32-bit address in 16-bit mode

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l4m2

Joined: 15 Jan 2015
Posts: 674

l4m2 12 Feb 2015, 08:29

I think I needn't be afraid to do so if used good.for example ,Mov cx,[4ax]
so how do you see it

12 Feb 2015, 08:29

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20513
Location: In your JS exploiting you and your system

revolution 12 Feb 2015, 08:33

What is wrong with the standard "mov cx,[eax]"?

12 Feb 2015, 08:33

l4m2

Joined: 15 Jan 2015
Posts: 674

l4m2 01 Mar 2015, 02:45

revolution wrote:

What is wrong with the standard "mov cx,[eax]"?

4ax = ax + ax+ ax + ax

01 Mar 2015, 02:45

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20513
Location: In your JS exploiting you and your system

revolution 01 Mar 2015, 04:15

Code:

movzx eax,ax
mov cx,[eax*4]

01 Mar 2015, 04:15

gens

Joined: 18 Feb 2013
Posts: 161

gens 01 Mar 2015, 04:16

l4m2 wrote:

revolution wrote:
What is wrong with the standard "mov cx,[eax]"?
4ax = ax + ax+ ax + ax

mov cx, [ax*4]
edit: scratch that

mov ecx, [eax*4]
or
mov cx, [eax*4]

first one gives error:
mov cx, [ax*4]
error: reserved word used as symbol.

what word is here reserved ?

Last edited by gens on 01 Mar 2015, 04:19; edited 1 time in total

01 Mar 2015, 04:16

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20513
Location: In your JS exploiting you and your system

revolution 01 Mar 2015, 04:19

gens wrote:

mov cx, [ax*4]

16-bit mod-reg-rm addressing doesn't support that. Neither "ax", nor "*4", is possible. You'll need the SIB addressing mode.

01 Mar 2015, 04:19

gens

Joined: 18 Feb 2013
Posts: 161

gens 01 Mar 2015, 04:20

revolution wrote:

gens wrote:
mov cx, [ax*4]
16-bit mod-reg-rm addressing doesn't support that. Neither "ax", nor "*4", is possible. You'll need the SIB addressing mode.

makes sense, thx
i already corrected above

01 Mar 2015, 04:20

l4m2

Joined: 15 Jan 2015
Posts: 674

l4m2 11 Mar 2015, 00:37

revolution wrote:

Code:

movzx eax,ax
mov cx,[eax*4]

I meant so but I did not say about movzx

11 Mar 2015, 00:37

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