RPATH Fix for portable_lib Python Extension (#14442)

Co-authored-by: Gregory Comer <gjcomer@meta.com>
Co-authored-by: Mergen Nachin <mnachin@meta.com>
fix from #13254
Fixes #14421.

Author: 3 people

.ci/scripts/wheel/test_base.py

@@ -41,6 +41,18 @@ class ModelTest:
 
 
 def run_tests(model_tests: List[ModelTest]) -> None:
+    # Test that we can import the portable_lib module - verifies RPATH is correct
+    print("Testing portable_lib import...")
+    try:
+        from executorch.extension.pybindings._portable_lib import (  # noqa: F401
+            _load_for_executorch,
+        )
+
+        print("✓ Successfully imported _load_for_executorch from portable_lib")
+    except ImportError as e:
+        print(f"✗ Failed to import portable_lib: {e}")
+        raise
+
     # Why are we doing this envvar shenanigans? Since we build the testers, which
     # uses buck, we cannot run as root. This is a sneaky of getting around that
     # test.

CMakeLists.txt

@@ -869,6 +869,21 @@ if(EXECUTORCH_BUILD_PYBIND)
   target_compile_options(portable_lib PUBLIC ${_pybind_compile_options})
   target_link_libraries(portable_lib PRIVATE ${_dep_libs})
 
+  # Set RPATH to find PyTorch libraries relative to the installation location
+  # This goes from executorch/extension/pybindings up to site-packages, then to
+  # torch/lib
+  if(APPLE)
+    set_target_properties(
+      portable_lib PROPERTIES BUILD_RPATH "@loader_path/../../../torch/lib"
+                              INSTALL_RPATH "@loader_path/../../../torch/lib"
+    )
+  else()
+    set_target_properties(
+      portable_lib PROPERTIES BUILD_RPATH "$ORIGIN/../../../torch/lib"
+                              INSTALL_RPATH "$ORIGIN/../../../torch/lib"
+    )
+  endif()
+
   install(
     TARGETS portable_lib
     EXPORT ExecuTorchTargets