Re: [PATCH v7 17/20] target/arm: Rebuild hflags at MSR writes

[Richard Henderson]

On 10/18/19 5:32 AM, Peter Maydell wrote:
> On Thu, 17 Oct 2019 at 19:51, Richard Henderson
> <address@hidden> wrote:
>>
>> Continue setting, but not relying upon, env->hflags.
>>
>> Reviewed-by: Alex Bennée <address@hidden>
>> Signed-off-by: Richard Henderson <address@hidden>
>> ---
>>  target/arm/translate-a64.c | 13 +++++++++++--
>>  target/arm/translate.c     | 28 +++++++++++++++++++++++-----
>>  2 files changed, 34 insertions(+), 7 deletions(-)
>> @@ -7068,14 +7070,30 @@ static int disas_coproc_insn(DisasContext *s, 
>> uint32_t insn)
>>              }
>>          }
>>
>> -        if ((tb_cflags(s->base.tb) & CF_USE_ICOUNT) && (ri->type & 
>> ARM_CP_IO)) {
>> -            /* I/O operations must end the TB here (whether read or write) 
>> */
>> -            gen_lookup_tb(s);
>> -        } else if (!isread && !(ri->type & ARM_CP_SUPPRESS_TB_END)) {
>> -            /* We default to ending the TB on a coprocessor register write,
>> +        /* I/O operations must end the TB here (whether read or write) */
>> +        need_exit_tb = ((tb_cflags(s->base.tb) & CF_USE_ICOUNT) &&
>> +                        (ri->type & ARM_CP_IO));
>> +
>> +        if (!isread && !(ri->type & ARM_CP_SUPPRESS_TB_END)) {
>> +            /*
>> +             * A write to any coprocessor regiser that ends a TB
> 
> (typo: "register")
> 
>> +             * must rebuild the hflags for the next TB.
>> +             */
>> +            TCGv_i32 tcg_el = tcg_const_i32(s->current_el);
>> +            if (arm_dc_feature(s, ARM_FEATURE_M)) {
>> +                gen_helper_rebuild_hflags_m32(cpu_env, tcg_el);
>> +            } else {
>> +                gen_helper_rebuild_hflags_a32(cpu_env, tcg_el);
>> +            }
>> +            tcg_temp_free_i32(tcg_el);
> 
> Why only rebuild hflags if !ARM_CP_SUPPRESS_TB_END ?
> For instance on the Xscale CPUs we set SUPPRESS_TB_END for the SCTLR,
> but some of the SCTLR bits are cached in hflags, right? Do we somehow
> arrange to rebuild the hflags when the TB does eventually end ?

No, we don't.  I assumed that all registers which change TB flags would in fact
end the TB.

Why did we suppress tb end for Xscale?


r~