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? --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/
