Re: [RFC v1 00/38] arm cleanup experiment for kvm-only build

[Peter Maydell]

On Thu, 4 Mar 2021 at 16:39, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> On 3/3/21 7:54 PM, Richard Henderson wrote:
> > On 3/3/21 10:45 AM, Claudio Fontana wrote:
> >> It is a bit weird that qemu-system-aarch64 runs with a cortex-a15
> >> model tbh, as cortex-a15 is not capable of aarch64.
> >
> > No, but qemu-system-aarch64 is capable of 32-bit emulation (because most
> > 64-bit cpus retain 32-bit mode).  It takes no extra effort to run
> > cortex-a15 than it does a cortex-a57.
>
> IIRC qemu-system-arm starts the aa64 cores in 32-bit mode, while

...no, it simply doesn't have them at all; it only has
the 32-bit-only cores. We only support '64-bit core that
starts in 32-bit mode' for KVM; it would be nice to have the
TCG support for that but nobody's ever written it.

> qemu-system-aarch64 in 64-bit (this gave me trouble because the
> kernels for the raspi 64-bit SoCs are in 32-bit mode -- because
> the GPU starts them in this mode).
>
> > I have wondered if we should have just one qemu-system-arm that does it
> > all and drop the separate qemu-system-aarch64 -- or vice versa.  But
> > we've had the separation around so long I'm sure someone would be confused.
>
> That would be great cleanup IMHO.

I figure it's not really worth the bother until/unless we ever
some day get to the holy grail of "one binary that supports
multiple target architectures", at which point we could have
one qemu-system for everything...

-- PMM