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LLDB Debugger Improvements

Link: Moritz Systems Project Description
Link: Git Repository

Contact: Kamil Rytarowski [email protected]
Contact: Michał Górny [email protected]

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 supports the executed application being debugged in the same process space as the debugger. 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 is expected to be complete in 2020.

The project schedule is divided into three milestones, each taking approximately one month:

  1. Introduce new FreeBSD Remote Process Plugin for x86_64 with basic support and upstream to LLVM.
  2. 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.
  3. 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.

We are nearing the completion of the first milestone. The new plugin is getting into shape, and it can already run simple single-threaded programs. The supported features include single-stepping, breakpoints, memory and register I/O on amd64. Both plugins are supported simultaneously. The new plugin is used if FREEBSD_REMOTE_PLUGIN environment variable is set to any value, or if lldb-server is spawned directly. Otherwise, the old plugin is used for compatibility. Once the new plugin matures, we are planning to enable it unconditionally on the architectures that it is ported to.

Sponsor: The FreeBSD Foundation