Re: [PATCH bpf-next v1 1/8] bpftool: Dump C from a detached BTF copy

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 2026-10-16 2:44 a.m., Alan Maguire wrote:
> On 10/16/26 2:18 AM, Alexei Starovoitov wrote:
>> On Thu, Oct 15, 2026 at 05:00 PM Ihor Solodrai <ihor.solodrai@linux.dev> wrote:
>>> Modifying the parsed BTF fails for some valid input: libbpf refuses to
>>> modify BTF whose header carries unknown nonzero extension bytes, so
>>> such a dump would stop with -EOPNOTSUPP.
>>>
>>> Dump from a flat copy built with btf__add_type(), which only requires
>>> the destination to be modifiable.
>>
>> can we do btf__new_empty_split(btf) and add decl attrs there
>> instead of copying all types ?
>> It fails on such BTF only because btf__add_str() does
>> btf__find_str(base) and that calls btf_ensure_modifiable(base).
>> The lookup shouldn't need it.
> 
> +1 on using split BTF for new decl tags; even in the case of module
> BTF we can use multi-split BTF to cover decl tags for vmlinux and
> module BTF I think.

Yeah, these are good points.

I briefly considered this, but didn't look closely at what needs to
change in libbpf to make it work and just went with the copy. The
libbpf fix should be simple, I'll use a split in v2.

Thanks.