He actually explains this too. You only know at compile time what you're building for. For example with microblaze-V, I often tweak what ISA I'm generating. If I ran the same elf without thinking about it, who knows what could happen given the instruction collision problem

Well, misa won't be in most cases since you'll be running ins mode rather than m mode for most kernels on an application core (and misa won't tell you about the X* and Z* extensions).

But you'll practically be passed a device tree from SBI that will tell you.