Function cont_new

crates/wasmtime/src/runtime/vm/stack_switching.rs:299–348

(
    store: &mut dyn crate::vm::VMStore,
    instance: crate::store::InstanceId,
    func: *mut u8,
    param_count: u32,
    result_count: u32,
)

#[cfg(feature = "stack-switching")]
#[inline(always)]
pub fn cont_new(
    store: &mut dyn crate::vm::VMStore,
    instance: crate::store::InstanceId,
    func: *mut u8,
    param_count: u32,
    result_count: u32,
) -> crate::Result<*mut VMContRef> {
    let instance = store.instance_mut(instance);
    let caller_vmctx = instance.vmctx();

    let stack_size = store.engine().config().async_stack_size;

    let contref = store.allocate_continuation()?;
    let contref = unsafe { contref.as_mut().unwrap() };

    let tsp = contref.stack.top().unwrap();
    contref.parent_chain = VMStackChain::Absent;
    // The continuation is fresh, which is a special case of being suspended.
    // Thus we need to set the correct end of the continuation chain: itself.
    contref.last_ancestor = contref;

    // The initialization function will allocate the actual args/return value buffer and
    // update this object (if needed).
    let contref_args_ptr = &mut contref.args as *mut _ as *mut VMHostArray<crate::ValRaw>;

    contref.stack.initialize(
        func.cast::<crate::vm::VMFuncRef>(),
        caller_vmctx.as_ptr(),
        contref_args_ptr,
        param_count,
        result_count,
    );

    // Now that the initial stack pointer was set by the initialization
    // function, use it to determine stack limit.
    let stack_pointer = contref.stack.control_context_stack_pointer();
    // Same caveat regarding stack_limit here as described in
    // `wasmtime::runtime::func::EntryStoreContext::enter_wasm`.
    let wasm_stack_limit = core::cmp::max(
        stack_pointer - store.engine().config().max_wasm_stack,
        tsp as usize - stack_size,
    );
    let limits = VMStackLimits::with_stack_limit(wasm_stack_limit);
    let csi = &mut contref.common_stack_information;
    csi.state = VMStackState::Fresh;
    csi.limits = limits;

    log::trace!("Created contref @ {contref:p}");
    Ok(contref)
}

/// This type represents a linked lists ("chain") of stacks, where the a
/// node's successor denotes its parent.