On Wed, Dec 9, 2015 at 9:42 PM, Brian Gerst <brge...@gmail.com> wrote: > 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.
Right, I always forget that they're sign-extended and not zero-extended. I folded that bit in to my queue. > >>>> 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. Agreed. I'll sleep on it, and maybe someone else has some reason to prefer one approach over the other. --Andy -- Andy Lutomirski AMA Capital Management, LLC -- 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/
