Let FileDescription::pread to do the actual read

Author: tiif

src/shims/unix/fd.rs

@@ -56,6 +56,8 @@ pub trait FileDescription: std::fmt::Debug + Any {
         _communicate_allowed: bool,
         _bytes: &mut [u8],
         _offset: u64,
+        _ptr: Pointer,
+        _dest: &MPlaceTy<'tcx>,
         _ecx: &mut MiriInterpCx<'tcx>,
     ) -> InterpResult<'tcx, io::Result<usize>> {
         throw_unsup_format!("cannot pread from {}", self.name());
@@ -584,9 +586,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     this.write_scalar(Scalar::from_target_isize(-1, this), dest)?;
                     return Ok(());
                 };
-                let result = fd.pread(communicate, &mut bytes, offset, this);
-                self.read_byte_helper(buf, bytes, result, dest)?;
-                return Ok(());
+                fd.pread(communicate, &mut bytes, offset, buf, dest, this)?
             }
         };
         Ok(())

src/shims/unix/fs.rs

@@ -62,7 +62,9 @@ impl FileDescription for FileHandle {
         communicate_allowed: bool,
         bytes: &mut [u8],
         offset: u64,
-        _ecx: &mut MiriInterpCx<'tcx>,
+        ptr: Pointer,
+        dest: &MPlaceTy<'tcx>,
+        ecx: &mut MiriInterpCx<'tcx>,
     ) -> InterpResult<'tcx, io::Result<usize>> {
         assert!(communicate_allowed, "isolation should have prevented even opening a file");
         // Emulates pread using seek + read + seek to restore cursor position.
@@ -78,7 +80,10 @@ impl FileDescription for FileHandle {
                 .expect("failed to restore file position, this shouldn't be possible");
             res
         };
-        Ok(f())
+        let result = Ok(f());
+        ecx.read_byte_helper(ptr, bytes.to_vec(), result, dest)?;
+        // TODO: remove the usize later
+        Ok(Ok(0))
     }
 
     fn pwrite<'tcx>(