Messages in this thread | | | Subject | Re: [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag | From | Stas Sergeev <> | Date | Sat, 5 Mar 2016 10:39:17 +0300 |
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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.
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