Re: [PATCH net-next v2 0/2] selftests: drv-net: Allow cross-compiling the hardware tests

[Matthieu Baerts <matttbe@kernel.org>]

Hi Andrew,

On 03/09/2026 22:55, Andrew Lunn wrote:
> On Thu, Sep 03, 2026 at 07:25:22PM +0200, Matthieu Baerts wrote:
>> Hi Andrew,
>>
>> On 03/09/2026 19:11, Andrew Lunn wrote:
>>>> Tested on an aarch64 target, built on x86_64.
>>>
>>> Probably a question for Jakub or Matthieu.
>>>
>>> As part of the CI system which is feeding into patchworks, I don't
>>> think we build the selftests? Do we have the CPU resources to build
>>> them?
>>
>> We do: the "build_tools" script [1] checks that. And they are also built
>> before launching the selftests.
>>
>>> We currently do x86 64 and 32 bit builds. Do we have the CPU resources
>>> to do an arm64 cross build?
>>
>> I think we do, but I don't know if we need to (see below)
>>
>>> I assume a cross build the self tests needs something like buildroot
>>> to be sensible? Or Debians multi-arch stuff where you can install .deb
>>> packages for libraries for other architectures? So maybe that is going
>>> too far?
>>
>> >From what I understood, the goal is to execute the selftests on embedded
>> systems as well, which will require building new image including the
>> kernel and the drivers/net selftests. Do we need to build the whole
>> kernel for arm64? :)
> 
> I see a few different goals.
> 
> Picking a patch at random:
> 
> https://patchwork.kernel.org/project/netdevbpf/patch/20260903-netcons_ipv6-v4-2-bdd183c844d3@gmail.com/
> 
> We see 32bit, allmodconfig, clang, and clang_rust. These are all
> native builds, which given are servers are AMD64, these are AMD64
> builds.
> 
> However, many of the network drivers are used on ARM platforms. Most
> probably do compile on AMD64, but i expect there are a few which
> don't. So we could do an ARM64 cross compile, to make sure the patches
> are clean on ARM64 as well as AMD64.
> 
> We are encouraging developers to write self tests. Ideally we want
> self test patches to be held to the same standard as driver
> patches. So if a patch touches the self tests, it would be good to
> build the self tests in order to show the number of warnings & errors
> has not gone up. I expect such a build will be native.
> 
> But if we have gone to the time/effort to cross compile the kernel,
> can we also cross compile the self tests? Can we ensure with cross
> compile self tests don't have more warnings/errors, because the self
> test write has AMD64 blinkers on?
> 
> And sometime down the road, we would like to get ARM servers, with
> NICs in them, to run the self tests on. At that point, we either need
> to cross compile the kernel to run all the self tests, or we need
> another build server which is ARM64, so it can do native ARM64 builds
> of the kernel to run on the ARM64 runners.
I agree that the Netdev CI currently doesn't build anything for the
ARM64 target. But what I meant is that the goal of Maxime's work (if I
understood correctly) is to execute the net selftests (or just the
drv-net ones?) on embedded systems, with different targets. From your
reply, I guess you meant that it might not be enough to have a good
coverage.

I don't think I can properly judge if this is required or not. My
feeling is that it might not be worth it: I don't recall having seen
many fixes specific to other architectures, plus the Intel's bot is
still building the kernel for many architectures. What is currently
missing is compiling the net selftests for different arch. But if ARM64
is added, which other ones should be added too? Plus maybe adding this
would no longer be needed thanks to Maxime's work where selftests will
be built for many architectures and issues reported to NIPA's dashboard?

But I'm aware I have probably missed something, and ARM64 builds might
be worth it. Should we discuss that at the next Netdev bi-weekly call?

Cheers,
Matt