linux-kernel - Re: [PATCH] libbpf: optimize the redundant code in the bpf_object__init_user_btf

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Message-ID: <aPsjSZtNxeQK239J@krava>
Date: Fri, 24 Oct 2025 08:57:13 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Jianyun Gao <jianyungao89@...il.com>
Cc: linux-kernel@...r.kernel.org, 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>,
	"open list:BPF [GENERAL] (Safe Dynamic Programs and Tools)" <bpf@...r.kernel.org>
Subject: Re: [PATCH] libbpf: optimize the redundant code in the
 bpf_object__init_user_btf_maps() function.

On Fri, Oct 24, 2025 at 02:07:20PM +0800, Jianyun Gao wrote:
> In the elf_sec_data() function, the input parameter 'scn' will be
> evaluated. If it is NULL, then it will directly return NULL. Therefore,
> the return value of the elf_sec_data() function already takes into
> account the case where the input parameter scn is NULL. Therefore,
> subsequently, the code only needs to check whether the return value of
> the elf_sec_data() function is NULL.
> 
> Signed-off-by: Jianyun Gao <jianyungao89@...il.com>
> ---
>  tools/lib/bpf/libbpf.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index b90574f39d1c..9e66104a61eb 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -2988,15 +2988,15 @@ static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict,
>  	int nr_types, i, vlen, err;
>  	const struct btf_type *t;
>  	const char *name;
> -	Elf_Data *data;
> +	Elf_Data *scn_data;

makes sense to me, but this rename breaks compilation later on

libbpf.c:3027:53: error: ‘data’ undeclared (first use in this function)

jirka

>  	Elf_Scn *scn;
>  
>  	if (obj->efile.btf_maps_shndx < 0)
>  		return 0;
>  
>  	scn = elf_sec_by_idx(obj, obj->efile.btf_maps_shndx);
> -	data = elf_sec_data(obj, scn);
> -	if (!scn || !data) {
> +	scn_data = elf_sec_data(obj, scn);
> +	if (!scn_data) {
>  		pr_warn("elf: failed to get %s map definitions for %s\n",
>  			MAPS_ELF_SEC, obj->path);
>  		return -EINVAL;
> -- 
> 2.34.1
>