Not OP, but here's an example of "random code" inserted by the compiler[1]: note the assembly instruction "ud2" ("invalid opcode exception" in x86 land) instead of "ret" in not_ok().

You might think this code would be fine if address 0 were mapped to RAM, but both gcc and clang know it's undefined behavior to use the null pointer like that, so they add "random code" that forces a processor exception.

[1] https://godbolt.org/z/sK55YsGz1

That doesn't sound very random to me!