126 lines
2.7 KiB
NASM
126 lines
2.7 KiB
NASM
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%if 0
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Example of entering 32-bit protected mode using DPMI
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Public Domain
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%endif
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;%include "CMMACROS.MAC"
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%define _4digitshex(h) ((((h)/1000h)% 10h)+'0' +(('A'-'9'-1)*((((h)/1000h)% 10h)/0Ah))), \
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((((h)/100h)% 10h)+'0' +(('A'-'9'-1)*((((h)/100h)% 10h)/0Ah))), \
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((((h)/10h)% 10h)+'0' +(('A'-'9'-1)*((((h)/10h)% 10h)/0Ah))), \
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(((h)% 10h)+'0' +(('A'-'9'-1)*(((h)% 10h)/0Ah)))
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; ASCIZ string
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;
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; %1+ = Optional string
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%imacro asciz 0-1+.nolist
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%if %0 >= 1
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db %1
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%endif
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db 0
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%endmacro
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cpu 386
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org 100h
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bits 16
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start:
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pop ax ; get word saved on stack for COM files
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mov bx, sp
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shr bx, 4
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jnz .smallstack
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mov bx, 1000h ; it was a full 64 KiB stack
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.smallstack:
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mov ah, 4Ah ; free unused memory
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int 21h
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xor ax, ax
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xchg ax, word [2Ch]
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mov es, ax
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mov ah, 49h
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int 21h ; free environment if any
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mov ax, 1687h
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int 2Fh
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or ax, ax ; DPMI host installed?
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jnz nohost
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push es ; save DPMI entry address
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push di
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or si, si ; host requires client-specific DOS memory?
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jz .nomemneeded ; no -->
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mov bx, si
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mov ah, 48h
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int 21h ; allocate memory
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jc nomemory
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mov es, ax
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.nomemneeded:
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mov si, msg.debuginfo
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call printstring
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int3
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mov bp, sp
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mov ax, 0001h ; start a 32-bit client
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call far [bp] ; initial switch to protected-mode
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jnc initsuccessful
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initfailed:
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mov si, msg.initfailed
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jmp short rmerror
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nohost:
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mov si, msg.nohost
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jmp short rmerror
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nomemory:
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mov si, msg.nomemory
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rmerror:
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call printstring
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mov ax, 4CFFh
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int 21h
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initsuccessful:
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initsuccessful_ofs equ (initsuccessful-$$+100h)
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; now in protected mode
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mov bx, cs
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mov cx, cs
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lar cx, cx
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shr cx, 8
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or ch, 40h ; make a 32-bit cs
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mov ax, 9
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int 31h
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; now in 32-bit PM
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bits 32
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now32bit:
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now32bit_ofs equ (now32bit-$$+100h)
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mov word [ data.pspsel ], es
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push ds
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pop es
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mov esi, msg.welcome
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call printstring
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mov ax, 4C00h
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int 21h ; normal client exit (terminates DOS process too)
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; Print a string with simple instructions. Don't use
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; pointers or instructions depending on the default operation
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; size, this is called in both 16- and 32-bit modes.
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printstring.next:
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mov dl, al
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mov ah, 2
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int 21h
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printstring:
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lodsb
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or al, al
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jnz .next
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retn
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align 2
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data:
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.pspsel: dw 0
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msg:
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.nohost: asciz "No DPMI host installed.",13,10
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.nomemory: asciz "Not enough DOS memory for child process creation or client initialization.",13,10
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.initfailed: asciz "DPMI initialization failed.",13,10
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.debuginfo: db "Protected mode breakpoint at ",_4digitshex(initsuccessful_ofs),"h.",13,10
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db "32-bit code segment breakpoint at ",_4digitshex(now32bit_ofs),"h.",13,10
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asciz 13,10
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.welcome: asciz "Welcome in 32-bit protected mode.",13,10
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