// 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 described
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// by 1-bit bitmaps in which 0 means uninteresting and 1 means live pointer
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// to be visited during GC. The bits in each byte are consumed starting with
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// the low bit: 1<<0, 1<<1, and so on.
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//
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// Heap bitmap
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//
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// The heap bitmap comprises 2 bits for each pointer-sized word in the heap,
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// stored in the heapArena metadata backing each heap arena.
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// That is, if ha is the heapArena for the arena starting a start,
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// then ha.bitmap[0] holds the 2-bit entries for the four words start
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// through start+3*ptrSize, ha.bitmap[1] holds the entries for
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// start+4*ptrSize through start+7*ptrSize, and so on.
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//
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// In each 2-bit entry, the lower bit holds the same information as in the 1-bit
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// bitmaps: 0 means uninteresting and 1 means live pointer to be visited during GC.
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// The meaning of the high bit depends on the position of the word being described
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// in its allocated object. In all words *except* the second word, the
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// high bit indicates that the object is still being described. In
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// these words, if a bit pair with a high bit 0 is encountered, the
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// low bit can also be assumed to be 0, and the object description is
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// over. This 00 is called the ``dead'' encoding: it signals that the
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// rest of the words in the object are uninteresting to the garbage
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// collector.
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//
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// In the second word, the high bit is the GC ``checkmarked'' bit (see below).
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//
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// The 2-bit entries are split when written into the byte, so that the top half
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// of the byte contains 4 high bits and the bottom half contains 4 low (pointer)
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// bits.
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// This form allows a copy from the 1-bit to the 4-bit form to keep the
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// pointer bits contiguous, instead of having to space them out.
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//
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// The code makes use of the fact that the zero value for a heap bitmap
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// has no live pointer bit set and is (depending on position), not used,
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// not checkmarked, and is the dead encoding.
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// These properties must be preserved when modifying the encoding.
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//
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// The bitmap for noscan spans is not maintained. Code must ensure
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// that an object is scannable before consulting its bitmap by
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// checking either the noscan bit in the span or by consulting its
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// type's information.
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//
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// Checkmarks
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//
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// In a concurrent garbage collector, one worries about failing to mark
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// a live object due to mutations without write barriers or bugs in the
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// collector implementation. As a sanity check, the GC has a 'checkmark'
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// mode that retraverses the object graph with the world stopped, to make
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// sure that everything that should be marked is marked.
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// In checkmark mode, in the heap bitmap, the high bit of the 2-bit entry
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// for the second word of the object holds the checkmark bit.
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// When not in checkmark mode, this bit is set to 1.
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//
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// The smallest possible allocation is 8 bytes. On a 32-bit machine, that
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// means every allocated object has two words, so there is room for the
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// checkmark bit. On a 64-bit machine, however, the 8-byte allocation is
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// just one word, so the second bit pair is not available for encoding the
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// checkmark. However, because non-pointer allocations are combined
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// into larger 16-byte (maxTinySize) allocations, a plain 8-byte allocation
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// must be a pointer, so the type bit in the first word is not actually needed.
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// It is still used in general, except in checkmark the type bit is repurposed
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// as the checkmark bit and then reinitialized (to 1) as the type bit when
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// finished.
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//
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package runtime
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import (
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"runtime/internal/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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bitPointer = 1 << 0
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bitScan = 1 << 4
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heapBitsShift = 1 // shift offset between successive bitPointer or bitScan entries
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wordsPerBitmapByte = 8 / 2 // heap words described by one bitmap byte
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// all scan/pointer bits in a byte
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bitScanAll = bitScan | bitScan<<heapBitsShift | bitScan<<(2*heapBitsShift) | bitScan<<(3*heapBitsShift)
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bitPointerAll = bitPointer | bitPointer<<heapBitsShift | bitPointer<<(2*heapBitsShift) | bitPointer<<(3*heapBitsShift)
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)
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// addb returns the byte pointer p+n.
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//go:nowritebarrier
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//go:nosplit
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func addb(p *byte, n uintptr) *byte {
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// Note: wrote out full expression instead of calling add(p, n)
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// to reduce the number of temporaries generated by the
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// compiler for this trivial expression during inlining.
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return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + n))
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}
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// subtractb returns the byte pointer p-n.
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//go:nowritebarrier
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//go:nosplit
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func subtractb(p *byte, n uintptr) *byte {
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// Note: wrote out full expression instead of calling add(p, -n)
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// to reduce the number of temporaries generated by the
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// compiler for this trivial expression during inlining.
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return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) - n))
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}
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// add1 returns the byte pointer p+1.
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//go:nowritebarrier
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//go:nosplit
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func add1(p *byte) *byte {
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// Note: wrote out full expression instead of calling addb(p, 1)
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// to reduce the number of temporaries generated by the
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// compiler for this trivial expression during inlining.
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return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + 1))
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}
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// subtract1 returns the byte pointer p-1.
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//go:nowritebarrier
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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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//go:nosplit
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func subtract1(p *byte) *byte {
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// Note: wrote out full expression instead of calling subtractb(p, 1)
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// to reduce the number of temporaries generated by the
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// compiler for this trivial expression during inlining.
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return (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) - 1))
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}
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// heapBits provides access to the bitmap bits for a single heap word.
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// The methods on heapBits take value receivers so that the compiler
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// can more easily inline calls to those methods and registerize the
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// struct fields independently.
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type heapBits struct {
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bitp *uint8
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shift uint32
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arena uint32 // Index of heap arena containing bitp
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last *uint8 // Last byte arena's bitmap
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}
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// Make the compiler check that heapBits.arena is large enough to hold
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// the maximum arena frame number.
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var _ = heapBits{arena: (1<<heapAddrBits)/heapArenaBytes - 1}
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// markBits provides access to the mark bit for an object in the heap.
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// bytep points to the byte holding the mark bit.
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// mask is a byte with a single bit set that can be &ed with *bytep
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// to see if the bit has been set.
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// *m.byte&m.mask != 0 indicates the mark bit is set.
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// index can be used along with span information to generate
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// the address of the object in the heap.
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// We maintain one set of mark bits for allocation and one for
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// marking purposes.
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type markBits struct {
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bytep *uint8
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mask uint8
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index uintptr
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}
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//go:nosplit
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func (s *mspan) allocBitsForIndex(allocBitIndex uintptr) markBits {
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bytep, mask := s.allocBits.bitp(allocBitIndex)
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return markBits{bytep, mask, allocBitIndex}
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}
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// refillAllocCache takes 8 bytes s.allocBits starting at whichByte
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// and negates them so that ctz (count trailing zeros) instructions
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// can be used. It then places these 8 bytes into the cached 64 bit
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// s.allocCache.
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func (s *mspan) refillAllocCache(whichByte uintptr) {
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bytes := (*[8]uint8)(unsafe.Pointer(s.allocBits.bytep(whichByte)))
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aCache := uint64(0)
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aCache |= uint64(bytes[0])
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aCache |= uint64(bytes[1]) << (1 * 8)
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aCache |= uint64(bytes[2]) << (2 * 8)
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aCache |= uint64(bytes[3]) << (3 * 8)
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aCache |= uint64(bytes[4]) << (4 * 8)
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aCache |= uint64(bytes[5]) << (5 * 8)
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aCache |= uint64(bytes[6]) << (6 * 8)
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aCache |= uint64(bytes[7]) << (7 * 8)
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s.allocCache = ^aCache
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}
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// nextFreeIndex returns the index of the next free object in s at
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// or after s.freeindex.
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// There are hardware instructions that can be used to make this
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// faster if profiling warrants it.
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func (s *mspan) nextFreeIndex() uintptr {
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sfreeindex := s.freeindex
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snelems := s.nelems
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if sfreeindex == snelems {
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return sfreeindex
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}
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if sfreeindex > snelems {
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throw("s.freeindex > s.nelems")
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}
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aCache := s.allocCache
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bitIndex := sys.Ctz64(aCache)
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for bitIndex == 64 {
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// Move index to start of next cached bits.
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sfreeindex = (sfreeindex + 64) &^ (64 - 1)
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if sfreeindex >= snelems {
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s.freeindex = snelems
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return snelems
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}
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whichByte := sfreeindex / 8
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// Refill s.allocCache with the next 64 alloc bits.
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s.refillAllocCache(whichByte)
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aCache = s.allocCache
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bitIndex = sys.Ctz64(aCache)
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// nothing available in cached bits
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// grab the next 8 bytes and try again.
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}
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result := sfreeindex + uintptr(bitIndex)
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if result >= snelems {
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s.freeindex = snelems
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return snelems
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}
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s.allocCache >>= uint(bitIndex + 1)
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sfreeindex = result + 1
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if sfreeindex%64 == 0 && sfreeindex != snelems {
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// We just incremented s.freeindex so it isn't 0.
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// As each 1 in s.allocCache was encountered and used for allocation
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// it was shifted away. At this point s.allocCache contains all 0s.
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// Refill s.allocCache so that it corresponds
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// to the bits at s.allocBits starting at s.freeindex.
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whichByte := sfreeindex / 8
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s.refillAllocCache(whichByte)
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}
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s.freeindex = sfreeindex
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return result
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}
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// isFree reports whether the index'th object in s is unallocated.
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func (s *mspan) isFree(index uintptr) bool {
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if index < s.freeindex {
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return false
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}
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bytep, mask := s.allocBits.bitp(index)
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return *bytep&mask == 0
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}
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func (s *mspan) objIndex(p uintptr) uintptr {
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byteOffset := p - s.base()
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if byteOffset == 0 {
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return 0
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}
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if s.baseMask != 0 {
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// s.baseMask is non-0, elemsize is a power of two, so shift by s.divShift
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return byteOffset >> s.divShift
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}
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return uintptr(((uint64(byteOffset) >> s.divShift) * uint64(s.divMul)) >> s.divShift2)
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}
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func markBitsForAddr(p uintptr) markBits {
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s := spanOf(p)
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objIndex := s.objIndex(p)
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return s.markBitsForIndex(objIndex)
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}
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func (s *mspan) markBitsForIndex(objIndex uintptr) markBits {
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bytep, mask := s.gcmarkBits.bitp(objIndex)
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return markBits{bytep, mask, objIndex}
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}
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func (s *mspan) markBitsForBase() markBits {
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return markBits{(*uint8)(s.gcmarkBits), uint8(1), 0}
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}
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// isMarked reports whether mark bit m is set.
