netdev - Re: [bpf-next V2 PATCH 5/5] tools/libbpf: handle issues with bpf ELF objects containing .eh

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Date:   Wed, 7 Feb 2018 14:19:00 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        netdev@...r.kernel.org, Daniel Borkmann <borkmann@...earbox.net>,
        wangnan0@...wei.com, jakub.kicinski@...ronome.com, joe@....org,
        acme@...hat.com, eric@...it.org, yhs@...com,
        Victor Julien <victor@...iniac.net>
Subject: Re: [bpf-next V2 PATCH 5/5] tools/libbpf: handle issues with bpf ELF
 objects containing .eh_frames

On 02/07/2018 01:40 PM, Jesper Dangaard Brouer wrote:
> On Tue, 6 Feb 2018 20:05:43 +0100 Daniel Borkmann <daniel@...earbox.net> wrote:
>> On 02/06/2018 06:03 PM, Jesper Dangaard Brouer wrote:
> [...]
>>> [...] I plan to follow up and do a more complete solution later. This
>>> is a workaround to get the Suricata use-case working and also that
>>> samples/bpf/ can be loaded.  
>>
>> Aside from a needed fix in any case, is there a specifc reason why Suricata
>> cannot rely on 'clang -target bpf'? Is it asm inline headers in your case?
> 
> Below is the error I get when using 'clang' with '-target bpf'
> 
> $ dirs
> ~/git/suricata/src/ebpf
> 
> $ clang -Wall -Iinclude -O2 -D__KERNEL__  -target bpf -emit-llvm -c xdp_filter.c -o - | llc -march=bpf -filetype=obj -o xdp_filter.bpf
> In file included from xdp_filter.c:19:
> In file included from /usr/bin/../lib64/clang/4.0.1/include/stdint.h:63:
> In file included from /usr/include/stdint.h:26:
> In file included from /usr/include/bits/libc-header-start.h:33:
> In file included from /usr/include/features.h:434:
> /usr/include/gnu/stubs.h:7:11: fatal error: 'gnu/stubs-32.h' file not found
> # include <gnu/stubs-32.h>
>           ^~~~~~~~~~~~~~~~
> 
> I'll leave it up to Eric Leblond to figure out that he need to change
> in the eBPF programs to make it compile with '-target bpf'.  Maybe you
> can offer him some guidance here?
> 
> Direct link to code:
>  https://github.com/OISF/suricata/blob/master/ebpf/xdp_filter.c

Sure, you just need glibc-devel.i686, see:

$ clang -Wall -Iinclude -O2 -D__KERNEL__ -target bpf -emit-llvm -c xdp_filter.c -o - | llc -march=bpf -filetype=obj -o xdp_filter.bpf
  In file included from xdp_filter.c:19:
  In file included from /home/darkstar/llvm/build/lib/clang/7.0.0/include/stdint.h:63:
  In file included from /usr/include/stdint.h:25:
  In file included from /usr/include/features.h:392:
  /usr/include/gnu/stubs.h:7:11: fatal error: 'gnu/stubs-32.h' file not found
  # include <gnu/stubs-32.h>
            ^~~~~~~~~~~~~~~~
  1 error generated.
# yum install glibc-devel.i686
  [...]
$ clang -Wall -Iinclude -O2 -D__KERNEL__ -target bpf -emit-llvm -c xdp_filter.c -o - | llc -march=bpf -filetype=obj -o xdp_filter.bpf
$

Alternatively, you could do something like done in selftests to provide a
dummy, see commit 1c2dd16add7e ("selftests/bpf: get rid of -D__x86_64__").

Cheers,
Daniel