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Fri, 25 Oct 2024 09:04:16 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGXy8L7yHeeXU1+w6XKn+whHOxFUNpZvJl/XFf2YkNAfAUz7/57mtu9FzHvuOujom4wD7U/xg== X-Received: by 2002:a05:6402:13d3:b0:5ca:e5b:bbdb with SMTP id 4fb4d7f45d1cf-5cb8acb7b16mr7338506a12.18.1729872255524; Fri, 25 Oct 2024 09:04:15 -0700 (PDT) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: manos.pitsidianakis@linaro.org, zhao1.liu@intel.com, junjie.mao@hotmail.com, berrange@redhat.com Subject: [PATCH 16/23] rust: do not use MaybeUninit::zeroed() Date: Fri, 25 Oct 2024 18:02:01 +0200 Message-ID: <20241025160209.194307-17-pbonzini@redhat.com> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241025160209.194307-1-pbonzini@redhat.com> References: <20241025160209.194307-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.454, 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_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1729872596110116600 Content-Type: text/plain; charset="utf-8" MaybeUninit::zeroed() is handy but is not available as a "const" function until Rust 1.75.0. Remove the default implementation of Zeroable::ZERO, and write by hand the definitions for those types that need it. It may be possible to add automatic implementation of the trait, via a procedural macro and/or a trick similar to offset_of!, but do it the easy way for now. Signed-off-by: Paolo Bonzini --- rust/qemu-api/src/zeroable.rs | 91 +++++++++++++++++++++++++++++------ 1 file changed, 77 insertions(+), 14 deletions(-) diff --git a/rust/qemu-api/src/zeroable.rs b/rust/qemu-api/src/zeroable.rs index 45ec95c9f70..13cdb2ccba5 100644 --- a/rust/qemu-api/src/zeroable.rs +++ b/rust/qemu-api/src/zeroable.rs @@ -1,23 +1,86 @@ // SPDX-License-Identifier: GPL-2.0-or-later =20 +use std::ptr; + /// Encapsulates the requirement that -/// `MaybeUninit::::zeroed().assume_init()` does not cause -/// undefined behavior. +/// `MaybeUninit::::zeroed().assume_init()` does not cause undefined +/// behavior. This trait in principle could be implemented as just: +/// +/// ``` +/// const ZERO: Self =3D unsafe { +/// ::core::mem::MaybeUninit::<$crate::bindings::Property>::zeroed= ().assume_init() +/// }, +/// ``` +/// +/// The need for a manual implementation is only because `zeroed()` cannot +/// be used as a `const fn` prior to Rust 1.75.0. Once we can assume a new +/// enough version of the compiler, we could provide a `#[derive(Zeroable)= ]` +/// macro to check at compile-time that all struct fields are Zeroable, and +/// use the above blanket implementation of the `ZERO` constant. /// /// # Safety /// -/// Do not add this trait to a type unless all-zeroes is -/// a valid value for the type. In particular, remember that raw -/// pointers can be zero, but references and `NonNull` cannot -/// unless wrapped with `Option<>`. +/// Because the implementation of `ZERO` is manual, it does not make +/// any assumption on the safety of `zeroed()`. However, other users of t= he +/// trait could use it that way. Do not add this trait to a type unless +/// all-zeroes is a valid value for the type. In particular, remember that +/// raw pointers can be zero, but references and `NonNull` cannot pub unsafe trait Zeroable: Default { - /// SAFETY: If the trait was added to a type, then by definition - /// this is safe. - const ZERO: Self =3D unsafe { ::core::mem::MaybeUninit::::zeroed= ().assume_init() }; + const ZERO: Self; } =20 -unsafe impl Zeroable for crate::bindings::Property__bindgen_ty_1 {} -unsafe impl Zeroable for crate::bindings::Property {} -unsafe impl Zeroable for crate::bindings::VMStateDescription {} -unsafe impl Zeroable for crate::bindings::MemoryRegionOps__bindgen_ty_1 {} -unsafe impl Zeroable for crate::bindings::MemoryRegionOps__bindgen_ty_2 {} +unsafe impl Zeroable for crate::bindings::Property__bindgen_ty_1 { + const ZERO: Self =3D Self { i: 0 }; +} + +unsafe impl Zeroable for crate::bindings::Property { + const ZERO: Self =3D Self { + name: ptr::null(), + info: ptr::null(), + offset: 0, + bitnr: 0, + bitmask: 0, + set_default: false, + defval: Zeroable::ZERO, + arrayoffset: 0, + arrayinfo: ptr::null(), + arrayfieldsize: 0, + link_type: ptr::null(), + }; +} + +unsafe impl Zeroable for crate::bindings::VMStateDescription { + const ZERO: Self =3D Self { + name: ptr::null(), + unmigratable: false, + early_setup: false, + version_id: 0, + minimum_version_id: 0, + priority: crate::bindings::MigrationPriority::MIG_PRI_DEFAULT, + pre_load: None, + post_load: None, + pre_save: None, + post_save: None, + needed: None, + dev_unplug_pending: None, + fields: ptr::null(), + subsections: ptr::null(), + }; +} + +unsafe impl Zeroable for crate::bindings::MemoryRegionOps__bindgen_ty_1 { + const ZERO: Self =3D Self { + min_access_size: 0, + max_access_size: 0, + unaligned: false, + accepts: None, + }; +} + +unsafe impl Zeroable for crate::bindings::MemoryRegionOps__bindgen_ty_2 { + const ZERO: Self =3D Self { + min_access_size: 0, + max_access_size: 0, + unaligned: false, + }; +} --=20 2.47.0