// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Export guts for testing.

package runtime

import (
	"math/bits"
	"runtime/internal/atomic"
	"runtime/internal/sys"
	"unsafe"
)

var Fadd64 = fadd64
var Fsub64 = fsub64
var Fmul64 = fmul64
var Fdiv64 = fdiv64
var F64to32 = f64to32
var F32to64 = f32to64
var Fcmp64 = fcmp64
var Fintto64 = fintto64
var F64toint = f64toint

var Entersyscall = entersyscall
var Exitsyscall = exitsyscall
var LockedOSThread = lockedOSThread
var Xadduintptr = atomic.Xadduintptr

var FuncPC = funcPC

var Fastlog2 = fastlog2

var Atoi = atoi
var Atoi32 = atoi32

var Nanotime = nanotime
var NetpollBreak = netpollBreak
var Usleep = usleep

var PhysPageSize = physPageSize
var PhysHugePageSize = physHugePageSize

var NetpollGenericInit = netpollGenericInit

const PreemptMSupported = preemptMSupported

type LFNode struct {
	Next    uint64
	Pushcnt uintptr
}

func LFStackPush(head *uint64, node *LFNode) {
	(*lfstack)(head).push((*lfnode)(unsafe.Pointer(node)))
}

func LFStackPop(head *uint64) *LFNode {
	return (*LFNode)(unsafe.Pointer((*lfstack)(head).pop()))
}

func Netpoll(delta int64) {
	systemstack(func() {
		netpoll(delta)
	})
}

func GCMask(x interface{}) (ret []byte) {
	systemstack(func() {
		ret = getgcmask(x)
	})
	return
}

func RunSchedLocalQueueTest() {
	_p_ := new(p)
	gs := make([]g, len(_p_.runq))
	for i := 0; i < len(_p_.runq); i++ {
		if g, _ := runqget(_p_); g != nil {
			throw("runq is not empty initially")
		}
		for j := 0; j < i; j++ {
			runqput(_p_, &gs[i], false)
		}
		for j := 0; j < i; j++ {
			if g, _ := runqget(_p_); g != &gs[i] {
				print("bad element at iter ", i, "/", j, "\n")
				throw("bad element")
			}
		}
		if g, _ := runqget(_p_); g != nil {
			throw("runq is not empty afterwards")
		}
	}
}

func RunSchedLocalQueueStealTest() {
	p1 := new(p)
	p2 := new(p)
	gs := make([]g, len(p1.runq))
	for i := 0; i < len(p1.runq); i++ {
		for j := 0; j < i; j++ {
			gs[j].sig = 0
			runqput(p1, &gs[j], false)
		}
		gp := runqsteal(p2, p1, true)
		s := 0
		if gp != nil {
			s++
			gp.sig++
		}
		for {
			gp, _ = runqget(p2)
			if gp == nil {
				break
			}
			s++
			gp.sig++
		}
		for {
			gp, _ = runqget(p1)
			if gp == nil {
				break
			}
			gp.sig++
		}
		for j := 0; j < i; j++ {
			if gs[j].sig != 1 {
				print("bad element ", j, "(", gs[j].sig, ") at iter ", i, "\n")
				throw("bad element")
			}
		}
		if s != i/2 && s != i/2+1 {
			print("bad steal ", s, ", want ", i/2, " or ", i/2+1, ", iter ", i, "\n")
			throw("bad steal")
		}
	}
}

func RunSchedLocalQueueEmptyTest(iters int) {
	// Test that runq is not spuriously reported as empty.
	// Runq emptiness affects scheduling decisions and spurious emptiness
	// can lead to underutilization (both runnable Gs and idle Ps coexist
	// for arbitrary long time).
	done := make(chan bool, 1)
	p := new(p)
	gs := make([]g, 2)
	ready := new(uint32)
	for i := 0; i < iters; i++ {
		*ready = 0
		next0 := (i & 1) == 0
		next1 := (i & 2) == 0
		runqput(p, &gs[0], next0)
		go func() {
			for atomic.Xadd(ready, 1); atomic.Load(ready) != 2; {
			}
			if runqempty(p) {
				println("next:", next0, next1)
				throw("queue is empty")
			}
			done <- true
		}()
		for atomic.Xadd(ready, 1); atomic.Load(ready) != 2; {
		}
		runqput(p, &gs[1], next1)
		runqget(p)
		<-done
		runqget(p)
	}
}

