Integer-to-pointer casts

[mkroening]

Running cargo +nightly clippy --all-targets -- -Wfuzzy_provenance_casts gives:

warning: strict provenance disallows casting integer `usize` to pointer `*mut u8`
   --> src/lib.rs:966:62
    |
966 |             assert2::assert!(let Ok(_) = Uart16550::new_mmio(0x1000 as *mut _, 1));
    |                                                              ^^^^^^^^^^^^^^^^
    |
    = help: if you can't comply with strict provenance and don't have a pointer with the correct provenance you can use `std::ptr::with_exposed_provenance()` instead
    = note: requested on the command line with `-W fuzzy-provenance-casts`
help: use `.with_addr()` to adjust a valid pointer in the same allocation, to this address
    |
966 -             assert2::assert!(let Ok(_) = Uart16550::new_mmio(0x1000 as *mut _, 1));
966 +             assert2::assert!(let Ok(_) = Uart16550::new_mmio((...).with_addr(0x1000), 1));
    |

Running cargo +nightly miri test gives:

test tests::constructors ... warning: integer-to-pointer cast
   --> src/lib.rs:968:62
    |
968 |             assert2::assert!(let Ok(_) = Uart16550::new_mmio(0x1000 as *mut _, 1));
    |                                                              ^^^^^^^^^^^^^^^^ integer-to-pointer cast
    |
    = help: this program is using integer-to-pointer casts or (equivalently) `ptr::with_exposed_provenance`, which means that Miri might miss pointer bugs in this program
    = help: see https://doc.rust-lang.org/nightly/std/ptr/fn.with_exposed_provenance.html for more details on that operation
    = help: to ensure that Miri does not miss bugs in your program, use Strict Provenance APIs (https://doc.rust-lang.org/nightly/std/ptr/index.html#strict-provenance, https://crates.io/crates/sptr) instead
    = help: you can then set `MIRIFLAGS=-Zmiri-strict-provenance` to ensure you are not relying on `with_exposed_provenance` semantics
    = help: alternatively, `MIRIFLAGS=-Zmiri-permissive-provenance` disables this warning
    = note: this is on thread `tests::constructors`
    = note: stack backtrace:
            0: tests::constructors
                at src/lib.rs:968:62: 968:78
            1: tests::constructors::{closure#0}
                at src/lib.rs:955:22: 955:22

It might make sense to either make the examples use existing pointers or be explicit about external provenance:

let ptr = ptr::with_exposed_provenance_mut::<u8>(0x1000);
unsafe { Uart16550::new_mmio(ptr, 1) }