// 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
+// Heap bitmaps
//
// 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/.)
-//
-// 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.
-//
-// The bitmap for noscan spans is set to all zero at span allocation time.
-//
-// The bitmap for unallocated objects in scannable spans is not maintained
+// is stored at the end of a span for small objects and is unrolled at
+// runtime from type metadata for all larger objects. Objects without
+// pointers have neither a bitmap nor associated type metadata.
+//
+// Bits in all cases correspond to words in little-endian order.
+//
+// For small objects, if s is the mspan for the span starting at "start",
+// then s.heapBits() returns a slice containing the bitmap for the whole span.
+// That is, s.heapBits()[0] holds the goarch.PtrSize*8 bits for the first
+// goarch.PtrSize*8 words from "start" through "start+63*ptrSize" in the span.
+// On a related note, small objects are always small enough that their bitmap
+// fits in goarch.PtrSize*8 bits, so writing out bitmap data takes two bitmap
+// writes at most (because object boundaries don't generally lie on
+// s.heapBits()[i] boundaries).
+//
+// For larger objects, if t is the type for the object starting at "start",
+// within some span whose mspan is s, then the bitmap at t.GCData is "tiled"
+// from "start" through "start+s.elemsize".
+// Specifically, the first bit of t.GCData corresponds to the word at "start",
+// the second to the word after "start", and so on up to t.PtrBytes. At t.PtrBytes,
+// we skip to "start+t.Size_" and begin again from there. This process is
+// repeated until we hit "start+s.elemsize".
+// This tiling algorithm supports array data, since the type always refers to
+// the element type of the array. Single objects are considered the same as
+// single-element arrays.
+// The tiling algorithm may scan data past the end of the compiler-recognized
+// object, but any unused data within the allocation slot (i.e. within s.elemsize)
+// is zeroed, so the GC just observes nil pointers.
+// Note that this "tiled" bitmap isn't stored anywhere; it is generated on-the-fly.
+//
+// For objects without their own span, the type metadata is stored in the last
+// word of the allocation slot. For objects with their own span, the type metadata
+// is stored in the mspan.
+//
+// The bitmap for small unallocated objects in scannable spans is not maintained
// (can be junk).
package runtime
"unsafe"
)
+const (
+ // A malloc header is functionally a single type pointer, but
+ // we need to use 8 here to ensure 8-byte alignment of allocations
+ // on 32-bit platforms. It's wasteful, but a lot of code relies on
+ // 8-byte alignment for 8-byte atomics.
+ mallocHeaderSize = 8
+
+ // The minimum object size that has a malloc header, exclusive.
+ //
+ // The size of this value controls overheads from the malloc header.
+ // The minimum size is bound by writeHeapBitsSmall, which assumes that the
+ // pointer bitmap for objects of a size smaller than this doesn't cross
+ // more than one pointer-word boundary. This sets an upper-bound on this
+ // value at the number of bits in a uintptr, multiplied by the pointer
+ // size in bytes.
+ //
+ // We choose a value here that has a natural cutover point in terms of memory
+ // overheads. This value just happens to be the maximum possible value this
+ // can be.
+ //
+ // A span with heap bits in it will have 128 bytes of heap bits on 64-bit
+ // platforms, and 256 bytes of heap bits on 32-bit platforms. The first size
+ // class where malloc headers match this overhead for 64-bit platforms is
+ // 512 bytes (8 KiB / 512 bytes * 8 bytes-per-header = 128 bytes of overhead).
+ // On 32-bit platforms, this same point is the 256 byte size class
+ // (8 KiB / 256 bytes * 8 bytes-per-header = 256 bytes of overhead).
+ //
+ // Guaranteed to be exactly at a size class boundary. The reason this value is
+ // an exclusive minimum is subtle. Suppose we're allocating a 504-byte object
+ // and its rounded up to 512 bytes for the size class. If minSizeForMallocHeader
+ // is 512 and an inclusive minimum, then a comparison against minSizeForMallocHeader
+ // by the two values would produce different results. In other words, the comparison
+ // would not be invariant to size-class rounding. Eschewing this property means a
+ // more complex check or possibly storing additional state to determine whether a
+ // span has malloc headers.
+ minSizeForMallocHeader = goarch.PtrSize * ptrBits
+)
+
+// heapBitsInSpan returns true if the size of an object implies its ptr/scalar
+// data is stored at the end of the span, and is accessible via span.heapBits.
+//
+// Note: this works for both rounded-up sizes (span.elemsize) and unrounded
+// type sizes because minSizeForMallocHeader is guaranteed to be at a size
+// class boundary.
+//
+//go:nosplit
+func heapBitsInSpan(userSize uintptr) bool {
+ // N.B. minSizeForMallocHeader is an exclusive minimum so that this function is
+ // invariant under size-class rounding on its input.
+ return userSize <= minSizeForMallocHeader
+}
+
// heapArenaPtrScalar contains the per-heapArena pointer/scalar metadata for the GC.
type heapArenaPtrScalar struct {
- // bitmap stores the pointer/scalar bitmap for the words in
- // this arena. See mbitmap.go for a description.
- // This array uses 1 bit per word of heap, or 1.6% of the heap size (for 64-bit).
- bitmap [heapArenaBitmapWords]uintptr
-
- // If the ith bit of noMorePtrs is true, then there are no more
- // pointers for the object containing the word described by the
- // high bit of bitmap[i].
- // In that case, bitmap[i+1], ... must be zero until the start
- // of the next object.
- // We never operate on these entries using bit-parallel techniques,
- // so it is ok if they are small. Also, they can't be bigger than
- // uint16 because at that size a single noMorePtrs entry
- // represents 8K of memory, the minimum size of a span. Any larger
- // and we'd have to worry about concurrent updates.
