# Re: \[PATCH 1/2\] sigaltstack: implement SS\_AUTODISARM flag

- From: Stas Sergeev \<hidden\>
- Date: 2016-03-05 07:41:18 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2016/03/4702070
- Thread: https://ratatoskr.run/linux-api/2016/02/4697311/t.md

```text
05.03.2016 10:39, Stas Sergeev пишет:
> 05.03.2016 01:22, Andy Lutomirski пишет:
>> On Mon, Feb 29, 2016 at 1:29 PM, Stas Sergeev [ref] wrote:
>>> This patch implements the SS_AUTODISARM flag that can be ORed with
>>> SS_ONSTACK when forming ss_flags.
>>> When this flag is set, sigaltstack will be disabled when entering
>>> the signal handler; more precisely, after saving sas to uc_stack.
>>> When leaving the signal handler, the sigaltstack is restored by
>>> uc_stack.
>>> When this flag is used, it is safe to switch from sighandler with
>>> swapcontext(). Without this flag, the subsequent signal will corrupt
>>> the state of the switched-away sighandler.
>>>
>> This looks reasonable to me with one exception: how does a user
>> program detect the presence of this feature?
> Compile-time detection:
> #ifdef SS_AUTODISARM
>   # I have this feature
>   ...
> #endif
>
> Run-time detection:
> int err = sigaltstack(SS_ONSTACK | SS_AUTODISARM);
> if (err == EINVAL) {
I guess I mean here
if (err && errno == EINVAL)
```