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func (m markBits) isMarked() bool {
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return *m.bytep&m.mask != 0
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}
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// setMarked sets the marked bit in the markbits, atomically.
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func (m markBits) setMarked() {
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// Might be racing with other updates, so use atomic update always.
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// We used to be clever here and use a non-atomic update in certain
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// cases, but it's not worth the risk.
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atomic.Or8(m.bytep, m.mask)
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}
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// setMarkedNonAtomic sets the marked bit in the markbits, non-atomically.
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func (m markBits) setMarkedNonAtomic() {
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*m.bytep |= m.mask
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}
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// clearMarked clears the marked bit in the markbits, atomically.
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func (m markBits) clearMarked() {
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// Might be racing with other updates, so use atomic update always.
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// We used to be clever here and use a non-atomic update in certain
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// cases, but it's not worth the risk.
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atomic.And8(m.bytep, ^m.mask)
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}
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// markBitsForSpan returns the markBits for the span base address base.
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func markBitsForSpan(base uintptr) (mbits markBits) {
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mbits = markBitsForAddr(base)
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if mbits.mask != 1 {
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throw("markBitsForSpan: unaligned start")
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}
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return mbits
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}
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// advance advances the markBits to the next object in the span.
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func (m *markBits) advance() {
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if m.mask == 1<<7 {
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m.bytep = (*uint8)(unsafe.Pointer(uintptr(unsafe.Pointer(m.bytep)) + 1))
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m.mask = 1
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} else {
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m.mask = m.mask << 1
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}
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m.index++
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}
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// heapBitsForAddr returns the heapBits for the address addr.
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// The caller must ensure addr is in an allocated span.
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// In particular, be careful not to point past the end of an object.
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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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//go:nosplit
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func heapBitsForAddr(addr uintptr) (h heapBits) {
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// 2 bits per word, 4 pairs per byte, and a mask is hard coded.
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arena := arenaIndex(addr)
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ha := mheap_.arenas[arena.l1()][arena.l2()]
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// The compiler uses a load for nil checking ha, but in this
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// case we'll almost never hit that cache line again, so it
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// makes more sense to do a value check.
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if ha == nil {
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// addr is not in the heap. Return nil heapBits, which
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// we expect to crash in the caller.
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return
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}
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h.bitp = &ha.bitmap[(addr/(sys.PtrSize*4))%heapArenaBitmapBytes]
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h.shift = uint32((addr / sys.PtrSize) & 3)
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h.arena = uint32(arena)
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h.last = &ha.bitmap[len(ha.bitmap)-1]
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return
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}
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// findObject returns the base address for the heap object containing
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// the address p, the object's span, and the index of the object in s.
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// If p does not point into a heap object, it returns base == 0.
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//
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// If p points is an invalid heap pointer and debug.invalidptr != 0,
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// findObject panics.
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//
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// refBase and refOff optionally give the base address of the object
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// in which the pointer p was found and the byte offset at which it
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// was found. These are used for error reporting.
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func findObject(p, refBase, refOff uintptr) (base uintptr, s *mspan, objIndex uintptr) {
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s = spanOf(p)
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// If p is a bad pointer, it may not be in s's bounds.
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if s == nil || p < s.base() || p >= s.limit || s.state != mSpanInUse {
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if s == nil || s.state == mSpanManual {
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// If s is nil, the virtual address has never been part of the heap.
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// This pointer may be to some mmap'd region, so we allow it.
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// Pointers into stacks are also ok, the runtime manages these explicitly.
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return
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}
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// The following ensures that we are rigorous about what data
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// structures hold valid pointers.
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if debug.invalidptr != 0 {
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// Typically this indicates an incorrect use
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// of unsafe or cgo to store a bad pointer in
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// the Go heap. It may also indicate a runtime
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// bug.
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//
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// TODO(austin): We could be more aggressive
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// and detect pointers to unallocated objects
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// in allocated spans.
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printlock()
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print("runtime: pointer ", hex(p))
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if s.state != mSpanInUse {
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print(" to unallocated span")
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} else {
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print(" to unused region of span")
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}
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print(" span.base()=", hex(s.base()), " span.limit=", hex(s.limit), " span.state=", s.state, "\n")
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if refBase != 0 {
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print("runtime: found in object at *(", hex(refBase), "+", hex(refOff), ")\n")
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gcDumpObject("object", refBase, refOff)
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}
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getg().m.traceback = 2
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throw("found bad pointer in Go heap (incorrect use of unsafe or cgo?)")
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}
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return
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}
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// If this span holds object of a power of 2 size, just mask off the bits to
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// the interior of the object. Otherwise use the size to get the base.
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if s.baseMask != 0 {
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// optimize for power of 2 sized objects.
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base = s.base()
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base = base + (p-base)&uintptr(s.baseMask)
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objIndex = (base - s.base()) >> s.divShift
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// base = p & s.baseMask is faster for small spans,
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// but doesn't work for large spans.
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// Overall, it's faster to use the more general computation above.
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} else {
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base = s.base()
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if p-base >= s.elemsize {
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// n := (p - base) / s.elemsize, using division by multiplication
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objIndex = uintptr(p-base) >> s.divShift * uintptr(s.divMul) >> s.divShift2
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base += objIndex * s.elemsize
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}
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}
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return
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}
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// next returns the heapBits describing the next pointer-sized word in memory.
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// That is, if h describes address p, h.next() describes p+ptrSize.
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// Note that next does not modify h. The caller must record the result.
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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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//go:nosplit
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func (h heapBits) next() heapBits {
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if h.shift < 3*heapBitsShift {
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h.shift += heapBitsShift
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} else if h.bitp != h.last {
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h.bitp, h.shift = add1(h.bitp), 0
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} else {
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// Move to the next arena.
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return h.nextArena()
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}
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return h
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}
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// nextArena advances h to the beginning of the next heap arena.
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//
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// This is a slow-path helper to next. gc's inliner knows that
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// heapBits.next can be inlined even though it calls this. This is
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// marked noinline so it doesn't get inlined into next and cause next
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// to be too big to inline.
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//
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//go:nosplit
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//go:noinline
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func (h heapBits) nextArena() heapBits {
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h.arena++
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ai := arenaIdx(h.arena)
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l2 := mheap_.arenas[ai.l1()]
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if l2 == nil {
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// We just passed the end of the object, which
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// was also the end of the heap. Poison h. It
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// should never be dereferenced at this point.
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return heapBits{}
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}
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ha := l2[ai.l2()]
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if ha == nil {
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return heapBits{}
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}
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h.bitp, h.shift = &ha.bitmap[0], 0
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h.last = &ha.bitmap[len(ha.bitmap)-1]
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return h
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}
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// forward returns the heapBits describing n pointer-sized words ahead of h in memory.
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// That is, if h describes address p, h.forward(n) describes p+n*ptrSize.
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// h.forward(1) is equivalent to h.next(), just slower.
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// Note that forward does not modify h. The caller must record the result.
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// bits returns the heap bits for the current word.
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//go:nosplit
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func (h heapBits) forward(n uintptr) heapBits {
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n += uintptr(h.shift) / heapBitsShift
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nbitp := uintptr(unsafe.Pointer(h.bitp)) + n/4
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h.shift = uint32(n%4) * heapBitsShift
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if nbitp <= uintptr(unsafe.Pointer(h.last)) {
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h.bitp = (*uint8)(unsafe.Pointer(nbitp))
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return h
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}
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// We're in a new heap arena.
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past := nbitp - (uintptr(unsafe.Pointer(h.last)) + 1)
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h.arena += 1 + uint32(past/heapArenaBitmapBytes)
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ai := arenaIdx(h.arena)
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if l2 := mheap_.arenas[ai.l1()]; l2 != nil && l2[ai.l2()] != nil {
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a := l2[ai.l2()]
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h.bitp = &a.bitmap[past%heapArenaBitmapBytes]
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h.last = &a.bitmap[len(a.bitmap)-1]
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} else {
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h.bitp, h.last = nil, nil
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}
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return h
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}
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// forwardOrBoundary is like forward, but stops at boundaries between
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// contiguous sections of the bitmap. It returns the number of words
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// advanced over, which will be <= n.
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func (h heapBits) forwardOrBoundary(n uintptr) (heapBits, uintptr) {
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maxn := 4 * ((uintptr(unsafe.Pointer(h.last)) + 1) - uintptr(unsafe.Pointer(h.bitp)))
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if n > maxn {
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n = maxn
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}
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return h.forward(n), n
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}
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// The caller can test morePointers and isPointer by &-ing with bitScan and bitPointer.
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// The result includes in its higher bits the bits for subsequent words
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// described by the same bitmap byte.
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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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//go:nosplit
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func (h heapBits) bits() uint32 {
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// The (shift & 31) eliminates a test and conditional branch
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// from the generated code.
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return uint32(*h.bitp) >> (h.shift & 31)
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}
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// morePointers reports whether this word and all remaining words in this object
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// are scalars.
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// h must not describe the second word of the object.
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func (h heapBits) morePointers() bool {
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return h.bits()&bitScan != 0
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}
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// isPointer reports whether the heap bits describe a pointer word.
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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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//go:nosplit
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func (h heapBits) isPointer() bool {
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return h.bits()&bitPointer != 0
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}
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// isCheckmarked reports whether the heap bits have the checkmarked bit set.
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// It must be told how large the object at h is, because the encoding of the
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// checkmark bit varies by size.
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// h must describe the initial word of the object.
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func (h heapBits) isCheckmarked(size uintptr) bool {
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if size == sys.PtrSize {
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return (*h.bitp>>h.shift)&bitPointer != 0
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}
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// All multiword objects are 2-word aligned,
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// so we know that the initial word's 2-bit pair
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// and the second word's 2-bit pair are in the
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// same heap bitmap byte, *h.bitp.
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return (*h.bitp>>(heapBitsShift+h.shift))&bitScan != 0
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}
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// setCheckmarked sets the checkmarked bit.
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// It must be told how large the object at h is, because the encoding of the
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// checkmark bit varies by size.
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// h must describe the initial word of the object.
