PR small fix

Signed-off-by: Chizkiyahu Raful <chizkiyahu.raful@arm.com>
Change-Id: Iae1bbafa0f38a7031d2bc805403e4075a523cd5e

Author: chizkiyahu

.github/workflows/validate_flatbuffer_gen.yml

@@ -5,7 +5,7 @@ on:
   pull_request:
     paths:
       - "schema/**"
-      - "executorch_flatbuffer/**"
+      - "exir/_serialize/generated/executorch_flatbuffer/**"
 
 jobs:
   exir-flatbuffer:

exir/_serialize/_flatbuffer_program.py

@@ -6,6 +6,7 @@
 # pyre-strict
 
 import enum
+import functools
 import importlib
 import tempfile
 
@@ -111,15 +112,12 @@ def _pack_backend_delegate_inline_data(self: Any, builder: Any) -> int:
     return _BackendDelegateInlineData.BackendDelegateInlineDataEnd(builder)
 
 
+@functools.lru_cache(maxsize=1)
 def _install_fast_packers() -> None:
-    global _PACKERS_INSTALLED
-    if _PACKERS_INSTALLED:
-        return
-    _Buffer.BufferT.Pack = _pack_buffer  # pyre-ignore[16]
-    _BackendDelegateInlineData.BackendDelegateInlineDataT.Pack = (  # pyre-ignore[16]
+    _Buffer.BufferT.Pack = _pack_buffer
+    _BackendDelegateInlineData.BackendDelegateInlineDataT.Pack = (
         _pack_backend_delegate_inline_data
     )
-    _PACKERS_INSTALLED = True
 
 
 def _set_pack_alignments(tensor_alignment: int, delegate_alignment: int) -> None:

exir/_serialize/generate_program.py

@@ -52,6 +52,14 @@ def _run_flatc(repo_root: Path) -> None:
 
 
 def _rewrite_imports(repo_root: Path) -> int:
+    """Rewrite flatc imports to the in-tree package path.
+
+    flatc derives the import path from the namespace declaration (executorch_flatbuffer).
+    Modifying the namespace results in widespread breaking
+    changes across both the Python and C++ codebases.
+    so we rewrite the generated files to import
+    from executorch.exir._serialize.generated.executorch_flatbuffer instead
+    """
     generated_dir = (
         repo_root / "exir" / "_serialize" / "generated" / "executorch_flatbuffer"
     )
@@ -106,7 +114,7 @@ def _write_init_files(repo_root: Path) -> int:
     top_init = generated_dir / "__init__.py"
     top_init_contents = "\n".join(
         [
-            "# automatically generated by exir/_serialize/generate.py, do not modify",
+            "# automatically generated by exir/_serialize/generate_program.py, do not modify",
             "",
             "from . import executorch_flatbuffer",
             "",
@@ -129,7 +137,7 @@ def _write_init_files(repo_root: Path) -> int:
     )
     fb_init = generated_fb_dir / "__init__.py"
     fb_init_contents = [
-        "# automatically generated by exir/_serialize/generate.py, do not modify",
+        "# automatically generated by exir/_serialize/generate_program.py, do not modify",
         "",
     ]
     fb_init_contents.extend(f"from . import {name}" for name in module_names)

exir/_serialize/generated/__init__.py

@@ -1,4 +1,4 @@
-# automatically generated by exir/_serialize/generate.py, do not modify
+# automatically generated by exir/_serialize/generate_program.py, do not modify
 
 from . import executorch_flatbuffer
 

exir/_serialize/generated/executorch_flatbuffer/__init__.py

@@ -1,4 +1,4 @@
-# automatically generated by exir/_serialize/generate.py, do not modify
+# automatically generated by exir/_serialize/generate_program.py, do not modify
 
 from . import AllocationDetails
 from . import BackendDelegate

exir/_serialize/test/test_flatbuffer.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env fbpython
 # Copyright (c) Meta Platforms, Inc. and affiliates.
+# Copyright 2026 Arm Limited and/or its affiliates.
 # All rights reserved.
 #
 # This source code is licensed under the BSD-style license found in the
@@ -76,6 +77,7 @@ def test_load_patch_and_write(self) -> None:
 SCHEMA_FILES: Dict[str, bytes] = {
     "program.fbs": b"\n".join(
         [
+            b'file_identifier "ET12";',
             b"table Program {",
             # Space after the colon.
             b"  tensor_data: [ubyte] (force_align: 8); // @executorch-tensor-alignment",
@@ -146,6 +148,7 @@ def test_update_tensor_alignment(self) -> None:
                 read_file(out_dir, "program.fbs"),
                 b"\n".join(
                     [
+                        b'file_identifier "ET12";',
                         b"table Program {",
                         # Now 128:
                         b"  tensor_data: [ubyte] (force_align: 128); // @executorch-tensor-alignment",
@@ -182,6 +185,7 @@ def test_update_delegate_alignment(self) -> None:
                 read_file(out_dir, "program.fbs"),
                 b"\n".join(
                     [
+                        b'file_identifier "ET12";',
                         b"table Program {",
                         b"  tensor_data: [ubyte] (force_align: 8); // @executorch-tensor-alignment",
                         # Now 256:
@@ -221,6 +225,7 @@ def test_update_tensor_and_delegate_alignment(self) -> None:
                 read_file(out_dir, "program.fbs"),
                 b"\n".join(
                     [
+                        b'file_identifier "ET12";',
                         b"table Program {",
                         # Now 1:
                         b"  tensor_data: [ubyte] (force_align: 1); // @executorch-tensor-alignment",

schema/README.md

@@ -7,7 +7,7 @@ The `scalar_type.fbs` file contains schema for scalar types.
 ## Regenerating generated code
 
 Schema changes require regenerating the Python bindings in
-`executorch_flatbuffer` and committing the updated files. From the repo root:
+`exir/_serialize/generated/executorch_flatbuffer` and committing the updated files. From the repo root:
 
 ```sh
 python exir/_serialize/generate_program.py

schema/program.fbs

@@ -1,4 +1,5 @@
 // Copyright (c) Meta Platforms, Inc. and affiliates.
+// Copyright 2026 Arm Limited and/or its affiliates.
 
 //
 // See README.md before modifying this file.
@@ -389,6 +390,10 @@ table ExecutionPlan {
 }
 
 // Constant tensor data stored directly in the flatbuffer.
+// NOTE: If you change Buffer or BackendDelegateInlineData fields, update the
+// custom packers in exir/_serialize/_flatbuffer_program.py
+// (_pack_buffer and _pack_backend_delegate_inline_data);
+// they override the flatc-generated packers.
 table Buffer {
   // During serialization, this alignment may be rewritten to a larger value.
   // The magic "@executorch-tensor-alignment" comment tells EXIR which lines to
@@ -399,6 +404,10 @@ table Buffer {
 // Delegate data stored directly in the flatbuffer. This is a different type
 // than Buffer because tensors and delegates can have different alignment
 // requirements.
+// NOTE: If you change Buffer or BackendDelegateInlineData fields, update the
+// custom packers in exir/_serialize/_flatbuffer_program.py
+// (_pack_buffer and _pack_backend_delegate_inline_data);
+// they override the flatc-generated packers.
 table BackendDelegateInlineData {
   // During serialization, this alignment may be rewritten to a larger value.
   // The magic "@executorch-delegate-alignment" comment tells EXIR which lines