On Sun, Feb 06, 2022 at 10:23:19PM -0800, Andrii Nakryiko wrote: > I'm not sure the origins of the need for user_pt_regs (as opposed to > using pt_regs directly, like x86-64 does), but with CO-RE and > vmlinux.h it would be more reliable and straightforward to just stick > to kernel-internal struct pt_regs everywhere. And for non-CO-RE macros > maybe just using an offset within struct pt_regs (i.e., > offsetofend(gprs)) would do it? user_pt_regs was introduced on s390 because struct pt_regs is _not_ stable. Only the first n entries (aka user_pt_regs) are supposed to be stable. We could of course reduce struct pt_regs to the bare minimum, which seems to be the current user_pt_regs plus orig_gpr2; which semantically would match more or less what x86 has. Then move pt_regs to uapi, so it is clear that it cannot be changed anymore, and have additional data in a separate structure on the stack, which has pt_regs at the beginning, and access this additional data with container_of & friends. I guess that could work, even though this requires to keep user_pt_regs "for historical reasons".
