Re: [PATCH v5 07/18] target/riscv: setup everything so that riscv128-softmmu compiles

[Frédéric Pétrot]

On 25/11/2021 12:47, Alistair Francis wrote:
> On Wed, Nov 24, 2021 at 5:33 PM Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
> > Hi Frédéric,
> >
> > On 11/24/21 07:55, Frédéric Pétrot wrote:
> > > On 24/11/2021 07:12, Alistair Francis wrote:
> > > > On Sat, Nov 13, 2021 at 1:16 AM Frédéric Pétrot
> > > > <frederic.petrot@univ-grenoble-alpes.fr> wrote:
> > > > > This patch is kind of a mess because several files have to be slightly
> > > > > modified to allow for a new target. In the current status, we have done
> > > > > our best to have RV64 and RV128 under the same RV64 umbrella, but there
> > > > > is still work to do to have a single executable for both.
> > > > > In particular, we have no atomic accesses for aligned 128-bit addresses.
> > > > >
> > > > > Once this patch applied, adding risc128-sofmmu to --target-list produces
> > > > > a (no so useful yet) executable.
> > > >
> > > > I can't remember if we discussed this before, but do we need the
> > > > riscv128-sofmmu executable? Can we instead just use a riscv64-sofmmu
> > > > executable?
> > >
> > >    Hello Alistair,
> > >    Richard was also advocating for a single executable, but pointed out that
> > >    we need to disable mttcg because there is a need for specific tcg
> > > support for
> > >    128-bit aligned atomics.
> > >    Given my understanding of that part of QEMU, I choose the easy way to
> > > disable
> > >    it once and for all at compile time until we have that.
> >
> >
> > In rv128_base_cpu_init():
> >
> >    if (qemu_tcg_mttcg_enabled) {
> >        /* Missing 128-bit aligned atomics */
> >        error_report("128-bit RISC-V currently does not work"
> >                     " with Multi Threaded TCG. Please use:"
> >                     " -accel tcg,thread=single");
> >        exit(EXIT_FAILURE);
> >    }
>
> That seems like a good option! I think we could add this to the CPU
> realise function.
>
> The problem with a riscv128-sofmmu executable is that it's hard to get
> rid of in the future. We are very slowly moving towards a single
> executable and adding a new one means we are stuck with it for a
> while.
>
> Alistair

  Ooups, I replied yesterday to Philippe that I would work that out, but I
  missed the reply all button, sorry.

  Frédéric
> > Regards,
> >
> > Phil.

--
+---------------------------------------------------------------------------+
| Frédéric Pétrot, Pr. Grenoble INP-Ensimag/TIMA,   Ensimag deputy director |
| Mob/Pho: +33 6 74 57 99 65/+33 4 76 57 48 70      Ad augusta  per angusta |
| http://tima.univ-grenoble-alpes.fr frederic.petrot@univ-grenoble-alpes.fr |
+---------------------------------------------------------------------------+