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Index > Compiler Internals > "short" TEST instruction

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vid
Verbosity in development


Joined: 05 Sep 2003
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Location: Slovakia
vid
"test eax, 8" has a MUCH different effect on x86-64 than "test al, 8"
Post 29 Sep 2006, 04:39
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Tomasz Grysztar



Joined: 16 Jun 2003
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Tomasz Grysztar
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.
Post 29 Sep 2006, 07:34
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
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Location: In your JS exploiting you and your system
revolution
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?
Post 29 Sep 2006, 10:42
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MazeGen



Joined: 06 Oct 2003
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MazeGen
(post by vid)

yes Razz Wink
Post 01 Oct 2006, 13:51
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UCM



Joined: 25 Feb 2005
Posts: 285
Location: Canada
UCM
Then... What is it?
Post 01 Oct 2006, 14:58
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MazeGen



Joined: 06 Oct 2003
Posts: 977
Location: Czechoslovakia
MazeGen
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.
Post 01 Oct 2006, 15:03
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