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dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58390 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kIHQe-00057C-6B for qemu-devel@archiver.kernel.org; Tue, 15 Sep 2020 16:19:52 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59566) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kIHPx-0004Zf-0R for qemu-devel@nongnu.org; Tue, 15 Sep 2020 16:19:09 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:55916) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kIHPu-00025i-DX for qemu-devel@nongnu.org; Tue, 15 Sep 2020 16:19:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600201145; 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=ytrKaJFGUbf39bPtEOpShZGZpXzbAoR/g9V7Ygb4Krw=; b=Bk6THXpryPVtc4ZZZRajrrJd7JyVVKQUeY/omQmjm1Y+4mRp1JfC6wHxB7IxJQnfv3ws9E /JAHtwYEMxTJAwS2TWivChsD0HCdBIXeYFmSvoFFUzn3IDznZPVZre4dJjwcWNJdXiB8AF zw+4jbXoH4SIUTngIHwc+LsGVSzRnNY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-69-uKnMl-IAPbyadTk7rXnA2g-1; Tue, 15 Sep 2020 16:19:03 -0400 X-MC-Unique: uKnMl-IAPbyadTk7rXnA2g-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 763746409A; Tue, 15 Sep 2020 20:19:02 +0000 (UTC) Received: from localhost (ovpn-119-217.rdu2.redhat.com [10.10.119.217]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3C2365DC08; Tue, 15 Sep 2020 20:19:02 +0000 (UTC) Date: Tue, 15 Sep 2020 16:19:01 -0400 From: Eduardo Habkost To: Richard Henderson Subject: Re: [PATCH 1/5] qom: Allow objects to be allocated with increased alignment Message-ID: <20200915201901.GD7594@habkost.net> References: <20200915174635.2333553-1-richard.henderson@linaro.org> <20200915174635.2333553-2-richard.henderson@linaro.org> <20200915180736.GB7594@habkost.net> <6d6a80bf-a542-6818-1638-0318f4aab336@linaro.org> MIME-Version: 1.0 In-Reply-To: <6d6a80bf-a542-6818-1638-0318f4aab336@linaro.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=ehabkost@redhat.com X-Mimecast-Spam-Score: 0.003 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=ehabkost@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/15 02:10:32 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -50 X-Spam_score: -5.1 X-Spam_bar: ----- X-Spam_report: (-5.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.999, 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_HELO_NONE=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Sep 15, 2020 at 12:09:59PM -0700, Richard Henderson wrote: > On 9/15/20 11:07 AM, Eduardo Habkost wrote: > > On Tue, Sep 15, 2020 at 10:46:31AM -0700, Richard Henderson wrote: > >> It turns out that some hosts have a default malloc alignment less > >> than that required for vectors. > >> > >> We assume that, with compiler annotation on CPUArchState, that we > >> can properly align the vector portion of the guest state. Fix the > >> alignment of the allocation by using qemu_memalloc when required. > >> > >> Signed-off-by: Richard Henderson > >> --- > >> Cc: Paolo Bonzini > >> Cc: "Daniel P. Berrangé" > >> Cc: Eduardo Habkost > >> --- > >> include/qom/object.h | 4 ++++ > >> qom/object.c | 16 +++++++++++++--- > >> 2 files changed, 17 insertions(+), 3 deletions(-) > >> > >> diff --git a/include/qom/object.h b/include/qom/object.h > >> index 056f67ab3b..d52d0781a3 100644 > >> --- a/include/qom/object.h > >> +++ b/include/qom/object.h > >> @@ -770,6 +770,9 @@ struct Object > >> * @instance_size: The size of the object (derivative of #Object). If > >> * @instance_size is 0, then the size of the object will be the size of the > >> * parent object. > >> + * @instance_align: The required alignment of the object. If @instance_align > >> + * is 0, then normal malloc alignment is sufficient; if non-zero, then we > >> + * must use qemu_memalign for allocation. > >> * @instance_init: This function is called to initialize an object. The parent > >> * class will have already been initialized so the type is only responsible > >> * for initializing its own members. > >> @@ -807,6 +810,7 @@ struct TypeInfo > >> const char *parent; > >> > >> size_t instance_size; > >> + size_t instance_align; > >> void (*instance_init)(Object *obj); > >> void (*instance_post_init)(Object *obj); > >> void (*instance_finalize)(Object *obj); > >> diff --git a/qom/object.c b/qom/object.c > >> index 387efb25eb..2e53cb44a6 100644 > >> --- a/qom/object.c > >> +++ b/qom/object.c > >> @@ -50,6 +50,7 @@ struct TypeImpl > >> size_t class_size; > >> > >> size_t instance_size; > >> + size_t instance_align; > >> > >> void (*class_init)(ObjectClass *klass, void *data); > >> void (*class_base_init)(ObjectClass *klass, void *data); > >> @@ -114,6 +115,7 @@ static TypeImpl *type_new(const TypeInfo *info) > >> > >> ti->class_size = info->class_size; > >> ti->instance_size = info->instance_size; > >> + ti->instance_align = info->instance_align; > >> > >> ti->class_init = info->class_init; > >> ti->class_base_init = info->class_base_init; > >> @@ -691,13 +693,21 @@ static void object_finalize(void *data) > >> static Object *object_new_with_type(Type type) > >> { > >> Object *obj; > >> + size_t size, align; > >> > >> g_assert(type != NULL); > >> type_initialize(type); > >> > >> - obj = g_malloc(type->instance_size); > >> - object_initialize_with_type(obj, type->instance_size, type); > >> - obj->free = g_free; > >> + size = type->instance_size; > >> + align = type->instance_align; > >> + if (align) { > > > > If we check for (align > G_MEM_ALIGN) instead, we will be able to > > set instance_align automatically at OBJECT_DEFINE_TYPE*. > > I agree a value check would be good here, as well as setting this by default. > > As for the value check itself... > > I see that G_MEM_ALIGN isn't actually defined in an interesting or even correct > way. E.g. it doesn't take the long double type into account. > > The usual mechanism is > > struct s { > char pad; > union { > long l; > void *p; > double d; > long double ld; > } u; > }; > > offsetof(s, u) > > since all of these types are required to be taken into account by the system > malloc. Due to the existence of G_MEM_ALIGN, I thought GLib alignment guarantees could be weaker than malloc(). I've just learned that GLib uses system malloc() since 2.46. > > E.g it doesn't take other host guarantees into account, e.g. i386-linux > guarantees 16-byte alignment. This possibly dubious ABI change was made 20+ > years ago with the introduction of SSE and is now set in stone. > > Glibc has a "malloc-alignment.h" internal header that defaults to > > MIN(2 * sizeof(size_t), __alignof__(long double)) > > and is overridden for i386. Sadly, it doesn't export MALLOC_ALIGNMENT. > > Musl has two different malloc implementations. One has UNIT = 16; the other > has SIZE_ALIGN = 4*sizeof(size_t). Both have a minimum value of 16, and this > is not target-specific. > > Any further comments on the subject, or should I put together something that > computes the MAX of the above? Once we move to C11, we can just use max_align_t. While we don't move to C11, why not just use __alignof__(union { long l; void *p; double d; long double ld;}) ? -- Eduardo