netdev - Re: [PATCH bpf] bpf: support pre-2.25-binutils objcopy for vmlinux BTF

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Message-ID: <CAEf4BzZ+e4vnW7Gconhq3AJ5od=TULAZC=-+UANFDGXcWCoOSA@mail.gmail.com>
Date:   Tue, 26 Nov 2019 14:30:31 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf] bpf: support pre-2.25-binutils objcopy for vmlinux BTF

On Tue, Nov 26, 2019 at 9:56 AM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> If vmlinux BTF generation fails, but CONFIG_DEBUG_INFO_BTF is set,
> .BTF section of vmlinux is empty and kernel will prohibit
> BPF loading and return "in-kernel BTF is malformed".
>
> --dump-section argument to binutils' objcopy was added in version 2.25.
> When using pre-2.25 binutils, BTF generation silently fails. Convert
> to --only-section which is present on pre-2.25 binutils.
>
> Documentation/process/changes.rst states that binutils 2.21+
> is supported, not sure those standards apply to BPF subsystem.
>
> Fixes: 341dfcf8d78ea ("btf: expose BTF info through sysfs")
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---

Looks good, still works for me :)

Tested-by: Andrii Nakryiko <andriin@...com>

>  scripts/link-vmlinux.sh | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 06495379fcd8..c56ba91f52b0 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -127,7 +127,8 @@ gen_btf()
>                 cut -d, -f1 | cut -d' ' -f2)
>         bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \
>                 awk '{print $4}')
> -       ${OBJCOPY} --dump-section .BTF=.btf.vmlinux.bin ${1} 2>/dev/null
> +       ${OBJCOPY} --set-section-flags .BTF=alloc -O binary \
> +               --only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null
>         ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \
>                 --rename-section .data=.BTF .btf.vmlinux.bin ${2}
>  }
> --
> 2.24.0.432.g9d3f5f5b63-goog
>