Which is why hardware used to run safety-critical software is made redundant.
Take the Boeing 777 Primary Flight Computer for example. This is a fully digital fly-by-wire aircraft. There are 3 separate racks of equipment housing identical flight computers; 2 in the avionics bay underneath the flight deck, 1 in the aft cargo section. Each flight computer has 3 separate processors, supporting 2 dissimilar instruction set architectures, running the same software built by 3 separate compilers. Each flight computer captures instances of the software not agreeing about an action to be undertaken and wins by majority vote. The processor that makes these decisions is different in each flight computer.
The power systems that provide each flight computer are also fully redundant; each computer gets power from a power supply assembly, which receives 2 power feeds from 3 separate power supplies; no 2 power supply assemblies share the same 2 sources of power. 2 of the 3 power systems (L engine generator, R engine generator, and the hot battery bus) would have to fail and the APU would have to be unavailable in order to knock out 1 of the 3 computers.
This system has never failed in 30 years of service. There's still a primary flight computer disconnect switch on the overhead panel in the cockpit, taking the software out of the loop, to logically connect all of your control inputs to the flight surface actuators. I'm not aware of it ever being used (edit: in a commercial flight).
Unless Intel, Motorola, and AMD all conspire to give you a faulty processor, you will get a working primary flight computer.
Besides, this is what flight testing is for. Aviation certification authorities don't let an aircraft serve passengers unless you can demonstrate that all of its safety-critical systems work properly and that it performs as described.
I find it hard to believe that automotive works much differently in this regard, which is what things like crumple zone crash tests are for.
