Re: [PATCH] compiler-gcc: require gcc 4.8 for powerpc __builtin_bswap16()

From: Sedat Dilek <sedat.dilek@gmail.com>
To: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-next@vger.kernel.org, linux-kernel@vger.kernel.org,
	Arnd Bergmann <arnd@arndb.de>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] compiler-gcc: require gcc 4.8 for powerpc __builtin_bswap16()
Date: Mon, 9 May 2016 07:39:24 +0200	[thread overview]
Message-ID: <CA+icZUWuybX42vW=ADLT_b+_P87DGjtcA3nXGpV+gq5LtkB3eA@mail.gmail.com> (raw)
In-Reply-To: <20160509105927.68dfa6d2@canb.auug.org.au>

On 5/9/16, Stephen Rothwell <sfr@canb.auug.org.au> wrote:
> Hi Josh,
>
> On Fri, 6 May 2016 09:22:25 -0500 Josh Poimboeuf <jpoimboe@redhat.com>
> wrote:
>>
>> I've also seen no problems on powerpc with 4.4 and 4.8.  I suspect it's
>> specific to gcc 4.6.  Stephen, can you confirm this patch fixes it?
>
> That will obviously fix the problem for us (since it will effectively
> restore the code to what it was before the other commit for our gcc
> 4.6.3 builds and we have not seen it in other builds).  I will add this
> patch to linux-next today.
>
> And since "byteswap: try to avoid __builtin_constant_p gcc bug" is not
> in Linus' tree, hopefully we can have this fix applied soon.
>

FYI, this patch is in Linus tree (v4.6-rc7 has it).

- Sedat -

[1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7322dd755e7dd34bc5359aa27abeed1687e0f628

>> From: Josh Poimboeuf <jpoimboe@redhat.com>
>> Subject: [PATCH] compiler-gcc: require gcc 4.8 for powerpc
>> __builtin_bswap16()
>>
>> gcc support for __builtin_bswap16() was supposedly added for powerpc in
>> gcc 4.6, and was then later added for other architectures in gcc 4.8.
>>
>> However, Stephen Rothwell reported that attempting to use it on powerpc
>> in gcc 4.6 fails with:
>>
>>   lib/vsprintf.c:160:2: error: initializer element is not constant
>>   lib/vsprintf.c:160:2: error: (near initialization for 'decpair[0]')
>>   lib/vsprintf.c:160:2: error: initializer element is not constant
>>   lib/vsprintf.c:160:2: error: (near initialization for 'decpair[1]')
>>   lib/vsprintf.c:160:2: error: initializer element is not constant
>>   lib/vsprintf.c:160:2: error: (near initialization for 'decpair[2]')
>>   lib/vsprintf.c:160:2: error: initializer element is not constant
>>   lib/vsprintf.c:160:2: error: (near initialization for 'decpair[3]')
>>   lib/vsprintf.c:160:2: error: initializer element is not constant
>>
>> I'm not entirely sure what those errors mean, but I don't see them on
>> gcc 4.8.  So let's consider gcc 4.8 to be the official starting point
>> for __builtin_bswap16().
>>
>> Fixes: 7322dd755e7d ("byteswap: try to avoid __builtin_constant_p gcc
>> bug")
>> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
>> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
>> ---
>>  include/linux/compiler-gcc.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
>> index eeae401..3d5202e 100644
>> --- a/include/linux/compiler-gcc.h
>> +++ b/include/linux/compiler-gcc.h
>> @@ -246,7 +246,7 @@
>>  #define __HAVE_BUILTIN_BSWAP32__
>>  #define __HAVE_BUILTIN_BSWAP64__
>>  #endif
>> -#if GCC_VERSION >= 40800 || (defined(__powerpc__) && GCC_VERSION >=
>> 40600)
>> +#if GCC_VERSION >= 40800
>>  #define __HAVE_BUILTIN_BSWAP16__
>>  #endif
>>  #endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */
>> --
>> 2.4.11
>
> --
> Cheers,
> Stephen Rothwell
> --
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