Re: [Qemu-devel] [PATCH 12/32] ppc: FP exceptions are always precise

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Jul 27, 2016 at 08:21:06AM +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.

I don't see any store_correct in the altered code, so the description
doesn't quite make sense to me.

> 
> 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 f4b115e..91fdf4b 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 cb4e313..a05fed7 100644
> --- a/target-ppc/translate.c
> +++ b/target-ppc/translate.c
> @@ -2846,7 +2846,6 @@ static void gen_conditional_store(DisasContext *ctx, TCGv EA,
>                                    int reg, int size)
>  {
>      TCGv t0 = tcg_temp_new();
> -    uint32_t save_exception = ctx->exception;

Also, this appears to be an unrelated change.

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

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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