On Wed, Feb 3, 2021 at 11:39 AM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > 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. So resolve_btfids does call libbpf's clean, but Linux Kbuild never calls resolve_btfids' clean. Jiri, do you think that could be improved? Basically, if something goes wrong with feature detection, no amount of `make clean` would help and users will be forced to struggle with frustrating experience trying to understand what's going on. I also still think that FEATURE-DUMP should be cleaned up by feature infra on clean and that's not happening today, but I'm unwilling to go and untangle all that complexity right now. > > > > > > > -- > > ~Randy > >