UB is UB. It might work. It might work now but not in the future. It might work in some situation but not others. It might appear to work but introduce subtle b

UB is UB. It might work. It might work now but not in the future. It might work in some situation but not others. It might appear to work but introduce subtle bugs elsewhere in the program. Linux, as Linus has said, isn't written in ISO C it's written (or was) in GNU C. The two had something of a symbiotic relationship for a long time. Which is why porting it to LLVM was such a tremendous effort. Which is to say, Linux conforms to the memory model of the compilers it compiles on (or vice versa). Not ISO C's memory model. So I'm not sure how your example is relevant.