Re: [Qemu-devel] [PATCHv2 11/31] ppc: FP exceptions are always precise

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2016-07-27 at 17:21 +1000, David Gibson wrote:
> On Wed, Jul 27, 2016 at 04:56:29PM +1000, Benjamin Herrenschmidt
> wrote:
> > 
> > We don't implement imprecise FP exceptions and using store_current
> > which sets SRR1 to the *previous* instruction never makes sense
> > for these. So let's be truthful and make them precise, which is
> > allowed by the architecture.
> > 
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > ---
> >  target-ppc/excp_helper.c | 11 ++++++-----
> >  target-ppc/translate.c   |  1 -
> >  2 files changed, 6 insertions(+), 6 deletions(-)
> > 
> > diff --git a/target-ppc/excp_helper.c b/target-ppc/excp_helper.c
> > index 96c6fd9..02d9e79 100644
> > --- a/target-ppc/excp_helper.c
> > +++ b/target-ppc/excp_helper.c
> > @@ -274,12 +274,13 @@ static inline void powerpc_excp(PowerPCCPU
> > *cpu, int excp_model, int excp)
> >                  env->error_code = 0;
> >                  return;
> >              }
> > +
> > +            /* FP exceptions always have NIP pointing to the
> > faulting
> > +             * instruction, so always use store_next and claim we
> > are
> > +             * precise in the MSR.
> > +             */
> >              msr |= 0x00100000;
> > -            if (msr_fe0 == msr_fe1) {
> > -                goto store_next;
> > -            }
> > -            msr |= 0x00010000;
> > -            break;
> > +            goto store_next;
> >          case POWERPC_EXCP_INVAL:
> >              LOG_EXCP("Invalid instruction at " TARGET_FMT_lx "\n",
> > env->nip);
> >              msr |= 0x00080000;
> > diff --git a/target-ppc/translate.c b/target-ppc/translate.c
> > index 3cfa40f..ba14bda 100644
> > --- a/target-ppc/translate.c
> > +++ b/target-ppc/translate.c
> > @@ -3060,7 +3060,6 @@ static void
> > gen_conditional_store(DisasContext *ctx, TCGv EA,
> >                                    int reg, int size)
> >  {
> >      TCGv t0 = tcg_temp_new();
> > -    uint32_t save_exception = ctx->exception;
> 
> This looks like an unrelated change, and one which would break
> compile
> without other changes in gen_conditional_store() that I don't see.
> 
> Have you compiled the user-only targets with this change?

Ah yes, the whole series does work in user-only, I tested, it's
just a messup beween 2 commits. The rest of the change is in:

"ppc: Rework NIP updates vs. exception generation"

What happened is that I initially forgot to remove that line
from the above commit, causing a warning. I did a fix, then
folded the fix into the wrong commmit :)

You can either take it out of this commit and put it into the
above mentioned one, or I can do a 3rd spin... but the fix is
trivial.

Cheers,
Ben.

> > 


> >      tcg_gen_st_tl(EA, cpu_env, offsetof(CPUPPCState, reserve_ea));
> >      tcg_gen_movi_tl(t0, (size << 5) | reg);
>