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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E2F2BC433EF for ; Thu, 12 May 2022 17:08:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1356849AbiELRIq (ORCPT ); Thu, 12 May 2022 13:08:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54018 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1356840AbiELRIn (ORCPT ); Thu, 12 May 2022 13:08:43 -0400 Received: from mail.nfschina.com (unknown [IPv6:2400:dd01:100f:2:72e2:84ff:fe10:5f45]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9EA1B2609D0; Thu, 12 May 2022 10:08:40 -0700 (PDT) Received: from localhost (unknown [127.0.0.1]) by mail.nfschina.com (Postfix) with ESMTP id 151A61E80D6B; Fri, 13 May 2022 01:03:03 +0800 (CST) X-Virus-Scanned: amavisd-new at test.com Received: from mail.nfschina.com ([127.0.0.1]) by localhost (mail.nfschina.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Rv1vvkAr3Ckd; Fri, 13 May 2022 01:03:00 +0800 (CST) Received: from [172.30.21.106] (unknown [180.167.10.98]) (Authenticated sender: liqiong@nfschina.com) by mail.nfschina.com (Postfix) with ESMTPA id 72B091E80D22; Fri, 13 May 2022 01:02:59 +0800 (CST) Subject: Re: [PATCH 1/2] kernel/bpf: change "char *" string form to "char []" To: Yonghong Song , Andrii Nakryiko , Martin KaFai Lau , Song Liu Cc: Alexei Starovoitov , Daniel Borkmann , John Fastabend , KP Singh , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, hukun@nfschina.com, qixu@nfschina.com, yuzhe@nfschina.com, renyu@nfschina.com References: <20220512142814.26705-1-liqiong@nfschina.com> From: liqiong Message-ID: <223f19c0-70a7-3b1f-6166-22d494b62b6e@nfschina.com> Date: Fri, 13 May 2022 01:08:35 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2022年05月12日 23:16, Yonghong Song 写道: > > > On 5/12/22 7:28 AM, liqiong wrote: >> The string form of "char []" declares a single variable. It is better >> than "char *" which creates two variables. > > Could you explain in details about why it is better in generated codes? > It is not clear to me why your patch is better than the original code. Hi there， The string form of "char *" creates two variables in the final assembly output, a static string, and a char pointer to the static string. Use "objdump -S -D *.o", can find out the static string occurring at "Contents of section .rodata". > >> >> Signed-off-by: liqiong >> --- >> kernel/bpf/btf.c | 4 ++-- >> kernel/bpf/verifier.c | 2 +- >> 2 files changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c >> index 0918a39279f6..218a8ac73644 100644 >> --- a/kernel/bpf/btf.c >> +++ b/kernel/bpf/btf.c >> @@ -894,10 +894,10 @@ static const struct btf_type *btf_type_skip_qualifiers(const struct btf *btf, >> static const char *btf_show_name(struct btf_show *show) >> { >> /* BTF_MAX_ITER array suffixes "[]" */ >> - const char *array_suffixes = "[][][][][][][][][][]"; >> + static const char array_suffixes[] = "[][][][][][][][][][]"; >> const char *array_suffix = &array_suffixes[strlen(array_suffixes)]; >> /* BTF_MAX_ITER pointer suffixes "*" */ >> - const char *ptr_suffixes = "**********"; >> + static const char ptr_suffixes[] = "**********"; >> const char *ptr_suffix = &ptr_suffixes[strlen(ptr_suffixes)]; >> const char *name = NULL, *prefix = "", *parens = ""; >> const struct btf_member *m = show->state.member; >> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >> index d175b70067b3..78a090fcbc72 100644 >> --- a/kernel/bpf/verifier.c >> +++ b/kernel/bpf/verifier.c >> @@ -7346,7 +7346,7 @@ static int sanitize_err(struct bpf_verifier_env *env, >> const struct bpf_reg_state *off_reg, >> const struct bpf_reg_state *dst_reg) >> { >> - static const char *err = "pointer arithmetic with it prohibited for !root"; >> + static const char err[] = "pointer arithmetic with it prohibited for !root"; >> const char *op = BPF_OP(insn->code) == BPF_ADD ? "add" : "sub"; >> u32 dst = insn->dst_reg, src = insn->src_reg; >> -- 李力琼 <13524287433> 上海市浦东新区海科路99号中科院上海高等研究院3号楼3楼