linux-kernel - Re: [PATCH] lib: bpf: Optimized variable usage in the btf_parse

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Date:   Sun, 9 Oct 2022 14:53:42 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     Li kunyu <kunyu@...china.com>
Cc:     lkp@...el.com, andrii@...nel.org, ast@...nel.org,
        bpf@...r.kernel.org, daniel@...earbox.net, haoluo@...gle.com,
        john.fastabend@...il.com, kbuild-all@...ts.01.org,
        kpsingh@...nel.org, linux-kernel@...r.kernel.org,
        martin.lau@...ux.dev, sdf@...gle.com, song@...nel.org, yhs@...com
Subject: Re: [PATCH] lib: bpf: Optimized variable usage in the btf_parse_elf
 function

On Sun, Oct 09, 2022 at 03:08:28PM +0800, Li kunyu wrote:
> The following changes were made in the btf_parse_elf function:
> 1. The initialization assignments of err, fd, scn and elf variables are
> removed, and they do not affect function security after analysis.
> 2. Remove unnecessary assignments to err variable (-error).
> 
> Signed-off-by: Li kunyu <kunyu@...china.com>
> ---
>  tools/lib/bpf/btf.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 2d14f1a52d7a..fa9d5fa03da4 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -910,10 +910,10 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
>  				 struct btf_ext **btf_ext)
>  {
>  	Elf_Data *btf_data = NULL, *btf_ext_data = NULL;
> -	int err = 0, fd = -1, idx = 0;
> +	int err, fd, idx = 0;
>  	struct btf *btf = NULL;
> -	Elf_Scn *scn = NULL;
> -	Elf *elf = NULL;
> +	Elf_Scn *scn;
> +	Elf *elf;
>  	GElf_Ehdr ehdr;
>  	size_t shstrndx;
>  
> @@ -924,9 +924,8 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
>  
>  	fd = open(path, O_RDONLY | O_CLOEXEC);
>  	if (fd < 0) {
> -		err = -errno;
>  		pr_warn("failed to open %s: %s\n", path, strerror(errno));
> -		return ERR_PTR(err);
> +		return ERR_PTR(-errno);

hum, pr_warn could potentionally change errno

jirka

>  	}
>  
>  	err = -LIBBPF_ERRNO__FORMAT;
> @@ -987,8 +986,6 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
>  		}
>  	}
>  
> -	err = 0;
> -
>  	if (!btf_data) {
>  		err = -ENOENT;
>  		goto done;
> -- 
> 2.18.2
>