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I made my own DOS implementation (Announce)

posted by samwdpckr, 02.02.2024, 20:20

If the "operating system" uses UEFI boot services, it is not an operating system - it is just a UEFI program. In that case the operating system is the UEFI.

UEFI has its own dynamic memory management. UEFI programs cannot just write to arbitrary memory addresses like operating system kernels do. The program has to do every memory allocation via UEFI boot services. That causes a serious problem, because some peripherals (such as graphics cards) have memory and/or registers that are mapped to some known physical address range in the CPU's memory address space.

Also some peripherals may not be usable without exitting from UEFI boot services. It may be unsafe and/or cause undefined side effects if the UEFI program tries to control those peripherals directly. Many peripherals are stateful from the programmer's perspective and the driver program needs to constantly know their state.

The UEFI specification has a large and constantly growing number of those so-called boot services and many of them aren't implemented in most UEFI implementations. In many cases the implementations are buggy and unusable. The only thing that is actually tested by the manufacturers is that it boots Windows.

UEFI boot services are not the same thing as BIOS runtime services. They are not meant to do the same things.

> I don't know any DOS program that uses VT-x
That does not mean that they don't exist, or will not exist in the near future. One of the basic principles of DOS is that the currently running program is in full control of the computer, so DOS programs can do basically anything.

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