Struct GuestPtr

pub struct GuestPtr<T: ?Sized + Pointee> { /* private fields */ }

A guest pointer.

This type represents a pointer from the guest that points into host memory. Internally a GuestPtr the offset into the memory that the pointer is pointing at. At this time this is always a 32-bit offset so this is not suitable for bindings where wasm has 64-bit addresses.

Presence of a GuestPtr does not imply any form of validity. Pointers can be out-of-bounds, misaligned, etc. It is safe to construct a GuestPtr with any offset at any time. Consider a GuestPtr<T> roughly equivalent to *mut T.

Slices and Strings

Note that the type parameter does not need to implement the Sized trait, so you can implement types such as this:

• GuestPtr<str> - a pointer to a guest string.
• GuestPtr<[T]> - a pointer to a guest array.

Note that generated bindings won’t use these types so you’ll have to otherwise construct the types with .cast() or .as_array(). Unsized types track both the pointer and length in guest memory.

Type parameter and pointee

The T type parameter is largely intended for more static safety in Rust as well as having a better handle on what we’re pointing to. A GuestPtr<T>, however, does not necessarily literally imply a guest pointer pointing to type T. Instead the GuestType trait is a layer of abstraction where GuestPtr<T> may actually be a pointer to U in guest memory, but you can construct a T from a U.

For example GuestPtr<GuestPtr<T>> is a valid type, but this is actually more equivalent to GuestPtr<u32> because guest pointers are always 32-bits. That being said you can create a GuestPtr<T> from a u32.

Additionally GuestPtr<MyEnum> will actually delegate, typically, to and implementation which loads the underlying data as GuestPtr<u8> (or similar) and then the bytes loaded are validated to fit within the definition of MyEnum before MyEnum is returned.

For more information see the GuestMemory::read and GuestMemory::write methods. In general though be extremely careful about writing unsafe code when working with a GuestPtr if you’re not using one of the already-attached helper methods.

Implementations

impl<T: ?Sized + Pointee> GuestPtr<T>

pub fn new(pointer: T::Pointer) -> GuestPtr<T>

Creates a new GuestPtr from the given mem and pointer values.

Note that for sized types like u32, GuestPtr<T>, etc, the pointer value is a u32 offset into guest memory. For slices and strings, pointer is a (u32, u32) offset/length pair.

pub fn offset(&self) -> T::Pointer

Returns the offset of this pointer in guest memory.

Note that for sized types this returns a u32, but for slices and strings it returns a (u32, u32) pointer/length pair.

pub fn cast<U>(&self) -> GuestPtr<U>

where U: Pointee<Pointer = T::Pointer> + ?Sized,

Casts this GuestPtr type to a different type.

This is a safe method which is useful for simply reinterpreting the type parameter on this GuestPtr. Note that this is a safe method, where again there’s no guarantees about alignment, validity, in-bounds-ness, etc of the returned pointer.

pub fn add(&self, amt: u32) -> Result<GuestPtr<T>, GuestError>

where T: GuestType + Pointee<Pointer = u32>,

Performs pointer arithmetic on this pointer, moving the pointer forward amt slots.

This will either return the resulting pointer or Err if the pointer arithmetic calculation would overflow around the end of the address space.

pub fn as_array(&self, elems: u32) -> GuestPtr<[T]>

where T: GuestType + Pointee<Pointer = u32>,

Returns a GuestPtr for an array of Ts using this pointer as the base.

impl<T> GuestPtr<[T]>

pub fn offset_base(&self) -> u32

For slices, specifically returns the relative pointer to the base of the array.

This is similar to <[T]>::as_ptr()

pub fn len(&self) -> u32

For slices, returns the length of the slice, in elements.

pub fn iter( &self, ) -> impl ExactSizeIterator<Item = Result<GuestPtr<T>, GuestError>> + '_

where T: GuestType,

Returns an iterator over interior pointers.

Each item is a Result indicating whether it overflowed past the end of the address space or not.

pub fn as_ptr(&self) -> GuestPtr<T>

Returns a GuestPtr pointing to the base of the array for the interior type T.

pub fn get(&self, index: u32) -> Option<GuestPtr<T>>

where T: GuestType,

pub fn get_range(&self, r: Range<u32>) -> Option<GuestPtr<[T]>>

where T: GuestType,

impl GuestPtr<str>

pub fn offset_base(&self) -> u32

For strings, returns the relative pointer to the base of the string allocation.

pub fn len(&self) -> u32

Returns the length, in bytes, of the string.

pub fn as_bytes(&self) -> GuestPtr<[u8]>

Returns a raw pointer for the underlying slice of bytes that this pointer points to.

Trait Implementations

impl<T: ?Sized + Pointee> Clone for GuestPtr<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: ?Sized + Pointee> Debug for GuestPtr<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> GuestType for GuestPtr<[T]>

where T: GuestType,

fn guest_size() -> u32

Returns the size, in bytes, of this type in the guest memory.

fn guest_align() -> usize

Returns the required alignment of this type, in bytes, for both guest and host memory.

fn read(mem: &GuestMemory<'_>, ptr: GuestPtr<Self>) -> Result<Self, GuestError>

Reads this value from the provided ptr.

fn write( mem: &mut GuestMemory<'_>, ptr: GuestPtr<Self>, val: Self, ) -> Result<(), GuestError>

Writes a value to ptr after verifying that ptr is indeed valid to store val.

impl<T> GuestType for GuestPtr<T>

fn guest_size() -> u32

Returns the size, in bytes, of this type in the guest memory.

fn guest_align() -> usize

Returns the required alignment of this type, in bytes, for both guest and host memory.

fn read(mem: &GuestMemory<'_>, ptr: GuestPtr<Self>) -> Result<Self, GuestError>

Reads this value from the provided ptr.

fn write( mem: &mut GuestMemory<'_>, ptr: GuestPtr<Self>, val: Self, ) -> Result<(), GuestError>

Writes a value to ptr after verifying that ptr is indeed valid to store val.

impl<T: ?Sized + Pointee> PartialEq for GuestPtr<T>

fn eq(&self, other: &Self) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T: ?Sized + Pointee> Copy for GuestPtr<T>