Make function imports unsafe

lib/runtime/examples/simple/main.rs

@@ -2,7 +2,7 @@ use wasmer_clif_backend::CraneliftCompiler;
 use wasmer_runtime::{
     self as runtime,
     types::{FuncSig, Type, Value},
-    vm, Import, Imports,
+    vm, Import, Imports, FuncRef,
 };
 
 static EXAMPLE_WASM: &'static [u8] = include_bytes!("simple.wasm");
@@ -15,7 +15,7 @@ fn main() -> Result<(), String> {
         "env".to_string(),
         "print_num".to_string(),
         Import::Func(
-            print_num as _,
+            unsafe { FuncRef::new(print_num as _) },
             FuncSig {
                 params: vec![Type::I32],
                 returns: vec![Type::I32],

lib/runtime/src/backing.rs

@@ -263,10 +263,10 @@ impl ImportBacking {
             let expected_sig = module.sig_registry.lookup_func_sig(sig_index);
             let import = imports.get(mod_name, item_name);
             match import {
-                Some(&Import::Func(func, ref signature)) => {
+                Some(&Import::Func(ref func, ref signature)) => {
                     if expected_sig == signature {
                         functions.push(vm::ImportedFunc {
-                            func,
+                            func: func.inner(),
                             // vmctx: ptr::null_mut(),
                         });
                     } else {

lib/runtime/src/instance.rs

@@ -134,9 +134,25 @@ impl Instance {
     }
 }
 
+#[derive(Debug)]
+pub struct FuncRef(*const vm::Func);
+
+impl FuncRef {
+    /// This needs to be unsafe because there is
+    /// no way to check whether the passed function
+    /// is valid and has the right signature.
+    pub unsafe fn new(f: *const vm::Func) -> Self {
+        FuncRef(f)
+    }
+
+    pub(crate) fn inner(&self) -> *const vm::Func {
+        self.0
+    }
+}
+
 #[derive(Debug)]
 pub enum Import {
-    Func(*const vm::Func, FuncSig),
+    Func(FuncRef, FuncSig),
     Table(Arc<TableBacking>, Table),
     Memory(Arc<LinearMemory>, Memory),
     Global(Value),

lib/runtime/src/lib.rs

@@ -15,7 +15,7 @@ pub mod vm;
 pub mod vmcalls;
 
 pub use self::backend::{Compiler, FuncResolver};
-pub use self::instance::{Import, ImportResolver, Imports, Instance};
+pub use self::instance::{Import, ImportResolver, Imports, FuncRef, Instance};
 pub use self::memory::LinearMemory;
 pub use self::module::{Module, ModuleInner};
 pub use self::sig_registry::SigRegistry;