//
// Heap bitmap
//
-// The heap bitmap comprises 1 bit for each pointer-sized word in the heap,
-// recording whether a pointer is stored in that word or not. This bitmap
-// is stored in the heapArena metadata backing each heap arena.
-// That is, if ha is the heapArena for the arena starting at "start",
-// then ha.bitmap[0] holds the 64 bits for the 64 words "start"
-// through start+63*ptrSize, ha.bitmap[1] holds the entries for
-// start+64*ptrSize through start+127*ptrSize, and so on.
-// Bits correspond to words in little-endian order. ha.bitmap[0]&1 represents
-// the word at "start", ha.bitmap[0]>>1&1 represents the word at start+8, etc.
-// (For 32-bit platforms, s/64/32/.)
+// 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.
//
-// We also keep a noMorePtrs bitmap which allows us to stop scanning
-// the heap bitmap early in certain situations. If ha.noMorePtrs[i]>>j&1
-// is 1, then the object containing the last word described by ha.bitmap[8*i+j]
-// has no more pointers beyond those described by ha.bitmap[8*i+j].
-// If ha.noMorePtrs[i]>>j&1 is set, the entries in ha.bitmap[8*i+j+1] and
-// beyond must all be zero until the start of the next object.
+// 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 bitmap for noscan spans is not maintained (can be junk). Code must
-// ensure that an object is scannable before consulting its bitmap by
+// 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.
-//
-// The bitmap for unallocated objects is also not maintained.
package runtime
"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
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
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/(goarch.PtrSize*4))%heapArenaBitmapBytes]
+ h.shift = uint32((addr / goarch.PtrSize) & 3)
+ h.arena = uint32(arena)
+ h.last = &ha.bitmap[len(ha.bitmap)-1]
+ return
+}
+
// clobberdeadPtr is a special value that is used by the compiler to
// clobber dead stack slots, when -clobberdead flag is set.
const clobberdeadPtr = uintptr(0xdeaddead | 0xdeaddead<<((^uintptr(0)>>63)*32))
return spanOf(p) == nil && p != clobberdeadPtr
}
-const ptrBits = 8 * goarch.PtrSize
-
-// 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 {
- // heapBits will report on pointers in the range [addr,addr+size).
- // The low bit of mask contains the pointerness of the word at addr
- // (assuming valid>0).
- addr, size uintptr
-
- // The next few pointer bits representing words starting at addr.
- // Those bits already returned by next() are zeroed.
- mask uintptr
- // Number of bits in mask that are valid. mask is always less than 1<<valid.
- valid uintptr
-}
-
-// heapBitsForAddr returns the heapBits for the address addr.
-// The caller must ensure [addr,addr+size) is in an allocated span.
-// In particular, be careful not to point past the end of an object.
+// 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 heapBitsForAddr(addr, size uintptr) heapBits {
- // Find arena
- ai := arenaIndex(addr)
- ha := mheap_.arenas[ai.l1()][ai.l2()]
-
- // Word index in arena.
- word := addr / goarch.PtrSize % heapArenaWords
-
- // Word index and bit offset in bitmap array.
- idx := word / ptrBits
- off := word % ptrBits
-
- // Grab relevant bits of bitmap.
- mask := ha.bitmap[idx] >> off
- valid := ptrBits - off
-
- // Process depending on where the object ends.
- nptr := size / goarch.PtrSize
- if nptr < valid {
- // Bits for this object end before the end of this bitmap word.
- // Squash bits for the following objects.
- mask &= 1<<(nptr&(ptrBits-1)) - 1
- valid = nptr
- } else if nptr == valid {
- // Bits for this object end at exactly the end of this bitmap word.
- // All good.
+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 {
- // Bits for this object extend into the next bitmap word. See if there
- // may be any pointers recorded there.
- if uintptr(ha.noMorePtrs[idx/8])>>(idx%8)&1 != 0 {
- // No more pointers in this object after this bitmap word.
- // Update size so we know not to look there.
- size = valid * goarch.PtrSize
- }
+ // Move to the next arena.
