Re: [PATCH v6 1/5] hw/riscv: Use misa_mxl instead of misa_mxl_max

[Alistair Francis]

On Thu, Nov 23, 2023 at 5:24 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>
> On 2023/11/23 12:04, Alistair Francis wrote:
> > On Mon, Oct 30, 2023 at 3:50 PM Akihiko Odaki <akihiko.odaki@daynix.com> 
> > wrote:
> >>
> >> The effective MXL value matters when booting.
> >
> > This doesn't sound right. Surely the max is what matters here
> >
> > Also, this was specifically changed to misa_mxl_max in db23e5d981a
> > "target/riscv: Replace riscv_cpu_is_32bit with riscv_cpu_mxl".
> >
> > This needs a much better description of why this change should be made
>  >
>  > Alistair
>
> The kernel will be executed with the current MXL rather than the initial
> MXL value so the current MXL should be used here.
>
> For example, if you are going to emulate a system that has a RV64 CPU
> and a firmware that sets the MXL to RV32, then mxl_max should be
> MXL_RV64 and mxl should be MXL_RV32, and the kernel should be assumed as
> a RV32 binary. Loading a 64-bit kernel will not work in such a case.

But this is called before the firmware runs, so it won't be changed by firmware.

Maybe it's worth putting what this fixes in the commit message?

Alistair

>
> You can find a similar example in x86_64: x86_64 systems typically
> starts in 16-bit mode, and the firmware switches to 64-bit mode. When
> emulating those systems, QEMU switches to 64-bit mode and loads a 64-bit
> kernel.
>
> Regards,
> Akihiko Odaki