It doesn't just "boot the system". The full EFI specification includes support for runtime services, i.e. proprietary code that keeps running even after your FLOSS operating system has booted. That's something Linux users should care about: it provides a backdoor for clinging to closed-source drivers on a pretend-open platform. There's already been proof-of-concept EFI viruses, it's only a matter of time until the first antivirus EFI service appears.

The UEFI runtime services provide functionality that is not generically exposed through any other OS environment. Linux could just refuse to provide those runtime features, and things would roughly work[1] - we'd still need to call some UEFI features in the boot stub, but the same is true of BIOS (look at what the 16-bit code does in terms of obtaining information that the kernel uses after init). If you want to drop all access to runtime services after kernel boot, you can by simply passing efi=noruntime to the kernel arguments.

[1] Some features would be broken, like recognising whether the system had booted successfully

Even back in the BIOS days Linux overrode lots of BIOS stuff such as partition size limits once it booted.

can efivarfs still be accessed after booting with efi=noruntime? If so, I might add that on my systems and see if anything breaks.

No, all runtime services are gone. You don't /strictly/ need them in order to boot - most Linux distributions will install a loader in the fallback path and the firmware will run it even if there are no boot entries.

Because "removing legacy" was one of the key arguments of EFI enthusiasts, and its still plenus bovis stercus.

Your point is a bit moot because removing bios support will actually allow the maintainer to stop maintaining the bios parts regardless of the fact some other old things are kept.

While actually not removing bios support won't allow you to get rid of the aformentionned MS techs such as fat support.

Having said that I think this is a wee bit early.

You made a factual mistake: MBR/BIOS based boot does not depend on a specific filesystem, nor does it depend on a specific executable file format except for the boot sector. You can safely remove FAT support from your kernel config, except when you need it for EFI.

> You made a factual mistake: MBR/BIOS based boot does not depend on a specific filesystem, nor does it depend on a specific executable file format except for the boot sector.

I never said that.

I said removing bios support allows you to remove anything that provides bios support and that choosing to not remove it won't allow you to get rid of the EFI dependencies so it is a moot point to talk about old techs used by EFI.

"Full of faeces from cows" is and remains vulgar no matter how it's spelled.

There's nothing "vulgar" whatsoever about cow dung. It is an eco-friendly, renewable material and commonly used for many sacred rituals in India.

The GP literally used it as a weird coded insult to UEFI (for whatever reason), India doesn't really enter this discussion.