On 29/02/2024 14:07, Jan Beulich wrote:
On 29.02.2024 14:44, Julien Grall wrote:
Hi Jan,
On 29/02/2024 12:51, Jan Beulich wrote:
On 29.02.2024 13:32, Julien Grall wrote:
On 29/02/2024 12:17, Jan Beulich wrote:
On 29.02.2024 13:05, Andrew Cooper wrote:
On 29/02/2024 10:23 am, Julien Grall wrote:
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.)
That's one way to see it. The problem with this statement is a user
today is mislead to think you can build Xen with any GCC versions
since 4.1. I don't believe we can guarantee that and we are exposing
our users to unnecessary risk.
In addition to that, I agree with Andrew. This is preventing us to
improve our code base and we have to carry hacks for older compilers.
I don't think anyone here is suggesting that we switch to a
bleeding-edge-only policy. But 15y of support is extreme in the
opposite direction.
Xen ought to be buildable in the contemporary distros of the day, and I
don't think anyone is going to credibly argue otherwise.
But, it's also fine for new things to have newer requirements.
Take CET for example. I know we have disagreements on exactly how it's
toolchain-conditionalness is implemented, but the basic principle of "If
you want shiny new optional feature $X, you need newer toolchain $Y" is
entirely fine.
A brand new architecture is exactly the same. Saying "this is the
minimum, because it's what we test" doesn't preclude someone coming
along and saying "can we use $N-1 ? See here it works, and here's a
change to CI test it".
Anyway, its clear we need to write some policy on this, before making
specific adjustments. To get started, is there going to be any
objection whatsoever on some principles which begin as follows:
Largely not, but one aspect needs clarifying up front:
* For established architectures, we expect Xen to be buildable on the
common contemporary distros. (i.e. minima is not newer than what's
available in contemporary distros, without a good reason)
What counts as contemporary distro? Still in normal support? LTS? Yet
more extreme forms?
LTS makes sense. More I am not sure. I am under the impression that
people using older distros are those that wants a stable system. So they
would unlikely try to upgrade the hypervisor.
Even for LTS, I would argue that if it has been released 5 years ago,
then you probably want to update it at the same time as moving to a
newer Xen version.
For the purposes of distros I agree. For the purposes of individuals
I don't: What's wrong with running a newer hypervisor and/or kernel
underneath an older distro?
There is nothing wrong. I just don't understand the benefits for us to
support that use case. To me there are two sorts of individuals:
1. The ones that are using distro packages. They will unlikely want to
switch to a newer hypervisor
2. The ones that are happy to compile and hack their system. Fairly
likely they will use a more distros and/or would not be put up by
upgrading it.
What individuals do you have in mind?
People like me.
Which means? From what I read you mostly use an older distros for smoke
testing/convenience.
Also, for me, the minimum doesn't prevent anyone to try to compile with
an older compiler. It is only here to say that as a community we will
not investigate or trying to workaround bugs in those compilers.
Besides this also allowing to use functionality you won't have an easy
way of replacing, what you say also doesn't make clear whether - for
cases where the issue can be (reasonably easily) worked around - patches
would be accepted, or rejected on the basis of only helping a below-the-
line compiler.
I would not accept them.
Cheers,
--
Julien Grall
