December 17, 2020

With FreeBSD Foundation grant, Moritz Systems improved 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 the 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 the simulator.

FreeBSD includes LLDB 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 used to rely on an obsolete plugin model in LLDB that was a growing technical debt. This project aimed 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 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 is now performed using the same approach.

After the migration to the new process model on 32 and 64-bit x86 CPUs, the project focused on reviewing the results of LLDB’s test suite and fixing tests as time permits.

The Project Schedule was divided into three milestones, each taking approximately one month and summarized with a detailed blog report:

During the Moritz Systems work, the FreeBSD Project gained numerous important improvements: in the kernel, userland base libraries (the dynamic loader) and the LLVM toolchain FreeBSD support.

The introduced changes are expected to be shipped with LLDB 12.0, and where applicable in FreeBSD 13.0.

The overall experience of FreeBSD/LLDB developers and advanced users on this rock solid Operating System reached the state known from other environments. Furthermore, the FreeBSD-focused work also resulted in generic improvements, enhancing the LLDB support for Linux and NetBSD.

This work was sponsored by The FreeBSD Foundation.

— contributed by Kamil Rytarowski, Moritz Systems