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func (h heapBits) setCheckmarked(size uintptr) {
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if size == sys.PtrSize {
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atomic.Or8(h.bitp, bitPointer<<h.shift)
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return
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}
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atomic.Or8(h.bitp, bitScan<<(heapBitsShift+h.shift))
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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),
|
// using pointer/scalar information from [dst, dst+size).
|
// This executes the write barriers necessary before a memmove.
|
// src, dst, and size must be pointer-aligned.
|
// The range [dst, dst+size) must lie within a single object.
|
// It does not perform the actual writes.
|
//
|
// As a special case, src == 0 indicates that this is being used for a
|
// memclr. bulkBarrierPreWrite will pass 0 for the src of each write
|
// barrier.
|
//
|
// Callers should call bulkBarrierPreWrite immediately before
|
// calling memmove(dst, src, size). This function is marked nosplit
|
// to avoid being preempted; the GC must not stop the goroutine
|
// between the memmove and the execution of the barriers.
|
// The caller is also responsible for cgo pointer checks if this
|
// may be writing Go pointers into non-Go memory.
|
//
|
// The pointer bitmap is not maintained for allocations containing
|
// no pointers at all; any caller of bulkBarrierPreWrite must first
|
// make sure the underlying allocation contains pointers, usually
|
// by checking typ.kind&kindNoPointers.
|
//
|
// Callers must perform cgo checks if writeBarrier.cgo.
|
//
|
//go:nosplit
|
func bulkBarrierPreWrite(dst, src, size uintptr) {
|
if (dst|src|size)&(sys.PtrSize-1) != 0 {
|
throw("bulkBarrierPreWrite: unaligned arguments")
|
}
|
if !writeBarrier.needed {
|
return
|
}
|
if s := spanOf(dst); s == nil {
|
// If dst is a global, use the data or BSS bitmaps to
|
// execute write barriers.
|
for _, datap := range activeModules() {
|
if datap.data <= dst && dst < datap.edata {
|
bulkBarrierBitmap(dst, src, size, dst-datap.data, datap.gcdatamask.bytedata)
|
return
|
}
|
}
|
for _, datap := range activeModules() {
|
if datap.bss <= dst && dst < datap.ebss {
|
bulkBarrierBitmap(dst, src, size, dst-datap.bss, datap.gcbssmask.bytedata)
|
return
|
}
|
}
|
return
|
} else if s.state != mSpanInUse || dst < s.base() || s.limit <= dst {
|
// dst was heap memory at some point, but isn't now.
|
// It can't be a global. It must be either our stack,
|
// or in the case of direct channel sends, it could be
|
// another stack. Either way, no need for barriers.
|
// This will also catch if dst is in a freed span,
|
// though that should never have.
|
return
|
}
|
|
buf := &getg().m.p.ptr().wbBuf
|
h := heapBitsForAddr(dst)
|
if src == 0 {
|
for i := uintptr(0); i < size; i += sys.PtrSize {
|
if h.isPointer() {
|
dstx := (*uintptr)(unsafe.Pointer(dst + i))
|
if !buf.putFast(*dstx, 0) {
|
wbBufFlush(nil, 0)
|
}
|
}
|
h = h.next()
|
}
|
} else {
|
for i := uintptr(0); i < size; i += sys.PtrSize {
|
if h.isPointer() {
|
dstx := (*uintptr)(unsafe.Pointer(dst + i))
|
srcx := (*uintptr)(unsafe.Pointer(src + i))
|
if !buf.putFast(*dstx, *srcx) {
|
wbBufFlush(nil, 0)
|
}
|
}
|
h = h.next()
|
}
|
}
|
}
|
|
// bulkBarrierPreWriteSrcOnly is like bulkBarrierPreWrite but
|
// does not execute write barriers for [dst, dst+size).
|
//
|
// In addition to the requirements of bulkBarrierPreWrite
|
// callers need to ensure [dst, dst+size) is zeroed.
|
//
|
// This is used for special cases where e.g. dst was just
|
// created and zeroed with malloc.
|
//go:nosplit
|
func bulkBarrierPreWriteSrcOnly(dst, src, size uintptr) {
|
if (dst|src|size)&(sys.PtrSize-1) != 0 {
|
throw("bulkBarrierPreWrite: unaligned arguments")
|
}
|
if !writeBarrier.needed {
|
return
|
}
|
buf := &getg().m.p.ptr().wbBuf
|
h := heapBitsForAddr(dst)
|
for i := uintptr(0); i < size; i += sys.PtrSize {
|
if h.isPointer() {
|
srcx := (*uintptr)(unsafe.Pointer(src + i))
|
if !buf.putFast(0, *srcx) {
|
wbBufFlush(nil, 0)
|
}
|
}
|
h = h.next()
|
}
|
}
|
|
// bulkBarrierBitmap executes write barriers for copying from [src,
|
// src+size) to [dst, dst+size) using a 1-bit pointer bitmap. src is
|
// assumed to start maskOffset bytes into the data covered by the
|
// bitmap in bits (which may not be a multiple of 8).
|
//
|
// This is used by bulkBarrierPreWrite for writes to data and BSS.
|
//
|
//go:nosplit
|
func bulkBarrierBitmap(dst, src, size, maskOffset uintptr, bits *uint8) {
|
word := maskOffset / sys.PtrSize
|
bits = addb(bits, word/8)
|
mask := uint8(1) << (word % 8)
|
|
buf := &getg().m.p.ptr().wbBuf
|
for i := uintptr(0); i < size; i += sys.PtrSize {
|
if mask == 0 {
|
bits = addb(bits, 1)
|
if *bits == 0 {
|
// Skip 8 words.
|
i += 7 * sys.PtrSize
|
continue
|
}
|
mask = 1
|
}
|
if *bits&mask != 0 {
|
dstx := (*uintptr)(unsafe.Pointer(dst + i))
|
if src == 0 {
|
if !buf.putFast(*dstx, 0) {
|
wbBufFlush(nil, 0)
|
}
|
} else {
|
srcx := (*uintptr)(unsafe.Pointer(src + i))
|
if !buf.putFast(*dstx, *srcx) {
|
wbBufFlush(nil, 0)
|
}
|
}
|
}
|
mask <<= 1
|
}
|
}
|
|
// typeBitsBulkBarrier executes a write barrier for every
|
// pointer that would be copied from [src, src+size) to [dst,
|
// dst+size) by a memmove using the type bitmap to locate those
|
// pointer slots.
|
//
|
// The type typ must correspond exactly to [src, src+size) and [dst, dst+size).
|
// dst, src, and size must be pointer-aligned.
|
// The type typ must have a plain bitmap, not a GC program.
|
// The only use of this function is in channel sends, and the
|
// 64 kB channel element limit takes care of this for us.
|
//
|
// Must not be preempted because it typically runs right before memmove,
|
// and the GC must observe them as an atomic action.
|
//
|
// Callers must perform cgo checks if writeBarrier.cgo.
|
//
|
//go:nosplit
|
func typeBitsBulkBarrier(typ *_type, dst, src, size uintptr) {
|
if typ == nil {
|
throw("runtime: typeBitsBulkBarrier without type")
|
}
|
if typ.size != size {
|
println("runtime: typeBitsBulkBarrier with type ", typ.string(), " of size ", typ.size, " but memory size", size)
|
throw("runtime: invalid typeBitsBulkBarrier")
|
}
|
if typ.kind&kindGCProg != 0 {
|
println("runtime: typeBitsBulkBarrier with type ", typ.string(), " with GC prog")
|
throw("runtime: invalid typeBitsBulkBarrier")
|
}
|
if !writeBarrier.needed {
|
return
|
}
|
ptrmask := typ.gcdata
|
buf := &getg().m.p.ptr().wbBuf
|
var bits uint32
|
for i := uintptr(0); i < typ.ptrdata; i += sys.PtrSize {
|
if i&(sys.PtrSize*8-1) == 0 {
|
bits = uint32(*ptrmask)
|
ptrmask = addb(ptrmask, 1)
|
} else {
|
bits = bits >> 1
|
}
|
if bits&1 != 0 {
|
dstx := (*uintptr)(unsafe.Pointer(dst + i))
|
srcx := (*uintptr)(unsafe.Pointer(src + i))
|
if !buf.putFast(*dstx, *srcx) {
|
wbBufFlush(nil, 0)
|
}
|
}
|
}
|
}
|
|
// The methods operating on spans all require that h has been returned
|
// by heapBitsForSpan and that size, n, total are the span layout description
|
// returned by the mspan's layout method.
|
// If total > size*n, it means that there is extra leftover memory in the span,
|
// usually due to rounding.
|
//
|
// TODO(rsc): Perhaps introduce a different heapBitsSpan type.
|
|
// initSpan initializes the heap bitmap for a span.
|
// It clears all checkmark bits.
|
// If this is a span of pointer-sized objects, it initializes all
|
// words to pointer/scan.
|
// Otherwise, it initializes all words to scalar/dead.
|
func (h heapBits) initSpan(s *mspan) {
|
size, n, total := s.layout()
|
|
// Init the markbit structures
|
s.freeindex = 0
|
s.allocCache = ^uint64(0) // all 1s indicating all free.
|
s.nelems = n
|
s.allocBits = nil
|
s.gcmarkBits = nil
|
s.gcmarkBits = newMarkBits(s.nelems)
|
s.allocBits = newAllocBits(s.nelems)
|
|
// Clear bits corresponding to objects.
|
nw := total / sys.PtrSize
|
if nw%wordsPerBitmapByte != 0 {
|
throw("initSpan: unaligned length")
|
}
|
if h.shift != 0 {
|
throw("initSpan: unaligned base")
|
}
|
for nw > 0 {
|
hNext, anw := h.forwardOrBoundary(nw)
|
nbyte := anw / wordsPerBitmapByte
|
if sys.PtrSize == 8 && size == sys.PtrSize {
|
bitp := h.bitp
|
for i := uintptr(0); i < nbyte; i++ {
|
*bitp = bitPointerAll | bitScanAll
|
bitp = add1(bitp)
|
}
|
} else {
|
memclrNoHeapPointers(unsafe.Pointer(h.bitp), nbyte)
|
}
|
h = hNext
|
nw -= anw
|
}
|
}
|
|
// initCheckmarkSpan initializes a span for being checkmarked.
