linux-kernel - Re: [PATCH bpf-next v2 3/4] resolve_btfids: introduce enum btf_id

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Message-ID: <CAEf4BzbNApf0n=Bwdar7UXBmHNJWaAmzuF68yfU4W5OYbYk2Bg@mail.gmail.com>
Date: Wed, 3 Dec 2025 16:42:59 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas.schier@...ux.dev>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Alan Maguire <alan.maguire@...cle.com>, 
	Donglin Peng <dolinux.peng@...il.com>, bpf@...r.kernel.org, dwarves@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 3/4] resolve_btfids: introduce enum btf_id_kind

On Tue, Dec 2, 2025 at 11:08 AM Ihor Solodrai <ihor.solodrai@...ux.dev> wrote:
>
> On 12/1/25 9:27 AM, Andrii Nakryiko wrote:
> > On Thu, Nov 27, 2025 at 10:53 AM Ihor Solodrai <ihor.solodrai@...ux.dev> wrote:
> >>
> >> Instead of using multiple flags, make struct btf_id tagged with an
> >> enum value indicating its kind in the context of resolve_btfids.
> >>
> >> Signed-off-by: Ihor Solodrai <ihor.solodrai@...ux.dev>
> >> ---
> >>  tools/bpf/resolve_btfids/main.c | 62 ++++++++++++++++++++++-----------
> >>  1 file changed, 42 insertions(+), 20 deletions(-)
> >
> > [...]
> >
> >>
> >> -static struct btf_id *add_set(struct object *obj, char *name, bool is_set8)
> >> +static struct btf_id *add_set(struct object *obj, char *name, enum btf_id_kind kind)
> >>  {
> >>         /*
> >>          * __BTF_ID__set__name
> >>          * name =    ^
> >>          * id   =         ^
> >>          */
> >> -       char *id = name + (is_set8 ? sizeof(BTF_SET8 "__") : sizeof(BTF_SET "__")) - 1;
> >> +       int prefixlen = kind == BTF_ID_KIND_SET8 ? sizeof(BTF_SET8 "__") : sizeof(BTF_SET "__");
> >> +       char *id = name + prefixlen - 1;
> >>         int len = strlen(name);
> >> +       struct btf_id *btf_id;
> >>
> >>         if (id >= name + len) {
> >>                 pr_err("FAILED to parse set name: %s\n", name);
> >>                 return NULL;
> >>         }
> >>
> >> -       return btf_id__add(&obj->sets, id, true);
> >> +       btf_id = btf_id__add(&obj->sets, id, true);
> >> +       if (btf_id)
> >> +               btf_id->kind = kind;
> >> +
> >> +       return btf_id;
> >>  }
> >>
> >>  static struct btf_id *add_symbol(struct rb_root *root, char *name, size_t size)
> >>  {
> >> +       struct btf_id *btf_id;
> >>         char *id;
> >>
> >>         id = get_id(name + size);
> >> @@ -288,7 +301,11 @@ static struct btf_id *add_symbol(struct rb_root *root, char *name, size_t size)
> >>                 return NULL;
> >>         }
> >>
> >> -       return btf_id__add(root, id, false);
> >> +       btf_id = btf_id__add(root, id, false);
> >> +       if (btf_id)
> >> +               btf_id->kind = BTF_ID_KIND_SYM;
> >
> > seeing this pattern repeated, wouldn't it make sense to just pass this
> > kind to btf_id__add() and set it there?
>
> I like the idea, because we could get rid the "unique" flag then.
>
> But the btf_id__add() does not necessarily create a new struct, and so
> if we pass the kind in, what do we do with existing objects?
> Overwrite the kind? If not, do we check for a mismatch?
>

no idea, don't know code well enough, but your newly added code seems
to overwrite the kind always, no?

> >
> >> +
> >> +       return btf_id;
> >>  }
> >>
> >
> > [...]
> >
> >> @@ -643,7 +656,7 @@ static int id_patch(struct object *obj, struct btf_id *id)
> >>         int i;
> >>
> >>         /* For set, set8, id->id may be 0 */
> >> -       if (!id->id && !id->is_set && !id->is_set8) {
> >> +       if (!id->id && id->kind == BTF_ID_KIND_SYM) {
> >
> > nit: comment says the exception is specifically for SET and SET8, so I
> > think checking for those two instead of for SYM (implying that only
> > other possible options are set and set8) would be a bit more
> > future-proof?
>
> ok
>
> >
> >>                 pr_err("WARN: resolve_btfids: unresolved symbol %s\n", id->name);
> >>                 warnings++;
> >>         }
> >
> > [...]
>