lock prefix freedom

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bitshifter

Joined: 04 Dec 2007
Posts: 796
Location: Massachusetts, USA

bitshifter 23 Jun 2011, 13:47

I can do anything i want with lock prefix.

Code:

lock mul bx

_________________
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.

23 Jun 2011, 13:47

ouadji

Joined: 24 Dec 2008
Posts: 1081
Location: Belgium

ouadji 23 Jun 2011, 14:56

#UD Invalid Opcode Exception

_________________
I am not young enough to know everything (Oscar Wilde)-

23 Jun 2011, 14:56

JoeCoder1

Joined: 13 Jun 2011
Posts: 62

JoeCoder1 23 Jun 2011, 17:10

haha isn't lock interpreted as a label there Wink

23 Jun 2011, 17:10

bitshifter

Joined: 04 Dec 2007
Posts: 796
Location: Massachusetts, USA

bitshifter 24 Jun 2011, 00:58

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?

24 Jun 2011, 00:58

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20451
Location: In your JS exploiting you and your system

revolution 28 Jun 2011, 03:49

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.

28 Jun 2011, 03:49

Madis731

Joined: 25 Sep 2003
Posts: 2139
Location: Estonia

Madis731 28 Jun 2011, 06:07

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

28 Jun 2011, 06:07

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20451
Location: In your JS exploiting you and your system

revolution 28 Jun 2011, 06:11

Madis731: Also ...

Code:

gs fs es ss cs ds lock rep lea eax,ebx

https://board.flatassembler.net/~flatasse/subdomains/board/topic.php?p=65787#65787

28 Jun 2011, 06:11

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