- // This array uses 1 bit per word of bitmap, or .024% of the heap size (for 64-bit).
- noMorePtrs [heapArenaBitmapWords / 8]uint8
-}
-
-// 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
+ // N.B. This is no longer necessary with allocation headers.
+}
- // The next few pointer bits representing words starting at addr.
- // Those bits already returned by next() are zeroed.
+// typePointers is an iterator over the pointers in a heap object.
+//
+// Iteration through this type implements the tiling algorithm described at the
+// top of this file.
+type typePointers struct {
+ // elem is the address of the current array element of type typ being iterated over.
+ // Objects that are not arrays are treated as single-element arrays, in which case
+ // this value does not change.
+ elem uintptr
+
+ // addr is the address the iterator is currently working from and describes
+ // the address of the first word referenced by mask.
+ addr uintptr
+
+ // mask is a bitmask where each bit corresponds to pointer-words after addr.
+ // Bit 0 is the pointer-word at addr, Bit 1 is the next word, and so on.
+ // If a bit is 1, then there is a pointer at that word.
+ // nextFast and next mask out bits in this mask as their pointers are processed.
mask uintptr
- // Number of bits in mask that are valid. mask is always less than 1<<valid.
- valid uintptr
+
+ // typ is a pointer to the type information for the heap object's type.
+ // This may be nil if the object is in a span where heapBitsInSpan(span.elemsize) is true.
+ typ *_type
}
-// 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.
+// typePointersOf returns an iterator over all heap pointers in the range [addr, addr+size).
+//
+// addr and addr+size must be in the range [span.base(), span.limit).
+//
+// Note: addr+size must be passed as the limit argument to the iterator's next method on
+// each iteration. This slightly awkward API is to allow typePointers to be destructured
+// by the compiler.
//
// 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.
- } 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
- }
+func (span *mspan) typePointersOf(addr, size uintptr) typePointers {
+ base := span.objBase(addr)
+ tp := span.typePointersOfUnchecked(base)
+ if base == addr && size == span.elemsize {
+ return tp
}
-
- return heapBits{addr: addr, size: size, mask: mask, valid: valid}
+ return tp.fastForward(addr-tp.addr, addr+size)
}
-// 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.
+// typePointersOfUnchecked is like typePointersOf, but assumes addr is the base
+// pointer of an object in span. It returns an iterator that generates all pointers
+// in the range [addr, addr+span.elemsize).
//
// nosplit because it is used during write barriers and must not be preempted.
//
//go:nosplit
-func (h heapBits) next() (heapBits, uintptr) {
- for {
- if h.mask != 0 {
- var i int
- if goarch.PtrSize == 8 {
- i = sys.TrailingZeros64(uint64(h.mask))
- } else {
- i = sys.TrailingZeros32(uint32(h.mask))
- }
- h.mask ^= uintptr(1) << (i & (ptrBits - 1))
- return h, h.addr + uintptr(i)*goarch.PtrSize
- }
+func (span *mspan) typePointersOfUnchecked(addr uintptr) typePointers {
+ const doubleCheck = false
+ if doubleCheck && span.objBase(addr) != addr {
+ print("runtime: addr=", addr, " base=", span.objBase(addr), "\n")
+ throw("typePointersOfUnchecked consisting of non-base-address for object")
+ }
- // 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
- }
+ spc := span.spanclass
+ if spc.noscan() {
+ return typePointers{}
+ }
+ if heapBitsInSpan(span.elemsize) {
+ // Handle header-less objects.
+ return typePointers{elem: addr, addr: addr, mask: span.heapBitsSmallForAddr(addr)}
+ }
- // Grab more bits and try again.
- h = heapBitsForAddr(h.addr, h.size)
+ // All of these objects have a header.
+ var typ *_type
+ if spc.sizeclass() != 0 {
+ // Pull the allocation header from the last word of the object.
+ typ = *(**_type)(unsafe.Pointer(addr + span.elemsize - mallocHeaderSize))
+ } else {
+ typ = span.largeType
}
+ gcdata := typ.GCData
+ return typePointers{elem: addr, addr: addr, mask: readUintptr(gcdata), typ: typ}
}
-// 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.
+// nextFast is the fast path of next. nextFast is written to be inlineable and,
+// as the name implies, fast.
//
-// if addr, h = h.nextFast(); addr == 0 {
-// if addr, h = h.next(); addr == 0 {
-// ... no more pointers ...
-// }
+// Callers that are performance-critical should iterate using the following
+// pattern:
+//
+// for {
+// var addr uintptr
+// if tp, addr = tp.nextFast(); addr == 0 {
+// if tp, addr = tp.next(limit); addr == 0 {
+// break
+// }
+// }
+// // Use addr.
+// ...
// }
-// ... process pointer at addr ...
//
-// nextFast is designed to be inlineable.
+// nosplit because it is used during write barriers and must not be preempted.
//
//go:nosplit
-func (h heapBits) nextFast() (heapBits, uintptr) {
+func (tp typePointers) nextFast() (typePointers, uintptr) {
// TESTQ/JEQ
- if h.mask == 0 {
- return h, 0
+ if tp.mask == 0 {
+ return tp, 0
}
// BSFQ
var i int
if goarch.PtrSize == 8 {
- i = sys.TrailingZeros64(uint64(h.mask))
+ i = sys.TrailingZeros64(uint64(tp.mask))
} else {
- i = sys.TrailingZeros32(uint32(h.mask))
+ i = sys.TrailingZeros32(uint32(tp.mask))
}
// BTCQ
- h.mask ^= uintptr(1) << (i & (ptrBits - 1))
+ tp.mask ^= uintptr(1) << (i & (ptrBits - 1))
// LEAQ (XX)(XX*8)
- return h, h.addr + uintptr(i)*goarch.PtrSize
+ return tp, tp.addr + uintptr(i)*goarch.PtrSize
+}
+
+// next advances the pointers iterator, returning the updated iterator and
+// the address of the next pointer.
