diff mbox

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

Message ID CAK8P3a1WfU9V1k2r=TfJSVRTymuD8n2hkJDr6u1KcmC_scAZMA@mail.gmail.com
State Not Applicable
Delegated to: David Miller
Headers show

Commit Message

Arnd Bergmann June 8, 2017, 8:01 a.m. UTC 
On Thu, Jun 8, 2017 at 1:07 AM, Babu Moger <babu.moger@oracle.com> wrote:
>
> On 5/29/2017 9:56 PM, Michael Ellerman wrote:
>>
>> 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:

>>>
>>> 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.
>
>
> Thanks for all the responses.  I see couple of options here.
>
> 1. Fix the c code in include/asm-generic/qrwlock.h using ifdef
> __BIG_ENDIAN__
>     This will fix the issue for us.
>
> 2. Define CPU_BIG_ENDIAN for all the missing fixed endian architectures.
> Because the problem is only for fixed big endian archs.
>
> I prefer the option 1.  What do you guys think ?

I would prefer option 2. If we leave out CONFIG_CPU_LITTLE_ENDIAN,
then the patch becomes much easier than what we had discussed earlier,
and we just need to patch a few Kconfig files to add

config CPU_BIG_ENDIAN
       def_bool y

I would also suggest adding a sanity check like


Fixing xtensa properly might still be tricky, but with that change, at least
we detect when things go wrong in this area.

        Arnd
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Comments

David Miller June 8, 2017, 2:02 p.m. UTC | #1 
From: Arnd Bergmann <arnd@arndb.de>
Date: Thu, 8 Jun 2017 10:01:59 +0200

> I would also suggest adding a sanity check like

Hmm, but this will kill the build for non-fixed endian architectures
won't it?
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Arnd Bergmann June 8, 2017, 2:36 p.m. UTC | #2 
On Thu, Jun 8, 2017 at 4:02 PM, David Miller <davem@davemloft.net> wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> Date: Thu, 8 Jun 2017 10:01:59 +0200
>
>> I would also suggest adding a sanity check like
>
> Hmm, but this will kill the build for non-fixed endian architectures
> won't it?

I think only xtensa, all others already define CONFIG_CPU_BIG_ENDIAN
conditionally, and include the right header depending on that.

For xtensa, the decision is apparently made by the toolchain, and the
kernel just detects the macros set by the compiler, but that is slightly
fragile because it prevents us from making Kconfig decisions based on
endianess.

       Arnd
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diff mbox

Patch

diff --git a/include/linux/byteorder/big_endian.h
b/include/linux/byteorder/big_endian.h
index 392041475c72..18a1ab5b0260 100644
--- a/include/linux/byteorder/big_endian.h
+++ b/include/linux/byteorder/big_endian.h
@@ -3,5 +3,9 @@ 

 #include <uapi/linux/byteorder/big_endian.h>

+#ifndef CONFIG_CPU_BIG_ENDIAN
+#warning inconsistent configuration, need CONFIG_CPU_BIG_ENDIAN
+#endif
+
 #include <linux/byteorder/generic.h>
 #endif /* _LINUX_BYTEORDER_BIG_ENDIAN_H */
diff --git a/include/linux/byteorder/little_endian.h
b/include/linux/byteorder/little_endian.h
index 08057377aa23..ba910bb9aad0 100644
--- a/include/linux/byteorder/little_endian.h
+++ b/include/linux/byteorder/little_endian.h
@@ -3,5 +3,9 @@ 

 #include <uapi/linux/byteorder/little_endian.h>

+#ifdef CONFIG_CPU_BIG_ENDIAN
+#warning inconsistent configuration, CONFIG_CPU_BIG_ENDIAN is set
+#endif
+
 #include <linux/byteorder/generic.h>
 #endif /* _LINUX_BYTEORDER_LITTLE_ENDIAN_H */