173 lines
2.6 KiB
NASM
173 lines
2.6 KiB
NASM
; All these functions assume DS=0 and ES=0
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malloc_reserve:
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push bx
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call malloc_mark_allocated
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pop bx
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add bx, 0x10
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loop malloc_reserve
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ret
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malloc_reset:
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xor ax, ax
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mov es, ax
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call malloc_get_table
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mov cx, 0x100 ; 256 words
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rep stosw
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; reserve IVT and BDA, the extra data area and this table itself
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xor bx, bx
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mov cx, 0x80
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call malloc_reserve
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; reserve location for chainloaded boot sector
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mov bx, 0x7C00
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mov cx, 0x20
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call malloc_reserve
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ret
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; Input:
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; 0:BX - ptr to mem paragraph
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; Output:
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; AL - bitmask for byte in table
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; BX - offset in table
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malloc_calc_offsets:
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; ch is bit offset
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; cl is operand for bit shifts
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push cx
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; strip last 4 bits (offset within paragraph)
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mov cl, 4
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shr bx, cl
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; backup the next 3 bits of bx (wll be bit offset)
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mov ch, bl
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and ch, 0x07
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; calculate byte offset by shifting off 3 bits
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mov cl, 3
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shr bx, cl
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; setup bit mask in al, shifted by bit offset
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mov al, 0x01
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mov cl, ch
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shl al, cl
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pop cx
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; fallthrough to setup DI
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malloc_get_table:
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mov di, 0x0600
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ret
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; IN: 0:BX ptr to paragraph to be marked as allocated
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malloc_mark_allocated:
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call malloc_calc_offsets
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or byte [bx+di], al
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ret
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malloc_dump:
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call malloc_get_table
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mov si, di
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mov cx, 0x200
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xor dx, dx
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.loop:
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lodsb
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call print8
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xor ah, ah
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call popcnt
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add dx, ax
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loop .loop
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mov cl, 6
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shr dx, cl
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push dx
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call printf
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db " data %UkB", 0x0A, 0x0D, 0x00
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pop dx
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ret
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; Allocate a paragraph
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; out BX ptr
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malloc:
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; search for a byte that is not 0xFF
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call malloc_get_table
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mov cx, 0x0200
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mov al, 0xFF
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repe scasb
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je fatal_oom
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dec di
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mov al, [es:di]
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sub di, 0x0600
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mov cl, 3
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shl di, cl
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jmp .ishere
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; advance one bit each time
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.nextbit:
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inc di
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shr al, 1
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.ishere:
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test al, 1
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jnz .nextbit
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mov cl, 4
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shl di, cl
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mov bx, di
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call malloc_mark_allocated
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mov bx, di
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ret
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; Free a paragraph
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; IN: 0:BX ptr to paragraph to be marked as free
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free:
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call malloc_calc_offsets
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not al
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and byte [bx+di], al
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ret
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; Allocate a sector, 512 bytes or 32 paragraphs
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; OUT BX ptr to sector
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malloc_sector:
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call malloc_get_table
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mov cx, 0x0200
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xor ax, ax
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.continue:
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repne scasw
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jne fatal_oom
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; we need a second word to be 0, otherwise continue search
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scasw
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jne .continue
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sub di, 4
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not ax
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stosw
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stosw
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sub di, 0x604
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mov cl, 7
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shl di, cl
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xchg bx, di
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ret
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; Free a sector
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; IN BX ptr to sector
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free_sector:
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call malloc_calc_offsets
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xor ax, ax
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add di, bx
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stosw
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stosw
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ret
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fatal_oom:
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call printf
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db "PANIC OOM", 0x0A, 0x0D, 0x00
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clip
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.loop:
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hlt
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jmp .loop
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