mirror of https://go.googlesource.com/go
1904 lines
60 KiB
Go
1904 lines
60 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Garbage collector: type and heap bitmaps.
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//
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// Stack, data, and bss bitmaps
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//
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// Stack frames and global variables in the data and bss sections are
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// described by bitmaps with 1 bit per pointer-sized word. A "1" bit
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// means the word is a live pointer to be visited by the GC (referred to
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// as "pointer"). A "0" bit means the word should be ignored by GC
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// (referred to as "scalar", though it could be a dead pointer value).
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//
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// Heap bitmaps
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//
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// The heap bitmap comprises 1 bit for each pointer-sized word in the heap,
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// recording whether a pointer is stored in that word or not. This bitmap
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// is stored at the end of a span for small objects and is unrolled at
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// runtime from type metadata for all larger objects. Objects without
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// pointers have neither a bitmap nor associated type metadata.
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//
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// Bits in all cases correspond to words in little-endian order.
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//
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// For small objects, if s is the mspan for the span starting at "start",
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// then s.heapBits() returns a slice containing the bitmap for the whole span.
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// That is, s.heapBits()[0] holds the goarch.PtrSize*8 bits for the first
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// goarch.PtrSize*8 words from "start" through "start+63*ptrSize" in the span.
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// On a related note, small objects are always small enough that their bitmap
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// fits in goarch.PtrSize*8 bits, so writing out bitmap data takes two bitmap
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// writes at most (because object boundaries don't generally lie on
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// s.heapBits()[i] boundaries).
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//
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// For larger objects, if t is the type for the object starting at "start",
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// within some span whose mspan is s, then the bitmap at t.GCData is "tiled"
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// from "start" through "start+s.elemsize".
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// Specifically, the first bit of t.GCData corresponds to the word at "start",
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// the second to the word after "start", and so on up to t.PtrBytes. At t.PtrBytes,
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// we skip to "start+t.Size_" and begin again from there. This process is
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// repeated until we hit "start+s.elemsize".
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// This tiling algorithm supports array data, since the type always refers to
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// the element type of the array. Single objects are considered the same as
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// single-element arrays.
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// The tiling algorithm may scan data past the end of the compiler-recognized
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// object, but any unused data within the allocation slot (i.e. within s.elemsize)
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// is zeroed, so the GC just observes nil pointers.
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// Note that this "tiled" bitmap isn't stored anywhere; it is generated on-the-fly.
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//
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// For objects without their own span, the type metadata is stored in the first
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// word before the object at the beginning of the allocation slot. For objects
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// with their own span, the type metadata is stored in the mspan.
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//
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// The bitmap for small unallocated objects in scannable spans is not maintained
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// (can be junk).
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package runtime
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import (
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"internal/abi"
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"internal/goarch"
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"internal/runtime/atomic"
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"runtime/internal/sys"
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"unsafe"
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)
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const (
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// A malloc header is functionally a single type pointer, but
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// we need to use 8 here to ensure 8-byte alignment of allocations
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// on 32-bit platforms. It's wasteful, but a lot of code relies on
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// 8-byte alignment for 8-byte atomics.
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mallocHeaderSize = 8
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// The minimum object size that has a malloc header, exclusive.
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//
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// The size of this value controls overheads from the malloc header.
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// The minimum size is bound by writeHeapBitsSmall, which assumes that the
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// pointer bitmap for objects of a size smaller than this doesn't cross
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// more than one pointer-word boundary. This sets an upper-bound on this
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// value at the number of bits in a uintptr, multiplied by the pointer
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// size in bytes.
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//
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// We choose a value here that has a natural cutover point in terms of memory
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// overheads. This value just happens to be the maximum possible value this
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// can be.
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//
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// A span with heap bits in it will have 128 bytes of heap bits on 64-bit
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// platforms, and 256 bytes of heap bits on 32-bit platforms. The first size
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// class where malloc headers match this overhead for 64-bit platforms is
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// 512 bytes (8 KiB / 512 bytes * 8 bytes-per-header = 128 bytes of overhead).
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// On 32-bit platforms, this same point is the 256 byte size class
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// (8 KiB / 256 bytes * 8 bytes-per-header = 256 bytes of overhead).
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//
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// Guaranteed to be exactly at a size class boundary. The reason this value is
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// an exclusive minimum is subtle. Suppose we're allocating a 504-byte object
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// and its rounded up to 512 bytes for the size class. If minSizeForMallocHeader
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// is 512 and an inclusive minimum, then a comparison against minSizeForMallocHeader
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// by the two values would produce different results. In other words, the comparison
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// would not be invariant to size-class rounding. Eschewing this property means a
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// more complex check or possibly storing additional state to determine whether a
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// span has malloc headers.
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minSizeForMallocHeader = goarch.PtrSize * ptrBits
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)
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// heapBitsInSpan returns true if the size of an object implies its ptr/scalar
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// data is stored at the end of the span, and is accessible via span.heapBits.
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//
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// Note: this works for both rounded-up sizes (span.elemsize) and unrounded
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// type sizes because minSizeForMallocHeader is guaranteed to be at a size
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// class boundary.
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//
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//go:nosplit
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func heapBitsInSpan(userSize uintptr) bool {
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// N.B. minSizeForMallocHeader is an exclusive minimum so that this function is
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// invariant under size-class rounding on its input.
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return userSize <= minSizeForMallocHeader
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}
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// typePointers is an iterator over the pointers in a heap object.
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//
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// Iteration through this type implements the tiling algorithm described at the
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// top of this file.
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type typePointers struct {
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// elem is the address of the current array element of type typ being iterated over.
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// Objects that are not arrays are treated as single-element arrays, in which case
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// this value does not change.
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elem uintptr
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// addr is the address the iterator is currently working from and describes
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// the address of the first word referenced by mask.
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addr uintptr
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// mask is a bitmask where each bit corresponds to pointer-words after addr.
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// Bit 0 is the pointer-word at addr, Bit 1 is the next word, and so on.
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// If a bit is 1, then there is a pointer at that word.
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// nextFast and next mask out bits in this mask as their pointers are processed.
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mask uintptr
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// typ is a pointer to the type information for the heap object's type.
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// This may be nil if the object is in a span where heapBitsInSpan(span.elemsize) is true.
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typ *_type
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}
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// typePointersOf returns an iterator over all heap pointers in the range [addr, addr+size).
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//
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// addr and addr+size must be in the range [span.base(), span.limit).
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//
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// Note: addr+size must be passed as the limit argument to the iterator's next method on
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// each iteration. This slightly awkward API is to allow typePointers to be destructured
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// by the compiler.
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//
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// nosplit because it is used during write barriers and must not be preempted.
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//
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//go:nosplit
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func (span *mspan) typePointersOf(addr, size uintptr) typePointers {
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base := span.objBase(addr)
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tp := span.typePointersOfUnchecked(base)
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if base == addr && size == span.elemsize {
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return tp
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}
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return tp.fastForward(addr-tp.addr, addr+size)
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}
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// typePointersOfUnchecked is like typePointersOf, but assumes addr is the base
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// of an allocation slot in a span (the start of the object if no header, the
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// header otherwise). It returns an iterator that generates all pointers
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// in the range [addr, addr+span.elemsize).
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//
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// nosplit because it is used during write barriers and must not be preempted.
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//
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//go:nosplit
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func (span *mspan) typePointersOfUnchecked(addr uintptr) typePointers {
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const doubleCheck = false
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if doubleCheck && span.objBase(addr) != addr {
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print("runtime: addr=", addr, " base=", span.objBase(addr), "\n")
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throw("typePointersOfUnchecked consisting of non-base-address for object")
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}
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spc := span.spanclass
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if spc.noscan() {
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return typePointers{}
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}
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if heapBitsInSpan(span.elemsize) {
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// Handle header-less objects.
