Re: finding libelf

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Wed, Feb 3, 2021 at 12:36 PM Randy Dunlap <rdunlap@infradead.org> 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.
>
> 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.

so can you confirm this by specifying the absolute path to subdir?

>
> --
> ~Randy
>