files: make read/write take callback to store result

src/shims/files.rs

@@ -1,6 +1,6 @@
 use std::any::Any;
 use std::collections::BTreeMap;
-use std::io::{IsTerminal, Read, SeekFrom, Write};
+use std::io::{IsTerminal, SeekFrom, Write};
 use std::marker::CoercePointee;
 use std::ops::Deref;
 use std::rc::{Rc, Weak};
@@ -140,8 +140,8 @@ pub trait FileDescription: std::fmt::Debug + FileDescriptionExt {
         _communicate_allowed: bool,
         _ptr: Pointer,
         _len: usize,
-        _dest: &MPlaceTy<'tcx>,
         _ecx: &mut MiriInterpCx<'tcx>,
+        _finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
         throw_unsup_format!("cannot read from {}", self.name());
     }
@@ -154,8 +154,8 @@ pub trait FileDescription: std::fmt::Debug + FileDescriptionExt {
         _communicate_allowed: bool,
         _ptr: Pointer,
         _len: usize,
-        _dest: &MPlaceTy<'tcx>,
         _ecx: &mut MiriInterpCx<'tcx>,
+        _finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
         throw_unsup_format!("cannot write to {}", self.name());
     }
@@ -207,19 +207,16 @@ impl FileDescription for io::Stdin {
         communicate_allowed: bool,
         ptr: Pointer,
         len: usize,
-        dest: &MPlaceTy<'tcx>,
         ecx: &mut MiriInterpCx<'tcx>,
+        finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
-        let mut bytes = vec![0; len];
         if !communicate_allowed {
             // We want isolation mode to be deterministic, so we have to disallow all reads, even stdin.
             helpers::isolation_abort_error("`read` from stdin")?;
         }
-        let result = Read::read(&mut &*self, &mut bytes);
-        match result {
-            Ok(read_size) => ecx.return_read_success(ptr, &bytes, read_size, dest),
-            Err(e) => ecx.set_last_error_and_return(e, dest),
-        }
+
+        let result = ecx.read_from_host(&*self, len, ptr)?;
+        finish.call(ecx, result)
     }
 
     fn is_tty(&self, communicate_allowed: bool) -> bool {
@@ -237,22 +234,19 @@ impl FileDescription for io::Stdout {
         _communicate_allowed: bool,
         ptr: Pointer,
         len: usize,
-        dest: &MPlaceTy<'tcx>,
         ecx: &mut MiriInterpCx<'tcx>,
+        finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
-        let bytes = ecx.read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(len))?;
-        // We allow writing to stderr even with isolation enabled.
-        let result = Write::write(&mut &*self, bytes);
+        // We allow writing to stdout even with isolation enabled.
+        let result = ecx.write_to_host(&*self, len, ptr)?;
         // Stdout is buffered, flush to make sure it appears on the
         // screen.  This is the write() syscall of the interpreted
         // program, we want it to correspond to a write() syscall on
         // the host -- there is no good in adding extra buffering
         // here.
         io::stdout().flush().unwrap();
-        match result {
-            Ok(write_size) => ecx.return_write_success(write_size, dest),
-            Err(e) => ecx.set_last_error_and_return(e, dest),
-        }
+
+        finish.call(ecx, result)
     }
 
     fn is_tty(&self, communicate_allowed: bool) -> bool {
@@ -270,17 +264,13 @@ impl FileDescription for io::Stderr {
         _communicate_allowed: bool,
         ptr: Pointer,
         len: usize,
-        dest: &MPlaceTy<'tcx>,
         ecx: &mut MiriInterpCx<'tcx>,
+        finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
-        let bytes = ecx.read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(len))?;
         // We allow writing to stderr even with isolation enabled.
+        let result = ecx.write_to_host(&*self, len, ptr)?;
         // No need to flush, stderr is not buffered.
-        let result = Write::write(&mut &*self, bytes);
-        match result {
-            Ok(write_size) => ecx.return_write_success(write_size, dest),
-            Err(e) => ecx.set_last_error_and_return(e, dest),
-        }
+        finish.call(ecx, result)
     }
 
     fn is_tty(&self, communicate_allowed: bool) -> bool {
@@ -302,11 +292,11 @@ impl FileDescription for NullOutput {
         _communicate_allowed: bool,
         _ptr: Pointer,
         len: usize,
-        dest: &MPlaceTy<'tcx>,
         ecx: &mut MiriInterpCx<'tcx>,
+        finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
         // We just don't write anything, but report to the user that we did.
-        ecx.return_write_success(len, dest)
+        finish.call(ecx, Ok(len))
     }
 }
 
