// Copyright 2020 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.

// GC checkmarks
//
// In a concurrent garbage collector, one worries about failing to mark
// a live object due to mutations without write barriers or bugs in the
// collector implementation. As a sanity check, the GC has a 'checkmark'
// mode that retraverses the object graph with the world stopped, to make
// sure that everything that should be marked is marked.

package runtime

import (
	
	
	
)

// A checkmarksMap stores the GC marks in "checkmarks" mode. It is a
// per-arena bitmap with a bit for every word in the arena. The mark
// is stored on the bit corresponding to the first word of the marked
// allocation.
//
//go:notinheap
type checkmarksMap [heapArenaBytes / goarch.PtrSize / 8]uint8

// If useCheckmark is true, marking of an object uses the checkmark
// bits instead of the standard mark bits.
var useCheckmark = false

// startCheckmarks prepares for the checkmarks phase.
//
// The world must be stopped.
func startCheckmarks() {
	assertWorldStopped()

	// Clear all checkmarks.
	for ,  := range mheap_.allArenas {
		 := mheap_.arenas[.l1()][.l2()]
		 := .checkmarks

		if  == nil {
			// Allocate bitmap on first use.
			 = (*checkmarksMap)(persistentalloc(unsafe.Sizeof(*), 0, &memstats.gcMiscSys))
			if  == nil {
				throw("out of memory allocating checkmarks bitmap")
			}
			.checkmarks = 
		} else {
			// Otherwise clear the existing bitmap.
			for  := range  {
				[] = 0
			}
		}
	}
	// Enable checkmarking.
	useCheckmark = true
}

// endCheckmarks ends the checkmarks phase.
func endCheckmarks() {
	if gcMarkWorkAvailable(nil) {
		throw("GC work not flushed")
	}
	useCheckmark = false
}

// setCheckmark throws if marking object is a checkmarks violation,
// and otherwise sets obj's checkmark. It returns true if obj was
// already checkmarked.
func setCheckmark(, ,  uintptr,  markBits) bool {
	if !.isMarked() {
		printlock()
		print("runtime: checkmarks found unexpected unmarked object obj=", hex(), "\n")
		print("runtime: found obj at *(", hex(), "+", hex(), ")\n")

		// Dump the source (base) object
		gcDumpObject("base", , )

		// Dump the object
		gcDumpObject("obj", , ^uintptr(0))

		getg().m.traceback = 2
		throw("checkmark found unmarked object")
	}

	 := arenaIndex()
	 := mheap_.arenas[.l1()][.l2()]
	 := ( / heapArenaBytes / 8) % uintptr(len(.checkmarks))
	 := byte(1 << (( / heapArenaBytes) % 8))
	 := &.checkmarks[]

	if atomic.Load8()& != 0 {
		// Already checkmarked.
		return true
	}

	atomic.Or8(, )
	return false
}