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Message-ID: <20250330234039.29814-2-christiansantoslima21@gmail.com>
Date: Sun, 30 Mar 2025 20:40:16 -0300
From: "Christian S. Lima" <christiansantoslima21@...il.com>
To: rust-for-linux@...r.kernel.org,
linux-kernel@...r.kernel.org,
Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Boqun Feng <boqun.feng@...il.com>,
Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
Andreas Hindborg <a.hindborg@...nel.org>,
Alice Ryhl <aliceryhl@...gle.com>,
Trevor Gross <tmgross@...ch.edu>,
Danilo Krummrich <dakr@...nel.org>,
~lkcamp/patches@...ts.sr.ht,
richard120310@...il.com
Subject: [PATCH] rust: transmute: Add methods for FromBytes trait
Methods receive a slice and perform size check to add a valid way to make
conversion safe. An Option is used, in error case just return `None`.
The conversion between slices `[T]` is separated from others, because I
couldn't implement it in the same way as the other conversions.
Link: https://github.com/Rust-for-Linux/linux/issues/1119
Signed-off-by: Christian S. Lima <christiansantoslima21@...il.com>
---
Changes in v2:
- Rollback the implementation for the macro in the repository and implement
methods in trait
- Link to v2: https://lore.kernel.org/rust-for-linux/20241012193657.290cc79c@eugeo/T/#t
Changes in v3:
- Fix grammar errors
- Remove repeated tests
- Fix alignment errors
- Fix tests not building
- Link to v3: https://lore.kernel.org/rust-for-linux/20241109055442.85190-1-christiansantoslima21@gmail.com/
Changes in v4:
- Removed core::simd::ToBytes
- Changed trait and methods to safe Add
- Result<&Self, Error> in order to make safe methods
- Link to v4: https://lore.kernel.org/rust-for-linux/20250314034910.134463-1-christiansantoslima21@gmail.com/
Changes in v5:
- Changed from Result to Option
- Removed commentaries
- Returned trait impl to unsafe
- Link to v5: https://lore.kernel.org/rust-for-linux/20250320014041.101470-1-christiansantoslima21@gmail.com/
Changes in v6:
- Add endianess check to doc test and use match to check
success case
- Reformulated safety comments
---
rust/kernel/transmute.rs | 89 +++++++++++++++++++++++++++++++++++++---
1 file changed, 83 insertions(+), 6 deletions(-)
diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs
index 1c7d43771a37..16dfa5c7d467 100644
--- a/rust/kernel/transmute.rs
+++ b/rust/kernel/transmute.rs
@@ -9,29 +9,106 @@
///
/// It's okay for the type to have padding, as initializing those bytes has no effect.
///
+/// # Example
+/// ```
+/// let foo = &[1, 2, 3, 4];
+///
+/// let result = u32::from_bytes(foo);
+///
+/// #[cfg(target_endian = "little")]
+/// match result {
+/// Some(x) => assert_eq!(*x, 0x4030201),
+/// None => unreachable!()
+/// }
+///
+/// #[cfg(target_endian = "big")]
+/// match result {
+/// Some(x) => assert_eq!(*x, 0x1020304),
+/// None => unreachable!()
+/// }
+/// ```
+///
/// # Safety
///
/// All bit-patterns must be valid for this type. This type must not have interior mutability.
-pub unsafe trait FromBytes {}
+pub unsafe trait FromBytes {
+ /// Converts a slice of bytes to a reference to `Self` when possible.
+ fn from_bytes(bytes: &[u8]) -> Option<&Self>;
+
+ /// Converts a mutable slice of bytes to a reference to `Self` when possible.
+ fn from_bytes_mut(bytes: &mut [u8]) -> Option<&mut Self>
+ where
+ Self: AsBytes;
+}
macro_rules! impl_frombytes {
($($({$($generics:tt)*})? $t:ty, )*) => {
// SAFETY: Safety comments written in the macro invocation.
- $(unsafe impl$($($generics)*)? FromBytes for $t {})*
+ $(unsafe impl$($($generics)*)? FromBytes for $t {
+ fn from_bytes(bytes: &[u8]) -> Option<&$t> {
+ if bytes.len() == core::mem::size_of::<$t>() {
+ let slice_ptr = bytes.as_ptr().cast::<$t>();
+ unsafe { Some(&*slice_ptr) }
+ } else {
+ None
+ }
+ }
+
+ fn from_bytes_mut(bytes: &mut [u8]) -> Option<&mut $t>
+ where
+ Self: AsBytes,
+ {
+ if bytes.len() == core::mem::size_of::<$t>() {
+ let slice_ptr = bytes.as_mut_ptr().cast::<$t>();
+ unsafe { Some(&mut *slice_ptr) }
+ } else {
+ None
+ }
+ }
+ })*
};
}
impl_frombytes! {
// SAFETY: All bit patterns are acceptable values of the types below.
+ // Checking the pointer size makes this operation safe and it's necessary
+ // to dereference to get the value and return it as a reference to `Self`.
u8, u16, u32, u64, usize,
i8, i16, i32, i64, isize,
-
- // SAFETY: If all bit patterns are acceptable for individual values in an array, then all bit
- // patterns are also acceptable for arrays of that type.
- {<T: FromBytes>} [T],
{<T: FromBytes, const N: usize>} [T; N],
}
+// SAFETY: If all bit patterns are acceptable for individual values in an array, then all bit
+// patterns are also acceptable for arrays of that type.
+unsafe impl<T: FromBytes> FromBytes for [T] {
+ fn from_bytes(bytes: &[u8]) -> Option<&Self> {
+ let slice_ptr = bytes.as_ptr().cast::<T>();
+ if bytes.len() % core::mem::size_of::<T>() == 0 {
+ let slice_len = bytes.len() / core::mem::size_of::<T>();
+ // SAFETY: Since the code checks the size and can be divided into blocks of size T
+ // the slice is valid because the size is multiple of T.
+ unsafe { Some(core::slice::from_raw_parts(slice_ptr, slice_len)) }
+ } else {
+ None
+ }
+ }
+
+ fn from_bytes_mut(bytes: &mut [u8]) -> Option<&mut Self>
+ where
+ Self: AsBytes,
+ {
+ let slice_ptr = bytes.as_mut_ptr().cast::<T>();
+ if bytes.len() % core::mem::size_of::<T>() == 0 {
+ let slice_len = bytes.len() / core::mem::size_of::<T>();
+ // SAFETY: Since the code checks the size and can be divided into blocks of size T
+ // the slice is valid because the size is multiple of T.
+ unsafe { Some(core::slice::from_raw_parts_mut(slice_ptr, slice_len)) }
+ } else {
+ None
+ }
+ }
+}
+
/// Types that can be viewed as an immutable slice of initialized bytes.
///
/// If a struct implements this trait, then it is okay to copy it byte-for-byte to userspace. This
--
2.49.0
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