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return typePointers{elem: addr, addr: addr, mask: span.heapBitsSmallForAddr(addr)}
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}
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// All of these objects have a header.
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var typ *_type
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if spc.sizeclass() != 0 {
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// Pull the allocation header from the first word of the object.
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typ = *(**_type)(unsafe.Pointer(addr))
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addr += mallocHeaderSize
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} else {
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typ = span.largeType
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if typ == nil {
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// Allow a nil type here for delayed zeroing. See mallocgc.
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return typePointers{}
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}
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}
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gcdata := typ.GCData
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return typePointers{elem: addr, addr: addr, mask: readUintptr(gcdata), typ: typ}
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}
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// typePointersOfType is like typePointersOf, but assumes addr points to one or more
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// contiguous instances of the provided type. The provided type must not be nil and
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// it must not have its type metadata encoded as a gcprog.
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//
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// It returns an iterator that tiles typ.GCData starting from addr. It's the caller's
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// responsibility to limit iteration.
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//
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// nosplit because its callers are nosplit and require all their callees to be nosplit.
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//
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//go:nosplit
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func (span *mspan) typePointersOfType(typ *abi.Type, addr uintptr) typePointers {
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const doubleCheck = false
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if doubleCheck && (typ == nil || typ.Kind_&abi.KindGCProg != 0) {
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throw("bad type passed to typePointersOfType")
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}
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if span.spanclass.noscan() {
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return typePointers{}
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}
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// Since we have the type, pretend we have a header.
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gcdata := typ.GCData
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return typePointers{elem: addr, addr: addr, mask: readUintptr(gcdata), typ: typ}
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}
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// nextFast is the fast path of next. nextFast is written to be inlineable and,
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// as the name implies, fast.
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//
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// Callers that are performance-critical should iterate using the following
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// pattern:
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//
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// for {
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// var addr uintptr
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// if tp, addr = tp.nextFast(); addr == 0 {
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// if tp, addr = tp.next(limit); addr == 0 {
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// break
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// }
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// }
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// // Use addr.
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// ...
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// }
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//
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// nosplit because it is used during write barriers and must not be preempted.
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//
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//go:nosplit
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func (tp typePointers) nextFast() (typePointers, uintptr) {
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// TESTQ/JEQ
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if tp.mask == 0 {
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return tp, 0
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}
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// BSFQ
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var i int
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if goarch.PtrSize == 8 {
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i = sys.TrailingZeros64(uint64(tp.mask))
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} else {
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i = sys.TrailingZeros32(uint32(tp.mask))
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}
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// BTCQ
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tp.mask ^= uintptr(1) << (i & (ptrBits - 1))
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// LEAQ (XX)(XX*8)
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return tp, tp.addr + uintptr(i)*goarch.PtrSize
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}
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// next advances the pointers iterator, returning the updated iterator and
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// the address of the next pointer.
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//
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// limit must be the same each time it is passed to next.
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//
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// nosplit because it is used during write barriers and must not be preempted.
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//
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//go:nosplit
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func (tp typePointers) next(limit uintptr) (typePointers, uintptr) {
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for {
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if tp.mask != 0 {
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return tp.nextFast()
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}
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// Stop if we don't actually have type information.
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if tp.typ == nil {
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return typePointers{}, 0
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}
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// Advance to the next element if necessary.
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if tp.addr+goarch.PtrSize*ptrBits >= tp.elem+tp.typ.PtrBytes {
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tp.elem += tp.typ.Size_
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tp.addr = tp.elem
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} else {
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tp.addr += ptrBits * goarch.PtrSize
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}
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// Check if we've exceeded the limit with the last update.
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if tp.addr >= limit {
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return typePointers{}, 0
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}
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// Grab more bits and try again.
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tp.mask = readUintptr(addb(tp.typ.GCData, (tp.addr-tp.elem)/goarch.PtrSize/8))
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if tp.addr+goarch.PtrSize*ptrBits > limit {
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bits := (tp.addr + goarch.PtrSize*ptrBits - limit) / goarch.PtrSize
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tp.mask &^= ((1 << (bits)) - 1) << (ptrBits - bits)
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}
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}
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}
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// fastForward moves the iterator forward by n bytes. n must be a multiple
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// of goarch.PtrSize. limit must be the same limit passed to next for this
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// iterator.
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//
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// nosplit because it is used during write barriers and must not be preempted.
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//
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//go:nosplit
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func (tp typePointers) fastForward(n, limit uintptr) typePointers {
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// Basic bounds check.
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target := tp.addr + n
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if target >= limit {
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return typePointers{}
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}
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if tp.typ == nil {
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// Handle small objects.
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// Clear any bits before the target address.
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tp.mask &^= (1 << ((target - tp.addr) / goarch.PtrSize)) - 1
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// Clear any bits past the limit.
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if tp.addr+goarch.PtrSize*ptrBits > limit {
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bits := (tp.addr + goarch.PtrSize*ptrBits - limit) / goarch.PtrSize
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tp.mask &^= ((1 << (bits)) - 1) << (ptrBits - bits)
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}
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return tp
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}
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// Move up elem and addr.
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// Offsets within an element are always at a ptrBits*goarch.PtrSize boundary.
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if n >= tp.typ.Size_ {
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// elem needs to be moved to the element containing
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// tp.addr + n.
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oldelem := tp.elem
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tp.elem += (tp.addr - tp.elem + n) / tp.typ.Size_ * tp.typ.Size_
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tp.addr = tp.elem + alignDown(n-(tp.elem-oldelem), ptrBits*goarch.PtrSize)
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} else {
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tp.addr += alignDown(n, ptrBits*goarch.PtrSize)
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}
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if tp.addr-tp.elem >= tp.typ.PtrBytes {
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// We're starting in the non-pointer area of an array.
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// Move up to the next element.
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tp.elem += tp.typ.Size_
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tp.addr = tp.elem
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tp.mask = readUintptr(tp.typ.GCData)
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// We may have exceeded the limit after this. Bail just like next does.
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if tp.addr >= limit {
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return typePointers{}
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}
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} else {
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// Grab the mask, but then clear any bits before the target address and any
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// bits over the limit.
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tp.mask = readUintptr(addb(tp.typ.GCData, (tp.addr-tp.elem)/goarch.PtrSize/8))
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tp.mask &^= (1 << ((target - tp.addr) / goarch.PtrSize)) - 1
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}
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if tp.addr+goarch.PtrSize*ptrBits > limit {
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bits := (tp.addr + goarch.PtrSize*ptrBits - limit) / goarch.PtrSize
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tp.mask &^= ((1 << (bits)) - 1) << (ptrBits - bits)
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}
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return tp
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}
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// objBase returns the base pointer for the object containing addr in span.
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//
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// Assumes that addr points into a valid part of span (span.base() <= addr < span.limit).
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//
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//go:nosplit
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func (span *mspan) objBase(addr uintptr) uintptr {
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return span.base() + span.objIndex(addr)*span.elemsize
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}
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// bulkBarrierPreWrite executes a write barrier
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// for every pointer slot in the memory range [src, src+size),
|
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// using pointer/scalar information from [dst, dst+size).
|
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// This executes the write barriers necessary before a memmove.
|
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// src, dst, and size must be pointer-aligned.
|
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// The range [dst, dst+size) must lie within a single object.
|
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// It does not perform the actual writes.
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//
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// As a special case, src == 0 indicates that this is being used for a
|
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// memclr. bulkBarrierPreWrite will pass 0 for the src of each write
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// barrier.
