[PATCH] powerpc64le build fails with GCC7

[Alexey Neyman]

On 08/21/2017 12:40 PM, Michael Meissner wrote:
> On Mon, Aug 21, 2017 at 08:56:48AM -0700, Alexey Neyman wrote:
>> Hi all,
>>
>> With GCC7, the test for -mfloat128 fails with a message that this
>> option requires -mfloat128-type to be supplied as well. Cannot
>> supply both options unconditionally, though, as GCC6 would choke on
>> unknown option.
>>
>> Patch attached, please review. Build-tested only, with GCC 7.2.0 and 6.4.0.
>>
>> Regards,
>> Alexey.
>>
>>  From ea42205587b557c604f165ffdb745d94035fd18d Mon Sep 17 00:00:00 2001
>> From: Alexey Neyman <stilor@att.net>
>> Date: Mon, 21 Aug 2017 08:50:02 -0700
>> Subject: [PATCH] Fix powerpc64le target with GCC7
>>
>> With GCC7, the test for -mfloat128 fails with a message that this
>> option requires -mfloat128-type to be supplied as well. Cannot
>> supply both options unconditionally, though, as GCC6 would choke
>> on unknown option.
>>
>>      * sysdeps/powerpc/powerpc64le/configure.ac:
>>      Detect if -mfloat128-type needs to be supplied in addition to
>>      -mfloat128
>>      * configure.ac (libc_cv_compiler_powerpc64le_float128_type):
>>      New variable.
>>      * config.make.in (config-cflags-mfloat128-type): New variable.
>>      * sysdeps/powerpc/powerpc64le/configure, configure: Regenerate.
> This comes up because when you configure a cross compiler, the test for whether
> long double defaults to 64 bits or 128 bits fails (i.e. glibc is at least 2.4
> or newer), and the compiler defaults long double to 64 bits.  If you add the
> --with-long-double-128 switch when you build the compiler, it should avoid the
> message.
Thanks, this explains it.

Shouldn't the GCC configuration fall back to 128-bit long double if the 
test fails - given that GLIBC requires it?

Regards,
Alexey.

>
> Similarly, when my patch to make -mfloat128 goes in, I reworked the test so
> that float128 no longer checks if long doubles are 64 bits or 128 bits.
> However, if you are doing a cross compiler, you should make sure the long
> double support matches your target system (presumably configure the cross
> compiler to use an appropriate glibc or add the --with-long-double-128
> configuration option).
>
>