osdev/assembly_interface.s at master · cstack/osdev · GitHub

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externUSER_DATA_SEGMENT_SELECTOR
externUSER_CODE_SEGMENT_SELECTOR

globaloutb ; make the label outb visible outside this file

; outb - send a byte to an I/O port
; stack: [esp + 8] the data byte
; [esp + 4] the I/O port
; [esp ] return address
outb:
moval,[esp+8] ; move the data to be sent into the al register
movdx,[esp+4] ; move the address of the I/O port into the dx register
outdx,al ; send the data to the I/O port
ret ; return to the calling function

globalinb

; inb - returns a byte from the given I/O port
; stack: [esp + 4] The address of the I/O port
; [esp ] The return address
inb:
movdx,[esp+4] ; move the address of the I/O port to the dx register
inal,dx ; read a byte from the I/O port and store it in the al register
ret

globalasm_lgdt

; asm_lgdt - load global descriptor table
; stack: [esp + 4] the address of the gdt description structure
; [esp ] return address
asm_lgdt:
movedx,[esp+4]
lgdt[edx]
ret

GLOBALtss_flush ; Allows our C code to call tss_flush().
tss_flush:
movax,0x2B ; Load the index of our TSS structure - The index is
 ; 0x28, as it is the 5th selector and each is 8 bytes
 ; long, but we set the bottom two bits (making 0x2B)
 ; so that it has an RPL of 3, not zero.
ltrax ; Load 0x2B into the task state register.
ret

global load_idt

; load_idt - Loads the interrupt descriptor table (IDT).
; stack: [esp + 4] the address of the idt description structure
; [esp ] the return address
load_idt:
moveax,[esp+4] ; load the address of the IDT into register eax
lidt[eax] ; load the IDT
ret ; return to the calling function

globalinterrupt
; interrupt - Generates a software interrupt
interrupt:
pushebp ; make the caller show up in the stack trace
movebp,esp
int49
popebp
ret

globalinterrupt_out_of_memory
interrupt_out_of_memory:
pushebp ; make the caller show up in the stack trace
movebp,esp
int50
popebp
ret

globalenable_hardware_interrupts
; enable_hardware_interrupts
enable_hardware_interrupts:
sti
ret

globaldisable_hardware_interrupts
; disable_hardware_interrupts
disable_hardware_interrupts:
cli
ret

globalset_page_directory
; sets cr3 to the physical address of a page directory
; page_directory: [esp + 4] the physical address of the page directory
; [esp ] the return address
set_page_directory:
moveax,[esp+4]
movcr3,eax
ret

globalenable_paging
; sets the paging bit on control register 0
enable_paging:
moveax,cr0
oreax,0x80000000
movcr0,eax
ret

globalcurrent_stack_pointer
current_stack_pointer:
moveax,esp
ret

globalenter_user_mode
enter_user_mode:
movax,0x23 ;user data segment with bottom 2 bits set for ring 3
movds,ax
moves,ax
movfs,ax
movgs,ax ;we don't need to worry about SS. it's handled by iret

push0x23 ;user data segment with bottom 2 bits set for ring 3
push0xBFFFFFFB ; the user mode stack pointer
pushf ; push current eflags
push0x1B ; user code segment with bottom 2 bits set for ring 3
push0x0 ; the instruction pointer of user mode code to execute
iret ; this copies values from the stack into the appropriate registers