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Index > Linux > non-volatile register as syscall buffer?

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Lurker



Joined: 07 Feb 2012
Posts: 6
Lurker
Code:
push 4
pop edx
;mov ecx,esi (does not work)
mov ecx,tsz;(does work)
mov ebx,eax
push 3
pop eax
int 0x80
    


I'm a novice to asm and I've been trying to code a program that needs to read 4 bytes from a file to esi/edi.
If ecx holds the offset of tsz (reserved memory) everything works fine and later I can mov esi,[tsz]. Is it possible to read to esi/edi directly?
Post 07 Feb 2012, 20:25
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17450
Location: In your JS exploiting you and your system
revolution
Lurker wrote:
Is it possible to read to esi/edi directly?
If I understand you properly then the answer is no. You have to supply a memory address for the destination. You can't make ecx point to esi, you can only copy the contents of esi into ecx.
Post 08 Feb 2012, 15:00
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Lurker



Joined: 07 Feb 2012
Posts: 6
Lurker
yes, I was asking If It was possible to make ecx point to esi.
Thanks.
Post 08 Feb 2012, 15:20
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edfed



Joined: 20 Feb 2006
Posts: 4240
Location: 2018
edfed
only instructions points to registers, you can change some opvalues to change the register reference in an instruction, and if you use ecx to contain that value (cl is enough), you can use as a pointer... but;;; hem.
Post 08 Feb 2012, 17:39
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