"short" TEST instruction

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vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 29 Sep 2006, 04:39

"test eax, 8" has a MUCH different effect on x86-64 than "test al, 8"

29 Sep 2006, 04:39

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 29 Sep 2006, 07:34

revolution wrote:

Quote:
x86-64 processor
I don't get your meaning here. What company makes that processor? It 'aint made by Intel or AMD.

You can consider the term "defined" in the beginning of section 2.1.19 of the fasm's manual.

29 Sep 2006, 07:34

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20303
Location: In your JS exploiting you and your system

revolution 29 Sep 2006, 10:42

vid wrote:

"test eax, 8" has a MUCH different effect on x86-64 than "test al, 8"

I don't think the effect is any different, both instructions update the flags only. Is there a functional difference that I overlooked?

29 Sep 2006, 10:42

MazeGen

Joined: 06 Oct 2003
Posts: 977
Location: Czechoslovakia

MazeGen 01 Oct 2006, 13:51

(post by vid)

yes Razz

01 Oct 2006, 13:51

UCM

Joined: 25 Feb 2005
Posts: 285
Location: Canada

UCM 01 Oct 2006, 14:58

Then... What is it?

01 Oct 2006, 14:58

MazeGen

Joined: 06 Oct 2003
Posts: 977
Location: Czechoslovakia

MazeGen 01 Oct 2006, 15:03

Sorry, we were mistaken by Intel manuals which state that in 64-bit mode, 32-bit operands generate a 32-bit result, zero-extended to a 64-bit result in the destination general-purpose register.

(Basic Architecture Manual rev 021, chapter 3.4.1.1 - General-Purpose Registers in 64-Bit Mode)

Our test showed that this is true only in case when the destination register is modified by instruction.

01 Oct 2006, 15:03

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