> Plus the fastpath couldn't clear those registers anyway, since it > didn't even _save_ them - exactly because the whole point of the > fastpath was that not all registers are clobbered by the calling > conventions.
Fast path saves more than just register saving. I changed the fast path to save all registers in my earlier clearregs branches https://git.kernel.org/pub/scm/linux/kernel/git/ak/linux-misc.git/log/?h=spec/clearregs-3 It is still quite a bit faster than all the slow stuff the C do_syscall code does (e.g. reloading all the arguments, setting up unnecessary frame pointers etc.). Just take a look at the disassembly of that function. It's really not very optimized. -Andi