Macro lucet_runtime_internals::lucet_hostcalls

macro_rules! lucet_hostcalls {
    {
        $(
            $(#[$attr:meta])*
            pub unsafe extern "C" fn $name:ident(
                &mut $vmctx:ident
                $(, $arg:ident : $arg_ty:ty )*,
            ) -> $ret_ty:ty {
                $($body:tt)*
            }
        )*
    } => { ... };
}

The macro that surrounds definitions of Lucet hostcalls in Rust.

It is important to use this macro for hostcalls, rather than exporting them directly, as it installs unwind protection that prevents panics from unwinding into the guest stack.

Since this is not yet a proc macro, the syntax is unfortunately fairly brittle. The functions it encloses must be of the form:

#[$attr1]
#[$attr2]
... // any number of attributes are supported; in most cases you will want `#[no_mangle]`
pub unsafe extern "C" fn $name( // must be `pub unsafe extern "C"`
    &mut $vmctx,
    $arg1: $arg1_ty,
    $arg2: $arg2_ty,
    ... , // trailing comma must always be present
) -> $ret_ty { // return type must always be present even if it is `()`
    // body
}