push ah

[fdig]

Hi,

why i cannot push byte registers (ah) on stack?

Here's what ml.exe assembler says:

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error A2149: byte register cannot be first operand

greetings

[Mark Jones]

Hello Fdig. AH is a BYTE and the stack in 32-bit windows is comprised of DWORD values, hence the two are incompatible. If you must push AH, try this:

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    xor ecx,ecx
    mov cl,ah
    push ecx


Is this for DOS assembly or WIN32 assembly?

Try looking in the ASMINTRO.HLP file - very useful stuff in there. Have Fun!

[Ratch]

fdig,

     Or the following.  Ratch

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MOVZX ECX,AH
PUSH ECX


[zcoder]

Or if nothing is in AL
       PUSH EAX


Zcoder....

[arafel]

how about:

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sub     esp, 4
mov     [esp], byte ptr ah

:wink

[zooba]

how about:

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sub     esp, 4
mov     [esp], byte ptr ah

:wink

Doesn't necessarily mean the rest of the value is clear:

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push 0
mov  [esp], ah

:U

[arafel]

Doesn't necessarily mean the rest of the value is clear:

Well, no one mentioned the necessity for the whole dword to be cleared. Original intent was to store a single byte on the stack, presumably for later extraction of the same single byte.

[zooba]

Doesn't necessarily mean the rest of the value is clear:

Well, no one mentioned the necessity for the whole dword to be cleared. Original intent was to store a single byte on the stack, presumably for later extraction of the same single byte.

Fair point. However, it does mean that EAX can be popped and the value is zero-extended already :bg

[fdig]

Hello Fdig. AH is a BYTE and the stack in 32-bit windows is comprised of DWORD values, hence the two are incompatible.

Hi, Ah ok!

Is this for DOS assembly or WIN32 assembly?

DOS assembly.

Thx for the many answers ;)

[MichaelW]

MASM returns an error because the processor does not support pushing (or popping) a byte-size register or memory operand, regardless of the stack address size.