linux-kernel - Re: [kbuild-all] mipsel-linux-gnu-gcc: error: unrecognized command line option '-mcompact-branches=optimal'

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Message-ID: <20160421203135.GJ24051@linux-mips.org>
Date:	Thu, 21 Apr 2016 22:31:35 +0200
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	kbuild-all@...org, Paul Burton <paul.burton@...tec.com>,
	linux-kernel@...r.kernel.org, Philip Li <philip.li@...el.com>
Subject: Re: [kbuild-all] mipsel-linux-gnu-gcc: error: unrecognized command
 line option '-mcompact-branches=optimal'

On Thu, Apr 21, 2016 at 12:51:29PM +0800, Fengguang Wu wrote:

> On Wed, Apr 20, 2016 at 03:30:21PM +0200, Ralf Baechle wrote:
> > On Wed, Apr 20, 2016 at 01:44:28PM +0800, kbuild test robot wrote:
> > 
> > > FYI, the error/warning still remains.
> > > 
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > head:   12566cc35d0e68308bde7aad615743d560cb097b
> > > commit: c1a0e9bc885d46e519fd87d35af6a7937abfb986 MIPS: Allow compact branch policy to be changed
> > > date:   6 months ago
> > > config: mips-malta_qemu_32r6_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 c1a0e9bc885d46e519fd87d35af6a7937abfb986
> > >         # save the attached .config to linux build tree
> > >         make.cross ARCH=mips 
> > > 
> > > All errors (new ones prefixed by >>):
> > > 
> > > >> mipsel-linux-gnu-gcc: error: unrecognized command line option '-mcompact-branches=optimal'
> > > >> mipsel-linux-gnu-gcc: error: unrecognized command line option '-mcompact-branches=optimal'
> > 
> > -mcompact-branches=optimal is an option for the latest version of the MIPS
> > architecture which is enabled by mips-malta_qemu_32r6_defconfig but your
> > compiler is too old, doesn't support R6.  Unfortunately there's no simple
> > way to run a test on the build environment from kconfig or even before
> > kconfig runs so we've just ignord this particular build issue.  Plus
> > there being the additional issue that we only know the toolchain to be
> > used after certain options have been picked.
> 
> We are running Debian's mips cross compiler.
> 
> % mips-linux-gnu-gcc --version
> mips-linux-gnu-gcc (Debian 5.2.1-16) 5.2.1 20150903
> Copyright (C) 2015 Free Software Foundation, Inc.
> 
> How about temporarily disable that error, until we upgrade to a new
> gcc version which supports the -mcompact-branches option?

Let's try to sort this properly :)

The culprit seems to be commit c1a0e9bc885d46e519fd87d35af6a7937abfb986
("MIPS: Allow compact branch policy to be changed").  Paul, any reason
why we don't offer the option of not using -mcompact-branches?  It seems
GCC 5.2 needs that.

  Ralf