| } |
| |
| // 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 object p for testing. |
| func getgcmask(ep interface{}) (mask []byte) { |
| e := *efaceOf(&ep) |
| p := e.data |
| t := e._type |
| // data or bss |
| for _, datap := range activeModules() { |
| // data |
| if datap.data <= uintptr(p) && uintptr(p) < datap.edata { |
| bitmap := datap.gcdatamask.bytedata |
| n := (*ptrtype)(unsafe.Pointer(t)).elem.size |
| mask = make([]byte, n/sys.PtrSize) |
| for i := uintptr(0); i < n; i += sys.PtrSize { |
| off := (uintptr(p) + i - datap.data) / sys.PtrSize |
| mask[i/sys.PtrSize] = (*addb(bitmap, off/8) >> (off % 8)) & 1 |
| } |
| return |
| } |
| |
| // bss |
| if datap.bss <= uintptr(p) && uintptr(p) < datap.ebss { |
| bitmap := datap.gcbssmask.bytedata |
| n := (*ptrtype)(unsafe.Pointer(t)).elem.size |
| mask = make([]byte, n/sys.PtrSize) |
| for i := uintptr(0); i < n; i += sys.PtrSize { |
| off := (uintptr(p) + i - datap.bss) / sys.PtrSize |
| mask[i/sys.PtrSize] = (*addb(bitmap, off/8) >> (off % 8)) & 1 |
| } |
| return |
| } |
| } |
| |
| // heap |
| var n uintptr |
| var base uintptr |
| if mlookup(uintptr(p), &base, &n, nil) != 0 { |
| mask = make([]byte, n/sys.PtrSize) |
| for i := uintptr(0); i < n; i += sys.PtrSize { |
| hbits := heapBitsForAddr(base + i) |
| if hbits.isPointer() { |
| mask[i/sys.PtrSize] = 1 |
| } |
| if i != 1*sys.PtrSize && !hbits.morePointers() { |
| mask = mask[:i/sys.PtrSize] |
| break |
| } |
| } |
| return |
| } |
| |
| // stack |
| if _g_ := getg(); _g_.m.curg.stack.lo <= uintptr(p) && uintptr(p) < _g_.m.curg.stack.hi { |
| var frame stkframe |
| frame.sp = uintptr(p) |
| _g_ := getg() |
| gentraceback(_g_.m.curg.sched.pc, _g_.m.curg.sched.sp, 0, _g_.m.curg, 0, nil, 1000, getgcmaskcb, noescape(unsafe.Pointer(&frame)), 0) |
| if frame.fn.valid() { |
| f := frame.fn |
| targetpc := frame.continpc |
| if targetpc == 0 { |
| return |
| } |
| if targetpc != f.entry { |
| targetpc-- |
| } |
| pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, targetpc, nil) |
| if pcdata == -1 { |
| return |
| } |
| stkmap := (*stackmap)(funcdata(f, _FUNCDATA_LocalsPointerMaps)) |
| if stkmap == nil || stkmap.n <= 0 { |
| return |
| } |
| bv := stackmapdata(stkmap, pcdata) |
| size := uintptr(bv.n) * sys.PtrSize |
| n := (*ptrtype)(unsafe.Pointer(t)).elem.size |
| mask = make([]byte, n/sys.PtrSize) |
| for i := uintptr(0); i < n; i += sys.PtrSize { |
| bitmap := bv.bytedata |
| off := (uintptr(p) + i - frame.varp + size) / sys.PtrSize |
| mask[i/sys.PtrSize] = (*addb(bitmap, off/8) >> (off % 8)) & 1 |
| } |
| } |
| return |
| } |
| |
| // otherwise, not something the GC knows about. |
| // possibly read-only data, like malloc(0). |
| // must not have pointers |
| return |
| } |