On Tue, Mar 21, 2023 at 5:19 PM Luca <l...@orpolo.org> wrote: > > Every thread needs to have its own values of fs_base / gs_base, and > > you need to store/restore them on context switch by accessing the > > appropriate MSR. There's also the swapgs instruction that I'm told is > > useful if you also use gs for kernel's own needs (such as per-CPU > > data). > > I see there are also the rdfsbase/wrfsbase/rdgsbase/wrfgsbase > instructions which would simplify a lot this part, but they are > relatively new (~10 years)... I guess we need to handle also the case > using MSRs/swapgs, which seems quite complicated if made efficient, as > it requires to keep track of the GS state on each trap entry. I'll try > to have a simple implementation that works, and eventually optimize it > later.
Also FWIW: x86_64 glibc isn't actually using gs, and I doubt it's ever going to. So while a full proper implementation should support gs as well as fs, just supporting fs should be enough to get glibc going. Sergey
