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Re: [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32

From Arnd Bergmann <arnd@arndb.de>
Newsgroups linux.kernel
Subject Re: [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32
Date 2015-12-16 20:20 +0100
Message-ID <qGpMd-5PL-5@gated-at.bofh.it> (permalink)
References <qG5DP-1iE-3@gated-at.bofh.it> <qGnAK-4iQ-37@gated-at.bofh.it> <qGnU5-4Ey-9@gated-at.bofh.it>
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On Wednesday 16 December 2015 17:19:05 Catalin Marinas wrote:
> On Wed, Dec 16, 2015 at 04:58:20PM +0000, Catalin Marinas wrote:
> > On Wed, Dec 16, 2015 at 04:54:34PM +0100, Arnd Bergmann wrote:
> > > On Wednesday 16 December 2015 00:42:35 Yury Norov wrote:
> > > > 
> > > >  #ifdef CONFIG_COMPAT
> > > > -#define COMPAT_ELF_HWCAP       (compat_elf_hwcap)
> > > > -#define COMPAT_ELF_HWCAP2      (compat_elf_hwcap2)
> > > >  extern unsigned int compat_elf_hwcap, compat_elf_hwcap2;
> > > > +#define COMPAT_ELF_HWCAP       \
> > > > +       (is_a32_compat_task()   \
> > > > +         ? compat_elf_hwcap    \
> > > > +         : elf_hwcap)
> > > > +
> > > > +#define COMPAT_ELF_HWCAP2      \
> > > > +       (is_a32_compat_task()   \
> > > > +         ? compat_elf_hwcap2   \
> > > > +         : 0)
> > > > +
> > > >  #endif
> > > 
> > > I'm trying to understand how this is used. Are you compiling
> > > fs/compat_binfmt_elf.c twice to handle both 32-bit ELF types?
> > 
> > It's the same compat_binfmt_elf.c which handles all 32-bit ELF types,
> > i.e. AArch32 and A64/ILP32. The above macros are not constants, so they
> > are evaluated every time a new ELF file is loaded. We do a similar trick
> > with COMPAT_SET_PERSONALITY in patch 11.

Ok, I see. I've also looked at other architectures, and found that
MIPS does it the way I thought it would be

git grep -w binfmt_elf.c
arch/mips/kernel/binfmt_elfn32.c:#include "../../../fs/binfmt_elf.c"
arch/mips/kernel/binfmt_elfo32.c:#include "../../../fs/binfmt_elf.c"

I still think doing the same for arm64 would result in more maintainable
code, because it completely separates the two different formats into
separate files. We'd obviously leave the existing compat handling as
it is, and just add one more file, not do both of them separately as
MIPS does.

Do you see any downsides of that approach?

> IIUC, we may have a problem with this. elf_hwcap is 64-bit long while
> elf_info[n] is 32-bit (Elf32_Addr), so we truncate AT_HWCAP if we ever
> go beyond bit 31. The above may need to look something like:
> 
> #define COMPAT_ELF_HWCAP        \
>         (is_a32_compat_task()   \
>          ? compat_elf_hwcap     \
>          : (u32)elf_hwcap)
> 
> #define COMPAT_ELF_HWCAP2       \
>         (is_a32_compat_task()   \
>          ? compat_elf_hwcap2    \
>          : (u32)(elf_hwcap >> 32))

Yes, interesting find.

