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sortix--sortix/sortix/x86/gdt.asm

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2011-08-05 08:25:00 -04:00
;
; Gdt.s -- contains global descriptor table and interrupt descriptor table
; setup code.
; Based on code from Bran's kernel development tutorials.
; Rewritten for JamesM's kernel development tutorials.
[GLOBAL gdt_flush] ; Allows the C code to call gdt_flush().
gdt_flush:
mov eax, [esp+4] ; Get the pointer to the GDT, passed as a parameter.
lgdt [eax] ; Load the new GDT pointer
mov ax, 0x10 ; 0x10 is the offset in the GDT to our data segment
mov ds, ax ; Load all data segment selectors
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
jmp 0x08:.flush ; 0x08 is the offset to our code segment: Far jump!
.flush:
ret
[GLOBAL tss_flush] ; Allows our C code to call tss_flush().
tss_flush:
mov ax, 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.
ltr ax ; Load 0x2B into the task state register.
ret