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//
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// Callers should call bulkBarrierPreWrite immediately before
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// calling memmove(dst, src, size). This function is marked nosplit
|
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// to avoid being preempted; the GC must not stop the goroutine
|
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// between the memmove and the execution of the barriers.
|
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// The caller is also responsible for cgo pointer checks if this
|
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// may be writing Go pointers into non-Go memory.
|
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//
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// Pointer data is not maintained for allocations containing
|
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// no pointers at all; any caller of bulkBarrierPreWrite must first
|
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// make sure the underlying allocation contains pointers, usually
|
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// by checking typ.PtrBytes.
|
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//
|
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// The typ argument is the type of the space at src and dst (and the
|
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// element type if src and dst refer to arrays) and it is optional.
|
||
// If typ is nil, the barrier will still behave as expected and typ
|
||
// is used purely as an optimization. However, it must be used with
|
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// care.
|
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//
|
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// If typ is not nil, then src and dst must point to one or more values
|
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// of type typ. The caller must ensure that the ranges [src, src+size)
|
||
// and [dst, dst+size) refer to one or more whole values of type src and
|
||
// dst (leaving off the pointerless tail of the space is OK). If this
|
||
// precondition is not followed, this function will fail to scan the
|
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// right pointers.
|
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//
|
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// When in doubt, pass nil for typ. That is safe and will always work.
|
||
//
|
||
// Callers must perform cgo checks if goexperiment.CgoCheck2.
|
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//
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//go:nosplit
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func bulkBarrierPreWrite(dst, src, size uintptr, typ *abi.Type) {
|
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if (dst|src|size)&(goarch.PtrSize-1) != 0 {
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throw("bulkBarrierPreWrite: unaligned arguments")
|
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}
|
||
if !writeBarrier.enabled {
|
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return
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}
|
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s := spanOf(dst)
|
||
if s == nil {
|
||
// If dst is a global, use the data or BSS bitmaps to
|
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// execute write barriers.
|
||
for _, datap := range activeModules() {
|
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if datap.data <= dst && dst < datap.edata {
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bulkBarrierBitmap(dst, src, size, dst-datap.data, datap.gcdatamask.bytedata)
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return
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}
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}
|
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for _, datap := range activeModules() {
|
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if datap.bss <= dst && dst < datap.ebss {
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bulkBarrierBitmap(dst, src, size, dst-datap.bss, datap.gcbssmask.bytedata)
|
||
return
|
||
}
|
||
}
|
||
return
|
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} else if s.state.get() != mSpanInUse || dst < s.base() || s.limit <= dst {
|
||
// dst was heap memory at some point, but isn't now.
|
||
// It can't be a global. It must be either our stack,
|
||
// or in the case of direct channel sends, it could be
|
||
// another stack. Either way, no need for barriers.
|
||
// This will also catch if dst is in a freed span,
|
||
// though that should never have.
|
||
return
|
||
}
|
||
buf := &getg().m.p.ptr().wbBuf
|
||
|
||
// Double-check that the bitmaps generated in the two possible paths match.
|
||
const doubleCheck = false
|
||
if doubleCheck {
|
||
doubleCheckTypePointersOfType(s, typ, dst, size)
|
||
}
|
||
|
||
var tp typePointers
|
||
if typ != nil && typ.Kind_&abi.KindGCProg == 0 {
|
||
tp = s.typePointersOfType(typ, dst)
|
||
} else {
|
||
tp = s.typePointersOf(dst, size)
|
||
}
|
||
if src == 0 {
|
||
for {
|
||
var addr uintptr
|
||
if tp, addr = tp.next(dst + size); addr == 0 {
|
||
break
|
||
}
|
||
dstx := (*uintptr)(unsafe.Pointer(addr))
|
||
p := buf.get1()
|
||
p[0] = *dstx
|
||
}
|
||
} else {
|
||
for {
|
||
var addr uintptr
|
||
if tp, addr = tp.next(dst + size); addr == 0 {
|
||
break
|
||
}
|
||
dstx := (*uintptr)(unsafe.Pointer(addr))
|
||
srcx := (*uintptr)(unsafe.Pointer(src + (addr - dst)))
|
||
p := buf.get2()
|
||
p[0] = *dstx
|
||
p[1] = *srcx
|
||
}
|
||
}
|
||
}
|
||
|
||
// bulkBarrierPreWriteSrcOnly is like bulkBarrierPreWrite but
|
||
// does not execute write barriers for [dst, dst+size).
|
||
//
|
||
// In addition to the requirements of bulkBarrierPreWrite
|
||
// callers need to ensure [dst, dst+size) is zeroed.
|
||
//
|
||
// This is used for special cases where e.g. dst was just
|
||
// created and zeroed with malloc.
|
||
//
|
||
// The type of the space can be provided purely as an optimization.
|
||
// See bulkBarrierPreWrite's comment for more details -- use this
|
||
// optimization with great care.
|
||
//
|
||
//go:nosplit
|
||
func bulkBarrierPreWriteSrcOnly(dst, src, size uintptr, typ *abi.Type) {
|
||
if (dst|src|size)&(goarch.PtrSize-1) != 0 {
|
||
throw("bulkBarrierPreWrite: unaligned arguments")
|
||
}
|
||
if !writeBarrier.enabled {
|
||
return
|
||
}
|
||
buf := &getg().m.p.ptr().wbBuf
|
||
s := spanOf(dst)
|
||
|
||
// Double-check that the bitmaps generated in the two possible paths match.
|
||
const doubleCheck = false
|
||
if doubleCheck {
|
||
doubleCheckTypePointersOfType(s, typ, dst, size)
|
||
}
|
||
|
||
var tp typePointers
|
||
if typ != nil && typ.Kind_&abi.KindGCProg == 0 {
|
||
tp = s.typePointersOfType(typ, dst)
|
||
} else {
|
||
tp = s.typePointersOf(dst, size)
|
||
}
|
||
for {
|
||
var addr uintptr
|
||
if tp, addr = tp.next(dst + size); addr == 0 {
|
||
break
|
||
}
|
||
srcx := (*uintptr)(unsafe.Pointer(addr - dst + src))
|
||
p := buf.get1()
|
||
p[0] = *srcx
|
||
}
|
||
}
|
||
|
||
// initHeapBits initializes the heap bitmap for a span.
|
||
//
|
||
// 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 (!s.spanclass.noscan() && heapBitsInSpan(s.elemsize)) || s.isUserArenaChunk {
|
||
b := s.heapBits()
|
||
clear(b)
|
||
}
|
||
}
|
||
|
||
// heapBits returns the heap ptr/scalar bits stored at the end of the span for
|
||
// small object spans and heap arena spans.
|
||
//
|
||
// Note that the uintptr of each element means something different for small object
|
||
// spans and for heap arena spans. Small object spans are easy: they're never interpreted
|
||
// as anything but uintptr, so they're immune to differences in endianness. However, the
|
||
// heapBits for user arena spans is exposed through a dummy type descriptor, so the byte
|
||
// ordering needs to match the same byte ordering the compiler would emit. The compiler always
|
||
// emits the bitmap data in little endian byte ordering, so on big endian platforms these
|
||
// uintptrs will have their byte orders swapped from what they normally would be.
|
||
//
|
||
// 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
|
||
}
|
||
|
||
// 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 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
|
||
// 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 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_&abi.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.Size_ = typ.Size_
|
||
gctyp.PtrBytes = typ.PtrBytes
|
||
gctyp.GCData = (*byte)(add(unsafe.Pointer(progSpan.base()), heapBitsOff))
|
||
gctyp.TFlag = abi.TFlagUnrolledBitmap
|
||
|
||
// Expand the GC program into space reserved at the end of the new span.
|
||
runGCProg(addb(typ.GCData, 4), gctyp.GCData)
|
||
}
|
||
|
||
// Write out the header.
