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Mon, 21 Oct 2024 09:36:24 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGutK9twdTD9IzG41Qe+bK1s3XPTEO6ajOcTHifNBWq2SKsw0liL4BCffFEnm/joHF1lZ+bEQ== X-Received: by 2002:a05:600c:4f09:b0:42c:c28c:e477 with SMTP id 5b1f17b1804b1-43161697686mr96761325e9.23.1729528583499; Mon, 21 Oct 2024 09:36:23 -0700 (PDT) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: Manos Pitsidianakis , Junjie Mao Subject: [PATCH v2 12/13] rust: provide safe wrapper for MaybeUninit::zeroed() Date: Mon, 21 Oct 2024 18:35:37 +0200 Message-ID: <20241021163538.136941-13-pbonzini@redhat.com> X-Mailer: git-send-email 2.46.2 In-Reply-To: <20241021163538.136941-1-pbonzini@redhat.com> References: <20241021163538.136941-1-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=-0.421, 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: 1729528744303116600 Content-Type: text/plain; charset="utf-8" MaybeUninit::zeroed() is handy, but it introduces unsafe (and has a pretty heavy syntax in general). Introduce a trait that provides the same functionality while staying within safe Rust. In addition, MaybeUninit::zeroed() is not available as a "const" function until Rust 1.75.0, so this also prepares for having handwritten implementations of the trait until we can assume that version. Reviewed-by: Junjie Mao Signed-off-by: Paolo Bonzini --- rust/hw/char/pl011/src/device_class.rs | 8 ++++++-- rust/hw/char/pl011/src/memory_ops.rs | 11 +++++++---- rust/qemu-api/meson.build | 1 + rust/qemu-api/src/device_class.rs | 8 ++++---- rust/qemu-api/src/lib.rs | 1 + rust/qemu-api/src/zeroable.rs | 23 +++++++++++++++++++++++ 6 files changed, 42 insertions(+), 10 deletions(-) create mode 100644 rust/qemu-api/src/zeroable.rs diff --git a/rust/hw/char/pl011/src/device_class.rs b/rust/hw/char/pl011/sr= c/device_class.rs index 2ad80451e87..78fa1cdd5b6 100644 --- a/rust/hw/char/pl011/src/device_class.rs +++ b/rust/hw/char/pl011/src/device_class.rs @@ -4,7 +4,11 @@ =20 use core::ptr::NonNull; =20 -use qemu_api::{bindings::*, definitions::ObjectImpl}; +use qemu_api::{ + bindings::*, + definitions::ObjectImpl, + zeroable::Zeroable, +}; =20 use crate::device::PL011State; =20 @@ -12,7 +16,7 @@ pub static VMSTATE_PL011: VMStateDescription =3D VMStateDescription { name: PL011State::TYPE_INFO.name, unmigratable: true, - ..unsafe { ::core::mem::MaybeUninit::::zeroed().as= sume_init() } + ..Zeroable::ZERO }; =20 qemu_api::declare_properties! { diff --git a/rust/hw/char/pl011/src/memory_ops.rs b/rust/hw/char/pl011/src/= memory_ops.rs index 5a5320e66c3..24ac9c870c1 100644 --- a/rust/hw/char/pl011/src/memory_ops.rs +++ b/rust/hw/char/pl011/src/memory_ops.rs @@ -2,9 +2,12 @@ // Author(s): Manos Pitsidianakis // SPDX-License-Identifier: GPL-2.0-or-later =20 -use core::{mem::MaybeUninit, ptr::NonNull}; +use core::ptr::NonNull; =20 -use qemu_api::bindings::*; +use qemu_api::{ + bindings::*, + zeroable::Zeroable +}; =20 use crate::device::PL011State; =20 @@ -14,11 +17,11 @@ read_with_attrs: None, write_with_attrs: None, endianness: device_endian::DEVICE_NATIVE_ENDIAN, - valid: unsafe { MaybeUninit::::zeroed()= .assume_init() }, + valid: Zeroable::ZERO, impl_: MemoryRegionOps__bindgen_ty_2 { min_access_size: 4, max_access_size: 4, - ..unsafe { MaybeUninit::::zeroed().= assume_init() } + ..Zeroable::ZERO }, }; =20 diff --git a/rust/qemu-api/meson.build b/rust/qemu-api/meson.build index 1fc36078027..1b0fd406378 100644 --- a/rust/qemu-api/meson.build +++ b/rust/qemu-api/meson.build @@ -5,6 +5,7 @@ _qemu_api_rs =3D static_library( 'src/lib.rs', 'src/definitions.rs', 'src/device_class.rs', + 'src/zeroable.rs', ], {'.' : bindings_rs}, ), diff --git a/rust/qemu-api/src/device_class.rs b/rust/qemu-api/src/device_c= lass.rs index d885f2fcf19..ed2d7ce1a54 100644 --- a/rust/qemu-api/src/device_class.rs +++ b/rust/qemu-api/src/device_class.rs @@ -31,7 +31,7 @@ macro_rules! define_property { offset: ::core::mem::offset_of!($state, $field) as isize, set_default: true, defval: $crate::bindings::Property__bindgen_ty_1 { u: $defval.= into() }, - ..unsafe { ::core::mem::MaybeUninit::<$crate::bindings::Proper= ty>::zeroed().assume_init() } + ..$crate::zeroable::Zeroable::ZERO } }; ($name:expr, $state:ty, $field:expr, $prop:expr, $type:expr$(,)*) =3D>= { @@ -41,7 +41,7 @@ macro_rules! define_property { info: $prop, offset: ::core::mem::offset_of!($state, $field) as isize, set_default: false, - ..unsafe { ::core::mem::MaybeUninit::<$crate::bindings::Proper= ty>::zeroed().assume_init() } + ..$crate::zeroable::Zeroable::ZERO } }; } @@ -58,7 +58,7 @@ macro_rules! declare_properties { len }] =3D [ $($prop),*, - unsafe { ::core::mem::MaybeUninit::<$crate::bindings::Property= >::zeroed().assume_init() }, + $crate::zeroable::Zeroable::ZERO, ]; }; } @@ -79,7 +79,7 @@ macro_rules! vm_state_description { $vname.as_ptr() },)* unmigratable: true, - ..unsafe { ::core::mem::MaybeUninit::<$crate::bindings::VMStat= eDescription>::zeroed().assume_init() } + ..$crate::zeroable::Zeroable::ZERO }; } } diff --git a/rust/qemu-api/src/lib.rs b/rust/qemu-api/src/lib.rs index 6bc68076aae..e94a15bb823 100644 --- a/rust/qemu-api/src/lib.rs +++ b/rust/qemu-api/src/lib.rs @@ -29,6 +29,7 @@ unsafe impl Sync for bindings::VMStateDescription {} =20 pub mod definitions; pub mod device_class; +pub mod zeroable; =20 use std::alloc::{GlobalAlloc, Layout}; =20 diff --git a/rust/qemu-api/src/zeroable.rs b/rust/qemu-api/src/zeroable.rs new file mode 100644 index 00000000000..45ec95c9f70 --- /dev/null +++ b/rust/qemu-api/src/zeroable.rs @@ -0,0 +1,23 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +/// Encapsulates the requirement that +/// `MaybeUninit::::zeroed().assume_init()` does not cause +/// undefined behavior. +/// +/// # 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<>`. +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() }; +} + +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 {} --=20 2.46.2