Re: [PATCH v5 06/11] riscv: Initial commit of OpenTitan machine

[Palmer Dabbelt]

On Wed, 09 Sep 2020 12:00:07 PDT (-0700), Peter Maydell wrote:
> On Wed, 9 Sep 2020 at 19:00, Alistair Francis <alistair23@gmail.com> wrote:
> > On Tue, Sep 8, 2020 at 7:52 AM Peter Maydell <peter.maydell@linaro.org> wrote:
> > > ...shouldn't the riscv64-softmmu config have CONFIG_OPENTITAN too?
> > > The usual principle is that the 64-bit executable can run the
> > > 32-bit boards too.
> >
> > I didn't know that was the general case. I'll send a patch to enable this.
>
> Somebody on IRC suggested that the riscv code currently
> assumes that #ifdef TARGET_RISCV64 implies a 64-bit CPU,
> ie that the 32-bit CPUs don't actually behave correctly
> if built into the qemu-system-riscv64 process, so you might
> want to check that things seem to work when you enable it...

IIRC there's a whole bunch of that floating around the RISC-V port, so just
tossing a 32-bit CPU into qemu-system-riscv64 is going to result in garbage.
At the time we originally did the port we though we weren't goin to have
mixed-XLEN systems, but the ISA now allows for it so in theory we should go fix
all that.

I don't think anyone has looked into doing it, though, as there isn't much
interest in mixed-XLEN systems (though oddly enough there was a glibc post
yesterday about them).