linux-kernel - Re: [PATCH bpf-next v2 04/13] resolve_btfids: Introduce finalize

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Message-ID: <c404446ab6d344338592dfa44f5a7e1b95492564.camel@gmail.com>
Date: Mon, 19 Jan 2026 16:13:23 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>, Alexei Starovoitov
 <ast@...nel.org>,  Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>
Cc: Mykyta Yatsenko <yatsenko@...a.com>, Tejun Heo <tj@...nel.org>, Alan
 Maguire <alan.maguire@...cle.com>, Benjamin Tissoires <bentiss@...nel.org>,
 Jiri Kosina	 <jikos@...nel.org>, Amery Hung <ameryhung@...il.com>,
 bpf@...r.kernel.org, 	linux-kernel@...r.kernel.org,
 linux-input@...r.kernel.org, 	sched-ext@...ts.linux.dev
Subject: Re: [PATCH bpf-next v2 04/13] resolve_btfids: Introduce
 finalize_btf() step

On Fri, 2026-01-16 at 12:16 -0800, Ihor Solodrai wrote:
> Since recently [1][2] resolve_btfids executes final adjustments to the
> kernel/module BTF before it's embedded into the target binary.
> 
> To keep the implementation simple, a clear and stable "pipeline" of
> how BTF data flows through resolve_btfids would be helpful. Some BTF
> modifications may change the ids of the types, so it is important to
> maintain correct order of operations with respect to .BTF_ids
> resolution too.
> 
> This patch refactors the BTF handling to establish the following
> sequence:
>   - load target ELF sections
>   - load .BTF_ids symbols
>     - this will be a dependency of btf2btf transformations in
>       subsequent patches
>   - load BTF and its base as is
>   - (*) btf2btf transformations will happen here
>   - finalize_btf(), introduced in this patch
>     - does distill base and sort BTF
>   - resolve and patch .BTF_ids
> 
> This approach helps to avoid fixups in .BTF_ids data in case the ids
> change at any point of BTF processing, because symbol resolution
> happens on the finalized, ready to dump, BTF data.
> 
> This also gives flexibility in BTF transformations, because they will
> happen on BTF that is not distilled and/or sorted yet, allowing to
> freely add, remove and modify BTF types.
> 
> [1] https://lore.kernel.org/bpf/20251219181321.1283664-1-ihor.solodrai@linux.dev/
> [2] https://lore.kernel.org/bpf/20260109130003.3313716-1-dolinux.peng@gmail.com/
> 
> Signed-off-by: Ihor Solodrai <ihor.solodrai@...ux.dev>
> ---

Acked-by: Eduard Zingerman <eddyz87@...il.com>

> @@ -1099,12 +1116,22 @@ int main(int argc, const char **argv)
>  	if (obj.efile.idlist_shndx == -1 ||
>  	    obj.efile.symbols_shndx == -1) {
>  		pr_debug("Cannot find .BTF_ids or symbols sections, skip symbols resolution\n");
> -		goto dump_btf;
> +		resolve_btfids = false;
>  	}
>  
> -	if (symbols_collect(&obj))
> +	if (resolve_btfids)
> +		if (symbols_collect(&obj))
> +			goto out;

Nit: check obj.efile.idlist_shndx and obj.efile.symbols_shndx inside symbols_collect()?
     To avoid resolve_btfids flag and the `goto dump_btf;` below.

> +
> +	if (load_btf(&obj))
>  		goto out;
>  
> +	if (finalize_btf(&obj))
> +		goto out;
> +
> +	if (!resolve_btfids)
> +		goto dump_btf;
> +
>  	if (symbols_resolve(&obj))
>  		goto out;
>