netdev - Re: [PATCH] tc, bpf: add option to dump bpf verifier as C program fragment

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Message-ID: <20180618131842.7b4d259f@cakuba.netronome.com>
Date:   Mon, 18 Jun 2018 13:18:42 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Ophir Munk <ophirmu@...lanox.com>
Cc:     netdev@...r.kernel.org,
        Stephen Hemminger <stephen@...workplumber.org>,
        David Ahern <dsahern@...il.com>,
        Thomas Monjalon <thomas@...jalon.net>,
        Olga Shern <olgas@...lanox.com>
Subject: Re: [PATCH] tc, bpf: add option to dump bpf verifier as C program
 fragment

On Sun, 17 Jun 2018 08:48:41 +0000, Ophir Munk wrote:
> Similar to cbpf used within tcpdump utility with a "-d" option to dump
> the compiled packet-matching code in a human readable form - tc has the
> "verbose" option to dump ebpf verifier output.
> Another useful option of cbpf using tcpdump "-dd" option is to dump
> packet-matching code a C program fragment. Similar to this - this commit
> adds a new tc ebpf option named "code" to dump ebpf verifier as C program
> fragment.
> 
> Existing "verbose" option sample output:
> 
> Verifier analysis:
> 0: (61) r2 = *(u32 *)(r1 +52)
> 1: (18) r3 = 0xdeadbeef
> 3: (63) *(u32 *)(r10 -4) = r3
> .
> .
> 11: (63) *(u32 *)(r1 +52) = r2
> 12: (18) r0 = 0xffffffff
> 14: (95) exit
> 
> New "code" option sample output:
> 
> /* struct bpf_insn cls_q_code[] = { */
> {0x61,    2,    1,       52, 0x00000000},
> {0x18,    3,    0,        0, 0xdeadbeef},
> {0x00,    0,    0,        0, 0x00000000},
> .
> .
> {0x63,    1,    2,       52, 0x00000000},
> {0x18,    0,    0,        0, 0xffffffff},
> {0x00,    0,    0,        0, 0x00000000},
> {0x95,    0,    0,        0, 0x00000000},
> 
> Signed-off-by: Ophir Munk <ophirmu@...lanox.com>

Hmm... printing C arrays looks like hacky integration with some C
code...  Would you not be better served by simply using libbpf in
whatever is consuming this output?