linux-kernel - Re: [PATCH bpf-next v3 3/6] resolve_btfids: Introduce enum btf_id

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Message-ID: <386068b11e146a9dbb502f770d7e012e3dea950f.camel@gmail.com>
Date: Fri, 12 Dec 2025 16:09:21 +0900
From: Eduard Zingerman <eddyz87@...il.com>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>, Alexei Starovoitov
 <ast@...nel.org>,  Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,  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>,  Andrew Morton <akpm@...ux-foundation.org>, Nathan
 Chancellor <nathan@...nel.org>, Nicolas Schier	 <nsc@...nel.org>, Tejun Heo
 <tj@...nel.org>, David Vernet <void@...ifault.com>,  Andrea Righi
 <arighi@...dia.com>, Changwoo Min <changwoo@...lia.com>, Shuah Khan
 <shuah@...nel.org>, 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>
Cc: bpf@...r.kernel.org, dwarves@...r.kernel.org,
 linux-kernel@...r.kernel.org, 	linux-kbuild@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 3/6] resolve_btfids: Introduce enum
 btf_id_kind

On Fri, 2025-12-05 at 14:30 -0800, Ihor Solodrai 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>
> ---

Acked-by: Eduard Zingerman <eddyz87@...il.com>

(But see a question below).

> @@ -213,14 +218,19 @@ btf_id__add(struct rb_root *root, char *name, bool unique)
>  			p = &(*p)->rb_left;
>  		else if (cmp > 0)
>  			p = &(*p)->rb_right;
> -		else
> -			return unique ? NULL : id;
> +		else if (kind == BTF_ID_KIND_SYM && id->kind == BTF_ID_KIND_SYM)

Nit: I'd keep the 'unique' parameter alongside 'kind' and resolve this
     condition on the function callsite.

> +			return id;
> +		else {
> +			pr_err("Unexpected duplicate symbol %s of kind %d\n", name, id->kind);
> +			return NULL;
> +		}

[...]

> @@ -491,28 +515,24 @@ static int symbols_collect(struct object *obj)
>  			id = add_symbol(&obj->funcs, prefix, sizeof(BTF_FUNC) - 1);
>  		/* set8 */
>  		} else if (!strncmp(prefix, BTF_SET8, sizeof(BTF_SET8) - 1)) {
> -			id = add_set(obj, prefix, true);
> +			id = add_set(obj, prefix, BTF_ID_KIND_SET8);
>  			/*
>  			 * SET8 objects store list's count, which is encoded
>  			 * in symbol's size, together with 'cnt' field hence
>  			 * that - 1.
>  			 */
> -			if (id) {
> +			if (id)
>  				id->cnt = sym.st_size / sizeof(uint64_t) - 1;
> -				id->is_set8 = true;
> -			}
>  		/* set */
>  		} else if (!strncmp(prefix, BTF_SET, sizeof(BTF_SET) - 1)) {
> -			id = add_set(obj, prefix, false);
> +			id = add_set(obj, prefix, BTF_ID_KIND_SET);
>  			/*
>  			 * SET objects store list's count, which is encoded
>  			 * in symbol's size, together with 'cnt' field hence
>  			 * that - 1.
>  			 */
> -			if (id) {
> +			if (id)

Current patch is not a culprit, but shouldn't resolve_btfids fail if
`id` cannot be added? (here and in a hunk above).

>  				id->cnt = sym.st_size / sizeof(int) - 1;
> -				id->is_set = true;
> -			}
>  		} else {
>  			pr_err("FAILED unsupported prefix %s\n", prefix);
>  			return -1;

[...]