Merge branch 'seed48-no-static-mut' into 'master'

Replace static mut in seed48()

See merge request redox-os/relibc!1178

src/header/stdlib/mod.rs

@@ -1248,19 +1248,24 @@ pub unsafe extern "C" fn secure_getenv(name: *const c_char) -> *mut c_char {
 /// state.
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn seed48(seed16v: *mut c_ushort) -> *mut c_ushort {
-    static mut BUFFER: [c_ushort; 3] = [0; 3];
+    static RETURN_BUFFER: RawCell<[c_ushort; 3]> = RawCell::new([0; 3]);
 
     let mut params = rand48::params_mut();
     let mut xsubi = rand48::xsubi_lock();
 
+    // SAFETY: the caller is required to ensure seed16v is convertible to
+    // &[c_ushort; 3].
     let seed16v_ref: &[c_ushort; 3] = unsafe { slice::from_raw_parts(seed16v, 3) }
         .try_into()
         .unwrap();
 
-    unsafe { BUFFER = (*xsubi).into() };
+    // SAFETY: the caller is required to ensure exclusive access to
+    // RETURN_BUFFER.
+    let return_buffer_mut = unsafe { RETURN_BUFFER.unsafe_mut() };
+    *return_buffer_mut = (*xsubi).into();
     *xsubi = seed16v_ref.into();
     params.reset();
-    (&raw mut BUFFER).cast()
+    RETURN_BUFFER.as_mut_ptr().cast()
 }
 
 unsafe fn copy_kv(