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 C8BC5EC1E81 for ; Thu, 5 Feb 2026 09:30:27 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vnvgY-0000w6-SK; Thu, 05 Feb 2026 04:30:02 -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 1vnvgW-0000vQ-UA for qemu-devel@nongnu.org; Thu, 05 Feb 2026 04:30:00 -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 1vnvgV-0000lQ-5s for qemu-devel@nongnu.org; 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Thu, 5 Feb 2026 09:29:53 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.22]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4FE21192C7C3; Thu, 5 Feb 2026 09:29:53 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id D6E3D21E692D; Thu, 05 Feb 2026 10:29:50 +0100 (CET) From: Markus Armbruster To: Pierrick Bouvier Cc: qemu-devel@nongnu.org, Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , richard.henderson@linaro.org Subject: Re: [PATCH] target-info: set target_arch statically In-Reply-To: <20260203194113.3026757-1-pierrick.bouvier@linaro.org> (Pierrick Bouvier's message of "Tue, 3 Feb 2026 11:41:13 -0800") References: <20260203194113.3026757-1-pierrick.bouvier@linaro.org> Date: Thu, 05 Feb 2026 10:29:50 +0100 Message-ID: <878qd735dd.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 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: -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_H2=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=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-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 Pierrick Bouvier writes: > target_arch() function will reparse target_name() every time if it was > not set to a proper SYS_EMU_TARGET_* value (when using > target-info-stub.c), which is not efficient. > > Since we want to preserve the constness of TargetInfo but C doesn't give > us flexible compile time expressions, we simply set target_arch using a > static constructor once instead. > > This was found when doing changes to virtio_access_is_big_endian() > function, having an overhead of 50% after switching to runtime checks. > With this, overhead left is around 3%, due to indirect function > calls. > > Signed-off-by: Pierrick Bouvier > --- > target-info-stub.c | 11 ++++++++++- > target-info.c | 9 +-------- > 2 files changed, 11 insertions(+), 9 deletions(-) > > diff --git a/target-info-stub.c b/target-info-stub.c > index 8392d81e8f8..ff86a02247a 100644 > --- a/target-info-stub.c > +++ b/target-info-stub.c > @@ -10,13 +10,14 @@ > #include "qemu/target-info.h" > #include "qemu/target-info-impl.h" > #include "hw/core/boards.h" > +#include "qapi/error.h" > #include "cpu.h" > > /* Validate correct placement of CPUArchState. */ > QEMU_BUILD_BUG_ON(offsetof(ArchCPU, parent_obj) != 0); > QEMU_BUILD_BUG_ON(offsetof(ArchCPU, env) != sizeof(CPUState)); > > -static const TargetInfo target_info_stub = { > +static TargetInfo target_info_stub = { > .target_name = TARGET_NAME, > .target_arch = SYS_EMU_TARGET__MAX, > .long_bits = TARGET_LONG_BITS, > @@ -29,3 +30,11 @@ const TargetInfo *target_info(void) > { > return &target_info_stub; > } > + > +__attribute__((constructor)) > +static void init_target_arch(void) > +{ > + target_info_stub.target_arch = qapi_enum_parse(&SysEmuTarget_lookup, > + target_name(), -1, > + &error_abort); > +} This is slightly unclean. Constructors run before main(). If qapi_enum_parse(..., &error_abort) fails here, error_handle() will report the unexpected error with error_report() before main() calls error_init(). See also From: Markus Armbruster Subject: Re: [PATCH v3 02/20] monitor: initialize global data from a constructor Date: Thu, 18 Sep 2025 08:30:23 +0200 Message-ID: <87frck1dds.fsf@pond.sub.org> Observation, not objection. > diff --git a/target-info.c b/target-info.c > index 24696ff4111..c3c0856d01a 100644 > --- a/target-info.c > +++ b/target-info.c > @@ -10,7 +10,6 @@ > #include "qemu/target-info.h" > #include "qemu/target-info-qapi.h" > #include "qemu/target-info-impl.h" > -#include "qapi/error.h" > > const char *target_name(void) > { > @@ -24,13 +23,7 @@ unsigned target_long_bits(void) > > SysEmuTarget target_arch(void) > { > - SysEmuTarget arch = target_info()->target_arch; > - > - if (arch == SYS_EMU_TARGET__MAX) { > - arch = qapi_enum_parse(&SysEmuTarget_lookup, target_name(), -1, > - &error_abort); > - } > - return arch; > + return target_info()->target_arch; > } > > const char *target_cpu_type(void)