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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 D4819C433B4 for ; Tue, 13 Apr 2021 15:16:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B89CD613B6 for ; Tue, 13 Apr 2021 15:16:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345735AbhDMPQn (ORCPT ); Tue, 13 Apr 2021 11:16:43 -0400 Received: from mx2.suse.de ([195.135.220.15]:33142 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229666AbhDMPQm (ORCPT ); Tue, 13 Apr 2021 11:16:42 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1618326981; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=JCBAk+URTFULVOvwnFTivKjGG4vL7/tzhoAqlGX41HQ=; b=FNFL457DJGyIhbJyS9rH5zvbZeL2hv9u22QMP280IKriTLDiiPrDQ8vevrk/0aa/MVU01k xL6n9kArPlzBOyNjb+LB8nPLuyUMmqAdNpgR41COB73Ly7l4O74sAat2/u+VLg6gcV6z0h LJOFwJ+tEYJ820YkyfYRRMqQG8eb1ME= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 273DCB138; Tue, 13 Apr 2021 15:16:21 +0000 (UTC) Date: Tue, 13 Apr 2021 17:16:20 +0200 From: Petr Mladek To: Andy Shevchenko Cc: Stephen Boyd , Andrew Morton , linux-kernel@vger.kernel.org, Jiri Olsa , Alexei Starovoitov , Jessica Yu , Evan Green , Hsin-Yi Wang , 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: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 2021-04-13 13:56:31, Andy Shevchenko wrote: > 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. I guess that you wanted to use it inside macro definition: #define VMCOREINFO_BUILD_ID(value) \ static_assert(ARRAY_SIZE(value) == BUILD_ID_SIZE_MAX); \ vmcoreinfo_append_str("BUILD-ID=%20phN\n", value) Instead, you should do it outside the macro: static_assert(ARRAY_SIZE(value) == BUILD_ID_SIZE_MAX); #define VMCOREINFO_BUILD_ID(value) \ vmcoreinfo_append_str("BUILD-ID=%20phN\n", value) > Sounds weird. static_assert() is a good one. Check, for example, lib/vsprintf.c > on how to use it. > > > Why is static_assert() > > preferred? I guess that it is because it is enough and more efficient for checks of constant values (no computation of the value). > 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. I would consider this written in stone (last famous words ;-) and use %20phN with the static_assert(). Best Regards, Petr