On 11/26/19 4:04 PM, Stanislav Fomichev wrote:
> On 11/26, Andrii Nakryiko wrote:
>> 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.
> We already have most of the messages about missing pahole or wrong version:
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/scripts/link-vmlinux.sh#n111
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/scripts/link-vmlinux.sh#n117
>
> They are 'info' though, but it seems logical to drop -s from make arguments
> if someone wants to debug further.
>
Fair enough. Please add back my Tested-by: tag.
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
