Re: finding libelf

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

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?

>
> --
> ~Randy
>