netdev - Re: samples don't build on v4.18

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Message-ID: <20180815030132.GA204101@joelaf.mtv.corp.google.com>
Date:   Tue, 14 Aug 2018 20:01:32 -0700
From:   Joel Fernandes <joelaf@...gle.com>
To:     LKML <linux-kernel@...r.kernel.org>, wangnan0@...wei.com,
        "open list:BPF (Safe dynamic programs and tools)" 
        <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        acme@...nel.org, Chenbo Feng <fengc@...gle.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: Re: samples don't build on v4.18

On Tue, Aug 14, 2018 at 06:22:21PM -0700, Joel Fernandes wrote:
> Forgot to add the patch author, doing so now. thanks
> 
> On Tue, Aug 14, 2018 at 6:20 PM, Joel Fernandes <joelaf@...gle.com> wrote:
> >
> > Hi,
> > When building BPF samples on v4.18, I get the following errors:
> >
> > $ cd samples/bpf/
> > $ make
> >
> > Auto-detecting system features:
> > ...                        libelf: [ OFF ]
> > ...                           bpf: [ OFF ]
> >
> > No libelf found
> > Makefile:213: recipe for target 'elfdep' failed
> > -----------
> >
> > I bissected it down to commit 5f9380572b4bb24f60cd492b1
> >
> > Author: Jakub Kicinski <jakub.kicinski@...ronome.com>
> > Date:   Thu May 10 10:24:39 2018 -0700
> >
> >     samples: bpf: compile and link against full libbpf
> > ---------
> >
> > Checking out a kernel before this commit makes the samples build. Also I do
> > have libelf on my system.
> >
> > Any thoughts on this issue?

There is some weirdness going on with my kernel tree. If I do a fresh clone
of v4.18 and build samples, everything works.

However if I take my existing checkout, do a:
git clean -f -d
make mrproper

Then I try to build the samples, I get the "No libelf found".

Obviously the existing checked out kernel tree is in some weird state that I
am not yet able to fix. But atleast if I blow the whole tree and clone again,
I'm able to build...

Is this related to the intermittent "No libelf found" issues that were
recently discussed?

- Joel