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From:   Changbin Du <changbin.du@gmail.com>
To:     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>
Cc:     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,
        Changbin Du <changbin.du@gmail.com>
Subject: [PATCH 1/2] libbpf: show more info about missing ".BTF" section
Date:   Sat, 26 Nov 2022 19:11:46 +0800
Message-Id: <20221126111147.199366-2-changbin.du@gmail.com>
In-Reply-To: <20221126111147.199366-1-changbin.du@gmail.com>
References: <20221126111147.199366-1-changbin.du@gmail.com>
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Show more information about why failed instead of just saying "No such file or
directory".

Now will print below info:
libbpf: can not find '.BTF' section
libbpf: is CONFIG_DEBUG_INFO_BTF enabled for kernel?
Error: failed to load BTF from /home/changbin/work/linux/vmlinux: No such file or directory

Signed-off-by: Changbin Du <changbin.du@gmail.com>
---
 tools/lib/bpf/btf.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index d88647da2c7f..3f661d991808 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -906,6 +906,15 @@ struct btf *btf__new(const void *data, __u32 size)
 	return libbpf_ptr(btf_new(data, size, NULL));
 }
 
+static bool is_vmlinux(const char *path)
+{
+	size_t path_len = strlen(path);
+	size_t suffix_len = strlen("vmlinux");
+
+	return (path_len >= suffix_len) &&
+	       (!memcmp(path + path_len - suffix_len, "vmlinux", suffix_len));
+}
+
 static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
 				 struct btf_ext **btf_ext)
 {
@@ -990,6 +999,9 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
 	err = 0;
 
 	if (!btf_data) {
+		pr_warn("can not find '%s' section\n", BTF_ELF_SEC);
+		if (is_vmlinux(path))
+			pr_warn("is CONFIG_DEBUG_INFO_BTF enabled for kernel?\n");
 		err = -ENOENT;
 		goto done;
 	}
-- 
2.37.2