On Thu, Aug 13, 2015 at 9:48 AM, Stas Sergeev <s...@list.ru> wrote: > 13.08.2015 19:42, Andy Lutomirski пишет: > >> On Thu, Aug 13, 2015 at 9:38 AM, Stas Sergeev <s...@list.ru> wrote: >>> >>> 13.08.2015 19:24, Andy Lutomirski пишет: >>> >>>> On Thu, Aug 13, 2015 at 9:20 AM, Stas Sergeev <s...@list.ru> wrote: >>>>> >>>>> 13.08.2015 19:09, Andy Lutomirski пишет: >>>>> >>>>>> On Thu, Aug 13, 2015 at 9:03 AM, Stas Sergeev <s...@list.ru> wrote: >>>>>>> >>>>>>> 13.08.2015 18:38, Andy Lutomirski пишет: >>>>>>>> >>>>>>>> >>>>>>>> So... what do we do about it? We could revert the whole mess. We >>>>>>>> could tell everyone to fix their DOSEMU, which violates policy and >>>>>>>> is >>>>>>>> especially annoying given how much effort we've put into keeping >>>>>>>> 16-bit mode fully functional lately. We could add yet more >>>>>>>> heuristics >>>>>>>> and teach sigreturn to ignore the saved SS value in sigcontext if >>>>>>>> the >>>>>>>> saved CS is 64-bit and the saved SS is unusable. >>>>>>> >>>>>>> Andy, why do you constantly ignore the proposal to make >>>>>>> new behaviour explicitly controlable? You don't have to agree >>>>>>> with it, but you could at least comment on that possibility >>>>>>> and/or mention it with the ones you listed above. >>>>>> >>>>>> I'm not sure what the proposal is exactly. >>>>>> >>>>>> We could add a new uc_flags flag. If set, it means that >>>>>> sigcontext->ss is valid and should be used by sigreturn. If clear, >>>>>> then we ignore sigcontext->ss and just restore __USER_DS. >>>>>> >>>>>> The problem is that, by itself, this won't fix old DOSEMU. We somehow >>>>>> need to either detect that something funny is going on or just leave >>>>>> the flag clear by default. >>>>>> >>>>>> We could do this: always save SS to sigcontext->ss, but only restore >>>>>> sigcontext->ss if userspace explicitly sets the flag before sigreturn. >>>>>> If we do that, we'd need to also add my patch to preserve the actual >>>>>> HW SS selector if possible so that old DOSEMU knows what SS to program >>>>>> into its trampoline. >>>>>> >>>>>> This at least lets *new* DOSEMU set the flag and get the improved >>>>>> behavior. I still don't know what effect it'll have on Wine and CRIU. >>>>>> >>>>>> Stas, is that what you were thinking, or were you thinking of >>>>>> something >>>>>> else? >>>>> >>>>> Not quite. >>>>> I mean the flag that will control not only sigreturn, but >>>>> the signal delivery as well. This may probably be a sigaction() >>>>> flag or some other. If not set - ss is ignored by both signal >>>>> delivery and sigreturn(). If set - ss is saved/restored (and in >>>>> the future - also fs/gs). >>>>> Is such a flag possible? >>>> >>>> Maybe. I think I'm more nervous about adding new flags in sigaction >>>> than I am in uc_flags. >>> >>> Isn't uc_flags read-only for the user? >>> I look into setup_rt_frame >>> <http://lxr.free-electrons.com/ident?v=2.4.37;i=setup_rt_frame>() and see >>> --- >>> /* Create the ucontext. */ >>> err |= __put_user(0, &frame->uc.uc_flags); >>> --- >>> so it doesn't look like the flag that user can use to _request_ >>> something from the kernel. And I am talking about exactly >>> the flag to request the new behaviour, as only that can remove >>> the regression completely without patching dosemu. >> >> User code could rewrite it in the signal handler to request something. > > But that's too late to affect the signal _delivery_ anyhow, no? > Any idea about the flag that can control both delivery and return?
I think my LAR patch should cover the signal delivery part. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
