Major update for 4.25 so can load system python shared library extension modules on debian/ubuntu eg ctypes/unittest.

David · David · commit 350998c92d7b · 2020-07-04T14:22:35.000+01:00
This may make it impossible to load Epics python and UnrealEnginePython together.
diff --git a/Source/UnrealEnginePython/Private/UnrealEnginePython.cpp b/Source/UnrealEnginePython/Private/UnrealEnginePython.cpp
@@ -28,8 +28,27 @@ void unreal_engine_init_py_module();
 void init_unreal_engine_builtin();
 
 #if PLATFORM_LINUX
+// so something seems to have changed between 4.18 and 4.25 which means we can no longer
+// import python extension modules that have/are dynamic libraries (ie site?dist-packages modules)
+// eg import ctypes fails with missing dynamic link symbol found in the primary python shared library
+// it seems that the python extension modules are not able to access the primary
+// python shared library /usr/lib/x86_64-linux-gnu/libpythonx.x.so symbols
+// OK so this gets even more confusing as apparently on other linux distributions the python extension libraries
+// ARE linked with the primary python shared library - this is a debian/ubuntu issue
+// it appears what happened is that the default symbol visibility for global symbols was changed from default to hidden
+// - likely to reduce chance of symbol clashes - it could be particularly true now with Unreals python implementation
+// although that seems to use static linking - but this fixup may mean we cannot have both python implementations
+// active
+// note that ue4_module_options is a symbol whose existence and value is checked in either LinuxPlatformProcess.cpp (4.18)
+// or UnixPlatformProcess.cpp (4.25) to determine if to load dynamic libraries using RTLD_GLOBAL
+// - otherwise RTLD_LOCAL is used
+// it apparently has to be a global symbol itself for this to work
+#if ENGINE_MINOR_VERSION >= 25
+const char *ue4_module_options __attribute__((visibility("default"))) = "linux_global_symbols";
+#else
 const char *ue4_module_options = "linux_global_symbols";
 #endif
+#endif
 
 #include "Runtime/Core/Public/Misc/CommandLine.h"
 #include "Runtime/Core/Public/Misc/ConfigCacheIni.h"
