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[209.132.180.67]) by mx.google.com with ESMTP id r197si13140352pfr.192.2019.01.21.00.20.48; Mon, 21 Jan 2019 00:21:13 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729309AbfAUIT1 (ORCPT + 99 others); Mon, 21 Jan 2019 03:19:27 -0500 Received: from mail-vs1-f67.google.com ([209.85.217.67]:41216 "EHLO mail-vs1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728554AbfAUITZ (ORCPT ); Mon, 21 Jan 2019 03:19:25 -0500 Received: by mail-vs1-f67.google.com with SMTP id t17so12087893vsc.8; Mon, 21 Jan 2019 00:19:23 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=eNwdIYQYJT6Pc3PhNslPpG4rGotSgFNPjN+8uubEzLc=; b=Vo89ajKOwug4ns6UZvMUCUEmNFht3W/Wx6abnzf9O5tKN9U1kYLoWjLOEvNh+CMkSV pKemCXcpNgtHZ410WfIIjTv2OhiKv9Ix5wisMRvLmmoYJ7nWvORqFlYY0SiiawXuk/Eb iddRCgLYkPQAi2Q5k5QRKsIy1TKtyavXX+QwWjivTOlJZh+LGsiDekmyIR95X3xsPe+u 2lUqRxDJLfbbrBLK9tDoFeaM0VkVkIXWWegzPHR5VzDgzw7kGGHTCDWLTzd6o1jiiyF0 KJngLy/50a1MroFrwCkj68ZCpUrNlRRneAd8D3Po0LSDzBomPaLp/sYW8fIJHf/lnjXX WwTQ== X-Gm-Message-State: AJcUukfGB3cNe9n0b5lieVnxC07tAKkZPYVwdg7An2iD11h/pRk2BJNi Kyo0djFImCANX0FAajFDz793Fw6jDJs1RIkqPHQ= X-Received: by 2002:a67:3885:: with SMTP id n5mr10324892vsi.96.1548058763095; Mon, 21 Jan 2019 00:19:23 -0800 (PST) MIME-Version: 1.0 References: <20190118161835.2259170-1-arnd@arndb.de> <20190118161835.2259170-30-arnd@arndb.de> <20190119142852.cntdihah4mpa3lgx@e5254000004ec.dyn.armlinux.org.uk> In-Reply-To: <20190119142852.cntdihah4mpa3lgx@e5254000004ec.dyn.armlinux.org.uk> From: Geert Uytterhoeven Date: Mon, 21 Jan 2019 09:19:11 +0100 Message-ID: Subject: Re: [PATCH v2 29/29] y2038: add 64-bit time_t syscalls to all 32-bit architectures To: Russell King - ARM Linux admin Cc: Andy Lutomirski , Arnd Bergmann , y2038 Mailman List , Linux API , LKML , linux-arch , Matt Turner , Catalin Marinas , Will Deacon , Tony Luck , Fenghua Yu , Michal Simek , Paul Burton , Helge Deller , Benjamin Herrenschmidt , Michael Ellerman , Martin Schwidefsky , Heiko Carstens , Rich Felker , "David S. Miller" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , X86 ML , Max Filippov , Andrew Morton , Deepa Dinamani , "Eric W. Biederman" , Firoz Khan , alpha , linux-arm-kernel , "linux-ia64@vger.kernel.org" , linux-m68k , linux-mips@vger.kernel.org, Parisc List , linuxppc-dev , linux-s390 , Linux-sh list , sparclinux , Network Development , Linux FS Devel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Russell, On Sat, Jan 19, 2019 at 3:29 PM Russell King - ARM Linux admin 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 wrote: > > > On Fri, Jan 18, 2019 at 7:50 PM Andy Lutomirski wrote: > > > > On Fri, Jan 18, 2019 at 8:25 AM Arnd Bergmann 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@linux-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