+ return h.nextArena()
}
-
- return heapBits{addr: addr, size: size, mask: mask, valid: valid}
+ return h
}
-// Returns the (absolute) address of the next known pointer and
-// a heapBits iterator representing any remaining pointers.
-// If there are no more pointers, returns address 0.
-// Note that next does not modify h. The caller must record the result.
+// nextArena advances h to the beginning of the next heap arena.
//
-// nosplit because it is used during write barriers and must not be preempted.
+// 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
-func (h heapBits) next() (heapBits, uintptr) {
- for {
- if h.mask != 0 {
- var i int
- if goarch.PtrSize == 8 {
- i = sys.Ctz64(uint64(h.mask))
- } else {
- i = sys.Ctz32(uint32(h.mask))
- }
- h.mask ^= uintptr(1) << (i & (ptrBits - 1))
- return h, h.addr + uintptr(i)*goarch.PtrSize
- }
-
- // Skip words that we've already processed.
- h.addr += h.valid * goarch.PtrSize
- h.size -= h.valid * goarch.PtrSize
- if h.size == 0 {
- return h, 0 // no more pointers
- }
-
- // Grab more bits and try again.
- h = heapBitsForAddr(h.addr, h.size)
+//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
}
-// nextFast is like next, but can return 0 even when there are more pointers
-// to be found. Callers should call next if nextFast returns 0 as its second
-// return value.
-// if addr, h = h.nextFast(); addr == 0 {
-// if addr, h = h.next(); addr == 0 {
-// ... no more pointers ...
-// }
-// }
-// ... process pointer at addr ...
-// nextFast is designed to be inlineable.
+// 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) nextFast() (heapBits, uintptr) {
- // TESTQ/JEQ
- if h.mask == 0 {
- return h, 0
+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
}
- // BSFQ
- var i int
- if goarch.PtrSize == 8 {
- i = sys.Ctz64(uint64(h.mask))
+
+ // 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 {
- i = sys.Ctz32(uint32(h.mask))
+ 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
}
- // BTCQ
- h.mask ^= uintptr(1) << (i & (ptrBits - 1))
- // LEAQ (XX)(XX*8)
- return h, h.addr + uintptr(i)*goarch.PtrSize
+ 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
}
buf := &getg().m.p.ptr().wbBuf
- h := heapBitsForAddr(dst, size)
+ h := heapBitsForAddr(dst)
if src == 0 {
- for {
- var addr uintptr
- if h, addr = h.next(); addr == 0 {
- break
- }
- dstx := (*uintptr)(unsafe.Pointer(addr))
- if !buf.putFast(*dstx, 0) {
- wbBufFlush(nil, 0)
+ for i := uintptr(0); i < size; i += goarch.PtrSize {
+ if h.isPointer() {
+ dstx := (*uintptr)(unsafe.Pointer(dst + i))
+ if !buf.putFast(*dstx, 0) {
+ wbBufFlush(nil, 0)
+ }
}
+ h = h.next()
}
} else {
- for {
- var addr uintptr
- if h, addr = h.next(); addr == 0 {
- break
- }
- dstx := (*uintptr)(unsafe.Pointer(addr))
- srcx := (*uintptr)(unsafe.Pointer(src + (addr - dst)))
- if !buf.putFast(*dstx, *srcx) {
- wbBufFlush(nil, 0)
+ for i := uintptr(0); i < size; i += goarch.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()
}
}
}
return
}
buf := &getg().m.p.ptr().wbBuf
- h := heapBitsForAddr(dst, size)
- for {
- var addr uintptr
- if h, addr = h.next(); addr == 0 {
- break
- }
- srcx := (*uintptr)(unsafe.Pointer(addr - dst + src))
- if !buf.putFast(0, *srcx) {
- wbBufFlush(nil, 0)
+ h := heapBitsForAddr(dst)
+ for i := uintptr(0); i < size; i += goarch.PtrSize {
+ if h.isPointer() {
+ srcx := (*uintptr)(unsafe.Pointer(src + i))
+ if !buf.putFast(0, *srcx) {
+ wbBufFlush(nil, 0)
+ }
}
+ h = h.next()
}
}
}
}
-// initHeapBits initializes the heap bitmap for a span.