	Arnd
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[RFC3 PATCH v6 00/20] ILP32 for ARM64 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
  [PATCH v6 10/20] arm64:ilp32 use the native LP64 'start_thread' for ILP32 threads Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
    Re: [PATCH v6 10/20] arm64:ilp32 use the native LP64 'start_thread' for ILP32 threads Arnd Bergmann <arnd@arndb.de> - 2015-12-16 17:00 +0100
      Re: [PATCH v6 10/20] arm64:ilp32 use the native LP64 'start_thread'  for ILP32 threads Yury Norov <ynorov@caviumnetworks.com> - 2015-12-18 15:00 +0100
  [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
    Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-16 17:10 +0100
    Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Catalin Marinas <catalin.marinas@arm.com> - 2015-12-17 19:30 +0100
      Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-17 21:20 +0100
        Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Andrew Pinski <pinskia@gmail.com> - 2015-12-17 21:20 +0100
          Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-17 22:00 +0100
          Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Catalin Marinas <catalin.marinas@arm.com> - 2015-12-18 12:50 +0100
            Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-18 14:00 +0100
              Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Catalin Marinas <catalin.marinas@arm.com> - 2015-12-21 19:40 +0100
                Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-21 23:30 +0100
              Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it "Dr. Philipp Tomsich" <philipp.tomsich@theobroma-systems.com> - 2015-12-21 19:50 +0100
                Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-21 23:20 +0100
    Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-21 23:40 +0100
      Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Yury Norov <ynorov@caviumnetworks.com> - 2015-12-23 19:40 +0100
        Re: [PATCH v6 12/20] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-23 22:50 +0100
  [PATCH v6 02/20] arm64: ensure the kernel is compiled for LP64 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
  [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to ilp32 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
    Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to ilp32 Andreas Schwab <schwab@suse.de> - 2015-12-17 15:40 +0100
      Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to  ilp32 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-18 15:00 +0100
    Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to  ilp32 Catalin Marinas <catalin.marinas@arm.com> - 2015-12-22 13:30 +0100
      Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to ilp32 Arnd Bergmann <arnd@arndb.de> - 2015-12-22 22:50 +0100
        Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to  ilp32 Catalin Marinas <catalin.marinas@arm.com> - 2015-12-23 14:40 +0100
          Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to ilp32 Arnd Bergmann <arnd@arndb.de> - 2015-12-23 21:50 +0100
            Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to  ilp32 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-30 18:30 +0100
              Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to ilp32 Arnd Bergmann <arnd@arndb.de> - 2015-12-30 23:40 +0100
      Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to  ilp32 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-23 05:30 +0100
  [PATCH v6 08/20] arm64: ilp32: add is_ilp32_compat_{task,thread} and TIF_32BIT_AARCH64 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
    Re: [PATCH v6 08/20] arm64: ilp32: add is_ilp32_compat_{task,  thread} and TIF_32BIT_AARCH64 Catalin Marinas <catalin.marinas@arm.com> - 2015-12-17 12:50 +0100
      Re: [PATCH v6 08/20] arm64: ilp32: add is_ilp32_compat_{task,  thread} and TIF_32BIT_AARCH64 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-18 15:20 +0100
        Re: [PATCH v6 08/20] arm64: ilp32: add is_ilp32_compat_{task,  thread} and TIF_32BIT_AARCH64 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-18 15:50 +0100
          Re: [PATCH v6 08/20] arm64: ilp32: add is_ilp32_compat_{task,  thread} and TIF_32BIT_AARCH64 Catalin Marinas <catalin.marinas@arm.com> - 2015-12-21 18:50 +0100
  [PATCH v6 04/20] arm64: change some CONFIG_COMPAT over to use CONFIG_AARCH32_EL0 instead Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
