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Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN)

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  Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN) Michael Ellerman <mpe@ellerman.id.au> - 2017-05-29 14:10 +0200
    Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7]  arch/sparc: Define config parameter CPU_BIG_ENDIAN) Geert Uytterhoeven <geert@linux-m68k.org> - 2017-05-29 14:20 +0200
      Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN) Michael Ellerman <mpe@ellerman.id.au> - 2017-05-30 05:00 +0200

#1652468 — Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN)

Geert Uytterhoeven <geert@linux-m68k.org> writes:

> On Tue, May 23, 2017 at 11:45 PM, Babu Moger <babu.moger@oracle.com> wrote:
>> Found this problem while enabling queued rwlock on SPARC.
>> The parameter CONFIG_CPU_BIG_ENDIAN is used to clear the
>> specific byte in qrwlock structure. Without this parameter,
>> we clear the wrong byte. Here is the code.
>>
>> static inline u8 *__qrwlock_write_byte(struct qrwlock *lock)
>>  {
>>         return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN);
>>  }
>>
>> Define CPU_BIG_ENDIAN for SPARC to fix it.
>
>> --- a/arch/sparc/Kconfig
>> +++ b/arch/sparc/Kconfig
>> @@ -92,6 +92,10 @@ config ARCH_DEFCONFIG
>>  config ARCH_PROC_KCORE_TEXT
>>         def_bool y
>>
>> +config CPU_BIG_ENDIAN
>> +       bool
>> +       default y if SPARC
>
> Nice catch!
>
> Traditionally, CPU_BIG_ENDIAN and CPU_LITTLE_ENDIAN were defined only on
> architectures that may support both.  And it was checked in platform code
> and drivers only.
> Hence the symbol is lacking from most architectures. Heck, even
> architectures that support both may default to one endiannes, and declare
> only the symbol for the other endianness:

I guess there's a reason we can't use __BIG_ENDIAN__ / __LITTLE_ENDIAN__ ?

cheers

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#1652484 — Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN)

Hi Michael,

On Mon, May 29, 2017 at 2:07 PM, Michael Ellerman <mpe@ellerman.id.au> wrote:
> Geert Uytterhoeven <geert@linux-m68k.org> writes:
>> On Tue, May 23, 2017 at 11:45 PM, Babu Moger <babu.moger@oracle.com> wrote:
>>> Found this problem while enabling queued rwlock on SPARC.
>>> The parameter CONFIG_CPU_BIG_ENDIAN is used to clear the
>>> specific byte in qrwlock structure. Without this parameter,
>>> we clear the wrong byte. Here is the code.
>>>
>>> static inline u8 *__qrwlock_write_byte(struct qrwlock *lock)
>>>  {
>>>         return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN);
>>>  }
>>>
>>> Define CPU_BIG_ENDIAN for SPARC to fix it.
>>
>>> --- a/arch/sparc/Kconfig
>>> +++ b/arch/sparc/Kconfig
>>> @@ -92,6 +92,10 @@ config ARCH_DEFCONFIG
>>>  config ARCH_PROC_KCORE_TEXT
>>>         def_bool y
>>>
>>> +config CPU_BIG_ENDIAN
>>> +       bool
>>> +       default y if SPARC
>>
>> Nice catch!
>>
>> Traditionally, CPU_BIG_ENDIAN and CPU_LITTLE_ENDIAN were defined only on
>> architectures that may support both.  And it was checked in platform code
>> and drivers only.
>> Hence the symbol is lacking from most architectures. Heck, even
>> architectures that support both may default to one endiannes, and declare
>> only the symbol for the other endianness:
>
> I guess there's a reason we can't use __BIG_ENDIAN__ / __LITTLE_ENDIAN__ ?

I (C/asm) code we can, in Kconfig we cannot.

So far we tried always doing that, but a few checks for the semi-existing
Kconfig symbol crept in in generic code. Those could be replaced by the __*__
variants, but consistently having the Kconfig symbols would be useful anyway
(e.g. to avoid building the broken-on-big-endian ISDN drivers).

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

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#1652784

Geert Uytterhoeven <geert@linux-m68k.org> writes:

> Hi Michael,
>
> On Mon, May 29, 2017 at 2:07 PM, Michael Ellerman <mpe@ellerman.id.au> wrote:
>> Geert Uytterhoeven <geert@linux-m68k.org> writes:
>>> On Tue, May 23, 2017 at 11:45 PM, Babu Moger <babu.moger@oracle.com> wrote:
>>>> Found this problem while enabling queued rwlock on SPARC.
>>>> The parameter CONFIG_CPU_BIG_ENDIAN is used to clear the
>>>> specific byte in qrwlock structure. Without this parameter,
>>>> we clear the wrong byte. Here is the code.
>>>>
>>>> static inline u8 *__qrwlock_write_byte(struct qrwlock *lock)
>>>>  {
>>>>         return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN);
>>>>  }
>>>>
>>>> Define CPU_BIG_ENDIAN for SPARC to fix it.
>>>
>>>> --- a/arch/sparc/Kconfig
>>>> +++ b/arch/sparc/Kconfig
>>>> @@ -92,6 +92,10 @@ config ARCH_DEFCONFIG
>>>>  config ARCH_PROC_KCORE_TEXT
>>>>         def_bool y
>>>>
>>>> +config CPU_BIG_ENDIAN
>>>> +       bool
>>>> +       default y if SPARC
>>>
>>> Nice catch!
>>>
>>> Traditionally, CPU_BIG_ENDIAN and CPU_LITTLE_ENDIAN were defined only on
>>> architectures that may support both.  And it was checked in platform code
>>> and drivers only.
>>> Hence the symbol is lacking from most architectures. Heck, even
>>> architectures that support both may default to one endiannes, and declare
>>> only the symbol for the other endianness:
>>
>> I guess there's a reason we can't use __BIG_ENDIAN__ / __LITTLE_ENDIAN__ ?
>
> I (C/asm) code we can, in Kconfig we cannot.
>
> So far we tried always doing that, but a few checks for the semi-existing
> Kconfig symbol crept in in generic code. Those could be replaced by the __*__
> variants, but consistently having the Kconfig symbols would be useful anyway
> (e.g. to avoid building the broken-on-big-endian ISDN drivers).

Ah OK, the original mail was citing C code, but yeah I guess it would be
handy in Makefiles etc.

cheers

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