Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1350816

Re: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag

Show all headers | View raw

05.03.2016 01:22, Andy Lutomirski пишет:
> On Mon, Feb 29, 2016 at 1:29 PM, Stas Sergeev <stsp@list.ru> 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_dont_have_this_feature = 1;
   err = sigaltstack(SS_ONSTACK);
}

Note: if you want to keep such detection for the future
additions, the mask can be enlarged to, say, ((1 << 24) - 1),
and whenever someone adds a new flag, he can lower the
mask by one bit.
But I think this would be an overkill in that particular case.

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag Andy Lutomirski <luto@amacapital.net> - 2016-03-04 23:30 +0100
  Re: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag Stas Sergeev <stsp@list.ru> - 2016-03-05 08:40 +0100
    Re: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag Stas Sergeev <stsp@list.ru> - 2016-03-05 08:50 +0100

csiph-web