From nobody Sat Feb 7 12:35:06 2026 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 31226EB64DA for ; Wed, 28 Jun 2023 18:19:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231731AbjF1STu (ORCPT ); Wed, 28 Jun 2023 14:19:50 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:20354 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231467AbjF1STo (ORCPT ); Wed, 28 Jun 2023 14:19:44 -0400 Received: from pps.filterd (m0044010.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 35SHwla9024479 for ; Wed, 28 Jun 2023 11:19:44 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : content-type : content-transfer-encoding : mime-version; s=facebook; bh=z0e8QttLPh/Q/9kNelSZTNeMoB4d8XPy6uAeGGRHDJE=; b=Sk8OibaWF5PZvTwQEeOU/jmAzItcoR2TAgesKoUjwVBC+85zto95Om++ikJz3cA2/BBK nIGDZSWDXULhMZdTIDaqi90Cxvv0uNTKgDCze4dYyKcwCjznKmYJoYLBJuwhnHyzMDLq Rq015CyZFnx3lOu1nhhIE9yrgPdpNY0gGGo= Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3rgart71bj-2 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Wed, 28 Jun 2023 11:19:43 -0700 Received: from twshared18891.17.frc2.facebook.com (2620:10d:c085:108::8) by mail.thefacebook.com (2620:10d:c085:21d::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Wed, 28 Jun 2023 11:19:42 -0700 Received: by devbig309.ftw3.facebook.com (Postfix, from userid 128203) id 994FE22169B1E; Wed, 28 Jun 2023 11:19:26 -0700 (PDT) From: Yonghong Song To: Nick Desaulniers , Petr Mladek , Song Liu , Steven Rostedt CC: Fangrui Song , , Leizhen , , Subject: [PATCH v2] kallsyms: strip LTO-only suffixes from promoted global functions Date: Wed, 28 Jun 2023 11:19:26 -0700 Message-ID: <20230628181926.4102448-1-yhs@fb.com> X-Mailer: git-send-email 2.34.1 X-FB-Internal: Safe X-Proofpoint-ORIG-GUID: MmlXjdY53bokJ4lboidNc5CLdEuKdNJ3 X-Proofpoint-GUID: MmlXjdY53bokJ4lboidNc5CLdEuKdNJ3 Content-Transfer-Encoding: quoted-printable X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.591,FMLib:17.11.176.26 definitions=2023-06-28_12,2023-06-27_01,2023-05-22_02 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions") stripped all function/variable suffixes started with '.' regardless of whether those suffixes are generated at LTO mode or not. In fact, as far as I know, in LTO mode, when a static function/variable is promoted to the global scope, '.llvm.<...>' suffix is added. The existing mechanism breaks live patch for a LTO kernel even if no .llvm.<...> symbols are involved. For example, for the following kernel symbols: $ grep bpf_verifier_vlog /proc/kallsyms ffffffff81549f60 t bpf_verifier_vlog ffffffff8268b430 d bpf_verifier_vlog._entry ffffffff8282a958 d bpf_verifier_vlog._entry_ptr ffffffff82e12a1f d bpf_verifier_vlog.__already_done 'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and '__already_done' are static variables used inside 'bpf_verifier_vlog', so llvm promotes them to file-level static with prefix 'bpf_verifier_vlog.'. Note that the func-level to file-level static function promotion also happens without LTO. Given a symbol name 'bpf_verifier_vlog', with LTO kernel, current mechanism= will return 4 symbols to live patch subsystem which current live patching subsystem cannot handle it. With non-LTO kernel, only one symbol is returned. In [1], we have a lengthy discussion, the suggestion is to separate two cases: (1). new symbols with suffix which are generated regardless of whether LTO is enabled or not, and (2). new symbols with suffix generated only when LTO is enabled. The cleanup_symbol_name() should only remove suffixes for case (2). Case (1) should not be changed so it can work uniformly with or without LTO. This patch removed LTO-only suffix '.llvm.<...>' so live patching and tracing should work the same way for non-LTO kernel. The cleanup_symbol_name() in scripts/kallsyms.c is also changed to have the= same filtering pattern so both kernel and kallsyms tool have the same expectation on the order of symbols. [1] https://lore.kernel.org/live-patching/20230615170048.2382735-1-song@ke= rnel.org/T/#u Fixes: 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions") Reported-by: Song Liu Signed-off-by: Yonghong Song Acked-by: Song Liu Reviewed-by: Nick Desaulniers Reviewed-by: Zhen Lei --- kernel/kallsyms.c | 5 ++--- scripts/kallsyms.c | 6 +++--- 2 files changed, 5 insertions(+), 6 deletions(-) Changelogs: v1 -> v2: . add 'Reported-by: Song Liu ' . also fix in scripts/kallsyms.c. diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 77747391f49b..4874508bb950 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -174,11 +174,10 @@ static bool cleanup_symbol_name(char *s) * LLVM appends various suffixes for local functions and variables that * must be promoted to global scope as part of LTO. This can break * hooking of static functions with kprobes. '.' is not a valid - * character in an identifier in C. Suffixes observed: + * character in an identifier in C. Suffixes only in LLVM LTO observed: * - foo.llvm.[0-9a-f]+ - * - foo.[0-9a-f]+ */ - res =3D strchr(s, '.'); + res =3D strstr(s, ".llvm."); if (res) { *res =3D '\0'; return true; diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c index 0d2db41177b2..13af6d0ff845 100644 --- a/scripts/kallsyms.c +++ b/scripts/kallsyms.c @@ -346,10 +346,10 @@ static void cleanup_symbol_name(char *s) * ASCII[_] =3D 5f * ASCII[a-z] =3D 61,7a * - * As above, replacing '.' with '\0' does not affect the main sorting, - * but it helps us with subsorting. + * As above, replacing the first '.' in ".llvm." with '\0' does not + * affect the main sorting, but it helps us with subsorting. */ - p =3D strchr(s, '.'); + p =3D strstr(s, ".llvm."); if (p) *p =3D '\0'; } --=20 2.34.1