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 <junjie.mao@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
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/src/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 @@
use core::ptr::NonNull;
-use qemu_api::{bindings::*, definitions::ObjectImpl};
+use qemu_api::{
+ bindings::*,
+ definitions::ObjectImpl,
+ zeroable::Zeroable,
+};
use crate::device::PL011State;
@@ -12,7 +16,7 @@
pub static VMSTATE_PL011: VMStateDescription = VMStateDescription {
name: PL011State::TYPE_INFO.name,
unmigratable: true,
- ..unsafe { ::core::mem::MaybeUninit::<VMStateDescription>::zeroed().assume_init() }
+ ..Zeroable::ZERO
};
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 <manos.pitsidianakis@linaro.org>
// SPDX-License-Identifier: GPL-2.0-or-later
-use core::{mem::MaybeUninit, ptr::NonNull};
+use core::ptr::NonNull;
-use qemu_api::bindings::*;
+use qemu_api::{
+ bindings::*,
+ zeroable::Zeroable
+};
use crate::device::PL011State;
@@ -14,11 +17,11 @@
read_with_attrs: None,
write_with_attrs: None,
endianness: device_endian::DEVICE_NATIVE_ENDIAN,
- valid: unsafe { MaybeUninit::<MemoryRegionOps__bindgen_ty_1>::zeroed().assume_init() },
+ valid: Zeroable::ZERO,
impl_: MemoryRegionOps__bindgen_ty_2 {
min_access_size: 4,
max_access_size: 4,
- ..unsafe { MaybeUninit::<MemoryRegionOps__bindgen_ty_2>::zeroed().assume_init() }
+ ..Zeroable::ZERO
},
};
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 = 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_class.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::Property>::zeroed().assume_init() }
+ ..$crate::zeroable::Zeroable::ZERO
}
};
($name:expr, $state:ty, $field:expr, $prop:expr, $type:expr$(,)*) => {
@@ -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::Property>::zeroed().assume_init() }
+ ..$crate::zeroable::Zeroable::ZERO
}
};
}
@@ -58,7 +58,7 @@ macro_rules! declare_properties {
len
}] = [
$($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::VMStateDescription>::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 {}
pub mod definitions;
pub mod device_class;
+pub mod zeroable;
use std::alloc::{GlobalAlloc, Layout};
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::<Self>::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<T>` 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 = unsafe { ::core::mem::MaybeUninit::<Self>::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 {}
--
2.46.2