fix(interpreter): impl fetch and decode

I parsed all instructions before executing, but this is not how
intel works.
We need to decode the instructions, pointed to by IP, on the fly.

src/aout.rs

@@ -1,9 +1,13 @@
 //! Internal a.out File abstraction.
 
 use core::fmt;
-use std::ffi::{c_uchar, c_ushort};
+use std::{
+    ffi::{c_uchar, c_ushort},
+    fs::File,
+    io::Read,
+};
 
-use crate::operands::Byte;
+use crate::{Args, disasm::DisasmError, operands::Byte};
 
 #[allow(non_camel_case_types)]
 pub type c_long = i32; // we use a a.out with 32 byte
@@ -25,6 +29,20 @@ impl fmt::Display for Aout {
 }
 
 impl Aout {
+    pub fn new_from_args(args: &Args) -> Self {
+        let path = args
+            .path
+            .clone()
+            .ok_or(DisasmError::NoFile(args.path.clone()))
+            .unwrap();
+        let mut file = File::open(path).unwrap();
+        let mut buf = Vec::new();
+        file.read_to_end(&mut buf).unwrap();
+        let aout = Aout::new(buf);
+        log::debug!("{:?}", aout);
+        aout
+    }
+
     pub fn new(buf: Vec<u8>) -> Self {
         let hdr = Header {
             magic: [buf[0], buf[1]],