netdev - Re: resolve_btfids breaks kernel cross-compilation

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Message-ID: <20200917080452.GB2411168@krava>
Date:   Thu, 17 Sep 2020 10:04:52 +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 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?

thanks,
jirka