linux-kernel - Re: [PATCH v3 1/2] libbpf: show error info about missing ".BTF" section

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Date:   Mon, 19 Dec 2022 11:45:08 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mykola Lysenko <mykolal@...com>,
        linux-perf-users@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 1/2] libbpf: show error info about missing ".BTF"
 section

Hi Changbin,

On Sun, Dec 18, 2022 at 06:35:08AM +0800, Changbin Du wrote:
> Show the real problem instead of just saying "No such file or directory".
> 
> Now will print below info:
> libbpf: failed to find '.BTF' ELF section in /home/changbin/work/linux/vmlinux

Recently I encountered the same issue, it could be caused by:
either missing to install tool pahole or missing to enable kernel
configuration CONFIG_DEBUG_INFO_BTF.

Could we give explict info for reasoning failure?  Like:

"libbpf: failed to find '.BTF' ELF section in /home/changbin/work/linux/vmlinux,
please install pahole and enable CONFIG_DEBUG_INFO_BTF=y for kernel building".

> Error: failed to load BTF from /home/changbin/work/linux/vmlinux: No such file or directory

This log is confusing when we can find vmlinux file but without BTF
section.  Consider to use a separate patch to detect vmlinux not
found case and print out "No such file or directory"?

Thanks,
Leo

> Signed-off-by: Changbin Du <changbin.du@...il.com>
> ---
>  tools/lib/bpf/btf.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 71e165b09ed5..dd2badf1a54e 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -990,6 +990,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
>  	err = 0;
>  
>  	if (!btf_data) {
> +		pr_warn("failed to find '%s' ELF section in %s\n", BTF_ELF_SEC, path);
>  		err = -ENOENT;
>  		goto done;
>  	}
> -- 
> 2.37.2
>