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 0DA05EB64D9 for ; Fri, 7 Jul 2023 22:27:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230245AbjGGW1j (ORCPT ); Fri, 7 Jul 2023 18:27:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53538 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229552AbjGGW1h (ORCPT ); Fri, 7 Jul 2023 18:27:37 -0400 Received: from mail-qk1-x736.google.com (mail-qk1-x736.google.com [IPv6:2607:f8b0:4864:20::736]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7FB1211F for ; Fri, 7 Jul 2023 15:27:35 -0700 (PDT) Received: by mail-qk1-x736.google.com with SMTP id af79cd13be357-7659dc74da1so219735485a.3 for ; Fri, 07 Jul 2023 15:27:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1688768855; x=1691360855; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=M11brMTtotbFVLzj4X4lTncnHIwCm2Zf8rkXtvsipsQ=; b=vC6qWQxkXGfXOLG5MVnh7rjsbsQpPKJlKIIfsHZnJyTf9E5goqA5DN13jqiy7u/qoX +pl6G4Ft4je/wY2W6JSrIJSdDan2iGXNbv4U1UABZRQe/TrzD3dHxf3aiZcLB5EENUBN Mbnu9hXeoNdXMTOUqZiv1L4jOEf2l5SJ+Eprv51B5XVR2dwlcTOjl8qPhGcOI1twm8MF nb2u7YKdlLiKTEuGDSJxcvNj0YkWT4LxpbzkpbZsgzN8mWStoCe4WFBAkdhzAevJKbGh rlQfJuL/vlPaJ2ez5sBj9bd9dvZryk1VxpDtVFPwxd5cPUAwwdVEqJj71uucgfQuQ/q6 g71g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688768855; x=1691360855; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=M11brMTtotbFVLzj4X4lTncnHIwCm2Zf8rkXtvsipsQ=; b=KTbArGPnZQHypRARyJB0x81R3R605RLNU8G13kSLmenmVqrrDL0TyCwm9ZshItKSzt MVs1iiKkOcFJLKO3G3uKuQCoUmwA1Ht0kSeiWsskMTzdJ0p909zMvjApz+fy7N6vQEuM Hxkdt979L3CRO6b9+78Ogs+Q7NF3r/+qyoQVMnOHpWc3OKxr9Zs25KiQqK0N0KYydXGr SiwW1FT/a7SECyw8aO+W/Jhba/mSwJsLcPRMDZejSEzn4ZZt8UTQZmr/gwyQFIy7xvUs mP2XJv0HEsKJ3MmUwQN8MWZlrIR6nBVqJ85uCEKz+V18XX8EF8pBFYQNkVq8VrUxZz67 CWuA== X-Gm-Message-State: ABy/qLaFxawjo723W7qmCnNoNGCuW6pt6eEqlOS2sDWxATw0P6wwEHl0 Ylb1BHAqhsrD48pGoRzAEi6luESRfG/w0esIHE0bpw== X-Google-Smtp-Source: APBJJlH89jF/4fQmPOPYtbkj8S3UrudUI50F/TSq49MlnMtbZRNScnk727WYFAglj3OAFCeaVzlUJdA5SnBQJFc2H1Y= X-Received: by 2002:a05:620a:2588:b0:767:2f4a:e07a with SMTP id x8-20020a05620a258800b007672f4ae07amr6955904qko.68.1688768854702; Fri, 07 Jul 2023 15:27:34 -0700 (PDT) MIME-Version: 1.0 References: <20230628181926.4102448-1-yhs@fb.com> In-Reply-To: <20230628181926.4102448-1-yhs@fb.com> From: Nick Desaulniers Date: Fri, 7 Jul 2023 15:27:23 -0700 Message-ID: Subject: Re: [PATCH v2] kallsyms: strip LTO-only suffixes from promoted global functions To: Yonghong Song Cc: Petr Mladek , Song Liu , Steven Rostedt , Fangrui Song , kernel-team@fb.com, Leizhen , linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Sami Tolvanen , "KE . LI" , Padmanabha Srinivasaiah Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 28, 2023 at 11:19=E2=80=AFAM Yonghong Song wrote: > > 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 followi= ng > 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 mechani= sm 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 L= TO. > > 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 t= he 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@= kernel.org/T/#u > > Fixes: 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions"= ) > Reported-by: Song Liu > Signed-off-by: Yonghong Song Thanks for the patch and improving live patch with LTO. Looking back at the internal report that resulted in commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions") your version was what I originally had. I did not leave a comment as to why I changed it when I sent it 2 years ago, and no longer recall the reason. Reviewed-by: Nick Desaulniers > --- > 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 variable= s that > * must be promoted to global scope as part of LTO. This can bre= ak > * 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 obs= erved: > * - 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 sor= ting, > - * but it helps us with subsorting. > + * As above, replacing the first '.' in ".llvm." with '\0' does n= ot > + * affect the main sorting, but it helps us with subsorting. > */ > - p =3D strchr(s, '.'); > + p =3D strstr(s, ".llvm."); > if (p) > *p =3D '\0'; > } > -- > 2.34.1 > --=20 Thanks, ~Nick Desaulniers