From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [PATCH] tc, bpf: add option to dump bpf verifier as C program fragment Date: Wed, 20 Jun 2018 00:13:52 +0200 Message-ID: References: <1529225321-15429-1-git-send-email-ophirmu@mellanox.com> <20180618131842.7b4d259f@cakuba.netronome.com> <30ac6974-a434-926b-5749-25c594e5841c@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, Stephen Hemminger , Thomas Monjalon , Olga Shern , ast@kernel.org To: David Ahern , Jakub Kicinski , Ophir Munk Return-path: Received: from www62.your-server.de ([213.133.104.62]:52391 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755448AbeFSWNz (ORCPT ); Tue, 19 Jun 2018 18:13:55 -0400 In-Reply-To: <30ac6974-a434-926b-5749-25c594e5841c@gmail.com> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 06/18/2018 11:44 PM, David Ahern wrote: > On 6/18/18 2:18 PM, Jakub Kicinski wrote: >> 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 >> >> 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? > > I was thinking the same. bpftool would provide options too -- print the > above, print in macro encodings and verifier. I gave an example of this > side by side dump at netconf 2.1. Does not look like the slides made it > online; see attached. +1, I would also doubt that this adds a lot in terms of debuggability when you're trying to load an object file with thousands of insns. Better way would be to use llvm-objdump on the obj file to get to the annotated disassembly, see also example in [0]. A .o to .c converter is wip for libbpf/bpftool as presented in [1], which should provide the flexibility to embedd an obj file. Cheers, Daniel [0] http://cilium.readthedocs.io/en/latest/bpf/#llvm [1] http://vger.kernel.org/netconf2018_files/AlexeiStarovoitov_netconf2018.pdf page 22