Reviewed-by: Manos Pitsidianakis <manos.pitsidiana...@linaro.org>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
docs/devel/rust.rst | 4 --
rust/hw/timer/hpet/src/fw_cfg.rs | 6 +-
rust/qemu-api/src/zeroable.rs | 104 +++++--------------------------
3 files changed, 18 insertions(+), 96 deletions(-)
diff --git a/docs/devel/rust.rst b/docs/devel/rust.rst
index 8167ff49aa9..13a002cfe69 100644
--- a/docs/devel/rust.rst
+++ b/docs/devel/rust.rst
@@ -83,10 +83,6 @@ are missing:
* "Return position ``impl Trait`` in Traits" (1.75.0, blocker for including
the pinned-init create).
-* ``MaybeUninit::zeroed()`` as a ``const`` function (1.75.0). QEMU's
- ``Zeroable`` trait can be implemented without ``MaybeUninit::zeroed()``,
- so this would be just a cleanup.
-
* ``c"" literals`` (stable in 1.77.0). QEMU provides a ``c_str!()`` macro
to define ``CStr`` constants easily
diff --git a/rust/hw/timer/hpet/src/fw_cfg.rs b/rust/hw/timer/hpet/src/fw_cfg.rs
index bef03727ea3..aa08d283519 100644
--- a/rust/hw/timer/hpet/src/fw_cfg.rs
+++ b/rust/hw/timer/hpet/src/fw_cfg.rs
@@ -4,7 +4,7 @@
use std::ptr::addr_of_mut;
-use qemu_api::{cell::bql_locked, impl_zeroable, zeroable::Zeroable};
+use qemu_api::{cell::bql_locked, zeroable::Zeroable};
/// Each `HPETState` represents a Event Timer Block. The v1 spec supports
/// up to 8 blocks. QEMU only uses 1 block (in PC machine).
@@ -18,7 +18,7 @@ pub struct HPETFwEntry {
pub min_tick: u16,
pub page_prot: u8,
}
-impl_zeroable!(HPETFwEntry);
+unsafe impl Zeroable for HPETFwEntry {}
#[repr(C, packed)]
#[derive(Copy, Clone, Default)]
@@ -26,7 +26,7 @@ pub struct HPETFwConfig {
pub count: u8,
pub hpet: [HPETFwEntry; HPET_MAX_NUM_EVENT_TIMER_BLOCK],
}
-impl_zeroable!(HPETFwConfig);
+unsafe impl Zeroable for HPETFwConfig {}
#[allow(non_upper_case_globals)]
#[no_mangle]
diff --git a/rust/qemu-api/src/zeroable.rs b/rust/qemu-api/src/zeroable.rs
index a3415a2ebcc..e0720345495 100644
--- a/rust/qemu-api/src/zeroable.rs
+++ b/rust/qemu-api/src/zeroable.rs
@@ -4,89 +4,15 @@
/// Encapsulates the requirement that
/// `MaybeUninit::<Self>::zeroed().assume_init()` does not cause undefined
-/// behavior. This trait in principle could be implemented as just:
-///
-/// ```
-/// pub unsafe trait Zeroable: Default {
-/// const ZERO: Self = unsafe {
::core::mem::MaybeUninit::<Self>::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.
+/// behavior.
///
/// # Safety
///
-/// Because the implementation of `ZERO` is manual, it does not make
-/// any assumption on the safety of `zeroed()`. However, other users of the
-/// 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<T>` cannot
+/// Do not add this trait to a type unless all-zeroes is a valid value for the
+/// type. In particular, raw pointers can be zero, but references and
+/// `NonNull<T>` cannot.
pub unsafe trait Zeroable: Default {
- const ZERO: Self;
-}
-
-/// A macro that acts similarly to [`core::mem::zeroed()`], only is const
-///
-/// ## Safety
-///
-/// Similar to `core::mem::zeroed()`, except this zeroes padding bits. Zeroed
-/// padding usually isn't relevant to safety, but might be if a C union is
used.
-///
-/// Just like for `core::mem::zeroed()`, an all zero byte pattern might not
-/// be a valid value for a type, as is the case for references `&T` and `&mut
-/// T`. Reference types trigger a (denied by default) lint and cause immediate
-/// undefined behavior if the lint is ignored
-///
-/// ```rust compile_fail
-/// use const_zero::const_zero;
-/// // error: any use of this value will cause an error
-/// // note: `#[deny(const_err)]` on by default
-/// const STR: &str = unsafe{const_zero!(&'static str)};
-/// ```
-///
-/// `const_zero` does not work on unsized types:
-///
-/// ```rust compile_fail
-/// use const_zero::const_zero;
-/// // error[E0277]: the size for values of type `[u8]` cannot be known at
compilation time
-/// const BYTES: [u8] = unsafe{const_zero!([u8])};
-/// ```
-/// ## Differences with `core::mem::zeroed`
-///
-/// `const_zero` zeroes padding bits, while `core::mem::zeroed` doesn't
-#[macro_export]
-macro_rules! const_zero {
- // This macro to produce a type-generic zero constant is taken from the
- // const_zero crate (v0.1.1):
- //
- // https://docs.rs/const-zero/latest/src/const_zero/lib.rs.html
- //
- // and used under MIT license
- ($type_:ty) => {{
- const TYPE_SIZE: ::core::primitive::usize =
::core::mem::size_of::<$type_>();
- union TypeAsBytes {
- bytes: [::core::primitive::u8; TYPE_SIZE],
- inner: ::core::mem::ManuallyDrop<$type_>,
- }
- const ZERO_BYTES: TypeAsBytes = TypeAsBytes {
- bytes: [0; TYPE_SIZE],
- };
- ::core::mem::ManuallyDrop::<$type_>::into_inner(ZERO_BYTES.inner)
- }};
-}
-
-/// A wrapper to implement the `Zeroable` trait through the `const_zero` macro.
-#[macro_export]
-macro_rules! impl_zeroable {
- ($type:ty) => {
- unsafe impl $crate::zeroable::Zeroable for $type {
- const ZERO: Self = unsafe { $crate::const_zero!($type) };
- }
- };
+ const ZERO: Self = unsafe {
::core::mem::MaybeUninit::<Self>::zeroed().assume_init() };
}
// bindgen does not derive Default here
@@ -97,13 +23,13 @@ fn default() -> Self {
}
}
-impl_zeroable!(crate::bindings::Property__bindgen_ty_1);
-impl_zeroable!(crate::bindings::Property);
-impl_zeroable!(crate::bindings::VMStateFlags);
-impl_zeroable!(crate::bindings::VMStateField);
-impl_zeroable!(crate::bindings::VMStateDescription);
-impl_zeroable!(crate::bindings::MemoryRegionOps__bindgen_ty_1);
-impl_zeroable!(crate::bindings::MemoryRegionOps__bindgen_ty_2);
-impl_zeroable!(crate::bindings::MemoryRegionOps);
-impl_zeroable!(crate::bindings::MemTxAttrs);
-impl_zeroable!(crate::bindings::CharBackend);
+unsafe impl Zeroable for crate::bindings::Property__bindgen_ty_1 {}
+unsafe impl Zeroable for crate::bindings::Property {}
+unsafe impl Zeroable for crate::bindings::VMStateFlags {}
+unsafe impl Zeroable for crate::bindings::VMStateField {}
+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::MemoryRegionOps {}
+unsafe impl Zeroable for crate::bindings::MemTxAttrs {}
+unsafe impl Zeroable for crate::bindings::CharBackend {}
--
2.49.0
