From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B482C606A32A for ; Wed, 21 Oct 2026 21:25:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=f5ADfDQG Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xJdnV-0004Oi-J8; Wed, 21 Oct 2026 17:24:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xJdnO-0004ON-1j for qemu-devel@nongnu.org; Wed, 21 Oct 2026 17:24:26 -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 1xJdnL-0002Ma-JZ for qemu-devel@nongnu.org; Wed, 21 Oct 2026 17:24:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1792617861; h=from:from: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=jUb02Z2NBUxpKMKJUXU4FIXxAdoJgO9oyRJRXB+kNb0=; b=f5ADfDQG+yCM6vC9EHrrbUDHis+FxODnkiLH9EktFQ4Rk3fxJ15Cve4uKopNBWO9DaG7df Etx3OA8aVOm8L+d5gaKgWHxF+WkVuAWSXBIceOaPWaAaJuI+66gJDpYNFIrePjNsC9EfZk zyHK/mQSm5pvg6y3g225dLwnwvVJAEk= Received: from mx-prod-mc-08.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-655-pjiRiZTjOj6nbDjG7Mmnig-1; Wed, 21 Oct 2026 21:24:19 +0000 X-MC-Unique: pjiRiZTjOj6nbDjG7Mmnig-1 X-Mimecast-MFC-AGG-ID: pjiRiZTjOj6nbDjG7Mmnig_1792617858 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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9389018001F3; Wed, 21 Oct 2026 21:24:18 +0000 (UTC) Received: from redhat.com (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 283DA30000E3; Wed, 21 Oct 2026 21:24:16 +0000 (UTC) Date: Wed, 21 Oct 2026 16:24:13 -0500 From: Eric Blake To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: qemu-devel@nongnu.org, Paolo Bonzini , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Stefan Hajnoczi Subject: Re: [PATCH v3 01/24] osdep: add 'ignore_value(x)' macro Message-ID: References: <20261005120855.421973-1-berrange@redhat.com> <20261005120855.421973-2-berrange@redhat.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20261005120855.421973-2-berrange@redhat.com> User-Agent: NeoMutt/20260616 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Archive: List-Post: List-Help: List-Subscribe: , Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org X-Spam-Status: No, score=-22.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Mon, Oct 05, 2026 at 01:08:32PM +0100, Daniel P. Berrangé wrote: > Functions annotated with 'warn_unused_result' cannot be cast > to (void) to silence the compiler. Add the ignore_value() > macro which tricks the compiler into thinking the result is > genuinely used, avoiding the need for manual workarounds where > the return value is intentionally ignored. > > This clever macro is derived from one originating with the > GNULIB project: > > https://gitweb.git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob;f=lib/ignore-value.h;hb=HEAD Hey, I recognize that :) (See gnulib commit 939dedd9a2 where I switched from an inline static function to use of __typeof__ 15 years ago) > > but simplified since we don't need compat with old GCC and > optimizing on clang is overkill. > > Reviewed-by: Marc-André Lureau > Signed-off-by: Daniel P. Berrangé Reviewed-by: Eric Blake > --- > include/qemu/osdep.h | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > index 1ec5b42230b..c1ca2c127b6 100644 > --- a/include/qemu/osdep.h > +++ b/include/qemu/osdep.h > @@ -251,6 +251,14 @@ extern "C" { > #endif > > > +/* > + * Merely casting to (void) is not sufficient for functions > + * annotated with the "warn_unused_result" attribute > + */ > +#define ignore_value(x) \ > + (__extension__ ({ __typeof__(x) __x = (x); (void) __x; })) > + > + > /* > * For mingw, as of v6.0.0, the function implementing the assert macro is > * not marked as noreturn, so the compiler cannot delete code following an > -- > 2.55.0 > > -- Eric Blake, Principal Software Engineer Red Hat, Inc. Virtualization: qemu.org | libguestfs.org