From: Edward Cree <ecree@solarflare.com>
To: Jiong Wang <jiong.wang@netronome.com>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andriin@fb.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
Daniel Borkmann <daniel@iogearbox.net>, bpf <bpf@vger.kernel.org>,
Network Development <netdev@vger.kernel.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Jakub Kicinski <jakub.kicinski@netronome.com>
Subject: Re: [PATCH] bpf: optimize constant blinding
Date: Mon, 17 Jun 2019 22:16:33 +0100 [thread overview]
Message-ID: <f2a74aac-7350-8b35-236a-b17323bb79e6@solarflare.com> (raw)
In-Reply-To: <877e9kgd39.fsf@netronome.com>
On 17/06/2019 21:40, Jiong Wang wrote:
> Now if we don't split patch when patch an insn inside patch, instead, if we
> replace the patched insn using what you suggested, then the logic looks to
> me becomes even more complex, something like
>
> for (idx = 0; idx < insn_cnt; idx++) {
> if (insns[idx] is not BPF_LIST_INSN) {
> do_insn(...)
> }
> else if (insns[idx] is BPF_LIST_INSN) {
> list = pool_base + insn.imm;
> while (list) {
> insn = list_head->insn;
> if (insn is BF_LIST_INSN) {
> sub_list = ...
> while ()
> do_insn()
> continue;
> }
> do_insn(...)
> list = pool_base + list->next;
> }
> }
> }
Why can't do_insn() just go like:
if (insn is BPF_LIST_INSN)
for (idx = 0; idx < LIST_COUNT(insn); idx++)
do_insn(pool_base + LIST_START(insn) + idx);
else
rest of processing
?
Alternatively, iterate with something more sophisticated than 'idx++'
(standard recursion-to-loop transformation).
You shouldn't ever need a for() tower statically in the code...
> So, I am thinking what Alexei and Andrii suggested make sense, just use
> single data structure (singly linked list) to represent everything, so the
> insn traversal etc could be simple
But then you have to also store orig_insn_idx with each insn, so you can
calculate the new jump offsets when you linearise. Having an array of
patched_orig_insns gives you that for free.
next prev parent reply other threads:[~2019-06-17 21:16 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-12 11:32 [PATCH] bpf: optimize constant blinding Naveen N. Rao
2019-06-12 14:47 ` Alexei Starovoitov
2019-06-12 15:04 ` Jiong Wang
2019-06-12 15:25 ` Jiong Wang
2019-06-12 15:28 ` Alexei Starovoitov
2019-06-14 15:13 ` Jiong Wang
2019-06-14 17:05 ` Alexei Starovoitov
2019-06-14 22:28 ` Andrii Nakryiko
2019-06-17 19:47 ` Edward Cree
2019-06-17 19:59 ` Jiong Wang
2019-06-17 20:11 ` Edward Cree
2019-06-17 20:40 ` Jiong Wang
2019-06-17 20:53 ` Alexei Starovoitov
2019-06-17 21:01 ` Jiong Wang
2019-06-17 21:16 ` Edward Cree [this message]
2019-06-19 20:45 ` Jiong Wang
2019-06-14 4:30 ` kbuild test robot
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