[lldb][windows] add support for out of PATH python.dll resolution

[charles-zablit]

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.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Charles Zablit (charles-zablit)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/162509.diff

3 Files Affected:

• (modified) lldb/cmake/modules/AddLLDB.cmake (+6)
• (modified) lldb/tools/driver/CMakeLists.txt (+4)
• (modified) lldb/tools/driver/Driver.cpp (+49)

diff --git a/lldb/cmake/modules/AddLLDB.cmake b/lldb/cmake/modules/AddLLDB.cmake
index 28bf8d816d89a..4d2036e68704f 100644
--- a/lldb/cmake/modules/AddLLDB.cmake
+++ b/lldb/cmake/modules/AddLLDB.cmake
@@ -167,6 +167,12 @@ function(add_lldb_executable name)
   )
 
   target_link_libraries(${name} PRIVATE ${ARG_LINK_LIBS})
+  if(WIN32)
+    list(FIND ARG_LINK_LIBS liblldb LIBLLD_INDEX)
+    if(NOT LIBLLD_INDEX EQUAL -1)
+      target_link_options(${name} PRIVATE "/DELAYLOAD:$<TARGET_FILE_BASE_NAME:liblldb>.dll")
+    endif()
+  endif()
   if(CLANG_LINK_CLANG_DYLIB)
     target_link_libraries(${name} PRIVATE clang-cpp)
   else()
diff --git a/lldb/tools/driver/CMakeLists.txt b/lldb/tools/driver/CMakeLists.txt
index 5c0cac484cc94..941ef0d83385b 100644
--- a/lldb/tools/driver/CMakeLists.txt
+++ b/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.
diff --git a/lldb/tools/driver/Driver.cpp b/lldb/tools/driver/Driver.cpp
index 16cc736441b59..df31d649ada48 100644
--- a/lldb/tools/driver/Driver.cpp
+++ b/lldb/tools/driver/Driver.cpp
@@ -22,11 +22,15 @@
 #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/Windows/WindowsSupport.h"
 #include "llvm/Support/WithColor.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -426,6 +430,47 @@ 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 max path length (32,767).
+  std::vector<WCHAR> buffer;
+  buffer.resize(MAX_PATH);
+  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()) {
+    WithColor::error() << "Unable to find python: " << GetLastError() << '\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 +773,10 @@ int main(int argc, char const *argv[]) {
                         "~/Library/Logs/DiagnosticReports/.\n");
 #endif
 
+#ifdef _WIN32
+  AddPythonDLLToSearchPath();
+#endif
+
   // Parse arguments.
   LLDBOptTable T;
   unsigned MissingArgIndex;

[bulbazord]

nit: missing a B -- LIBLLDB_INDEX

[bulbazord]

Should this be an ifdef?

[adrian-prantl]

Suggested change

	// Returns the full path to the lldb.exe executable
	// Returns the full path to the lldb.exe executable.

[adrian-prantl]

if MAX_PATH is 32767 isn't this condition always false?

[compnerd]

There is a doubling on failure, so this shouldn't be always false.

[charles-zablit]

MAX_PATH is defined in the Windows API as 260. However, a lot of the Windows API functions can return Unicode paths that are up to 32,767 bytes long.

I have updated the comments to explain this better.

[adrian-prantl]

We typically with the word "error:" in the error color, and not the entire message.

[charles-zablit]

Fixed by using llvm::errs() and changing the message to start with error:

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.