No kernel data segment?

[samueltardieu]

There seems to be no Descriptor::kernel_data_segment(). If I understand correctly, the presence of such a segment is expected in IA32_STAR when doing a syscall, as it is used to load the SS register. Or did I misunderstand the x86_64/amd64 manual?

If needed, I'd be happy to propose a PR.

[xfoxfu]

In GlobalDescriptorTable document, there says Data segment registers in ring 0 can be loaded with the null segment selector. So I think using just the null segment selector maybe is ok.

[samueltardieu]

Unfortunately when doing a syscall the data selector is necessarily the one after the code selector (there is only one offset for both kernel code and data segment in register IA32_STAR), so I cannot use the null segment selector which is at offset 0.

Note that even the code to install this offset into IA32_STAR checks that the data selector is located right after the code selector: https://github.com/rust-osdev/x86_64/blob/master/src/registers/model_specific.rs#L339-L341

[phil-opp]

This seems to be resolved by #181. It introduced a new kernel_data_segment function.