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

[Stefano Stabellini]

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);

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.