netdev - Re: [PATCH bpf-next] tools: bpftool: restore message on failure to guess program type

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Message-ID: <CAADnVQ+i_y89KkiGe2aZbDstvND17esMCz=uegCSGwq47vXsuQ@mail.gmail.com>
Date:   Thu, 12 Mar 2020 18:11:54 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Quentin Monnet <quentin@...valent.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH bpf-next] tools: bpftool: restore message on failure to
 guess program type

On Tue, Mar 10, 2020 at 7:12 PM Quentin Monnet <quentin@...valent.com> wrote:
>
> In commit 4a3d6c6a6e4d ("libbpf: Reduce log level for custom section
> names"), log level for messages for libbpf_attach_type_by_name() and
> libbpf_prog_type_by_name() was downgraded from "info" to "debug". The
> latter function, in particular, is used by bpftool when attempting to
> load programs, and this change caused bpftool to exit with no hint or
> error message when it fails to detect the type of the program to load
> (unless "-d" option was provided).
>
> To help users understand why bpftool fails to load the program, let's do
> a second run of the function with log level in "debug" mode in case of
> failure.
>
> Before:
>
>     # bpftool prog load sample_ret0.o /sys/fs/bpf/sample_ret0
>     # echo $?
>     255
>
> Or really verbose with -d flag:
>
>     # bpftool -d prog load sample_ret0.o /sys/fs/bpf/sample_ret0
>     libbpf: loading sample_ret0.o
>     libbpf: section(1) .strtab, size 134, link 0, flags 0, type=3
>     libbpf: skip section(1) .strtab
>     libbpf: section(2) .text, size 16, link 0, flags 6, type=1
>     libbpf: found program .text
>     libbpf: section(3) .debug_abbrev, size 55, link 0, flags 0, type=1
>     libbpf: skip section(3) .debug_abbrev
>     libbpf: section(4) .debug_info, size 75, link 0, flags 0, type=1
>     libbpf: skip section(4) .debug_info
>     libbpf: section(5) .rel.debug_info, size 32, link 14, flags 0, type=9
>     libbpf: skip relo .rel.debug_info(5) for section(4)
>     libbpf: section(6) .debug_str, size 150, link 0, flags 30, type=1
>     libbpf: skip section(6) .debug_str
>     libbpf: section(7) .BTF, size 155, link 0, flags 0, type=1
>     libbpf: section(8) .BTF.ext, size 80, link 0, flags 0, type=1
>     libbpf: section(9) .rel.BTF.ext, size 32, link 14, flags 0, type=9
>     libbpf: skip relo .rel.BTF.ext(9) for section(8)
>     libbpf: section(10) .debug_frame, size 40, link 0, flags 0, type=1
>     libbpf: skip section(10) .debug_frame
>     libbpf: section(11) .rel.debug_frame, size 16, link 14, flags 0, type=9
>     libbpf: skip relo .rel.debug_frame(11) for section(10)
>     libbpf: section(12) .debug_line, size 74, link 0, flags 0, type=1
>     libbpf: skip section(12) .debug_line
>     libbpf: section(13) .rel.debug_line, size 16, link 14, flags 0, type=9
>     libbpf: skip relo .rel.debug_line(13) for section(12)
>     libbpf: section(14) .symtab, size 96, link 1, flags 0, type=2
>     libbpf: looking for externs among 4 symbols...
>     libbpf: collected 0 externs total
>     libbpf: failed to guess program type from ELF section '.text'
>     libbpf: supported section(type) names are: socket sk_reuseport kprobe/ [...]
>
> After:
>
>     # bpftool prog load sample_ret0.o /sys/fs/bpf/sample_ret0
>     libbpf: failed to guess program type from ELF section '.text'
>     libbpf: supported section(type) names are: socket sk_reuseport kprobe/ [...]
>
> Signed-off-by: Quentin Monnet <quentin@...valent.com>

Applied. Thanks