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=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 15281C4708A for ; Thu, 27 May 2021 14:55:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EE3AB613BC for ; Thu, 27 May 2021 14:55:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236670AbhE0O4r (ORCPT ); Thu, 27 May 2021 10:56:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:38138 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229793AbhE0O4q (ORCPT ); Thu, 27 May 2021 10:56:46 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5F5F6611AE; Thu, 27 May 2021 14:55:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1622127313; bh=h1ngFTq9Zb/SdBnGTwA4Kdpzfw4n5hmVIPGwvKay894=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Eo0+vHf+CWES7JSqq5j9FsitfdsmnmmoaHObOBp9VHAR5qYMu1Bs4PX2KhUeWPCpZ AwhSbBrRvZCLXaZGyv55Kfql/HH4I2S3vcquYHYimZjIJxmJixg3LgTaiRWtkDLl5U hV/tyF5tQWNhZc9SsBih0unJL3Puxv0xqLIQ7EIO9mhfRiZfj5ABPENFg9X/fb4unw vcuk7rJRhLbDs/bXbMp3dpxTWG0OE4HSOMOX9Q+UnkkeQlp7dyf1CzRkFQg3qB6x55 qiCcbMuavjpY/TCDNMvewyMzsejJ2ocizy9ROCTZy6CPrbHUlLKU/cWbyFDMRj76zl ucS7Un5P6ZjhQ== Received: by quaco.ghostprotocols.net (Postfix, from userid 1000) id 36F144011C; Thu, 27 May 2021 11:55:10 -0300 (-03) Date: Thu, 27 May 2021 11:55:10 -0300 From: Arnaldo Carvalho de Melo To: Andrii Nakryiko Cc: dwarves@vger.kernel.org, bpf@vger.kernel.org, jolsa@kernel.org, kernel-team@fb.com Subject: Re: [PATCH dwarves] btf_encoder: fix and complete filtering out zero-sized per-CPU variables Message-ID: References: <20210524234222.278676-1-andrii@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210524234222.278676-1-andrii@kernel.org> X-Url: http://acmel.wordpress.com Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Em Mon, May 24, 2021 at 04:42:22PM -0700, Andrii Nakryiko escreveu: > btf_encoder is ignoring zero-sized per-CPU ELF symbols, but the same has to be > done for DWARF variables when matching them with ELF symbols. This is due to > zero-sized DWARF variables matching unrelated (non-zero-sized) variable that > happens to be allocated at the exact same address, leading to a lot of > confusion in BTF. > See [0] for when this causes big problems. > [0] https://lore.kernel.org/bpf/CAEf4BzZ0-sihSL-UAm21JcaCCY92CqfNxycHRZYXcoj8OYb=wA@mail.gmail.com/ > +++ b/btf_encoder.c > @@ -550,6 +551,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, > > /* addr has to be recorded before we follow spec */ > addr = var->ip.addr; > + dwarf_name = variable__name(var, cu); > > /* DWARF takes into account .data..percpu section offset > * within its segment, which for vmlinux is 0, but for kernel > @@ -582,11 +584,9 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, > * modules per-CPU data section has non-zero offset so all > * per-CPU symbols have non-zero values. > */ > - if (var->ip.addr == 0) { > - dwarf_name = variable__name(var, cu); > + if (var->ip.addr == 0) > if (!dwarf_name || strcmp(dwarf_name, name)) > continue; > - } > > if (var->spec) > var = var->spec; > @@ -600,6 +600,13 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, I just changed the above hunk to be: @@ -583,7 +585,6 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, * per-CPU symbols have non-zero values. */ if (var->ip.addr == 0) { - dwarf_name = variable__name(var, cu); if (!dwarf_name || strcmp(dwarf_name, name)) continue; } Which is shorter and keeps the {} around a multi line if block, ok? Thanks, applied! - Arnaldo