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IronFelix



Joined: 09 Dec 2004
Posts: 141
Location: Russia, Murmansk region
IronFelix
Hi all!
The question is - is there any difference in takts with using ESP or EBP addressing.
Some example:
Code:
 mov eax,[ebp + 8]    

and
Code:
 mov eax,[esp + 4]    

Second one is 1 byte longer, but what about takts? The question comes from fact, that some functions can avoid using stack frames by using ESP instead of EBP, beacause push ebp/mov ebp,esp/leave = 4 bytes, and if leave replaced by mov esp,ebp/pop ebp - 6 bytes. As a result - smaller size.
Please, tell your opinion.
Thanks.

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Post 13 Jan 2009, 09:26
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17664
Location: In your JS exploiting you and your system
revolution
Regardless of what they may tell you "size doesn't matter".

But, seriously, yes, you can use ESP addressing. But it has some problems also. I would recommend that you limit use to leaf procedures only that don't use push/pop inside.

Search this very forum for some other discussions about using ESP to access stack parameters.
Post 13 Jan 2009, 09:30
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bitRAKE



Joined: 21 Jul 2003
Posts: 3043
Location: vpcmipstrm
bitRAKE
The instruction dispatcher is limited in the bytes and instructions processed. So, size will have an impact in optimization, but having another register usually proves more advantageous. The stack frame is only needed in situations of local dynamic allocation.

x64 is another matter, imho. The calling convension requires some stack massaging and there are plenty of registers.
Post 13 Jan 2009, 16:16
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vid
Verbosity in development


Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia
vid
I suggest you to google and read some links on "stack frame", there is lot of it online and explains what you seek to understand.
Post 13 Jan 2009, 16:38
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IronFelix



Joined: 09 Dec 2004
Posts: 141
Location: Russia, Murmansk region
IronFelix
Thanks a lot. Thats quite enough for me to understand.
Post 13 Jan 2009, 17:20
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