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 D630BD16819 for ; Fri, 9 Jan 2026 11:47:20 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1veAx2-0006S9-N5; Fri, 09 Jan 2026 06:46:44 -0500 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 1veAx0-0006Ou-Eu for qemu-rust@nongnu.org; Fri, 09 Jan 2026 06:46:42 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1veAwx-0005OK-8P for qemu-rust@nongnu.org; Fri, 09 Jan 2026 06:46:41 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1767959194; 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=sWPj3vU2t3wTODadJPf5AGD901cq/tufjmG+KdpOeVU=; b=czFgs2ynyw0uxWC8Ttf4RBZTAS4siPFVcCeseggVbWEqE57yBbN/MsNqA3RY5dxaAnhsHk yBgOpExMf/lhKAVTnp3cu71+GgUTqMF4eizNfbZgddREtBgDNJ9SpKObL1COq7v5xlBHuA jCc2JNkF9BLXx0YVv/vB6kYWmytzg34= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-374-iXWbRJSwPmqcpYCpby4cbQ-1; Fri, 09 Jan 2026 06:46:28 -0500 X-MC-Unique: iXWbRJSwPmqcpYCpby4cbQ-1 X-Mimecast-MFC-AGG-ID: iXWbRJSwPmqcpYCpby4cbQ_1767959187 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3F4A918005B2; Fri, 9 Jan 2026 11:46:26 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.39]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2156230002D2; Fri, 9 Jan 2026 11:46:20 +0000 (UTC) Date: Fri, 9 Jan 2026 11:46:17 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Paolo Bonzini Cc: qemu-devel@nongnu.org, Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Manos Pitsidianakis , Hanna Reitz , Gerd Hoffmann , Christian Schoenebeck , "Dr. David Alan Gilbert" , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , devel@lists.libvirt.org, qemu-block@nongnu.org, qemu-rust@nongnu.org, Markus Armbruster , Stefan Weil , Kevin Wolf , Richard Henderson Subject: Re: [PATCH v5 02/24] include: define constant for early constructor priority Message-ID: References: <20260108170338.2693853-1-berrange@redhat.com> <20260108170338.2693853-3-berrange@redhat.com> 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 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-rust@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: QEMU Rust-related patches and discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-rust-bounces+qemu-rust=archiver.kernel.org@nongnu.org Sender: qemu-rust-bounces+qemu-rust=archiver.kernel.org@nongnu.org On Fri, Jan 09, 2026 at 12:39:59PM +0100, Paolo Bonzini wrote: > On 1/8/26 18:03, Daniel P. Berrangé wrote: > > Functions marked with __attribute__((__constructor__)) will be > > invoked in linker order. In theory this is well defined, but > > in practice, it is hard to determine what this order will be > > with the layers of indirection through meson, ninja and the > > static libraries QEMU builds. > > > > Notably, the order currently appears different between Linux > > and Windows (as tested with Wine on Linux). This can cause > > problems when certain QEMU constructors have a dependancy on > > other QEMU constructors. > > What dependency are you seeing, or introducing? > > In theory QEMU constructors should not have any dependency, as we only use > them to initialize static data structures (such as the various *_init > macros). > > Not an objection, but I'd like to understand this better. See the commit message in patch 2. Essentially the RCU thread gets spawned from a constructor, and if anything it does results in an error_report() call, it will trigger use of monitor APIs before the monitor constructor has had a chance to run. IMHO the root problem is that it is pretty dubious for us to be spawning the RCU thread from a constructor. Constructors should be limited to minimal initialization of state. Spawning threads is outside the boundary of what I'd consider reasonable for a constructor todo. I didn't want try to tackle refactoring the RCU thread creation though, hence this gross workaround. > > Paolo > > > To address this define a QEMU_CONSTRUCTOR_EARLY constant which > > provides a priority value that will run before other default > > constructors. This is to be used for QEMU constructors that > > are themselves self-contained, but may be relied upon by other > > constructors. > > > > Reviewed-by: Richard Henderson > > Reviewed-by: Dr. David Alan Gilbert > > Signed-off-by: Daniel P. Berrangé > > --- > > include/qemu/compiler.h | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h > > index 1c2b673c05..4c49f52eb0 100644 > > --- a/include/qemu/compiler.h > > +++ b/include/qemu/compiler.h > > @@ -194,6 +194,14 @@ > > # define QEMU_USED > > #endif > > +/* > > + * A priority for __attribute__((constructor(...))) that > > + * will run earlier than the default constructors. Must > > + * only be used for functions that have no dependency > > + * on global initialization of other QEMU subsystems. > > + */ > > +#define QEMU_CONSTRUCTOR_EARLY 101 > > + > > /* > > * Disable -ftrivial-auto-var-init on a local variable. > > * > 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 :|