diff --git a/rust-runner/src/alloc.rs b/rust-runner/src/alloc.rs
index ffb29cf..92c046e 100644
--- a/rust-runner/src/alloc.rs
+++ b/rust-runner/src/alloc.rs
@@ -4,6 +4,7 @@ pub struct Arena {
     dynamic_top: u32,
 }
 
+#[derive(Debug)]
 pub struct Error;
 
 impl Arena {
@@ -13,7 +14,7 @@ impl Arena {
         }
     }
 
-    fn alloc(&mut self, size: u32) -> Result<u32, Error> {
+    pub fn alloc(&mut self, size: u32) -> Result<u32, Error> {
         let previous_top = self.dynamic_top;
         self.dynamic_top += size;
         Ok(previous_top)
diff --git a/rust-runner/src/call_args.rs b/rust-runner/src/call_args.rs
new file mode 100644
index 0000000..08457be
--- /dev/null
+++ b/rust-runner/src/call_args.rs
@@ -0,0 +1,61 @@
+use parity_wasm::interpreter::{self, ModuleInstanceInterface};
+use alloc;
+
+use {DEFAULT_MEMORY_INDEX, WasmMemoryPtr};
+
+fn write_u32(dst: &mut [u8], val: u32) {
+    dst[0] = (val & 0x000000ff) as u8;
+    dst[1] = ((val & 0x0000ff00) >> 8) as u8;
+    dst[2] = ((val & 0x00ff0000) >> 16) as u8;
+    dst[3] = ((val & 0xff000000) >> 24) as u8;
+}
+
+#[derive(Debug)]
+pub enum Error {
+    Allocator(alloc::Error),
+    Interpreter(interpreter::Error),
+}
+
+impl From<alloc::Error> for Error {
+    fn from(err: alloc::Error) -> Self {
+        Error::Allocator(err)
+    }
+}
+
+impl From<interpreter::Error> for Error {
+    fn from(err: interpreter::Error) -> Self {
+        Error::Interpreter(err)
+    }
+}
+
+pub fn init(
+    env: &interpreter::ModuleInstanceInterface, 
+    allocator: &mut alloc::Arena,
+    context: &[u8], 
+    input: &[u8],
+) -> Result<WasmMemoryPtr, Error> {
+    let mut context_ptr_slc = [0u8; 4];
+    let mut context_length = [0u8; 4];
+    let mut input_ptr_slc = [0u8; 4];
+    let mut input_length = [0u8; 4];
+
+    let descriptor_ptr = allocator.alloc(16)?;
+    let context_ptr = allocator.alloc(context.len() as u32)?;
+    let input_ptr = allocator.alloc(input.len() as u32)?;
+
+    write_u32(&mut context_ptr_slc, context_ptr);
+    write_u32(&mut context_length, context.len() as u32);
+    write_u32(&mut input_ptr_slc, input_ptr);
+    write_u32(&mut input_length, input.len() as u32);
+
+    let memory = env.memory(DEFAULT_MEMORY_INDEX)?;
+
+    memory.set(descriptor_ptr, &context_ptr_slc)?;
+    memory.set(descriptor_ptr+4, &context_length)?;
+    memory.set(descriptor_ptr+8, &input_ptr_slc)?;
+    memory.set(descriptor_ptr+12, &input_length)?;
+    memory.set(context_ptr, context)?;
+    memory.set(input_ptr, input)?;
+
+    Ok(descriptor_ptr as i32)
+}
\ No newline at end of file
diff --git a/rust-runner/src/main.rs b/rust-runner/src/main.rs
index 22940fb..0e6e7dd 100644
--- a/rust-runner/src/main.rs
+++ b/rust-runner/src/main.rs
@@ -9,9 +9,13 @@ extern crate wasm_utils;
 
 mod alloc;
 mod storage;
+mod call_args;
 
 use std::env;
-use parity_wasm::interpreter::ModuleInstanceInterface;
+use parity_wasm::interpreter::{self, ModuleInstanceInterface, RuntimeValue};
+
+pub const DEFAULT_MEMORY_INDEX: interpreter::ItemIndex = interpreter::ItemIndex::Internal(0);
+pub type WasmMemoryPtr = i32;
 
 fn main() {
     // First, load wasm contract as a module
@@ -34,8 +38,16 @@ fn main() {
     // Create allocator
     let mut allocator = alloc::Arena::new(5*1024*1024);
 
+    // Initialize call descriptor
+    let descriptor = call_args::init(
+        &*program.module("env").expect("env module to exist"), 
+        &mut allocator, 
+        &[], 
+        &[0u8; 128],
+    ).expect("call descriptor initialization to succeed");
+
     // Invoke _call method of the module
-    module_instance.execute_export("_call", vec![]).expect("_call to execute successfully");
+    module_instance.execute_export("_call", vec![descriptor.into()]).expect("_call to execute successfully");
 
     // ???
 }
\ No newline at end of file
diff --git a/rust-runner/src/storage.rs b/rust-runner/src/storage.rs
index 70412f2..f35e2bd 100644
--- a/rust-runner/src/storage.rs
+++ b/rust-runner/src/storage.rs
@@ -2,7 +2,7 @@ use parity_wasm::interpreter::ModuleInstanceInterface;
 use parity_wasm::interpreter::ItemIndex;
 use std::sync::Arc;
 
-const DEFAULT_MEMORY_INDEX: ItemIndex = ItemIndex::Internal(0);
+use DEFAULT_MEMORY_INDEX;
 
 pub struct Storage {
     data: Vec<u8>,