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Message-ID: <CAErzpmuCgR+q8Yndb9bd_W7GO8H4rUv7oEJpeZtwd12tkMU8QA@mail.gmail.com>
Date: Sat, 20 Dec 2025 16:44:00 +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,
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 Sat, Dec 20, 2025 at 1:12 AM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Dec 18, 2025 at 7:42 PM Donglin Peng <dolinux.peng@...il.com> wrote:
> >
> > On Fri, Dec 19, 2025 at 7:09 AM Andrii Nakryiko
> > <andrii.nakryiko@...il.com> wrote:
> > >
> > > 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?
> >
> > Sorry, I will fix this in the next version. The reason is that our
> > company's Gerrit only accepts "pengdonglin" and does not
> > accept "Donglin Peng".
> >
> > >
> > > > 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?
> >
> > Because I think that if there are zero or only one type,
> > there is no need to sort.
>
> There is also no need to special-case and add more checks just for
> these corner cases. Keep it simple.
Thanks, I agree and and will fix 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?
> >
> > Sorting BTF is a type of `btf2btf` process. There may be other
> > types of `btf2btf` processes, which could be grouped together
> > here. If we currently don't care about these other processes,
> > I will retain only `sort_btf_by_name` in the next version.
>
> Let's have sort as is, when necessary we can refactor this into
> logical steps further (or perhaps sorting will be its own logical
> step, I don't know, but let's not over design it just yet)
Okay, I will invoke sort_btf_by_name directly in the next version.
>
> >
> > >
> > > > +{
> > > > + 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
> > > >
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