netdev - Re: [bpf PATCH] bpf, selftests: test_maps generating unrecognized data section

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Date:   Thu, 25 Mar 2021 22:07:10 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     John Fastabend <john.fastabend@...il.com>, andrii@...nel.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...com
Subject: Re: [bpf PATCH] bpf, selftests: test_maps generating unrecognized
 data section

On 3/24/21 10:07 PM, John Fastabend wrote:
> With a relatively recent clang master branch test_map skips a section,
> 
>   libbpf: elf: skipping unrecognized data section(5) .rodata.str1.1
> 
> the cause is some pointless strings from bpf_printks in the BPF program
> loaded during testing. Remove them so we stop tripping our test bots.
> 
> Signed-off-by: John Fastabend <john.fastabend@...il.com>
> ---
>   .../selftests/bpf/progs/sockmap_tcp_msg_prog.c     |    3 ---
>   1 file changed, 3 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/progs/sockmap_tcp_msg_prog.c b/tools/testing/selftests/bpf/progs/sockmap_tcp_msg_prog.c
> index fdb4bf4408fa..0f603253f4ed 100644
> --- a/tools/testing/selftests/bpf/progs/sockmap_tcp_msg_prog.c
> +++ b/tools/testing/selftests/bpf/progs/sockmap_tcp_msg_prog.c
> @@ -16,10 +16,7 @@ int bpf_prog1(struct sk_msg_md *msg)
>   	if (data + 8 > data_end)
>   		return SK_DROP;
>   
> -	bpf_printk("data length %i\n", (__u64)msg->data_end - (__u64)msg->data);
>   	d = (char *)data;

Do we still need 'd' as well in that case, or the data + 8 > data_end test if we don't
read any of the data? I'm not sure what was the original purpose of the prog, perhaps
just to test that we can attach /something/ in general? Maybe in that case empty prog
is sufficient if we don't do anything useful with the rest?

> -	bpf_printk("hello sendmsg hook %i %i\n", d[0], d[1]);
> -
>   	return SK_PASS;
>   }
>   
>