Struct SharedPtr

pub struct SharedPtr<T> { /* private fields */ }

Shared memory physical address raw pointer with type annotation.

This is a structure wrapping a raw pointer to the value of the type T without a pointer metadata. SharedPtr’s are thin; they won’t include metadata as RISC-V SBI does not provide an approach to pass them via SBI calls, thus the length of type T should be decided independently of raw pointer structure.

SharedPtr can be used as a parameter to pass the shared memory physical pointer with a given base address in RISC-V SBI calls. For example, a SharedPtr<[u8; 64]> would represent a fixed-size 64 byte array on a RISC-V SBI function argument type.

This structure cannot be dereferenced directly with physical addresses, because on RISC-V systems the physical address space could be larger than the virtual ones. Hence, this structure describes the physical memory range by two usize values: the upper phys_addr_hi and lower phys_addr_lo.

RISC-V SBI extensions may declare special pointer values for shared memory raw pointers. For example, SBI STA declares that steal-time information should stop from reporting when the SBI call is invoked using all-ones bitwise shared pointer, i.e. phys_addr_hi and phys_addr_lo both equals usize::MAX. SharedPtr can be constructed using such special values by providing them to the SharedPtr::new function.

Requirements

If an SBI function needs to pass a shared memory physical address range to the SBI implementation (or higher privilege mode), then this physical memory address range MUST satisfy the following requirements:

• The SBI implementation MUST check that the supervisor-mode software is allowed to access the specified physical memory range with the access type requested (read and/or write).
• The SBI implementation MUST access the specified physical memory range using the PMA attributes.
• The data in the shared memory MUST follow little-endian byte ordering.

NOTE: If the supervisor-mode software accesses the same physical memory range using a memory type different from the PMA, then a loss of coherence or unexpected memory ordering may occur. The invoking software should follow the rules and sequences defined in the RISC-V Svpbmt specification to prevent the loss of coherence and memory ordering.

It is recommended that a memory physical address passed to an SBI function should use at least two usize parameters to support platforms which have memory physical addresses wider than XLEN bits.

Implementations

impl<T> SharedPtr<T>

pub const fn new(phys_addr_lo: usize, phys_addr_hi: usize) -> Self

Create a shared physical memory pointer by physical address.

pub const fn phys_addr_lo(self) -> usize

Returns low-part physical address of the shared physical memory pointer.

pub const fn phys_addr_hi(self) -> usize

Returns high-part physical address of the shared physical memory pointer.

Trait Implementations

impl<T> Clone for SharedPtr<T>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T> Copy for SharedPtr<T>