From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9AAF8C10F14 for ; Wed, 2 Oct 2019 23:45:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C86321848 for ; Wed, 2 Oct 2019 23:45:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726152AbfJBXpV (ORCPT ); Wed, 2 Oct 2019 19:45:21 -0400 Received: from www62.your-server.de ([213.133.104.62]:50930 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725893AbfJBXpV (ORCPT ); Wed, 2 Oct 2019 19:45:21 -0400 Received: from 57.248.197.178.dynamic.dsl-lte-bonding.zhbmb00p-msn.res.cust.swisscom.ch ([178.197.248.57] helo=localhost) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1iFoJ5-0001sC-5I; Thu, 03 Oct 2019 01:45:19 +0200 From: Daniel Borkmann To: ast@kernel.org Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, Daniel Borkmann Subject: [PATCH bpf-next 1/2] bpf, x86: Small optimization in comparing against imm0 Date: Thu, 3 Oct 2019 01:45:11 +0200 Message-Id: <20191002234512.25902-1-daniel@iogearbox.net> X-Mailer: git-send-email 2.21.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.101.4/25590/Wed Oct 2 10:31:24 2019) Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Replace 'cmp reg, 0' with 'test reg, reg' for comparisons against zero. Saves 1 byte of instruction encoding per occurrence. The flag results of test 'reg, reg' are identical to 'cmp reg, 0' in all cases except for AF which we don't use/care about. In terms of macro-fusibility in combination with a subsequent conditional jump instruction, both have the same properties for the jumps used in the JIT translation. For example, same JITed Cilium program can shrink a bit from e.g. 12,455 to 12,317 bytes as tests with 0 are used quite frequently. Signed-off-by: Daniel Borkmann --- arch/x86/net/bpf_jit_comp.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 991549a1c5f3..3ad2ba1ad855 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -909,6 +909,16 @@ xadd: if (is_imm8(insn->off)) case BPF_JMP32 | BPF_JSLT | BPF_K: case BPF_JMP32 | BPF_JSGE | BPF_K: case BPF_JMP32 | BPF_JSLE | BPF_K: + /* test dst_reg, dst_reg to save one extra byte */ + if (imm32 == 0) { + if (BPF_CLASS(insn->code) == BPF_JMP) + EMIT1(add_2mod(0x48, dst_reg, dst_reg)); + else if (is_ereg(dst_reg)) + EMIT1(add_2mod(0x40, dst_reg, dst_reg)); + EMIT2(0x85, add_2reg(0xC0, dst_reg, dst_reg)); + goto emit_cond_jmp; + } + /* cmp dst_reg, imm8/32 */ if (BPF_CLASS(insn->code) == BPF_JMP) EMIT1(add_1mod(0x48, dst_reg)); -- 2.17.1