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=-6.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 91010C433DB for ; Wed, 10 Feb 2021 00:28:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4A06364E53 for ; Wed, 10 Feb 2021 00:28:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234446AbhBJA1q (ORCPT ); Tue, 9 Feb 2021 19:27:46 -0500 Received: from mail.kernel.org ([198.145.29.99]:59864 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234774AbhBJADk (ORCPT ); Tue, 9 Feb 2021 19:03:40 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id D94C164E42; Wed, 10 Feb 2021 00:02:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1612915379; bh=/9zjf6RObGkGCMF7oOa3KfpvjKGFcmQSd9nZzvEVr00=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=vI+C4co13VkpKpF7c4nYz2E3SFgymNijm7IbZTeJDEywSMILm4ZGnLXXjwx2QR1F1 Q1WC+7zQFU4UCvX7s+ZmpKgSn6SXD6biDqLFMizzNqSf15pr3QLoqBK6BssNVLnL/d z/VQ1GwurpMYmOJOwLun7ksWBUwkYL7VQXuw6J3cEeTFA446GiEM7bYo39hw2eE6bJ 0AoYptCguKDFUSNmVF9oHnzxminkLFsB48TzyYSZrYtIYb17VeW3v2QybFs1+7RV9M 8Hwk5o/a5oZuMLjxlWyD8IKJkvC3Jk0+xjF5Mo/BCdUNHgUFfhr/bgN0xvzl1LM6U9 kJqV1HteITluw== Date: Tue, 9 Feb 2021 17:02:57 -0700 From: Nathan Chancellor To: Nick Desaulniers Cc: Jiri Olsa , Andrii Nakryiko , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Networking , bpf , clang-built-linux , Veronika Kabatova , Jiri Olsa , Arnaldo Carvalho de Melo , Daniel Kiss Subject: Re: FAILED unresolved symbol vfs_truncate on arm64 with LLVM Message-ID: <20210210000257.GA1683281@ubuntu-m3-large-x86> References: <20210209052311.GA125918@ubuntu-m3-large-x86> <20210209074904.GA286822@ubuntu-m3-large-x86> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Feb 09, 2021 at 12:09:31PM -0800, Nick Desaulniers wrote: > On Tue, Feb 9, 2021 at 11:06 AM Jiri Olsa wrote: > > > > On Tue, Feb 09, 2021 at 05:13:42PM +0100, Jiri Olsa wrote: > > > On Tue, Feb 09, 2021 at 04:09:36PM +0100, Jiri Olsa wrote: > > > > > > SNIP > > > > > > > > > > > DW_AT_prototyped (true) > > > > > > > > DW_AT_type (0x01cfdfe4 "long int") > > > > > > > > DW_AT_external (true) > > > > > > > > > > > > > > > > > > > > > > Ok, the problem appears to be not in DWARF, but in mcount_loc data. > > > > > > > vfs_truncate's address is not recorded as ftrace-attachable, and thus > > > > > > > pahole ignores it. I don't know why this happens and it's quite > > > > > > > strange, given vfs_truncate is just a normal global function. > > > > > > > > > > right, I can't see it in mcount adresses.. but it begins with instructions > > > > > that appears to be nops, which would suggest it's traceable > > > > > > > > > > ffff80001031f430 : > > > > > ffff80001031f430: 5f 24 03 d5 hint #34 > > > > > ffff80001031f434: 1f 20 03 d5 nop > > > > > ffff80001031f438: 1f 20 03 d5 nop > > > > > ffff80001031f43c: 3f 23 03 d5 hint #25 > > > > > > > > > > > > > > > > > > > I'd like to understand this issue before we try to fix it, but there > > > > > > > is at least one improvement we can make: pahole should check ftrace > > > > > > > addresses only for static functions, not the global ones (global ones > > > > > > > should be always attachable, unless they are special, e.g., notrace > > > > > > > and stuff). We can easily check that by looking at the corresponding > > > > > > > symbol. But I'd like to verify that vfs_truncate is ftrace-attachable > > > > > > > > I'm still trying to build the kernel.. however ;-) > > > > > > I finally reproduced.. however arm's not using mcount_loc > > > but some other special section.. so it's new mess for me > > > > so ftrace data actualy has vfs_truncate address but with extra 4 bytes: > > > > ffff80001031f434 > > > > real vfs_truncate address: > > > > ffff80001031f430 g F .text 0000000000000168 vfs_truncate > > > > vfs_truncate disasm: > > > > ffff80001031f430 : > > ffff80001031f430: 5f 24 03 d5 hint #34 > > ffff80001031f434: 1f 20 03 d5 nop > > ffff80001031f438: 1f 20 03 d5 nop > > ffff80001031f43c: 3f 23 03 d5 hint #25 > > > > thats why we don't match it in pahole.. I checked few other functions > > and some have the same problem and some match the function boundary > > > > those that match don't have that first hint instrucion, like: > > > > ffff800010321e40 : > > ffff800010321e40: 1f 20 03 d5 nop > > ffff800010321e44: 1f 20 03 d5 nop > > ffff800010321e48: 3f 23 03 d5 hint #25 > > > > any hints about hint instructions? ;-) > > aarch64 makes *some* newer instructions reuse the "hint" ie "nop" > encoding space to make software backwards compatible on older hardware > that doesn't support such instructions. Is this BTI, perhaps? (The > function is perhaps the destination of an indirect call?) It seems like it. The issue is not reproducible when CONFIG_ARM64_BTI_KERNEL is not set. Cheers, Nathan