var (
	StringHash = stringHash
	BytesHash  = bytesHash
	Int32Hash  = int32Hash
	Int64Hash  = int64Hash
	MemHash    = memhash
	MemHash32  = memhash32
	MemHash64  = memhash64
	EfaceHash  = efaceHash
	IfaceHash  = ifaceHash
)

var UseAeshash = &useAeshash

func MemclrBytes(b []byte) {
	s := (*slice)(unsafe.Pointer(&b))
	memclrNoHeapPointers(s.array, uintptr(s.len))
}

var HashLoad = &hashLoad

// entry point for testing
func GostringW(w []uint16) (s string) {
	systemstack(func() {
		s = gostringw(&w[0])
	})
	return
}

type Uintreg sys.Uintreg

var Open = open
var Close = closefd
var Read = read
var Write = write

func Envs() []string     { return envs }
func SetEnvs(e []string) { envs = e }

var BigEndian = sys.BigEndian

// For benchmarking.

func BenchSetType(n int, x interface{}) {
	e := *efaceOf(&x)
	t := e._type
	var size uintptr
	var p unsafe.Pointer
	switch t.kind & kindMask {
	case kindPtr:
		t = (*ptrtype)(unsafe.Pointer(t)).elem
		size = t.size
		p = e.data
	case kindSlice:
		slice := *(*struct {
			ptr      unsafe.Pointer
			len, cap uintptr
		})(e.data)
		t = (*slicetype)(unsafe.Pointer(t)).elem
		size = t.size * slice.len
		p = slice.ptr
	}
	allocSize := roundupsize(size)
	systemstack(func() {
		for i := 0; i < n; i++ {
			heapBitsSetType(uintptr(p), allocSize, size, t)
		}
	})
}

const PtrSize = sys.PtrSize

var ForceGCPeriod = &forcegcperiod

// SetTracebackEnv is like runtime/debug.SetTraceback, but it raises
// the "environment" traceback level, so later calls to
// debug.SetTraceback (e.g., from testing timeouts) can't lower it.
func SetTracebackEnv(level string) {
	setTraceback(level)
	traceback_env = traceback_cache
}

var ReadUnaligned32 = readUnaligned32
var ReadUnaligned64 = readUnaligned64

func CountPagesInUse() (pagesInUse, counted uintptr) {
	stopTheWorld("CountPagesInUse")

	pagesInUse = uintptr(mheap_.pagesInUse)

	for _, s := range mheap_.allspans {
		if s.state.get() == mSpanInUse {
			counted += s.npages
		}
	}

	startTheWorld()

	return
}

func Fastrand() uint32          { return fastrand() }
func Fastrandn(n uint32) uint32 { return fastrandn(n) }

type ProfBuf profBuf

func NewProfBuf(hdrsize, bufwords, tags int) *ProfBuf {
	return (*ProfBuf)(newProfBuf(hdrsize, bufwords, tags))
}

func (p *ProfBuf) Write(tag *unsafe.Pointer, now int64, hdr []uint64, stk []uintptr) {
	(*profBuf)(p).write(tag, now, hdr, stk)
}

const (
	ProfBufBlocking    = profBufBlocking
	ProfBufNonBlocking = profBufNonBlocking
)

func (p *ProfBuf) Read(mode profBufReadMode) ([]uint64, []unsafe.Pointer, bool) {
	return (*profBuf)(p).read(profBufReadMode(mode))
}

func (p *ProfBuf) Close() {
	(*profBuf)(p).close()
}

// ReadMemStatsSlow returns both the runtime-computed MemStats and
// MemStats accumulated by scanning the heap.
func ReadMemStatsSlow() (base, slow MemStats) {
	stopTheWorld("ReadMemStatsSlow")