|
// It clears the checkmark bits, which are set to 1 in normal operation.
|
func (h heapBits) initCheckmarkSpan(size, n, total uintptr) {
|
// The ptrSize == 8 is a compile-time constant false on 32-bit and eliminates this code entirely.
|
if sys.PtrSize == 8 && size == sys.PtrSize {
|
// Checkmark bit is type bit, bottom bit of every 2-bit entry.
|
// Only possible on 64-bit system, since minimum size is 8.
|
// Must clear type bit (checkmark bit) of every word.
|
// The type bit is the lower of every two-bit pair.
|
for i := uintptr(0); i < n; i += wordsPerBitmapByte {
|
*h.bitp &^= bitPointerAll
|
h = h.forward(wordsPerBitmapByte)
|
}
|
return
|
}
|
for i := uintptr(0); i < n; i++ {
|
*h.bitp &^= bitScan << (heapBitsShift + h.shift)
|
h = h.forward(size / sys.PtrSize)
|
}
|
}
|
|
// clearCheckmarkSpan undoes all the checkmarking in a span.
|
// The actual checkmark bits are ignored, so the only work to do
|
// is to fix the pointer bits. (Pointer bits are ignored by scanobject
|
// but consulted by typedmemmove.)
|
func (h heapBits) clearCheckmarkSpan(size, n, total uintptr) {
|
// The ptrSize == 8 is a compile-time constant false on 32-bit and eliminates this code entirely.
|
if sys.PtrSize == 8 && size == sys.PtrSize {
|
// Checkmark bit is type bit, bottom bit of every 2-bit entry.
|
// Only possible on 64-bit system, since minimum size is 8.
|
// Must clear type bit (checkmark bit) of every word.
|
// The type bit is the lower of every two-bit pair.
|
for i := uintptr(0); i < n; i += wordsPerBitmapByte {
|
*h.bitp |= bitPointerAll
|
h = h.forward(wordsPerBitmapByte)
|
}
|
}
|
}
|
|
// oneBitCount is indexed by byte and produces the
|
// number of 1 bits in that byte. For example 128 has 1 bit set
|
// and oneBitCount[128] will holds 1.
|
var oneBitCount = [256]uint8{
|
0, 1, 1, 2, 1, 2, 2, 3,
|
1, 2, 2, 3, 2, 3, 3, 4,
|
1, 2, 2, 3, 2, 3, 3, 4,
|
2, 3, 3, 4, 3, 4, 4, 5,
|
1, 2, 2, 3, 2, 3, 3, 4,
|
2, 3, 3, 4, 3, 4, 4, 5,
|
2, 3, 3, 4, 3, 4, 4, 5,
|
3, 4, 4, 5, 4, 5, 5, 6,
|
1, 2, 2, 3, 2, 3, 3, 4,
|
2, 3, 3, 4, 3, 4, 4, 5,
|
2, 3, 3, 4, 3, 4, 4, 5,
|
3, 4, 4, 5, 4, 5, 5, 6,
|
2, 3, 3, 4, 3, 4, 4, 5,
|
3, 4, 4, 5, 4, 5, 5, 6,
|
3, 4, 4, 5, 4, 5, 5, 6,
|
4, 5, 5, 6, 5, 6, 6, 7,
|
1, 2, 2, 3, 2, 3, 3, 4,
|
2, 3, 3, 4, 3, 4, 4, 5,
|
2, 3, 3, 4, 3, 4, 4, 5,
|
3, 4, 4, 5, 4, 5, 5, 6,
|
2, 3, 3, 4, 3, 4, 4, 5,
|
3, 4, 4, 5, 4, 5, 5, 6,
|
3, 4, 4, 5, 4, 5, 5, 6,
|
4, 5, 5, 6, 5, 6, 6, 7,
|
2, 3, 3, 4, 3, 4, 4, 5,
|
3, 4, 4, 5, 4, 5, 5, 6,
|
3, 4, 4, 5, 4, 5, 5, 6,
|
4, 5, 5, 6, 5, 6, 6, 7,
|
3, 4, 4, 5, 4, 5, 5, 6,
|
4, 5, 5, 6, 5, 6, 6, 7,
|
4, 5, 5, 6, 5, 6, 6, 7,
|
5, 6, 6, 7, 6, 7, 7, 8}
|
|
// countAlloc returns the number of objects allocated in span s by
|
// scanning the allocation bitmap.
|
// TODO:(rlh) Use popcount intrinsic.
|
func (s *mspan) countAlloc() int {
|
count := 0
|
maxIndex := s.nelems / 8
|
for i := uintptr(0); i < maxIndex; i++ {
|
mrkBits := *s.gcmarkBits.bytep(i)
|
count += int(oneBitCount[mrkBits])
|
}
|
if bitsInLastByte := s.nelems % 8; bitsInLastByte != 0 {
|
mrkBits := *s.gcmarkBits.bytep(maxIndex)
|
mask := uint8((1 << bitsInLastByte) - 1)
|
bits := mrkBits & mask
|
count += int(oneBitCount[bits])
|
}
|
return count
|
}
|
|
// heapBitsSetType records that the new allocation [x, x+size)
|
// holds in [x, x+dataSize) one or more values of type typ.
|
// (The number of values is given by dataSize / typ.size.)
|
// If dataSize < size, the fragment [x+dataSize, x+size) is
|
// recorded as non-pointer data.
|
// It is known that the type has pointers somewhere;
|
// malloc does not call heapBitsSetType when there are no pointers,
|
// because all free objects are marked as noscan during
|
// heapBitsSweepSpan.
|
//
|
// There can only be one allocation from a given span active at a time,
|
// and the bitmap for a span always falls on byte boundaries,
|
// so there are no write-write races for access to the heap bitmap.
|
// Hence, heapBitsSetType can access the bitmap without atomics.
|
//
|
// There can be read-write races between heapBitsSetType and things
|
// that read the heap bitmap like scanobject. However, since
|
// heapBitsSetType is only used for objects that have not yet been
|
// made reachable, readers will ignore bits being modified by this
|
// function. This does mean this function cannot transiently modify
|
// bits that belong to neighboring objects. Also, on weakly-ordered
|
// machines, callers must execute a store/store (publication) barrier
|
// between calling this function and making the object reachable.
|
func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
|
const doubleCheck = false // slow but helpful; enable to test modifications to this code
|
|
// dataSize is always size rounded up to the next malloc size class,
|
// except in the case of allocating a defer block, in which case
|
// size is sizeof(_defer{}) (at least 6 words) and dataSize may be
|
// arbitrarily larger.
|
//
|
// The checks for size == sys.PtrSize and size == 2*sys.PtrSize can therefore
|
// assume that dataSize == size without checking it explicitly.
|
|
if sys.PtrSize == 8 && size == sys.PtrSize {
|
// It's one word and it has pointers, it must be a pointer.
|
// Since all allocated one-word objects are pointers
|
// (non-pointers are aggregated into tinySize allocations),
|
// initSpan sets the pointer bits for us. Nothing to do here.
|
if doubleCheck {
|
h := heapBitsForAddr(x)
|
if !h.isPointer() {
|
throw("heapBitsSetType: pointer bit missing")
|
}
|
if !h.morePointers() {
|
throw("heapBitsSetType: scan bit missing")
|
}
|
}
|
return
|
}
|
|
h := heapBitsForAddr(x)
|
ptrmask := typ.gcdata // start of 1-bit pointer mask (or GC program, handled below)
|
|
// Heap bitmap bits for 2-word object are only 4 bits,
|
// so also shared with objects next to it.
|
// This is called out as a special case primarily for 32-bit systems,
|
// so that on 32-bit systems the code below can assume all objects
|
// are 4-word aligned (because they're all 16-byte aligned).
|
if size == 2*sys.PtrSize {
|
if typ.size == sys.PtrSize {
|
// We're allocating a block big enough to hold two pointers.
|
// On 64-bit, that means the actual object must be two pointers,
|
// or else we'd have used the one-pointer-sized block.
|
// On 32-bit, however, this is the 8-byte block, the smallest one.
|
// So it could be that we're allocating one pointer and this was
|
// just the smallest block available. Distinguish by checking dataSize.
|
// (In general the number of instances of typ being allocated is
|
// dataSize/typ.size.)
|
if sys.PtrSize == 4 && dataSize == sys.PtrSize {
|
// 1 pointer object. On 32-bit machines clear the bit for the
|
// unused second word.
|
*h.bitp &^= (bitPointer | bitScan | ((bitPointer | bitScan) << heapBitsShift)) << h.shift
|
*h.bitp |= (bitPointer | bitScan) << h.shift
|
} else {
|
// 2-element slice of pointer.
|
*h.bitp |= (bitPointer | bitScan | bitPointer<<heapBitsShift) << h.shift
|
}
|
return
|
}
|
// Otherwise typ.size must be 2*sys.PtrSize,
|
// and typ.kind&kindGCProg == 0.
|
if doubleCheck {
|
if typ.size != 2*sys.PtrSize || typ.kind&kindGCProg != 0 {
|
print("runtime: heapBitsSetType size=", size, " but typ.size=", typ.size, " gcprog=", typ.kind&kindGCProg != 0, "\n")
|
throw("heapBitsSetType")
|
}
|
}
|
b := uint32(*ptrmask)
|
hb := (b & 3) | bitScan
|
// bitPointer == 1, bitScan is 1 << 4, heapBitsShift is 1.
|
// 110011 is shifted h.shift and complemented.
|
// This clears out the bits that are about to be
|
// ored into *h.hbitp in the next instructions.
|
*h.bitp &^= (bitPointer | bitScan | ((bitPointer | bitScan) << heapBitsShift)) << h.shift
|
*h.bitp |= uint8(hb << h.shift)
|
return
|
}
|
|
// Copy from 1-bit ptrmask into 2-bit bitmap.
|
// The basic approach is to use a single uintptr as a bit buffer,
|
// alternating between reloading the buffer and writing bitmap bytes.
|
// In general, one load can supply two bitmap byte writes.
|
// This is a lot of lines of code, but it compiles into relatively few
|
// machine instructions.
