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assemblyx86memory-segmentation

How to set up a LDT?

I have been developing an 32 bit operating system and I want to allow programs to separate segments from the kernel.

To do that I need to make SS, and DS registers actually point to the programs stack and .data section.

From my research I believe this is done through setting up a local descriptor table.

I am assuming this is very similar to the GDT and the LDT is loaded through lldt.

However I do not get how I use this once my segments are set up. Could anyone explain?

Solution

  • No, there's no need to set up a separate LDT just to set up userspace SS/CS/DS segment descriptors.

    It's possible to do that just saving registers state in interrupt handlers and using an entry for task selector in GDT (it is required by CPU to loookup a kernel-space SS of the process to go into an interrupt from userspace).