	// Run on the system stack to avoid stack growth allocation.
	systemstack(func() {
		// Make sure stats don't change.
		getg().m.mallocing++

		readmemstats_m(&base)

		// Initialize slow from base and zero the fields we're
		// recomputing.
		slow = base
		slow.Alloc = 0
		slow.TotalAlloc = 0
		slow.Mallocs = 0
		slow.Frees = 0
		slow.HeapReleased = 0
		var bySize [_NumSizeClasses]struct {
			Mallocs, Frees uint64
		}

		// Add up current allocations in spans.
		for _, s := range mheap_.allspans {
			if s.state.get() != mSpanInUse {
				continue
			}
			if sizeclass := s.spanclass.sizeclass(); sizeclass == 0 {
				slow.Mallocs++
				slow.Alloc += uint64(s.elemsize)
			} else {
				slow.Mallocs += uint64(s.allocCount)
				slow.Alloc += uint64(s.allocCount) * uint64(s.elemsize)
				bySize[sizeclass].Mallocs += uint64(s.allocCount)
			}
		}

		// Add in frees. readmemstats_m flushed the cached stats, so
		// these are up-to-date.
		var smallFree uint64
		slow.Frees = mheap_.nlargefree
		for i := range mheap_.nsmallfree {
			slow.Frees += mheap_.nsmallfree[i]
			bySize[i].Frees = mheap_.nsmallfree[i]
			bySize[i].Mallocs += mheap_.nsmallfree[i]
			smallFree += mheap_.nsmallfree[i] * uint64(class_to_size[i])
		}
		slow.Frees += memstats.tinyallocs
		slow.Mallocs += slow.Frees

		slow.TotalAlloc = slow.Alloc + mheap_.largefree + smallFree

		for i := range slow.BySize {
			slow.BySize[i].Mallocs = bySize[i].Mallocs
			slow.BySize[i].Frees = bySize[i].Frees
		}

		for i := mheap_.pages.start; i < mheap_.pages.end; i++ {
			pg := mheap_.pages.chunks[i].scavenged.popcntRange(0, pallocChunkPages)
			slow.HeapReleased += uint64(pg) * pageSize
		}
		for _, p := range allp {
			pg := bits.OnesCount64(p.pcache.scav)
			slow.HeapReleased += uint64(pg) * pageSize
		}

		// Unused space in the current arena also counts as released space.
		slow.HeapReleased += uint64(mheap_.curArena.end - mheap_.curArena.base)

		getg().m.mallocing--
	})

	startTheWorld()
	return
}

// BlockOnSystemStack switches to the system stack, prints "x\n" to
// stderr, and blocks in a stack containing
// "runtime.blockOnSystemStackInternal".
func BlockOnSystemStack() {
	systemstack(blockOnSystemStackInternal)
}

func blockOnSystemStackInternal() {
	print("x\n")
	lock(&deadlock)
	lock(&deadlock)
}

type RWMutex struct {
	rw rwmutex
}

func (rw *RWMutex) RLock() {
	rw.rw.rlock()
}

func (rw *RWMutex) RUnlock() {
	rw.rw.runlock()
}

func (rw *RWMutex) Lock() {
	rw.rw.lock()
}

func (rw *RWMutex) Unlock() {
	rw.rw.unlock()
}

const RuntimeHmapSize = unsafe.Sizeof(hmap{})

func MapBucketsCount(m map[int]int) int {
	h := *(**hmap)(unsafe.Pointer(&m))
	return 1 << h.B
}

func MapBucketsPointerIsNil(m map[int]int) bool {
	h := *(**hmap)(unsafe.Pointer(&m))
	return h.buckets == nil
}

func LockOSCounts() (external, internal uint32) {
	g := getg()
	if g.m.lockedExt+g.m.lockedInt == 0 {
		if g.lockedm != 0 {
			panic("lockedm on non-locked goroutine")
		}
	} else {
		if g.lockedm == 0 {
			panic("nil lockedm on locked goroutine")
		}
	}
	return g.m.lockedExt, g.m.lockedInt
}

