Safe Compilation for Hidden Deterministic Hardware Aliasing

Abstract

Hardware aliasing occurs when the same logical address can access different physical memory locations. This is a problem for software on some embedded systems and more generally when hardware becomes faulty in irretrievable locations, such as on a Mars Lander. We show how to work around the hardware problem with software logic, compiling code so it works on any platform with hardware aliasing with hidden determinism. That is: (i) a copy of an address accesses the same location, and (ii) repeating an address calculation exactly will repeat the same access again. Stuck bits can mean that even adding zero to an address can make a difference in that environment so nothing but a systematic approach has a chance of working. The technique is extended to generate aliasing as well as compensate for it, in so-called chaotic compilation, and a sketch proof is included to show it may produce object code that is secure against discovery of the programmer's intention. A prototype compiler implementing the technology covers all of ANSI C except longjmp/setjmp.