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=-22.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 2CDF9C433DB for ; Fri, 15 Jan 2021 08:15:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D4B582220B for ; Fri, 15 Jan 2021 08:15:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732281AbhAOIPb (ORCPT ); Fri, 15 Jan 2021 03:15:31 -0500 Received: from mail.kernel.org ([198.145.29.99]:55292 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727679AbhAOIP2 (ORCPT ); Fri, 15 Jan 2021 03:15:28 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 513C52072D; Fri, 15 Jan 2021 08:14:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1610698487; bh=VDBSNkhjih0ytWUhVsQuY2EtZRagprXKw9fTDS9CCDs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=j3lziUWJc66mIc65O04sk7hiw5QKBQL2GnpTYf7OeJhH83aiZdrSjYpLSQChdhI/D N/2QP9z8AnLTX2s+diTRuSWpiSahvJJes6J7PDPmp+SuctM1tpkr+IZkjvdPkGDDKF tGF60IlD3kaGZMWWzIqB3xN0ZRj8SduaI5Wywp4qdbLtYirNlth9b12GmSR/Gxm2kA z4Uzsfm6h94mYE9ioqzRbbtvkIsT0lVfKJGdSICvuRKCt0c2WpA9HVwHZWWWM/elI9 upDpmBtLAyLmLDRuoP7QKdVGe+Muej35iQ2jTrApVOxtxUhieE5YjKH/vc1hR9PZll kPhuUrP33HRTw== Date: Fri, 15 Jan 2021 09:14:42 +0100 From: Jessica Yu To: Marco Elver Cc: Fangrui Song , LKML , clang-built-linux , Sam Ravnborg Subject: Re: [PATCH v2] module: Ignore _GLOBAL_OFFSET_TABLE_ when warning for undefined symbols Message-ID: <20210115081442.GB9637@linux-8ccs> References: <20210114211840.GA5617@linux-8ccs> <20210114215416.993167-1-maskray@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: X-OS: Linux linux-8ccs 5.8.0-rc6-lp150.12.61-default+ x86_64 User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org +++ Marco Elver [15/01/21 08:03 +0100]: >On Thu, 14 Jan 2021 at 22:54, Fangrui Song wrote: >> clang-12 -fno-pic (since >> https://github.com/llvm/llvm-project/commit/a084c0388e2a59b9556f2de0083333232da3f1d6) >> can emit `call __stack_chk_fail@PLT` instead of `call __stack_chk_fail` >> on x86. The two forms should have identical behaviors on x86-64 but the >> former causes GNU as<2.37 to produce an unreferenced undefined symbol >> _GLOBAL_OFFSET_TABLE_. >> >> (On x86-32, there is an R_386_PC32 vs R_386_PLT32 difference but the >> linker behavior is identical as far as Linux kernel is concerned.) >> >> Simply ignore _GLOBAL_OFFSET_TABLE_ for now, like what >> scripts/mod/modpost.c:ignore_undef_symbol does. This also fixes the >> problem for gcc/clang -fpie and -fpic, which may emit `call foo@PLT` for >> external function calls on x86. >> >> Note: ld -z defs and dynamic loaders do not error for unreferenced >> undefined symbols so the module loader is reading too much. If we ever >> need to ignore more symbols, the code should be refactored to ignore >> unreferenced symbols. >> >> Reported-by: Marco Elver >> Link: https://github.com/ClangBuiltLinux/linux/issues/1250 >> Signed-off-by: Fangrui Song > >Tested-by: Marco Elver > >Thank you for the patch! > >> --- >> kernel/module.c | 20 ++++++++++++++++++-- >> 1 file changed, 18 insertions(+), 2 deletions(-) >> --- >> Changes in v2: >> * Fix Marco's email address >> * Add a function ignore_undef_symbol similar to scripts/mod/modpost.c:ignore_undef_symbol >> >> diff --git a/kernel/module.c b/kernel/module.c >> index 4bf30e4b3eaa..278f5129bde2 100644 >> --- a/kernel/module.c >> +++ b/kernel/module.c >> @@ -2348,6 +2348,20 @@ static int verify_exported_symbols(struct module *mod) >> return 0; >> } >> >> +static int ignore_undef_symbol(Elf_Half emachine, const char *name) > >Why not 'bool' return-type? > >> +{ >> + /* On x86, PIC code and Clang non-PIC code may have call foo@PLT. GNU as > >Not sure if checkpatch.pl warns about this, but this multi-line >comment does not follow the normal kernel-style (see elsewhere in >file): > >/* > * ... > */ +1 to Marco's comments. Otherwise, patch looks good to me. Thanks Fangrui! Jessica