%include "startup-common.asm"

startup_arch:
    cli
    ; setting up Page Tables
    ; Identity Mapping first GB
    mov ax, 0x7000
    mov es, ax

    xor edi, edi
    xor eax, eax
    mov ecx, 3 * 4096 / 4 ;PML4, PDP, PD / moves 4 Bytes at once
    cld
    rep stosd

    xor edi, edi
    ;Link first PML4 to PDP
    mov DWORD [es:edi], 0x71000 | 1 << 1 | 1
    add edi, 0x1000
    ;Link last PML4 to PML4
    mov DWORD [es:edi - 8], 0x70000 | 1 << 1 | 1
    ;Link first PDP to PD
    mov DWORD [es:edi], 0x72000 | 1 << 1 | 1
    add edi, 0x1000
    ;Link all PD's (512 per PDP, 2MB each)y
    mov ebx, 1 << 7 | 1 << 1 | 1
    mov ecx, 512
.setpd:
    mov [es:edi], ebx
    add ebx, 0x200000
    add edi, 8
    loop .setpd

    xor ax, ax
    mov es, ax

    ;cr3 holds pointer to PML4
    mov edi, 0x70000
    mov cr3, edi

    ;enable Page Address Extension and Page Size Extension
    mov eax, cr4
    or eax, 1 << 5 | 1 << 4
    mov cr4, eax

    ; load protected mode GDT
    lgdt [gdtr]

    mov ecx, 0xC0000080               ; Read from the EFER MSR.
    rdmsr
    or eax, 1 << 11 | 1 << 8          ; Set the Long-Mode-Enable and NXE bit.
    wrmsr

    ;enabling paging and protection simultaneously
    mov ebx, cr0
    or ebx, 1 << 31 | 1 << 16 | 1                ;Bit 31: Paging, Bit 16: write protect kernel, Bit 0: Protected Mode
    mov cr0, ebx

    ; far jump to enable Long Mode and load CS with 64 bit segment
    jmp gdt.kernel_code:long_mode

USE64
long_mode:
    ; load all the other segments with 64 bit data segments
    mov rax, gdt.kernel_data
    mov ds, rax
    mov es, rax
    mov fs, rax
    mov gs, rax
    mov ss, rax

    mov rsp, 0x0009F000

    ;rust init
    xor rax, rax
    mov eax, [kernel_base + 0x18]
    mov rbx, gdtr
    jmp rax

    gdtr:
        dw gdt.end + 1  ; size
        dq gdt          ; offset

    gdt:
    .null equ $ - gdt
        dq 0

    .kernel_code equ $ - gdt
    istruc GDTEntry
        at GDTEntry.limitl, dw 0
        at GDTEntry.basel, dw 0
        at GDTEntry.basem, db 0
        at GDTEntry.attribute, db attrib.present | attrib.user | attrib.code
        at GDTEntry.flags__limith, db flags.long_mode
        at GDTEntry.baseh, db 0
    iend

    .kernel_data equ $ - gdt
    istruc GDTEntry
        at GDTEntry.limitl, dw 0
        at GDTEntry.basel, dw 0
        at GDTEntry.basem, db 0
    ; AMD System Programming Manual states that the writeable bit is ignored in long mode, but ss can not be set to this descriptor without it
        at GDTEntry.attribute, db attrib.present | attrib.user | attrib.writable
        at GDTEntry.flags__limith, db 0
        at GDTEntry.baseh, db 0
    iend

    .user_code equ $ - gdt
    istruc GDTEntry
        at GDTEntry.limitl, dw 0
        at GDTEntry.basel, dw 0
        at GDTEntry.basem, db 0
        at GDTEntry.attribute, db attrib.present | attrib.ring3 | attrib.user | attrib.code
        at GDTEntry.flags__limith, db flags.long_mode
        at GDTEntry.baseh, db 0
    iend

    .user_data equ $ - gdt
    istruc GDTEntry
        at GDTEntry.limitl, dw 0
        at GDTEntry.basel, dw 0
        at GDTEntry.basem, db 0
    ; AMD System Programming Manual states that the writeable bit is ignored in long mode, but ss can not be set to this descriptor without it
        at GDTEntry.attribute, db attrib.present | attrib.ring3 | attrib.user | attrib.writable
        at GDTEntry.flags__limith, db 0
        at GDTEntry.baseh, db 0
    iend

    .user_tls equ $ - gdt
    istruc GDTEntry
        at GDTEntry.limitl, dw 0
        at GDTEntry.basel, dw 0
        at GDTEntry.basem, db 0
    ; AMD System Programming Manual states that the writeable bit is ignored in long mode, but ss can not be set to this descriptor without it
        at GDTEntry.attribute, db attrib.present | attrib.ring3 | attrib.user | attrib.writable
        at GDTEntry.flags__limith, db 0
        at GDTEntry.baseh, db 0
    iend

    .tss equ $ - gdt
    istruc GDTEntry
        at GDTEntry.limitl, dw (tss.end - tss) & 0xFFFF
        at GDTEntry.basel, dw (tss-$$+0x7C00) & 0xFFFF
        at GDTEntry.basem, db ((tss-$$+0x7C00) >> 16) & 0xFF
        at GDTEntry.attribute, db attrib.present | attrib.ring3 | attrib.tssAvailabe64
        at GDTEntry.flags__limith, db ((tss.end - tss) >> 16) & 0xF
        at GDTEntry.baseh, db ((tss-$$+0x7C00) >> 24) & 0xFF
    iend
    dq 0 ;tss descriptors are extended to 16 Bytes

    .end equ $ - gdt

    struc TSS
        .reserved1 resd 1    ;The previous TSS - if we used hardware task switching this would form a linked list.
        .rsp0 resq 1        ;The stack pointer to load when we change to kernel mode.
        .rsp1 resq 1        ;everything below here is unused now..
        .rsp2 resq 1
        .reserved2 resd 1
        .reserved3 resd 1
        .ist1 resq 1
        .ist2 resq 1
        .ist3 resq 1
        .ist4 resq 1
        .ist5 resq 1
        .ist6 resq 1
        .ist7 resq 1
        .reserved4 resd 1
        .reserved5 resd 1
        .reserved6 resw 1
        .iomap_base resw 1
    endstruc

    tss:
        istruc TSS
            at TSS.rsp0, dd 0x800000 - 128
            at TSS.iomap_base, dw 0xFFFF
        iend
    .end: