; 
; Copyright 2010 Stefan Lankes, Chair for Operating Systems,
;                               RWTH Aachen University
;
; Licensed under the Apache License, Version 2.0 (the "License");
; you may not use this file except in compliance with the License.
; You may obtain a copy of the License at
;
;     http://www.apache.org/licenses/LICENSE-2.0
;
; Unless required by applicable law or agreed to in writing, software
; distributed under the License is distributed on an "AS IS" BASIS,
; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
; See the License for the specific language governing permissions and
; limitations under the License.
;
; This file is part of metalsvm.

; This is the kernel's entry point. We could either call main here,
; or we can use this to setup the stack or other nice stuff, like
; perhaps setting up the GDT and segments. Please note that interrupts
; are disabled at this point: More on interrupts later!

[BITS 32]
; We use a special name to map this section at the begin of our kernel
; =>  Multiboot needs its magic number at the begin of the kernel
SECTION multiboot
global start
start:
    mov esp, _sys_stack     ; This points the stack to our new stack area
    jmp stublet

; This part MUST be 4byte aligned, so we solve that issue using 'ALIGN 4'
ALIGN 4
mboot:
    ; Multiboot macros to make a few lines later more readable
    MULTIBOOT_PAGE_ALIGN	equ 1<<0
    MULTIBOOT_MEMORY_INFO	equ 1<<1
    MULTIBOOT_AOUT_KLUDGE	equ 1<<16
    MULTIBOOT_HEADER_MAGIC	equ 0x1BADB002
    MULTIBOOT_HEADER_FLAGS	equ MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO | MULTIBOOT_AOUT_KLUDGE
    MULTIBOOT_CHECKSUM	equ -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)
    EXTERN code, bss, end

    ; This is the GRUB Multiboot header. A boot signature
    dd MULTIBOOT_HEADER_MAGIC
    dd MULTIBOOT_HEADER_FLAGS
    dd MULTIBOOT_CHECKSUM
    
    ; AOUT kludge - must be physical addresses. Make a note of these:
    ; The linker script fills in the data for these ones!
    dd mboot
    dd code
    dd bss
    dd end
    dd start

stublet:
    ; interpret multiboot information
    extern multiboot_init
    push ebx
    call multiboot_init
    pop ebp

; This is an endless loop here. Make a note of this: Later on, we
; will insert an 'extern _main', followed by 'call _main', right
; before the 'jmp $'.
    extern main
    call main
    jmp $

; This will set up our new segment registers. We need to do
; something special in order to set CS. We do what is called a
; far jump. A jump that includes a segment as well as an offset.
; This is declared in C as 'extern void gdt_flush();'
global gdt_flush
extern gp
gdt_flush:
    lgdt [gp]
    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov ss, ax
    jmp 0x08:flush2
flush2:
    ret

; Loads the IDT defined in '_idtp' into the processor.
; This is declared in C as 'extern void idt_load();'
global idt_load
extern idtp
idt_load:
    lidt [idtp]
    ret

; In just a few pages in this tutorial, we will add our Interrupt
; Service Routines (ISRs) right here!
global isr0
global isr1
global isr2
global isr3
global isr4
global isr5
global isr6
global isr7
global isr8
global isr9
global isr10
global isr11
global isr12
global isr13
global isr14
global isr15
global isr16
global isr17
global isr18
global isr19
global isr20
global isr21
global isr22
global isr23
global isr24
global isr25
global isr26
global isr27
global isr28
global isr29
global isr30
global isr31
global isrsyscall

;  0: Divide By Zero Exception
isr0:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 0
    jmp isr_common_stub

;  1: Debug Exception
isr1:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 1
    jmp isr_common_stub

;  2: Non Maskable Interrupt Exception
isr2:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 2
    jmp isr_common_stub

;  3: Int 3 Exception
isr3:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 3
    jmp isr_common_stub

;  4: INTO Exception
isr4:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 4
    jmp isr_common_stub

;  5: Out of Bounds Exception
isr5:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 5
    jmp isr_common_stub

;  6: Invalid Opcode Exception
isr6:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 6
    jmp isr_common_stub

;  7: Coprocessor Not Available Exception
isr7:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 7
    jmp isr_common_stub

;  8: Double Fault Exception (With Error Code!)
isr8:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 8
    jmp isr_common_stub

;  9: Coprocessor Segment Overrun Exception
isr9:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 9
    jmp isr_common_stub

; 10: Bad TSS Exception (With Error Code!)
isr10:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 10
    jmp isr_common_stub

; 11: Segment Not Present Exception (With Error Code!)
isr11:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 11
    jmp isr_common_stub

; 12: Stack Fault Exception (With Error Code!)
isr12:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 12
    jmp isr_common_stub

; 13: General Protection Fault Exception (With Error Code!)
isr13:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 13
    jmp isr_common_stub

; 14: Page Fault Exception (With Error Code!)
isr14:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 14
    jmp isr_common_stub

; 15: Reserved Exception
isr15:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 15
    jmp isr_common_stub