//go:noinline
func TracebackSystemstack(stk []uintptr, i int) int {
	if i == 0 {
		pc, sp := getcallerpc(), getcallersp()
		return gentraceback(pc, sp, 0, getg(), 0, &stk[0], len(stk), nil, nil, _TraceJumpStack)
	}
	n := 0
	systemstack(func() {
		n = TracebackSystemstack(stk, i-1)
	})
	return n
}

func KeepNArenaHints(n int) {
	hint := mheap_.arenaHints
	for i := 1; i < n; i++ {
		hint = hint.next
		if hint == nil {
			return
		}
	}
	hint.next = nil
}

// MapNextArenaHint reserves a page at the next arena growth hint,
// preventing the arena from growing there, and returns the range of
// addresses that are no longer viable.
func MapNextArenaHint() (start, end uintptr) {
	hint := mheap_.arenaHints
	addr := hint.addr
	if hint.down {
		start, end = addr-heapArenaBytes, addr
		addr -= physPageSize
	} else {
		start, end = addr, addr+heapArenaBytes
	}
	sysReserve(unsafe.Pointer(addr), physPageSize)
	return
}

func GetNextArenaHint() uintptr {
	return mheap_.arenaHints.addr
}

type G = g

func Getg() *G {
	return getg()
}

//go:noinline
func PanicForTesting(b []byte, i int) byte {
	return unexportedPanicForTesting(b, i)
}

//go:noinline
func unexportedPanicForTesting(b []byte, i int) byte {
	return b[i]
}

func G0StackOverflow() {
	systemstack(func() {
		stackOverflow(nil)
	})
}

func stackOverflow(x *byte) {
	var buf [256]byte
	stackOverflow(&buf[0])
}

func MapTombstoneCheck(m map[int]int) {
	// Make sure emptyOne and emptyRest are distributed correctly.
	// We should have a series of filled and emptyOne cells, followed by
	// a series of emptyRest cells.
	h := *(**hmap)(unsafe.Pointer(&m))
	i := interface{}(m)
	t := *(**maptype)(unsafe.Pointer(&i))

	for x := 0; x < 1<<h.B; x++ {
		b0 := (*bmap)(add(h.buckets, uintptr(x)*uintptr(t.bucketsize)))
		n := 0
		for b := b0; b != nil; b = b.overflow(t) {
			for i := 0; i < bucketCnt; i++ {
				if b.tophash[i] != emptyRest {
					n++
				}
			}
		}
		k := 0
		for b := b0; b != nil; b = b.overflow(t) {
			for i := 0; i < bucketCnt; i++ {
				if k < n && b.tophash[i] == emptyRest {
					panic("early emptyRest")
				}
				if k >= n && b.tophash[i] != emptyRest {
					panic("late non-emptyRest")
				}
				if k == n-1 && b.tophash[i] == emptyOne {
					panic("last non-emptyRest entry is emptyOne")
				}
				k++
			}
		}
	}
}

func RunGetgThreadSwitchTest() {
	// Test that getg works correctly with thread switch.
	// With gccgo, if we generate getg inlined, the backend
	// may cache the address of the TLS variable, which
	// will become invalid after a thread switch. This test
	// checks that the bad caching doesn't happen.

	ch := make(chan int)
	go func(ch chan int) {
		ch <- 5
		LockOSThread()
	}(ch)

	g1 := getg()

	// Block on a receive. This is likely to get us a thread
	// switch. If we yield to the sender goroutine, it will
	// lock the thread, forcing us to resume on a different
	// thread.
	<-ch

	g2 := getg()
	if g1 != g2 {
		panic("g1 != g2")
	}

	// Also test getg after some control flow, as the
	// backend is sensitive to control flow.
	g3 := getg()
	if g1 != g3 {
		panic("g1 != g3")
	}
}

const (
	PageSize         = pageSize
	PallocChunkPages = pallocChunkPages
)

