LLDB Debugger Improvements for FreeBSD

The Moritz Systems team has started a new contract on improving the LLDB support for FreeBSD.

The LLDB project builds on libraries provided by LLVM and Clang to provide a great modern debugger. It uses the Clang ASTs and expression parser, LLVM JIT, LLVM disassembler, etc so that it provides an experience that “just works”. It is also blazing fast and more permissively licensed than GDB, the GNU Debugger.

LLDB is the default debugger in Xcode on macOS and supports debugging C, Objective-C and C++ on the desktop and iOS devices and simulator.

FreeBSD includes LLDB, the debugger in the LLVM family, in the base system. At present it has some limitations in comparison with the GNU GDB debugger, and does not yet provide a complete replacement. It relies on an obsolete plugin model in LLDB that causes growing technical debt. This project aims to bring LLDB closer to a fully featured replacement for GDB, and therefore for FreeBSD to feature a modern debugger for software developers.

The legacy monolithic target support executed the frontend and backend of the debugger in the same process space. The modern LLDB plugin approach, used on other supported targets, executes the target process under a separate lldb-server process. This improves reliability and simplifies the process / thread model in LLDB itself. In addition, remote and local debugging will both be performed using the same approach.

After the migration to the new process model is complete the project will include reviewing the results of LLDB’s test suite and fixing tests as time permits. The work will complete in 2020.

The Project Schedule is divided into three milestones, each taking approximately one month:

• M1 Introduce new FreeBSD Remote Process Plugin for x86_64 with basic support and upstream to LLVM.
• M2 Ensure and add the mandated features in the project (process launch, process attach (pid), process attach (name), userland core files, breakpoints, watchpoints, threads, remote debugging) for FreeBSD/amd64 and FreeBSD/i386.
• M3 Iterate over the LLDB tests. Detect and as time permits fix bugs. Ensure bug reports for each non-fixed and known problem. Add missing man pages and update the FreeBSD Handbook.

This work is sponsored by The FreeBSD Foundation.