How Conditional Breakpoints Work

Conditional breakpoints are a powerful debugging tool, but their performance can be a concern. Debuggers like Visual Studio and raddbg can take seconds to execute simple loop iterations with conditional breakpoints. The implementation typically involves saving the condition as a string and evaluating it each time the breakpoint is hit. This process of stopping and evaluating conditions can significantly impact performance, especially in tight loops. Modern debuggers like LLDB use a variety of techniques, including parsing expressions with the clang compiler and JIT-compiling complex conditions. To address the performance issues, some debuggers are exploring injecting code to check conditions directly into the process code, bypassing the need to stop and evaluate conditions externally. This approach, exemplified by GDB's in-process agent, has shown significant performance improvements, with UDB reporting a ~1000x boost in performance. While the idea of using JIT compilation to speed up conditional breakpoints is promising, there are still challenges in its full implementation.