Merge pull request PacktPublishing#10 from SteveMcFarlin/conditional-comp

Conditionaly compile based on architecture

Author: cfsamson

ch04/a-epoll/src/ffi.rs

@@ -1,3 +1,13 @@
+//! # FIXES:
+//! The number is identical to the number in the GitHub issue tracker
+//!
+//! ## FIX ISSUE #5
+//! See: https://github.com/PacktPublishing/Asynchronous-Programming-in-Rust/issues/5
+//! Readers reported wrong results when running the example on ARM64 instruction set
+//! (aarch64). The reason turned out to be that the `Event` struct is only `repr(packed)`
+//! on `x86-64` systems due to backwards compatibility. Fixed by conditionally
+//! compiling the #[repr(packed)] attribute.
+
 pub const EPOLL_CTL_ADD: i32 = 1;
 pub const EPOLLIN: i32 = 0x1;
 pub const EPOLLET: i32 = 1 << 31;
@@ -11,7 +21,9 @@ extern "C" {
 }
 
 #[derive(Debug)]
-#[repr(C, packed)]
+#[repr(C)]
+// FIX #5
+#[cfg_attr(target_arch = "x86_64", repr(packed))]
 pub struct Event {
     pub(crate) events: u32,
     // Token to identify event