How would I do this: "rep movsd fs:"

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madmatt

Joined: 07 Oct 2003
Posts: 1045
Location: Michigan, USA

madmatt

Little question here, how would I do this

Code:

rep movsd fs:

in fasm?

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10 May 2012, 00:14

typedef

Joined: 25 Jul 2010
Posts: 2909
Location: 0x77760000

typedef

...

Last edited by typedef on 10 May 2012, 01:13; edited 2 times in total

10 May 2012, 01:06

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 18743
Location: In your JS exploiting you and your system

revolution

Like this is one way:

Code:

rep fs movsd

10 May 2012, 01:08

madmatt

Joined: 07 Oct 2003
Posts: 1045
Location: Michigan, USA

madmatt

revolution wrote:

Like this is one way:
Code:
rep fs movsd    

Allright, yeh, I was using the colon.

Quote:

typedef:

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10 May 2012, 01:44

typedef

Joined: 25 Jul 2010
Posts: 2909
Location: 0x77760000

typedef

madmatt wrote:

revolution wrote:
Like this is one way:
Code:
rep fs movsd    
Allright, yeh, I was using the colon.

Quote:
typedef:

I wrote this

typedef wrote:

fs: what ?

and I thought it was harsh and you'd seen the post so I edited my post. Sorry for that.

10 May 2012, 01:50

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8019
Location: Kraków, Poland

Tomasz Grysztar

revolution wrote:

Like this is one way:
Code:
rep fs movsd    

This is not an official way, though. See section 2.1.8 of the manual.

10 May 2012, 08:50

madmatt

Joined: 07 Oct 2003
Posts: 1045
Location: Michigan, USA

madmatt

Tomasz Grysztar wrote:

revolution wrote:
Like this is one way:
Code:
rep fs movsd    
This is not an official way, though. See section 2.1.8 of the manual.

I don't see anything about a segment override though, just this

Code:

movsd                      ; transfer double word

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10 May 2012, 12:20

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 18743
Location: In your JS exploiting you and your system

revolution

The manual show an SS override:

Code:

movs word [es:di],[ss:si]  ; transfer word

Just replace: word with dword - di with edi - si with esi - ss with fs.

10 May 2012, 12:24

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8019
Location: Kraków, Poland

Tomasz Grysztar

section 2.1.8 wrote:

Full form of string operation needs operands providing the size operator and the memory addresses, which can be SI or ESI with any segment prefix, DI or EDI always with ES segment prefix.

10 May 2012, 12:47

bitshifter

Joined: 04 Dec 2007
Posts: 786
Location: Massachusetts, USA

bitshifter

revolution wrote:

The manual show an SS override:
Code:
movs word [es:di],[ss:si]  ; transfer word    

Hmm, now you got my attention...
I am studying opcoding myself here.
Seems like mov m16/m16 which i thought doesnt exist.
Now i need to figure it out for myself by decoding...

PS: Hello to my fasm friends, i have been idle for quite some time Smile

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09 Jun 2012, 13:54

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 18743
Location: In your JS exploiting you and your system

revolution

bitshifter wrote:

Seems like mov m16/m16 which i thought doesnt exist.

I doesn't exist. Only movs can do mem/mem transfers using fixed source and destination registers and a fixed count register with the rep prefix.

09 Jun 2012, 14:04

edfed

Joined: 20 Feb 2006
Posts: 4270
Location: Now

edfed

very good information. i remember it is evocated somewhere in fasm manual, but it is not highlighted that much.

i wonder if that a generic segment override applyable to every string operations that way.

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09 Jun 2012, 14:39

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