use start_position to handle little/big endians

Signed-off-by: onur-ozkan <[email protected]>

Author: onur-ozkan

compiler/rustc_middle/src/mir/interpret/mod.rs

@@ -668,14 +668,15 @@ pub fn write_target_uint(
 pub fn read_target_uint(endianness: Endian, mut source: &[u8]) -> Result<u128, io::Error> {
     // This u128 holds an "any-size uint" (since smaller uints can fits in it)
     let mut buf = [0u8; std::mem::size_of::<u128>()];
+    let start_position = 16 - source.len();
     // So we do not read exactly 16 bytes into the u128, just the "payload".
     let uint = match endianness {
         Endian::Little => {
-            let _ = source.read(&mut buf)?;
+            source.read_exact(&mut buf[..start_position])?;
             Ok(u128::from_le_bytes(buf))
         }
         Endian::Big => {
-            source.read_exact(&mut buf[16 - source.len()..])?;
+            source.read_exact(&mut buf[start_position..])?;
             Ok(u128::from_be_bytes(buf))
         }
     };

compiler/stable_mir/src/mir/alloc.rs

@@ -55,13 +55,14 @@ impl IndexedVal for AllocId {
 /// Utility function used to read an allocation data into a unassigned integer.
 pub(crate) fn read_target_uint(mut bytes: &[u8]) -> Result<u128, Error> {
     let mut buf = [0u8; std::mem::size_of::<u128>()];
+    let start_position = 16 - bytes.len();
     match MachineInfo::target_endianess() {
         Endian::Little => {
-            let _ = bytes.read(&mut buf)?;
+            bytes.read_exact(&mut buf[..start_position])?;
             Ok(u128::from_le_bytes(buf))
         }
         Endian::Big => {
-            bytes.read_exact(&mut buf[16 - bytes.len()..])?;
+            bytes.read_exact(&mut buf[start_position..])?;
             Ok(u128::from_be_bytes(buf))
         }
     }
@@ -70,13 +71,14 @@ pub(crate) fn read_target_uint(mut bytes: &[u8]) -> Result<u128, Error> {
 /// Utility function used to read an allocation data into an assigned integer.
 pub(crate) fn read_target_int(mut bytes: &[u8]) -> Result<i128, Error> {
     let mut buf = [0u8; std::mem::size_of::<i128>()];
+    let start_position = 16 - bytes.len();
     match MachineInfo::target_endianess() {
         Endian::Little => {
-            let _ = bytes.read(&mut buf)?;
+            bytes.read_exact(&mut buf[..start_position])?;
             Ok(i128::from_le_bytes(buf))
         }
         Endian::Big => {
-            bytes.read_exact(&mut buf[16 - bytes.len()..])?;
+            bytes.read_exact(&mut buf[start_position..])?;
             Ok(i128::from_be_bytes(buf))
         }
     }