|
||
*header = gctyp
|
||
scanSize = span.elemsize
|
||
}
|
||
|
||
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(cheaprand())%dataSize, goarch.PtrSize)
|
||
size := dataSize - off
|
||
if size == 0 {
|
||
off -= goarch.PtrSize
|
||
size += goarch.PtrSize
|
||
}
|
||
interior := x + off
|
||
size -= alignDown(uintptr(cheaprand())%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
|
||
}
|
||
|
||
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
|
||
}
|
||
}
|
||
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
|
||
}
|
||
}
|
||
}
|
||
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_&abi.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")
|
||
}
|
||
|
||
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
|
||
}
|
||
}
|
||
if want {
|
||
var addr uintptr
|
||
tp, addr = tp.next(interior + size)
|
||
if addr == 0 {
|
||
println("runtime: found bad iterator")
|
||
bad = true
|
||
}
|
||
if addr != x+i {
|
||
print("runtime: addr=", hex(addr), " x+i=", hex(x+i), "\n")
|
||
bad = true
|
||
}
|
||
}
|
||
}
|
||
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)
|
||
}
|
||
|
||
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 want {
|
||
print("1")
|
||
} else {
|
||
print("0")
|
||
}
|
||
}
|
||
println()
|
||
|
||
throw("heapSetType: pointer entry not correct")
|
||
}
|
||
|
||
//go:nosplit
|
||
func doubleCheckTypePointersOfType(s *mspan, typ *_type, addr, size uintptr) {
|
||
if typ == nil || typ.Kind_&abi.KindGCProg != 0 {
|
||
return
|
||
}
|
||
if typ.Kind_&abi.KindMask == abi.Interface {
|
||
// Interfaces are unfortunately inconsistently handled
|
||
// when it comes to the type pointer, so it's easy to
|
||
// produce a lot of false positives here.
|
||
return
|
||
}
|
||
tp0 := s.typePointersOfType(typ, addr)
|
||
tp1 := s.typePointersOf(addr, size)
|
||
failed := false
|
||
for {
|
||
var addr0, addr1 uintptr
|
||
tp0, addr0 = tp0.next(addr + size)
|
||
tp1, addr1 = tp1.next(addr + size)
|
||
if addr0 != addr1 {
|
||
failed = true
|
||
break
|
||
}
|
||
if addr0 == 0 {
|
||
break
|
||
}
|
||
}
|
||
if failed {
|
||
tp0 := s.typePointersOfType(typ, addr)
|
||
tp1 := s.typePointersOf(addr, size)
|
||
print("runtime: addr=", hex(addr), " size=", size, "\n")
|
||
print("runtime: type=", toRType(typ).string(), "\n")
|
||
dumpTypePointers(tp0)
|
||
dumpTypePointers(tp1)
|
||
for {
|
||
var addr0, addr1 uintptr
|
||
tp0, addr0 = tp0.next(addr + size)
|
||
tp1, addr1 = tp1.next(addr + size)
|
||
print("runtime: ", hex(addr0), " ", hex(addr1), "\n")
|
||
if addr0 == 0 && addr1 == 0 {
|
||
break
|
||
}
|
||
}
|
||
throw("mismatch between typePointersOfType and typePointersOf")
|
||
}
|
||
}
|
||
|
||
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()
|
||
}
|
||
|
||
// addb returns the byte pointer p+n.
|
||
//
|
||
//go:nowritebarrier
|
||
//go:nosplit
|
||
func addb(p *byte, n uintptr) *byte {
|
||
// Note: wrote out full expression instead of calling add(p, n)
|
||
// to reduce the number of temporaries generated by the
|
||
// compiler for this trivial expression during inlining.
|
||
return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + n))
|
||
}
|
||
|
||
// subtractb returns the byte pointer p-n.
|
||
//
|
||
//go:nowritebarrier
|
||
//go:nosplit
|
||
func subtractb(p *byte, n uintptr) *byte {
|
||
// Note: wrote out full expression instead of calling add(p, -n)
|
||
// to reduce the number of temporaries generated by the
|
||
// compiler for this trivial expression during inlining.
|
||
return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) - n))
|
||
}
|
||
|
||
// add1 returns the byte pointer p+1.
|
||
//
|
||
//go:nowritebarrier
|
||
//go:nosplit
|
||
func add1(p *byte) *byte {
|
||
// Note: wrote out full expression instead of calling addb(p, 1)
|
||
// to reduce the number of temporaries generated by the
|
||
// compiler for this trivial expression during inlining.
|
||
return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + 1))
|
||
}
|
||
|
||
// subtract1 returns the byte pointer p-1.
|
||
//
|
||
// nosplit because it is used during write barriers and must not be preempted.
|
||
//
|
||
//go:nowritebarrier
|
||
//go:nosplit
|
||
func subtract1(p *byte) *byte {
|
||
// Note: wrote out full expression instead of calling subtractb(p, 1)
|
||
// to reduce the number of temporaries generated by the
|
||
// compiler for this trivial expression during inlining.
|
||
return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) - 1))
|
||
}
|
||
|
||
// markBits provides access to the mark bit for an object in the heap.
|
||
// bytep points to the byte holding the mark bit.
|
||
// mask is a byte with a single bit set that can be &ed with *bytep
|
||
// to see if the bit has been set.
|
||
// *m.byte&m.mask != 0 indicates the mark bit is set.
|
||
// index can be used along with span information to generate
|
||
// the address of the object in the heap.
|
||
// We maintain one set of mark bits for allocation and one for
|
||
// marking purposes.
|
||
type markBits struct {
|
||
bytep *uint8
|
||
mask uint8
|
||
index uintptr
|
||
}
|
||
|
||
//go:nosplit
|
||
func (s *mspan) allocBitsForIndex(allocBitIndex uintptr) markBits {
|
||
bytep, mask := s.allocBits.bitp(allocBitIndex)
|
||
return markBits{bytep, mask, allocBitIndex}
|
||
}
|
||
|
||
// refillAllocCache takes 8 bytes s.allocBits starting at whichByte
|
||
// and negates them so that ctz (count trailing zeros) instructions
|
||
// can be used. It then places these 8 bytes into the cached 64 bit
|
||
// s.allocCache.
|
||
func (s *mspan) refillAllocCache(whichByte uint16) {
|
||
bytes := (*[8]uint8)(unsafe.Pointer(s.allocBits.bytep(uintptr(whichByte))))
|
||
aCache := uint64(0)
|
||
aCache |= uint64(bytes[0])
|
||
aCache |= uint64(bytes[1]) << (1 * 8)
|
||
aCache |= uint64(bytes[2]) << (2 * 8)
|
||
aCache |= uint64(bytes[3]) << (3 * 8)
|
||
aCache |= uint64(bytes[4]) << (4 * 8)
|
||
aCache |= uint64(bytes[5]) << (5 * 8)
|
||
aCache |= uint64(bytes[6]) << (6 * 8)
|
||
aCache |= uint64(bytes[7]) << (7 * 8)
|
||
s.allocCache = ^aCache
|
||
}
|
||
|
||
// nextFreeIndex returns the index of the next free object in s at
|
||
// or after s.freeindex.
|
||
// There are hardware instructions that can be used to make this
|
||
// faster if profiling warrants it.
|
||
func (s *mspan) nextFreeIndex() uint16 {
|
||
sfreeindex := s.freeindex
|
||
snelems := s.nelems
|
||
if sfreeindex == snelems {
|
||
return sfreeindex
|
||
}
|
||
if sfreeindex > snelems {
|
||
throw("s.freeindex > s.nelems")
|
||
}
|
||
|
||
aCache := s.allocCache
|
||
|
||
bitIndex := sys.TrailingZeros64(aCache)
|
||
for bitIndex == 64 {
|
||
// Move index to start of next cached bits.
