On Wed, Dec 9, 2015 at 6:50 PM, Andy Lutomirski <l...@amacapital.net> wrote: > 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.
It should have been cmpq. leaq isn't necessary, since immediates are sign-extended to 64-bit. >>> 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. I can go either way at this point. My main concern was getting rid of the duplicate table. -- Brian Gerst -- 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/