-// If this is a span of single pointer allocations, it initializes all
-// words to pointer.
-func (s *mspan) initHeapBits() {
- isPtrs := goarch.PtrSize == 8 && s.elemsize == goarch.PtrSize
- if !isPtrs {
- return // nothing to do
+// 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) / goarch.PtrSize
+ if nw%wordsPerBitmapByte != 0 {
+ throw("initSpan: unaligned length")
}
- h := writeHeapBitsForAddr(s.base())
- size := s.npages * pageSize
- nptrs := size / goarch.PtrSize
- for i := uintptr(0); i < nptrs; i += ptrBits {
- h = h.write(^uintptr(0), ptrBits)
+ if h.shift != 0 {
+ throw("initSpan: unaligned base")
+ }
+ isPtrs := goarch.PtrSize == 8 && s.elemsize == goarch.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
}
- h.flush(s.base(), size)
}
// countAlloc returns the number of objects allocated in span s by
return count
}
-type writeHeapBits struct {
- addr uintptr // address that the low bit of mask represents the pointer state of.
- mask uintptr // some pointer bits starting at the address addr.
- valid uintptr // number of bits in buf that are valid (including low)
- low uintptr // number of low-order bits to not overwrite
-}
-
-func writeHeapBitsForAddr(addr uintptr) (h writeHeapBits) {
- // We start writing bits maybe in the middle of a heap bitmap word.
- // Remember how many bits into the word we started, so we can be sure
- // not to overwrite the previous bits.
- h.low = addr / goarch.PtrSize % ptrBits
-
- // round down to heap word that starts the bitmap word.
- h.addr = addr - h.low*goarch.PtrSize
-
- // We don't have any bits yet.
- h.mask = 0
- h.valid = h.low
-
- return
-}
-
-// write appends the pointerness of the next valid pointer slots
-// using the low valid bits of bits. 1=pointer, 0=scalar.
-func (h writeHeapBits) write(bits, valid uintptr) writeHeapBits {
- if h.valid+valid <= ptrBits {
- // Fast path - just accumulate the bits.
- h.mask |= bits << h.valid
- h.valid += valid
- return h
- }
- // Too many bits to fit in this word. Write the current word
- // out and move on to the next word.
-
- data := h.mask | bits<<h.valid // mask for this word
- h.mask = bits >> (ptrBits - h.valid) // leftover for next word
- h.valid += valid - ptrBits // have h.valid+valid bits, writing ptrBits of them
-
- // Flush mask to the memory bitmap.
- // TODO: figure out how to cache arena lookup.
- ai := arenaIndex(h.addr)
- ha := mheap_.arenas[ai.l1()][ai.l2()]
- idx := h.addr / (ptrBits * goarch.PtrSize) % heapArenaBitmapWords
- m := uintptr(1)<<h.low - 1
- ha.bitmap[idx] = ha.bitmap[idx]&m | data
- // Note: no synchronization required for this write because
- // the allocator has exclusive access to the page, and the bitmap
- // entries are all for a single page. Also, visibility of these
- // writes is guaranteed by the publication barrier in mallocgc.
-
- // Clear noMorePtrs bit, since we're going to be writing bits
- // into the following word.
- ha.noMorePtrs[idx/8] &^= uint8(1) << (idx % 8)
- // Note: same as above
-
- // Move to next word of bitmap.
- h.addr += ptrBits * goarch.PtrSize
- h.low = 0
- return h
-}
-
-// Add padding of size bytes.
-func (h writeHeapBits) pad(size uintptr) writeHeapBits {
- if size == 0 {
- return h
- }
- words := size / goarch.PtrSize
- for words > ptrBits {
- h = h.write(0, ptrBits)
- words -= ptrBits
- }
- return h.write(0, words)
-}
-
-// Flush the bits that have been written, and add zeros as needed
-// to cover the full object [addr, addr+size).
-func (h writeHeapBits) flush(addr, size uintptr) {
- // zeros counts the number of bits needed to represent the object minus the
- // number of bits we've already written. This is the number of 0 bits
- // that need to be added.