// Expose pallocSum for testing.
type PallocSum pallocSum

func PackPallocSum(start, max, end uint) PallocSum { return PallocSum(packPallocSum(start, max, end)) }
func (m PallocSum) Start() uint                    { return pallocSum(m).start() }
func (m PallocSum) Max() uint                      { return pallocSum(m).max() }
func (m PallocSum) End() uint                      { return pallocSum(m).end() }

// Expose pallocBits for testing.
type PallocBits pallocBits

func (b *PallocBits) Find(npages uintptr, searchIdx uint) (uint, uint) {
	return (*pallocBits)(b).find(npages, searchIdx)
}
func (b *PallocBits) AllocRange(i, n uint)       { (*pallocBits)(b).allocRange(i, n) }
func (b *PallocBits) Free(i, n uint)             { (*pallocBits)(b).free(i, n) }
func (b *PallocBits) Summarize() PallocSum       { return PallocSum((*pallocBits)(b).summarize()) }
func (b *PallocBits) PopcntRange(i, n uint) uint { return (*pageBits)(b).popcntRange(i, n) }

// SummarizeSlow is a slow but more obviously correct implementation
// of (*pallocBits).summarize. Used for testing.
func SummarizeSlow(b *PallocBits) PallocSum {
	var start, max, end uint

	const N = uint(len(b)) * 64
	for start < N && (*pageBits)(b).get(start) == 0 {
		start++
	}
	for end < N && (*pageBits)(b).get(N-end-1) == 0 {
		end++
	}
	run := uint(0)
	for i := uint(0); i < N; i++ {
		if (*pageBits)(b).get(i) == 0 {
			run++
		} else {
			run = 0
		}
		if run > max {
			max = run
		}
	}
	return PackPallocSum(start, max, end)
}

// Expose non-trivial helpers for testing.
func FindBitRange64(c uint64, n uint) uint { return findBitRange64(c, n) }

// Given two PallocBits, returns a set of bit ranges where
// they differ.
func DiffPallocBits(a, b *PallocBits) []BitRange {
	ba := (*pageBits)(a)
	bb := (*pageBits)(b)

	var d []BitRange
	base, size := uint(0), uint(0)
	for i := uint(0); i < uint(len(ba))*64; i++ {
		if ba.get(i) != bb.get(i) {
			if size == 0 {
				base = i
			}
			size++
		} else {
			if size != 0 {
				d = append(d, BitRange{base, size})
			}
			size = 0
		}
	}
	if size != 0 {
		d = append(d, BitRange{base, size})
	}
	return d
}

// StringifyPallocBits gets the bits in the bit range r from b,
// and returns a string containing the bits as ASCII 0 and 1
// characters.
func StringifyPallocBits(b *PallocBits, r BitRange) string {
	str := ""
	for j := r.I; j < r.I+r.N; j++ {
		if (*pageBits)(b).get(j) != 0 {
			str += "1"
		} else {
			str += "0"
		}
	}
	return str
}

// Expose pallocData for testing.
type PallocData pallocData

func (d *PallocData) FindScavengeCandidate(searchIdx uint, min, max uintptr) (uint, uint) {
	return (*pallocData)(d).findScavengeCandidate(searchIdx, min, max)
}
func (d *PallocData) AllocRange(i, n uint) { (*pallocData)(d).allocRange(i, n) }
func (d *PallocData) ScavengedSetRange(i, n uint) {
	(*pallocData)(d).scavenged.setRange(i, n)
}
func (d *PallocData) PallocBits() *PallocBits {
	return (*PallocBits)(&(*pallocData)(d).pallocBits)
}
func (d *PallocData) Scavenged() *PallocBits {
	return (*PallocBits)(&(*pallocData)(d).scavenged)
}

