[wasmtime-api] Implementation of classes for run-{reflect,start,global,memory}-c (#295)

Implements apis for reflect-c, start-c, run-global-c and run-memory-c

wasmtime-api/src/trampoline/global.rs

@@ -0,0 +1,47 @@
+use cranelift_entity::PrimaryMap;
+use failure::Error;
+use wasmtime_environ::Module;
+use wasmtime_runtime::{InstanceHandle, VMGlobalDefinition};
+
+use super::create_handle::create_handle;
+use crate::{GlobalType, Mutability, Val};
+
+#[allow(dead_code)]
+pub struct GlobalState {
+    definition: Box<VMGlobalDefinition>,
+    handle: InstanceHandle,
+}
+
+pub fn create_global(
+    gt: &GlobalType,
+    val: Val,
+) -> Result<(wasmtime_runtime::Export, GlobalState), Error> {
+    let mut definition = Box::new(VMGlobalDefinition::new());
+    unsafe {
+        match val {
+            Val::I32(i) => *definition.as_i32_mut() = i,
+            Val::I64(i) => *definition.as_i64_mut() = i,
+            Val::F32(f) => *definition.as_u32_mut() = f,
+            Val::F64(f) => *definition.as_u64_mut() = f,
+            _ => unimplemented!("create_global for {:?}", gt),
+        }
+    }
+
+    let global = cranelift_wasm::Global {
+        ty: gt.content().get_cranelift_type(),
+        mutability: match gt.mutability() {
+            Mutability::Const => false,
+            Mutability::Var => true,
+        },
+        initializer: cranelift_wasm::GlobalInit::Import, // TODO is it right?
+    };
+    let mut handle = create_handle(Module::new(), PrimaryMap::new(), Box::new(())).expect("handle");
+    Ok((
+        wasmtime_runtime::Export::Global {
+            definition: definition.as_mut(),
+            vmctx: handle.vmctx_mut_ptr(),
+            global,
+        },
+        GlobalState { definition, handle },
+    ))
+}