notes.txt

TO RUN:
then in root dir run "make run"

TO DEBUG:
in one term "make debug"
in other term "gdb"

Copying kernel successfully.

Working on getting everything setup and ready to jump to kernel

- IDT
- disable PIC
- APIC
- GDT and TSS


we have until 0x7FFFF
boot0: 0x7c00-0x7e00 # will get paved over
boot1: 0x1000-0x3000
stack: < 0x7c00 (do 0x8000 before jumping to kernel )
memorymap: 0x8000
bootloader pagetables: 0x9000-0x34000 (51GiB max)
kernel pagetables: 0x34000-0x70000 (52 GiB max)

bootloader paging:
0x9000 -> 0xa000 -> [0xb000, 0xc000) point to 0x200000 byte regions.
          0xa008 -> [0xc000, 0xd000) point to 0x200000 byte regions.
          ...

kernel paging:
0x34000 -> 0x35000 -> [0x36000, 0x37000) point to 0x200000 byte regions.
           0x35008 -> [0x37000, 0x38000) point to 0x200000 byte regions.
           ...

what we want to do is:
PD = 0xc000, 0xd000, ... as many as we need
PDPT[RDX] = PD
PD[RCX] = Physaddr

lets try loading kernel at 0x4000000

http://www.skyfree.org/linux/references/ELF_Format.pdf

REMEMBER MEMORY IS NOT CONTIGUOUS!!!

TODO memory stuff:
- create new pagetable from heap
- create heap allocator

- create new pagetable from allocated pages
    - how to access tables:
    - have index 0x1ff of every table point to the table itself
    - so here is a couple examples of how to access any table
    - start with virt addr of PML4
    - To get PML4E index 3:
        - PML4E index (0x1ff) PDPT ind (0x1ff) PD ind (0x1ff) PT ind (0x1ff) offset (3 * 8)

    - To get PML4E index 3 PDPT index 7 PD index 2:
        - PML4E index (0x1ff) PDPT ind (0x1ff) PD ind (3) PT ind (7) offset (2 * 8)

- create heap for current pagetable
- create new pagetable
    - map in everthing needed:
        - ELF regions in target and temporarily matching current mapping for context switch
        - pagetable with recursive entry
        - stack
        - heap
    - load pagetable
    - unmap old mapping for ELF
- adjust heap

- create method on PML4 to create new PML4 and to add PDPT at index

How to use page table after remapping

    for i_pml4e in 0..pml4.entries.len() {
        if pml4.entries[i_pml4e].present() {
            let pdpt = pml4.get_pdpt_recursive(i_pml4e, &heap_phys_regions);
            // println!("pdpt: {:p}", pdpt);

            for i_pdpt in 0..pdpt.entries.len() {
                if pdpt.entries[i_pdpt].present() {
                    // println!("pd present at {:#x}:{:#x}", i_pml4e, i_pdpt);
                }
            }
        }
    }

b my_kernel/src/lib.rs:62

FLUSH PAGETABLE BUFFER

at this point we now have a clean entry into phase 2 where memory is working very nicely

Now things to setup:
- File system
- processes and threads
    - context switching
    - scheduling
    - user space
- process synch
- IPC
- IRQs and Exceptions, PIC, NMI, APIC, OPIC
- Clocks, Timers and Counters
- Basic video
- IO 
- Networking?


Notes about ints and exceptions:

Interrupts - external to processor, or generated using int instruction
Exception - processor detects error condition

IDT holds both interrupts and exception handlers

exceptions are: Faults, Traps, Aborts

You can call exceptions using int instruction but it will behave as if
it was an interrupt and will not push any error code.

Fault - can generally be corrected. restores to before the instruction was executed
Trap - restores to after the instruction was executed
Abort - should not be restored

use the RTC/CMOS timer to keep track of real time (the system timer tick)