|
|
outOfPlace := false
|
if arenaIndex(x+size-1) != arenaIdx(h.arena) || (doubleCheck && fastrand()%2 == 0) {
|
// This object spans heap arenas, so the bitmap may be
|
// discontiguous. Unroll it into the object instead
|
// and then copy it out.
|
//
|
// In doubleCheck mode, we randomly do this anyway to
|
// stress test the bitmap copying path.
|
outOfPlace = true
|
h.bitp = (*uint8)(unsafe.Pointer(x))
|
h.last = nil
|
}
|
|
var (
|
// Ptrmask input.
|
p *byte // last ptrmask byte read
|
b uintptr // ptrmask bits already loaded
|
nb uintptr // number of bits in b at next read
|
endp *byte // final ptrmask byte to read (then repeat)
|
endnb uintptr // number of valid bits in *endp
|
pbits uintptr // alternate source of bits
|
|
// Heap bitmap output.
|
w uintptr // words processed
|
nw uintptr // number of words to process
|
hbitp *byte // next heap bitmap byte to write
|
hb uintptr // bits being prepared for *hbitp
|
)
|
|
hbitp = h.bitp
|
|
// Handle GC program. Delayed until this part of the code
|
// so that we can use the same double-checking mechanism
|
// as the 1-bit case. Nothing above could have encountered
|
// GC programs: the cases were all too small.
|
if typ.kind&kindGCProg != 0 {
|
heapBitsSetTypeGCProg(h, typ.ptrdata, typ.size, dataSize, size, addb(typ.gcdata, 4))
|
if doubleCheck {
|
// Double-check the heap bits written by GC program
|
// by running the GC program to create a 1-bit pointer mask
|
// and then jumping to the double-check code below.
|
// This doesn't catch bugs shared between the 1-bit and 4-bit
|
// GC program execution, but it does catch mistakes specific
|
// to just one of those and bugs in heapBitsSetTypeGCProg's
|
// implementation of arrays.
|
lock(&debugPtrmask.lock)
|
if debugPtrmask.data == nil {
|
debugPtrmask.data = (*byte)(persistentalloc(1<<20, 1, &memstats.other_sys))
|
}
|
ptrmask = debugPtrmask.data
|
runGCProg(addb(typ.gcdata, 4), nil, ptrmask, 1)
|
}
|
goto Phase4
|
}
|
|
// Note about sizes:
|
//
|
// typ.size is the number of words in the object,
|
// and typ.ptrdata is the number of words in the prefix
|
// of the object that contains pointers. That is, the final
|
// typ.size - typ.ptrdata words contain no pointers.
|
// This allows optimization of a common pattern where
|
// an object has a small header followed by a large scalar
|
// buffer. If we know the pointers are over, we don't have
|
// to scan the buffer's heap bitmap at all.
|
// The 1-bit ptrmasks are sized to contain only bits for
|
// the typ.ptrdata prefix, zero padded out to a full byte
|
// of bitmap. This code sets nw (below) so that heap bitmap
|
// bits are only written for the typ.ptrdata prefix; if there is
|
// more room in the allocated object, the next heap bitmap
|
// entry is a 00, indicating that there are no more pointers
|
// to scan. So only the ptrmask for the ptrdata bytes is needed.
|
//
|
// Replicated copies are not as nice: if there is an array of
|
// objects with scalar tails, all but the last tail does have to
|
// be initialized, because there is no way to say "skip forward".
|
// However, because of the possibility of a repeated type with
|
// size not a multiple of 4 pointers (one heap bitmap byte),
|
// the code already must handle the last ptrmask byte specially
|
// by treating it as containing only the bits for endnb pointers,
|
// where endnb <= 4. We represent large scalar tails that must
|
// be expanded in the replication by setting endnb larger than 4.
|
// This will have the effect of reading many bits out of b,
|
// but once the real bits are shifted out, b will supply as many
|
// zero bits as we try to read, which is exactly what we need.
|
|
p = ptrmask
|
if typ.size < dataSize {
|
// Filling in bits for an array of typ.
|
// Set up for repetition of ptrmask during main loop.
|
// Note that ptrmask describes only a prefix of
|
const maxBits = sys.PtrSize*8 - 7
|
if typ.ptrdata/sys.PtrSize <= maxBits {
|
// Entire ptrmask fits in uintptr with room for a byte fragment.
|
// Load into pbits and never read from ptrmask again.
|
// This is especially important when the ptrmask has
|
// fewer than 8 bits in it; otherwise the reload in the middle
|
// of the Phase 2 loop would itself need to loop to gather
|
// at least 8 bits.
|
|
// Accumulate ptrmask into b.
|
// ptrmask is sized to describe only typ.ptrdata, but we record
|
// it as describing typ.size bytes, since all the high bits are zero.
|
nb = typ.ptrdata / sys.PtrSize
|
for i := uintptr(0); i < nb; i += 8 {
|
b |= uintptr(*p) << i
|
p = add1(p)
|
}
|
nb = typ.size / sys.PtrSize
|
|
// Replicate ptrmask to fill entire pbits uintptr.
|
// Doubling and truncating is fewer steps than
|
// iterating by nb each time. (nb could be 1.)
|
// Since we loaded typ.ptrdata/sys.PtrSize bits
|
// but are pretending to have typ.size/sys.PtrSize,
|
// there might be no replication necessary/possible.
|
pbits = b
|
endnb = nb
|
if nb+nb <= maxBits {
|
for endnb <= sys.PtrSize*8 {
|
pbits |= pbits << endnb
|
endnb += endnb
|
}
|
// Truncate to a multiple of original ptrmask.
|
// Because nb+nb <= maxBits, nb fits in a byte.
|
// Byte division is cheaper than uintptr division.
|
endnb = uintptr(maxBits/byte(nb)) * nb
|
pbits &= 1<<endnb - 1
|
b = pbits
|
nb = endnb
|
}
|
|
// Clear p and endp as sentinel for using pbits.
|
// Checked during Phase 2 loop.
|
p = nil
|
endp = nil
|
} else {
|
// Ptrmask is larger. Read it multiple times.
|
n := (typ.ptrdata/sys.PtrSize+7)/8 - 1
|
endp = addb(ptrmask, n)
|
endnb = typ.size/sys.PtrSize - n*8
|
}
|
}
|
if p != nil {
|
b = uintptr(*p)
|
p = add1(p)
|
nb = 8
|
}
|
|
if typ.size == dataSize {
|
// Single entry: can stop once we reach the non-pointer data.
|
nw = typ.ptrdata / sys.PtrSize
|
} else {
|
// Repeated instances of typ in an array.
|
// Have to process first N-1 entries in full, but can stop
|
// once we reach the non-pointer data in the final entry.
|
nw = ((dataSize/typ.size-1)*typ.size + typ.ptrdata) / sys.PtrSize
|
}
|
if nw == 0 {
|
// No pointers! Caller was supposed to check.
|
println("runtime: invalid type ", typ.string())
|
throw("heapBitsSetType: called with non-pointer type")
|
return
|
}
|
if nw < 2 {
|
// Must write at least 2 words, because the "no scan"
|
// encoding doesn't take effect until the third word.
|
nw = 2
|
}
|
|
// Phase 1: Special case for leading byte (shift==0) or half-byte (shift==2).
|
// The leading byte is special because it contains the bits for word 1,
|
// which does not have the scan bit set.
|
// The leading half-byte is special because it's a half a byte,
|
// so we have to be careful with the bits already there.
|
switch {
|
default:
|
throw("heapBitsSetType: unexpected shift")
|
|
case h.shift == 0:
|
// Ptrmask and heap bitmap are aligned.
|
// Handle first byte of bitmap specially.
|
//
|
// The first byte we write out covers the first four
|
// words of the object. The scan/dead bit on the first
|
// word must be set to scan since there are pointers
|
// somewhere in the object. The scan/dead bit on the
|
// second word is the checkmark, so we don't set it.
|
// In all following words, we set the scan/dead
|
// appropriately to indicate that the object contains
|
// to the next 2-bit entry in the bitmap.
|
//
|
// TODO: It doesn't matter if we set the checkmark, so
|
// maybe this case isn't needed any more.
|
hb = b & bitPointerAll
|
hb |= bitScan | bitScan<<(2*heapBitsShift) | bitScan<<(3*heapBitsShift)
|
if w += 4; w >= nw {
|
goto Phase3
|
}
|
*hbitp = uint8(hb)
|
hbitp = add1(hbitp)
|
b >>= 4
|
nb -= 4
|
|
case sys.PtrSize == 8 && h.shift == 2:
|
// Ptrmask and heap bitmap are misaligned.
|
// The bits for the first two words are in a byte shared
|
// with another object, so we must be careful with the bits
|
// already there.
|
// We took care of 1-word and 2-word objects above,
|
// so this is at least a 6-word object.
|
hb = (b & (bitPointer | bitPointer<<heapBitsShift)) << (2 * heapBitsShift)
|
// This is not noscan, so set the scan bit in the
|
// first word.
|
hb |= bitScan << (2 * heapBitsShift)
|
b >>= 2
|
nb -= 2
|
// Note: no bitScan for second word because that's
|
// the checkmark.
|
*hbitp &^= uint8((bitPointer | bitScan | (bitPointer << heapBitsShift)) << (2 * heapBitsShift))
|
*hbitp |= uint8(hb)
|
hbitp = add1(hbitp)
|
if w += 2; w >= nw {
|
// We know that there is more data, because we handled 2-word objects above.
|
// This must be at least a 6-word object. If we're out of pointer words,
|
// mark no scan in next bitmap byte and finish.
|
hb = 0
|
w += 4
|
goto Phase3
|
}
|
}
|
|
// Phase 2: Full bytes in bitmap, up to but not including write to last byte (full or partial) in bitmap.
|
// The loop computes the bits for that last write but does not execute the write;
|
// it leaves the bits in hb for processing by phase 3.
|
// To avoid repeated adjustment of nb, we subtract out the 4 bits we're going to
|
// use in the first half of the loop right now, and then we only adjust nb explicitly
|
// if the 8 bits used by each iteration isn't balanced by 8 bits loaded mid-loop.
|
nb -= 4
|
for {
|
// Emit bitmap byte.
|
// b has at least nb+4 bits, with one exception:
|
// if w+4 >= nw, then b has only nw-w bits,
|
// but we'll stop at the break and then truncate
|
// appropriately in Phase 3.