+//
+// limit must be the same each time it is passed to next.
+//
+// nosplit because it is used during write barriers and must not be preempted.
+//
+//go:nosplit
+func (tp typePointers) next(limit uintptr) (typePointers, uintptr) {
+ for {
+ if tp.mask != 0 {
+ return tp.nextFast()
+ }
+
+ // Stop if we don't actually have type information.
+ if tp.typ == nil {
+ return typePointers{}, 0
+ }
+
+ // Advance to the next element if necessary.
+ if tp.addr+goarch.PtrSize*ptrBits >= tp.elem+tp.typ.PtrBytes {
+ tp.elem += tp.typ.Size_
+ tp.addr = tp.elem
+ } else {
+ tp.addr += ptrBits * goarch.PtrSize
+ }
+
+ // Check if we've exceeded the limit with the last update.
+ if tp.addr >= limit {
+ return typePointers{}, 0
+ }
+
+ // Grab more bits and try again.
+ tp.mask = readUintptr(addb(tp.typ.GCData, (tp.addr-tp.elem)/goarch.PtrSize/8))
+ if tp.addr+goarch.PtrSize*ptrBits > limit {
+ bits := (tp.addr + goarch.PtrSize*ptrBits - limit) / goarch.PtrSize
+ tp.mask &^= ((1 << (bits)) - 1) << (ptrBits - bits)
+ }
+ }
+}
+
+// fastForward moves the iterator forward by n bytes. n must be a multiple
+// of goarch.PtrSize. limit must be the same limit passed to next for this
+// iterator.
+//
+// nosplit because it is used during write barriers and must not be preempted.
+//
+//go:nosplit
+func (tp typePointers) fastForward(n, limit uintptr) typePointers {
+ // Basic bounds check.
+ target := tp.addr + n
+ if target >= limit {
+ return typePointers{}
+ }
+ if tp.typ == nil {
+ // Handle small objects.
+ // Clear any bits before the target address.
+ tp.mask &^= (1 << ((target - tp.addr) / goarch.PtrSize)) - 1
+ // Clear any bits past the limit.
+ if tp.addr+goarch.PtrSize*ptrBits > limit {
+ bits := (tp.addr + goarch.PtrSize*ptrBits - limit) / goarch.PtrSize
+ tp.mask &^= ((1 << (bits)) - 1) << (ptrBits - bits)
+ }
+ return tp
+ }
+
+ // Move up elem and addr.
+ // Offsets within an element are always at a ptrBits*goarch.PtrSize boundary.
+ if n >= tp.typ.Size_ {
+ // elem needs to be moved to the element containing
+ // tp.addr + n.
+ oldelem := tp.elem
+ tp.elem += (tp.addr - tp.elem + n) / tp.typ.Size_ * tp.typ.Size_
+ tp.addr = tp.elem + alignDown(n-(tp.elem-oldelem), ptrBits*goarch.PtrSize)
+ } else {
+ tp.addr += alignDown(n, ptrBits*goarch.PtrSize)
+ }
+
+ if tp.addr-tp.elem >= tp.typ.PtrBytes {
+ // We're starting in the non-pointer area of an array.
+ // Move up to the next element.
+ tp.elem += tp.typ.Size_
+ tp.addr = tp.elem
+ tp.mask = readUintptr(tp.typ.GCData)
+
+ // We may have exceeded the limit after this. Bail just like next does.
+ if tp.addr >= limit {
+ return typePointers{}
+ }
+ } else {
+ // Grab the mask, but then clear any bits before the target address and any
+ // bits over the limit.
+ tp.mask = readUintptr(addb(tp.typ.GCData, (tp.addr-tp.elem)/goarch.PtrSize/8))
+ tp.mask &^= (1 << ((target - tp.addr) / goarch.PtrSize)) - 1
+ }
+ if tp.addr+goarch.PtrSize*ptrBits > limit {
+ bits := (tp.addr + goarch.PtrSize*ptrBits - limit) / goarch.PtrSize
+ tp.mask &^= ((1 << (bits)) - 1) << (ptrBits - bits)
+ }
+ return tp
+}
+
+// objBase returns the base pointer for the object containing addr in span.
+//
+// Assumes that addr points into a valid part of span (span.base() <= addr < span.limit).
+//
+//go:nosplit
+func (span *mspan) objBase(addr uintptr) uintptr {
+ return span.base() + span.objIndex(addr)*span.elemsize
}
// bulkBarrierPreWrite executes a write barrier
if !writeBarrier.enabled {
return
}
- if s := spanOf(dst); s == nil {
+ s := spanOf(dst)
+ if s == nil {
// If dst is a global, use the data or BSS bitmaps to
// execute write barriers.
for _, datap := range activeModules() {
// though that should never have.
return
}
-
buf := &getg().m.p.ptr().wbBuf
- h := heapBitsForAddr(dst, size)
+
+ tp := s.typePointersOf(dst, size)
if src == 0 {
for {
var addr uintptr
- if h, addr = h.next(); addr == 0 {
+ if tp, addr = tp.next(dst + size); addr == 0 {
break
}
dstx := (*uintptr)(unsafe.Pointer(addr))
} else {
for {
var addr uintptr
- if h, addr = h.next(); addr == 0 {
+ if tp, addr = tp.next(dst + size); addr == 0 {
break
}
dstx := (*uintptr)(unsafe.Pointer(addr))
return
}
buf := &getg().m.p.ptr().wbBuf
- h := heapBitsForAddr(dst, size)
+ tp := spanOf(dst).typePointersOf(dst, size)
for {
var addr uintptr
- if h, addr = h.next(); addr == 0 {
+ if tp, addr = tp.next(dst + size); addr == 0 {
break
}
srcx := (*uintptr)(unsafe.Pointer(addr - dst + src))
}
// initHeapBits initializes the heap bitmap for a span.
