ARM_SUB_I
emit(ARM_SUB_I(ARM_IP, rt, 32), ctx);
emit(ARM_SUB_I(ARM_FP, ARM_IP, 4), ctx);
emit(ARM_SUB_I(bpf_r1[1], ARM_SP, SCRATCH_SIZE), ctx);
emit(ARM_SUB_I(ARM_SP, ARM_SP, ctx->stack_size), ctx);
emit(ARM_SUB_I(ARM_SP, ARM_FP, hweight16(reg_set) * 4), ctx);