Subject: Re: [PATCH bpf-next v2 0/5] samples: bpf: fix build after move to full libbpf

From: Jesper Dangaard Brouer <[email-masked]>
Date: Tue, 15 May 2018 11:16:43 +0200

SOLVED, how see below

On Tue, 15 May 2018 08:10:09 +0200
Jesper Dangaard Brouer <[email-masked]> wrote:

> On Mon, 14 May 2018 22:57:53 -0700
> Alexei Starovoitov <[email-masked]> wrote:
> 
> > On Mon, May 14, 2018 at 10:35:01PM -0700, Jakub Kicinski wrote:  
> > > Hi!
> > > 
> > > Following patches address build issues after recent move to libbpf.
> > > For out-of-tree builds we would see the following error:
> > > 
> > > gcc: error: samples/bpf/../../tools/lib/bpf/libbpf.a: No such file or directory
> > > 
> > > libbpf build system is now always invoked explicitly rather than
> > > relying on building single objects most of the time.  We need to
> > > resolve the friction between Kbuild and tools/ build system.
> > > 
> > > Mini-library called libbpf.h in samples is renamed to bpf_insn.h,
> > > using linux/filter.h seems not completely trivial since some samples
> > > get upset when order on include search path in changed.  We do have
> > > to rename libbpf.h, however, because otherwise it's hard to reliably
> > > get to libbpf's header in out-of-tree builds.
> > > 
> > > v2:
> > >  - fix the build error harder (patch 3);
> > >  - add patch 5 (make clang less noisy).    
> > 
> > Applied, Thanks  
> 
> I just tried it out, but the build fails.
> 
> $ make samples/bpf/
>   CHK     include/config/kernel.release
>   CHK     include/generated/uapi/linux/version.h
>   CHK     include/generated/utsrelease.h
>   CHK     include/generated/bounds.h
>   CHK     include/generated/timeconst.h
>   CHK     include/generated/asm-offsets.h
>   CALL    scripts/checksyscalls.sh
>   DESCEND  objtool
>   CHK     scripts/mod/devicetable-offsets.h
> make -C /home/jbrouer/git/kernel/bpf-next/samples/bpf/../../tools/lib/bpf/ RM='rm -rf' LDFLAGS= srctree=/home/jbrouer/git/kernel/bpf-next/samples/bpf/../../ O=
> 
> Auto-detecting system features:
> ...                        libelf: [ OFF ]
> ...                           bpf: [ OFF ]
> 
> No libelf found
> make[2]: *** [Makefile:212: elfdep] Error 1
> make[1]: *** [samples/bpf/Makefile:207: /home/jbrouer/git/kernel/bpf-next/samples/bpf/../../tools/lib/bpf/libbpf.a] Error 2
> make: *** [Makefile:1743: samples/bpf/] Error 2
>  
> 
> But it might not be related to this change, as the problem seems to the
> with the "Auto-detecting system features".  It is the build of libbpf
> that is the problem.
> 
> $ cd tools/lib/bpf/
> $ make
> 
> Auto-detecting system features:
> ...                        libelf: [ OFF ]
> ...                           bpf: [ OFF ]
> 
> No libelf found
> make: *** [Makefile:212: elfdep] Error 1
> 
> 
> And do have 'libelf' installed on this system... the same build/make
> commands works on net-next.
> 
> On net-next I see:
> 
> $ cd tools/lib/bpf/
> $ make
> 
> Auto-detecting system features:
> ...                        libelf: [ on  ]
> ...                           bpf: [ on  ]
> 
> Warning: Kernel ABI header at 'tools/include/uapi/linux/bpf.h' differs from latest version at 'include/uapi/linux/bpf.h'
> Warning: Kernel ABI header at 'tools/include/uapi/linux/if_link.h' differs from latest version at 'include/uapi/linux/if_link.h'
>   CC       libbpf.o
>   CC       bpf.o
>   CC       nlattr.o
>   CC       btf.o
>   LD       libbpf-in.o
>   LINK     libbpf.a
>   LINK     libbpf.so

SOLVED

It seems that the "Auto-detecting system" needed a 'make clean'.
My problem goes away when I did the following:

$ cd tools/
$ make clean

$ cd lib/bpf/
$ make

Auto-detecting system features:
...                        libelf: [ on  ]
...                           bpf: [ on  ]

  HOSTCC   fixdep.o
  HOSTLD   fixdep-in.o
  LINK     fixdep
Warning: Kernel ABI header at 'tools/include/uapi/linux/if_link.h' differs from latest version at 'include/uapi/linux/if_link.h'
  CC       libbpf.o
  CC       bpf.o
  CC       nlattr.o
  CC       btf.o
  LD       libbpf-in.o
  LINK     libbpf.a
  LINK     libbpf.so

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer