Messages in this thread Patch in this message | | | Date | Tue, 4 Apr 2023 14:24:15 +0100 | From | Gary Guo <> | Subject | Re: [PATCH v5 11/15] rust: init: add `Zeroable` trait and `init::zeroed` function |
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On Mon, 03 Apr 2023 16:05:40 +0000 Benno Lossin <y86-dev@protonmail.com> wrote:
> Add the `Zeroable` trait which marks types that can be initialized by > writing `0x00` to every byte of the type. Also add the `init::zeroed` > function that creates an initializer for a `Zeroable` type that writes > `0x00` to every byte. > > Signed-off-by: Benno Lossin <y86-dev@protonmail.com> > Cc: Gary Guo <gary@garyguo.net> > Cc: Alice Ryhl <aliceryhl@google.com> > Cc: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
> --- > rust/kernel/init.rs | 94 ++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 92 insertions(+), 2 deletions(-) > > diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs > index 1343cafdd760..09bba4e86ace 100644 > --- a/rust/kernel/init.rs > +++ b/rust/kernel/init.rs > @@ -195,8 +195,14 @@ use crate::{ > }; > use alloc::boxed::Box; > use core::{ > - alloc::AllocError, cell::Cell, convert::Infallible, marker::PhantomData, mem::MaybeUninit, > - pin::Pin, ptr, > + alloc::AllocError, > + cell::Cell, > + convert::Infallible, > + marker::PhantomData, > + mem::MaybeUninit, > + num::*, > + pin::Pin, > + ptr::{self, NonNull}, > }; > > #[doc(hidden)] > @@ -1329,3 +1335,87 @@ pub unsafe trait PinnedDrop: __internal::HasPinData { > /// automatically. > fn drop(self: Pin<&mut Self>, only_call_from_drop: __internal::OnlyCallFromDrop); > } > + > +/// Marker trait for types that can be initialized by writing just zeroes. > +/// > +/// # Safety > +/// > +/// The bit pattern consisting of only zeroes is a valid bit pattern for this type. In other words, > +/// this is not UB: > +/// > +/// ```rust,ignore > +/// let val: Self = unsafe { core::mem::zeroed() }; > +/// ``` > +pub unsafe trait Zeroable {} > + > +/// Create a new zeroed T. > +/// > +/// The returned initializer will write `0x00` to every byte of the given `slot`. > +#[inline] > +pub fn zeroed<T: Zeroable + Unpin>() -> impl Init<T> { > + // SAFETY: Because `T: Zeroable`, all bytes zero is a valid bit pattern for `T` > + // and because we write all zeroes, the memory is initialized. > + unsafe { > + init_from_closure(|slot: *mut T| { > + slot.write_bytes(0, 1); > + Ok(()) > + }) > + } > +} > + > +macro_rules! impl_zeroable { > + ($($({$($generics:tt)*})? $t:ty, )*) => { > + $(unsafe impl$($($generics)*)? Zeroable for $t {})* > + }; > +} > + > +impl_zeroable! { > + // SAFETY: All primitives that are allowed to be zero. > + bool, > + char, > + u8, u16, u32, u64, u128, usize, > + i8, i16, i32, i64, i128, isize, > + f32, f64, > + > + // SAFETY: These are ZSTs, there is nothing to zero. > + {<T: ?Sized>} PhantomData<T>, core::marker::PhantomPinned, Infallible, (), > + > + // SAFETY: Type is allowed to take any value, including all zeros. > + {<T>} MaybeUninit<T>, > + > + // SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee). > + Option<NonZeroU8>, Option<NonZeroU16>, Option<NonZeroU32>, Option<NonZeroU64>, > + Option<NonZeroU128>, Option<NonZeroUsize>, > + Option<NonZeroI8>, Option<NonZeroI16>, Option<NonZeroI32>, Option<NonZeroI64>, > + Option<NonZeroI128>, Option<NonZeroIsize>, > + > + // SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee). > + // > + // In this case we are allowed to use `T: ?Sized`, since all zeros is the `None` variant. > + {<T: ?Sized>} Option<NonNull<T>>, > + {<T: ?Sized>} Option<Box<T>>, > + > + // SAFETY: `null` pointer is valid. > + // > + // We cannot use `T: ?Sized`, since the VTABLE pointer part of fat pointers is not allowed to be > + // null. > + {<T>} *mut T, {<T>} *const T, > + > + // SAFETY: `null` pointer is valid and the metadata part of these fat pointers is allowed to be > + // zero. > + {<T>} *mut [T], {<T>} *const [T], *mut str, *const str,
Just a note: if `Pointee` trait is stabilised, this could be changed to
impl<T: ?Sized> Zeroable for *const T where <T as Pointee>::Metadata: Zeroable {}
> + > + // SAFETY: `T` is `Zeroable`. > + {<const N: usize, T: Zeroable>} [T; N], {<T: Zeroable>} Wrapping<T>, > +} > + > +macro_rules! impl_tuple_zeroable { > + ($(,)?) => {}; > + ($first:ident, $($t:ident),* $(,)?) => { > + // SAFETY: All elements are zeroable and padding can be zero. > + unsafe impl<$first: Zeroable, $($t: Zeroable),*> Zeroable for ($first, $($t),*) {} > + impl_tuple_zeroable!($($t),* ,); > + } > +} > + > +impl_tuple_zeroable!(A, B, C, D, E, F, G, H, I, J); > -- > 2.39.2 >
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