On monday, at 2pm - UPEC CMC - Room P2-131

September 30, 2019

Generation of Signals under Temporal Constraints for CPS Testing

Benoit Barbot (LACL - UPEC)

This work is concerned with validation of cyber-physical systems (CPS) via simulation based on sampling of the input signal space. Such a space is infinite and in general too difficult to treat symbolically meaning that the only reasonable option is to sample a finite subset of it and simulate the corresponding system behaviours. It is thus of great interest to choose a finite sample so that it best “covers” the whole space of input signals. We use timed automata to model temporal constraints, in order to avoid spurious bugs coming from unrealistic inputs and this can also reduce the input space to explore. We propose a method for low discrepancy generation of signals with temporal constraints recognised by timed automata. The discrepancy notion reflects how uniform the input signal space is sampled and additionally allows deriving validation and performance guarantees. We also show how this notion can be used to measure the discrepancy of a given set of input signals. We describe a prototype tool chain and demonstrate the proposed methods on a Kinetic Battery Model (KiBaM) and a Sigma Delta modulator.

September 23, 2019

Fast and Reliable DWARF-based Stack Unwinding

Francesco Zappa Nardelli (INRIA - ENS)

Debug information, usually encoded in the DWARF format, is a hidden and obscure component of our computing infrastructure. Debug information is obviously used by debuggers, but it also plays a key role in program analysis tools, and, most surprisingly, it can be relied upon by the runtime of high-level programming languages. For instance the C++ runtime leverages DWARF stack unwind tables to implement exceptions! Alas, generating debug information adds significant burden to compiler implementations, and the debug information itself can be pervaded by subtle bugs, making the whole infrastructure unreliable. Additionally, interpreting the debug tables is time consuming and for applications as sampling profilers it is a performance bottle-neck.

In this talk I will focus on the DWARF unwind table, that enables stack unwinding in absence of frame-pointer information. I will describe two techniques to perform validation and synthesis of the DWARF stack unwinding tables, and their implementation for the x86_64 architecture. The validation tool has proven effective for compiler and inline assembly testing, while the synthesis tool can generate DWARF unwind tables for arbitrary binaries lacking debug information. Additionally, I will report on a technique to precompile unwind tables into native x86_64 code, which we have implemented and integrated into libunwind, resulting in a 25x DWARF-based unwind speedup.