Merge pull request PacktPublishing#13 from PacktPublishing/fix#11

Make example ch01/a-assembly-dereference work on aarch64

Author: cfsamson

ch01/a-assembly-dereference/src/main.rs

@@ -1,20 +1,42 @@
+//! # FIXES:
+//! The number is identical to the number in the GitHub issue tracker
+//!
+//! ## FIX ISSUE #11:
+//! See:https://github.com/PacktPublishing/Asynchronous-Programming-in-Rust/issues/11
+//! The book didn't make it clear that this example will only work on `x86-64` architecture,
+//! so users on newer M-series macs (which uses the ARM64 instruciton set), will get a
+//! compilation error. This is solved by conditionally compiling a version that works
+//! with the  ARM64 instruction set.
 
 use std::arch::asm;
 
 fn main() {
     let t = 100;
     let t_ptr: *const usize = &t; // if you comment out this...
-    // ...and uncomment the line below. The program will fail.   
+    // ...and uncomment the line below. The program will fail.
     // let t_ptr = 99999999999999 as *const usize;
     let x = dereference(t_ptr);
 
     println!("{}", x);
 }
 
+#[cfg(target_arch = "x86-64")]
 fn dereference(ptr: *const usize) -> usize {
     let mut res: usize;
-    unsafe { 
+    unsafe {
         asm!("mov {0}, [{1}]", out(reg) res, in(reg) ptr)
     };
     res
 }
+
+// FIX #11
+#[cfg(target_arch = "aarch64")]
+fn dereference(ptr: *const usize) -> usize {
+    let mut res: usize;
+    unsafe {
+        asm!("ldr {0}, [{1}]", out(reg) res, in(reg) ptr)
+    };
+    res
+}
+
+