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Date:   Tue, 20 Dec 2022 09:31:14 +0800
From:   Changbin Du <changbin.du@gmail.com>
To:     Leo Yan <leo.yan@linaro.org>
Cc:     Changbin Du <changbin.du@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Quentin Monnet <quentin@isovalent.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Shuah Khan <shuah@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Mykola Lysenko <mykolal@fb.com>,
        linux-perf-users@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v3 1/2] libbpf: show error info about missing ".BTF"
 section
Message-ID: <20221220013114.zkkxkqh7orahxbzh@mail.google.com>
References: <20221217223509.88254-1-changbin.du@gmail.com>
 <20221217223509.88254-2-changbin.du@gmail.com>
 <Y5/eE+ds+e+k3VJO@leoy-yangtze.lan>
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On Mon, Dec 19, 2022 at 11:45:08AM +0800, Leo Yan wrote:
> 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".
>
This is vmlinux special information and similar tips are removed from
patch V2. libbpf is common for all ELFs.

> > 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"?
>
I think it's already there. If the file doesn't exist, open will fail.

> Thanks,
> Leo
> 
> > Signed-off-by: Changbin Du <changbin.du@gmail.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
> > 

-- 
Cheers,
Changbin Du