netdev - Re: [PATCH bpf-next] selftests/bpf: don't use bpf helpers in non-bpf environment

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Date:   Tue, 11 Dec 2018 13:49:37 -0800
From:   Stanislav Fomichev <sdf@...ichev.me>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, ast@...nel.org,
        daniel@...earbox.net
Subject: Re: [PATCH bpf-next] selftests/bpf: don't use bpf helpers in non-bpf
 environment

On 12/11, Stanislav Fomichev wrote:
> We're using bpf_htons in test_progs.c to initialize some static
> global data and I think I hit some weird case on an older compiler
> which doesn't have __builtin_bswap16 (and __builtin_constant_p
> expands to false).
> 
> In this case I see:
> error: implicit declaration of function '__builtin_bswap16'
> 
> Let's explicitly use __constant_htons which should be exposed by the
> linux/byteorder.h uapi header.

Forgot to mention, that using simple htons produces the following:
    test_progs.c:54:17: error: braced-group within expression allowed only
    inside a function
      .eth.h_proto = htons(ETH_P_IP),

> 
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>  tools/testing/selftests/bpf/test_progs.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> index 26f1fdf3e2bf..61593d319c0e 100644
> --- a/tools/testing/selftests/bpf/test_progs.c
> +++ b/tools/testing/selftests/bpf/test_progs.c
> @@ -51,10 +51,10 @@ static struct {
>  	struct iphdr iph;
>  	struct tcphdr tcp;
>  } __packed pkt_v4 = {
> -	.eth.h_proto = bpf_htons(ETH_P_IP),
> +	.eth.h_proto = __constant_htons(ETH_P_IP),
>  	.iph.ihl = 5,
>  	.iph.protocol = 6,
> -	.iph.tot_len = bpf_htons(MAGIC_BYTES),
> +	.iph.tot_len = __constant_htons(MAGIC_BYTES),
>  	.tcp.urg_ptr = 123,
>  };
>  
> @@ -64,9 +64,9 @@ static struct {
>  	struct ipv6hdr iph;
>  	struct tcphdr tcp;
>  } __packed pkt_v6 = {
> -	.eth.h_proto = bpf_htons(ETH_P_IPV6),
> +	.eth.h_proto = __constant_htons(ETH_P_IPV6),
>  	.iph.nexthdr = 6,
> -	.iph.payload_len = bpf_htons(MAGIC_BYTES),
> +	.iph.payload_len = __constant_htons(MAGIC_BYTES),
>  	.tcp.urg_ptr = 123,
>  };
>  
> -- 
> 2.20.0.rc2.403.gdbc3b29805-goog
>