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SubjectRe: Let me start over - "FPU & ptrace function"
Linux, like many OSes, save the fpu state in a lazy manner.  They
don't save the fpu state when it changes processes. However, when
another app tries to uses the fpu, the system traps and finally saves
the data. The "fnop" is there to force the system to save the child's
fpu state if it hasn't done so already.

Regards,

Steve

David Howells wrote:
>
> > I have a lot of FPU knowledge, but little kernel experience.
> Well, I don't know much about the FPU, but a do know something about the
> kernel. I'm not sure about why you're using the "fnop" instruction, because
> surely that'll apply to the process/thread issuing the ptrace() and not the
> one who is being ptraced.
>
> David Howells

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