On Wed, Feb 3, 2021 at 9:22 AM Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
>
> On 2/3/21 2:57 AM, Toke Høiland-Jørgensen wrote:
> > Randy Dunlap <rdunlap@xxxxxxxxxxxxx> 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.
>
>
> --
> ~Randy
>
