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-rw-r--r--src/runtime/mbitmap.go2026
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diff --git a/src/runtime/mbitmap.go b/src/runtime/mbitmap.go
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+// 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.
+//
+// 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) (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 {
+ 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 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.
+ 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
+ } 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.
+
+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 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
+ 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
+ if base, s, _ := findObject(uintptr(p), 0, 0); 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
+ }
+
+ // 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() {
+ locals, _, _ := getStackMap(&frame, nil, false)
+ if locals.n == 0 {
+ return
+ }
+ size := uintptr(locals.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 {
+ off := (uintptr(p) + i - frame.varp + size) / sys.PtrSize
+ mask[i/sys.PtrSize] = locals.ptrbit(off)
+ }
+ }
+ return
+ }
+
+ // otherwise, not something the GC knows about.
+ // possibly read-only data, like malloc(0).
+ // must not have pointers
+ return
+}