Re: [PATCH v5 00/23] ILP32 for ARM64

From	Catalin Marinas <catalin.marinas@arm.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v5 00/23] ILP32 for ARM64
Date	2015-10-02 11:40 +0200
Message-ID	<qf4YN-7RN-1@gated-at.bofh.it> (permalink)
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On Thu, Oct 01, 2015 at 09:49:46PM +0000, Pinski, Andrew wrote:
> Ok, we will rewrite these patches using 32bit time_t and 32bit off_t
> and redo the toolchain support for them.  Note this is going back to
> the abi I had originally done when I submitted my original version
> when it was asked to change time_t to be 64bit. 

One of the key aspects of kernel development is the ability to adapt
quickly to new requests/insights. This implies releasing early and often
rather than a new version roughly twice a year (IIRC, v1 was posted
September 2013). Moreover, the success of the kernel is partly based on
not getting stuck on old decisions (well, unless it breaks accepted user
ABI).

So, at the time, following x32 discussions, we thought of using the
native ABI as much as possible. However, two important things happened
since:

1. libc community didn't like breaking the POSIX compliance
2. No-one seems desperate for ILP32 on AArch64

(1) is a fair point and I would rather be careful as we don't know the
extent of the code affected. In the meantime, we've also had ongoing
work for addressing the 2038 issue on 32-bit architectures.

The second point is equally important. The benchmarks I've seen didn't
show a significant improvement and the messages I got on various
channels pretty much labeled ILP32 as a transitional stage to full LP64.
In this case, we need to balance the benefits of a close to native ABI
(future proof, slightly higher performance) vs. the cost of maintaining
such ABI in the kernel on the long term, especially if it's not widely
used/tested.

We've seen the kernel patches and, following discussions on the lists,
decided to change the original recommendation. IIRC, the main ideas (but
you need to read various threads as I can't remember the details from
6-7 months ago):

a) separate syscall table for ILP32
b) close to compat ABI with 32-bit time_t, off_t
c) asm-generic/unistd.h rather than asm/unistd32.h (that's where it
   would differ from compat, together with places where pointers are
   passed)

As I said previously, I'm not going to pay any attention to the patches
in this series, it's nothing more than a rebase of a version I already
reviewed.

