Test registers?

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Tyler

Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA

Tyler 11 Jul 2010, 01:05

I was looking through HelpPC, under "Assembler Programming Topics" -> "8086 architecture" -> "Special Registers (386+ only)", in the list of special registers, they list CR0-CR3, and then TR4-TR7. Are TRx registers just mnemonics for CRx?

11 Jul 2010, 01:05

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 11 Jul 2010, 01:19

Intel Vol. 3A wrote:

18.14 OBSOLETE INSTRUCTIONS
The MOV to and from test registers instructions were removed from the Pentium processor and future IA-32 processors. Execution of these instructions generates an invalid-opcode exception (#UD).

11 Jul 2010, 01:19

Tyler

Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA

Tyler 11 Jul 2010, 01:52

What were they used for? Google returns nil.

11 Jul 2010, 01:52

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 11 Jul 2010, 02:25

Seems that TR6 and TR7 where designed to test the TLB: http://www.logix.cz/michal/doc/i386/chp10-06.htm

The Wikipedia says that TR4-7 were introduced in the 80486. Although false, it may be true that this processor introduced TR4 for something (haven't googled anything about it).

11 Jul 2010, 02:25

sinsi

Joined: 10 Aug 2007
Posts: 789
Location: Adelaide

sinsi 11 Jul 2010, 02:27

Something to do with prefetch or cache in the 386/486 I think.

edit: http://www.rcollins.org/secrets/TR4Bug.html

11 Jul 2010, 02:27

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 11 Jul 2010, 06:35

IIRC, the functionality of the TRx registers was replaced by the more flexible MSR mechanism.

11 Jul 2010, 06:35

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