netdev - Re: [PATCH bpf 0/9] Fix various issues with 32-bit libbpf

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Message-ID: <20200813192042.ntv6ybry6ck2s6jg@ast-mbp.dhcp.thefacebook.com>
Date:   Thu, 13 Aug 2020 12:20:42 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...com,
        daniel@...earbox.net, andrii.nakryiko@...il.com, kernel-team@...com
Subject: Re: [PATCH bpf 0/9] Fix various issues with 32-bit libbpf

On Thu, Aug 13, 2020 at 12:17:13AM -0700, Andrii Nakryiko wrote:
> This patch set contains fixes to libbpf, bpftool, and selftests that were
> found while testing libbpf and selftests built in 32-bit mode. 64-bit nature
> of BPF target and 32-bit host environment don't always mix together well
> without extra care, so there were a bunch of problems discovered and fixed.
> 
> Each individual patch contains additional explanations, where necessary.
> 
> This series is really a mix of bpf tree fixes and patches that are better
> landed into bpf-next, once it opens. This is due to a bit riskier changes and
> new APIs added to allow solving this 32/64-bit mix problem. It would be great
> to apply patches #1 through #3 to bpf tree right now, and the rest into
> bpf-next, but I would appreciate reviewing all of them, of course.

why first three only?
I think btf__set_pointer_size() and friends are necessary in bpf tree.
The only thing I would suggest is to rename guess_ptr_size() into
determine_ptr_size() or something.
It's not guessing it. Looking for 'long' in BTF is precise.
We can teach pahole and llvm to always emit 'long' type and libbpf can
fail parsing BTF if 'long' is not found.