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=-12.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 3D266C43441 for ; Wed, 21 Nov 2018 06:14:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9521521479 for ; Wed, 21 Nov 2018 06:14:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nifty.com header.i=@nifty.com header.b="azHCHf4t" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9521521479 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=socionext.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728014AbeKUQrq (ORCPT ); Wed, 21 Nov 2018 11:47:46 -0500 Received: from conssluserg-06.nifty.com ([210.131.2.91]:23129 "EHLO conssluserg-06.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725995AbeKUQrq (ORCPT ); Wed, 21 Nov 2018 11:47:46 -0500 Received: from mail-ua1-f52.google.com (mail-ua1-f52.google.com [209.85.222.52]) (authenticated) by conssluserg-06.nifty.com with ESMTP id wAL6EXX9026287; Wed, 21 Nov 2018 15:14:33 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-06.nifty.com wAL6EXX9026287 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1542780874; bh=mgpSrIsKXJH6ElVAIqePo1isY/4rmeh1rH2/vKCvkb4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=azHCHf4tK2JDvYq5k3tpoXrK7C9LtMDA3bsbP3q6wkREzn+0it7mDBSHE9K7hYxVb KWRU3tcYjBcTxZspW9IekYBUCxfTz0uYGERo0lEGpAX8hMyTmZJ2JtJaDnCKhIdCoa M727z4SJpszxyp7VBYwCPhMoaa8Uk16QMSOgENytUQOFBdJBLcxEmEI2qWaxiiAPxM N0Z4y4BxM6oOuwEBuTFOMs4rgG5b/7BXxzUO/gMN9uKSuErDcsxrqYjE04tVxBTR2/ kHmaMN7CwhrUtfXg45xo8nQHpBJxyQWmyLzuBDjjwHTcIBeMl4bDhmUfeDmMpWqMS3 y1cOLwl6P2/Ew== X-Nifty-SrcIP: [209.85.222.52] Received: by mail-ua1-f52.google.com with SMTP id k10so1527345ual.6; Tue, 20 Nov 2018 22:14:33 -0800 (PST) X-Gm-Message-State: AA+aEWY9iI2JinJSJaU1Y9kQcJor39CerbMS70VMzrYvdUJaPSD7xdEQ eVJbGT0QxOUD3hxPKKpCpM54ZPZVzortm4gl9Hw= X-Google-Smtp-Source: AFSGD/VU+wvHS1lYoKm83fbye3uYhJV3Adq6YmLBvr0D5B7WEldGAkaCjbOD+bF+yNlZZlkHtmXfCFX/wJbGmSl1erU= X-Received: by 2002:ab0:6705:: with SMTP id q5mr2295859uam.89.1542780872554; Tue, 20 Nov 2018 22:14:32 -0800 (PST) MIME-Version: 1.0 References: <20181115005602.30746-1-paul.walmsley@sifive.com> <20181115005602.30746-3-paul.walmsley@sifive.com> In-Reply-To: <20181115005602.30746-3-paul.walmsley@sifive.com> From: Masahiro Yamada Date: Wed, 21 Nov 2018 15:13:56 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 2/2] modpost: skip ELF local symbols by default during section mismatch check To: paul.walmsley@sifive.com Cc: Linux Kernel Mailing List , Russell King , jimw@sifive.com, Michal Marek , Sam Ravnborg , Linux Kbuild mailing list , Paul Walmsley Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, On Thu, Nov 15, 2018 at 9:57 AM Paul Walmsley wrote: > > During development of a serial console driver with a gcc 8.2.0 > toolchain for RISC-V, the following modpost warning appeared: > > ---- > WARNING: vmlinux.o(.data+0x19b10): Section mismatch in reference from the variable .LANCHOR1 to the function .init.text:sifive_serial_console_setup() > The variable .LANCHOR1 references > the function __init sifive_serial_console_setup() > If the reference is valid then annotate the > variable with __init* or __refdata (see linux/init.h) or name the variable: > *_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console > ---- > > ".LANCHOR1" is an ELF local symbol, automatically created by gcc's section > anchor generation code: > > https://gcc.gnu.org/onlinedocs/gccint/Anchored-Addresses.html > > https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/varasm.c;h=cd9591a45617464946dcf9a126dde277d9de9804;hb=9fb89fa845c1b2e0a18d85ada0b077c84508ab78#l7473 > > This was verified by compiling the kernel with -fno-section-anchors. > The serial driver code idiom triggering the warning is standard serial > driver practice, and one that has a specific whitelist inclusion in > modpost.c. > > I'm neither a modpost nor an ELF expert, but naively, it doesn't seem > useful for modpost to report section mismatch warnings caused by ELF > local symbols by default. Local symbols have compiler-generated > names, and thus bypass modpost's whitelisting algorithm, which relies > on the presence of a non-autogenerated symbol name. This increases > the likelihood that false positive warnings will be generated (as in > the above case). > > Thus, disable section mismatch reporting on ELF local symbols. The > rationale here is similar to that of commit 2e3a10a1551d ("ARM: avoid > ARM binutils leaking ELF local symbols") and of similar code already > present in modpost.c: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/mod/modpost.c?h=v4.19-rc4&id=7876320f88802b22d4e2daf7eb027dd14175a0f8#n1256 > > This second version of the patch drops the option to keep section > mismatch warnings for local sections, based on feedback from Sam > Ravnborg ; and clarifies that these warnings > appear with gcc 8.2.0. > > Cc: Russell King > Cc: Jim Wilson > Cc: Masahiro Yamada > Cc: Michal Marek > Cc: Sam Ravnborg > Cc: linux-kbuild@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Paul Walmsley > Signed-off-by: Paul Walmsley > --- > scripts/mod/modpost.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c > index 85bd93c63180..0fb148171b78 100644 > --- a/scripts/mod/modpost.c > +++ b/scripts/mod/modpost.c > @@ -1253,6 +1253,17 @@ static inline int is_arm_mapping_symbol(const char *str) > && (str[2] == '\0' || str[2] == '.'); > } > > +/* > + * If a symbol name follows the convention for ELF-local symbols (i.e., the > + * name begins with a ".L"), return true; otherwise false. This is used to > + * skip section mismatch reporting on ELF-local symbols, due to the risk of > + * false positives. > + */ > +static inline int is_local_symbol(const char *str) > +{ > + return str[0] == '.' && str[1] == 'L'; > +} > + > /* > * If there's no name there, ignore it; likewise, ignore it if it's > * one of the magic symbols emitted used by current ARM tools. > @@ -1535,6 +1546,9 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf, > if (strstarts(fromsym, "reference___initcall")) > return; > > + if (is_local_symbol(fromsym)) > + return; > + > tosec = sec_name(elf, get_secindex(elf, sym)); > to = find_elf_symbol(elf, r->r_addend, sym); > tosym = sym_name(elf, to); > -- > 2.19.1 > I think this is almost good. Just a nit. Maybe, putting this check in secref_whitelist() (with a comment "Pattern 6:") could look more consistency. Also, if you use strstart() helper, you can remove is_local_symbol() function. /* Check for pattern 6 */ if (strstarts(fromsym, ".L")) return 0; -- Best Regards Masahiro Yamada