- zeros := (addr+size-h.addr)/goarch.PtrSize - h.valid
-
- // Add zero bits up to the bitmap word boundary
- if zeros > 0 {
- z := ptrBits - h.valid
- if z > zeros {
- z = zeros
- }
- h.valid += z
- zeros -= z
- }
-
- // Find word in bitmap that we're going to write.
- ai := arenaIndex(h.addr)
- ha := mheap_.arenas[ai.l1()][ai.l2()]
- idx := h.addr / (ptrBits * goarch.PtrSize) % heapArenaBitmapWords
-
- // Write remaining bits.
- if h.valid != h.low {
- m := uintptr(1)<<h.low - 1 // don't clear existing bits below "low"
- m |= ^(uintptr(1)<<h.valid - 1) // don't clear existing bits above "valid"
- ha.bitmap[idx] = ha.bitmap[idx]&m | h.mask
- }
- if zeros == 0 {
- return
- }
-
- // Record in the noMorePtrs map that there won't be any more 1 bits,
- // so readers can stop early.
- ha.noMorePtrs[idx/8] |= uint8(1) << (idx % 8)
-
- // Advance to next bitmap word.
- h.addr += ptrBits * goarch.PtrSize
-
- // Continue on writing zeros for the rest of the object.
- // For standard use of the ptr bits this is not required, as
- // the bits are read from the beginning of the object. Some uses,
- // like oblets, bulk write barriers, and cgocheck, might
- // start mid-object, so these writes are still required.
- for {
- // Write zero bits.
- ai := arenaIndex(h.addr)
- ha := mheap_.arenas[ai.l1()][ai.l2()]
- idx := h.addr / (ptrBits * goarch.PtrSize) % heapArenaBitmapWords
- if zeros < ptrBits {
- ha.bitmap[idx] &^= uintptr(1)<<zeros - 1
- break
- } else if zeros == ptrBits {
- ha.bitmap[idx] = 0
- break
- } else {
- ha.bitmap[idx] = 0
- zeros -= ptrBits
- }
- ha.noMorePtrs[idx/8] |= uint8(1) << (idx % 8)
- h.addr += ptrBits * goarch.PtrSize
- }
-}
-
// 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.)
// heapBitsSweepSpan.
//
// There can only be one allocation from a given span active at a time,
-// and the bitmap for a span always falls on word boundaries,
+// 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.
//
// 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 = true // slow but helpful; enable to test modifications to this code
-
- if doubleCheck && dataSize%typ.size != 0 {
- throw("heapBitsSetType: dataSize not a multiple of typ.size")
- }
+ 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 == goarch.PtrSize and size == 2*goarch.PtrSize can therefore
+ // assume that dataSize == size without checking it explicitly.
if goarch.PtrSize == 8 && size == goarch.PtrSize {
// It's one word and it has pointers, it must be a pointer.
// (non-pointers are aggregated into tinySize allocations),
// initSpan sets the pointer bits for us. Nothing to do here.
if doubleCheck {
- h, addr := heapBitsForAddr(x, size).next()
- if addr != x {
+ h := heapBitsForAddr(x)
+ if !h.isPointer() {
throw("heapBitsSetType: pointer bit missing")
}
- _, addr = h.next()
- if addr != 0 {
- throw("heapBitsSetType: second pointer bit found")
+ if !h.morePointers() {
+ throw("heapBitsSetType: scan bit missing")
}
}
return
}
- h := writeHeapBitsForAddr(x)
-
- // Handle GC program.
- if typ.kind&kindGCProg != 0 {
- // Expand the gc program into the storage we're going to use for the actual object.
- obj := (*uint8)(unsafe.Pointer(x))
- n := runGCProg(addb(typ.gcdata, 4), obj)
- // Use the expanded program to set the heap bits.
- for i := uintptr(0); true; i += typ.size {
- // Copy expanded program to heap bitmap.
- p := obj
- j := n
- for j > 8 {
- h = h.write(uintptr(*p), 8)
- p = add1(p)
- j -= 8
+ 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*goarch.PtrSize {
+ if typ.size == goarch.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 goarch.PtrSize == 4 && dataSize == goarch.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
}
- h = h.write(uintptr(*p), j)
-
- if i+typ.size == dataSize {
- break // no padding after last element
+ return
+ }
+ // Otherwise typ.size must be 2*goarch.PtrSize,
+ // and typ.kind&kindGCProg == 0.
