CLI/STI crashes multiboot kernel on Grub?

[Jun Koi]

Hi,

I am writing a simple kernel based on the sample code in the
Documentation directory of Grub 0.97. The kernel is compiled as ELF
file, and can be loaded well by Grub. So the sample code is perfectly
fine.

Now I make a simple change to the code: I add 2 lines like this into
the boot.S file:

  cli
  sti

The reason I want to add these because I want to setup the GDT for the
kernel (actually the GDT setup code will be inserted between CLI and
STI). The problem is that my kernel now, with 2 above lines, crashes.

Anybody have any idea why adding CLI and STI (immediately behind CLI)
into the code makes the kernel crash? I looked at the Multiboot
documentation, but dont see anywhere mention or any caution about
this.

All the help are very much appreciated!

Many thanks,
Jun