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

Leo Yan
2022-12-19T03:45:34Z

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@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
>