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clarify how write_bytes can lead to UB due to invalid values

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This commit is contained in:
Ralf Jung 2022-07-09 09:38:07 -04:00
parent c4693bc946
commit f6247ffa5a
1 changed files with 4 additions and 4 deletions
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8
library/core/src/intrinsics.rs
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@ -2550,10 +2550,10 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
///
/// * `dst` must be properly aligned.
///
/// Additionally, the caller must ensure that writing `count *
/// size_of::<T>()` bytes to the given region of memory results in a valid
/// value of `T`. Using a region of memory typed as a `T` that contains an
/// invalid value of `T` is undefined behavior.
/// Additionally, note that changing `*dst` in this way can lead to undefined behavior later if the
/// written bytes are not a valid representation of some `T`. For instance, if `dst: *mut bool`, a
/// `dst.write_bytes(0xFFu8, 1)` followed by `dst.read()` is undefined behavior since the `read`
/// tries to construct a `bool` value from `0xFF` which does not represent any `bool`.
///
/// Note that even if the effectively copied size (`count * size_of::<T>()`) is
/// `0`, the pointer must be non-null and properly aligned.