Allow customized relative PYTHONHOME

Summary:
This change allows a hard coded relative PYTHONHOME setting. So that
python can easily be packaged together with lldb.

The change includes:
1. Extend LLDB_RELOCATABLE_PYTHON to all platforms. It defaults to ON
for platforms other than Windows, to keep the behavior compatible.
2. Allows to customize LLDB_PYTHON_HOME. But still defaults to
PYTHON_HOME.
3. LLDB_PYTHON_HOME can be a path relative to liblldb. If it is
relative, we will resolve it before send it to Py_DecodeLocale.

Subscribers: mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D74727

lldb/cmake/modules/LLDBConfig.cmake

@@ -59,7 +59,6 @@ add_optional_dependency(LLDB_ENABLE_LUA "Enable Lua scripting support in LLDB" L
 add_optional_dependency(LLDB_ENABLE_PYTHON "Enable Python scripting support in LLDB" PythonInterpAndLibs PYTHONINTERPANDLIBS_FOUND)
 add_optional_dependency(LLDB_ENABLE_LIBXML2 "Enable Libxml 2 support in LLDB" LibXml2 LIBXML2_FOUND VERSION 2.8)
 
-option(LLDB_RELOCATABLE_PYTHON "Use the PYTHONHOME environment variable to locate Python." OFF)
 option(LLDB_USE_SYSTEM_SIX "Use six.py shipped with system and do not install a copy of it" OFF)
 option(LLDB_USE_ENTITLEMENTS "When codesigning, use entitlements if available" ON)
 option(LLDB_BUILD_FRAMEWORK "Build LLDB.framework (Darwin only)" OFF)
@@ -140,10 +139,20 @@ if (LLDB_ENABLE_LIBEDIT)
 endif()
 
 if (LLDB_ENABLE_PYTHON)
+  if(CMAKE_SYSTEM_NAME MATCHES "Windows")
+    set(default_embed_python_home ON)
+  else()
+    set(default_embed_python_home OFF)
+  endif()
+  option(LLDB_EMBED_PYTHON_HOME
+    "Embed PYTHONHOME in the binary. If set to OFF, PYTHONHOME environment variable will be used to to locate Python."
+    ${default_embed_python_home})
+
   include_directories(${PYTHON_INCLUDE_DIRS})
-  if ("${CMAKE_SYSTEM_NAME}" STREQUAL "Windows" AND NOT LLDB_RELOCATABLE_PYTHON)
+  if (LLDB_EMBED_PYTHON_HOME)
     get_filename_component(PYTHON_HOME "${PYTHON_EXECUTABLE}" DIRECTORY)
-    file(TO_CMAKE_PATH "${PYTHON_HOME}" LLDB_PYTHON_HOME)
+    set(LLDB_PYTHON_HOME "${PYTHON_HOME}" CACHE STRING
+      "Path to use as PYTHONHOME in lldb. If a relative path is specified, it will be resolved at runtime relative to liblldb directory.")
   endif()
 endif()
 

lldb/include/lldb/Host/Config.h.cmake

@@ -46,6 +46,8 @@
 
 #cmakedefine01 LLDB_ENABLE_PYTHON
 
+#cmakedefine01 LLDB_EMBED_PYTHON_HOME
+
 #cmakedefine LLDB_PYTHON_HOME "${LLDB_PYTHON_HOME}"
 
 #define LLDB_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}"

lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp

@@ -277,14 +277,36 @@ struct InitializePythonRAII {
 
 private:
   void InitializePythonHome() {
-#if defined(LLDB_PYTHON_HOME)
+#if LLDB_EMBED_PYTHON_HOME
 #if PY_MAJOR_VERSION >= 3
-    size_t size = 0;
-    static wchar_t *g_python_home = Py_DecodeLocale(LLDB_PYTHON_HOME, &size);
+    typedef const wchar_t* str_type;
 #else
-    static char g_python_home[] = LLDB_PYTHON_HOME;
+    typedef char* str_type;
 #endif
-    Py_SetPythonHome(g_python_home);
+    static str_type g_python_home = []() -> str_type {
+      const char *lldb_python_home = LLDB_PYTHON_HOME;
+      const char *absolute_python_home = nullptr;
+      llvm::SmallString<64> path;
+      if (llvm::sys::path::is_absolute(lldb_python_home)) {
+        absolute_python_home = lldb_python_home;
+      } else {
+        FileSpec spec = HostInfo::GetShlibDir();
+        if (!spec)
+          return nullptr;
+        spec.GetPath(path);
+        llvm::sys::path::append(path, lldb_python_home);
+        absolute_python_home = path.c_str();
+      }
+#if PY_MAJOR_VERSION >= 3
+      size_t size = 0;
+      return Py_DecodeLocale(absolute_python_home, &size);
+#else
+      return strdup(absolute_python_home);
+#endif
+    }();
+    if (g_python_home != nullptr) {
+      Py_SetPythonHome(g_python_home);
+    }
 #else
 #if defined(__APPLE__) && PY_MAJOR_VERSION == 2 && PY_MINOR_VERSION == 7
     // For Darwin, the only Python version supported is the one shipped in the