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 5E8E8C4828F for ; Wed, 7 Feb 2024 07:38:05 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rXcVF-0006j1-VF; Wed, 07 Feb 2024 02:37:53 -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 1rXcVE-0006ir-U0 for qemu-devel@nongnu.org; Wed, 07 Feb 2024 02:37:52 -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 1rXcV9-00072d-HF for qemu-devel@nongnu.org; Wed, 07 Feb 2024 02:37:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1707291466; 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=8ok3EJpVPnm+pT+p11+wWibWFEL5GlzkBygC3L9VcAo=; b=V9SYPumjuYZ1DmCN1W2r638eKptMNVEPYt+/OAR9DaMLpO/TE46XdJpMOsbHKtmz8xgSjx OJ8rTjzO+gMyyfGF0zOpGi8sqPZxxMd1kcya2RtLhYlY2wYx7wmDQ9VmIQzbC9+TcKZHFL 4aZMgcAG45hMnb863DeObGQs7QF+nZ4= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-668-drSoRE3LPqWyXZHXAOhgpw-1; Wed, 07 Feb 2024 02:37:43 -0500 X-MC-Unique: drSoRE3LPqWyXZHXAOhgpw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id AAC561C0651B; Wed, 7 Feb 2024 07:37:42 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.123]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 50E681C05E0F; Wed, 7 Feb 2024 07:37:42 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 6023E21E66D0; Wed, 7 Feb 2024 08:37:41 +0100 (CET) From: Markus Armbruster To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Cc: Daniel P. =?utf-8?Q?Berrang=C3=A9?= , Stefan Hajnoczi , qemu-devel@nongnu.org, Hanna Czenczek , Peter Maydell , Richard Henderson , Thomas Huth , Alex =?utf-8?Q?Benn=C3=A9e?= , Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH] docs/style: allow C99 mixed declarations In-Reply-To: <683557e9-fa84-4384-961f-7c29daafe860@linaro.org> ("Philippe =?utf-8?Q?Mathieu-Daud=C3=A9=22's?= message of "Wed, 7 Feb 2024 06:28:01 +0100") References: <20240205171819.474283-1-stefanha@redhat.com> <87r0hqyw8k.fsf@pond.sub.org> <683557e9-fa84-4384-961f-7c29daafe860@linaro.org> Date: Wed, 07 Feb 2024 08:37:41 +0100 Message-ID: <87msscn2re.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.294, 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, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01, T_SPF_HELO_TEMPERROR=0.01 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: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Philippe Mathieu-Daud=C3=A9 writes: > On 6/2/24 06:53, Markus Armbruster wrote: >> Daniel P. Berrang=C3=A9 writes: >>=20 >>> On Mon, Feb 05, 2024 at 12:18:19PM -0500, Stefan Hajnoczi wrote: >>>> C99 mixed declarations support interleaving of local variable >>>> declarations and code. >>>> >>>> The coding style "generally" forbids C99 mixed declarations with some >>>> exceptions to the rule. This rule is not checked by checkpatch.pl and >>>> naturally there are violations in the source tree. >>>> >>>> While contemplating adding another exception, I came to the conclusion >>>> that the best location for declarations depends on context. Let the >>>> programmer declare variables where it is best for legibility. Don't try >>>> to define all possible scenarios/exceptions. > ... > >>> Even if the compiler does reliably warn, I think the code pattern >>> remains misleading to contributors, as the flow control flaw is >>> very non-obvious. >>=20 >> Yup. Strong dislike. >>=20 >>> Rather than accept the status quo and remove the coding guideline, >>> I think we should strengthen the guidelines, such that it is >>> explicitly forbidden in any method that uses 'goto'. Personally >>> I'd go all the way to -Werror=3Ddeclaration-after-statement, as >>=20 >> I support this. >>=20 >>> while C99 mixed decl is appealing, >>=20 >> Not to me. >>=20 >> I much prefer declarations and statements to be visually distinct. >> Putting declarations first and separating from statements them with a >> blank line accomplishes that. Less necessary in languages where >> declarations are syntactically obvious. > > But we already implicitly suggest C99, see commit ae7c80a7bd > ("error: New macro ERRP_GUARD()"): > > * To use ERRP_GUARD(), add it right at the beginning of the function. > * @errp can then be used without worrying about the argument being > * NULL or &error_fatal. > > #define ERRP_GUARD() \ > g_auto(ErrorPropagator) _auto_errp_prop =3D {.errp =3D errp}; \ > do { \ > if (!errp || errp =3D=3D &error_fatal) { \ > errp =3D &_auto_errp_prop.local_err; \ > } \ > } while (0) We can make ERRP_GUARD() expand into just a declaration: #define ERRP_GUARD() \ g_auto(ErrorPropagator) _auto_errp_prop =3D { \ .errp =3D errp, \ .local_err =3D ((!errp || errp =3D=3D &error_fatal \ ? errp =3D &_auto_errp_prop.local_err \ : NULL), \ NULL) } > Or commit 5626f8c6d4 ("rcu: Add automatically released rcu_read_lock > variants") with WITH_RCU_READ*: > > util/aio-posix.c:540:5: error: mixing declarations and code is=20 > incompatible with standards before C99=20 > [-Werror,-Wdeclaration-after-statement] > RCU_READ_LOCK_GUARD(); > ^ > include/qemu/rcu.h:189:28: note: expanded from macro 'RCU_READ_LOCK_GUARD' > g_autoptr(RCUReadAuto) _rcu_read_auto __attribute__((unused)) =3D=20 > rcu_read_auto_lock() > ^ Valid example; RCU_READ_LOCK_GUARD() expands into a declaration. To enable -Wdeclaration-after-statement, we'd have to futz around with _Pragma.