diff --git a/rust-runner/src/alloc.rs b/rust-runner/src/alloc.rs
index 92c046e..05822c3 100644
--- a/rust-runner/src/alloc.rs
+++ b/rust-runner/src/alloc.rs
@@ -1,22 +1,27 @@
-use parity_wasm::interpreter::ModuleInstanceInterface;
+use parity_wasm::interpreter;
+use runtime::Runtime;
 
 pub struct Arena {
-    dynamic_top: u32,
+    pub runtime: Runtime,
 }
 
 #[derive(Debug)]
 pub struct Error;
 
 impl Arena {
-    pub fn new(stack_top: u32) -> Self {
-        Arena {
-            dynamic_top: stack_top,
-        }
-    }
-
-    pub fn alloc(&mut self, size: u32) -> Result<u32, Error> {
-        let previous_top = self.dynamic_top;
-        self.dynamic_top += size;
+    pub fn alloc(&self, size: u32) -> Result<u32, Error> {
+        // todo: maybe use unsafe cell since it has nothing to do with threads
+        let previous_top = self.runtime.env().dynamic_top.get();
+        self.runtime.env().dynamic_top.set(previous_top + size);
         Ok(previous_top)
     }
+}
+
+impl interpreter::UserFunctionInterface for Arena {
+    fn call(&mut self, context: interpreter::CallerContext) -> Result<Option<interpreter::RuntimeValue>, interpreter::Error> {
+        let amount = context.value_stack.pop_as::<i32>()?;
+        self.alloc(amount as u32)
+            .map(|val| Some((val as i32).into()))
+            .map_err(|e| interpreter::Error::Trap(format!("Allocator failure: {}", "todo: format arg")))
+    }    
 }
\ No newline at end of file
diff --git a/rust-runner/src/call_args.rs b/rust-runner/src/call_args.rs
index 08457be..6a4afb6 100644
--- a/rust-runner/src/call_args.rs
+++ b/rust-runner/src/call_args.rs
@@ -1,5 +1,5 @@
 use parity_wasm::interpreter::{self, ModuleInstanceInterface};
-use alloc;
+use {alloc, runtime};
 
 use {DEFAULT_MEMORY_INDEX, WasmMemoryPtr};
 
@@ -30,7 +30,7 @@ impl From<interpreter::Error> for Error {
 
 pub fn init(
     env: &interpreter::ModuleInstanceInterface, 
-    allocator: &mut alloc::Arena,
+    runtime: &runtime::Runtime,
     context: &[u8], 
     input: &[u8],
 ) -> Result<WasmMemoryPtr, Error> {
@@ -39,6 +39,8 @@ pub fn init(
     let mut input_ptr_slc = [0u8; 4];
     let mut input_length = [0u8; 4];
 
+    let allocator = runtime.allocator();
+
     let descriptor_ptr = allocator.alloc(16)?;
     let context_ptr = allocator.alloc(context.len() as u32)?;
     let input_ptr = allocator.alloc(input.len() as u32)?;
diff --git a/rust-runner/src/main.rs b/rust-runner/src/main.rs
index 0e6e7dd..1f1733d 100644
--- a/rust-runner/src/main.rs
+++ b/rust-runner/src/main.rs
@@ -10,9 +10,11 @@ extern crate wasm_utils;
 mod alloc;
 mod storage;
 mod call_args;
+mod runtime;
+mod gas_counter;
 
 use std::env;
-use parity_wasm::interpreter::{self, ModuleInstanceInterface, RuntimeValue};
+use parity_wasm::interpreter::{self, ModuleInstanceInterface};
 
 pub const DEFAULT_MEMORY_INDEX: interpreter::ItemIndex = interpreter::ItemIndex::Internal(0);
 pub type WasmMemoryPtr = i32;
@@ -36,12 +38,13 @@ fn main() {
     let module_instance = program.add_module("contract", module).expect("Module to be added successfully");
 
     // Create allocator
-    let mut allocator = alloc::Arena::new(5*1024*1024);
+    let runtime = runtime::Runtime::default();
+    runtime.allocator().alloc(5*1024*1024).expect("to allocate 5mb successfully"); // reserve stack space
 
     // Initialize call descriptor
     let descriptor = call_args::init(
         &*program.module("env").expect("env module to exist"), 
-        &mut allocator, 
+        &runtime, 
         &[], 
         &[0u8; 128],
     ).expect("call descriptor initialization to succeed");