Re: [OSDev] How to switch to long mode in x86 CPUs?

On 27/02/2025 16:57, Ar Rakin wrote:

Hello there,
 I am trying to develop my own, simple operating system to learn more
about how kernels work and low level stuff like that.  However, I am
stuck at setting up paging while switching long mode (64-bit protected
mode) in x86 processors.
 

Are you trying to learn about OS kernels, or about the complexities of low-level x86 stuff?  Those are different things.
If you want to learn about how operating systems work, you might consider starting on microcontrollers.  There are lots of RTOS's available to study, and it is much easier to understand what is going on - there is none of the multi-layered disaster of x86 modes to deal with.
Once you are happy with threads, context switches, locks, priorities, and all the rest of that stuff, you can start moving up and adding features for MMU's, SMP, and more, using bigger target processors.
On the other hand, if you are interested in learning the intricacies of the x86 world, you need to look elsewhere for information - as Keith says, it is not really C related when you are writing assembly. comp.arch might be a helpful group.
However, it is possible to use C for almost all code here.  But it will not be standard C - it is not even standard free-standing C.  You will make use of compiler extensions, bits of inline assembly, pre-main C code (so none of the library will be initialised, and program-lifetime data will not be set up), and other such highly non-portable code.  I remember reading once about LinuxBIOS (now coreboot) having just four lines of assembly running out of reset, before everything else was in C.