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 22594C433ED for ; Mon, 12 Apr 2021 11:58:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E450161287 for ; Mon, 12 Apr 2021 11:58:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240419AbhDLL61 (ORCPT ); Mon, 12 Apr 2021 07:58:27 -0400 Received: from mga07.intel.com ([134.134.136.100]:56834 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239202AbhDLL61 (ORCPT ); Mon, 12 Apr 2021 07:58:27 -0400 IronPort-SDR: 9vSVJyOOVXgDfekoe8ZVOgc7CKWyo/W0xNZ4oIwRnyNy6br2UTkLUn33HyOo4pOXMmORFB9wXI Z5aP2BEno+5Q== X-IronPort-AV: E=McAfee;i="6000,8403,9951"; a="258147864" X-IronPort-AV: E=Sophos;i="5.82,216,1613462400"; d="scan'208";a="258147864" Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Apr 2021 04:58:09 -0700 IronPort-SDR: rKHGOAXFMcA0XwI4I3cgEJDjg/9sWLOEEzeWWEaJPwbwG/rVdc+ElNjgm9OZdFIbjetr/DOitf n+j7KKGOkrHA== X-IronPort-AV: E=Sophos;i="5.82,216,1613462400"; d="scan'208";a="443033483" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by fmsmga004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Apr 2021 04:58:06 -0700 Received: from andy by smile with local (Exim 4.94) (envelope-from ) id 1lVvCc-003RkA-Vz; Mon, 12 Apr 2021 14:58:02 +0300 Date: Mon, 12 Apr 2021 14:58:02 +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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210410015300.3764485-6-swboyd@chromium.org> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org 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? > + 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); ? -- With Best Regards, Andy Shevchenko