linux-kernel - Re: arch/mips/vdso/gettimeofday.c:1:0: error: '-march=r3900' requires '-mfp32'

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Date:	Tue, 5 Jan 2016 07:15:44 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	kbuild-all@...org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Alex Smith <alex.smith@...tec.com>
Subject: Re: arch/mips/vdso/gettimeofday.c:1:0: error: '-march=r3900' requires
 '-mfp32'

Hi Fengguang,

On 01/05/2016 06:30 AM, Fengguang Wu wrote:
> Hi Guenter,
>
> On Tue, Jan 05, 2016 at 06:02:47AM -0800, Guenter Roeck wrote:
>> On 01/05/2016 12:22 AM, Fengguang Wu wrote:
>>> On Tue, Jan 05, 2016 at 12:09:14AM -0800, Guenter Roeck wrote:
>>>> On 01/04/2016 11:23 PM, kbuild test robot wrote:
>>>>> Hi Guenter,
>>>>>
>>>>> First bad commit (maybe != root cause):
>>>>>
>>>>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>>>>> head:   168309855a7d1e16db751e9c647119fe2d2dc878
>>>>> commit: 398c7500a1f5f74e207bd2edca1b1721b3cc1f1e MIPS: VDSO: Fix build error with binutils 2.24 and earlier
>>>>> date:   6 days ago
>>>>> config: mips-jmr3927_defconfig (attached as .config)
>>>>> reproduce:
>>>>>          wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
>>>>>          chmod +x ~/bin/make.cross
>>>>>          git checkout 398c7500a1f5f74e207bd2edca1b1721b3cc1f1e
>>>>>          # save the attached .config to linux build tree
>>>>>          make.cross ARCH=mips
>>>>>
>>>>> All errors (new ones prefixed by >>):
>>>>>
>>>>>>> arch/mips/vdso/gettimeofday.c:1:0: error: '-march=r3900' requires '-mfp32'
>>>>>      /*
>>>>>      ^
>>>>>
>>>> AFAICS this is using the mips cross compiler version 4.9.0 from kernel.org [1],
>>>> which in turn uses binutils 2.24. At least this is what make.cross tries to install.
>>>
>>> Oops, sorry. I'm now using the debian MIPS cross compiler 5.2.1 ...
>>> make.cross has not been updated yet.
>>>
>> No problem. FWIW, I tested my patch with the compiler from Yocto 2.0, which
>> uses gcc 5.2.0 and binutils 2.25.1, with no problem.
>>
>> Do you have directions on how to install a debian cross compiler into a Ubuntu system ?
>> Alternatively, what version of binutils does the mips cross compiler use ?
>
> These are the installed version in my Debian:
>
> ||/ Name                                 Version                 Architecture            Description
> +++-====================================-=======================-=======================-=============================================================================
> ii  gcc-5-mips-linux-gnu                 5.2.1-16cross1          amd64                   GNU C compiler
> ii  gcc-5-mipsel-linux-gnu               5.2.1-16cross1          amd64                   GNU C compiler
> ii  binutils-mips-linux-gnu              2.25-8                  amd64                   GNU binary utilities, for mips-linux-gnu target
> ii  binutils-mipsel-linux-gnu            2.25-8                  amd64                   GNU binary utilities, for mipsel-linux-gnu target
>
> You may check if these packages are available on Ubuntu.  Anyway the

Unfortunately it looks like they are not available.

> versions are close to yours. This is interesting, I'll do more checks.
>

The problem is an interesting one: Due to my patch, arch/mips/vdso/gettimeofday.c
actually compiles with your toolchain (as it should, since its binutils version
is >= 2.25). Previously that was not the case. In other words, my patch exposes
a previously existing problem.

The underlying problem seems to be that your toolchain, as the error suggests,
does not support '-march=r3900' (which is set with the affected configuration)
without '-mfp32'. This may be a problem only for gettimeofday.c because that
file is compiled with different options than everything else. I _suspect_
the reason to be that -msoft-float and -Wa,-msoft-float are dropped from the
gettimeofday compile options, but I am not sure. Ralf and/or Alex (copying)
may have a better understanding of the problem.

Thanks,
Guenter

> Thanks,
> Fengguang
>
>>>> I downloaded it and used it to compile both the attached configuration as well
>>>> as jmr3927_defconfig. Both are building just fine for me. On top of that,
>>>> arch/mips/vdso/gettimeofday.c should not build in the first place with binutils 2.24
>>>> (and doesn't build for me).
>>>>
>>>> What am I missing ?
>>>>
>>>> Guenter
>>>>
>>>> ---
>>>> [1] https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.9.0/x86_64-gcc-4.9.0-nolibc_mips-linux.tar.xz
>>>
>

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