}
		return
	}
	disallowed := [][2]uintptr{}
	// Drop all but the next 3 hints. 64-bit has a lot of hints,
	// so it would take a lot of memory to go through all of them.
	KeepNArenaHints(3)
	// Consume these 3 hints and force the runtime to find some
	// fallback hints.
	for i := 0; i < 5; i++ {
		// Reserve memory at the next hint so it can't be used
		// for the heap.

		return tracebackPCs(&u, 0, stk)
	}
	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
}