Correctly handle possibly misaligned pointers in readdir (#615)

crates/test-programs/wasi-tests/src/bin/fd_readdir.rs

@@ -36,7 +36,7 @@ impl<'a> Iterator for ReadDir<'a> {
 
             // Read the data
             let dirent_ptr = self.buf.as_ptr() as *const wasi_unstable::Dirent;
-            let dirent = *dirent_ptr;
+            let dirent = dirent_ptr.read_unaligned();
             let name_ptr = dirent_ptr.offset(1) as *const u8;
             // NOTE Linux syscall returns a NULL-terminated name, but WASI doesn't
             let namelen = dirent.d_namlen as usize;

crates/wasi-common/src/hostcalls_impl/fs.rs

@@ -1088,12 +1088,12 @@ impl Dirent {
 
         let sys_dirent = raw.as_mut_ptr() as *mut wasi::__wasi_dirent_t;
         unsafe {
-            *sys_dirent = wasi::__wasi_dirent_t {
+            sys_dirent.write_unaligned(wasi::__wasi_dirent_t {
                 d_namlen: namlen.try_into()?,
                 d_ino: self.ino,
                 d_next: self.cookie,
                 d_type: self.ftype.to_wasi(),
-            };
+            });
         }
 
         let sys_name = unsafe { sys_dirent.offset(1) as *mut u8 };