Re: [PATCH v6 5/9] target/ppc: Simplify syscall exception handlers

[Nicholas Piggin]

On Thu Feb 22, 2024 at 9:33 PM AEST, BALATON Zoltan wrote:
> After previous changes the hypercall handling in 7xx and 74xx
> exception handlers can be folded into one if statement to simpilfy
> this code. Also add "unlikely" to mark the less freqiently used branch
> for the compiler.
>
> Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
> Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
> ---
>  target/ppc/excp_helper.c | 24 ++++++++----------------
>  1 file changed, 8 insertions(+), 16 deletions(-)
>
> diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
> index 411d67376c..035a9fd968 100644
> --- a/target/ppc/excp_helper.c
> +++ b/target/ppc/excp_helper.c
> @@ -762,26 +762,22 @@ static void powerpc_excp_7xx(PowerPCCPU *cpu, int excp)
>      case POWERPC_EXCP_SYSCALL:   /* System call exception                    
> */
>      {
>          int lev = env->error_code;
> -
> -        if (lev == 1 && cpu->vhyp) {
> -            dump_hcall(env);
> -        } else {
> -            dump_syscall(env);
> -        }
>          /*
>           * The Virtual Open Firmware (VOF) relies on the 'sc 1'
>           * instruction to communicate with QEMU. The pegasos2 machine
>           * uses VOF and the 7xx CPUs, so although the 7xx don't have
>           * HV mode, we need to keep hypercall support.
>           */
> -        if (lev == 1 && cpu->vhyp) {
> +        if (unlikely(lev == 1 && cpu->vhyp)) {
>              PPCVirtualHypervisorClass *vhc =
>                  PPC_VIRTUAL_HYPERVISOR_GET_CLASS(cpu->vhyp);
> +            dump_hcall(env);
>              vhc->hypercall(cpu->vhyp, cpu);
>              powerpc_reset_excp_state(cpu);
>              return;
> +        } else {
> +            dump_syscall(env);
>          }
> -
>          break;

You could avoid the else statement for these because the
hcall branch returns.

Actually books could be changed similarly too, I think dump_hcall can be
done in the books_vhyp_handles_hcall() branch. But you don't need to
change that in your patch since it's behaviour change.

Thanks,
Nick