prevent cursor r/w optimization

src/libio/cursor.rs

@@ -2,6 +2,7 @@
 use alloc::vec::Vec;
 
 use core_io::{Error as IoError, Read, Write};
+use core::arch::asm;
 
 #[derive(Debug, Clone)]
 pub struct Cursor<T> {
@@ -47,6 +48,7 @@ impl<T: AsRef<[u8]>> Read for Cursor<T> {
         let len = buf.len().min(data.len());
         // ``copy_from_slice`` generates AXI bursts, use a regular loop instead
         for i in 0..len {
+            unsafe { asm!("", options(preserves_flags, nostack, readonly)); }            
             buf[i] = data[i];
         }
         self.pos += len;
@@ -59,6 +61,7 @@ impl Write for Cursor<&mut [u8]> {
         let data = &mut self.inner[self.pos..];
         let len = buf.len().min(data.len());
         for i in 0..len {
+            unsafe { asm!("", options(preserves_flags, nostack, readonly)); }            
             data[i] = buf[i];
         }
         self.pos += len;

src/libio/lib.rs

@@ -1,5 +1,6 @@
 #![no_std]
 #![feature(never_type)]
+#![feature(asm)]
 
 #[cfg(feature = "alloc")]
 extern crate alloc;