gas utility initial

gas/src/main.rs

@@ -0,0 +1,64 @@
+extern crate parity_wasm;
+
+use std::env;
+use parity_wasm::{builder, elements};
+
+pub fn update_call_index(opcodes: &mut elements::Opcodes, inserted_index: u32) {
+    use parity_wasm::elements::Opcode::*;
+    for opcode in opcodes.elements_mut().iter_mut() {
+        match opcode {
+            &mut Block(_, ref mut block) | &mut If(_, ref mut block) => {
+                update_call_index(block, inserted_index)
+            },
+            &mut Call(ref mut call_index) | &mut CallIndirect(ref mut call_index, _) => {
+                if *call_index >= inserted_index { *call_index += 1}
+            },
+            _ => { }
+        }
+    }
+}
+
+fn main() {
+
+    let args = env::args().collect::<Vec<_>>();
+    if args.len() != 3 {
+        println!("Usage: {} input_file.wasm output_file.wasm", args[0]);
+        return;
+    }
+
+    // Loading module
+    let module = parity_wasm::deserialize_file(&args[1]).unwrap();
+
+    // Injecting gas counting external
+    let mut mbuilder = builder::from_module(module);
+    let import_sig = mbuilder.push_signature(
+        builder::signature()
+            .param().i32()
+            .param().i32()
+            .return_type().i32()
+            .build_sig()
+        );
+
+    let gas_func = mbuilder.push_import(
+        builder::import()
+            .module("env")
+            .field("gas")
+            .external().func(import_sig)
+            .build()
+        );
+
+    // Updating calling addresses (all calls to function index >= `gas_func` should be incremented)
+    let mut module = mbuilder.build();
+    for section in module.sections_mut() {
+        match section {
+            &mut elements::Section::Code(ref mut code_section) => {
+                for ref mut func_body in code_section.bodies_mut() {
+                    update_call_index(func_body.code_mut(), gas_func);
+                }
+            },
+            _ => { }
+        }
+    }
+
+    parity_wasm::serialize_to_file(&args[2], module).unwrap();    
+}