-// If this is a span of single pointer allocations, it initializes all
-// words to pointer. If force is true, clears all bits.
+//
+// TODO(mknyszek): This should set the heap bits for single pointer
+// allocations eagerly to avoid calling heapSetType at allocation time,
+// just to write one bit.
func (s *mspan) initHeapBits(forceClear bool) {
- if forceClear || s.spanclass.noscan() {
- // Set all the pointer bits to zero. We do this once
- // when the span is allocated so we don't have to do it
- // for each object allocation.
- base := s.base()
- size := s.npages * pageSize
- h := writeHeapBitsForAddr(base)
- h.flush(base, size)
- return
- }
- isPtrs := goarch.PtrSize == 8 && s.elemsize == goarch.PtrSize
- if !isPtrs {
- return // nothing to do
- }
- 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 (!s.spanclass.noscan() && heapBitsInSpan(s.elemsize)) || s.isUserArenaChunk {
+ b := s.heapBits()
+ for i := range b {
+ b[i] = 0
+ }
}
- h.flush(s.base(), size)
}
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
+ offset uintptr // offset in span 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) {
+func (s *mspan) writeHeapBits(addr uintptr) (h writeHeapBits) {
+ offset := addr - s.base()
+
// 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
+ h.low = offset / goarch.PtrSize % ptrBits
// round down to heap word that starts the bitmap word.
- h.addr = addr - h.low*goarch.PtrSize
+ h.offset = offset - h.low*goarch.PtrSize
// We don't have any bits yet.
h.mask = 0
// 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 {
+func (h writeHeapBits) write(s *mspan, bits, valid uintptr) writeHeapBits {
if h.valid+valid <= ptrBits {
// Fast path - just accumulate the bits.
h.mask |= bits << h.valid
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
+ idx := h.offset / (ptrBits * goarch.PtrSize)
m := uintptr(1)<<h.low - 1
- ha.bitmap[idx] = ha.bitmap[idx]&m | data
+ bitmap := s.heapBits()
+ bitmap[idx] = 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.offset += ptrBits * goarch.PtrSize
h.low = 0
return h
}
// Add padding of size bytes.
-func (h writeHeapBits) pad(size uintptr) writeHeapBits {
+func (h writeHeapBits) pad(s *mspan, size uintptr) writeHeapBits {
if size == 0 {
return h
}
words := size / goarch.PtrSize
for words > ptrBits {
- h = h.write(0, ptrBits)
+ h = h.write(s, 0, ptrBits)
words -= ptrBits
}
- return h.write(0, words)
+ return h.write(s, 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) {
+func (h writeHeapBits) flush(s *mspan, addr, size uintptr) {
+ offset := addr - s.base()
+
// 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
+ zeros := (offset+size-h.offset)/goarch.PtrSize - h.valid
// Add zero bits up to the bitmap word boundary
if zeros > 0 {
}
// 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
+ bitmap := s.heapBits()
+ idx := h.offset / (ptrBits * goarch.PtrSize)
// 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
+ bitmap[idx] = 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
+ h.offset += 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
// 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
+ idx := h.offset / (ptrBits * goarch.PtrSize)
if zeros < ptrBits {
- ha.bitmap[idx] &^= uintptr(1)<<zeros - 1
+ bitmap[idx] &^= uintptr(1)<<zeros - 1
break
} else if zeros == ptrBits {
- ha.bitmap[idx] = 0
+ bitmap[idx] = 0
break
} else {
- ha.bitmap[idx] = 0
+ bitmap[idx] = 0
zeros -= ptrBits
}
- ha.noMorePtrs[idx/8] |= uint8(1) << (idx % 8)
- h.addr += ptrBits * goarch.PtrSize
+ h.offset += ptrBits * goarch.PtrSize
}
}
-// heapBitsSetType records that the new allocation [x, x+size)
+// heapBits returns the heap ptr/scalar bits stored at the end of the span for
+// small object spans.
+//
+// heapBitsInSpan(span.elemsize) or span.isUserArenaChunk must be true.
+//
+//go:nosplit
+func (span *mspan) heapBits() []uintptr {
+ const doubleCheck = false
+
+ if doubleCheck && !span.isUserArenaChunk {
+ if span.spanclass.noscan() {
+ throw("heapBits called for noscan")
+ }
+ if span.elemsize > minSizeForMallocHeader {
+ throw("heapBits called for span class that should have a malloc header")
+ }
+ }
+ // Find the bitmap at the end of the span.
+ //
+ // Nearly every span with heap bits is exactly one page in size. Arenas are the only exception.
+ if span.npages == 1 {
+ // This will be inlined and constant-folded down.
+ return heapBitsSlice(span.base(), pageSize)
+ }
+ return heapBitsSlice(span.base(), span.npages*pageSize)
+}
+
+// Helper for constructing a slice for the span's heap bits.
+//
+//go:nosplit
+func heapBitsSlice(spanBase, spanSize uintptr) []uintptr {
+ bitmapSize := spanSize / goarch.PtrSize / 8
+ elems := int(bitmapSize / goarch.PtrSize)
+ var sl notInHeapSlice
+ sl = notInHeapSlice{(*notInHeap)(unsafe.Pointer(spanBase + spanSize - bitmapSize)), elems, elems}
+ return *(*[]uintptr)(unsafe.Pointer(&sl))
+}
+
+// heapBitsSmallForAddr loads the heap bits for the object stored at addr from span.heapBits.
