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31 lines
1.1 KiB
NASM
31 lines
1.1 KiB
NASM
;
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; Gdt.s -- contains global descriptor table and interrupt descriptor table
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; setup code.
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; Based on code from Bran's kernel development tutorials.
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; Rewritten for JamesM's kernel development tutorials.
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[GLOBAL gdt_flush] ; Allows the C code to call gdt_flush().
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gdt_flush:
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mov eax, [esp+4] ; Get the pointer to the GDT, passed as a parameter.
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lgdt [eax] ; Load the new GDT pointer
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mov ax, 0x10 ; 0x10 is the offset in the GDT to our data segment
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mov ds, ax ; Load all data segment selectors
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mov es, ax
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mov fs, ax
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mov gs, ax
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mov ss, ax
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jmp 0x08:.flush ; 0x08 is the offset to our code segment: Far jump!
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.flush:
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ret
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[GLOBAL tss_flush] ; Allows our C code to call tss_flush().
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tss_flush:
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mov ax, 0x2B ; Load the index of our TSS structure - The index is
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; 0x28, as it is the 5th selector and each is 8 bytes
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; long, but we set the bottom two bits (making 0x2B)
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; so that it has an RPL of 3, not zero.
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ltr ax ; Load 0x2B into the task state register.
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ret
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