Re: [Qemu-arm] [PATCH v2] fix WFI/WFE length in syndrome register

[Stefano Stabellini]

On Tue, 24 Oct 2017, Stefano Stabellini wrote:
> On Tue, 24 Oct 2017, Peter Maydell wrote:
> > On 24 October 2017 at 16:53, Peter Maydell <address@hidden> wrote:
> > > On 21 October 2017 at 19:09, Stefano Stabellini <address@hidden> wrote:
> > >> diff --git a/target/arm/translate.c b/target/arm/translate.c
> > >> index 4da1a4c..a89518f 100644
> > >> --- a/target/arm/translate.c
> > >> +++ b/target/arm/translate.c
> > >> @@ -12325,12 +12325,15 @@ static void arm_tr_tb_stop(DisasContextBase 
> > >> *dcbase, CPUState *cpu)
> > >>              /* nothing more to generate */
> > >>              break;
> > >>          case DISAS_WFI:
> > >> -            gen_helper_wfi(cpu_env);
> > >> +        {
> > >> +            TCGv_i32 tmp = tcg_const_i32((dc->insn & (1U << 31)) ? 4 : 
> > >> 2);
> > >
> > > This won't work, because dc->insn is only populated by the translate-a64.c
> > > A64 translator, not by the A32/T32 code. I guess 'principle of least
> > > surprise' suggests we should populate it for Thumb and ARM too.
> > 
> > ...and also, this code path is used for both A32 and Thumb instruction
> > sets, so just looking at the top bit of dc->insn isn't sufficient, because
> > you might have the A32 encoding with a cond field with the top bit clear.
> > You can either look also at dc->thumb, or alternatively have a new
> > field is_16bit in DisasContext which you populate in arm_tr_translate_insn()
> > and thumb_tr_translate_insn().
> 
> Thank you for the explanation. I went for changing this line to:
> 
>   TCGv_i32 tmp = tcg_const_i32((dc->thumb &&
>                                (dc->insn & !(1U << 31))) ? 4 : 2);

Sorry, this should be:

   TCGv_i32 tmp = tcg_const_i32((dc->thumb &&
                                !(dc->insn & (1U << 31))) ? 2 : 4);


> and I have also added a call to tcg_temp_free_i32, and dc->insn = insn
> in arm_tr_translate_insn and thumb_tr_translate_insn.
> 
> I'll send another patch.
>