+//
+// addr must be the base pointer of an object in the span. heapBitsInSpan(span.elemsize)
+// must be true.
+//
+//go:nosplit
+func (span *mspan) heapBitsSmallForAddr(addr uintptr) uintptr {
+ spanSize := span.npages * pageSize
+ bitmapSize := spanSize / goarch.PtrSize / 8
+ hbits := (*byte)(unsafe.Pointer(span.base() + spanSize - bitmapSize))
+
+ // These objects are always small enough that their bitmaps
+ // fit in a single word, so just load the word or two we need.
+ //
+ // Mirrors mspan.writeHeapBitsSmall.
+ //
+ // We should be using heapBits(), but unfortunately it introduces
+ // both bounds checks panics and throw which causes us to exceed
+ // the nosplit limit in quite a few cases.
+ i := (addr - span.base()) / goarch.PtrSize / ptrBits
+ j := (addr - span.base()) / goarch.PtrSize % ptrBits
+ bits := span.elemsize / goarch.PtrSize
+ word0 := (*uintptr)(unsafe.Pointer(addb(hbits, goarch.PtrSize*(i+0))))
+ word1 := (*uintptr)(unsafe.Pointer(addb(hbits, goarch.PtrSize*(i+1))))
+
+ var read uintptr
+ if j+bits > ptrBits {
+ // Two reads.
+ bits0 := ptrBits - j
+ bits1 := bits - bits0
+ read = *word0 >> j
+ read |= (*word1 & ((1 << bits1) - 1)) << bits0
+ } else {
+ // One read.
+ read = (*word0 >> j) & ((1 << bits) - 1)
+ }
+ return read
+}
+
+// writeHeapBitsSmall writes the heap bits for small objects whose ptr/scalar data is
+// stored as a bitmap at the end of the span.
+//
+// Assumes dataSize is <= ptrBits*goarch.PtrSize. x must be a pointer into the span.
+// heapBitsInSpan(dataSize) must be true. dataSize must be >= typ.Size_.
+//
+//go:nosplit
+func (span *mspan) writeHeapBitsSmall(x, dataSize uintptr, typ *_type) (scanSize uintptr) {
+ // The objects here are always really small, so a single load is sufficient.
+ src0 := readUintptr(typ.GCData)
+
+ // Create repetitions of the bitmap if we have a small array.
+ bits := span.elemsize / goarch.PtrSize
+ scanSize = typ.PtrBytes
+ src := src0
+ switch typ.Size_ {
+ case goarch.PtrSize:
+ src = (1 << (dataSize / goarch.PtrSize)) - 1
+ default:
+ for i := typ.Size_; i < dataSize; i += typ.Size_ {
+ src |= src0 << (i / goarch.PtrSize)
+ scanSize += typ.Size_
+ }
+ }
+
+ // Since we're never writing more than one uintptr's worth of bits, we're either going
+ // to do one or two writes.
+ dst := span.heapBits()
+ o := (x - span.base()) / goarch.PtrSize
+ i := o / ptrBits
+ j := o % ptrBits
+ if j+bits > ptrBits {
+ // Two writes.
+ bits0 := ptrBits - j
+ bits1 := bits - bits0
+ dst[i+0] = dst[i+0]&(^uintptr(0)>>bits0) | (src << j)
+ dst[i+1] = dst[i+1]&^((1<<bits1)-1) | (src >> bits0)
+ } else {
+ // One write.
+ dst[i] = (dst[i] &^ (((1 << bits) - 1) << j)) | (src << j)
+ }
+
+ const doubleCheck = false
+ if doubleCheck {
+ srcRead := span.heapBitsSmallForAddr(x)
+ if srcRead != src {
+ print("runtime: x=", hex(x), " i=", i, " j=", j, " bits=", bits, "\n")
+ print("runtime: dataSize=", dataSize, " typ.Size_=", typ.Size_, " typ.PtrBytes=", typ.PtrBytes, "\n")
+ print("runtime: src0=", hex(src0), " src=", hex(src), " srcRead=", hex(srcRead), "\n")
+ throw("bad pointer bits written for small object")
+ }
+ }
+ return
+}
+
+// For !goexperiment.AllocHeaders.
+func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
+}
+
+// heapSetType 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 word 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
+// malloc does not call heapSetType when there are no pointers.
+//
+// There can be read-write races between heapSetType and things
+// that read the heap metadata like scanobject. However, since
+// heapSetType 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
+// shared memory that belongs 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
-
- if doubleCheck && dataSize%typ.Size_ != 0 {
- throw("heapBitsSetType: dataSize not a multiple of typ.Size")
- }
-
- if goarch.PtrSize == 8 && size == goarch.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),
- // (*mspan).initHeapBits sets the pointer bits for us.
- // Nothing to do here.
- if doubleCheck {
- h, addr := heapBitsForAddr(x, size).next()
- if addr != x {
- throw("heapBitsSetType: pointer bit missing")
- }
- _, addr = h.next()
- if addr != 0 {
- throw("heapBitsSetType: second pointer bit found")
+func heapSetType(x, dataSize uintptr, typ *_type, header **_type, span *mspan) (scanSize uintptr) {
+ const doubleCheck = false
+
+ gctyp := typ
+ if header == nil {
+ if doubleCheck && (!heapBitsInSpan(dataSize) || !heapBitsInSpan(span.elemsize)) {
+ throw("tried to write heap bits, but no heap bits in span")
+ }
+ // Handle the case where we have no malloc header.
+ scanSize = span.writeHeapBitsSmall(x, dataSize, typ)
+ } else {
+ if typ.Kind_&kindGCProg != 0 {
+ // Allocate space to unroll the gcprog. This space will consist of
+ // a dummy _type value and the unrolled gcprog. The dummy _type will
+ // refer to the bitmap, and the mspan will refer to the dummy _type.
