linux-kernel - Re: [PATCH bpf-next v10 03/13] tools/resolve

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Message-ID: <CAEf4Bzb0HEFsJ7KG6upatR792baKTKFV6n+91dHdXNL174ud5Q@mail.gmail.com>
Date: Thu, 18 Dec 2025 15:09:35 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Donglin Peng <dolinux.peng@...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, 
	pengdonglin <pengdonglin@...omi.com>, Alan Maguire <alan.maguire@...cle.com>
Subject: Re: [PATCH bpf-next v10 03/13] tools/resolve_btfids: Support BTF
 sorting feature

On Thu, Dec 18, 2025 at 3:31 AM Donglin Peng <dolinux.peng@...il.com> wrote:
>
> From: pengdonglin <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: pengdonglin <pengdonglin@...omi.com>

Signed-off-by is supposed to use properly spelled full name, this
should be "Donglin Peng", right?

> Acked-by: Eduard Zingerman <eddyz87@...il.com>
> ---
>  tools/bpf/resolve_btfids/main.c | 68 +++++++++++++++++++++++++++++++++
>  1 file changed, 68 insertions(+)
>
> diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
> index 3e88dc862d87..659de35748ec 100644
> --- a/tools/bpf/resolve_btfids/main.c
> +++ b/tools/bpf/resolve_btfids/main.c
> @@ -848,6 +848,71 @@ 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);
> +}
> +
> +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 = 1, id;
> +
> +       if (btf__base_btf(btf))
> +               start_id = btf__type_cnt(btf__base_btf(btf));
> +       nr_types = btf__type_cnt(btf) - start_id;
> +       if (nr_types < 2)
> +               goto out;

why this check, will anything break if you don't do it?

> +
> +       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, nr_types, 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 int btf2btf(struct object *obj)

what's the point of having this function?

> +{
> +       return sort_btf_by_name(obj->btf);
> +}
> +
>  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);
> @@ -906,6 +971,9 @@ int main(int argc, const char **argv)
>         if (load_btf(&obj))
>                 goto out;
>
> +       if (btf2btf(&obj))
> +               goto out;
> +
>         if (elf_collect(&obj))
>                 goto out;
>
> --
> 2.34.1
>