make the obsucre truncating variant of this.write_os_str_to_wide_str a non-default function

src/tools/miri/src/shims/env.rs

@@ -178,7 +178,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     &var,
                     buf_ptr,
                     buf_size.into(),
-                    /*truncate*/ false,
                 )?))
                 // This can in fact return 0. It is up to the caller to set last_error to 0
                 // beforehand and check it afterwards to exclude that case.
@@ -380,7 +379,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 // This can in fact return 0. It is up to the caller to set last_error to 0
                 // beforehand and check it afterwards to exclude that case.
                 return Ok(Scalar::from_u32(windows_check_buffer_size(
-                    this.write_path_to_wide_str(&cwd, buf, size, /*truncate*/ false)?,
+                    this.write_path_to_wide_str(&cwd, buf, size)?,
                 )));
             }
             Err(e) => this.set_last_error_from_io_error(e.kind())?,
@@ -535,12 +534,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 };
                 // Of course we cannot use `windows_check_buffer_size` here since this uses
                 // a different method for dealing with a too-small buffer than the other functions...
-                let (success, len) = this.write_path_to_wide_str(
+                let (success, len) = this.write_path_to_wide_str(home, buf, size_avail.into())?;
-                    home,
-                    buf,
-                    size_avail.into(),
-                    /*truncate*/ false,
-                )?;
                 // The Windows docs just say that this is written on failure. But std
                 // seems to rely on it always being written.
                 this.write_scalar(Scalar::from_u32(len.try_into().unwrap()), &size)?;

src/tools/miri/src/shims/os_str.rs

@@ -72,11 +72,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         u16vec_to_osstring(u16_vec)
     }
 
-    /// Helper function to write an OsStr as a null-terminated sequence of bytes, which is what
+    /// Helper function to write an OsStr as a null-terminated sequence of bytes, which is what the
-    /// the Unix APIs usually handle. This function returns `Ok((false, length))` without trying
+    /// Unix APIs usually handle. Returns `(success, full_len)`, where length includes the null
-    /// to write if `size` is not large enough to fit the contents of `os_string` plus a null
+    /// terminator. On failure, nothing is written.
-    /// terminator. It returns `Ok((true, length))` if the writing process was successful. The
-    /// string length returned does include the null terminator.
     fn write_os_str_to_c_str(
         &mut self,
         os_str: &OsStr,
@@ -87,19 +85,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         self.eval_context_mut().write_c_str(bytes, ptr, size)
     }
 
-    /// Helper function to write an OsStr as a 0x0000-terminated u16-sequence, which is what the
+    /// Internal helper to share code between `write_os_str_to_wide_str` and
-    /// Windows APIs usually handle.
+    /// `write_os_str_to_wide_str_truncated`.
-    ///
+    fn write_os_str_to_wide_str_helper(
-    /// If `truncate == false` (the usual mode of operation), this function returns `Ok((false,
-    /// length))` without trying to write if `size` is not large enough to fit the contents of
-    /// `os_string` plus a null terminator. It returns `Ok((true, length))` if the writing process
-    /// was successful. The string length returned does include the null terminator. Length is
-    /// measured in units of `u16.`
-    ///
-    /// If `truncate == true`, then in case `size` is not large enough it *will* write the first
-    /// `size.saturating_sub(1)` many items, followed by a null terminator (if `size > 0`).
-    /// The return value is still `(false, length)` in that case.
-    fn write_os_str_to_wide_str(
         &mut self,
         os_str: &OsStr,
         ptr: Pointer<Option<Provenance>>,
@@ -133,6 +121,29 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         Ok((written, size_needed))
     }
 