-- 
Catalin
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Thread

[PATCH v5 00/23] ILP32 for ARM64 Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
  [PATCH v5 08/23] arm64:ilp32: use 64bit syscall-names for ILP32 when passing 64bit registers Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
  [PATCH v5 17/23] arm64:ilp32: add vdso-ilp32 and use for signal return Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
    Re: [PATCH v5 17/23] arm64:ilp32: add vdso-ilp32 and use for signal  return Nathan Lynch <Nathan_Lynch@mentor.com> - 2015-09-30 06:10 +0200
      Re: [PATCH v5 17/23] arm64:ilp32: add vdso-ilp32 and use for signal  return Yury Norov <ynorov@caviumnetworks.com> - 2015-10-01 21:50 +0200
        Re: [PATCH v5 17/23] arm64:ilp32: add vdso-ilp32 and use for signal return "Dr. Philipp Tomsich" <philipp.tomsich@theobroma-systems.com> - 2015-10-01 22:40 +0200
  [PATCH v5 09/23] arm64:ilp32: use non-compat syscall names for ILP32 as for LP64 Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
  [PATCH v5 23/23] arm64:ilp32: add ARM64_ILP32 to Kconfig Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
  [PATCH v5 13/23] arm64:ilp32: share HWCAP between LP64 and ILP32 Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
  [PATCH v5 04/23] arm64: change some CONFIG_COMPAT over to use CONFIG_AARCH32_EL0 instead Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
    Re: [PATCH v5 04/23] arm64: change some CONFIG_COMPAT over to use  CONFIG_AARCH32_EL0 instead kbuild test robot <lkp@intel.com> - 2015-09-30 05:40 +0200
  [PATCH v5 02/23] arm64: ensure the kernel is compiled for LP64 Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
  [PATCH v5 16/23] arm64: add support for starting ILP32 (ELFCLASS32) binaries Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
  [PATCH v5 15/23] arm64:ilp32: support core dump generation for ILP32 Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
  [PATCH v5 05/23] arm64:ilp32: expose 'kernel_long' as 'long long' for ILP32 Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
  [PATCH v5 10/23] arm64: introduce is_a32_task and is_a32_thread (for AArch32 compat) Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:20 +0200
    Re: [PATCH v5 10/23] arm64: introduce is_a32_task and is_a32_thread  (for AArch32 compat) kbuild test robot <lkp@intel.com> - 2015-09-30 05:50 +0200
  [PATCH v5 22/23] aarch64: ilp32: msgrcv, msgsnd handlers Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:30 +0200
  [PATCH v5 20/23] arm64:ilp32: use the native siginfo instead of the compat siginfo Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:30 +0200
  [PATCH v5 07/23] arm64:ilp32: share signal structures between ILP32 and LP64 ABIs Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:30 +0200
  [PATCH v5 19/23] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:30 +0200
  [PATCH v5 21/23] arm64:ilp32: change COMPAT_ELF_PLATFORM to report a a subplatform for ILP32 Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:30 +0200
  [PATCH v5 18/23] ptrace: Allow compat to use the native siginfo Yury Norov <ynorov@caviumnetworks.com> - 2015-09-30 00:30 +0200
  Re: [PATCH v5 00/23] ILP32 for ARM64 Catalin Marinas <catalin.marinas@arm.com> - 2015-09-30 12:20 +0200
    Re: [PATCH v5 00/23] ILP32 for ARM64 Mark Brown <broonie@kernel.org> - 2015-09-30 18:50 +0200
      Re: [PATCH v5 00/23] ILP32 for ARM64 Catalin Marinas <catalin.marinas@arm.com> - 2015-10-01 13:20 +0200
        Re: [PATCH v5 00/23] ILP32 for ARM64 Mark Brown <broonie@kernel.org> - 2015-10-01 13:40 +0200
          Re: [PATCH v5 00/23] ILP32 for ARM64 Andrey Konovalov <andrey.konovalov@linaro.org> - 2015-10-01 18:50 +0200
      Re: [PATCH v5 00/23] ILP32 for ARM64 Yury Norov <ynorov@caviumnetworks.com> - 2015-10-01 21:40 +0200
    Re: [PATCH v5 00/23] ILP32 for ARM64 Yury Norov <ynorov@caviumnetworks.com> - 2015-10-01 21:20 +0200
      Re: [PATCH v5 00/23] ILP32 for ARM64 Arnd Bergmann <arnd@arndb.de> - 2015-10-01 23:30 +0200
        Re: [PATCH v5 00/23] ILP32 for ARM64 "Pinski, Andrew" <Andrew.Pinski@caviumnetworks.com> - 2015-10-01 23:50 +0200
          Re: [PATCH v5 00/23] ILP32 for ARM64 Catalin Marinas <catalin.marinas@arm.com> - 2015-10-02 11:40 +0200
            Re: [PATCH v5 00/23] ILP32 for ARM64 "Kapoor, Prasun" <Prasun.Kapoor@caviumnetworks.com> - 2015-10-03 05:00 +0200
              Re: [PATCH v5 00/23] ILP32 for ARM64 Catalin Marinas <catalin.marinas@arm.com> - 2015-10-05 18:00 +0200
                Re: [PATCH v5 00/23] ILP32 for ARM64 "Pinski, Andrew" <Andrew.Pinski@caviumnetworks.com> - 2015-10-05 23:10 +0200
          Re: [PATCH v5 00/23] ILP32 for ARM64 Yury Norov <ynorov@caviumnetworks.com> - 2015-10-05 21:20 +0200

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