Re: finding libelf

[Randy Dunlap <rdunlap@infradead.org>]

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.

-- 
~Randy