    Re: [PATCH v6 04/20] arm64: change some CONFIG_COMPAT over to use  CONFIG_AARCH32_EL0 instead Yury Norov <ynorov@caviumnetworks.com> - 2015-12-23 15:20 +0100
    > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile Bamvor Jian Zhang <bamvor.zhangjian@linaro.org> - 2015-12-28 09:50 +0100
      Re: [PATCH v6 04/20] arm64: change some CONFIG_COMPAT over to use  CONFIG_AARCH32_EL0 instead "Zhangjian (Bamvor)" <bamvor.zhangjian@huawei.com> - 2015-12-28 10:10 +0100
        Re: [PATCH v6 04/20] arm64: change some CONFIG_COMPAT over to use  CONFIG_AARCH32_EL0 instead Yury Norov <ynorov@caviumnetworks.com> - 2015-12-29 13:40 +0100
          [PATCH] arm64: compat: fix wrong dependency Bamvor Jian Zhang <bamvor.zhangjian@linaro.org> - 2015-12-29 16:10 +0100
        Re: [PATCH v6 04/20] arm64: change some CONFIG_COMPAT over to use  CONFIG_AARCH32_EL0 instead Yury Norov <ynorov@caviumnetworks.com> - 2015-12-29 14:20 +0100
  [PATCH v6 01/20] arm64: ilp32: add documentation on the ILP32 ABI for ARM64 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
  [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
    Re: [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32 Arnd Bergmann <arnd@arndb.de> - 2015-12-16 17:00 +0100
      Re: [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32 Catalin Marinas <catalin.marinas@arm.com> - 2015-12-16 18:00 +0100
        Re: [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32 Catalin Marinas <catalin.marinas@arm.com> - 2015-12-16 18:20 +0100
          Re: [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32 Arnd Bergmann <arnd@arndb.de> - 2015-12-16 20:20 +0100
            Re: [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32 Catalin Marinas <catalin.marinas@arm.com> - 2015-12-17 12:00 +0100
              Re: [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32 Arnd Bergmann <arnd@arndb.de> - 2015-12-17 15:00 +0100
  [PATCH v6 07/20] arm64: introduce is_a32_task and is_a32_thread (for AArch32 compat) Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
    Re: [PATCH v6 07/20] arm64: introduce is_a32_task and is_a32_thread  (for AArch32 compat) Catalin Marinas <catalin.marinas@arm.com> - 2015-12-17 12:40 +0100
  [PATCH v6 05/20] arm64:uapi: set __BITS_PER_LONG correctly for ILP32 and LP64 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
  [PATCH v6 11/20] arm64:ilp32: support core dump generation for ILP32 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
    Re: [PATCH v6 11/20] arm64:ilp32: support core dump generation for  ILP32 Catalin Marinas <catalin.marinas@arm.com> - 2015-12-17 15:10 +0100
  [PATCH v6 15/20] arm64: signal: move ilp32 and lp64 common code to separated file Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 22:50 +0100
    Re: [PATCH v6 15/20] arm64: signal: move ilp32 and lp64 common code to separated file Arnd Bergmann <arnd@arndb.de> - 2015-12-16 17:10 +0100
      Re: [PATCH v6 15/20] arm64: signal: move ilp32 and lp64 common code  to separated file Yury Norov <ynorov@caviumnetworks.com> - 2015-12-18 14:50 +0100
        Re: [PATCH v6 15/20] arm64: signal: move ilp32 and lp64 common code to separated file Arnd Bergmann <arnd@arndb.de> - 2015-12-18 15:20 +0100
    Re: [PATCH v6 15/20] arm64: signal: move ilp32 and lp64 common code  to separated file Catalin Marinas <catalin.marinas@arm.com> - 2015-12-22 18:20 +0100
  [PATCH v6 17/20] arm64: ilp32: introduce ilp32-specific handlers for sigframe Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 23:00 +0100
    Re: [PATCH v6 17/20] arm64: ilp32: introduce ilp32-specific handlers  for sigframe Catalin Marinas <catalin.marinas@arm.com> - 2015-12-22 18:20 +0100
  [PATCH v6 18/20] arm64:ilp32: add vdso-ilp32 and use for signal return Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 23:00 +0100
  [PATCH v6 19/20] arm64:ilp32: change COMPAT_ELF_PLATFORM to report a a subplatform for ILP32 Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 23:00 +0100
  [PATCH v6 20/20] arm64:ilp32: add ARM64_ILP32 to Kconfig Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 23:00 +0100
  [PATCH v6 16/20] arm64: signal32: move ilp32 and aarch32 common code to separated file Yury Norov <ynorov@caviumnetworks.com> - 2015-12-15 23:00 +0100
    Re: [PATCH v6 16/20] arm64: signal32: move ilp32 and aarch32 common  code to separated file Catalin Marinas <catalin.marinas@arm.com> - 2015-12-22 15:30 +0100
  Re: [RFC3 PATCH v6 00/20] ILP32 for ARM64 Arnd Bergmann <arnd@arndb.de> - 2015-12-16 17:30 +0100

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