netdev - Re: [PATCH bpf] selftests/bpf: fix sendmsg6

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Date:   Fri, 19 Jul 2019 16:21:30 +0000
From:   Andrey Ignatov <rdna@...com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>
CC:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "gor@...ux.ibm.com" <gor@...ux.ibm.com>,
        "heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>
Subject: Re: [PATCH bpf] selftests/bpf: fix sendmsg6_prog on s390

Ilya Leoshkevich <iii@...ux.ibm.com> [Fri, 2019-07-19 02:07 -0700]:
> "sendmsg6: rewrite IP & port (C)" fails on s390, because the code in
> sendmsg_v6_prog() assumes that (ctx->user_ip6[0] & 0xFFFF) refers to
> leading IPv6 address digits, which is not the case on big-endian
> machines.
> 
> Since checking bitwise operations doesn't seem to be the point of the
> test, replace two short comparisons with a single int comparison.
> 
> Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>

Acked-by: Andrey Ignatov <rdna@...com>

IIRC I did it this way to test 16bit loads from C program, but such
loads are already tested by asm prog in test_sock_addr.c.

Thanks for the fix!

> ---
>  tools/testing/selftests/bpf/progs/sendmsg6_prog.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/progs/sendmsg6_prog.c b/tools/testing/selftests/bpf/progs/sendmsg6_prog.c
> index 5aeaa284fc47..a68062820410 100644
> --- a/tools/testing/selftests/bpf/progs/sendmsg6_prog.c
> +++ b/tools/testing/selftests/bpf/progs/sendmsg6_prog.c
> @@ -41,8 +41,7 @@ int sendmsg_v6_prog(struct bpf_sock_addr *ctx)
>  	}
>  
>  	/* Rewrite destination. */
> -	if ((ctx->user_ip6[0] & 0xFFFF) == bpf_htons(0xFACE) &&
> -	     ctx->user_ip6[0] >> 16 == bpf_htons(0xB00C)) {
> +	if (ctx->user_ip6[0] == bpf_htonl(0xFACEB00C)) {
>  		ctx->user_ip6[0] = bpf_htonl(DST_REWRITE_IP6_0);
>  		ctx->user_ip6[1] = bpf_htonl(DST_REWRITE_IP6_1);
>  		ctx->user_ip6[2] = bpf_htonl(DST_REWRITE_IP6_2);
> -- 
> 2.21.0
> 

-- 
Andrey Ignatov