netdev - Re: resolve_btfids breaks kernel cross-compilation

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Date:   Thu, 17 Sep 2020 10:38:09 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Seth Forshee <seth.forshee@...onical.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: resolve_btfids breaks kernel cross-compilation

On Thu, Sep 17, 2020 at 10:04:55AM +0200, Jiri Olsa wrote:
> On Wed, Sep 16, 2020 at 02:47:33PM -0500, Seth Forshee wrote:
> > The requirement to build resolve_btfids whenever CONFIG_DEBUG_INFO_BTF
> > is enabled breaks some cross builds. For example, when building a 64-bit
> > powerpc kernel on amd64 I get:
> > 
> >  Auto-detecting system features:
> >  ...                        libelf: [ [32mon[m  ]
> >  ...                          zlib: [ [32mon[m  ]
> >  ...                           bpf: [ [31mOFF[m ]
> >  
> >  BPF API too old
> >  make[6]: *** [Makefile:295: bpfdep] Error 1
> > 
> > The contents of tools/bpf/resolve_btfids/feature/test-bpf.make.output:
> > 
> >  In file included from /home/sforshee/src/u-k/unstable/tools/arch/powerpc/include/uapi/asm/bitsperlong.h:11,
> >                   from /usr/include/asm-generic/int-ll64.h:12,
> >                   from /usr/include/asm-generic/types.h:7,
> >                   from /usr/include/x86_64-linux-gnu/asm/types.h:1,
> >                   from /home/sforshee/src/u-k/unstable/tools/include/linux/types.h:10,
> >                   from /home/sforshee/src/u-k/unstable/tools/include/uapi/linux/bpf.h:11,
> >                   from test-bpf.c:3:
> >  /home/sforshee/src/u-k/unstable/tools/include/asm-generic/bitsperlong.h:14:2: error: #error Inconsistent word size. Check asm/bitsperlong.h
> >     14 | #error Inconsistent word size. Check asm/bitsperlong.h
> >        |  ^~~~~
> > 
> > This is because tools/arch/powerpc/include/uapi/asm/bitsperlong.h sets
> > __BITS_PER_LONG based on the predefinied compiler macro __powerpc64__,
> > which is not defined by the host compiler. What can we do to get cross
> > builds working again?
> 
> could you please share the command line and setup?

I just reproduced.. checking on fix

jirka