|
hb = b & bitPointerAll
|
hb |= bitScanAll
|
if w += 4; w >= nw {
|
break
|
}
|
*hbitp = uint8(hb)
|
hbitp = add1(hbitp)
|
b >>= 4
|
|
// Load more bits. b has nb right now.
|
if p != endp {
|
// Fast path: keep reading from ptrmask.
|
// nb unmodified: we just loaded 8 bits,
|
// and the next iteration will consume 8 bits,
|
// leaving us with the same nb the next time we're here.
|
if nb < 8 {
|
b |= uintptr(*p) << nb
|
p = add1(p)
|
} else {
|
// Reduce the number of bits in b.
|
// This is important if we skipped
|
// over a scalar tail, since nb could
|
// be larger than the bit width of b.
|
nb -= 8
|
}
|
} else if p == nil {
|
// Almost as fast path: track bit count and refill from pbits.
|
// For short repetitions.
|
if nb < 8 {
|
b |= pbits << nb
|
nb += endnb
|
}
|
nb -= 8 // for next iteration
|
} else {
|
// Slow path: reached end of ptrmask.
|
// Process final partial byte and rewind to start.
|
b |= uintptr(*p) << nb
|
nb += endnb
|
if nb < 8 {
|
b |= uintptr(*ptrmask) << nb
|
p = add1(ptrmask)
|
} else {
|
nb -= 8
|
p = ptrmask
|
}
|
}
|
|
// Emit bitmap byte.
|
hb = b & bitPointerAll
|
hb |= bitScanAll
|
if w += 4; w >= nw {
|
break
|
}
|
*hbitp = uint8(hb)
|
hbitp = add1(hbitp)
|
b >>= 4
|
}
|
|
Phase3:
|
// Phase 3: Write last byte or partial byte and zero the rest of the bitmap entries.
|
if w > nw {
|
// Counting the 4 entries in hb not yet written to memory,
|
// there are more entries than possible pointer slots.
|
// Discard the excess entries (can't be more than 3).
|
mask := uintptr(1)<<(4-(w-nw)) - 1
|
hb &= mask | mask<<4 // apply mask to both pointer bits and scan bits
|
}
|
|
// Change nw from counting possibly-pointer words to total words in allocation.
|
nw = size / sys.PtrSize
|
|
// Write whole bitmap bytes.
|
// The first is hb, the rest are zero.
|
if w <= nw {
|
*hbitp = uint8(hb)
|
hbitp = add1(hbitp)
|
hb = 0 // for possible final half-byte below
|
for w += 4; w <= nw; w += 4 {
|
*hbitp = 0
|
hbitp = add1(hbitp)
|
}
|
}
|
|
// Write final partial bitmap byte if any.
|
// We know w > nw, or else we'd still be in the loop above.
|
// It can be bigger only due to the 4 entries in hb that it counts.
|
// If w == nw+4 then there's nothing left to do: we wrote all nw entries
|
// and can discard the 4 sitting in hb.
|
// But if w == nw+2, we need to write first two in hb.
|
// The byte is shared with the next object, so be careful with
|
// existing bits.
|
if w == nw+2 {
|
*hbitp = *hbitp&^(bitPointer|bitScan|(bitPointer|bitScan)<<heapBitsShift) | uint8(hb)
|
}
|
|
Phase4:
|
// Phase 4: Copy unrolled bitmap to per-arena bitmaps, if necessary.
|
if outOfPlace {
|
// TODO: We could probably make this faster by
|
// handling [x+dataSize, x+size) specially.
|
h := heapBitsForAddr(x)
|
// cnw is the number of heap words, or bit pairs
|
// remaining (like nw above).
|
cnw := size / sys.PtrSize
|
src := (*uint8)(unsafe.Pointer(x))
|
// We know the first and last byte of the bitmap are
|
// not the same, but it's still possible for small
|
// objects span arenas, so it may share bitmap bytes
|
// with neighboring objects.
|
//
|
// Handle the first byte specially if it's shared. See
|
// Phase 1 for why this is the only special case we need.
|
if doubleCheck {
|
if !(h.shift == 0 || (sys.PtrSize == 8 && h.shift == 2)) {
|
print("x=", x, " size=", size, " cnw=", h.shift, "\n")
|
throw("bad start shift")
|
}
|
}
|
if sys.PtrSize == 8 && h.shift == 2 {
|
*h.bitp = *h.bitp&^((bitPointer|bitScan|(bitPointer|bitScan)<<heapBitsShift)<<(2*heapBitsShift)) | *src
|
h = h.next().next()
|
cnw -= 2
|
src = addb(src, 1)
|
}
|
// We're now byte aligned. Copy out to per-arena
|
// bitmaps until the last byte (which may again be
|
// partial).
|
for cnw >= 4 {
|
// This loop processes four words at a time,
|
// so round cnw down accordingly.
|
hNext, words := h.forwardOrBoundary(cnw / 4 * 4)
|
|
// n is the number of bitmap bytes to copy.
|
n := words / 4
|
memmove(unsafe.Pointer(h.bitp), unsafe.Pointer(src), n)
|
cnw -= words
|
h = hNext
|
src = addb(src, n)
|
}
|
if doubleCheck && h.shift != 0 {
|
print("cnw=", cnw, " h.shift=", h.shift, "\n")
|
throw("bad shift after block copy")
|
}
|
// Handle the last byte if it's shared.
|
if cnw == 2 {
|
*h.bitp = *h.bitp&^(bitPointer|bitScan|(bitPointer|bitScan)<<heapBitsShift) | *src
|
src = addb(src, 1)
|
h = h.next().next()
|
}
|
if doubleCheck {
|
if uintptr(unsafe.Pointer(src)) > x+size {
|
throw("copy exceeded object size")
|
}
|
if !(cnw == 0 || cnw == 2) {
|
print("x=", x, " size=", size, " cnw=", cnw, "\n")
|
throw("bad number of remaining words")
|
}
|
// Set up hbitp so doubleCheck code below can check it.
|
hbitp = h.bitp
|
}
|
// Zero the object where we wrote the bitmap.
|
memclrNoHeapPointers(unsafe.Pointer(x), uintptr(unsafe.Pointer(src))-x)
|
}
|
|
// Double check the whole bitmap.
|
if doubleCheck {
|
// x+size may not point to the heap, so back up one
|
// word and then call next().
|
end := heapBitsForAddr(x + size - sys.PtrSize).next()
|
endAI := arenaIdx(end.arena)
|
if !outOfPlace && (end.bitp == nil || (end.shift == 0 && end.bitp == &mheap_.arenas[endAI.l1()][endAI.l2()].bitmap[0])) {
|
// The unrolling code above walks hbitp just
|
// past the bitmap without moving to the next
|
// arena. Synthesize this for end.bitp.
|
end.arena--
|
endAI = arenaIdx(end.arena)
|
end.bitp = addb(&mheap_.arenas[endAI.l1()][endAI.l2()].bitmap[0], heapArenaBitmapBytes)
|
end.last = nil
|
}
|
if typ.kind&kindGCProg == 0 && (hbitp != end.bitp || (w == nw+2) != (end.shift == 2)) {
|
println("ended at wrong bitmap byte for", typ.string(), "x", dataSize/typ.size)
|
print("typ.size=", typ.size, " typ.ptrdata=", typ.ptrdata, " dataSize=", dataSize, " size=", size, "\n")
|
print("w=", w, " nw=", nw, " b=", hex(b), " nb=", nb, " hb=", hex(hb), "\n")
|
h0 := heapBitsForAddr(x)
|
print("initial bits h0.bitp=", h0.bitp, " h0.shift=", h0.shift, "\n")
|
print("ended at hbitp=", hbitp, " but next starts at bitp=", end.bitp, " shift=", end.shift, "\n")
|
throw("bad heapBitsSetType")
|
}
|
|
// Double-check that bits to be written were written correctly.
|
// Does not check that other bits were not written, unfortunately.
|
h := heapBitsForAddr(x)
|
nptr := typ.ptrdata / sys.PtrSize
|
ndata := typ.size / sys.PtrSize
|
count := dataSize / typ.size
|
totalptr := ((count-1)*typ.size + typ.ptrdata) / sys.PtrSize
|
for i := uintptr(0); i < size/sys.PtrSize; i++ {
|
j := i % ndata
|
var have, want uint8
|
have = (*h.bitp >> h.shift) & (bitPointer | bitScan)
|
if i >= totalptr {
|
want = 0 // deadmarker
|
if typ.kind&kindGCProg != 0 && i < (totalptr+3)/4*4 {
|
want = bitScan
|
}
|
} else {
|
if j < nptr && (*addb(ptrmask, j/8)>>(j%8))&1 != 0 {
|
want |= bitPointer
|
}
|
if i != 1 {
|
want |= bitScan
|
} else {
|
have &^= bitScan
|
}
|
}
|
if have != want {
|
println("mismatch writing bits for", typ.string(), "x", dataSize/typ.size)
|
print("typ.size=", typ.size, " typ.ptrdata=", typ.ptrdata, " dataSize=", dataSize, " size=", size, "\n")
|
print("kindGCProg=", typ.kind&kindGCProg != 0, " outOfPlace=", outOfPlace, "\n")
|
print("w=", w, " nw=", nw, " b=", hex(b), " nb=", nb, " hb=", hex(hb), "\n")
|
h0 := heapBitsForAddr(x)
|
print("initial bits h0.bitp=", h0.bitp, " h0.shift=", h0.shift, "\n")
|
print("current bits h.bitp=", h.bitp, " h.shift=", h.shift, " *h.bitp=", hex(*h.bitp), "\n")
|
print("ptrmask=", ptrmask, " p=", p, " endp=", endp, " endnb=", endnb, " pbits=", hex(pbits), " b=", hex(b), " nb=", nb, "\n")
|
println("at word", i, "offset", i*sys.PtrSize, "have", hex(have), "want", hex(want))
|
if typ.kind&kindGCProg != 0 {
|
println("GC program:")
|
dumpGCProg(addb(typ.gcdata, 4))
|
}
|
throw("bad heapBitsSetType")
|
}
|
h = h.next()
|
}
|
if ptrmask == debugPtrmask.data {
|
unlock(&debugPtrmask.lock)
|
}
|
}
|
}
|
|
var debugPtrmask struct {
|
lock mutex
|
data *byte
|
}
|
|
// heapBitsSetTypeGCProg implements heapBitsSetType using a GC program.
