{name: "disablethp", value: &debug.disablethp},
	{name: "dontfreezetheworld", value: &debug.dontfreezetheworld},
	{name: "efence", value: &debug.efence},
	{name: "gccheckmark", value: &debug.gccheckmark},
	{name: "gcpacertrace", value: &debug.gcpacertrace},
	{name: "gcshrinkstackoff", value: &debug.gcshrinkstackoff},
	{name: "gcstoptheworld", value: &debug.gcstoptheworld},

	state and thus may hide problems.

	efence: setting efence=1 causes the allocator to run in a mode
	where each object is allocated on a unique page and addresses are
	never recycled.

	gccheckmark: setting gccheckmark=1 enables verification of the
	garbage collector's concurrent mark phase by performing a
	second mark pass while the world is stopped.  If the second
	pass finds a reachable object that was not found by concurrent

		// non-system stack to pick up the new addresses
		// before continuing.
	})

	var stwSwept bool
	systemstack(func() {
		work.heap2 = work.bytesMarked
		if debug.gccheckmark > 0 {
			// Run a full non-parallel, stop-the-world
			// mark using checkmark bits, to check that we
			// didn't forget to mark anything during the
			// concurrent mark process.
			startCheckmarks()
			gcResetMarkState()

	// Reads are done atomically to find spans containing specials
	// during marking.
	pageSpecials [pagesPerArena / 8]uint8

	// checkmarks stores the debug.gccheckmark state. It is only
	// used if debug.gccheckmark > 0.
	checkmarks *checkmarksMap

	// zeroedBase marks the first byte of the first page in this
	// arena which hasn't been used yet and is therefore already

	}
	mbits := span.markBitsForIndex(objIndex)

	if useCheckmark {
		if setCheckmark(obj, base, off, mbits) {
			// Already marked.
			return
		}
	} else {
		if debug.gccheckmark > 0 && span.isFree(objIndex) {
			print("runtime: marking free object ", hex(obj), " found at *(", hex(base), "+", hex(off), ")\n")
			gcDumpObject("base", base, off)
			gcDumpObject("obj", obj, ^uintptr(0))