Re: finding libelf

[Randy Dunlap <rdunlap@infradead.org>]

On 2/3/21 12:36 PM, Randy Dunlap wrote:
> On 2/3/21 12:33 PM, Andrii Nakryiko wrote:
>> On Wed, Feb 3, 2021 at 12:15 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>>>
>>> On 2/3/21 12:12 PM, Andrii Nakryiko wrote:
>>>> On Wed, Feb 3, 2021 at 12:09 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>>>>>
>>>>> On 2/3/21 11:39 AM, Andrii Nakryiko wrote:
>>>>>> On Wed, Feb 3, 2021 at 9:22 AM Randy Dunlap <rdunlap@infradead.org> wrote:
>>>>>>>
>>>>>>> On 2/3/21 2:57 AM, Toke Høiland-Jørgensen wrote:
>>>>>>>> Randy Dunlap <rdunlap@infradead.org> writes:
>>>>>>>>
>>>>>>>>> Hi,
>>>>>>>>>
>>>>>>>>> I see this sometimes when building a kernel: (on x86_64,
>>>>>>>>> with today's linux-next 20210202):
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> CONFIG_CGROUP_BPF=y
>>>>>>>>> CONFIG_BPF=y
>>>>>>>>> CONFIG_BPF_SYSCALL=y
>>>>>>>>> CONFIG_ARCH_WANT_DEFAULT_BPF_JIT=y
>>>>>>>>> CONFIG_BPF_PRELOAD=y
>>>>>>>>> CONFIG_BPF_PRELOAD_UMD=m
>>>>>>>>> CONFIG_HAVE_EBPF_JIT=y
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Auto-detecting system features:
>>>>>>>>> ...                        libelf: [ [31mOFF[m ]
>>>>>>>>> ...                          zlib: [ [31mOFF[m ]
>>>>>>>>> ...                           bpf: [ [31mOFF[m ]
>>>>>>>>>
>>>>>>>>> No libelf found
>>>>>>>>> make[5]: [Makefile:287: elfdep] Error 1 (ignored)
>>>>>>>>> No zlib found
>>>>>>>>> make[5]: [Makefile:290: zdep] Error 1 (ignored)
>>>>>>>>> BPF API too old
>>>>>>>>> make[5]: [Makefile:293: bpfdep] Error 1 (ignored)
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> but pkg-config tells me:
>>>>>>>>>
>>>>>>>>> $ pkg-config --modversion  libelf
>>>>>>>>> 0.168
>>>>>>>>> $ pkg-config --libs  libelf
>>>>>>>>> -lelf
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Any ideas?
>>>>>>>>
>>>>>>>> This usually happens because there's a stale cache of the feature
>>>>>>>> detection tests lying around somewhere. Look for a 'feature' directory
>>>>>>>> in whatever subdir you got that error. Just removing the feature
>>>>>>>> directory usually fixes this; I've fixed a couple of places where this
>>>>>>>> is not picked up by 'make clean' (see, e.g., 9d9aae53b96d ("bpf/preload:
>>>>>>>> Make sure Makefile cleans up after itself, and add .gitignore")) but I
>>>>>>>> wouldn't be surprised if there are still some that are broken.
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> Thanks for replying.
>>>>>>>
>>>>>>> I removed the feature subdir and still got this build error, so I
>>>>>>> removed everything in BUILDDIR/kernel/bpf/preload and rebuilt --
>>>>>>> and still got the same libelf build error.
>>>>>>
>>>>>> I hate the complexity of feature detection framework to the point that
>>>>>> I'm willing to rip it out from libbpf's Makefile completely. I just
>>>>>> spent an hour trying to understand what's going on in a very similar
>>>>>> situation. Extremely frustrating.
>>>>>>
>>>>>> In your case, it might be feature detection triggered from
>>>>>> resolve_btfids, so try removing
>>>>>> $(OUTPUT)/tools/bpf/resolve_btfids/{feature/,FEATURE-DUMP.libbpf}.
>>>>>>
>>>>>> It seems like we don't do proper cleanup in resolve_btfids (it should
>>>>>> probably call libbpf's clean as well). And it's beyond me why `make -C
>>>>>> tools/build/feature clean` doesn't clean up FEATURE-DUMP.<use-case>
>>>>>> file as well.
>>>>>
>>>>>
>>>>> I don't think it's related to improper cleanup or old files/dirs
>>>>> laying around. I say that because I did a full build in a new output dir.
>>>>> and it still failed in the same way.
>>>>
>>>> If you cd tools/lib/bpf and run make there, does it detect those libraries?
>>>
>>> Yes:
>>>
>>> Auto-detecting system features:
>>> ...                        libelf: [ on  ]
>>> ...                          zlib: [ on  ]
>>> ...                           bpf: [ on  ]
>>>
>>>
>>
>> Sounds exactly like my case. I removed
>> $(O)/tools/bpf/resolve_btfids/{feature/,FEATURE-DUMP.libbpf} and it
>> started working.

In fact, with my build description [below], there is no
$(O)/tools/bpf/* created at all, so there is nothing
to remove.


> I already tried that with no success.
> 
> I suppose that it could be related to how I do builds:
> 
> make ARCH=x86_64 O=subdir -j4 all
> 
> so subdir is a relative path, not an absolute path.
> 


-- 
~Randy