|
// progSize is the size of the memory described by the program.
|
// elemSize is the size of the element that the GC program describes (a prefix of).
|
// dataSize is the total size of the intended data, a multiple of elemSize.
|
// allocSize is the total size of the allocated memory.
|
//
|
// GC programs are only used for large allocations.
|
// heapBitsSetType requires that allocSize is a multiple of 4 words,
|
// so that the relevant bitmap bytes are not shared with surrounding
|
// objects.
|
func heapBitsSetTypeGCProg(h heapBits, progSize, elemSize, dataSize, allocSize uintptr, prog *byte) {
|
if sys.PtrSize == 8 && allocSize%(4*sys.PtrSize) != 0 {
|
// Alignment will be wrong.
|
throw("heapBitsSetTypeGCProg: small allocation")
|
}
|
var totalBits uintptr
|
if elemSize == dataSize {
|
totalBits = runGCProg(prog, nil, h.bitp, 2)
|
if totalBits*sys.PtrSize != progSize {
|
println("runtime: heapBitsSetTypeGCProg: total bits", totalBits, "but progSize", progSize)
|
throw("heapBitsSetTypeGCProg: unexpected bit count")
|
}
|
} else {
|
count := dataSize / elemSize
|
|
// Piece together program trailer to run after prog that does:
|
// literal(0)
|
// repeat(1, elemSize-progSize-1) // zeros to fill element size
|
// repeat(elemSize, count-1) // repeat that element for count
|
// This zero-pads the data remaining in the first element and then
|
// repeats that first element to fill the array.
|
var trailer [40]byte // 3 varints (max 10 each) + some bytes
|
i := 0
|
if n := elemSize/sys.PtrSize - progSize/sys.PtrSize; n > 0 {
|
// literal(0)
|
trailer[i] = 0x01
|
i++
|
trailer[i] = 0
|
i++
|
if n > 1 {
|
// repeat(1, n-1)
|
trailer[i] = 0x81
|
i++
|
n--
|
for ; n >= 0x80; n >>= 7 {
|
trailer[i] = byte(n | 0x80)
|
i++
|
}
|
trailer[i] = byte(n)
|
i++
|
}
|
}
|
// repeat(elemSize/ptrSize, count-1)
|
trailer[i] = 0x80
|
i++
|
n := elemSize / sys.PtrSize
|
for ; n >= 0x80; n >>= 7 {
|
trailer[i] = byte(n | 0x80)
|
i++
|
}
|
trailer[i] = byte(n)
|
i++
|
n = count - 1
|
for ; n >= 0x80; n >>= 7 {
|
trailer[i] = byte(n | 0x80)
|
i++
|
}
|
trailer[i] = byte(n)
|
i++
|
trailer[i] = 0
|
i++
|
|
runGCProg(prog, &trailer[0], h.bitp, 2)
|
|
// Even though we filled in the full array just now,
|
// record that we only filled in up to the ptrdata of the
|
// last element. This will cause the code below to
|
// memclr the dead section of the final array element,
|
// so that scanobject can stop early in the final element.
|
totalBits = (elemSize*(count-1) + progSize) / sys.PtrSize
|
}
|
endProg := unsafe.Pointer(addb(h.bitp, (totalBits+3)/4))
|
endAlloc := unsafe.Pointer(addb(h.bitp, allocSize/sys.PtrSize/wordsPerBitmapByte))
|
memclrNoHeapPointers(endProg, uintptr(endAlloc)-uintptr(endProg))
|
}
|
|
// progToPointerMask returns the 1-bit pointer mask output by the GC program prog.
|
// size the size of the region described by prog, in bytes.
|
// The resulting bitvector will have no more than size/sys.PtrSize bits.
|
func progToPointerMask(prog *byte, size uintptr) bitvector {
|
n := (size/sys.PtrSize + 7) / 8
|
x := (*[1 << 30]byte)(persistentalloc(n+1, 1, &memstats.buckhash_sys))[:n+1]
|
x[len(x)-1] = 0xa1 // overflow check sentinel
|
n = runGCProg(prog, nil, &x[0], 1)
|
if x[len(x)-1] != 0xa1 {
|
throw("progToPointerMask: overflow")
|
}
|
return bitvector{int32(n), &x[0]}
|
}
|
|
// Packed GC pointer bitmaps, aka GC programs.
|
//
|
// For large types containing arrays, the type information has a
|
// natural repetition that can be encoded to save space in the
|
// binary and in the memory representation of the type information.
|
//
|
// The encoding is a simple Lempel-Ziv style bytecode machine
|
// with the following instructions:
|
//
|
// 00000000: stop
|
// 0nnnnnnn: emit n bits copied from the next (n+7)/8 bytes
|
// 10000000 n c: repeat the previous n bits c times; n, c are varints
|
// 1nnnnnnn c: repeat the previous n bits c times; c is a varint
|
|
// runGCProg executes the GC program prog, and then trailer if non-nil,
|
// writing to dst with entries of the given size.
|
// If size == 1, dst is a 1-bit pointer mask laid out moving forward from dst.
|
// If size == 2, dst is the 2-bit heap bitmap, and writes move backward
|
// starting at dst (because the heap bitmap does). In this case, the caller guarantees
|
// that only whole bytes in dst need to be written.
|
//
|
// runGCProg returns the number of 1- or 2-bit entries written to memory.
|
func runGCProg(prog, trailer, dst *byte, size int) uintptr {
|
dstStart := dst
|
|
// Bits waiting to be written to memory.
|
var bits uintptr
|
var nbits uintptr
|
|
p := prog
|
Run:
|
for {
|
// Flush accumulated full bytes.
|
// The rest of the loop assumes that nbits <= 7.
|
for ; nbits >= 8; nbits -= 8 {
|
if size == 1 {
|
*dst = uint8(bits)
|
dst = add1(dst)
|
bits >>= 8
|
} else {
|
v := bits&bitPointerAll | bitScanAll
|
*dst = uint8(v)
|
dst = add1(dst)
|
bits >>= 4
|
v = bits&bitPointerAll | bitScanAll
|
*dst = uint8(v)
|
dst = add1(dst)
|
bits >>= 4
|
}
|
}
|
|
// Process one instruction.
|
inst := uintptr(*p)
|
p = add1(p)
|
n := inst & 0x7F
|
if inst&0x80 == 0 {
|
// Literal bits; n == 0 means end of program.
|
if n == 0 {
|
// Program is over; continue in trailer if present.
|
if trailer != nil {
|
//println("trailer")
|
p = trailer
|
trailer = nil
|
continue
|
}
|
//println("done")
|
break Run
|
}
|
//println("lit", n, dst)
|
nbyte := n / 8
|
for i := uintptr(0); i < nbyte; i++ {
|
bits |= uintptr(*p) << nbits
|
p = add1(p)
|
if size == 1 {
|
*dst = uint8(bits)
|
dst = add1(dst)
|
bits >>= 8
|
} else {
|
v := bits&0xf | bitScanAll
|
*dst = uint8(v)
|
dst = add1(dst)
|
bits >>= 4
|
v = bits&0xf | bitScanAll
|
*dst = uint8(v)
|
dst = add1(dst)
|
bits >>= 4
|
}
|
}
|
if n %= 8; n > 0 {
|
bits |= uintptr(*p) << nbits
|
p = add1(p)
|
nbits += n
|
}
|
continue Run
|
}
|
|
// Repeat. If n == 0, it is encoded in a varint in the next bytes.
|
if n == 0 {
|
for off := uint(0); ; off += 7 {
|
x := uintptr(*p)
|
p = add1(p)
|
n |= (x & 0x7F) << off
|
if x&0x80 == 0 {
|
break
|
}
|
}
|
}
|
|
// Count is encoded in a varint in the next bytes.
|
c := uintptr(0)
|
for off := uint(0); ; off += 7 {
|
x := uintptr(*p)
|
p = add1(p)
|
c |= (x & 0x7F) << off
|
if x&0x80 == 0 {
|
break
|
}
|
}
|
c *= n // now total number of bits to copy
|
|
// If the number of bits being repeated is small, load them
|
// into a register and use that register for the entire loop
|
// instead of repeatedly reading from memory.
|
// Handling fewer than 8 bits here makes the general loop simpler.
|
// The cutoff is sys.PtrSize*8 - 7 to guarantee that when we add
|
// the pattern to a bit buffer holding at most 7 bits (a partial byte)
|
// it will not overflow.
|
src := dst
|
const maxBits = sys.PtrSize*8 - 7
|
if n <= maxBits {
|
// Start with bits in output buffer.
|
pattern := bits
|
npattern := nbits
|
|
// If we need more bits, fetch them from memory.
|
if size == 1 {
|
src = subtract1(src)
|
for npattern < n {
|
pattern <<= 8
|
pattern |= uintptr(*src)
|
src = subtract1(src)
|
npattern += 8
|
}
|
} else {
|
src = subtract1(src)
|
for npattern < n {
|
pattern <<= 4
|
pattern |= uintptr(*src) & 0xf
|
src = subtract1(src)
|
npattern += 4
|
}
|
}
|
|
// We started with the whole bit output buffer,
|
// and then we loaded bits from whole bytes.
|
// Either way, we might now have too many instead of too few.
|
// Discard the extra.
|
if npattern > n {
|
pattern >>= npattern - n
|
npattern = n
|
}
|
|
// Replicate pattern to at most maxBits.
|
if npattern == 1 {
|
// One bit being repeated.
|
// If the bit is 1, make the pattern all 1s.
|
// If the bit is 0, the pattern is already all 0s,
|
// but we can claim that the number of bits
|
// in the word is equal to the number we need (c),
|
// because right shift of bits will zero fill.
|
if pattern == 1 {
|
pattern = 1<<maxBits - 1
|
npattern = maxBits
|
} else {
|
npattern = c
|
}
|
} else {
|
b := pattern
|
nb := npattern
|
if nb+nb <= maxBits {
|
// Double pattern until the whole uintptr is filled.
