On Tue, 6 Sep 2011, Richard Henderson wrote: > On 09/04/2011 08:03 AM, malc wrote: > > On Sun, 4 Sep 2011, Richard Henderson wrote: > > > >> On 09/03/2011 03:47 PM, malc wrote: > >>> Doesn't make much sense to me, guest clearly asked for 0 and not -1, > >>> besides -1 violates TCG's sar constraints and PPC obliges by emiting > >>> illegal instruction in this case. > >> > >> The shift that the guest asked for was completely folded away. > >> > >> The -1 comes from gen_shift_rm_T1 in the computation of the new > >> flags value. This could instead be moved inside the test for != 0, > >> which is the only place that value is actually used anyway. > >> > >> Try this. Lightly tested. > > > > Now i either get hosts illegal instruction or (with logging enabled) a > > guest kenrnel panic. > > Hum. Well, it's possible I made some silly mistake in the patch. > You now know where to look for the problem.
Correct me if i'm wrong, previously the code worked like this: mov tmp, 0 sub tmp, 1 sar r, r, tmp Still UB as far as TCG is concerned but since no immediates are involved things worked, now, with constant folding, we are asked to sar by -1 directly. > > That said, it seems easier for you in the PPC port to mask the > immediate operand so that you don't produce an illegal instruction. > It doesn't really matter what value that insn produces, as the > result won't be used. > I did that when first hit this problem, but decided not to push it. -- mailto:av1...@comtv.ru
