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Re: undefined reference to `__multi3' when building with gcc 7.x

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: undefined reference to `__multi3' when building with gcc 7.x
From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Date: Fri, 4 Aug 2017 17:41:51 +0200
Cc: linux-mips@linux-mips.org, Waldemar Brodkorb <wbx@openadk.org>
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Hello,

On Fri, 4 Aug 2017 17:19:20 +0200, Ralf Baechle wrote:

> > > The bug can be reproduced by building with the toolchain available at
> > > http://toolchains.free-electrons.com/downloads/2017.08-rc1-fix-binutils/toolchains/mips64r6el-n32/tarballs/mips64r6el-n32--glibc--bleeding-edge-2017.05-1453-ga703fdd-1.tar.bz2
> > > and building with the attached kernel configuration file.
> > > 
> > > It is not clear to me if this is a kernel issue (lack of __multi3 in
> > > arch/mips/lib/), or a gcc bug in that it shouldn't emit a call to this
> > > function.
> > > 
> > > FWIW, sparc64 had a similar issue, and they added __multi3 in their
> > > libgcc replacement, see commit
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/sparc/lib?id=1b4af13ff2cc6897557bb0b8d9e2fad4fa4d67aa.
> > >   
> > 
> > I think these days we've given up the stuborn resistance of the old days
> > against adding new libgcc1 functions to the kernel, so we should probably
> > just add it.
> > 
> > I'm looking into this but a small wrench into the gear is that I'm still
> > on GCC 6 so I'm off to building myself a cross-gcc first ...  
> 
> I now can reproduce the issue with vanilla FSF binutils 2.28 and GCC 7.1.0.

Great! However, looking at the functions that end up calling __multi3,
I'm wondering why suddenly gcc 7.x needs to call such a function, while
the same code was compiling without __multi3 in libgcc with gcc 6.x.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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