hardening: mark decode_fixed_vec_le as unsafe#19
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Compute size_of::<T>() inside the function instead of taking it as a parameter. This makes a size mismatch impossible by construction, replacing the debug_assert added in the previous commit.
Split into a doc-level safety contract (what callers must uphold) and a block-level SAFETY comment (why the operations are sound).
The function has a safety contract that the type system cannot enforce (T must have no padding and be valid for any bit pattern), so callers should explicitly acknowledge it via an unsafe block.
Split the doc comment into a Safety section (valid-for-any-bit-pattern, the actual soundness requirement) and a Correctness section (little-endian layout, enforced by cfg).
Split the doc comment into a Safety section (valid-for-any-bit-pattern, the actual soundness requirement) and a Correctness section (little-endian layout, enforced by cfg).
MegaRedHand
changed the title
decode_fixed_vec_ledecode_fixed_vec_le as unsafe
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Summary
This PR marks
decode_fixed_vec_leasunsafe, documenting the safety and correctness requirements, which were already upheld. It also removes the second parameter, since it could be computed inside the function, and doing so simplifies safety requirements.The reason the function is unsafe is only because some types have invalid values, which can be represented in the raw byte format, but don't really have a representable value in the type. See "Producing invalid values" in the Rustonomicon
For example,
boolcan only betrueorfalse, which are1and0, respectively. However, interpreting an arbitrary byte (boolhas a size of 1 byte) as aboolcould result in interpreting unrepresentable values like2, `3, etc.