Re: [PATCH bpf-next v1] libbpf: ensure new BTF objects inherit input endianness

[Alan Maguire <alan.maguire@oracle.com>]

On 30/08/2024 12:15, Eduard Zingerman wrote:
> On Fri, 2024-08-30 at 02:51 -0700, Tony Ambardar wrote:
>> The pahole master branch recently added support for "distilled BTF" based
>> on libbpf v1.5, but may add .BTF and .BTF.base sections with the wrong byte
>> order (e.g. on s390x BPF CI), which then lead to kernel Oops when loaded.
>>
>> Fix by updating libbpf's btf__distill_base() and btf_new_empty() to retain
>> the byte order of any source BTF objects when creating new ones.
>>
>> Reported-by: Song Liu <song@kernel.org>
>> Reported-by: Eduard Zingerman <eddyz87@gmail.com>
>> Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
>> Link: https://lore.kernel.org/bpf/6358db36c5f68b07873a0a5be2d062b1af5ea5f8.camel@gmail.com/
>> Signed-off-by: Tony Ambardar <tony.ambardar@gmail.com>
>> ---
> 
> Acked-by: Eduard Zingerman <eddyz87@gmail.com>
>

Tested-by: Alan Maguire <alan.maguire@oracle.com>

Thanks for the fix!

> But we also need a test for this. Like the one attached.
> Or Alan can share his test, which is much shorter but skips round trip to bytes and back.
>

Eduard's test is better than mine; mine was a simple addition to
btf_endian() tests that checked split/distilled BTF matched endianness
of the originating BTF for non-native endianness. Having actual
non-native endianness _use_ as in Eduard's test is much preferred I think.

> [...]