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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,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 EDD43C433B4 for ; Tue, 13 Apr 2021 10:56:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D1F2A61278 for ; Tue, 13 Apr 2021 10:56:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344148AbhDMK5C (ORCPT ); Tue, 13 Apr 2021 06:57:02 -0400 Received: from mga12.intel.com ([192.55.52.136]:27338 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230123AbhDMK46 (ORCPT ); Tue, 13 Apr 2021 06:56:58 -0400 IronPort-SDR: cG9tJ9X1iC8w9HBnd4ZDBGtwuJkqMRECGpfB4R0SLFrqUULsah8a1bu0B9B0b65W7BMVFOXOlq 6UNSJQzvQpOA== X-IronPort-AV: E=McAfee;i="6200,9189,9952"; a="173879378" X-IronPort-AV: E=Sophos;i="5.82,219,1613462400"; d="scan'208";a="173879378" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Apr 2021 03:56:38 -0700 IronPort-SDR: W1PGx1Fem+EzIGod2hof2or+FyXeJZvRMhMHQOMbWx26CeExzgvAEFlEkDffy7NxM00SG9OYUb 7GuoZkaXlVTA== X-IronPort-AV: E=Sophos;i="5.82,219,1613462400"; d="scan'208";a="381932951" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Apr 2021 03:56:34 -0700 Received: from andy by smile with local (Exim 4.94) (envelope-from ) id 1lWGid-003jmD-M5; Tue, 13 Apr 2021 13:56:31 +0300 Date: Tue, 13 Apr 2021 13:56:31 +0300 From: Andy Shevchenko To: Stephen Boyd Cc: Andrew Morton , linux-kernel@vger.kernel.org, Jiri Olsa , Alexei Starovoitov , Jessica Yu , Evan Green , Hsin-Yi Wang , Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Rasmus Villemoes , linux-doc@vger.kernel.org, Matthew Wilcox Subject: Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces Message-ID: References: <20210410015300.3764485-1-swboyd@chromium.org> <20210410015300.3764485-6-swboyd@chromium.org> <161825574550.3764895.4387100574176584209@swboyd.mtv.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <161825574550.3764895.4387100574176584209@swboyd.mtv.corp.google.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 12, 2021 at 12:29:05PM -0700, Stephen Boyd wrote: > Quoting Andy Shevchenko (2021-04-12 04:58:02) > > On Fri, Apr 09, 2021 at 06:52:52PM -0700, Stephen Boyd wrote: > > > Let's make kernel stacktraces easier to identify by including the build > > > ID[1] of a module if the stacktrace is printing a symbol from a module. > > > This makes it simpler for developers to locate a kernel module's full > > > debuginfo for a particular stacktrace. Combined with > > > scripts/decode_stracktrace.sh, a developer can download the matching > > > debuginfo from a debuginfod[2] server and find the exact file and line > > > number for the functions plus offsets in a stacktrace that match the > > > module. This is especially useful for pstore crash debugging where the > > > kernel crashes are recorded in something like console-ramoops and the > > > recovery kernel/modules are different or the debuginfo doesn't exist on > > > the device due to space concerns (the debuginfo can be too large for > > > space limited devices). > > > > > > Originally, I put this on the %pS format, but that was quickly rejected > > > given that %pS is used in other places such as ftrace where build IDs > > > aren't meaningful. There was some discussions on the list to put every > > > module build ID into the "Modules linked in:" section of the stacktrace > > > message but that quickly becomes very hard to read once you have more > > > than three or four modules linked in. It also provides too much > > > information when we don't expect each module to be traversed in a > > > stacktrace. Having the build ID for modules that aren't important just > > > makes things messy. Splitting it to multiple lines for each module > > > quickly explodes the number of lines printed in an oops too, possibly > > > wrapping the warning off the console. And finally, trying to stash away > > > each module used in a callstack to provide the ID of each symbol printed > > > is cumbersome and would require changes to each architecture to stash > > > away modules and return their build IDs once unwinding has completed. > > > > > > Instead, we opt for the simpler approach of introducing new printk > > > formats '%pS[R]b' for "pointer symbolic backtrace with module build ID" > > > and '%pBb' for "pointer backtrace with module build ID" and then > > > updating the few places in the architecture layer where the stacktrace > > > is printed to use this new format. > > > > > > Example: > > > > Can you trim a bit the example, so we will see only important lines. > > In such case you may provide "before" and "after" variants. > > > > ... > > > > > - if (modname) > > > - len += sprintf(buffer + len, " [%s]", modname); > > > + if (modname) { > > > + len += sprintf(buffer + len, " [%s", modname); > > > > > + /* build ID should match length of sprintf below */ > > > + BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20); > > > > First of all, why not static_assert() defined near to the actual macro? > > Which macro? BUILD_ID_SIZE_MAX? Yes. > I tried static_assert() and it didn't > work for me but maybe I missed something. Sounds weird. static_assert() is a good one. Check, for example, lib/vsprintf.c on how to use it. > Why is static_assert() > preferred? Because it's cleaner way to achieve it and as a bonus it can be put outside of the functions (be in the header or so). > > > + if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid) > > > + len += sprintf(buffer + len, " %20phN", buildid); > > > > len += sprintf(buffer + len, " %*phN", BUILD_ID_SIZE_MAX, buildid); > > > > Are you suggesting to use sprintf format here so that the size is part > of the printf? Sounds good to me. Thanks. I prefer %20phN when the size is carved in stone (for example by specification), but if you are really expecting that it may be changed in the future, use variadic approach as I showed above. -- With Best Regards, Andy Shevchenko