// Expose fillAligned for testing.
func FillAligned(x uint64, m uint) uint64 { return fillAligned(x, m) }

// Expose pageCache for testing.
type PageCache pageCache

const PageCachePages = pageCachePages

func NewPageCache(base uintptr, cache, scav uint64) PageCache {
	return PageCache(pageCache{base: base, cache: cache, scav: scav})
}
func (c *PageCache) Empty() bool   { return (*pageCache)(c).empty() }
func (c *PageCache) Base() uintptr { return (*pageCache)(c).base }
func (c *PageCache) Cache() uint64 { return (*pageCache)(c).cache }
func (c *PageCache) Scav() uint64  { return (*pageCache)(c).scav }
func (c *PageCache) Alloc(npages uintptr) (uintptr, uintptr) {
	return (*pageCache)(c).alloc(npages)
}
func (c *PageCache) Flush(s *PageAlloc) {
	(*pageCache)(c).flush((*pageAlloc)(s))
}

// Expose chunk index type.
type ChunkIdx chunkIdx

// Expose pageAlloc for testing. Note that because pageAlloc is
// not in the heap, so is PageAlloc.
type PageAlloc pageAlloc

func (p *PageAlloc) Alloc(npages uintptr) (uintptr, uintptr) {
	return (*pageAlloc)(p).alloc(npages)
}
func (p *PageAlloc) AllocToCache() PageCache {
	return PageCache((*pageAlloc)(p).allocToCache())
}
func (p *PageAlloc) Free(base, npages uintptr) {
	(*pageAlloc)(p).free(base, npages)
}
func (p *PageAlloc) Bounds() (ChunkIdx, ChunkIdx) {
	return ChunkIdx((*pageAlloc)(p).start), ChunkIdx((*pageAlloc)(p).end)
}
func (p *PageAlloc) PallocData(i ChunkIdx) *PallocData {
	return (*PallocData)(&((*pageAlloc)(p).chunks[i]))
}
func (p *PageAlloc) Scavenge(nbytes uintptr, locked bool) (r uintptr) {
	systemstack(func() {
		r = (*pageAlloc)(p).scavenge(nbytes, locked)
	})
	return
}

// BitRange represents a range over a bitmap.
type BitRange struct {
	I, N uint // bit index and length in bits
}

// NewPageAlloc creates a new page allocator for testing and
// initializes it with the scav and chunks maps. Each key in these maps
// represents a chunk index and each value is a series of bit ranges to
// set within each bitmap's chunk.
//
// The initialization of the pageAlloc preserves the invariant that if a
// scavenged bit is set the alloc bit is necessarily unset, so some
// of the bits described by scav may be cleared in the final bitmap if
// ranges in chunks overlap with them.
//
// scav is optional, and if nil, the scavenged bitmap will be cleared
// (as opposed to all 1s, which it usually is). Furthermore, every
// chunk index in scav must appear in chunks; ones that do not are
// ignored.
func NewPageAlloc(chunks, scav map[ChunkIdx][]BitRange) *PageAlloc {
	p := new(pageAlloc)

	// We've got an entry, so initialize the pageAlloc.
	p.init(new(mutex), nil)
	p.test = true

	for i, init := range chunks {
		addr := chunkBase(chunkIdx(i))

		// Mark the chunk's existence in the pageAlloc.
		p.grow(addr, pallocChunkBytes)

		// Initialize the bitmap and update pageAlloc metadata.
		chunk := &p.chunks[chunkIndex(addr)]

		// Clear all the scavenged bits which grow set.
		chunk.scavenged.clearRange(0, pallocChunkPages)

		// Apply scavenge state if applicable.
		if scav != nil {
			if scvg, ok := scav[i]; ok {
				for _, s := range scvg {
					// Ignore the case of s.N == 0. setRange doesn't handle
					// it and it's a no-op anyway.
					if s.N != 0 {
						chunk.scavenged.setRange(s.I, s.N)
					}
				}
			}
		}
		p.resetScavengeAddr()

