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Update safety comments for DataInit.

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Previously DataInit did not specify that any implementor `T` must not
contain implicit padding, though implementors of DataInit often include
a safety statement mentioning that they have no implicit padding. This
CL updates DataInit to clarify that any implementor must certify it has
no implicit padding to be safe / free of undefined behavior.

BUG=none
TEST=none (comment only change)

Change-Id: Ieddce51949bfa65de65a891deae071a744b0a4ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2439301
Reviewed-by: Zach Reizner <zachr@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Noah Gold <nkgold@google.com>
This commit is contained in:
Noah Gold 2020-09-29 20:21:49 -07:00 committed by Commit Bot
parent cf68ea6f3e
commit b0e9842602
1 changed files with 10 additions and 3 deletions
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13
data_model/src/lib.rs
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@ -8,11 +8,18 @@ use std::slice::{from_raw_parts, from_raw_parts_mut};
/// Types for which it is safe to initialize from raw data.
///
/// A type `T` is `DataInit` if and only if it can be initialized by reading its contents from a
/// byte array. This is generally true for all plain-old-data structs. It is notably not true for
/// any type that includes a reference.
///
/// Implementing this trait guarantees that it is safe to instantiate the struct with random data.
///
/// # Safety
/// A type `T` is `DataInit` if it can be initialized by reading its contents from a byte array.
/// This is generally true for all plain-old-data structs. It is notably not true for any type
/// that includes a reference.
///
/// It is unsafe for `T` to be `DataInit` if `T` contains implicit padding. (LLVM considers access
/// to implicit padding to be undefined behavior, which can cause UB when working with `T`.
/// For details on structure padding in Rust, see
/// https://doc.rust-lang.org/reference/type-layout.html#the-c-representation
pub unsafe trait DataInit: Copy + Send + Sync {
/// Converts a slice of raw data into a reference of `Self`.
///