Mark `MemoryRange::as_slice()` and `MemoryRange::as_slice_mut()` as
unsafe.
This is due to the fact that not all representable types can be cast to
an arbitrary value. For example, if Process A sends random values to
Process B, then Process B casts the memory to a slice of `bool`, then
any values that are not 0 or 1 are undefined.
Because these functions can leak UB into the program, they are marked as
unsafe.
This patch adds `unsafe {}` blocks to all instances where this function
is called. Additionally, all instances have been checked to verify that
they do not cast to any invalid types -- most use `u8` or `u32`.
Additionally, the long-deprecated `MemoryRange::from_parts()` call was
removed, since that causes UB without being marked as unsafe.
Signed-off-by: Sean Cross <sean@xobs.io>
- make the "base" field no longer public. It is accessible, but only
through an `unsafe` method, because, it is unsafe.
- add accessors to offest/mask fields. Because, it's not at all
unsafe to access these, and it can be useful for bit-ops that are
not part of the generic set of UTRA.
- add Arc to AtomicCSR, and require `std` for AtomicCSR types.
This should not break anything, I checked inside @foundation-devices
keyOS and they don't seem to be using AtomicCSR anywhere.
The Arc makes it a bit safer to clone the AtomicCSR base pointer
and share it between threads, but it will have an impact on performance.
The USB stack (which requires AtomicCSR) was regression testing and the
impact seems minimal.
Recall that the main purpose of AtomicCSR is to provide a CSR accessor
that does not require a mutable reference to the base object. This
can make certain Rust idioms a bit cleaner. We wrap the base accessor
in Arc+Atomic to try and improve the safety of throwing the borrow
checker under the bus, but it's still not perfect because hardware
mutable state can have side-effects within hardware itself that cannot
be modeled or checked by Rust's borrow checker.
