PUSH -> "clear" code doesn't work

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dieboy

Joined: 30 Dec 2004
Posts: 41
Location: Poland, Elblag

dieboy

Hello!

Code:

push ax
;is like :
sub sp, 2
mov ss:[sp], ax
;but in TASM

and how to write this code in FASM? if I write ... [ss:sp] i have an error. Can you tell me ?

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18 May 2005, 18:37

YONG

Joined: 16 Mar 2005
Posts: 7997
Location: 22° 15' N | 114° 10' E

YONG

Try this:

Code:

                sub     sp, 2
                mov     bp, sp
                mov     [bp], ax

Your error was not related to ss. It was about [sp] which is illegal.

Listed below are the legal 16-bit Memory Addressing Modes:
- Displacement
- bx or bp
- si or di
- Any combinations of the above three

YONG

18 May 2005, 19:45

mike.dld

Joined: 03 Oct 2003
Posts: 235
Location: Belarus, Minsk

mike.dld

In 16-bit code there is no SP-relative addressing (only BP,BX,SI,DI can be used). But you can probably write

Code:

sub sp, 2
mov [esp], ax

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18 May 2005, 19:53

YONG

Joined: 16 Mar 2005
Posts: 7997
Location: 22° 15' N | 114° 10' E

YONG

One more point.

Even though the [bp] addressing mode uses ss by default,
you may code [ss:bp] to make it clear and unambiguous.

YONG

18 May 2005, 20:21

MazeGen

Joined: 06 Oct 2003
Posts: 977
Location: Czechoslovakia

MazeGen

mike.dld wrote:

In 16-bit code there is no SP-relative addressing (only BP,BX,SI,DI can be used). But you can probably write
Code:
sub sp, 2
mov [esp], ax     

You can never be sure that high word of ESP is zero, so MOVZX ESP,SP should be used before such code.

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18 May 2005, 20:59

dieboy

Joined: 30 Dec 2004
Posts: 41
Location: Poland, Elblag

dieboy

Ok. Thank you very much! Smile

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...

19 May 2005, 06:15

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