On 11/26/19 3:45 PM, Stanislav Fomichev wrote:
> On 11/26, John Fastabend wrote:
>> 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.
> With the conversion from --dump-section to --only-section that I
> did in this patch, binutils 2.25+ is no longer a requirement.
> 2.21 (minimal version from Documentation/process/changes.rst) should work
> just fine.
Yeah, instead it's better to mention that pahole v1.13+ is required.
>
