linux-kernel - Re: [RFC PATCH v7 3/7] tools/resolve_btfids: Add --btf

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Message-ID: <CAErzpmv-nRh701i6p8F5p=zgfOMoKzd8uXTwiqi9+nNVbaAj3w@mail.gmail.com>
Date: Tue, 25 Nov 2025 18:54:51 +0800
From: Donglin Peng <dolinux.peng@...il.com>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>
Cc: ast@...nel.org, andrii.nakryiko@...il.com, eddyz87@...il.com, 
	zhangxiaoqin@...omi.com, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Donglin Peng <pengdonglin@...omi.com>, Alan Maguire <alan.maguire@...cle.com>, 
	Song Liu <song@...nel.org>
Subject: Re: [RFC PATCH v7 3/7] tools/resolve_btfids: Add --btf_sort option
 for BTF name sorting

On Tue, Nov 25, 2025 at 3:35 AM Ihor Solodrai <ihor.solodrai@...ux.dev> wrote:
>
> On 11/21/25 7:36 AM, Donglin Peng wrote:
> > On Fri, Nov 21, 2025 at 5:34 AM Ihor Solodrai <ihor.solodrai@...ux.dev> wrote:
> >>
> >> On 11/18/25 7:15 PM, Donglin Peng wrote:
> >>> From: Donglin Peng <pengdonglin@...omi.com>
> >>>
> >>> This patch introduces a new --btf_sort option that leverages libbpf's
> >>> btf__permute interface to reorganize BTF layout. The implementation
> >>> sorts BTF types by name in ascending order, placing anonymous types at
> >>> the end to enable efficient binary search lookup.
> >>
> >> [...]
> >>
> >> Hi Dongling.
> >>
> >> Thanks for working on this, it's a great optimization. Just want to
> >> give you a heads up that I am preparing a patchset changing
> >> resolve_btfids behavior.
> >
> > Thanks. I'm curious about the new behavior of resolve_btfids. Does it
> > replace pahole and generate the sorted .BTF data directly from the
> > DWARF data? Also, does its sorting method differ from the cmp_type_names
> > approach mentioned above — specifically, does it place named types
> > before all anonymous types? I'm asking because the search method
> > needs to be compatible with this sorting approach.
>
> No, replacing pahole entirely isn't really feasible, and unnecessary.
>
> TL;DR is that resolve_btfids will also do kernel-specific btf2btf
> transformations. The sorting feature is independent, it's relevant
> only in that it is also a btf2btf transformation and will be included
> in the pipeline.
>
> I described the approach here:
> https://lore.kernel.org/dwarves/ba1650aa-fafd-49a8-bea4-bdddee7c38c9@linux.dev/

Thanks for the explanation.

>
>
> >
> >>
> >> In particular, instead of updating the .BTF_ids section (and now with
> >> your and upcoming changes the .BTF section) *in-place*, resolve_btfids
> >> will only emit the data for the sections. And then it'll be integrated
> >> into vmlinux with objcopy and linker. We already do a similar thing
> >> with .BTF for vmlinux [1].
> >>
> >> For your patchset it means that the parts handling ELF update will be
> >> unnecessary.
> >>
> >> Also I think the --btf_sort flag is unnecessary. We probably want
> >> kernel BTF to always be sorted in this way. And if resolve_btfids will
> >> be handling more btf2btf transformation, we should avoid adding a
> >> flags for every one of them.
> >>
> >> [1] https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/scripts/link-vmlinux.sh#n110
> >>