From: Christian Brauner <christian.brauner@canonical.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>,
Florian Weimer <fweimer@redhat.com>,
Mike Frysinger <vapier@gentoo.org>,
"H. J. Lu" <hjl.tools@gmail.com>, Rich Felker <dalias@libc.org>,
x32@buildd.debian.org, Arnd Bergmann <arnd@arndb.de>,
Will Deacon <will.deacon@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: Can we drop upstream Linux x32 support?
Date: Tue, 11 Dec 2018 06:46:16 +0100 [thread overview]
Message-ID: <20181211054615.f2oefxhf6cuvx5ex@gmail.com> (raw)
In-Reply-To: <CALCETrXoRAibsbWa9nfbDrt0iEuebMnCMhSFg-d9W-J2g8mDjw@mail.gmail.com>
On Mon, Dec 10, 2018 at 05:23:39PM -0800, Andy Lutomirski wrote:
> Hi all-
>
> I'm seriously considering sending a patch to remove x32 support from
> upstream Linux. Here are some problems with it:
>
> 1. It's not entirely clear that it has users. As far as I know, it's
> supported on Gentoo and Debian, and the Debian popcon graph for x32
> has been falling off dramatically. I don't think that any enterprise
> distro has ever supported x32.
>
> 2. The way that system calls work is very strange. Most syscalls on
> x32 enter through their *native* (i.e. not COMPAT_SYSCALL_DEFINE)
> entry point, and this is intentional. For example, adjtimex() uses
> the native entry, not the compat entry, because x32's struct timex
> matches the x86_64 layout. But a handful of syscalls have separate
> entry points -- these are the syscalls starting at 512. These enter
> through the COMPAT_SYSCALL_DEFINE entry points.
>
> The x32 syscalls that are *not* in the 512 range violate all semblance
> of kernel syscall convention. In the syscall handlers,
> in_compat_syscall() returns true, but the COMPAT_SYSCALL_DEFINE entry
> is not invoked. This is nutty and risks breaking things when people
> refactor their syscall implementations. And no one tests these
> things. Similarly, if someone calls any of the syscalls below 512 but
> sets bit 31 in RAX, then the native entry will be called with
> in_compat_set().
>
> Conversely, if you call a syscall in the 512 range with bit 31
> *clear*, then the compat entry is set with in_compat_syscall()
> *clear*. This is also nutty.
>
> Finally, the kernel has a weird distinction between CONFIG_X86_X32_ABI
> and and CONFIG_X86_X32, which I suspect results in incorrect builds if
> the host doesn't have an x32 toolchain installed.
>
> I propose that we make CONFIG_X86_X32 depend on BROKEN for a release
> or two and then remove all the code if no one complains. If anyone
Based on the discussion we had at the beginning of the pidfd_send_signal
syscall patchset I think this is a good idea. For once, the complex
compat handling can make adding new syscalls that need to rely on compat
types because of precedent established by older syscalls icky.
> wants to re-add it, IMO they're welcome to do so, but they need to do
> it in a way that is maintainable.
>
> --Andy
next prev parent reply other threads:[~2018-12-11 5:46 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-11 1:23 Can we drop upstream Linux x32 support? Andy Lutomirski
2018-12-11 1:40 ` Linus Torvalds
2018-12-11 2:22 ` hpa
2018-12-11 8:16 ` Florian Weimer
2018-12-11 21:53 ` Thorsten Glaser
2018-12-11 23:22 ` Andy Lutomirski
2018-12-11 23:35 ` Thorsten Glaser
2018-12-11 23:55 ` Arnd Bergmann
2018-12-12 2:24 ` Andy Lutomirski
2018-12-12 2:33 ` Thorsten Glaser
2018-12-12 9:04 ` Arnd Bergmann
2018-12-12 18:14 ` Joseph Myers
2018-12-12 18:50 ` Ivan Ivanov
2018-12-12 19:12 ` Andy Lutomirski
2018-12-12 19:18 ` Ivan Ivanov
2018-12-12 16:39 ` Andy Lutomirski
2018-12-12 16:52 ` Rich Felker
2018-12-12 18:03 ` Andy Lutomirski
2018-12-13 12:40 ` Catalin Marinas
2018-12-13 15:57 ` Rich Felker
2018-12-13 16:04 ` Florian Weimer
2018-12-13 16:28 ` Rich Felker
2018-12-14 11:42 ` Florian Weimer
2018-12-14 16:13 ` Rich Felker
2018-12-13 18:42 ` Joseph Myers
2018-12-15 4:53 ` Thorsten Glaser
2018-12-11 23:38 ` Rich Felker
2018-12-11 23:40 ` Maciej W. Rozycki
2018-12-13 14:38 ` Olof Johansson
2018-12-13 15:46 ` Lance Richardson
2018-12-13 16:11 ` Richard Purdie
2018-12-11 3:14 ` H.J. Lu
2018-12-11 5:35 ` Andy Lutomirski
2018-12-11 9:02 ` Arnd Bergmann
2018-12-11 11:32 ` Catalin Marinas
2018-12-11 11:37 ` Florian Weimer
2018-12-11 11:52 ` Catalin Marinas
2018-12-11 5:46 ` Christian Brauner [this message]
2018-12-11 10:29 ` John Paul Adrian Glaubitz
2018-12-11 10:37 ` Florian Weimer
2018-12-11 10:44 ` John Paul Adrian Glaubitz
2018-12-11 21:59 ` Thorsten Glaser
2018-12-11 23:33 ` Rich Felker
2018-12-13 5:03 ` Kevin Easton
2018-12-13 9:05 ` Richard Weinberger
2018-12-13 9:37 ` Sven Hartrumpf
2018-12-13 9:57 ` Adam Borowski
2018-12-13 18:50 ` Sven Hartrumpf
2018-12-13 12:12 ` Kevin Easton
2018-12-14 14:38 ` David Laight
2018-12-14 15:17 ` Richard Weinberger
2018-12-13 16:02 ` Rich Felker
2018-12-14 14:13 ` Bernd Petrovitsch
2018-12-14 16:17 ` Rich Felker
2018-12-14 16:29 ` Bernd Petrovitsch
2018-12-14 16:38 ` Florian Weimer
2018-12-14 16:55 ` Rich Felker
2018-12-14 18:58 ` Andy Lutomirski
2018-12-14 19:59 ` Lance Richardson
2018-12-14 20:13 ` Linus Torvalds
2018-12-14 21:27 ` Andy Lutomirski
2018-12-14 21:16 ` Thomas Schöbel-Theuer
2018-12-14 21:24 ` Andy Lutomirski
2018-12-14 21:41 ` Thomas Schöbel-Theuer
2018-12-15 7:41 ` Thomas Schoebel-Theuer
2018-12-15 15:30 ` Andy Lutomirski
2019-01-09 12:41 ` Florian Weimer
2019-01-09 16:02 ` Rich Felker
2019-01-22 13:34 ` Enrico Weigelt, metux IT consult
2018-12-11 20:38 Shawn Rutledge
2018-12-12 0:00 ` Maciej W. Rozycki
2018-12-12 9:12 Steven Newbury
2018-12-12 10:48 ` Thorsten Glaser
2018-12-12 13:27 ` Steven Newbury
2018-12-12 14:01 ` Rich Felker
2018-12-12 14:46 ` Steven Newbury
2018-12-12 16:05 ` Rich Felker
2018-12-13 16:17 tedheadster
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