Re: [PATCH v5 23/23] xen/README: add compiler and binutils versions for RISC-V64

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.02.2024 23:58, Julien Grall wrote:
> On 27/02/2024 07:55, Jan Beulich wrote:
>> On 26.02.2024 18:39, Oleksii Kurochko wrote:
>>> This patch doesn't represent a strict lower bound for GCC and
>>> GNU Binutils; rather, these versions are specifically employed by
>>> the Xen RISC-V container and are anticipated to undergo continuous
>>> testing.
>>
>> Up and until that container would be updated to a newer gcc. I'm
>> afraid I view this as too weak a criteria,
> 
> I disagree. We have to decide a limit at some point. It is sensible to 
> say that we are only supporting what we can tests. AFAIK, this is what 
> QEMU has been doing.

I view qemu as a particularly bad example. They raise their baselines
far too aggressively for my taste.

>> IOW it is hard for me to see why RISC-V needs stronger restrictions here
>> than other architectures. It ought to be possible to determine a baseline
>> version. Even if taking the desire to have "pause" available as a
>> requirement, gas (and presumably gld) 2.36.1 would already suffice.
> 
> I think we want to bump it on Arm. There are zero reasons to try to keep 
> a lower versions if nobody tests/use it in production.
> 
> I would suggest to do the same on x86. What's the point of try to 
> support Xen with a 15+ years old compiler?

It could have long been bumped if only a proper scheme to follow for
this and future bumping would have been put forward by anyone keen on
such bumping, like - see his reply - e.g. Andrew. You may recall that
this was discussed more than once on meetings, with no real outcome.
I'm personally not meaning to stand in the way of such bumping as long
as it's done in a predictable manner, but I'm not keen on doing so and
hence I don't view it as my obligation to try to invent a reasonable
scheme. (My personal view is that basic functionality should be
possible to have virtually everywhere, whereas for advanced stuff it
is fine to require a more modern tool chain.)

The one additional concern I've raised in the past is that in the end
it's not just minimal tool chain versions we rely on, but also other
core system tools (see the recent move from "which" to "command -v"
for an example of such a dependency, where luckily it turned out to
not be an issue that the -v had only become a standard thing at some
point). While for the tool chain I can arrange for making newer
versions available, for core system tools I can't. Therefore being too
eager there would mean I can't really / easily (smoke) test Xen
anymore on ancient hardware every once in a while. When afaict we do
too little of such testing already anyway, despite not having any
lower bound on hardware that formally we support running Xen on. (And
no, upgrading the ancient distros on that ancient hardware is not an
option for me.)

Jan