linux-kernel - Re: [PATCH bpf-next v12 03/11] tools/resolve

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Message-ID: <CAErzpmtvKM41=_VXcRAQknbcc_Hjna71FbMd+XYXWxANBPxoqQ@mail.gmail.com>
Date: Wed, 14 Jan 2026 09:44:19 +0800
From: Donglin Peng <dolinux.peng@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: ast@...nel.org, eddyz87@...il.com, zhangxiaoqin@...omi.com, 
	ihor.solodrai@...ux.dev, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Donglin Peng <pengdonglin@...omi.com>, Alan Maguire <alan.maguire@...cle.com>
Subject: Re: [PATCH bpf-next v12 03/11] tools/resolve_btfids: Support BTF
 sorting feature

On Wed, Jan 14, 2026 at 8:29 AM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Fri, Jan 9, 2026 at 5:00 AM Donglin Peng <dolinux.peng@...il.com> wrote:
> >
> > From: Donglin Peng <pengdonglin@...omi.com>
> >
> > This introduces a new BTF sorting phase that specifically sorts
> > BTF types by name in ascending order, so that the binary search
> > can be used to look up types.
> >
> > Cc: Eduard Zingerman <eddyz87@...il.com>
> > Cc: Alexei Starovoitov <ast@...nel.org>
> > Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> > Cc: Alan Maguire <alan.maguire@...cle.com>
> > Cc: Ihor Solodrai <ihor.solodrai@...ux.dev>
> > Cc: Xiaoqin Zhang <zhangxiaoqin@...omi.com>
> > Signed-off-by: Donglin Peng <pengdonglin@...omi.com>
> > Acked-by: Eduard Zingerman <eddyz87@...il.com>
> > ---
> >  tools/bpf/resolve_btfids/main.c | 64 +++++++++++++++++++++++++++++++++
> >  1 file changed, 64 insertions(+)
> >
> > diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
> > index df39982f51df..343d08050116 100644
> > --- a/tools/bpf/resolve_btfids/main.c
> > +++ b/tools/bpf/resolve_btfids/main.c
> > @@ -850,6 +850,67 @@ static int dump_raw_btf(struct btf *btf, const char *out_path)
> >         return 0;
> >  }
> >
> > +/*
> > + * Sort types by name in ascending order resulting in all
> > + * anonymous types being placed before named types.
> > + */
> > +static int cmp_type_names(const void *a, const void *b, void *priv)
> > +{
> > +       struct btf *btf = (struct btf *)priv;
> > +       const struct btf_type *ta = btf__type_by_id(btf, *(__u32 *)a);
> > +       const struct btf_type *tb = btf__type_by_id(btf, *(__u32 *)b);
> > +       const char *na, *nb;
> > +
> > +       na = btf__str_by_offset(btf, ta->name_off);
> > +       nb = btf__str_by_offset(btf, tb->name_off);
> > +       return strcmp(na, nb);
>
> let's disambiguate the case when strcmp() == 0:
>
> int r = strcmp(na, nb);
> if (r != 0)
>     return r;
>
> /* preserve original relative order of anonymous or same-named types */
> return *(__u32 *)a < *(__u32 *)b ? -1 : 1;

Thanks, I see.

>
> (please send as a follow up)

Ok.

>
>
> > +}
> > +
> > +static int sort_btf_by_name(struct btf *btf)
> > +{
> > +       __u32 *permute_ids = NULL, *id_map = NULL;
> > +       int nr_types, i, err = 0;
> > +       __u32 start_id = 0, start_offs = 1, id;
> > +
> > +       if (btf__base_btf(btf)) {
> > +               start_id = btf__type_cnt(btf__base_btf(btf));
> > +               start_offs = 0;
>
> with the above cmp_type_names disambiguation sorting becomes stable,
> so you won't need this start_offs thing here, you can safely compare
> VOID with any other type and it will stay the very first one

Great, I will fix it in v13 of this patch.

>
> (please include in the follow up as well)

Okay, thanks.

>
>
>
> > +       }
> > +       nr_types = btf__type_cnt(btf) - start_id;
> > +
> > +       permute_ids = calloc(nr_types, sizeof(*permute_ids));
> > +       if (!permute_ids) {
> > +               err = -ENOMEM;
> > +               goto out;
> > +       }
> > +
> > +       id_map = calloc(nr_types, sizeof(*id_map));
> > +       if (!id_map) {
> > +               err = -ENOMEM;
> > +               goto out;
> > +       }
> > +
> > +       for (i = 0, id = start_id; i < nr_types; i++, id++)
> > +               permute_ids[i] = id;
> > +
> > +       qsort_r(permute_ids + start_offs, nr_types - start_offs,
> > +               sizeof(*permute_ids), cmp_type_names, btf);
> > +
> > +       for (i = 0; i < nr_types; i++) {
> > +               id = permute_ids[i] - start_id;
> > +               id_map[id] = i + start_id;
> > +       }
> > +
> > +       err = btf__permute(btf, id_map, nr_types, NULL);
> > +       if (err)
> > +               pr_err("FAILED: btf permute: %s\n", strerror(-err));
> > +
> > +out:
> > +       free(permute_ids);
> > +       free(id_map);
> > +       return err;
> > +}
> > +
> >  static inline int make_out_path(char *buf, u32 buf_sz, const char *in_path, const char *suffix)
> >  {
> >         int len = snprintf(buf, buf_sz, "%s%s", in_path, suffix);
> > @@ -1025,6 +1086,9 @@ int main(int argc, const char **argv)
> >         if (load_btf(&obj))
> >                 goto out;
> >
> > +       if (sort_btf_by_name(obj.btf))
> > +               goto out;
> > +
> >         if (elf_collect(&obj))
> >                 goto out;
> >
> > --
> > 2.34.1
> >