Debugger Toolchain Validation via Cross-Level Debugging

Ensuring the correctness of debugger toolchains is of paramount importance, as they play a vital role in understanding and resolving programming errors during software development. Bugs hidden within these toolchains can significantly mislead developers. Unfortunately, comprehensive testing of debugger toolchains is lacking due to the absence of effective test oracles. Existing studies on debugger toolchain validation have primarily focused on validating the debug information within optimized executables by comparing the traces between debugging optimized and unoptimized executables (i.e., different executables) in the debugger, under the assumption that the traces obtained from debugging unoptimized executables serve as a reliable oracle. However, these techniques suffer from inherent limitations, as compiler optimizations can drastically alter source code elements, variable representations, and instruction order, rendering the traces obtained from debugging different executables incomparable and failing to uncover bugs in debugger toolchains when debugging unoptimized executables. To address these limitations, we propose a novel concept called Cross-Level Debugging (CLD) for validating the debugger toolchain. CLD compares the traces obtained from debugging the same executable using source-level and instruction-level strategies within the same debugger. The core insight of CLD is that the execution traces obtained from different debugging levels for the same executable should adhere to specific relationships, regardless of whether the executable is generated with or without optimization. We formulate three key relations in CLD: reachability preservation of program locations, order preservation for reachable program locations, and value consistency at program locations, which apply to traces at different debugging levels. We implement Devil, a practical framework that employs these relations for debugger toolchain validation. We evaluate the effectiveness of Devil using two widely used production debugger toolchains, GDB and LLDB. Ultimately, Devil successfully identified 27 new bug reports, of which 18 have been confirmed and 12 have been fixed by developers.