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Message-ID: <CAMuHMdXzQNEEDjWrmTph8Krovj1g2WhnBUaM=FvKB+J2fZqctA@mail.gmail.com> Date: Mon, 21 Jan 2019 09:19:11 +0100 From: Geert Uytterhoeven <geert@...ux-m68k.org> To: Russell King - ARM Linux admin <linux@...linux.org.uk> Cc: Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>, y2038 Mailman List <y2038@...ts.linaro.org>, Linux API <linux-api@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, Matt Turner <mattst88@...il.com>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>, Michal Simek <monstr@...str.eu>, Paul Burton <paul.burton@...s.com>, Helge Deller <deller@....de>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Michael Ellerman <mpe@...erman.id.au>, Martin Schwidefsky <schwidefsky@...ibm.com>, Heiko Carstens <heiko.carstens@...ibm.com>, Rich Felker <dalias@...c.org>, "David S. Miller" <davem@...emloft.net>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>, Max Filippov <jcmvbkbc@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Deepa Dinamani <deepa.kernel@...il.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Firoz Khan <firoz.khan@...aro.org>, alpha <linux-alpha@...r.kernel.org>, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>, linux-m68k <linux-m68k@...ts.linux-m68k.org>, linux-mips@...r.kernel.org, Parisc List <linux-parisc@...r.kernel.org>, linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, linux-s390 <linux-s390@...r.kernel.org>, Linux-sh list <linux-sh@...r.kernel.org>, sparclinux <sparclinux@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, Linux FS Devel <linux-fsdevel@...r.kernel.org> Subject: Re: [PATCH v2 29/29] y2038: add 64-bit time_t syscalls to all 32-bit architectures Hi Russell, On Sat, Jan 19, 2019 at 3:29 PM Russell King - ARM Linux admin <linux@...linux.org.uk> wrote: > 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@...db.de> wrote: > > > On Fri, Jan 18, 2019 at 7:50 PM Andy Lutomirski <luto@...nel.org> wrote: > > > > On Fri, Jan 18, 2019 at 8:25 AM Arnd Bergmann <arnd@...db.de> 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 Same for m68k, and probably other architectures. > 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. I believe the plan is to add future syscalls for all architectures in a single commit, to keep everything in sync. Regardless, I'm wondering what to do with the holes marked "room for arch specific calls". When is a syscall really arch-specific, and can it be added there, and when does it turn out (later) that it isn't, breaking the synchronization again? The pkey syscalls may be a bad example, as AFAIU they can be implemented on some architectures, but not on some others. Still, I had skipped them when adding new syscalls to m68k. Perhaps we should get rid of the notion of "arch-specific syscalls", and reserve a slot everywhere anyway? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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