+ if span.spanclass.sizeclass() != 0 {
+ throw("GCProg for type that isn't large")
}
+ spaceNeeded := alignUp(unsafe.Sizeof(_type{}), goarch.PtrSize)
+ heapBitsOff := spaceNeeded
+ spaceNeeded += alignUp(typ.PtrBytes/goarch.PtrSize/8, goarch.PtrSize)
+ npages := alignUp(spaceNeeded, pageSize) / pageSize
+ var progSpan *mspan
+ systemstack(func() {
+ progSpan = mheap_.allocManual(npages, spanAllocPtrScalarBits)
+ memclrNoHeapPointers(unsafe.Pointer(progSpan.base()), progSpan.npages*pageSize)
+ })
+ // Write a dummy _type in the new space.
+ //
+ // We only need to write size, PtrBytes, and GCData, since that's all
+ // the GC cares about.
+ gctyp = (*_type)(unsafe.Pointer(progSpan.base()))
+ gctyp.Kind_ |= kindGCProg
+ gctyp.Size_ = typ.Size_
+ gctyp.PtrBytes = typ.PtrBytes
+ gctyp.GCData = (*byte)(add(unsafe.Pointer(progSpan.base()), heapBitsOff))
+
+ // Expand the GC program into space reserved at the end of the object.
+ runGCProg(addb(typ.GCData, 4), gctyp.GCData)
}
- return
+
+ // Write out the header.
+ *header = gctyp
+ scanSize = span.elemsize
}
- h := writeHeapBitsForAddr(x)
+ if doubleCheck {
+ doubleCheckHeapPointers(x, dataSize, gctyp, header, span)
+
+ // To exercise the less common path more often, generate
+ // a random interior pointer and make sure iterating from
+ // that point works correctly too.
+ maxIterBytes := span.elemsize
+ if header == nil {
+ maxIterBytes = dataSize
+ }
+ off := alignUp(uintptr(fastrand())%dataSize, goarch.PtrSize)
+ size := dataSize - off
+ if size == 0 {
+ off -= goarch.PtrSize
+ size += goarch.PtrSize
+ }
+ interior := x + off
+ size -= alignDown(uintptr(fastrand())%size, goarch.PtrSize)
+ if size == 0 {
+ size = goarch.PtrSize
+ }
+ // Round up the type to the size of the type.
+ size = (size + gctyp.Size_ - 1) / gctyp.Size_ * gctyp.Size_
+ if interior+size > x+maxIterBytes {
+ size = x + maxIterBytes - interior
+ }
+ doubleCheckHeapPointersInterior(x, interior, size, dataSize, gctyp, header, span)
+ }
+ return
+}
- // 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
+func doubleCheckHeapPointers(x, dataSize uintptr, typ *_type, header **_type, span *mspan) {
+ // Check that scanning the full object works.
+ tp := span.typePointersOfUnchecked(span.objBase(x))
+ maxIterBytes := span.elemsize
+ if header == nil {
+ maxIterBytes = dataSize
+ }
+ bad := false
+ for i := uintptr(0); i < maxIterBytes; i += goarch.PtrSize {
+ // Compute the pointer bit we want at offset i.
+ want := false
+ if i < span.elemsize {
+ off := i % typ.Size_
+ if off < typ.PtrBytes {
+ j := off / goarch.PtrSize
+ want = *addb(typ.GCData, j/8)>>(j%8)&1 != 0
}
- h = h.write(uintptr(*p), j)
-
- if i+typ.Size_ == dataSize {
- break // no padding after last element
+ }
+ if want {
+ var addr uintptr
+ tp, addr = tp.next(x + span.elemsize)
+ if addr == 0 {
+ println("runtime: found bad iterator")
+ }
+ if addr != x+i {
+ print("runtime: addr=", hex(addr), " x+i=", hex(x+i), "\n")
+ bad = true
}
-
- // Pad with zeros to the start of the next element.
- h = h.pad(typ.Size_ - n*goarch.PtrSize)
}
-
- h.flush(x, size)
-
- // Erase the expanded GC program.
- memclrNoHeapPointers(unsafe.Pointer(obj), (n+7)/8)
- return
}
+ if !bad {
+ var addr uintptr
+ tp, addr = tp.next(x + span.elemsize)
+ if addr == 0 {
+ return
+ }
+ println("runtime: extra pointer:", hex(addr))
+ }
+ print("runtime: hasHeader=", header != nil, " typ.Size_=", typ.Size_, " hasGCProg=", typ.Kind_&kindGCProg != 0, "\n")
+ print("runtime: x=", hex(x), " dataSize=", dataSize, " elemsize=", span.elemsize, "\n")
+ print("runtime: typ=", unsafe.Pointer(typ), " typ.PtrBytes=", typ.PtrBytes, "\n")
+ print("runtime: limit=", hex(x+span.elemsize), "\n")
+ tp = span.typePointersOfUnchecked(x)
+ dumpTypePointers(tp)
+ for {
+ var addr uintptr
+ if tp, addr = tp.next(x + span.elemsize); addr == 0 {
+ println("runtime: would've stopped here")
+ dumpTypePointers(tp)
+ break
+ }
+ print("runtime: addr=", hex(addr), "\n")
+ dumpTypePointers(tp)
+ }
+ throw("heapSetType: pointer entry not correct")
+}
- // Note about sizes:
- //
- // typ.Size is the number of words in the object,
- // and typ.PtrBytes is the number of words in the prefix
- // of the object that contains pointers. That is, the final
- // typ.Size - typ.PtrBytes 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.PtrBytes 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.
- //
- // 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".
