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I was trying to find out where the page table and gdt is in UEFI.Then I found that gdt is located in RT_data,while page table is located in BS_data.It is easy to prevent my OS from overwriting gdt,but how can I deal with the page table?It is said that BS_data would be reclaimed after exiting boot services,and can I reclaim the RT_data?

wishedtobe wrote: ↑Fri Jul 05, 2024 8:00 pmIt is easy to prevent my OS from overwriting gdt,but how can I deal with the page table?

You need to create your own GDT and page tables. You can't reuse the ones set up by UEFI.

wishedtobe wrote: ↑Fri Jul 05, 2024 8:00 pmIt is said that BS_data would be reclaimed after exiting boot services,and can I reclaim the RT_data?

No, you can't reclaim memory containing runtime data.

Octocontrabass wrote: ↑Fri Jul 05, 2024 8:07 pm

wishedtobe wrote: ↑Fri Jul 05, 2024 8:00 pmIt is easy to prevent my OS from overwriting gdt,but how can I deal with the page table?

You need to create your own GDT and page tables. You can't reuse the ones set up by UEFI.

wishedtobe wrote: ↑Fri Jul 05, 2024 8:00 pmIt is said that BS_data would be reclaimed after exiting boot services,and can I reclaim the RT_data?

No, you can't reclaim memory containing runtime data.

Due to the dirty memory space, I can hardly use any part of the memory (overwriting the page table may cause serious problems), making me unable to create my own page tables.

Why not create your page tables before you reclaim the boot services data?

Octocontrabass wrote: ↑Fri Jul 05, 2024 8:28 pm Why not create your page tables before you reclaim the boot services data?

Maybe you are right.Then what will it be if I overwrite the runtime services?

Probably something bad will happen, but you shouldn't do it because the UEFI spec says you're not allowed to do it.