@@ -405,40 +395,41 @@ impl FdTable {
 
 impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
 pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
-    /// Helper to implement `FileDescription::read`:
-    /// This is only used when `read` is successful.
-    /// `actual_read_size` should be the return value of some underlying `read` call that used
-    /// `bytes` as its output buffer.
-    /// The length of `bytes` must not exceed either the host's or the target's `isize`.
-    /// `bytes` is written to `buf` and the size is written to `dest`.
-    fn return_read_success(
+    /// Read data from a host `Read` type, store the result into machine memory,
+    /// and return whether that worked.
+    fn read_from_host(
         &mut self,
-        buf: Pointer,
-        bytes: &[u8],
-        actual_read_size: usize,
-        dest: &MPlaceTy<'tcx>,
-    ) -> InterpResult<'tcx> {
+        mut file: impl io::Read,
+        len: usize,
+        ptr: Pointer,
+    ) -> InterpResult<'tcx, Result<usize, IoError>> {
         let this = self.eval_context_mut();
-        // If reading to `bytes` did not fail, we write those bytes to the buffer.
-        // Crucially, if fewer than `bytes.len()` bytes were read, only write
-        // that much into the output buffer!
-        this.write_bytes_ptr(buf, bytes[..actual_read_size].iter().copied())?;
 
-        // The actual read size is always less than what got originally requested so this cannot fail.
-        this.write_int(u64::try_from(actual_read_size).unwrap(), dest)?;
-        interp_ok(())
+        let mut bytes = vec![0; len];
+        let result = file.read(&mut bytes);
+        match result {
+            Ok(read_size) => {
+                // If reading to `bytes` did not fail, we write those bytes to the buffer.
+                // Crucially, if fewer than `bytes.len()` bytes were read, only write
+                // that much into the output buffer!
+                this.write_bytes_ptr(ptr, bytes[..read_size].iter().copied())?;
+                interp_ok(Ok(read_size))
+            }
+            Err(e) => interp_ok(Err(IoError::HostError(e))),
+        }
     }
 
-    /// Helper to implement `FileDescription::write`:
-    /// This function is only used when `write` is successful, and writes `actual_write_size` to `dest`
-    fn return_write_success(
+    /// Write data to a host `Write` type, withthe bytes taken from machine memory.
+    fn write_to_host(
         &mut self,
-        actual_write_size: usize,
-        dest: &MPlaceTy<'tcx>,
-    ) -> InterpResult<'tcx> {
+        mut file: impl io::Write,
+        len: usize,
+        ptr: Pointer,
+    ) -> InterpResult<'tcx, Result<usize, IoError>> {
         let this = self.eval_context_mut();
-        // The actual write size is always less than what got originally requested so this cannot fail.
-        this.write_int(u64::try_from(actual_write_size).unwrap(), dest)?;
-        interp_ok(())
+
+        let bytes = this.read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(len))?;
+        let result = file.write(bytes);
+        interp_ok(result.map_err(IoError::HostError))
     }
 }

src/shims/unix/fd.rs

@@ -30,8 +30,8 @@ pub trait UnixFileDescription: FileDescription {
         _offset: u64,
         _ptr: Pointer,
         _len: usize,
-        _dest: &MPlaceTy<'tcx>,
         _ecx: &mut MiriInterpCx<'tcx>,
+        _finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
         throw_unsup_format!("cannot pread from {}", self.name());
     }
@@ -46,8 +46,8 @@ pub trait UnixFileDescription: FileDescription {
         _ptr: Pointer,
         _len: usize,
         _offset: u64,
-        _dest: &MPlaceTy<'tcx>,
         _ecx: &mut MiriInterpCx<'tcx>,
+        _finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
         throw_unsup_format!("cannot pwrite to {}", self.name());
     }
@@ -236,7 +236,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         let count = usize::try_from(count).unwrap(); // now it fits in a `usize`
         let communicate = this.machine.communicate();
 
-        // We temporarily dup the FD to be able to retain mutable access to `this`.
+        // Get the FD.
         let Some(fd) = this.machine.fds.get(fd_num) else {
             trace!("read: FD not found");
             return this.set_last_error_and_return(LibcError("EBADF"), dest);
@@ -247,13 +247,33 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         // because it was a target's `usize`. Also we are sure that its smaller than
         // `usize::MAX` because it is bounded by the host's `isize`.
 
+        let finish = {
+            let dest = dest.clone();
+            callback!(
+                @capture<'tcx> {
+                    count: usize,
+                    dest: MPlaceTy<'tcx>,
+                }
+                |this, result: Result<usize, IoError>| {
+                    match result {
+                        Ok(read_size) => {
+                            assert!(read_size <= count);
+                            // This must fit since `count` fits.
+                            this.write_int(u64::try_from(read_size).unwrap(), &dest)
+                        }
+                        Err(e) => {
+                            this.set_last_error_and_return(e, &dest)
+                        }
+                }}
+            )
+        };
         match offset {
-            None => fd.read(communicate, buf, count, dest, this)?,
+            None => fd.read(communicate, buf, count, this, finish)?,
             Some(offset) => {
                 let Ok(offset) = u64::try_from(offset) else {
                     return this.set_last_error_and_return(LibcError("EINVAL"), dest);
                 };
-                fd.as_unix().pread(communicate, offset, buf, count, dest, this)?
+                fd.as_unix().pread(communicate, offset, buf, count, this, finish)?
             }
         };
         interp_ok(())
@@ -287,13 +307,33 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             return this.set_last_error_and_return(LibcError("EBADF"), dest);
         };
 
