Messages in this thread | | | Subject | Re: [PATCH 4/4] sigaltstack: allow disabling and re-enabling sas within sighandler | From | Stas Sergeev <> | Date | Mon, 1 Feb 2016 22:01:49 +0300 |
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01.02.2016 21:52, Oleg Nesterov пишет: > Stas, I probably missed something, but I don't understand your concerns, > > On 02/01, Stas Sergeev wrote: >> 01.02.2016 21:04, Oleg Nesterov пишет: >>> Yes, and SS_FORCE means "I know what I do", looks very simple. >> But to me its not because I don't know what to do with >> uc_stack after SS_FORCE is applied. > Nothing? restore_sigaltstack() should work as expected? That's likely the reason for EPERM: restore_sigaltstack() does the job, so manual modifications are disallowed. Allowing them will bring in the surprises where the changes done by the user are ignored.
>>> I won't argue, but to me it would be better to keep this EPERM if !force. >>> Just because we should avoid the incompatible changes if possible. >> Ok then. Lets implement SS_FORCE. >> What semantic should it have wrt uc_stack? >> >> sigaltstack(SS_DISABLE | SS_FORCE); >> swapcontext(); >> sigaltstack(set up new_sas); >> rt_sigreturn(); > Yes, or > > sigaltstack({ DISABLE | FORCE}, &old_ss); > swapcontext(); > sigaltstack(&old_ss, NULL); > rt_sigreturn(); > > and if you are going to return from sighandler you do not even need the 2nd > sigaltstack(), you can rely on sigreturn. Yes, that's what I do in my app already. But its only there when SA_SIGINFO is used.
>> What's at the end? Do we want a surprise for the user >> that he's new_sas got ignored? > Can't understand.... do you mean "set up new_sas" will be ignored because > rt_sigreturn() does restore_sigaltstack() ? I see no problem here... Allowing the modifications that were previously EPERMed but will now be silently ignored, may be seen as a problem. But if it isn't - fine, lets code that.
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