On Wed, Oct 14, 2015 at 2:37 PM, Stas Sergeev <s...@list.ru> wrote: > 14.10.2015 21:52, Andy Lutomirski пишет: >> >> On Wed, Oct 14, 2015 at 11:34 AM, Stas Sergeev <s...@list.ru> wrote: >>> >>> 14.10.2015 21:06, Andy Lutomirski пишет: >>>>> >>>>> Also it doesn't seem to be saying what happens if CS is 32-bit >>>>> and SS is invalid (the flag is not set). >>>> >>>> A new signal will be delivered. sigreturn doesn't modify its behavior >>>> in this case -- it does the default thing, which is to honor the SS in >>>> the saved context. >>> >>> Hmm, no, it didn't do this in the past for sure. >>> It simply ignored SS, no matter to what mode it returns. >>> >> What I mean is: it has the behavior it would have normally on a new >> kernel, which is to honor the saved SS. I'll try to improve the >> comment. >> >>>> So it will actually try to use that saved SS >>>> value, which will fail, causing SIGSEGV. >>> >>> So it seems this logic assumes that when dosemu returns to 32bit, >>> the previous SS is always still valid, am I right with the understanding? >>> I.e. the one that kernel have saved on a signal delivery (because >>> old dosemu does not overwrite it). >>> If it is so, I'd say this assumption is very risky and will likely >>> not hold. But maybe I am missing the point. >>> >> That's the assumption. If I understand correctly, though, old DOSEMU >> never actually returns to 32-bit using sigreturn in the first place, >> since old kernels gave no control over SS. Doesn't old DOSEMU always >> return to the 64-bit IRET trampoline? > > Ah, so the old progs simply never return to 32bit, so you > implement the "Right Thing" (tm) for them, thanks. So the whole > point of UC_STRICT_RESTORE_SS flag is not for the software to > control it, but just for the kernel itself, so that it knows from > whether 32 or 64 bit the signal came. This is probably quite > undocumented in both the comments and the patch description, > and I was confused because the approaches we discussed before, > were targeted on the flag that is written by user-space.
Yes, that's the idea. I'll improve the comments. > If this my > understanding is correct and the flag is just an indication rather > than a requested action, perhaps the name should be different, > e.g. UC_SIG_FROM_32BIT or the like? > Anyway, this is minor. :) > I'll try to test the patch within a few days, thanks for you time! No problem. Thanks for being willing to test! --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/