+        let finish = {
+            let dest = dest.clone();
+            callback!(
+                @capture<'tcx> {
+                    count: usize,
+                    dest: MPlaceTy<'tcx>,
+                }
+                |this, result: Result<usize, IoError>| {
+                    match result {
+                        Ok(write_size) => {
+                            assert!(write_size <= count);
+                            // This must fit since `count` fits.
+                            this.write_int(u64::try_from(write_size).unwrap(), &dest)
+                        }
+                        Err(e) => {
+                            this.set_last_error_and_return(e, &dest)
+                        }
+                }}
+            )
+        };
         match offset {
-            None => fd.write(communicate, buf, count, dest, this)?,
+            None => fd.write(communicate, buf, count, this, finish)?,
             Some(offset) => {
                 let Ok(offset) = u64::try_from(offset) else {
                     return this.set_last_error_and_return(LibcError("EINVAL"), dest);
                 };
-                fd.as_unix().pwrite(communicate, buf, count, offset, dest, this)?
+                fd.as_unix().pwrite(communicate, buf, count, offset, this, finish)?
             }
         };
         interp_ok(())

src/shims/unix/fs.rs

@@ -35,33 +35,27 @@ impl FileDescription for FileHandle {
         communicate_allowed: bool,
         ptr: Pointer,
         len: usize,
-        dest: &MPlaceTy<'tcx>,
         ecx: &mut MiriInterpCx<'tcx>,
+        finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
         assert!(communicate_allowed, "isolation should have prevented even opening a file");
-        let mut bytes = vec![0; len];
-        let result = (&mut &self.file).read(&mut bytes);
-        match result {
-            Ok(read_size) => ecx.return_read_success(ptr, &bytes, read_size, dest),
-            Err(e) => ecx.set_last_error_and_return(e, dest),
-        }
+
+        let result = ecx.read_from_host(&self.file, len, ptr)?;
+        finish.call(ecx, result)
     }
 
     fn write<'tcx>(
         self: FileDescriptionRef<Self>,
         communicate_allowed: bool,
         ptr: Pointer,
         len: usize,
-        dest: &MPlaceTy<'tcx>,
         ecx: &mut MiriInterpCx<'tcx>,
+        finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
         assert!(communicate_allowed, "isolation should have prevented even opening a file");
-        let bytes = ecx.read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(len))?;
-        let result = (&mut &self.file).write(bytes);
-        match result {
-            Ok(write_size) => ecx.return_write_success(write_size, dest),
-            Err(e) => ecx.set_last_error_and_return(e, dest),
-        }
+
+        let result = ecx.write_to_host(&self.file, len, ptr)?;
+        finish.call(ecx, result)
     }
 
     fn seek<'tcx>(
@@ -119,8 +113,8 @@ impl UnixFileDescription for FileHandle {
         offset: u64,
         ptr: Pointer,
         len: usize,
-        dest: &MPlaceTy<'tcx>,
         ecx: &mut MiriInterpCx<'tcx>,
+        finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
         assert!(communicate_allowed, "isolation should have prevented even opening a file");
         let mut bytes = vec![0; len];
@@ -137,11 +131,17 @@ impl UnixFileDescription for FileHandle {
                 .expect("failed to restore file position, this shouldn't be possible");
             res
         };
-        let result = f();
-        match result {
-            Ok(read_size) => ecx.return_read_success(ptr, &bytes, read_size, dest),
-            Err(e) => ecx.set_last_error_and_return(e, dest),
-        }
+        let result = match f() {
+            Ok(read_size) => {
+                // If reading to `bytes` did not fail, we write those bytes to the buffer.
+                // Crucially, if fewer than `bytes.len()` bytes were read, only write
+                // that much into the output buffer!
+                ecx.write_bytes_ptr(ptr, bytes[..read_size].iter().copied())?;
+                Ok(read_size)
+            }
+            Err(e) => Err(IoError::HostError(e)),
+        };
+        finish.call(ecx, result)
     }
 
     fn pwrite<'tcx>(
@@ -150,8 +150,8 @@ impl UnixFileDescription for FileHandle {
         ptr: Pointer,
         len: usize,
         offset: u64,
-        dest: &MPlaceTy<'tcx>,
         ecx: &mut MiriInterpCx<'tcx>,
+        finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
     ) -> InterpResult<'tcx> {
         assert!(communicate_allowed, "isolation should have prevented even opening a file");
         // Emulates pwrite using seek + write + seek to restore cursor position.
@@ -169,10 +169,7 @@ impl UnixFileDescription for FileHandle {
             res
         };
         let result = f();
-        match result {
-            Ok(write_size) => ecx.return_write_success(write_size, dest),
-            Err(e) => ecx.set_last_error_and_return(e, dest),
-        }
+        finish.call(ecx, result.map_err(IoError::HostError))
     }
 
     fn flock<'tcx>(