> So please post your adjustments!
; FASM example of writing 32-bit program using DPMI
; True FLAT ZERO based memory model
; requires a GOOD DPMI host installed in system
format MZ
heap 0 ; no additional memory
use16
push cs
pop ds
push cs
pop ax
mov [ss:0],ax
mov ax,1687h
int 2Fh
or ax,ax ; DPMI installed?
jnz error
test bl,1 ; 32-bit programs supported?
jz error
mov word [mode_switch],di
mov word [mode_switch+2],es
mov bx,si ; allocate memory for DPMI data
mov ah,48h
int 21h
jc error
mov es,ax
mov ax,1
call far [mode_switch] ; switch to protected mode
jc error
mov cx,1
xor ax,ax
int 31h ; allocate descriptor for code
mov si,ax
xor ax,ax
int 31h ; allocate descriptor for data
mov di,ax
mov dx,cs
lar cx,dx
shr cx,8
or cx,0C000h
mov bx,si
mov ax,9
int 31h ; set code descriptor access rights
mov dx,ds
lar cx,dx
shr cx,8
or cx,0C000h
mov bx,di
int 31h ; set data descriptor access rights
xor cx,cx ; & Our ZERO base 
xor dx,dx ; &
mov es,cx ; #
mov fs,cx ; # Not used by now
mov gs,cx ; #
mov ax,7 ; set descriptor base address
int 31h
mov bx,si
int 31h
mov cx,$FFFF
mov dx,$FFFF
mov ax,8 ; set segment limit to 4 GB
int 31h
mov bx,di
int 31h
mov ds,di
pushw 0
pushw si ; Will land in CS one day 
mov cx, [ss:0]
add cx, rmcodesizepar
shl ecx, 4 ; "paragraph" -> linear
pushd ecx ; Start address in new segment
retfd
error:
mov ax,4CFFh
int 21h
mode_switch dd ?
;
; Padding to 16-byte integer multiply + calculations
;
rmcodeend: ; No code, just for padding
temp1=rmcodeend mod 16
if (temp1<>0) ; then
db (16-temp1) dup (0)
end if
rmcodesize: ; No code, this is the aligned RM code size (starts at 0 !!!)
rmcodesizepar = rmcodesize shr 4 ; In 16-byte "parag" units
use32
org 0
call lleipbase
lleipbase: pop edx
lea esi,[edx+txhello-5]
lloop:
lodsb
test al,al
jz ldone
mov dl,al
mov ah,2
int $21
jmp lloop
ldone: ud2
txhello db 13,10,'Hello from PM, FLAT ZERO based memory model !',13,10,13,10,0
Done in above ^^^ code:
- ZEROized model
- got rid of MZ-fixup 
- probably "fixed" BOCHS crash
ToDo:
- Get rid of 16-bit stack, SS:=DS
- format MZ -> format binary
- Save linear addresses of PSP/DTA/ENV
> the problem is that "near32" addresses (=offsets
IIRC FASM doesn't suffer from offsets
> in MZ are always relative to the address the binary is loaded to,
> and this address is never 0 in DOS.
Very true, but don't see the problem 
> However, due to the way Intel cpus handle "call" and "jmp" opcodes it is
> possible to set the base of CS, SS, DS, ES to 0 and indeed run "non-flat"
Or FLAT ?
> code then ... if it avoids certain things. Among these "certain things" is
> access to global variables, so it won't be a true option usually.
Depends how one implements the global variables 
Seems to be an issue of fixuping and linking 
Question: is it possible / good idea to place a breakpoint at bottom of the stack with INT $31/$0B00 ?  ---
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