|
||
sfreeindex = (sfreeindex + 64) &^ (64 - 1)
|
||
if sfreeindex >= snelems {
|
||
s.freeindex = snelems
|
||
return snelems
|
||
}
|
||
whichByte := sfreeindex / 8
|
||
// Refill s.allocCache with the next 64 alloc bits.
|
||
s.refillAllocCache(whichByte)
|
||
aCache = s.allocCache
|
||
bitIndex = sys.TrailingZeros64(aCache)
|
||
// nothing available in cached bits
|
||
// grab the next 8 bytes and try again.
|
||
}
|
||
result := sfreeindex + uint16(bitIndex)
|
||
if result >= snelems {
|
||
s.freeindex = snelems
|
||
return snelems
|
||
}
|
||
|
||
s.allocCache >>= uint(bitIndex + 1)
|
||
sfreeindex = result + 1
|
||
|
||
if sfreeindex%64 == 0 && sfreeindex != snelems {
|
||
// We just incremented s.freeindex so it isn't 0.
|
||
// As each 1 in s.allocCache was encountered and used for allocation
|
||
// it was shifted away. At this point s.allocCache contains all 0s.
|
||
// Refill s.allocCache so that it corresponds
|
||
// to the bits at s.allocBits starting at s.freeindex.
|
||
whichByte := sfreeindex / 8
|
||
s.refillAllocCache(whichByte)
|
||
}
|
||
s.freeindex = sfreeindex
|
||
return result
|
||
}
|
||
|
||
// isFree reports whether the index'th object in s is unallocated.
|
||
//
|
||
// The caller must ensure s.state is mSpanInUse, and there must have
|
||
// been no preemption points since ensuring this (which could allow a
|
||
// GC transition, which would allow the state to change).
|
||
func (s *mspan) isFree(index uintptr) bool {
|
||
if index < uintptr(s.freeIndexForScan) {
|
||
return false
|
||
}
|
||
bytep, mask := s.allocBits.bitp(index)
|
||
return *bytep&mask == 0
|
||
}
|
||
|
||
// divideByElemSize returns n/s.elemsize.
|
||
// n must be within [0, s.npages*_PageSize),
|
||
// or may be exactly s.npages*_PageSize
|
||
// if s.elemsize is from sizeclasses.go.
|
||
//
|
||
// nosplit, because it is called by objIndex, which is nosplit
|
||
//
|
||
//go:nosplit
|
||
func (s *mspan) divideByElemSize(n uintptr) uintptr {
|
||
const doubleCheck = false
|
||
|
||
// See explanation in mksizeclasses.go's computeDivMagic.
|
||
q := uintptr((uint64(n) * uint64(s.divMul)) >> 32)
|
||
|
||
if doubleCheck && q != n/s.elemsize {
|
||
println(n, "/", s.elemsize, "should be", n/s.elemsize, "but got", q)
|
||
throw("bad magic division")
|
||
}
|
||
return q
|
||
}
|
||
|
||
// nosplit, because it is called by other nosplit code like findObject
|
||
//
|
||
//go:nosplit
|
||
func (s *mspan) objIndex(p uintptr) uintptr {
|
||
return s.divideByElemSize(p - s.base())
|
||
}
|
||
|
||
func markBitsForAddr(p uintptr) markBits {
|
||
s := spanOf(p)
|
||
objIndex := s.objIndex(p)
|
||
return s.markBitsForIndex(objIndex)
|
||
}
|
||
|
||
func (s *mspan) markBitsForIndex(objIndex uintptr) markBits {
|
||
bytep, mask := s.gcmarkBits.bitp(objIndex)
|
||
return markBits{bytep, mask, objIndex}
|
||
}
|
||
|
||
func (s *mspan) markBitsForBase() markBits {
|
||
return markBits{&s.gcmarkBits.x, uint8(1), 0}
|
||
}
|
||
|
||
// isMarked reports whether mark bit m is set.
|
||
func (m markBits) isMarked() bool {
|
||
return *m.bytep&m.mask != 0
|
||
}
|
||
|
||
// setMarked sets the marked bit in the markbits, atomically.
|
||
func (m markBits) setMarked() {
|
||
// Might be racing with other updates, so use atomic update always.
|
||
// We used to be clever here and use a non-atomic update in certain
|
||
// cases, but it's not worth the risk.
|
||
atomic.Or8(m.bytep, m.mask)
|
||
}
|
||
|
||
// setMarkedNonAtomic sets the marked bit in the markbits, non-atomically.
|
||
func (m markBits) setMarkedNonAtomic() {
|
||
*m.bytep |= m.mask
|
||
}
|
||
|
||
// clearMarked clears the marked bit in the markbits, atomically.
|
||
func (m markBits) clearMarked() {
|
||
// Might be racing with other updates, so use atomic update always.
|
||
// We used to be clever here and use a non-atomic update in certain
|
||
// cases, but it's not worth the risk.
|
||
atomic.And8(m.bytep, ^m.mask)
|
||
}
|
||
|
||
// markBitsForSpan returns the markBits for the span base address base.
|
||
func markBitsForSpan(base uintptr) (mbits markBits) {
|
||
mbits = markBitsForAddr(base)
|
||
if mbits.mask != 1 {
|
||
throw("markBitsForSpan: unaligned start")
|
||
}
|
||
return mbits
|
||
}
|
||
|
||
// advance advances the markBits to the next object in the span.
|
||
func (m *markBits) advance() {
|
||
if m.mask == 1<<7 {
|
||
m.bytep = (*uint8)(unsafe.Pointer(uintptr(unsafe.Pointer(m.bytep)) + 1))
|
||
m.mask = 1
|
||
} else {
|
||
m.mask = m.mask << 1
|
||
}
|
||
m.index++
|
||
}
|
||
|
||
// 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))
|
||
|
||
// badPointer throws bad pointer in heap panic.
|
||
func badPointer(s *mspan, p, refBase, refOff uintptr) {
|
||
// Typically this indicates an incorrect use
|
||
// of unsafe or cgo to store a bad pointer in
|
||
// the Go heap. It may also indicate a runtime
|
||
// bug.
|
||
//
|
||
// TODO(austin): We could be more aggressive
|
||
// and detect pointers to unallocated objects
|
||
// in allocated spans.
|
||
printlock()
|
||
print("runtime: pointer ", hex(p))
|
||
if s != nil {
|
||
state := s.state.get()
|
||
if state != mSpanInUse {
|
||
print(" to unallocated span")
|
||
} else {
|
||
print(" to unused region of span")
|
||
}
|
||
print(" span.base()=", hex(s.base()), " span.limit=", hex(s.limit), " span.state=", state)
|
||
}
|
||
print("\n")
|
||
if refBase != 0 {
|
||
print("runtime: found in object at *(", hex(refBase), "+", hex(refOff), ")\n")
|
||
gcDumpObject("object", refBase, refOff)
|
||
}
|
||
getg().m.traceback = 2
|
||
throw("found bad pointer in Go heap (incorrect use of unsafe or cgo?)")
|
||
}
|
||
|
||
// findObject returns the base address for the heap object containing
|
||
// the address p, the object's span, and the index of the object in s.
|
||
// If p does not point into a heap object, it returns base == 0.
|
||
//
|
||
// If p points is an invalid heap pointer and debug.invalidptr != 0,
|
||
// findObject panics.
|
||
//
|
||
// refBase and refOff optionally give the base address of the object
|
||
// in which the pointer p was found and the byte offset at which it
|
||
// was found. These are used for error reporting.
|
||
//
|
||
// It is nosplit so it is safe for p to be a pointer to the current goroutine's stack.
|
||
// Since p is a uintptr, it would not be adjusted if the stack were to move.
|
||
//
|
||
//go:nosplit
|
||
func findObject(p, refBase, refOff uintptr) (base uintptr, s *mspan, objIndex uintptr) {
|
||
s = spanOf(p)
|
||
// If s is nil, the virtual address has never been part of the heap.
