How to check firmware reliabily without commands?

So I'm writing a program in c, and I want to get the firmware (e.g. BIOS, UEFI, Coreboot). Since I'm writing a c program it shouldn't really be running commands, I want to be able to check via files or a library but preferably files. I know /sys/firmware/efi in created for UEFI systems, but then what about BIOS and Coreboot? DMI doesn't even seem to have a nice answer either since it seems to consider UEFI as BIOS I guess for compatibility reasons, meaning it's all just called BIOS when it may or may not be. I couldn't find anything under /sys/class/dmi/id that mentioned what firmware was running, only stuff about that firmware, though somehow the command dmidecode listed 'UEFI is supported' under the characteristics of my 'BIOS Information' (I'm using UEFI, not BIOS), I couldn't find where it got that information from though. In the first place DMI instead a great solution since I need this to be able to work for ARM and RISC-V, not just x86 which I think DMI is for.