FreeDOSKernel/utils/upxentry.asm at master · codegear/FreeDOSKernel

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%if 0

UPX preparation stub for DOS/EXE format compressed FreeDOS kernel

Public Domain by C. Masloch, 2022

%endif

cpu 8086

org 0

bootloadunit: ; (byte of short jump re-used)

start:

jmp strict short entry

times (32 - 4) - ($ - $$) db 0

; area for CONFIG block

bootloadstack: ; (dword re-used for original ss:sp)

entry:

; common setup (copied from kernel.asm)

push cs

pop ds

xor di, di

mov byte [di + bootloadunit - $$], bl

push bp

mov word [di + bootloadstack - $$], sp

mov word [di + bootloadstack + 2 - $$], ss

; the UPX DOS/EXE depacker needs a certain ss:sp

cli

mov ax, 0

patchstacksegment: equ $ - 2

mov ss, ax

mov sp, 0

patchstackpointer: equ $ - 2

sti

mov ax, -10h

patchpspsegment: equ $ - 2

mov ds, ax

mov es, ax

jmp 0:0

patchcsip: equ $ - 4

end:

times 0C0h - ($ - $$) nop

entry_common:

times 100h - ($ - $$) db 0

dw patchstackpointer

dw patchstacksegment

dw patchpspsegment

dw patchcsip

dw end

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