AVX Support

[tsdnz]

Hi, I am adding AVX support to my OS.

Does AVX only work in protected mode?
I get an Invalid Opcode exception
I have setup AVX support and the server has AVX
Under exceptions in the docs it looks like AVX is only supported in Protected Mode.

Anyone else come across this?

Ali

[tsdnz]

The instruction causing the exception is vldmxcsr

[JAAman]

Note: In VEX-encoded versions, VEX.vvvv is reserved and must be 1111b, otherwise instructions will #UD.

#UD If VEX.vvvv ≠ 1111B.

also, Intel manual volume 2, 2.4.5 Exceptions Type 5 includes a table (labeled table 2-22 in my latest edition) gives a list of causes of various causes for exceptions in various modes

in #UD in RMode for type 5 exception-class can be caused by:
-VEX prefix
-legacy SSE instructions if CR0.EM=1 or CR4.OSFXSR=0
-if preceded by lock instruction
-if any corresponding CPUID feature flag is 0

there is nothing in the "ldmxcsr" section that says it only works in PMode

[tsdnz]

Cheers for the reply, it reminded me to have another look.

I had two issues.

• Forgot to xsetbv to enable the features. AVX, SSE, FPU.
• Then I forgot to do this for each core, I was only setting this in BSP, which made the other cores crash, and I was only showing BSP on the screen at the time to try to figue this out, which made me think it was BSP exception.

Thanks for your reply.

Ali