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Index > Compiler Internals > CR8 (and CR9-CR15, DR8-DR15)

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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17278
Location: In your JS exploiting you and your system
revolution
Code:
use64
mov rax,cr8 ;<----Error: Undefined Symbol    
I can't program the Task Priority Register in my OS Sad

Also I see mentioned in the Intel docs that CR9 thru CR15 and DR8 thru DR15 are defined (using REX.R) but as yet unimplemented.
Quote:
In 64-bit mode, more encodings for control and debug registers are available. The REX.R bit is used to modify the ModR/M reg field when that field encodes a control or debug register (see Table 2-4). These encodings enable the processor to address CR8-CR15 and DR8- DR15. An additional control register (CR8) is defined in 64-bit mode. CR8 becomes the Task Priority Register (TPR).

In the first implementation of IA-32e mode, CR9-CR15 and DR8-DR15 are not implemented. Any attempt to access unimplemented registers results in an invalid-opcode exception (#UD).
Post 02 Sep 2005, 09:29
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Tomasz Grysztar
Assembly Artist


Joined: 16 Jun 2003
Posts: 7724
Location: Kraków, Poland
Tomasz Grysztar
I just forgot to add those registers to table. I'm fixing it now.
Post 02 Sep 2005, 15:13
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