Re: [RFC dwarves 5/6] btf_encoder: Do not error out if BTF is not found in some input files

["Jose E. Marchesi" <jose.marchesi@oracle.com>]

> On Thu, Aug 7, 2025 at 7:42 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>>
>> This is no substitute for link-time BTF deduplication of course, but
>> it does provide a simple way to see the BTF that gcc generates for vmlinux.
>>
>> The idea is that we can explore differences in BTF generation across
>> the various combinations
>>
>> 1. debug info source: DWARF; dedup done via pahole (traditional)
>> 2. debug info source: compiler-generated BTF; dedup done via pahole (above)
>> 3. debug info source: compiler-generated BTF; dedup done via linker (TBD)
>>
>> Handling 3 - linker-based dedup - will require BTF archives so that is the
>> next step we need to explore.
>
> Overall, the patch set makes sense and we need to make this step in pahole,
> but before we start any discussion about 3 and BTF archives
> the 1 and 2 above need to reach parity.
> Not just being close enough, but an exact equivalence.
>
> But, frankly, gcc support for btf_decl_tags is much much higher priority
> than any of this.
>
> We're tired of adding hacks through the bpf subsystem, because
> gcc cannot do decl_tags.
> Here are the hacks that will be removed:
> 1. BTF_TYPE_SAFE*
> 2. raw_tp_null_args[]
> 3. KF_ARENA_ARG
> and probably other cases.

We are getting there.  The C front-end maintainer just looked at the
latest version of the series [1] and, other than a small observation
concerning wide char strings, he seems to be ok with the attributes.

[1] https://gcc.gnu.org/pipermail/gcc-patches/2025-August/692057.html