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rust: transmute: Add implementation for FromBytes trait
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Add implementation and documentation for FromBytes trait.

Add new feature block in order to allow using ToBytes
and bound to from_bytes_mut function.

Link: Rust-for-Linux#1119
Signed-off-by: Christian dos Santos de Lima <[email protected]>
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@Every2 @intel-lab-lkp
Every2 authored and intel-lab-lkp committed Oct 9, 2024
1 parent c9b5ce6 commit 508534f
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2 changes: 2 additions & 0 deletions rust/kernel/lib.rs
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Expand Up @@ -18,6 +18,8 @@
#![feature(lint_reasons)]
#![feature(new_uninit)]
#![feature(unsize)]
#![feature(portable_simd)]
#![feature(trivial_bounds)]

// Ensure conditional compilation based on the kernel configuration works;
// otherwise we may silently break things like initcall handling.
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302 changes: 288 additions & 14 deletions rust/kernel/transmute.rs
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Expand Up @@ -12,24 +12,298 @@
/// # 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 into a Reference to Self
///
/// # Examples
/// ```
/// pub unsafe trait FromBytes {
/// unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self;
/// unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
/// where
/// Self: ToBytes;
/// }
///
///unsafe impl FromBytes for u32 {
/// unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
/// let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
/// &*slice_ptr
/// }
///
/// unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
/// where
/// Self: ToBytes,
/// {
/// let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
/// &mut *slice_ptr
/// }
///}
///
///let slice_of_bytes : &[u8] = &[1, 2, 3, 4];
///let result = u32::from_bytes(slice_of_bytes);
///assert_eq!(*result, 0x4030201);
///```
///# Safety
///
///Guarantee that all values are initiliazed
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self;
///Converts a mutabble slice of Bytes into a mutable Reference to Self
/// # Safety
///
/// ToBytes in order to allow only types that implements ToBytes
unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes;
}

macro_rules! impl_frombytes {
($($({$($generics:tt)*})? $t:ty, )*) => {
// SAFETY: Safety comments written in the macro invocation.
$(unsafe impl$($($generics)*)? FromBytes for $t {})*
};
// SAFETY: All bit patterns are acceptable values of the types below.
unsafe impl FromBytes for u8 {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
&*slice_ptr
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
&mut *slice_ptr
}
}
}

impl_frombytes! {
// SAFETY: All bit patterns are acceptable values of the types below.
u8, u16, u32, u64, usize,
i8, i16, i32, i64, isize,
unsafe impl FromBytes for u16 {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
&*slice_ptr
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
&mut *slice_ptr
}
}
}

unsafe impl FromBytes for u32 {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
&*slice_ptr
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
&mut *slice_ptr
}
}
}

unsafe impl FromBytes for u64 {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
&*slice_ptr
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
&mut *slice_ptr
}
}
}

unsafe impl FromBytes for usize {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
&*slice_ptr
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
&mut *slice_ptr
}
}
}

unsafe impl FromBytes for i8 {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
&*slice_ptr
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
&mut *slice_ptr
}
}
}

unsafe impl FromBytes for i16 {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
&*slice_ptr
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
&mut *slice_ptr
}
}
}

unsafe impl FromBytes for i32 {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
&*slice_ptr
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
&mut *slice_ptr
}
}
}

unsafe impl FromBytes for i64 {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
&*slice_ptr
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
&mut *slice_ptr
}
}
}

unsafe impl FromBytes for isize {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const Self;
&*slice_ptr
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut Self;
&mut *slice_ptr
}
}
}
// 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] {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const T;
let slice_len = slice_of_bytes.len() / core::mem::size_of::<T>();
core::slice::from_raw_parts(slice_ptr, slice_len)
}
}

unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_mut_ptr() as *mut T;
let slice_len = slice_of_bytes.len() / core::mem::size_of::<T>();
core::slice::from_raw_parts_mut(slice_ptr, slice_len)
}
}
}

/// # Examples
///```
///let slice_of_bytes: &[u8] = &[
/// 1, 0, 0, 0,
/// 2, 0, 0, 0,
/// 3, 0, 0, 0,
/// 4, 0, 0, 0,
/// 5, 0, 0, 0,
/// 6, 0, 0, 0,
/// 7, 0, 0, 0,
/// 8, 0, 0, 0,
///];
///
///let foo = <[u32; 8]>::from_bytes(slice_of_bytes);
///let expected: [u32; 8] = [1, 2, 3, 4, 5, 6, 7, 8];
///
///assert_eq!(*foo, expected);
///```
unsafe impl<T: FromBytes, const N: usize> FromBytes for [T; N] {
unsafe fn from_bytes(slice_of_bytes: &[u8]) -> &Self {
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *const T;
&*(slice_ptr as *const [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.
{<T: FromBytes>} [T],
{<T: FromBytes, const N: usize>} [T; N],
unsafe fn from_bytes_mut(slice_of_bytes: &mut [u8]) -> &mut Self
where
Self: ToBytes,
{
unsafe {
let slice_ptr = slice_of_bytes.as_ptr() as *mut T;
&mut *(slice_ptr as *mut [T; N])
}
}
}

/// Types that can be viewed as an immutable slice of initialized bytes.
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