Struct wasmtime_runtime::VMOpaqueContext

pub struct VMOpaqueContext { /* private fields */ }

An “opaque” version of VMContext which must be explicitly casted to a target context.

This context is used to represent that contexts specified in VMCallerCheckedFuncRef can have any type and don’t have an implicit structure. Neither wasmtime nor cranelift-generated code can rely on the structure of an opaque context in general and only the code which configured the context is able to rely on a particular structure. This is because the context pointer configured for VMCallerCheckedFuncRef is guaranteed to be the first parameter passed.

Note that Wasmtime currently has a layout where all contexts that are casted to an opaque context start with a 32-bit “magic” which can be used in debug mode to debug-assert that the casts here are correct and have at least a little protection against incorrect casts.

Implementations

impl VMOpaqueContext

pub fn from_vmcontext(ptr: *mut VMContext) -> *mut VMOpaqueContext

Helper function to clearly indicate that casts are desired.

pub fn from_vm_host_func_context( ptr: *mut VMHostFuncContext, ) -> *mut VMOpaqueContext

Helper function to clearly indicate that casts are desired.