On Wed, Dec 9, 2015 at 1:15 PM, Andy Lutomirski <l...@amacapital.net> wrote: > On Wed, Dec 9, 2015 at 1:08 PM, Brian Gerst <brge...@gmail.com> wrote: >> Simplified version: >> ENTRY(stub_ptregs_64) >> cmpl $fast_path_return, (%rsp) > > Does that instruction actually work the way you want it to? (Does it > link?) I think you might need to use leaq the way I did in my patch. > >> jne 1f >> SAVE_EXTRA_REGS offset=8 >> call *%rax >> RESTORE_EXTRA_REGS offset=8 >> ret >> 1: >> jmp *%rax >> END(stub_ptregs_64) > > This'll work, I think, but I still think I prefer keeping as much > complexity as possible in the slow path. I could be convinced > otherwise, though -- this variant is reasonably clean.
On further reflection, there's at least one functional difference. With my variant, modifying pt_regs from sys_foo/ptregs is safe. In your variant, it's unsafe unless force_iret() is called. I don't know whether we care. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