; 16: Floating Point Exception
isr16:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 16
    jmp isr_common_stub

; 17: Alignment Check Exception
isr17:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 17
    jmp isr_common_stub

; 18: Machine Check Exception
isr18:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 18
    jmp isr_common_stub

; 19: Reserved
isr19:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 19
    jmp isr_common_stub

; 20: Reserved
isr20:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 20
    jmp isr_common_stub

; 21: Reserved
isr21:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 21
    jmp isr_common_stub

; 22: Reserved
isr22:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 22
    jmp isr_common_stub

; 23: Reserved
isr23:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 23
    jmp isr_common_stub

; 24: Reserved
isr24:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 24
    jmp isr_common_stub

; 25: Reserved
isr25:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 25
    jmp isr_common_stub

; 26: Reserved
isr26:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 26
    jmp isr_common_stub

; 27: Reserved
isr27:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 27
    jmp isr_common_stub

; 28: Reserved
isr28:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 28
    jmp isr_common_stub

; 29: Reserved
isr29:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 29
    jmp isr_common_stub

; 30: Reserved
isr30:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 30
    jmp isr_common_stub

; 31: Reserved
isr31:
    ; isr0 - isr31 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 31
    jmp isr_common_stub

extern syscall_handler

; used to realize system calls
isrsyscall:
    push ebp
    push edi
    push esi
    push edx
    push ecx
    push ebx
    push eax
    call syscall_handler
    add esp, 4 ; eax contains the return value
	       ; => we did not restore eax
    pop ebx 
    pop ecx
    pop edx
    pop esi
    pop edi
    pop ebp
    iret

; We call a C function in here. We need to let the assembler know
; that 'fault_handler' exists in another file
extern fault_handler

; This is our common ISR stub. It saves the processor state, sets
; up for kernel mode segments, calls the C-level fault handler,
; and finally restores the stack frame.
isr_common_stub:
    pusha

    push esp
    call fault_handler
    add esp, 4

    popa
    add esp, 8
    iret

global irq0
global irq1
global irq2
global irq3
global irq4
global irq5
global irq6
global irq7
global irq8
global irq9
global irq10
global irq11
global irq12
global irq13
global irq14
global irq15

extern irq_handler
extern current_task
extern scheduler

global reschedule
reschedule:
    cli
    ; eax could change across a function call
    ; => we have not to save the original eax value
    push ebx 

    push DWORD [current_task]
    call scheduler
    pop ebx
    mov eax, DWORD [current_task]
    cmp eax, ebx
    je no_task_switch1

    mov eax, [eax]
    add ax, WORD 5
    mov bx, WORD 8
    mul bx
    mov [hack1+5], ax
hack1:
    jmp 0x00 : 0xDEADBEAF

no_task_switch1:
    pop ebx
    sti
    ret

; 32: IRQ0
irq0:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 32
    pusha

    push esp
    call irq_handler
    add esp, 4

    mov eax, DWORD [current_task]
    push eax
    call scheduler
    pop ebx
    mov eax, DWORD [current_task]
    cmp eax, ebx
    je no_task_switch2

    mov eax, [eax]
    add ax, WORD 5
    mov bx, WORD 8
    mul bx
    mov [hack2+5], ax
hack2:	
    jmp 0x00 : 0xDEADBEAF

no_task_switch2:
    popa
    add esp, 8
    iret

; 33: IRQ1
irq1:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 33
    jmp irq_common_stub

; 34: IRQ2
irq2:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 34
    jmp irq_common_stub

; 35: IRQ3
irq3:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 35
    jmp irq_common_stub

; 36: IRQ4
irq4:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 36
    jmp irq_common_stub

; 37: IRQ5
irq5:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 37
    jmp irq_common_stub

; 38: IRQ6
irq6:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 38
    jmp irq_common_stub

; 39: IRQ7
irq7:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 39
    jmp irq_common_stub

; 40: IRQ8
irq8:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 40
    jmp irq_common_stub

; 41: IRQ9
irq9:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 41
    jmp irq_common_stub

; 42: IRQ10
irq10:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 42
    jmp irq_common_stub

; 43: IRQ11
irq11:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 43
    jmp irq_common_stub

; 44: IRQ12
irq12:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 44
    jmp irq_common_stub

; 45: IRQ13
irq13:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 45
    jmp irq_common_stub

; 46: IRQ14
irq14:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 46
    jmp irq_common_stub

; 47: IRQ15
irq15:
    ; irq0 - irq15 are registered as "Interrupt Gate"
    ; Therefore, the interrupt flag (IF) is already cleared.
    ; cli
    push byte 0
    push byte 47
    jmp irq_common_stub

irq_common_stub:
    pusha

    push esp
    call irq_handler
    add esp, 4

    popa
    add esp, 8
    iret

; Here is the definition of our BSS section. Right now, we'll use
; it just to store the stack. Remember that a stack actually grows
; downwards, so we declare the size of the data before declaring
; the identifier '_sys_stack'
SECTION .bss
    resb 8192               ; This reserves 8KBytes of memory here
_sys_stack: