Harden drive.asm against unexpected DS and ES values
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df243e668e
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440187c2a8
@ -38,7 +38,9 @@ relinit: ; print banner
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db "RDOS ",2,2, 0x0A, 0x0D, 0
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push dx
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push ds
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call dinit
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pop ds
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pop dx
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mov word [0x21*4], int21
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116
kernel/drive.asm
116
kernel/drive.asm
@ -34,63 +34,66 @@ section .text
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; initial setup for disk i/o
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dinit: ; copy previously set DPT to our data area
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lds si, [4*0x1E]
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push cs
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pop es
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lds si, [es:4*0x1E]
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mov di, dpt
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mov cx, 11
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rep movsb
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; restore DS
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xor ax, ax
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mov ds, ax
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; set vector
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mov word [4*0x1E], dpt
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mov word [4*0x1E+2], ds
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mov word [cs:4*0x1E], dpt
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mov word [cs:4*0x1E+2], ds
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; set to invalid drive
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mov byte [dsknum], 0xFF
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mov byte [cs:dsknum], 0xFF
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ret
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; int 13 stub
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int13: ; debug output
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;push bx
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;push dx
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;push cx
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;push ax
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;call printf
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;db "int13 CALL AX=",2," CX=",2," DX=",2," BX=",2,0x0A,0x0D,0
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push bx
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push dx
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push cx
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push ax
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call printf
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db "int13 CALL AX=",2," CX=",2," DX=",2," BX=",2,0x0A,0x0D,0
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; do the call
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int 0x13
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;jc .err
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jc .err
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ret
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.err: push ax
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call printf
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db "DISK ERR AX=",2,0x0A,0x0D,0
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stc
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ret
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.err: ;push ax
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;call printf
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;db "DISK ERR AX=",2,0x0A,0x0D,0
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;stc
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;ret
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; get drive parameters
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; read BIOS int13h/AH=8 values
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; DPT data gets copied over our dpt
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; CHS data gets inserted into our bpb
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getprm: test byte [dskflag], 4
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jnz .nodpt
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getprm: ; skip if EBIOS extension enabled
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test byte [cs:dskflag], 4
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jnz .ret
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; do the query
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mov ah, 8
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mov dl, [biosnum]
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mov dl, [cs:biosnum]
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call int13
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; bail out if error
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jc .nodpt
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jc .ret
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; ignore CHS values if odd
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test cl, cl
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jz .nochs
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; get and store sector number
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and cx, 0x3F
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mov word [bpb+BPBSPT], cx
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mov word [cs:bpb+BPBSPT], cx
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; get and store number of heads
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xchg dl, dh
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and dx, 0xFF
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inc dx
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mov [bpb+BPBNOS], dx
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mov [cs:bpb+BPBNOS], dx
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; test if DPT ptr is non-zero
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.nochs: mov ax, es
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or ax, di
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test ax, ax
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jz .nodpt
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jz .ret
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; DS:SI = ES:DI
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mov ax, es
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mov ds, ax
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@ -102,20 +105,21 @@ getprm: test byte [dskflag], 4
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; do the copy
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mov cx, 11
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rep movsb
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.nodpt: ; restore segment registers
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xor ax, ax
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mov ds, ax
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mov es, ax
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ret
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.ret: ret
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; log in drive
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; IN dl drive number
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logdrv: ; dont do anything if drive already selected
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logdrv: ; DS := CS
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push cs
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pop ds
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; dont do anything if drive already selected
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cmp dl, [dsknum]
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je logfdd.ret
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; clear out current contents
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push dx
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push ds
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call flush
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pop ds
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mov ax, 0xFFFF
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mov [dskseek], ax
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mov [dskseek+2], ax
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@ -130,16 +134,22 @@ logdrv: ; dont do anything if drive already selected
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logfdd: ; save info for bios
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mov [biosnum], dl
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; reset dpt to defaults
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push ds
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call getprm
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pop ds
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; set default geometry (1.44 MB floppy)
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mov word [bpb+BPBNOS], 2
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mov word [bpb+BPBSPT], 18
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; load boot sector
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push ds
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xor ax, ax
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xor dx, dx
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call mapabs
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pop ds
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; copy bios parameter block
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; TODO: guess from first byte of FAT if BPB invalid
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push ds
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pop es
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mov si, dskbuf+BPBOFF
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mov di, bpb
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mov cx, BPBSIZ4
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@ -153,6 +163,7 @@ logfdd: ; save info for bios
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mov [bpb+BPBHS+2], ax
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.ret: ret
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; assumes that DS == CS
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loghdd: sub dl, 2
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cmp dl, 4
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jnc logerr
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@ -187,17 +198,20 @@ loghdd: sub dl, 2
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mov cl, 4
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sal bx, cl
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; bail out if no partition
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cmp byte [dskbuf+0x1be+bx+4], 0
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cmp byte [cs:dskbuf+0x1be+bx+4], 0
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je logerr
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; load partition offset
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mov ax, [dskbuf+0x1be+bx+8]
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mov dx, [dskbuf+0x1be+bx+8+2]
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mov ax, [cs:dskbuf+0x1be+bx+8]
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mov dx, [cs:dskbuf+0x1be+bx+8+2]
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; save to to stack
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push dx
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push ax
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; load vbr
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call mapabs
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; copy bpb
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mov ax, cs
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mov ds, ax
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mov es, ax
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mov si, dskbuf+BPBOFF
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mov di, bpb
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mov cx, BPBSIZ4
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@ -207,15 +221,15 @@ loghdd: sub dl, 2
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; fix partition offset
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pop ax
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pop dx
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mov [bpb+BPBHS], ax
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mov [bpb+BPBHS+2], dx
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mov [cs:bpb+BPBHS], ax
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mov [cs:bpb+BPBHS+2], dx
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ret
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logerr: stc
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ret
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mapclu: ; counting from begin of cluster area
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mov bx, [bpb+BPBRDE]
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mov bx, [cs:bpb+BPBRDE]
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mov cl, 4
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shr bx, cl ; 32 bytes per entry
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add ax, bx
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@ -223,22 +237,22 @@ mapclu: ; counting from begin of cluster area
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maprd: ; counting from beginning of dir
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; add fat table sizes
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xor ch, ch
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mov cl, byte [bpb+BPBFN]
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.loop: add ax, [bpb+BPBFS]
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mov cl, byte [cs:bpb+BPBFN]
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.loop: add ax, [cs:bpb+BPBFS]
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adc dx, 0
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loop .loop
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mapfat: ; counting from beginning of FAT
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; add reserved sector count
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add ax, [bpb+BPBRSC]
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add ax, [cs:bpb+BPBRSC]
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adc dx, 0
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map: ; count from partition start
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add ax, [bpb+BPBHS]
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add dx, [bpb+BPBHS+2]
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add ax, [cs:bpb+BPBHS]
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add dx, [cs:bpb+BPBHS+2]
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mapabs: ; absolute sector count
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; skip doing a read if sector number matches
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cmp ax, [dskseek]
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cmp ax, [cs:dskseek]
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jne read
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cmp dx, [dskseek+2]
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cmp dx, [cs:dskseek+2]
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jne read
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ret
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@ -248,8 +262,8 @@ read: push ax
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pop dx
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pop ax
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; store the sector number
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mov [dskseek], ax
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mov [dskseek+2], dx
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mov [cs:dskseek], ax
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mov [cs:dskseek+2], dx
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; do the actual read
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; low level read and write
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@ -259,6 +273,10 @@ _read: mov ch, 2
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db 0x3D ; cmp ax, imm16: causes next instr to be skipped
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_write: mov ch, 3
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mov cl, 1 ; read len
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; DS := ES := CS
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mov ax, cs
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mov ds, ax
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mov es, ax
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; check if ebios supported
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test byte [dskflag], 4
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jz .l00
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@ -322,11 +340,11 @@ _write: mov ch, 3
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ret
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; mark dskbuf as containing unwritten changes
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dirty: or byte [dskflag], 1 ; dirty
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dirty: or byte [cs:dskflag], 1 ; dirty
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ret
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; flush buffer if dirty
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flush: test byte [dskflag], 1
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flush: test byte [cs:dskflag], 1
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jz .ret
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; TODO: error handling & retries
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jmp _write
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@ -3,7 +3,7 @@ section .text
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; set default drive for current process
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; IN dl drive number
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setdd: push ds
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mov ds, [ss:curpsp]
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mov ds, [cs:curpsp]
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mov [PSPDD], dl
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pop ds
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ret
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@ -11,11 +11,23 @@ setdd: push ds
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; get default drive for current process
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; OUT al drive number
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getdd: push ds
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mov ds, [ss:curpsp]
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mov ds, [cs:curpsp]
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mov al, [PSPDD]
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pop ds
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ret
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; auto-complete drive field in fcb
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; IN ds:dx far ptr FCB
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; OUT si copy of dx
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fixfcb: mov si, dx
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cmp byte [si], 0
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jne .ret
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call getdd
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inc dl
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mov byte [si], dl
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.ret: mov dx, si
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ret
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; Load root directory entry
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; IN ax number of directory entry
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lddir: push ax
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@ -56,22 +68,8 @@ fnfile: mov ax, [es:bx+FCBDEN]
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.err: stc
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ret
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; initialize a FCB for directory scanning
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open: mov word [es:bx+FCBDEN], 0
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.search: call fnfile
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mov al, 0xFF
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jc .ret
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push si
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lea di, [bx+1]
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mov cx, 11
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rep cmpsb
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pop si
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jne .search
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mov al, 0
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.ret: ret
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putfn: mov cx, 11
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.loop: lodsb
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call pputc
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loop .loop
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; Open file using FCB
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; IN DS:DX far ptr to FCB
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open: call fixfcb
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int 3
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ret
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