[ros-dev] Re: [ros-svn] [hbirr] 13102: - Set the limit of the user mode code/data segment back to 4GB.

[Alex Ionescu]

Hi,

>
> adding the stack segment register to one instruction at the begin of 
> _KiFastCallEntry does fix the fpu problem for me. 


That's really great! But how did you come to discover this? i.e, what is 
the reason for the behavior? I'm glad it's fixed but I would like to 
understand what's up.

> And I don't understand why the interrupt flag is manipulated after 
> sysenter and before sysexit.

Because on SYSENTER, the interrupt flag is not on, while in INT3, it is. 
Therefore, if any function tries to read saved EFLAGS in the trap frame, 
we must be sure that it thinks IF is on. All the examples I've seen do 
this hack to IF.

>
> - Hartmut
>
Best regards,
Alex Ionescu