+ if doubleCheck {
+ if typ.size != 2*goarch.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 / goarch.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*goarch.PtrSize {
+ b := uint8(*ptrmask)
+ if doubleCheck {
+ if b == 0 {
+ println("runtime: invalid type ", typ.string())
+ throw("heapBitsSetType: called with non-pointer type")
+ }
+ if goarch.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*goarch.PtrSize {
+ print("runtime: heapBitsSetType size=", size, " but typ.size=", typ.size, "\n")
+ throw("heapBitsSetType: inconsistent object sizes")
+ }
+ }
+ if typ.size == goarch.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
+ }
- // Pad with zeros to the start of the next element.
- h = h.pad(typ.size - n*goarch.PtrSize)
+ 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
+ }
- h.flush(x, size)
+ // 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 && fastrandn(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
+ }
- // Erase the expanded GC program.
- memclrNoHeapPointers(unsafe.Pointer(obj), (n+7)/8)
- return
+ 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:
// 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. If there is more room in the allocated object,
- // that space is pointerless. The noMorePtrs bitmap will prevent
- // scanning large pointerless tails of an object.
+ // 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 = goarch.PtrSize*8 - 7
+ if typ.ptrdata/goarch.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 / goarch.PtrSize
+ for i := uintptr(0); i < nb; i += 8 {
+ b |= uintptr(*p) << i
+ p = add1(p)
+ }
+ nb = typ.size / goarch.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/goarch.PtrSize bits
+ // but are pretending to have typ.size/goarch.PtrSize,
+ // there might be no replication necessary/possible.
+ pbits = b
+ endnb = nb
+ if nb+nb <= maxBits {
+ for endnb <= goarch.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
+ }
- for i := uintptr(0); true; i += typ.size {
- p := typ.gcdata
- var j uintptr
- for j = 0; j+8*goarch.PtrSize < typ.ptrdata; j += 8 * goarch.PtrSize {
- h = h.write(uintptr(*p), 8)
- p = add1(p)
+ // 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/goarch.PtrSize+7)/8 - 1
+ endp = addb(ptrmask, n)
+ endnb = typ.size/goarch.PtrSize - n*8
}
- h = h.write(uintptr(*p), (typ.ptrdata-j)/goarch.PtrSize)
- if i+typ.size == dataSize {
- break // don't need the trailing nonptr bits on the last element.
+ }
+ 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 / goarch.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) / goarch.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
}
- // Pad with zeros to the start of the next element.
- h = h.pad(typ.size - typ.ptrdata)
}
- h.flush(x, size)
+ // 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 / goarch.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 / goarch.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 {
- h := heapBitsForAddr(x, size)
- for i := uintptr(0); i < size; i += goarch.PtrSize {
- // Compute the pointer bit we want at offset i.
- want := false
- if i < dataSize {
- off := i % typ.size
- if off < typ.ptrdata {
- j := off / goarch.PtrSize
- want = *addb(typ.gcdata, j/8)>>(j%8)&1 != 0
+ // 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 - goarch.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 / goarch.PtrSize
+ ndata := typ.size / goarch.PtrSize
+ count := dataSize / typ.size
+ totalptr := ((count-1)*typ.size + typ.ptrdata) / goarch.PtrSize
+ for i := uintptr(0); i < size/goarch.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 want {
- var addr uintptr
- h, addr = h.next()
- if addr != x+i {
- throw("heapBitsSetType: pointer entry not correct")
+ 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*goarch.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 _, addr := h.next(); addr != 0 {
- throw("heapBitsSetType: extra pointer")
+ if ptrmask == debugPtrmask.data {
+ unlock(&debugPtrmask.lock)
}
}
}
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 goarch.PtrSize == 8 && allocSize%(4*goarch.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*goarch.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/goarch.PtrSize - progSize/goarch.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 / goarch.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) / goarch.PtrSize
+ }
+ endProg := unsafe.Pointer(addb(h.bitp, (totalBits+3)/4))
+ endAlloc := unsafe.Pointer(addb(h.bitp, allocSize/goarch.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/goarch.PtrSize bits.
n := (size/goarch.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, &x[0])
+ n = runGCProg(prog, nil, &x[0], 1)
if x[len(x)-1] != 0xa1 {
throw("progToPointerMask: overflow")
}
// 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 returns the number of 1-bit entries written to memory.
