Re: [PATCH v4 10/17] target/ppc: Create helper_scv

[David Gibson]

On Mon, Mar 22, 2021 at 11:05:00AM -0600, Richard Henderson wrote:
> On 3/21/21 10:00 PM, David Gibson wrote:
> > On Mon, Mar 15, 2021 at 12:46:08PM -0600, Richard Henderson wrote:
> > > Perform the test against FSCR_SCV at runtime, in the helper.
> > > 
> > > This means we can remove the incorrect set against SCV in
> > > ppc_tr_init_disas_context and do not need to add an HFLAGS bit.
> > > 
> > > Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> > > ---
> > >   target/ppc/helper.h      |  1 +
> > >   target/ppc/excp_helper.c |  9 +++++++++
> > >   target/ppc/translate.c   | 20 +++++++-------------
> > >   3 files changed, 17 insertions(+), 13 deletions(-)
> > > 
> > > diff --git a/target/ppc/helper.h b/target/ppc/helper.h
> > > index 6a4dccf70c..513066d54d 100644
> > > --- a/target/ppc/helper.h
> > > +++ b/target/ppc/helper.h
> > > @@ -13,6 +13,7 @@ DEF_HELPER_1(rfci, void, env)
> > >   DEF_HELPER_1(rfdi, void, env)
> > >   DEF_HELPER_1(rfmci, void, env)
> > >   #if defined(TARGET_PPC64)
> > > +DEF_HELPER_2(scv, noreturn, env, i32)
> > >   DEF_HELPER_2(pminsn, void, env, i32)
> > >   DEF_HELPER_1(rfid, void, env)
> > >   DEF_HELPER_1(rfscv, void, env)
> > > diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
> > > index 85de7e6c90..5c95e0c103 100644
> > > --- a/target/ppc/excp_helper.c
> > > +++ b/target/ppc/excp_helper.c
> > > @@ -1130,6 +1130,15 @@ void helper_store_msr(CPUPPCState *env, 
> > > target_ulong val)
> > >   }
> > >   #if defined(TARGET_PPC64)
> > > +void helper_scv(CPUPPCState *env, uint32_t lev)
> > > +{
> > > +    if (env->spr[SPR_FSCR] & (1ull << FSCR_SCV)) {
> > > +        raise_exception_err(env, POWERPC_EXCP_SYSCALL_VECTORED, lev);
> > > +    } else {
> > > +        raise_exception_err(env, POWERPC_EXCP_FU, FSCR_IC_SCV);
> > > +    }
> > > +}
> > > +
> > >   void helper_pminsn(CPUPPCState *env, powerpc_pm_insn_t insn)
> > >   {
> > >       CPUState *cs;
> > > diff --git a/target/ppc/translate.c b/target/ppc/translate.c
> > > index 7912495f28..d48c554290 100644
> > > --- a/target/ppc/translate.c
> > > +++ b/target/ppc/translate.c
> > > @@ -173,7 +173,6 @@ struct DisasContext {
> > >       bool vsx_enabled;
> > >       bool spe_enabled;
> > >       bool tm_enabled;
> > > -    bool scv_enabled;
> > >       bool gtse;
> > >       ppc_spr_t *spr_cb; /* Needed to check rights for mfspr/mtspr */
> > >       int singlestep_enabled;
> > > @@ -4081,15 +4080,16 @@ static void gen_sc(DisasContext *ctx)
> > >   #if !defined(CONFIG_USER_ONLY)
> > >   static void gen_scv(DisasContext *ctx)
> > >   {
> > > -    uint32_t lev;
> > > +    uint32_t lev = (ctx->opcode >> 5) & 0x7F;
> > > -    if (unlikely(!ctx->scv_enabled)) {
> > > -        gen_exception_err(ctx, POWERPC_EXCP_FU, FSCR_IC_SCV);
> > > -        return;
> > > +    /* Set the PC back to the faulting instruction. */
> > > +    if (ctx->exception == POWERPC_EXCP_NONE) {
> > > +        gen_update_nip(ctx, ctx->base.pc_next - 4);
> > >       }
> > 
> > I don't quite understand this.  Don't we need the NIP to be on the scv
> > instruction itself for the case where we get a facility unavailable
> > exception, but on the next instruction if we actually take the system
> > call?  This appears to be unconditional.
> > 
> > > +    gen_helper_scv(cpu_env, tcg_constant_i32(lev));
> > > -    lev = (ctx->opcode >> 5) & 0x7F;
> > > -    gen_exception_err(ctx, POWERPC_SYSCALL_VECTORED, lev);
> 
> Hmm.  In the old code, both paths use gen_exception_err, without otherwise
> manipulating NIP.  That suggests to me that both exceptions receive the same
> value in NIP.
> 
> Is there an adjustment to NIP when delivering the SCV exception?  Yep:

Ok.  Just shows my ignorance of the exception handling code.

> 
>     case POWERPC_EXCP_SYSCALL_VECTORED:
>         lev = env->error_code;
>         dump_syscall_vectored(env);
>         env->nip += 4;
>         new_msr |= env->msr & ((target_ulong)1 << MSR_EE);
>         new_msr |= env->msr & ((target_ulong)1 << MSR_RI);
>         break;
> 
> 
> r~
> 

-- 
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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