if (!kernel_addr(entry)) {
assert(th->ustack);
ptr_t ustack_top = align_stack(th->ustack->end - 1);
ustack_top -= 16; // pre_allocate a 16 byte for inject parameter
if (!kernel_addr(entry)) {
assert(th->ustack);
ptr_t ustack_top = align_stack(th->ustack->end - 1);
ustack_top -= 16; // pre_allocate a 16 byte for inject parameter