Stanislav Fomichev 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.
>
> v2:
> * exit and print an error if gen_btf fails (John Fastabend)
>
> Cc: Andrii Nakryiko <andriin@xxxxxx>
> Cc: John Fastabend <john.fastabend@xxxxxxxxx>
> Fixes: 341dfcf8d78ea ("btf: expose BTF info through sysfs")
> Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> ---
> scripts/link-vmlinux.sh | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 06495379fcd8..2998ddb323e3 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 ${2}
> }
> @@ -253,6 +254,10 @@ btf_vmlinux_bin_o=""
> if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
> if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
> btf_vmlinux_bin_o=.btf.vmlinux.bin.o
> + else
> + echo >&2 "Failed to generate BTF for vmlinux"
> + echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
I think we should encourage upgrading binutils first? Maybe
"binutils 2.25+ required for BTF please upgrade or disable CONFIG_DEBUG_INFO_BTF"
otherwise I guess its going to be a bit mystical why it works in
cases and not others to folks unfamiliar with the details.
> + exit 1
> fi
> fi
>
> --
> 2.24.0.432.g9d3f5f5b63-goog
>
