Struct wasmtime_runtime::VMContext

#[repr(C, align(16))]
pub struct VMContext {
    pub _marker: PhantomPinned,
}

The VM “context”, which is pointed to by the vmctx arg in Cranelift. This has information about globals, memories, tables, and other runtime state associated with the current instance.

The struct here is empty, as the sizes of these fields are dynamic, and we can’t describe them in Rust’s type system. Sufficient memory is allocated at runtime.

Fields

_marker: PhantomPinned

There’s some more discussion about this within wasmtime/src/lib.rs but the idea is that we want to tell the compiler that this contains pointers which transitively refers to itself, to suppress some optimizations that might otherwise assume this doesn’t exist.

The self-referential pointer we care about is the *mut Store pointer early on in this context, which if you follow through enough levels of nesting, eventually can refer back to this VMContext

Implementations

impl VMContext

pub unsafe fn from_opaque(opaque: *mut VMOpaqueContext) -> *mut VMContext

Helper function to cast between context types using a debug assertion to protect against some mistakes.

pub unsafe fn host_state(&self) -> &dyn Any

Return a reference to the host state associated with this Instance.

Safety

This is unsafe because it doesn’t work on just any VMContext, it must be a VMContext allocated as part of an Instance.

Trait Implementations

impl Debug for VMContext

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

Formats the value using the given formatter.