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Old 2020-10-26, 11:58   #5
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"The unspeakable one"
Jun 2006
My evil lair

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Originally Posted by xilman View Post
I am curious.

Can you give a specific example of an instruction which is supported by the bare metal but which can not be executed because of a restriction imposed by the overlying OS?

This is a genuine question because I have never come across an example before.
There are many.

The AVX instructions that use ZMM registers, for example, must be enabled by the OS before anyone can use them. I believe this is because the FXSAVE/FXRESTORE type instructions have a different format for the extra registers. So if the OS is unaware of how, or unwilling, to enable such instructions, then the applications also can't use them.
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