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

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Message-ID: <87pmad63jb.fsf@all.your.base.are.belong.to.us>
Date:   Mon, 13 Feb 2023 15:30:48 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     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
Subject: Re: [PATCH bpf-next] selftests/bpf: Cross-compile bpftool

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.

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