<html><head></head><body bgcolor="#FFFFFF"><div><span class="Apple-style-span" style>On Jul 23, 2012, at 7:08 PM, Fan Yang <<a href="mailto:lljyangfan@gmail.com">lljyangfan@gmail.com</a>> wrote:</span><br></div><div>
<br></div><div></div><blockquote type="cite"><div><br><br><div class="gmail_quote">2012/7/23 Ram Tummala <span dir="ltr"><<a href="mailto:venkatram867@gmail.com" target="_blank">venkatram867@gmail.com</a>></span><br>
<blockquote style="margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid" class="gmail_quote">
<div class="HOEnZb"><div class="h5">On Jul 23, 2012, at 9:32 AM, Fan Yang <<a href="mailto:lljyangfan@gmail.com">lljyangfan@gmail.com</a>> wrote:<br>
<br>
> hi all:<br>
> when I change the cr0 register I get a "Segmentation fault (core dumped)".<br>
> my code is :<br>
><br>
><br>
> .data<br>
> .text<br>
> .global _start<br>
> _start:<br>
> movl %eax, %cr0<br>
><br>
> this code can work well in ubuntu system when I use root to run it. So what can I do to work it in redhat system?<br>
</div></div><p>Changing a control register is a privileged operation. You can't do it<br>
from the user space. You can only do it from ring 0.<br>
<br>
Venkatram Tummala<br>
><br>
> thanks<br>
><br>
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</p><p> </p></blockquote><div>May be I can work it by adding a new syscall in the kernel, right?</div></div>
</div></blockquote>Yes you can add a syscall in the kernel or can use procfs or sysfs but you should fully understand the consequences. The code will never be accepted by the kernel community. Exporting such functionality to the user space is recipe for disaster. It would open up a simple DOS attack and that is just a start. <div>
<br></div><div>Hardware Control registers are just not supposed to be handled by the user space. </div><div><br></div><div>Venkatram Tummala</div></body></html>