Re: [Qemu-devel] [PATCH v3 2/4] target/arm: handle A-profile semihosting at translate time

["Alex Bennée" <alex.bennee@linaro.org>]

Peter Maydell <peter.maydell@linaro.org> writes:

> On Fri, 6 Sep 2019 at 13:47, Alex Bennée <alex.bennee@linaro.org> wrote:
>>
>> As for the other semihosting calls we can resolve this at translate
>> time.
>>
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>
>> ---
>> v2
>>   - update for change to gen_exception_internal_insn API
>> v3
>>   - update for decode tree, merge T32 & A32 commits
>>   - dropped r-b due to changes
>> ---
>>  target/arm/translate.c | 19 +++++++++++++++----
>>  1 file changed, 15 insertions(+), 4 deletions(-)
>>
>> diff --git a/target/arm/translate.c b/target/arm/translate.c
>> index 4cda7812bcb..ed4a97cfb44 100644
>> --- a/target/arm/translate.c
>> +++ b/target/arm/translate.c
>> @@ -10222,14 +10222,25 @@ static bool trans_CBZ(DisasContext *s, arg_CBZ *a)
>>  }
>>
>>  /*
>> - * Supervisor call
>> + * Supervisor call - both T32 & A32 come here so we need to check
>> + * which mode we are in when checking for semihosting.
>>   */
>>
>>  static bool trans_SVC(DisasContext *s, arg_SVC *a)
>>  {
>> -    gen_set_pc_im(s, s->base.pc_next);
>> -    s->svc_imm = a->imm;
>> -    s->base.is_jmp = DISAS_SWI;
>> +    const uint32_t semihost_imm = s->thumb ? 0xab : 0x123456;
>> +
>> +    if (semihosting_enabled() &&
>> +#ifndef CONFIG_USER_ONLY
>> +        s->current_el != 0 &&
>> +#endif
>> +        (a->imm == semihost_imm)) {
>> +        gen_exception_internal_insn(s, s->base.pc_next, EXCP_SEMIHOST);
>> +    } else {
>> +        gen_set_pc_im(s, s->base.pc_next);
>> +        s->svc_imm = a->imm;
>> +        s->base.is_jmp = DISAS_SWI;
>> +    }
>>      return true;
>>  }
>
> Doesn't this accidentally enable semihosting via SVC for
> M-profile ?

We must have done that before then. Just gate it with &&
!arm_dc_feature(s, ARM_FEATURE_M) then?

>
> thanks
> -- PMM


--
Alex Bennée