stackentry
RB_ENTRY(stackentry) se_node;
stackentry_compare(struct stackentry *a, struct stackentry *b)
RB_HEAD(stacktree, stackentry) epoch_stacks = RB_INITIALIZER(&epoch_stacks);
RB_GENERATE_STATIC(stacktree, stackentry, se_node, stackentry_compare);
struct stackentry se, *new;