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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7AF31C87FD1 for ; Tue, 5 Aug 2025 16:50:17 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ujKrN-0006VG-RB; Tue, 05 Aug 2025 12:49:59 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ujKqk-0006Nx-36 for qemu-devel@nongnu.org; Tue, 05 Aug 2025 12:49:24 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ujKqf-0002mH-5L for qemu-devel@nongnu.org; Tue, 05 Aug 2025 12:49:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1754412546; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sajRLYXbVIcxBq6uBjjRcmri4TXSJVjyc8qpJadwF+o=; b=DhgyX+xD5ZXK1T5oOjY0A7ev+4GufIlEyfDaEOFWLJKA3RlPv025F7WIJiy3VNJcr2U+f3 dnpbX0wXi26+rtfc6cbQy6WieGirvRdFZgeI4bPkht7Og1FXkJ2jEyCcwRIcmSfVishe8q KTS3lO1t46RTnq1vcbExbcxNwzapeVE= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-567-jCkMj_K4Nbudz46mujjlVQ-1; Tue, 05 Aug 2025 12:48:57 -0400 X-MC-Unique: jCkMj_K4Nbudz46mujjlVQ-1 X-Mimecast-MFC-AGG-ID: jCkMj_K4Nbudz46mujjlVQ_1754412536 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 062EB19560AD; Tue, 5 Aug 2025 16:48:56 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.80]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AD1AD1800298; Tue, 5 Aug 2025 16:48:52 +0000 (UTC) Date: Tue, 5 Aug 2025 17:48:49 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Manos Pitsidianakis Cc: qemu-devel@nongnu.org, Paolo Bonzini , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Markus Armbruster , Alex =?utf-8?Q?Benn=C3=A9e?= , Gustavo Romero , Pierrick Bouvier Subject: Re: [PATCH RFC] util/error.c: Print backtrace on error Message-ID: References: <20250805-backtrace-v1-1-d189d09b1e92@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Aug 05, 2025 at 07:22:14PM +0300, Manos Pitsidianakis wrote: > On Tue, Aug 5, 2025 at 7:00 PM Daniel P. Berrangé wrote: > > > > On Tue, Aug 05, 2025 at 12:19:26PM +0300, Manos Pitsidianakis wrote: > > > Add a backtrace_on_error meson feature (enabled with > > > --enable-backtrace-on-error) that compiles system binaries with > > > -rdynamic option and prints a function backtrace on error to stderr. > > > > > > Example output by adding an unconditional error_setg on error_abort in hw/arm/boot.c: > > > > > > ./qemu-system-aarch64(+0x13b4a2c) [0x55d015406a2c] > > > ./qemu-system-aarch64(+0x13b4abd) [0x55d015406abd] > > > ./qemu-system-aarch64(+0x13b4d49) [0x55d015406d49] > > > ./qemu-system-aarch64(error_setg_internal+0xe7) [0x55d015406f62] > > > ./qemu-system-aarch64(arm_load_dtb+0xbf) [0x55d014d7686f] > > > ./qemu-system-aarch64(+0xd2f1d8) [0x55d014d811d8] > > > ./qemu-system-aarch64(notifier_list_notify+0x44) [0x55d01540a282] > > > ./qemu-system-aarch64(qdev_machine_creation_done+0xa0) [0x55d01476ae17] > > > ./qemu-system-aarch64(+0xaa691e) [0x55d014af891e] > > > ./qemu-system-aarch64(qmp_x_exit_preconfig+0x72) [0x55d014af8a5d] > > > ./qemu-system-aarch64(qemu_init+0x2a89) [0x55d014afb657] > > > ./qemu-system-aarch64(main+0x2f) [0x55d01521e836] > > > /lib/x86_64-linux-gnu/libc.so.6(+0x29ca8) [0x7f3033d67ca8] > > > /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x85) [0x7f3033d67d65] > > > ./qemu-system-aarch64(_start+0x21) [0x55d0146814f1] > > > > > > Unexpected error in arm_load_dtb() at ../hw/arm/boot.c:529: > > > > From an end-user POV, IMHO the error messages need to be good enough > > that such backtraces aren't needed to understand the problem. For > > developers, GDB can give much better backtraces (file+line numbers, > > plus parameters plus local variables) in the ideally rare cases that > > the error message alone has insufficient info. So I'm not really > > convinced that programs (in general, not just QEMU) should try to > > create backtraces themselves. > > I don't think there's value in replacing gdb debugging with this, I > agree. I think it has value for "fire and forget" uses, when errors > happen unexpectedly and are hard to replicate and you only end up with > log entries and no easy way to debug it. If the log entry with the error message is useless for devs, then it is even worse for end users... who will be copying that message into bug reports anyway. This patch doesn't feel like something we could enable in formal builds in the distro, so we still need better error reporting without it, such that user bug reports are actionable. Was there a specific place where you found things hard to debug from the error message alone ? I'm sure we have plenty of examples of errors that can be improved, but wondering if there are some general patterns we're doing badly that would be a good win to improve ? With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|