-
- ptrs := typ.PtrBytes / goarch.PtrSize
- if typ.Size_ == dataSize { // Single element
- if ptrs <= ptrBits { // Single small element
- m := readUintptr(typ.GCData)
- h = h.write(m, ptrs)
- } else { // Single large element
- p := typ.GCData
- for {
- h = h.write(readUintptr(p), ptrBits)
- p = addb(p, ptrBits/8)
- ptrs -= ptrBits
- if ptrs <= ptrBits {
- break
- }
- }
- m := readUintptr(p)
- h = h.write(m, ptrs)
- }
- } else { // Repeated element
- words := typ.Size_ / goarch.PtrSize // total words, including scalar tail
- if words <= ptrBits { // Repeated small element
- n := dataSize / typ.Size_
- m := readUintptr(typ.GCData)
- // Make larger unit to repeat
- for words <= ptrBits/2 {
- if n&1 != 0 {
- h = h.write(m, words)
- }
- n /= 2
- m |= m << words
- ptrs += words
- words *= 2
- if n == 1 {
- break
- }
+func doubleCheckHeapPointersInterior(x, interior, size, dataSize uintptr, typ *_type, header **_type, span *mspan) {
+ bad := false
+ if interior < x {
+ print("runtime: interior=", hex(interior), " x=", hex(x), "\n")
+ throw("found bad interior pointer")
+ }
+ off := interior - x
+ tp := span.typePointersOf(interior, size)
+ for i := off; i < off+size; i += goarch.PtrSize {
+ // Compute the pointer bit we want at offset i.
+ want := false
+ if i < span.elemsize {
+ off := i % typ.Size_
+ if off < typ.PtrBytes {
+ j := off / goarch.PtrSize
+ want = *addb(typ.GCData, j/8)>>(j%8)&1 != 0
}
- for n > 1 {
- h = h.write(m, words)
- n--
+ }
+ if want {
+ var addr uintptr
+ tp, addr = tp.next(interior + size)
+ if addr == 0 {
+ println("runtime: found bad iterator")
+ bad = true
}
- h = h.write(m, ptrs)
- } else { // Repeated large element
- for i := uintptr(0); true; i += typ.Size_ {
- p := typ.GCData
- j := ptrs
- for j > ptrBits {
- h = h.write(readUintptr(p), ptrBits)
- p = addb(p, ptrBits/8)
- j -= ptrBits
- }
- m := readUintptr(p)
- h = h.write(m, j)
- if i+typ.Size_ == dataSize {
- break // don't need the trailing nonptr bits on the last element.
- }
- // Pad with zeros to the start of the next element.
- h = h.pad(typ.Size_ - typ.PtrBytes)
+ if addr != x+i {
+ print("runtime: addr=", hex(addr), " x+i=", hex(x+i), "\n")
+ bad = true
}
}
}
- h.flush(x, size)
+ if !bad {
+ var addr uintptr
+ tp, addr = tp.next(interior + size)
+ if addr == 0 {
+ return
+ }
+ println("runtime: extra pointer:", hex(addr))
+ }
+ print("runtime: hasHeader=", header != nil, " typ.Size_=", typ.Size_, "\n")
+ print("runtime: x=", hex(x), " dataSize=", dataSize, " elemsize=", span.elemsize, " interior=", hex(interior), " size=", size, "\n")
+ print("runtime: limit=", hex(interior+size), "\n")
+ tp = span.typePointersOf(interior, size)
+ dumpTypePointers(tp)
+ for {
+ var addr uintptr
+ if tp, addr = tp.next(interior + size); addr == 0 {
+ println("runtime: would've stopped here")
+ dumpTypePointers(tp)
+ break
+ }
+ print("runtime: addr=", hex(addr), "\n")
+ dumpTypePointers(tp)
+ }
- 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.PtrBytes {
- j := off / goarch.PtrSize
- want = *addb(typ.GCData, j/8)>>(j%8)&1 != 0
- }
- }
- if want {
- var addr uintptr
- h, addr = h.next()
- if addr != x+i {
- throw("heapBitsSetType: pointer entry not correct")
- }
+ print("runtime: want: ")
+ for i := off; i < off+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.PtrBytes {
+ j := off / goarch.PtrSize
+ want = *addb(typ.GCData, j/8)>>(j%8)&1 != 0
}
}
- if _, addr := h.next(); addr != 0 {
- throw("heapBitsSetType: extra pointer")
+ if want {
+ print("1")
+ } else {
+ print("0")
+ }
+ }
+ println()
+
+ throw("heapSetType: pointer entry not correct")
+}
+
+func dumpTypePointers(tp typePointers) {
+ print("runtime: tp.elem=", hex(tp.elem), " tp.typ=", unsafe.Pointer(tp.typ), "\n")
+ print("runtime: tp.addr=", hex(tp.addr), " tp.mask=")
+ for i := uintptr(0); i < ptrBits; i++ {
+ if tp.mask&(uintptr(1)<<i) != 0 {
+ print("1")
+ } else {
+ print("0")
}
}
+ println()
}
// Testing.
if s.spanclass.noscan() {
return nil
}
- n := s.elemsize
- hbits := heapBitsForAddr(base, n)
- mask = make([]byte, n/goarch.PtrSize)
+ limit := base + s.elemsize
+
+ // Move the base up to the iterator's start, because
+ // we want to hide evidence of a malloc header from the
+ // caller.
+ tp := s.typePointersOfUnchecked(base)
+ base = tp.addr
+
+ // Unroll the full bitmap the GC would actually observe.
+ mask = make([]byte, (limit-base)/goarch.PtrSize)
for {
var addr uintptr
- if hbits, addr = hbits.next(); addr == 0 {
+ if tp, addr = tp.next(limit); addr == 0 {
break
}
mask[(addr-base)/goarch.PtrSize] = 1
}
+
+ // Double-check that every part of the ptr/scalar we're not
+ // showing the caller is zeroed. This keeps us honest that
+ // that information is actually irrelevant.