|
||
// This pointer may be to some mmap'd region, so we allow it.
|
||
if s == nil {
|
||
if (GOARCH == "amd64" || GOARCH == "arm64") && p == clobberdeadPtr && debug.invalidptr != 0 {
|
||
// Crash if clobberdeadPtr is seen. Only on AMD64 and ARM64 for now,
|
||
// as they are the only platform where compiler's clobberdead mode is
|
||
// implemented. On these platforms clobberdeadPtr cannot be a valid address.
|
||
badPointer(s, p, refBase, refOff)
|
||
}
|
||
return
|
||
}
|
||
// If p is a bad pointer, it may not be in s's bounds.
|
||
//
|
||
// Check s.state to synchronize with span initialization
|
||
// before checking other fields. See also spanOfHeap.
|
||
if state := s.state.get(); state != mSpanInUse || p < s.base() || p >= s.limit {
|
||
// Pointers into stacks are also ok, the runtime manages these explicitly.
|
||
if state == mSpanManual {
|
||
return
|
||
}
|
||
// The following ensures that we are rigorous about what data
|
||
// structures hold valid pointers.
|
||
if debug.invalidptr != 0 {
|
||
badPointer(s, p, refBase, refOff)
|
||
}
|
||
return
|
||
}
|
||
|
||
objIndex = s.objIndex(p)
|
||
base = s.base() + objIndex*s.elemsize
|
||
return
|
||
}
|
||
|
||
// reflect_verifyNotInHeapPtr reports whether converting the not-in-heap pointer into a unsafe.Pointer is ok.
|
||
//
|
||
//go:linkname reflect_verifyNotInHeapPtr reflect.verifyNotInHeapPtr
|
||
func reflect_verifyNotInHeapPtr(p uintptr) bool {
|
||
// Conversion to a pointer is ok as long as findObject above does not call badPointer.
|
||
// Since we're already promised that p doesn't point into the heap, just disallow heap
|
||
// pointers and the special clobbered pointer.
|
||
return spanOf(p) == nil && p != clobberdeadPtr
|
||
}
|
||
|
||
const ptrBits = 8 * goarch.PtrSize
|
||
|
||
// bulkBarrierBitmap executes write barriers for copying from [src,
|
||
// src+size) to [dst, dst+size) using a 1-bit pointer bitmap. src is
|
||
// assumed to start maskOffset bytes into the data covered by the
|
||
// bitmap in bits (which may not be a multiple of 8).
|
||
//
|
||
// This is used by bulkBarrierPreWrite for writes to data and BSS.
|
||
//
|
||
//go:nosplit
|
||
func bulkBarrierBitmap(dst, src, size, maskOffset uintptr, bits *uint8) {
|
||
word := maskOffset / goarch.PtrSize
|
||
bits = addb(bits, word/8)
|
||
mask := uint8(1) << (word % 8)
|
||
|
||
buf := &getg().m.p.ptr().wbBuf
|
||
for i := uintptr(0); i < size; i += goarch.PtrSize {
|
||
if mask == 0 {
|
||
bits = addb(bits, 1)
|
||
if *bits == 0 {
|
||
// Skip 8 words.
|
||
i += 7 * goarch.PtrSize
|
||
continue
|
||
}
|
||
mask = 1
|
||
}
|
||
if *bits&mask != 0 {
|
||
dstx := (*uintptr)(unsafe.Pointer(dst + i))
|
||
if src == 0 {
|
||
p := buf.get1()
|
||
p[0] = *dstx
|
||
} else {
|
||
srcx := (*uintptr)(unsafe.Pointer(src + i))
|
||
p := buf.get2()
|
||
p[0] = *dstx
|
||
p[1] = *srcx
|
||
}
|
||
}
|
||
mask <<= 1
|
||
}
|
||
}
|
||
|
||
// typeBitsBulkBarrier executes a write barrier for every
|
||
// pointer that would be copied from [src, src+size) to [dst,
|
||
// dst+size) by a memmove using the type bitmap to locate those
|
||
// pointer slots.
|
||
//
|
||
// The type typ must correspond exactly to [src, src+size) and [dst, dst+size).
|
||
// dst, src, and size must be pointer-aligned.
|
||
// The type typ must have a plain bitmap, not a GC program.
|
||
// The only use of this function is in channel sends, and the
|
||
// 64 kB channel element limit takes care of this for us.
|
||
//
|
||
// Must not be preempted because it typically runs right before memmove,
|
||
// and the GC must observe them as an atomic action.
|
||
//
|
||
// Callers must perform cgo checks if goexperiment.CgoCheck2.
|
||
//
|
||
//go:nosplit
|
||
func typeBitsBulkBarrier(typ *_type, dst, src, size uintptr) {
|
||
if typ == nil {
|
||
throw("runtime: typeBitsBulkBarrier without type")
|
||
}
|
||
if typ.Size_ != size {
|
||
println("runtime: typeBitsBulkBarrier with type ", toRType(typ).string(), " of size ", typ.Size_, " but memory size", size)
|
||
throw("runtime: invalid typeBitsBulkBarrier")
|
||
}
|
||
if typ.Kind_&abi.KindGCProg != 0 {
|
||
println("runtime: typeBitsBulkBarrier with type ", toRType(typ).string(), " with GC prog")
|
||
throw("runtime: invalid typeBitsBulkBarrier")
|
||
}
|
||
if !writeBarrier.enabled {
|
||
return
|
||
}
|
||
ptrmask := typ.GCData
|
||
buf := &getg().m.p.ptr().wbBuf
|
||
var bits uint32
|
||
for i := uintptr(0); i < typ.PtrBytes; i += goarch.PtrSize {
|
||
if i&(goarch.PtrSize*8-1) == 0 {
|
||
bits = uint32(*ptrmask)
|
||
ptrmask = addb(ptrmask, 1)
|
||
} else {
|
||
bits = bits >> 1
|
||
}
|
||
if bits&1 != 0 {
|
||
dstx := (*uintptr)(unsafe.Pointer(dst + i))
|
||
srcx := (*uintptr)(unsafe.Pointer(src + i))
|
||
p := buf.get2()
|
||
p[0] = *dstx
|
||
p[1] = *srcx
|
||
}
|
||
}
|
||
}
|
||
|
||
// countAlloc returns the number of objects allocated in span s by
|
||
// scanning the mark bitmap.
|
||
func (s *mspan) countAlloc() int {
|
||
count := 0
|
||
bytes := divRoundUp(uintptr(s.nelems), 8)
|
||
// Iterate over each 8-byte chunk and count allocations
|
||
// with an intrinsic. Note that newMarkBits guarantees that
|
||
// gcmarkBits will be 8-byte aligned, so we don't have to
|
||
// worry about edge cases, irrelevant bits will simply be zero.
|
||
for i := uintptr(0); i < bytes; i += 8 {
|
||
// Extract 64 bits from the byte pointer and get a OnesCount.
|
||
// Note that the unsafe cast here doesn't preserve endianness,
|
||
// but that's OK. We only care about how many bits are 1, not
|
||
// about the order we discover them in.
|
||
mrkBits := *(*uint64)(unsafe.Pointer(s.gcmarkBits.bytep(i)))
|
||
count += sys.OnesCount64(mrkBits)
|
||
}
|
||
return count
|
||
}
|
||
|
||
// Read the bytes starting at the aligned pointer p into a uintptr.
|
||
// Read is little-endian.
