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Index > Compiler Internals > lock prefix freedom

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bitshifter



Joined: 04 Dec 2007
Posts: 764
Location: Massachusetts, USA
bitshifter
I can do anything i want with lock prefix.
Code:
lock mul bx    

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Coding a 3D game engine with fasm is like trying to eat an elephant,
you just have to keep focused and take it one 'byte' at a time.
Post 23 Jun 2011, 13:47
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

#UD Invalid Opcode Exception

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I am not young enough to know everything (Oscar Wilde)- Image
Post 23 Jun 2011, 14:56
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JoeCoder1



Joined: 13 Jun 2011
Posts: 62
JoeCoder1
haha isn't lock interpreted as a label there Wink
Post 23 Jun 2011, 17:10
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bitshifter



Joined: 04 Dec 2007
Posts: 764
Location: Massachusetts, USA
bitshifter
No, its a prefix, like rep is also a prefix
Code:
repe stos byte[edi]    

A lock label would be like
Code:
_lock: lock mul bx    


Now the real question is:
Should FASM be allowed to generate invalid opcodes?
Post 24 Jun 2011, 00:58
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17279
Location: In your JS exploiting you and your system
revolution
bitshifter wrote:
Should FASM be allowed to generate invalid opcodes?
The LOCK prefix only has restricted usage on a subset of CPUs (i.e. the later ones), so actually your question is more like this: Should fasm disallow opcode combinations that are perfectly valid on older CPUs but now cause a fault on newer CPUs? I think the answer is obvious: NO.

I even have some old 80286 boards that used the hardware lock signal for some special purposes other than locking memory accesses. Subsequently the code had some lock's in places that looked very weird until one realised that it was simply raising an external signal and not controlling any memory functionality.
Post 28 Jun 2011, 03:49
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Madis731



Joined: 25 Sep 2003
Posts: 2141
Location: Estonia
Madis731
Code:
cs gs lock repe mul bx
    

Sometimes it just HAS to make sense Smile

Its an oldie, but I couldn't resist Razz
Code:
who | grep -i blonde | talk ; cd ~; wine; talk; touch; unzip; touch; strip; gasp; finger; gasp; mount; fsck; more; yes; gasp; umount; make clean; sleep
    


Last edited by Madis731 on 28 Jun 2011, 06:16; edited 1 time in total
Post 28 Jun 2011, 06:07
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17279
Location: In your JS exploiting you and your system
revolution
Madis731: Also ...
Code:
gs fs es ss cs ds lock rep lea eax,ebx    
Razz

https://board.flatassembler.net/~flatasse/subdomains/board/topic.php?p=65787#65787
Post 28 Jun 2011, 06:11
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