+ for i := limit; i < s.elemsize; i++ {
+ if *(*byte)(unsafe.Pointer(i)) != 0 {
+ throw("found non-zeroed tail of allocation")
+ }
+ }
+
// Callers expect this mask to end at the last pointer.
for len(mask) > 0 && mask[len(mask)-1] == 0 {
mask = mask[:len(mask)-1]
return
}
-// userArenaHeapBitsSetType is the equivalent of heapBitsSetType but for
+// userArenaHeapBitsSetType is the equivalent of heapSetType but for
// non-slice-backing-store Go values allocated in a user arena chunk. It
-// sets up the heap bitmap for the value with type typ allocated at address ptr.
+// sets up the type metadata for the value with type typ allocated at address ptr.
// base is the base address of the arena chunk.
-func userArenaHeapBitsSetType(typ *_type, ptr unsafe.Pointer, base uintptr) {
- h := writeHeapBitsForAddr(uintptr(ptr))
-
- // Our last allocation might have ended right at a noMorePtrs mark,
- // which we would not have erased. We need to erase that mark here,
- // because we're going to start adding new heap bitmap bits.
- // We only need to clear one mark, because below we make sure to
- // pad out the bits with zeroes and only write one noMorePtrs bit
- // for each new object.
- // (This is only necessary at noMorePtrs boundaries, as noMorePtrs
- // marks within an object allocated with newAt will be erased by
- // the normal writeHeapBitsForAddr mechanism.)
- //
- // Note that we skip this if this is the first allocation in the
- // arena because there's definitely no previous noMorePtrs mark
- // (in fact, we *must* do this, because we're going to try to back
- // up a pointer to fix this up).
- if uintptr(ptr)%(8*goarch.PtrSize*goarch.PtrSize) == 0 && uintptr(ptr) != base {
- // Back up one pointer and rewrite that pointer. That will
- // cause the writeHeapBits implementation to clear the
- // noMorePtrs bit we need to clear.
- r := heapBitsForAddr(uintptr(ptr)-goarch.PtrSize, goarch.PtrSize)
- _, p := r.next()
- b := uintptr(0)
- if p == uintptr(ptr)-goarch.PtrSize {
- b = 1
- }
- h = writeHeapBitsForAddr(uintptr(ptr) - goarch.PtrSize)
- h = h.write(b, 1)
- }
+func userArenaHeapBitsSetType(typ *_type, ptr unsafe.Pointer, s *mspan) {
+ base := s.base()
+ h := s.writeHeapBits(uintptr(ptr))
p := typ.GCData // start of 1-bit pointer mask (or GC program)
var gcProgBits uintptr
if k > ptrBits {
k = ptrBits
}
- h = h.write(readUintptr(addb(p, i/8)), k)
+ h = h.write(s, readUintptr(addb(p, i/8)), k)
}
// Note: we call pad here to ensure we emit explicit 0 bits
// for the pointerless tail of the object. This ensures that
// to clear. We don't need to do this to clear stale noMorePtrs
// markers from previous uses because arena chunk pointer bitmaps
// are always fully cleared when reused.
- h = h.pad(typ.Size_ - typ.PtrBytes)
- h.flush(uintptr(ptr), typ.Size_)
+ h = h.pad(s, typ.Size_-typ.PtrBytes)
+ h.flush(s, uintptr(ptr), typ.Size_)
if typ.Kind_&kindGCProg != 0 {
// Zero out temporary ptrmask buffer inside object.
memclrNoHeapPointers(ptr, (gcProgBits+7)/8)
}
+ // Update the PtrBytes value in the type information. After this
+ // point, the GC will observe the new bitmap.
+ s.largeType.PtrBytes = uintptr(ptr) - base + typ.PtrBytes
+
// Double-check that the bitmap was written out correctly.
- //
- // Derived from heapBitsSetType.
const doubleCheck = false
if doubleCheck {
- size := typ.Size_
- x := uintptr(ptr)
- h := heapBitsForAddr(x, size)
- for i := uintptr(0); i < size; i += goarch.PtrSize {
- // Compute the pointer bit we want at offset i.
- want := false
- off := i % typ.Size_
- if off < typ.PtrBytes {
- j := off / goarch.PtrSize
- want = *addb(typ.GCData, j/8)>>(j%8)&1 != 0
- }
- if want {
- var addr uintptr
- h, addr = h.next()
- if addr != x+i {
- throw("userArenaHeapBitsSetType: pointer entry not correct")
- }
- }
- }
- if _, addr := h.next(); addr != 0 {
- throw("userArenaHeapBitsSetType: extra pointer")
- }
+ doubleCheckHeapPointersInterior(uintptr(ptr), uintptr(ptr), typ.Size_, typ.Size_, typ, &s.largeType, s)
}
}
+
+// For !goexperiment.AllocHeaders, to pass TestIntendedInlining.
+func writeHeapBitsForAddr() {
+ panic("not implemented")
+}
+
+// For !goexperiment.AllocHeaders.
+type heapBits struct {
+}
+
+// For !goexperiment.AllocHeaders.
+//
+//go:nosplit
+func heapBitsForAddr(addr, size uintptr) heapBits {
+ panic("not implemented")
+}
+
+// For !goexperiment.AllocHeaders.
+//
+//go:nosplit
+func (h heapBits) next() (heapBits, uintptr) {
+ panic("not implemented")
+}
+
+// For !goexperiment.AllocHeaders.
+//
+//go:nosplit
+func (h heapBits) nextFast() (heapBits, uintptr) {
+ panic("not implemented")
+}