netdev - Re: [PATCH bpf-next] selftests/bpf: Cross-compile bpftool

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Date:   Tue, 14 Feb 2023 09:16:07 +0000
From:   Zachary Leaf <zachary.leaf@....com>
To:     Björn Töpel <bjorn@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     Björn Töpel <bjorn@...osinc.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        linux-kselftest@...r.kernel.org,
        Anders Roxell <anders.roxell@...aro.org>,
        linux-riscv@...ts.infradead.org,
        Quentin Monnet <quentin@...valent.com>,
        linux-morello@...lists.linaro.org
Subject: Re: [PATCH bpf-next] selftests/bpf: Cross-compile bpftool

On 13/02/2023 14:30, Björn Töpel wrote:
> Björn Töpel <bjorn@...nel.org> writes:
> 
>> From: Björn Töpel <bjorn@...osinc.com>
>>
>> When the BPF selftests are cross-compiled, only the a host version of
>> bpftool is built. This version of bpftool is used to generate various
>> intermediates, e.g., skeletons.
>>
>> The test runners are also using bpftool. The Makefile will symlink
>> bpftool from the selftest/bpf root, where the test runners will look
>> for the tool:
>>
>>   | ...
>>   | $(Q)ln -sf $(if $2,..,.)/tools/build/bpftool/bootstrap/bpftool \
>>   |    $(OUTPUT)/$(if $2,$2/)bpftool
>>
>> There are two issues for cross-compilation builds:
>>
>>  1. There is no native (cross-compilation target) build of bpftool
>>  2. The bootstrap variant of bpftool is never cross-compiled (by
>>     design)
>>
>> Make sure that a native/cross-compiled version of bpftool is built,
>> and if CROSS_COMPILE is set, symlink to the native/non-bootstrap
>> version.
> 
> ...and the grand master plan is to add BPF CI support for riscv64, where
> this patch a prerequisite to [1]. I would suspect that other platforms
> might benefit from cross-compilation builds as well.

Similar use case. There also seems to be a lot of issues building these
tests out of tree.

I have some potential fixes up to 6.1 but linux-next seems to have
introduced a few more issues on top.

> 
> [1] https://github.com/kernel-patches/vmtest/pull/194