		// Apply alloc state.
		for _, s := range init {
			// Ignore the case of s.N == 0. allocRange doesn't handle
			// it and it's a no-op anyway.
			if s.N != 0 {
				chunk.allocRange(s.I, s.N)
			}
		}

		// Update heap metadata for the allocRange calls above.
		p.update(addr, pallocChunkPages, false, false)
	}
	return (*PageAlloc)(p)
}

// FreePageAlloc releases hard OS resources owned by the pageAlloc. Once this
// is called the pageAlloc may no longer be used. The object itself will be
// collected by the garbage collector once it is no longer live.
func FreePageAlloc(pp *PageAlloc) {
	p := (*pageAlloc)(pp)

	// Free all the mapped space for the summary levels.
	if pageAlloc64Bit != 0 {
		for l := 0; l < summaryLevels; l++ {
			sysFree(unsafe.Pointer(&p.summary[l][0]), uintptr(cap(p.summary[l]))*pallocSumBytes, nil)
		}
	} else {
		resSize := uintptr(0)
		for _, s := range p.summary {
			resSize += uintptr(cap(s)) * pallocSumBytes
		}
		sysFree(unsafe.Pointer(&p.summary[0][0]), alignUp(resSize, physPageSize), nil)
	}

	// Free the mapped space for chunks.
	chunksLen := uintptr(cap(p.chunks)) * unsafe.Sizeof(p.chunks[0])
	sysFree(unsafe.Pointer(&p.chunks[0]), alignUp(chunksLen, physPageSize), nil)
}

// BaseChunkIdx is a convenient chunkIdx value which works on both
// 64 bit and 32 bit platforms, allowing the tests to share code
// between the two.
var BaseChunkIdx = ChunkIdx(chunkIndex((0xc000*pageAlloc64Bit + 0x200*pageAlloc32Bit) * pallocChunkBytes))

// PageBase returns an address given a chunk index and a page index
// relative to that chunk.
func PageBase(c ChunkIdx, pageIdx uint) uintptr {
	return chunkBase(chunkIdx(c)) + uintptr(pageIdx)*pageSize
}

type BitsMismatch struct {
	Base      uintptr
	Got, Want uint64
}

func CheckScavengedBitsCleared(mismatches []BitsMismatch) (n int, ok bool) {
	ok = true

	// Run on the system stack to avoid stack growth allocation.
	systemstack(func() {
		getg().m.mallocing++

		// Lock so that we can safely access the bitmap.
		lock(&mheap_.lock)
	chunkLoop:
		for i := mheap_.pages.start; i < mheap_.pages.end; i++ {
			chunk := &mheap_.pages.chunks[i]
			for j := 0; j < pallocChunkPages/64; j++ {
				// Run over each 64-bit bitmap section and ensure
				// scavenged is being cleared properly on allocation.
				// If a used bit and scavenged bit are both set, that's
				// an error, and could indicate a larger problem, or
				// an accounting problem.
				want := chunk.scavenged[j] &^ chunk.pallocBits[j]
				got := chunk.scavenged[j]
				if want != got {
					ok = false
					if n >= len(mismatches) {
						break chunkLoop
					}
					mismatches[n] = BitsMismatch{
						Base: chunkBase(i) + uintptr(j)*64*pageSize,
						Got:  got,
						Want: want,
					}
					n++
				}
			}
		}
		unlock(&mheap_.lock)

		getg().m.mallocing--
	})
	return
}

func PageCachePagesLeaked() (leaked uintptr) {
	stopTheWorld("PageCachePagesLeaked")

	// Walk over destroyed Ps and look for unflushed caches.
	deadp := allp[len(allp):cap(allp)]
	for _, p := range deadp {
		// Since we're going past len(allp) we may see nil Ps.
		// Just ignore them.
		if p != nil {
			leaked += uintptr(bits.OnesCount64(p.pcache.cache))
		}
	}

	startTheWorld()
	return
}