Re: [PATCH v2 08/14] target/ppc: 405: System call exception cleanup

[Cédric Le Goater]

On 1/19/22 07:09, David Gibson wrote:
> On Tue, Jan 18, 2022 at 03:44:42PM -0300, Fabiano Rosas wrote:
> > There's no sc 1.
>
> No... but what exactly should and will happen if you attempt to
> execute an "sc 1" on 40x.  Will it be treated as an "sc 0", or will it
> cause a 0x700?  If it's a 0x700, better double check that that is
> generated at translation time, if you're removing the check on level
> here.

A Program Interrupt with the illegal instruction error code should be
generated at translation time but it is not the case today. It never
was correctly implemented AFAICT :

  /* Top bit of opc2 corresponds with low bit of LEV, so use two handlers */
  GEN_HANDLER(sc, 0x11, 0x11, 0xFF, 0x03FFF01D, PPC_FLOW),
  GEN_HANDLER(sc, 0x11, 0x01, 0xFF, 0x03FFF01D, PPC_FLOW),

We would need a simple 'sc' instruction for the PPC405 and other
processors. Let's add that to the TODO list.

Thanks,

C.


> > Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
> > ---
> >   target/ppc/excp_helper.c | 21 ++-------------------
> >   1 file changed, 2 insertions(+), 19 deletions(-)
> >
> > diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
> > index 8fae8aa0be..9a6f8365d6 100644
> > --- a/target/ppc/excp_helper.c
> > +++ b/target/ppc/excp_helper.c
> > @@ -398,7 +398,7 @@ static void powerpc_excp_40x(PowerPCCPU *cpu, int excp)
> >       CPUPPCState *env = &cpu->env;
> >       int excp_model = env->excp_model;
> >       target_ulong msr, new_msr, vector;
> > -    int srr0, srr1, lev = -1;
> > +    int srr0, srr1;
> >   
> >       if (excp <= POWERPC_EXCP_NONE || excp >= POWERPC_EXCP_NB) {
> >           cpu_abort(cs, "Invalid PowerPC exception %d. Aborting\n", excp);
> > @@ -521,30 +521,13 @@ static void powerpc_excp_40x(PowerPCCPU *cpu, int excp)
> >           }
> >           break;
> >       case POWERPC_EXCP_SYSCALL:   /* System call exception                    
> > */
> > -        lev = env->error_code;
> > -
> > -        if ((lev == 1) && cpu->vhyp) {
> > -            dump_hcall(env);
> > -        } else {
> > -            dump_syscall(env);
> > -        }
> > +        dump_syscall(env);
> >   
> >           /*
> >            * We need to correct the NIP which in this case is supposed
> >            * to point to the next instruction
> >            */
> >           env->nip += 4;
> > -
> > -        /* "PAPR mode" built-in hypercall emulation */
> > -        if ((lev == 1) && cpu->vhyp) {
> > -            PPCVirtualHypervisorClass *vhc =
> > -                PPC_VIRTUAL_HYPERVISOR_GET_CLASS(cpu->vhyp);
> > -            vhc->hypercall(cpu->vhyp, cpu);
> > -            return;
> > -        }
> > -        if (lev == 1) {
> > -            new_msr |= (target_ulong)MSR_HVB;
> > -        }
> >           break;
> >       case POWERPC_EXCP_FIT:       /* Fixed-interval timer interrupt           
> > */
> >           trace_ppc_excp_print("FIT");