99 lines
6.4 KiB
NASM
99 lines
6.4 KiB
NASM
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;=----------------------------------------------------------------------------=;
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; GNU GPL OS/K ;
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; ;
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; Authors: spectral` ;
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; NeoX ;
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; ;
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; Desc: Basic Memory Realmode Driver ;
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; (x86_64 architecture only) ;
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;=----------------------------------------------------------------------------=;
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[BITS 16]
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;; GDT WITH DOC
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GDT64:
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NULL_SELECTOR: ;; null selector within 64 bits
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dw GDT_LENGTH ; limit of GDT
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dw GDT64 ; linear address of GDT
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dd 0x0 ;
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CODE_SELECTOR: ;; 32-bit code selector (ring 0)
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dw 0x0000FFFF ; Segment Limit
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db 0x0, 0x0, 0x0 ; Base Address
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db 10011010b ; |7|6|5|4|3|2|1|0|
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; | | | | | | | `----- 1 when segment used.
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; | | | | | | `------ 1 when writable.
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; | | | | | `------- 1 if "conformant". Don't know what is it... spectral ? xD
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; | | | | `-------- 1 always
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; | | | `--------- 1 for segment descriptor, 0 for system descriptor
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; | | `---------- DPL !!! 0 for ring 0
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; | `----------- DPL (2/2)
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; `------------ 1 if in physical memory, 0 if page fault
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db 11001111b ; |7|6|5|4|3|2|1|0|
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; | | | | | | | `----- Limit 16
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; | | | | | | `------ Limit 17
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; | | | | | `------- Limit 18
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; | | | | `-------- Limit 19
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; | | | `--------- available for use
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; | | `---------- 0 always
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; | `----------- size of data. 1 for 32bits
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; `------------ 0 if limit is in Bytes, 1 if it's in pages (4ko)
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db 0x0 ; Base Address
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DATA_SELECTOR: ;; flat data selector (ring 0)
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dw 0x0000FFFF ; Segment Limit
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db 0x0, 0x0, 0x0 ; Base Address
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db 10010010b ; |7|6|5|4|3|2|1|0|
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; | | | | | | | `----- 1 when segment used.
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; | | | | | | `------ 1 when writable.
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; | | | | | `------- expansion direction. 1 for a LIFO
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; | | | | `-------- 1 always
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; | | | `--------- 1 for segment descriptor, 0 for system descriptor
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; | | `---------- DPL !!! 0 for ring 0
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; | `----------- DPL (2/2)
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; `------------ 1 if in physical memory, 0 if page fault
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db 10001111b ; |7|6|5|4|3|2|1|0|
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; | | | | | | | `----- Limit 16
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; | | | | | | `------ Limit 17
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; | | | | | `------- Limit 18
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; | | | | `-------- Limit 19
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; | | | `--------- available for use
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; | | `---------- 0 always
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; | `----------- size of data. 1 for 32bits
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; `------------ 0 if limit is in Bytes, 1 if it's in pages (4ko)
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db 0x0 ; Base Address
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LONG_SELECTOR: ;; 64-bit code selector (ring 0)
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dw 0x0000FFFF ; Segment Limit
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db 0x0, 0x0, 0x0 ; Base Address
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db 10011010b ; |7|6|5|4|3|2|1|0|
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; | | | | | | | `----- 1 when segment used.
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; | | | | | | `------ 1 when writable.
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; | | | | | `------- 1 if "conformant". Don't know what is it... spectral ? xD
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; | | | | `-------- 1 always
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; | | | `--------- 1 for segment descriptor, 0 for system descriptor
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; | | `---------- DPL !!! 0 for ring 0
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; | `----------- DPL (2/2)
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; `------------ 1 if in physical memory, 0 if page fault
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db 10101111b ; |7|6|5|4|3|2|1|0|
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; | | | | | | | `----- Limit 16
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; | | | | | | `------ Limit 17
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; | | | | | `------- Limit 18
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; | | | | `-------- Limit 19
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; | | | `--------- available for use
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; | | `---------- 0 always
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; | `----------- size of data. 1 for 32bits
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; `------------ 0 if limit is in Bytes, 1 if it's in pages (4ko)
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db 0x0 ; Base Address
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GDT_LENGTH:
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;; TEXT
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set_a20:
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push ax
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in al, 0x92
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or al, 2
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out 0x92, al
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pop ax
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ret
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