Use a u64 for the rmeta root position

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -700,28 +700,26 @@ impl MetadataBlob {
     }
 
     pub(crate) fn get_rustc_version(&self) -> String {
-        LazyValue::<String>::from_position(NonZeroUsize::new(METADATA_HEADER.len() + 4).unwrap())
+        LazyValue::<String>::from_position(NonZeroUsize::new(METADATA_HEADER.len() + 8).unwrap())
             .decode(self)
     }
 
-    pub(crate) fn get_header(&self) -> CrateHeader {
+    fn root_pos(&self) -> NonZeroUsize {
         let slice = &self.blob()[..];
         let offset = METADATA_HEADER.len();
+        let pos_bytes = slice[offset..][..8].try_into().unwrap();
+        let pos = u64::from_le_bytes(pos_bytes);
+        NonZeroUsize::new(pos as usize).unwrap()
+    }
 
-        let pos_bytes = slice[offset..][..4].try_into().unwrap();
-        let pos = u32::from_be_bytes(pos_bytes) as usize;
-
-        LazyValue::<CrateHeader>::from_position(NonZeroUsize::new(pos).unwrap()).decode(self)
+    pub(crate) fn get_header(&self) -> CrateHeader {
+        let pos = self.root_pos();
+        LazyValue::<CrateHeader>::from_position(pos).decode(self)
     }
 
     pub(crate) fn get_root(&self) -> CrateRoot {
-        let slice = &self.blob()[..];
-        let offset = METADATA_HEADER.len();
-
-        let pos_bytes = slice[offset..][..4].try_into().unwrap();
-        let pos = u32::from_be_bytes(pos_bytes) as usize;
-
-        LazyValue::<CrateRoot>::from_position(NonZeroUsize::new(pos).unwrap()).decode(self)
+        let pos = self.root_pos();
+        LazyValue::<CrateRoot>::from_position(pos).decode(self)
     }
 
     pub(crate) fn list_crate_metadata(

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -2213,7 +2213,7 @@ fn encode_metadata_impl(tcx: TyCtxt<'_>, path: &Path) {
     encoder.emit_raw_bytes(METADATA_HEADER);
 
     // Will be filled with the root position after encoding everything.
-    encoder.emit_raw_bytes(&[0, 0, 0, 0]);
+    encoder.emit_raw_bytes(&[0u8; 8]);
 
     let source_map_files = tcx.sess.source_map().files();
     let source_file_cache = (source_map_files[0].clone(), 0);
@@ -2269,7 +2269,7 @@ fn encode_root_position(mut file: &File, pos: usize) -> Result<(), std::io::Erro
     // Encode the root position.
     let header = METADATA_HEADER.len();
     file.seek(std::io::SeekFrom::Start(header as u64))?;
-    file.write_all(&[(pos >> 24) as u8, (pos >> 16) as u8, (pos >> 8) as u8, (pos >> 0) as u8])?;
+    file.write_all(&pos.to_le_bytes())?;
 
     // Return to the position where we are before writing the root position.
     file.seek(std::io::SeekFrom::Start(pos_before_seek))?;

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -57,12 +57,12 @@ pub(crate) fn rustc_version(cfg_version: &'static str) -> String {
 /// Metadata encoding version.
 /// N.B., increment this if you change the format of metadata such that
 /// the rustc version can't be found to compare with `rustc_version()`.
-const METADATA_VERSION: u8 = 8;
+const METADATA_VERSION: u8 = 9;
 
 /// Metadata header which includes `METADATA_VERSION`.
 ///
 /// This header is followed by the length of the compressed data, then
-/// the position of the `CrateRoot`, which is encoded as a 32-bit big-endian
+/// the position of the `CrateRoot`, which is encoded as a 64-bit little-endian
 /// unsigned integer, and further followed by the rustc version string.
 pub const METADATA_HEADER: &[u8] = &[b'r', b'u', b's', b't', 0, 0, 0, METADATA_VERSION];