default_handler
xtensa_exception_handler *default_handler[EXCCAUSE_N];
DEFINE(EXC_TABLE_DEFAULT, offsetof(struct exc_table, default_handler));
void *previous = per_cpu(exc_table, 0).default_handler[cause];
set_handler(default_handler, cause, handler);
set_handler(default_handler, i, do_unhandled);
set_handler(default_handler, cause, handler);
sa.sa_sigaction = default_handler;