|
||
func readUintptr(p *byte) uintptr {
|
||
x := *(*uintptr)(unsafe.Pointer(p))
|
||
if goarch.BigEndian {
|
||
if goarch.PtrSize == 8 {
|
||
return uintptr(sys.Bswap64(uint64(x)))
|
||
}
|
||
return uintptr(sys.Bswap32(uint32(x)))
|
||
}
|
||
return x
|
||
}
|
||
|
||
var debugPtrmask struct {
|
||
lock mutex
|
||
data *byte
|
||
}
|
||
|
||
// 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.
|
||
func progToPointerMask(prog *byte, size uintptr) bitvector {
|
||
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])
|
||
if x[len(x)-1] != 0xa1 {
|
||
throw("progToPointerMask: overflow")
|
||
}
|
||
return bitvector{int32(n), &x[0]}
|
||
}
|
||
|
||
// Packed GC pointer bitmaps, aka GC programs.
|
||
//
|
||
// For large types containing arrays, the type information has a
|
||
// natural repetition that can be encoded to save space in the
|
||
// binary and in the memory representation of the type information.
|
||
//
|
||
// The encoding is a simple Lempel-Ziv style bytecode machine
|
||
// with the following instructions:
|
||
//
|
||
// 00000000: stop
|
||
// 0nnnnnnn: emit n bits copied from the next (n+7)/8 bytes
|
||
// 10000000 n c: repeat the previous n bits c times; n, c are varints
|
||
// 1nnnnnnn c: repeat the previous n bits c times; c is a varint
|
||
|
||
// runGCProg returns the number of 1-bit entries written to memory.
|
||
func runGCProg(prog, dst *byte) uintptr {
|
||
dstStart := dst
|
||
|
||
// Bits waiting to be written to memory.
|
||
var bits uintptr
|
||
var nbits uintptr
|
||
|
||
p := prog
|
||
Run:
|
||
for {
|
||
// Flush accumulated full bytes.
|
||
// The rest of the loop assumes that nbits <= 7.
|
||
for ; nbits >= 8; nbits -= 8 {
|
||
*dst = uint8(bits)
|
||
dst = add1(dst)
|
||
bits >>= 8
|
||
}
|
||
|
||
// Process one instruction.
|
||
inst := uintptr(*p)
|
||
p = add1(p)
|
||
n := inst & 0x7F
|
||
if inst&0x80 == 0 {
|
||
// Literal bits; n == 0 means end of program.
|
||
if n == 0 {
|
||
// Program is over.
|
||
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 n %= 8; n > 0 {
|
||
bits |= uintptr(*p) << nbits
|
||
p = add1(p)
|
||
nbits += n
|
||
}
|
||
continue Run
|
||
}
|
||
|
||
// Repeat. If n == 0, it is encoded in a varint in the next bytes.
|
||
if n == 0 {
|
||
for off := uint(0); ; off += 7 {
|
||
x := uintptr(*p)
|
||
p = add1(p)
|
||
n |= (x & 0x7F) << off
|
||
if x&0x80 == 0 {
|
||
break
|
||
}
|
||
}
|
||
}
|
||
|
||
// Count is encoded in a varint in the next bytes.
|
||
c := uintptr(0)
|
||
for off := uint(0); ; off += 7 {
|
||
x := uintptr(*p)
|
||
p = add1(p)
|
||
c |= (x & 0x7F) << off
|
||
if x&0x80 == 0 {
|
||
break
|
||
}
|
||
}
|
||
c *= n // now total number of bits to copy
|
||
|
||
// If the number of bits being repeated is small, load them
|
||
// into a register and use that register for the entire loop
|
||
// instead of repeatedly reading from memory.
|
||
// Handling fewer than 8 bits here makes the general loop simpler.
|
||
// The cutoff is goarch.PtrSize*8 - 7 to guarantee that when we add
|
||
// the pattern to a bit buffer holding at most 7 bits (a partial byte)
|
||
// it will not overflow.
|
||
src := dst
|
||
const maxBits = goarch.PtrSize*8 - 7
|
||
if n <= maxBits {
|
||
// Start with bits in output buffer.
|
||
pattern := bits
|
||
npattern := nbits
|
||
|
||
// If we need more bits, fetch them from memory.
|
||
src = subtract1(src)
|
||
for npattern < n {
|
||
pattern <<= 8
|
||
pattern |= uintptr(*src)
|
||
src = subtract1(src)
|
||
npattern += 8
|
||
}
|
||
|
||
// We started with the whole bit output buffer,
|
||
// and then we loaded bits from whole bytes.
|
||
// Either way, we might now have too many instead of too few.
|
||
// Discard the extra.
|
||
if npattern > n {
|
||
pattern >>= npattern - n
|
||
npattern = n
|
||
}
|
||
|
||
// Replicate pattern to at most maxBits.
|
||
if npattern == 1 {
|
||
// One bit being repeated.
|
||
// If the bit is 1, make the pattern all 1s.
|
||
// If the bit is 0, the pattern is already all 0s,
|
||
// but we can claim that the number of bits
|
||
// in the word is equal to the number we need (c),
|
||
// because right shift of bits will zero fill.
|
||
if pattern == 1 {
|
||
pattern = 1<<maxBits - 1
|
||
npattern = maxBits
|
||
} else {
|
||
npattern = c
|
||
}
|
||
} else {
|
||
b := pattern
|
||
nb := npattern
|
||
if nb+nb <= maxBits {
|
||
// Double pattern until the whole uintptr is filled.
|
||
for nb <= goarch.PtrSize*8 {
|
||
b |= b << nb
|
||
nb += nb
|
||
}
|
||
// Trim away incomplete copy of original pattern in high bits.
|
||
// TODO(rsc): Replace with table lookup or loop on systems without divide?
|
||
nb = maxBits / npattern * npattern
|
||
b &= 1<<nb - 1
|
||
pattern = b
|
||
npattern = nb
|
||
}
|
||
}
|
||
|
||
// Add pattern to bit buffer and flush bit buffer, c/npattern times.
|
||
// Since pattern contains >8 bits, there will be full bytes to flush
|
||
// on each iteration.
|
||
for ; c >= npattern; c -= npattern {
|
||
bits |= pattern << nbits
|
||
nbits += npattern
|
||
for nbits >= 8 {
|
||
*dst = uint8(bits)
|
||
dst = add1(dst)
|
||
bits >>= 8
|
||
nbits -= 8
|
||
}
|
||
}
|
||
|
||
// Add final fragment to bit buffer.
|
||
if c > 0 {
|
||
pattern &= 1<<c - 1
|
||
bits |= pattern << nbits
|
||
nbits += c
|
||
}
|
||
continue Run
|
||
}
|
||
|
||
// Repeat; n too large to fit in a register.
|
||
// Since nbits <= 7, we know the first few bytes of repeated data
|
||
// are already written to memory.
|
||
off := n - nbits // n > nbits because n > maxBits and nbits <= 7
|
||
// 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
|
||
}
|
||
}
|
||
|
||
// 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
|
||
}
|
||
|
||
// materializeGCProg allocates space for the (1-bit) pointer bitmask
|
||
// for an object of size ptrdata. Then it fills that space with the
|
||
// pointer bitmask specified by the program prog.
|
||
// The bitmask starts at s.startAddr.
|
||
// The result must be deallocated with dematerializeGCProg.
|
||
func materializeGCProg(ptrdata uintptr, prog *byte) *mspan {
|
||
// Each word of ptrdata needs one bit in the bitmap.