|
for nb <= sys.PtrSize*8 {
|
b |= b << nb
|
nb += nb
|
}
|
// Trim away incomplete copy of original pattern in high bits.
|
// TODO(rsc): Replace with table lookup or loop on systems without divide?
|
nb = maxBits / npattern * npattern
|
b &= 1<<nb - 1
|
pattern = b
|
npattern = nb
|
}
|
}
|
|
// Add pattern to bit buffer and flush bit buffer, c/npattern times.
|
// Since pattern contains >8 bits, there will be full bytes to flush
|
// on each iteration.
|
for ; c >= npattern; c -= npattern {
|
bits |= pattern << nbits
|
nbits += npattern
|
if size == 1 {
|
for nbits >= 8 {
|
*dst = uint8(bits)
|
dst = add1(dst)
|
bits >>= 8
|
nbits -= 8
|
}
|
} else {
|
for nbits >= 4 {
|
*dst = uint8(bits&0xf | bitScanAll)
|
dst = add1(dst)
|
bits >>= 4
|
nbits -= 4
|
}
|
}
|
}
|
|
// Add final fragment to bit buffer.
|
if c > 0 {
|
pattern &= 1<<c - 1
|
bits |= pattern << nbits
|
nbits += c
|
}
|
continue Run
|
}
|
|
// Repeat; n too large to fit in a register.
|
// Since nbits <= 7, we know the first few bytes of repeated data
|
// are already written to memory.
|
off := n - nbits // n > nbits because n > maxBits and nbits <= 7
|
if size == 1 {
|
// Leading src fragment.
|
src = subtractb(src, (off+7)/8)
|
if frag := off & 7; frag != 0 {
|
bits |= uintptr(*src) >> (8 - frag) << nbits
|
src = add1(src)
|
nbits += frag
|
c -= frag
|
}
|
// Main loop: load one byte, write another.
|
// The bits are rotating through the bit buffer.
|
for i := c / 8; i > 0; i-- {
|
bits |= uintptr(*src) << nbits
|
src = add1(src)
|
*dst = uint8(bits)
|
dst = add1(dst)
|
bits >>= 8
|
}
|
// Final src fragment.
|
if c %= 8; c > 0 {
|
bits |= (uintptr(*src) & (1<<c - 1)) << nbits
|
nbits += c
|
}
|
} else {
|
// Leading src fragment.
|
src = subtractb(src, (off+3)/4)
|
if frag := off & 3; frag != 0 {
|
bits |= (uintptr(*src) & 0xf) >> (4 - frag) << nbits
|
src = add1(src)
|
nbits += frag
|
c -= frag
|
}
|
// Main loop: load one byte, write another.
|
// The bits are rotating through the bit buffer.
|
for i := c / 4; i > 0; i-- {
|
bits |= (uintptr(*src) & 0xf) << nbits
|
src = add1(src)
|
*dst = uint8(bits&0xf | bitScanAll)
|
dst = add1(dst)
|
bits >>= 4
|
}
|
// Final src fragment.
|
if c %= 4; c > 0 {
|
bits |= (uintptr(*src) & (1<<c - 1)) << nbits
|
nbits += c
|
}
|
}
|
}
|
|
// Write any final bits out, using full-byte writes, even for the final byte.
|
var totalBits uintptr
|
if size == 1 {
|
totalBits = (uintptr(unsafe.Pointer(dst))-uintptr(unsafe.Pointer(dstStart)))*8 + nbits
|
nbits += -nbits & 7
|
for ; nbits > 0; nbits -= 8 {
|
*dst = uint8(bits)
|
dst = add1(dst)
|
bits >>= 8
|
}
|
} else {
|
totalBits = (uintptr(unsafe.Pointer(dst))-uintptr(unsafe.Pointer(dstStart)))*4 + nbits
|
nbits += -nbits & 3
|
for ; nbits > 0; nbits -= 4 {
|
v := bits&0xf | bitScanAll
|
*dst = uint8(v)
|
dst = add1(dst)
|
bits >>= 4
|
}
|
}
|
return totalBits
|
}
|
|
// materializeGCProg allocates space for the (1-bit) pointer bitmask
|
// for an object of size ptrdata. Then it fills that space with the
|
// pointer bitmask specified by the program prog.
|
// The bitmask starts at s.startAddr.
|
// The result must be deallocated with dematerializeGCProg.
|
func materializeGCProg(ptrdata uintptr, prog *byte) *mspan {
|
s := mheap_.allocManual((ptrdata/(8*sys.PtrSize)+pageSize-1)/pageSize, &memstats.gc_sys)
|
runGCProg(addb(prog, 4), nil, (*byte)(unsafe.Pointer(s.startAddr)), 1)
|
return s
|
}
|
func dematerializeGCProg(s *mspan) {
|
mheap_.freeManual(s, &memstats.gc_sys)
|
}
|
|
func dumpGCProg(p *byte) {
|
nptr := 0
|
for {
|
x := *p
|
p = add1(p)
|
if x == 0 {
|
print("\t", nptr, " end\n")
|
break
|
}
|
if x&0x80 == 0 {
|
print("\t", nptr, " lit ", x, ":")
|
n := int(x+7) / 8
|
for i := 0; i < n; i++ {
|
print(" ", hex(*p))
|
p = add1(p)
|
}
|
print("\n")
|
nptr += int(x)
|
} else {
|
nbit := int(x &^ 0x80)
|
if nbit == 0 {
|
for nb := uint(0); ; nb += 7 {
|
x := *p
|
p = add1(p)
|
nbit |= int(x&0x7f) << nb
|
if x&0x80 == 0 {
|
break
|
}
|
}
|
}
|
count := 0
|
for nb := uint(0); ; nb += 7 {
|
x := *p
|
p = add1(p)
|
count |= int(x&0x7f) << nb
|
if x&0x80 == 0 {
|
break
|
}
|
}
|
print("\t", nptr, " repeat ", nbit, " × ", count, "\n")
|
nptr += nbit * count
|
}
|
}
|
}
|
|
// Testing.
|
|
func getgcmaskcb(frame *stkframe, ctxt unsafe.Pointer) bool {
|
target := (*stkframe)(ctxt)
|
if frame.sp <= target.sp && target.sp < frame.varp {
|
*target = *frame
|
return false
|
}
|
return true
|
}
|
|
// gcbits returns the GC type info for x, for testing.
|
// The result is the bitmap entries (0 or 1), one entry per byte.
|
//go:linkname reflect_gcbits reflect.gcbits
|
func reflect_gcbits(x interface{}) []byte {
|
ret := getgcmask(x)
|
typ := (*ptrtype)(unsafe.Pointer(efaceOf(&x)._type)).elem
|
nptr := typ.ptrdata / sys.PtrSize
|
for uintptr(len(ret)) > nptr && ret[len(ret)-1] == 0 {
|
ret = ret[:len(ret)-1]
|
}
|
return ret
|
}
|
|
// Returns GC type info for the pointer stored in ep for testing.
|
// If ep points to the stack, only static live information will be returned
|
// (i.e. not for objects which are only dynamically live stack objects).
|
func getgcmask(ep interface{}) (mask []byte) {
|
e := *efaceOf(&ep)
|
p := e.data
|
t := e._type
|
// data or bss
|
for _, datap := range activeModules() {
|
// data
|
if datap.data <= uintptr(p) && uintptr(p) < datap.edata {
|
bitmap := datap.gcdatamask.bytedata
|
n := (*ptrtype)(unsafe.Pointer(t)).elem.size
|
mask = make([]byte, n/sys.PtrSize)
|
for i := uintptr(0); i < n; i += sys.PtrSize {
|
off := (uintptr(p) + i - datap.data) / sys.PtrSize
|
mask[i/sys.PtrSize] = (*addb(bitmap, off/8) >> (off % 8)) & 1
|
}
|
return
|
}
|
|
// bss
|
if datap.bss <= uintptr(p) && uintptr(p) < datap.ebss {
|
bitmap := datap.gcbssmask.bytedata
|
n := (*ptrtype)(unsafe.Pointer(t)).elem.size
|
mask = make([]byte, n/sys.PtrSize)
|
for i := uintptr(0); i < n; i += sys.PtrSize {
|
off := (uintptr(p) + i - datap.bss) / sys.PtrSize
|
mask[i/sys.PtrSize] = (*addb(bitmap, off/8) >> (off % 8)) & 1
|
}
|
return
|
}
|
}
|
|
// heap
|
if base, s, _ := findObject(uintptr(p), 0, 0); base != 0 {
|
hbits := heapBitsForAddr(base)
|
n := s.elemsize
|
mask = make([]byte, n/sys.PtrSize)
|
for i := uintptr(0); i < n; i += sys.PtrSize {
|
if hbits.isPointer() {
|
mask[i/sys.PtrSize] = 1
|
}
|
if i != 1*sys.PtrSize && !hbits.morePointers() {
|
mask = mask[:i/sys.PtrSize]
|
break
|
}
|
hbits = hbits.next()
|
}
|
return
|
}
|
|
// stack
|
if _g_ := getg(); _g_.m.curg.stack.lo <= uintptr(p) && uintptr(p) < _g_.m.curg.stack.hi {
|
var frame stkframe
|
frame.sp = uintptr(p)
|
_g_ := getg()
|
gentraceback(_g_.m.curg.sched.pc, _g_.m.curg.sched.sp, 0, _g_.m.curg, 0, nil, 1000, getgcmaskcb, noescape(unsafe.Pointer(&frame)), 0)
|
if frame.fn.valid() {
|
locals, _, _ := getStackMap(&frame, nil, false)
|
if locals.n == 0 {
|
return
|
}
|
size := uintptr(locals.n) * sys.PtrSize
|
n := (*ptrtype)(unsafe.Pointer(t)).elem.size
|
mask = make([]byte, n/sys.PtrSize)
|
for i := uintptr(0); i < n; i += sys.PtrSize {
|
off := (uintptr(p) + i - frame.varp + size) / sys.PtrSize
|
mask[i/sys.PtrSize] = locals.ptrbit(off)
|
}
|
}
|
return
|
}
|
|
// otherwise, not something the GC knows about.
|
// possibly read-only data, like malloc(0).
|
// must not have pointers
|
return
|
}
|
