Use read_unaligned when reading u64#257
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Sorry to jump into this PR, but I am not sure I follow the reason for this being undefined behaviour. The runtime serialization guarantees that the input pointer will be aligned to an |
No worries - your comment is welcome :) Yes, if we include the ABI behavior in the calculation, then these reads are actually safe. I read this tutorial up to this point, and while it is possible that I've missed it, I did not see the VM ABI alignment behavior stated anywhere. So if I consider just the content of the tutorial, it is unsafe to do an unaligned read here. |
Casting an arbitrary pointer to `u64` is an undefined behavior. Not sure if casting of the discriminator value is really necessary, as it is just a `u8` in this example. But using the same `*ptr.cast::<uXX>()` pattern in there seems wrong. It is a noop for `u8`, but if a `u64` is used, it becomes undefined behavior as well. Also, the `unsafe` usage is somewhat unclear. Dereferencing a pointer is an unsafe operation, but the first two examples do not have `unsafe`. Yet in the last example, when a slice is constructed, `unsafe` is present. I assume that the first two examples are expected to be in an unsafe context already?
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Casting an arbitrary pointer to
u64is an undefined behavior.Not sure if casting of the discriminator value is really necessary, as it is just a
u8in this example. But using the same*ptr.cast::<uXX>()pattern in there seems wrong. It is a noop foru8, but if au64is used, it becomes undefined behavior as well.Also, the
unsafeusage is somewhat unclear. Dereferencing a pointer is an unsafe operation, but the first two examples do not haveunsafe. Yet in the last example, when a slice is constructed,unsafeis present. I assume that the first two examples are expected to be in an unsafe context already?