+    /// Helper function to write an OsStr as a 0x0000-terminated u16-sequence, which is what the
+    /// Windows APIs usually handle. Returns `(success, full_len)`, where length is measured
+    /// in units of `u16` and includes the null terminator. On failure, nothing is written.
+    fn write_os_str_to_wide_str(
+        &mut self,
+        os_str: &OsStr,
+        ptr: Pointer<Option<Provenance>>,
+        size: u64,
+    ) -> InterpResult<'tcx, (bool, u64)> {
+        self.write_os_str_to_wide_str_helper(os_str, ptr, size, /*truncate*/ false)
+    }
+
+    /// Like `write_os_str_to_wide_str`, but on failure as much as possible is written into
+    /// the buffer (always with a null terminator).
+    fn write_os_str_to_wide_str_truncated(
+        &mut self,
+        os_str: &OsStr,
+        ptr: Pointer<Option<Provenance>>,
+        size: u64,
+    ) -> InterpResult<'tcx, (bool, u64)> {
+        self.write_os_str_to_wide_str_helper(os_str, ptr, size, /*truncate*/ true)
+    }
+
     /// Allocate enough memory to store the given `OsStr` as a null-terminated sequence of bytes.
     fn alloc_os_str_as_c_str(
         &mut self,
@@ -160,9 +171,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
         let arg_type = Ty::new_array(this.tcx.tcx, this.tcx.types.u16, size);
         let arg_place = this.allocate(this.layout_of(arg_type).unwrap(), memkind)?;
-        let (written, _) = self
+        let (written, _) = self.write_os_str_to_wide_str(os_str, arg_place.ptr(), size).unwrap();
-            .write_os_str_to_wide_str(os_str, arg_place.ptr(), size, /*truncate*/ false)
-            .unwrap();
         assert!(written);
         Ok(arg_place.ptr())
     }
@@ -217,12 +226,25 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         path: &Path,
         ptr: Pointer<Option<Provenance>>,
         size: u64,
-        truncate: bool,
     ) -> InterpResult<'tcx, (bool, u64)> {
         let this = self.eval_context_mut();
         let os_str =
             this.convert_path(Cow::Borrowed(path.as_os_str()), PathConversion::HostToTarget);
-        this.write_os_str_to_wide_str(&os_str, ptr, size, truncate)
+        this.write_os_str_to_wide_str(&os_str, ptr, size)
+    }
+
+    /// Write a Path to the machine memory (as a null-terminated sequence of `u16`s),
+    /// adjusting path separators if needed.
+    fn write_path_to_wide_str_truncated(
+        &mut self,
+        path: &Path,
+        ptr: Pointer<Option<Provenance>>,
+        size: u64,
+    ) -> InterpResult<'tcx, (bool, u64)> {
+        let this = self.eval_context_mut();
+        let os_str =
+            this.convert_path(Cow::Borrowed(path.as_os_str()), PathConversion::HostToTarget);
+        this.write_os_str_to_wide_str_truncated(&os_str, ptr, size)
     }
 
     /// Allocate enough memory to store a Path as a null-terminated sequence of bytes,

src/tools/miri/src/shims/windows/foreign_items.rs

@@ -232,12 +232,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     }
                     Ok(abs_filename) => {
                         Scalar::from_u32(helpers::windows_check_buffer_size(
-                            this.write_path_to_wide_str(
+                            this.write_path_to_wide_str(&abs_filename, buffer, size.into())?,
-                                &abs_filename,
-                                buffer,
-                                size.into(),
-                                /*truncate*/ false,
-                            )?,
                         ))
                         // This can in fact return 0. It is up to the caller to set last_error to 0
                         // beforehand and check it afterwards to exclude that case.
@@ -608,15 +603,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
                 // Using the host current_exe is a bit off, but consistent with Linux
                 // (where stdlib reads /proc/self/exe).
-                // Unfortunately this Windows function has a crazy behavior so we can't just use
-                // `write_path_to_wide_str`...
                 let path = std::env::current_exe().unwrap();
-                let (all_written, size_needed) = this.write_path_to_wide_str(
+                let (all_written, size_needed) =
-                    &path,
+                    this.write_path_to_wide_str_truncated(&path, filename, size.into())?;
-                    filename,
-                    size.into(),
-                    /*truncate*/ true,
-                )?;
 
                 if all_written {
                     // If the function succeeds, the return value is the length of the string that
@@ -656,12 +645,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     Some(err) => format!("{err}"),
                     None => format!("<unknown error in FormatMessageW: {message_id}>"),
                 };
-                let (complete, length) = this.write_os_str_to_wide_str(
+                let (complete, length) =
-                    OsStr::new(&formatted),
+                    this.write_os_str_to_wide_str(OsStr::new(&formatted), buffer, size.into())?;
-                    buffer,
-                    size.into(),
-                    /*truncate*/ false,
-                )?;
                 if !complete {
                     // The API docs don't say what happens when the buffer is not big enough...
                     // Let's just bail.