Re: bpf selftest compiling error

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

Hi,

On Wed, May 18, 2022 at 10:51:44PM +0800, Shung-Hsi Yu wrote:
> On Thu, May 12, 2022 at 06:12:36PM -0700, Vincent Li wrote:
> > On Thu, May 12, 2022 at 5:49 PM Vincent Li <vincent.mc.li@gmail.com> wrote:
> > >
> > > Hi,
> > >
> > > I cloned the bpf-next and tried to compile the bpf selftest.
> > >
> > > first I got error
> > >
> > > "
> > > CC      /usr/src/bpf
> > > next/tools/testing/selftests/bpf/tools/build/bpftool/xlated_dumper.o
> > >
> > > make[1]: *** No rule to make target
> > > '/usr/src/bpf-next/tools/include/asm-generic/bitops/find.h', needed by
> > > '/usr/src/bpf-next/tools/testing/selftests/bpf/tools/build/bpftool/btf_dumper.o'.
> > > Stop.
> 
> I also ran into the same issue on bpf-next, and the error seems rather
> absurd as
> 
>   1. asm-generic/bitops/find.h was removed back in 47d8c15615c0a "include:
>      move find.h from asm_generic to linux", so perhaps this error has
>      something to do with Makefile.asm-generic
>   2. normal way of building bpftool with `make tools/bpf/bpftool` still
>      works fine
> 
> Anyway removing ARCH= CROSS_COMPILE= in the bpf selftests Makefile
> (reverting change added in ea79020a2d9e "selftests/bpf: Enable
> cross-building with clang") can be used as a workaround to get the build
> working again. Adding the commit author to the thread to see if there is
> better approach available.

Could you share the commands that lead to this error?  And did you make
sure to clean the build tree?  I often get errors when building tools
because my toolchains changed and some dependencies in generated .*.d
files do not exist anymore.

I can't reproduce this specific error on today's linux-next (but found
another issue with out-of-tree build that I'll investigate). This is what
I run, on an x86 host for an x86 target:

 $ make defconfig
 $ cat tools/testing/selftests/bpf/config >> .config
   # and enable CONFIG_DEBUG_INFO_BTF
 $ make
 $ make -C tools/testing/selftests TARGETS=bpf SKIP_TARGETS=

Thanks,
Jean

> 
> 
> Best,
> Shung-Hsi
> 
> > > I could not find find.h in
> > > /usr/src/bpf-next/tools/include/asm-generic/bitops/find.h but I found
> > > it in /usr/src/bpf-next/tools/include/linux/find.h, copied it to
> > > /usr/src/bpf-next/tools/include/asm-generic/bitops, seems resolved the
> > > problem,
> > >
> > > then I got another error below,
> > >
> > >   CLNG-BPF [test_maps] map_kptr.o
> > >
> > > progs/map_kptr.c:7:29: error: unknown attribute 'btf_type_tag' ignored
> > > [-Werror,-Wunknown-attributes]
> > >
> > >         struct prog_test_ref_kfunc __kptr *unref_ptr;
> > >
> > >                                    ^~~~~~
> > >
> > > /usr/src/bpf-next/tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:176:31:
> > > note: expanded from macro '__kptr'
> > >
> > > #define __kptr __attribute__((btf_type_tag("kptr")))
> > >
> > >                               ^~~~~~~~~~~~~~~~~~~~
> > >
> > > progs/map_kptr.c:8:29: error: unknown attribute 'btf_type_tag' ignored
> > > [-Werror,-Wunknown-attributes]
> > >
> > >         struct prog_test_ref_kfunc __kptr_ref *ref_ptr;
> > >
> > >                                    ^~~~~~~~~~
> > >
> > > /usr/src/bpf-next/tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:177:35:
> > > note: expanded from macro '__kptr_ref'
> > >
> > > #define __kptr_ref __attribute__((btf_type_tag("kptr_ref")))
> > > "
> > >
> > > my clang is 12.0.1 and installed new clang from llvm github repository
> > >
> > > clang version 15.0.0 (https://github.com/llvm/llvm-project.git
> > > e91a73de24d60954700d7ac0293c050ab2cbe90b)
> > >
> > > it resolved the problem, but now I got error
> > >
> > >   GEN-SKEL [test_progs] test_bpf_nf.skel.h
> > >
> > > libbpf: failed to find BTF info for global/extern symbol 'bpf_skb_ct_lookup'
> > >
> > > Error: failed to link
> > > '/usr/src/bpf-next/tools/testing/selftests/bpf/test_bpf_nf.o': Unknown
> > > error -2 (-2)
> > >
> > > make: *** [Makefile:508:
> > > /usr/src/bpf-next/tools/testing/selftests/bpf/test_bpf_nf.skel.h]
> > > Error 254
> > >
> > > running out of ideas on how to fix the compiling error. I hope I am
> > > not doing something wrong :)
> > 
> > I recompiled the bpf-next kernel tree after clang 15 installation with
> > make bzImage; make modules; make and then recompiled bpf selftest, all
> > compiling errors are gone, sorry for the noise.
>