[0.2] Windows `BCryptGenRandom` uses wrong signature

[CraftSpider]

In version 0.2, the return type of BCryptGenRandom is declared as u32, when NTSTATUS is defined as an i32. This was noticed by miri, as it's about to start catching this UB on Windows shim functions: rust-lang/miri#4779.

[josephlr]

Looking at https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-erref/87fba13e-bf06-450e-83b1-9241dc81e781 it seems like NTSTATUS is just defined to be a 32-bit value, and the values are defined with Unsigned (rather than Signed) semantics.

Given that i32 and u32 are ABI compatible on Windows, I'm very confused why this would even be considered UB.

[RalfJung]

The ABI compatibility rules are defined here. Both C and Rust make it UB to call a function defined with a signed integer using an unsigned integer declaration, and vice versa. I'm not aware of any systematic compiler documentation for either language that would add special exceptions for certain ABIs on certain targets -- and there are targets and mechanisms (such as CFI) that actually make such calls not work.