Function revm::precompile::primitives::bitvec::ptr::write_volatile

source · 
pub unsafe fn write_volatile<T, O>(dst: BitPtr<Mut, T, O>, value: bool)
where
    T: BitStore,
    O: BitOrder,
Expand description

§Single-Bit Volatile Write

This writes a bit into dst directly, using a volatile I/O intrinsic to prevent compiler reördering or removal.

You should not use bitvec to perform any volatile I/O operations. You should instead do volatile I/O work on integer values directly, or use a crate like voladdress to perform I/O transactions, and use bitvec only on stack locals that have no additional memory semantics.

§Original

`ptr::write_volatile

§Safety

Because this performs a dereference of memory, it inherits the original ptr::write_volatile’s requirements:

  • dst must be valid to write
  • dst must be properly aligned. This is an invariant of the BitPtr type as well as of the memory access.

Additionally, dst must point to an initialized value of T. Integers cannot be initialized one bit at a time.

§Behavior

This is required to perform a read/modify/write cycle on the memory location. LLVM may or may not emit a bit-write instruction on targets that have them in the ISA, but this is not specified in any way.

§Examples

use bitvec::prelude::*;
use bitvec::ptr as bv_ptr;

let mut data = 0u8;
let ptr = BitPtr::<_, _, Lsb0>::from_mut(&mut data);
unsafe { bv_ptr::write_volatile(ptr.add(2), true); }
assert_eq!(data, 4);