linux-kernel - Re: [PATCH v2 bpf-next] libbpf: Improve debug message when the base BTF cannot be found

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Message-ID: <6740181acbe77_86d22083@john.notmuch>
Date: Thu, 21 Nov 2024 21:35:22 -0800
From: John Fastabend <john.fastabend@...il.com>
To: "Olson, Matthew" <matthew.olson@...el.com>, 
 Andrii Nakryiko <andrii@...nel.org>, 
 Eduard Zingerman <eddyz87@...il.com>, 
 bpf@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>, 
 Daniel Borkmann <daniel@...earbox.net>, 
 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>, 
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 bpf-next] libbpf: Improve debug message when the base
 BTF cannot be found

Olson, Matthew wrote:
> From 22ed11ee2153fc921987eac7de24f564da9f9230 Mon Sep 17 00:00:00 2001
> From: Ben Olson <matthew.olson@...el.com>
> Date: Thu, 21 Nov 2024 11:26:35 -0600
> Subject: [PATCH v2 bpf-next] libbpf: Improve debug message when the base BTF
>  cannot be found
> 
> When running `bpftool` on a kernel module installed in `/lib/modules...`,
> this error is encountered if the user does not specify `--base-btf` to
> point to a valid base BTF (e.g. usually in `/sys/kernel/btf/vmlinux`).
> However, looking at the debug output to determine the cause of the error
> simply says `Invalid BTF string section`, which does not point to the
> actual source of the error. This just improves that debug message to tell
> users what happened.
> 
> Signed-off-by: Ben Olson <matthew.olson@...el.com>
> ---


LGTM

Acked-by: John Fastabend <john.fastabend@...il.com>

> 
> Changed in v2:
>   * Made error message better reflect the condition
> 
>  tools/lib/bpf/btf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 12468ae0d573..a4ae2df68b91 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -283,7 +283,7 @@ static int btf_parse_str_sec(struct btf *btf)
>      return -EINVAL;
>    }
>    if (!btf->base_btf && start[0]) {
> -    pr_debug("Invalid BTF string section\n");
> +    pr_debug("Malformed BTF string section, did you forget to provide base BTF?\n");
>      return -EINVAL;
>    }
>    return 0;
> --
> 2.47.0