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Re: [PATCH] powerpc64le build fails with GCC7

• From: Alexey Neyman <stilor at att dot net>
• To: Michael Meissner <meissner at linux dot vnet dot ibm dot com>
• Cc: libc-alpha at sourceware dot org
• Date: Mon, 21 Aug 2017 14:19:34 -0700
• Subject: Re: [PATCH] powerpc64le build fails with GCC7
• Authentication-results: sourceware.org; auth=none
• References: <1d46726e-05d0-4b16-4960-c2ab68133fef@att.net> <20170821194027.GA6814@ibm-tiger.the-meissners.org> <536399b2-ee34-3bce-1f3f-6906e5ac52f4@att.net>

On 08/21/2017 02:08 PM, Alexey Neyman wrote:

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 thisoption requires -mfloat128-type to be supplied as well. Cannotsupply both options unconditionally, though, as GCC6 would choke onunknown option.

Patch attached, please review. Build-tested only, with GCC 7.2.0 and6.4.0.

Regards,Alexey. From ea42205587b557c604f165ffdb745d94035fd18d Mon Sep 17 00:00:00 2001From: Alexey Neyman <stilor@att.net>Date: Mon, 21 Aug 2017 08:50:02 -0700Subject: [PATCH] Fix powerpc64le target with GCC7With GCC7, the test for -mfloat128 fails with a message that thisoption requires -mfloat128-type to be supplied as well. Cannotsupply both options unconditionally, though, as GCC6 would chokeon 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 testfor whetherlong double defaults to 64 bits or 128 bits fails (i.e. glibc is atleast 2.4or newer), and the compiler defaults long double to 64 bits. If youadd the--with-long-double-128 switch when you build the compiler, it shouldavoid the

message.

Thanks, this explains it.

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

This should've been:

Sorry, hit "send" too fast.

Regards,Alexey.

Similarly, when my patch to make -mfloat128 goes in, I reworked thetest 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 thelongdouble support matches your target system (presumably configure thecross

compiler to use an appropriate glibc or add the --with-long-double-128configuration option).

• References:
  • [PATCH] powerpc64le build fails with GCC7
    • From: Alexey Neyman
  • Re: [PATCH] powerpc64le build fails with GCC7
    • From: Michael Meissner
  • Re: [PATCH] powerpc64le build fails with GCC7
    • From: Alexey Neyman