# Function with_exposed_provenance_mut

1.84.0 (const: unstable) · Source

    pub fn with_exposed_provenance_mut<T>(addr: usize) -> *mut T

Expand description

Converts an address back to a mutable pointer, picking up some previously ‘exposed’ provenance.

This is fully equivalent to `addr as *mut T`. The provenance of the returned pointer is that of some pointer that was previously exposed by passing it to `expose_provenance`, or a `ptr as usize` cast. In addition, memory which is outside the control of the Rust abstract machine (MMIO registers, for example) is always considered to be accessible with an exposed provenance, so long as this memory is disjoint from memory that will be used by the abstract machine such as the stack, heap, and statics.

The exact provenance that gets picked is not specified. The compiler will do its best to pick the “right” provenance for you (whatever that may be), but currently we cannot provide any guarantees about which provenance the resulting pointer will have – and therefore there is no definite specification for which memory the resulting pointer may access.

If there is no previously ‘exposed’ provenance that justifies the way the returned pointer will be used, the program has undefined behavior. In particular, the aliasing rules still apply: pointers and references that have been invalidated due to aliasing accesses cannot be used anymore, even if they have been exposed!

Due to its inherent ambiguity, this operation may not be supported by tools that help you to stay conformant with the Rust memory model. It is recommended to use Strict Provenance APIs such as `with_addr` wherever possible.

On most platforms this will produce a value with the same bytes as the address. Platforms which need to store additional information in a pointer may not support this operation, since it is generally not possible to actually compute which provenance the returned pointer has to pick up.

This is an Exposed Provenance API.