From d82b7a7c1d73c0674698d9601b1bbb0200933f29 Mon Sep 17 00:00:00 2001
From: Aleksei Nikiforov
 <103434461+AlekseiNikiforovIBM@users.noreply.github.com>
Date: Fri, 28 Nov 2025 20:53:01 +0100
Subject: [PATCH] gguf-py : fix passing non-native endian tensors (editor-gui
 and new-metadata) (#17553)

gguf_new_metadata.py reads data from reader.
Reader doesn't byteswap tensors to native endianness.
But writer does expect tensors in native endianness to convert them
into requested endianness.

There are two ways to fix this: update reader and do conversion to native endianness and back,
or skip converting endianness in writer in this particular USE-case.

gguf_editor_gui.py doesn't allow editing or viewing tensor data.
Let's go with skipping excessive byteswapping.

If eventually capability to view or edit tensor data is added,
tensor data should be instead byteswapped when reading it.
---
 gguf-py/gguf/gguf_writer.py               | 18 ++++++++++++------
 gguf-py/gguf/scripts/gguf_editor_gui.py   |  2 +-
 gguf-py/gguf/scripts/gguf_new_metadata.py |  2 +-
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/gguf-py/gguf/gguf_writer.py b/gguf-py/gguf/gguf_writer.py
index 57ca2035fe..8ddd895cb7 100644
--- a/gguf-py/gguf/gguf_writer.py
+++ b/gguf-py/gguf/gguf_writer.py
@@ -371,10 +371,13 @@ class GGUFWriter:
 
     def add_tensor(
         self, name: str, tensor: np.ndarray[Any, Any], raw_shape: Sequence[int] | None = None,
-        raw_dtype: GGMLQuantizationType | None = None,
+        raw_dtype: GGMLQuantizationType | None = None, tensor_endianess: GGUFEndian | None = None
     ) -> None:
-        if (self.endianess == GGUFEndian.BIG and sys.byteorder != 'big') or \
-                (self.endianess == GGUFEndian.LITTLE and sys.byteorder != 'little'):
+        # if tensor endianness is not passed, assume it's native to system
+        if tensor_endianess is None:
+            tensor_endianess = GGUFEndian.BIG if sys.byteorder == 'big' else GGUFEndian.LITTLE
+
+        if tensor_endianess != self.endianess:
             # Don't byteswap inplace since lazy copies cannot handle it
             tensor = tensor.byteswap(inplace=False)
         if self.use_temp_file and self.temp_file is None:
@@ -397,13 +400,16 @@ class GGUFWriter:
         if pad != 0:
             fp.write(bytes([0] * pad))
 
-    def write_tensor_data(self, tensor: np.ndarray[Any, Any]) -> None:
+    def write_tensor_data(self, tensor: np.ndarray[Any, Any], tensor_endianess: GGUFEndian | None = None) -> None:
         if self.state is not WriterState.TI_DATA and self.state is not WriterState.WEIGHTS:
             raise ValueError(f'Expected output file to contain tensor info or weights, got {self.state}')
         assert self.fout is not None
 
-        if (self.endianess == GGUFEndian.BIG and sys.byteorder != 'big') or \
-                (self.endianess == GGUFEndian.LITTLE and sys.byteorder != 'little'):
+        # if tensor endianness is not passed, assume it's native to system
+        if tensor_endianess is None:
+            tensor_endianess = GGUFEndian.BIG if sys.byteorder == 'big' else GGUFEndian.LITTLE
+
+        if tensor_endianess != self.endianess:
             # Don't byteswap inplace since lazy copies cannot handle it
             tensor = tensor.byteswap(inplace=False)
 
diff --git a/gguf-py/gguf/scripts/gguf_editor_gui.py b/gguf-py/gguf/scripts/gguf_editor_gui.py
index 05f4db0f8c..293316afed 100755
--- a/gguf-py/gguf/scripts/gguf_editor_gui.py
+++ b/gguf-py/gguf/scripts/gguf_editor_gui.py
@@ -1552,7 +1552,7 @@ class GGUFEditorWindow(QMainWindow):
 
             # Add tensors (including data)
             for tensor in self.reader.tensors:
-                writer.add_tensor(tensor.name, tensor.data, raw_shape=tensor.data.shape, raw_dtype=tensor.tensor_type)
+                writer.add_tensor(tensor.name, tensor.data, raw_shape=tensor.data.shape, raw_dtype=tensor.tensor_type, tensor_endianess=self.reader.endianess)
 
             # Write header and metadata
             writer.open_output_file(Path(file_path))
diff --git a/gguf-py/gguf/scripts/gguf_new_metadata.py b/gguf-py/gguf/scripts/gguf_new_metadata.py
index 2fa5800cf7..c67436bad4 100755
--- a/gguf-py/gguf/scripts/gguf_new_metadata.py
+++ b/gguf-py/gguf/scripts/gguf_new_metadata.py
@@ -94,7 +94,7 @@ def copy_with_new_metadata(reader: gguf.GGUFReader, writer: gguf.GGUFWriter, new
     writer.write_ti_data_to_file()
 
     for tensor in reader.tensors:
-        writer.write_tensor_data(tensor.data)
+        writer.write_tensor_data(tensor.data, tensor_endianess=reader.endianess)
         bar.update(tensor.n_bytes)
 
     writer.close()