[lldb][windows] add support for out of PATH python.dll resolution (#162509)

This patch adds the `LLDB_PYTHON_DLL_RELATIVE_PATH` Cmake variable which
is the relative path to the directory containing `python.dll`. The path
is relative to the directory containing `lldb.exe`.

If this variable is set and the resolved path points to an existing
directory, we call `SetDllDirectoryW` to add `python.dll` to the list of
DLL search paths.

This, combined with `liblldb.dll` being delay loaded, allows to package
`python.dll` with the `llvm` installer.

Author: charles-zablit

lldb/cmake/modules/AddLLDB.cmake

@@ -167,6 +167,12 @@ function(add_lldb_executable name)
   )
 
   target_link_libraries(${name} PRIVATE ${ARG_LINK_LIBS})
+  if(WIN32)
+    list(FIND ARG_LINK_LIBS liblldb LIBLLDB_INDEX)
+    if(NOT LIBLLDB_INDEX EQUAL -1)
+      target_link_options(${name} PRIVATE "/DELAYLOAD:$<TARGET_FILE_BASE_NAME:liblldb>.dll")
+    endif()
+  endif()
   if(CLANG_LINK_CLANG_DYLIB)
     target_link_libraries(${name} PRIVATE clang-cpp)
   else()

lldb/tools/driver/CMakeLists.txt

@@ -34,6 +34,10 @@ add_dependencies(lldb
   ${tablegen_deps}
 )
 
+if(DEFINED LLDB_PYTHON_DLL_RELATIVE_PATH)
+  target_compile_definitions(lldb PRIVATE LLDB_PYTHON_DLL_RELATIVE_PATH="${LLDB_PYTHON_DLL_RELATIVE_PATH}")
+endif()
+
 if(LLDB_BUILD_FRAMEWORK)
   # In the build-tree, we know the exact path to the framework directory.
   # The installed framework can be in different locations.

lldb/tools/driver/Driver.cpp

@@ -22,14 +22,21 @@
 #include "lldb/Host/MainLoop.h"
 #include "lldb/Host/MainLoopBase.h"
 #include "lldb/Utility/Status.h"
+#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Support/ConvertUTF.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/WithColor.h"
 #include "llvm/Support/raw_ostream.h"
 
+#ifdef _WIN32
+#include "llvm/Support/Windows/WindowsSupport.h"
+#endif
+
 #include <algorithm>
 #include <atomic>
 #include <bitset>
@@ -426,6 +433,47 @@ SBError Driver::ProcessArgs(const opt::InputArgList &args, bool &exiting) {
   return error;
 }
 
+#ifdef _WIN32
+/// Returns the full path to the lldb.exe executable.
+inline std::wstring GetPathToExecutableW() {
+  // Iterate until we reach the Windows API maximum path length (32,767).
+  std::vector<WCHAR> buffer;
+  buffer.resize(MAX_PATH /*=260*/);
+  while (buffer.size() < 32767) {
+    if (GetModuleFileNameW(NULL, buffer.data(), buffer.size()) < buffer.size())
+      return std::wstring(buffer.begin(), buffer.end());
+    buffer.resize(buffer.size() * 2);
+  }
+  return L"";
+}
+
+/// Resolve the full path of the directory defined by
+/// LLDB_PYTHON_DLL_RELATIVE_PATH. If it exists, add it to the list of DLL
+/// search directories.
+void AddPythonDLLToSearchPath() {
+  std::wstring modulePath = GetPathToExecutableW();
+  if (modulePath.empty()) {
+    llvm::errs() << "error: unable to find python.dll." << '\n';
+    return;
+  }
+
+  SmallVector<char, MAX_PATH> utf8Path;
+  if (sys::windows::UTF16ToUTF8(modulePath.c_str(), modulePath.length(),
+                                utf8Path))
+    return;
+  sys::path::remove_filename(utf8Path);
+  sys::path::append(utf8Path, LLDB_PYTHON_DLL_RELATIVE_PATH);
+  sys::fs::make_absolute(utf8Path);
+
+  SmallVector<wchar_t, 1> widePath;
+  if (sys::windows::widenPath(utf8Path.data(), widePath))
+    return;
+
+  if (sys::fs::exists(utf8Path))
+    SetDllDirectoryW(widePath.data());
+}
+#endif
+
 std::string EscapeString(std::string arg) {
   std::string::size_type pos = 0;
   while ((pos = arg.find_first_of("\"\\", pos)) != std::string::npos) {
@@ -728,6 +776,10 @@ int main(int argc, char const *argv[]) {
                         "~/Library/Logs/DiagnosticReports/.\n");
 #endif
 
+#if defined(_WIN32) && defined(LLDB_PYTHON_DLL_RELATIVE_PATH)
+  AddPythonDLLToSearchPath();
+#endif
+
   // Parse arguments.
   LLDBOptTable T;
   unsigned MissingArgIndex;