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implement ptr.addr() via transmute As per the discussion in https://github.com/rust-lang/unsafe-code-guidelines/issues/286, the semantics for ptr-to-int transmutes that we are going with for now is to make them strip provenance without exposing it. That's exactly what `ptr.addr()` does! So we can implement `ptr.addr()` via `transmute`. This also means that once https://github.com/rust-lang/rust/pull/97684 lands, Miri can distinguish `ptr.addr()` from `ptr.expose_addr()`, and the following code will correctly be called out as having UB (if permissive provenance mode is enabled, which will become the default once the [implementation is complete](https://github.com/rust-lang/miri/issues/2133)): ```rust fn main() { let x: i32 = 3; let x_ptr = &x as *const i32; let x_usize: usize = x_ptr.addr(); // Cast back an address that did *not* get exposed. let ptr = std::ptr::from_exposed_addr::<i32>(x_usize); assert_eq!(unsafe { *ptr }, 3); //~ ERROR Undefined Behavior: dereferencing pointer failed } ``` This completes the Miri implementation of the new distinctions introduced by strict provenance. :) Cc `@Gankra` -- for now I left in your `FIXME(strict_provenance_magic)` saying these should be intrinsics, but I do not necessarily agree that they should be. Or if we have an intrinsic, I think it should behave exactly like the `transmute` does, which makes one wonder why the intrinsic should be needed. |
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