Higher Half Kernel and GDT

pini · Post by **pini** » Thu Feb 28, 2008 3:52 pm

I successfully wrote a HigherHalf kernel with paging enabled which gets loaded through Tim Robinson's GDT trick (as described in the wiki http://www.osdev.org/osfaq2/index.php/HigherHalfWithGdt).

My question is the following : once paging has been set up and enabled, what is the purpose of setting up a new 0-based GDT instead of keeping the base-biased GDT ?

JamesM · Post by **JamesM** » Thu Feb 28, 2008 4:02 pm

Because segmentation isn't fully supported in x86_64, many instructions (such as SYSCALL, SYSRET) assume a flat memory model.

Generally speaking, segmentation is deprecated. Not only that, but paging is a much more portable concretion of the virtual memory abstraction, and is implemented in many more architectures than segmentation is.

pini · Post by **pini** » Fri Feb 29, 2008 1:20 am

yeah I thought about that in my sleep...

01000101 · Post by **01000101** » Fri Feb 29, 2008 1:24 am

you dream about OS Devving?

weird.

pini · Post by **pini** » Fri Feb 29, 2008 5:55 am

01000101 wrote:you dream about OS Devving?
weird.

If I go to sleep just after some deving (not os-specifically), I sometimes find the solution in my dreams. I'm getting very frustrated when I wake up having forgotten everything except the fact that I did find the solution, but that doesn't happen too often (fortunately)