A MOV question

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bolzano_1989

Joined: 06 Oct 2011
Posts: 4

bolzano_1989

In the following tutorial:
http://www.friedspace.com/assembly/moving.php
, could you tell me the differences and the effects of the differences between the following statements?

Code:

MOV [myvar1],CH

Code:

MOV myvar1,CH

I've just read FASM's document and know that the following 2 statements are different:

Code:

mov eax,3

Code:

mov eax,[3]

How about these 2 statements?

Code:

MOV [myvar1],CH

Code:

MOV myvar1,CH

06 Oct 2011, 09:56

ouadji

Joined: 24 Dec 2008
Posts: 1081
Location: Belgium

ouadji

the bottle "x", and the contents of the bottle "[x]" Razz

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I am not young enough to know everything (Oscar Wilde)-

06 Oct 2011, 10:03

Teehee

Joined: 05 Aug 2009
Posts: 570
Location: Brazil

Teehee

in other words,

Code:

mov eax,3   ; = mov value 3 to eax
mov eax,[3] ; = mov the content of the addresss 3 to eax

MOV [myvar1],CH ; = mov CH value to the address pointed for myvar1.
MOV myvar1,CH   ; this is a invalid operand, doesn't?

lets say,

Code:

myvar1 dd 33

mov eax,[myvar1] ; eax = 33
mov eax,myvar1   ; eax = 0x04F00000

06 Oct 2011, 12:51

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly

For the assemblers supporting such syntax, mov mem, reg/imm and mov [mem], reg/imm are exactly the same thing, however in fasm no such thing is supported to make sure there is a single way to indicate memory access (i.e. since mov ebx+esi, reg/imm is not supported because you need square brackets in the first operand, then neither mov var, reg/imm is supported, you have to always use mov [var], reg/imm instead).

In the last instruction of Teehee's example, in other assemblers you'd need "mov eax, OFFSET myvar1", but in fasm, using symbos "naked" (without brackets), is the equivalent of using OFFSET.

06 Oct 2011, 13:22

bolzano_1989

Joined: 06 Oct 2011
Posts: 4

bolzano_1989

Thank you Teehee and LocoDelAssembly Very Happy

07 Oct 2011, 05:38

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