-func runGCProg(prog, dst *byte) uintptr {
+// 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.
// Flush accumulated full bytes.
// The rest of the loop assumes that nbits <= 7.
for ; nbits >= 8; nbits -= 8 {
- *dst = uint8(bits)
- dst = add1(dst)
- bits >>= 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.
if inst&0x80 == 0 {
// Literal bits; n == 0 means end of program.
if n == 0 {
- // Program is over.
+ // 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)
- *dst = uint8(bits)
- dst = add1(dst)
- bits >>= 8
+ 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
npattern := nbits
// If we need more bits, fetch them from memory.
- src = subtract1(src)
- for npattern < n {
- pattern <<= 8
- pattern |= uintptr(*src)
+ if size == 1 {
+ src = subtract1(src)
+ for npattern < n {
+ pattern <<= 8
+ pattern |= uintptr(*src)
+ src = subtract1(src)
+ npattern += 8
+ }
+ } else {
src = subtract1(src)
- npattern += 8
+ for npattern < n {
+ pattern <<= 4
+ pattern |= uintptr(*src) & 0xf
+ src = subtract1(src)
+ npattern += 4
+ }
}
// We started with the whole bit output buffer,
for ; c >= npattern; c -= npattern {
bits |= pattern << nbits
nbits += npattern
- for nbits >= 8 {
- *dst = uint8(bits)
- dst = add1(dst)
- bits >>= 8
- nbits -= 8
+ 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
+ }
}
}
// 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
- // 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
+ 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
+ }
}
- // 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)
+ }
+
+ // 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
}
- // Final src fragment.
- if c %= 8; c > 0 {
- bits |= (uintptr(*src) & (1<<c - 1)) << nbits
- nbits += c
+ } 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
}
}
-
- // Write any final bits out, using full-byte writes, even for the final byte.
- 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
- }
return totalBits
}
// Compute the number of pages needed for bitmapBytes.
pages := divRoundUp(bitmapBytes, pageSize)
s := mheap_.allocManual(pages, spanAllocPtrScalarBits)
- runGCProg(addb(prog, 4), (*byte)(unsafe.Pointer(s.startAddr)))
+ runGCProg(addb(prog, 4), nil, (*byte)(unsafe.Pointer(s.startAddr)), 1)
return s
}
func dematerializeGCProg(s *mspan) {
//
//go:linkname reflect_gcbits reflect.gcbits
func reflect_gcbits(x any) []byte {
- return getgcmask(x)
+ ret := getgcmask(x)
+ typ := (*ptrtype)(unsafe.Pointer(efaceOf(&x)._type)).elem
+ nptr := typ.ptrdata / goarch.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.
// heap
if base, s, _ := findObject(uintptr(p), 0, 0); base != 0 {
- if s.spanclass.noscan() {
- return nil
- }
+ hbits := heapBitsForAddr(base)
n := s.elemsize
- hbits := heapBitsForAddr(base, n)
mask = make([]byte, n/goarch.PtrSize)
- for {
- var addr uintptr
- if hbits, addr = hbits.next(); addr == 0 {
+ for i := uintptr(0); i < n; i += goarch.PtrSize {
+ if hbits.isPointer() {
+ mask[i/goarch.PtrSize] = 1
+ }
+ if !hbits.morePointers() {
+ mask = mask[:i/goarch.PtrSize]
break
}
- mask[(addr-base)/goarch.PtrSize] = 1
- }
- // Callers expect this mask to end at the last pointer.
- for len(mask) > 0 && mask[len(mask)-1] == 0 {
- mask = mask[:len(mask)-1]
+ hbits = hbits.next()
}
return
}