On Fri, Jan 18, 2019 at 11:53:25AM -0800, Andy Lutomirski wrote: > On Fri, Jan 18, 2019 at 11:33 AM Arnd Bergmann <arnd@xxxxxxxx> wrote: > > > > On Fri, Jan 18, 2019 at 7:50 PM Andy Lutomirski <luto@xxxxxxxxxx> wrote: > > > On Fri, Jan 18, 2019 at 8:25 AM Arnd Bergmann <arnd@xxxxxxxx> wrote: > > > > - Once we get to 512, we clash with the x32 numbers (unless > > > > we remove x32 support first), and probably have to skip > > > > a few more. I also considered using the 512..547 space > > > > for 32-bit-only calls (which never clash with x32), but > > > > that also seems to add a bit of complexity. > > > > > > I have a patch that I'll send soon to make x32 use its own table. As > > > far as I'm concerned, 547 is *it*. 548 is just a normal number and is > > > not special. But let's please not reuse 512..547 for other purposes > > > on x86 variants -- that way lies even more confusion, IMO. > > > > Fair enough, the space for those numbers is cheap enough here. > > I take it you mean we also should not reuse that number space if > > we were to decide to remove x32 soon, but you are not worried > > about clashing with arch/alpha when everything else uses consistent > > numbers? > > > > I think we have two issues if we reuse those numbers for new syscalls. > First, I'd really like to see new syscalls be numbered consistently > everywhere, or at least on all x86 variants, and we can't on x32 > because they mean something else. Perhaps more importantly, due to > what is arguably a rather severe bug, issuing a native x86_64 syscall > (x32 bit clear) with nr in the range 512..547 does *not* return > -ENOSYS on a kernel with x32 enabled. Instead it does something that > is somewhat arbitrary. With my patch applied, it will return -ENOSYS, > but old kernels will still exist, and this will break syscall probing. > > Can we perhaps just start the consistent numbers above 547 or maybe > block out 512..547 in the new regime? I don't think you gain much with that kind of scheme - it won't take very long before an architecture misses having a syscall added, and then someone else adds their own. Been there with ARM - I was keeping the syscall table in the same order as x86 for new syscalls, but now that others have been adding syscalls to the table since I converted ARM to the tabular form, that's now gone out the window. So, I think it's completely pointless to do what you're suggesting. We'll just end up with a big hole in the middle of the syscall table and then revert back to random numbering of syscalls thereafter again. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up