|
||
bitmapBytes := divRoundUp(ptrdata, 8*goarch.PtrSize)
|
||
// 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)))
|
||
return s
|
||
}
|
||
func dematerializeGCProg(s *mspan) {
|
||
mheap_.freeManual(s, spanAllocPtrScalarBits)
|
||
}
|
||
|
||
func dumpGCProg(p *byte) {
|
||
nptr := 0
|
||
for {
|
||
x := *p
|
||
p = add1(p)
|
||
if x == 0 {
|
||
print("\t", nptr, " end\n")
|
||
break
|
||
}
|
||
if x&0x80 == 0 {
|
||
print("\t", nptr, " lit ", x, ":")
|
||
n := int(x+7) / 8
|
||
for i := 0; i < n; i++ {
|
||
print(" ", hex(*p))
|
||
p = add1(p)
|
||
}
|
||
print("\n")
|
||
nptr += int(x)
|
||
} else {
|
||
nbit := int(x &^ 0x80)
|
||
if nbit == 0 {
|
||
for nb := uint(0); ; nb += 7 {
|
||
x := *p
|
||
p = add1(p)
|
||
nbit |= int(x&0x7f) << nb
|
||
if x&0x80 == 0 {
|
||
break
|
||
}
|
||
}
|
||
}
|
||
count := 0
|
||
for nb := uint(0); ; nb += 7 {
|
||
x := *p
|
||
p = add1(p)
|
||
count |= int(x&0x7f) << nb
|
||
if x&0x80 == 0 {
|
||
break
|
||
}
|
||
}
|
||
print("\t", nptr, " repeat ", nbit, " × ", count, "\n")
|
||
nptr += nbit * count
|
||
}
|
||
}
|
||
}
|
||
|
||
// Testing.
|
||
|
||
// reflect_gcbits returns the GC type info for x, for testing.
|
||
// The result is the bitmap entries (0 or 1), one entry per byte.
|
||
//
|
||
//go:linkname reflect_gcbits reflect.gcbits
|
||
func reflect_gcbits(x any) []byte {
|
||
return getgcmask(x)
|
||
}
|
||
|
||
// Returns GC type info for the pointer stored in ep for testing.
|
||
// If ep points to the stack, only static live information will be returned
|
||
// (i.e. not for objects which are only dynamically live stack objects).
|
||
func getgcmask(ep any) (mask []byte) {
|
||
e := *efaceOf(&ep)
|
||
p := e.data
|
||
t := e._type
|
||
|
||
var et *_type
|
||
if t.Kind_&abi.KindMask != abi.Pointer {
|
||
throw("bad argument to getgcmask: expected type to be a pointer to the value type whose mask is being queried")
|
||
}
|
||
et = (*ptrtype)(unsafe.Pointer(t)).Elem
|
||
|
||
// data or bss
|
||
for _, datap := range activeModules() {
|
||
// data
|
||
if datap.data <= uintptr(p) && uintptr(p) < datap.edata {
|
||
bitmap := datap.gcdatamask.bytedata
|
||
n := et.Size_
|
||
mask = make([]byte, n/goarch.PtrSize)
|
||
for i := uintptr(0); i < n; i += goarch.PtrSize {
|
||
off := (uintptr(p) + i - datap.data) / goarch.PtrSize
|
||
mask[i/goarch.PtrSize] = (*addb(bitmap, off/8) >> (off % 8)) & 1
|
||
}
|
||
return
|
||
}
|
||
|
||
// bss
|
||
if datap.bss <= uintptr(p) && uintptr(p) < datap.ebss {
|
||
bitmap := datap.gcbssmask.bytedata
|
||
n := et.Size_
|
||
mask = make([]byte, n/goarch.PtrSize)
|
||
for i := uintptr(0); i < n; i += goarch.PtrSize {
|
||
off := (uintptr(p) + i - datap.bss) / goarch.PtrSize
|
||
mask[i/goarch.PtrSize] = (*addb(bitmap, off/8) >> (off % 8)) & 1
|
||
}
|
||
return
|
||
}
|
||
}
|
||
|
||
// heap
|
||
if base, s, _ := findObject(uintptr(p), 0, 0); base != 0 {
|
||
if s.spanclass.noscan() {
|
||
return nil
|
||
}
|
||
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.
|
||
maskFromHeap := make([]byte, (limit-base)/goarch.PtrSize)
|
||
for {
|
||
var addr uintptr
|
||
if tp, addr = tp.next(limit); addr == 0 {
|
||
break
|
||
}
|
||
maskFromHeap[(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 (and a check we're about to run) expects this mask
|
||
// to end at the last pointer.
|
||
for len(maskFromHeap) > 0 && maskFromHeap[len(maskFromHeap)-1] == 0 {
|
||
maskFromHeap = maskFromHeap[:len(maskFromHeap)-1]
|
||
}
|
||
|
||
if et.Kind_&abi.KindGCProg == 0 {
|
||
// Unroll again, but this time from the type information.
|
||
maskFromType := make([]byte, (limit-base)/goarch.PtrSize)
|
||
tp = s.typePointersOfType(et, base)
|
||
for {
|
||
var addr uintptr
|
||
if tp, addr = tp.next(limit); addr == 0 {
|
||
break
|
||
}
|
||
maskFromType[(addr-base)/goarch.PtrSize] = 1
|
||
}
|
||
|
||
// Validate that the prefix of maskFromType is equal to
|
||
// maskFromHeap. maskFromType may contain more pointers than
|
||
// maskFromHeap produces because maskFromHeap may be able to
|
||
// get exact type information for certain classes of objects.
|
||
// With maskFromType, we're always just tiling the type bitmap
|
||
// through to the elemsize.
|
||
//
|
||
// It's OK if maskFromType has pointers in elemsize that extend
|
||
// past the actual populated space; we checked above that all
|
||
// that space is zeroed, so just the GC will just see nil pointers.
|
||
differs := false
|
||
for i := range maskFromHeap {
|
||
if maskFromHeap[i] != maskFromType[i] {
|
||
differs = true
|
||
break
|
||
}
|
||
}
|
||
|
||
if differs {
|
||
print("runtime: heap mask=")
|
||
for _, b := range maskFromHeap {
|
||
print(b)
|
||
}
|
||
println()
|
||
print("runtime: type mask=")
|
||
for _, b := range maskFromType {
|
||
print(b)
|
||
}
|
||
println()
|
||
print("runtime: type=", toRType(et).string(), "\n")
|
||
throw("found two different masks from two different methods")
|
||
}
|
||
}
|
||
|
||
// Select the heap mask to return. We may not have a type mask.
|
||
mask = maskFromHeap
|
||
|
||
// Make sure we keep ep alive. We may have stopped referencing
|
||
// ep's data pointer sometime before this point and it's possible
|
||
// for that memory to get freed.
|
||
KeepAlive(ep)
|
||
return
|
||
}
|
||
|
||
// stack
|
||
if gp := getg(); gp.m.curg.stack.lo <= uintptr(p) && uintptr(p) < gp.m.curg.stack.hi {
|
||
found := false
|
||
var u unwinder
|
||
for u.initAt(gp.m.curg.sched.pc, gp.m.curg.sched.sp, 0, gp.m.curg, 0); u.valid(); u.next() {
|
||
if u.frame.sp <= uintptr(p) && uintptr(p) < u.frame.varp {
|
||
found = true
|
||
break
|
||
}
|
||
}
|
||
if found {
|
||
locals, _, _ := u.frame.getStackMap(false)
|
||
if locals.n == 0 {
|
||
return
|
||
}
|
||
size := uintptr(locals.n) * goarch.PtrSize
|
||
n := (*ptrtype)(unsafe.Pointer(t)).Elem.Size_
|
||
mask = make([]byte, n/goarch.PtrSize)
|
||
for i := uintptr(0); i < n; i += goarch.PtrSize {
|
||
off := (uintptr(p) + i - u.frame.varp + size) / goarch.PtrSize
|
||
mask[i/goarch.PtrSize] = locals.ptrbit(off)
|
||
}
|
||
}
|
||
return
|
||
}
|
||
|
||
// otherwise, not something the GC knows about.
|
||
// possibly read-only data, like malloc(0).
|
||
// must not have pointers
|
||
return
|
||
}
|