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Subject: Re: [PATCH] powerpc: Blacklist GCC 5.4 6.1 and 6.2
From: Cyril Bur <cyrilbur@gmail.com>
To: Christophe LEROY <christophe.leroy@c-s.fr>, linuxppc-dev@lists.ozlabs.org
Cc: akshay.adiga@linux.vnet.ibm.com
Date: Mon, 13 Feb 2017 11:23:28 +1100
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On Fri, 2017-02-10 at 08:48 +0100, Christophe LEROY wrote:
> 
> Le 10/02/2017 à 06:31, Cyril Bur a écrit :
> > A bug in the -02 optimisation of GCC 5.4 6.1 and 6.2 causes
> > setup_command_line() to not pass the correct first argument to strcpy
> > and therefore not actually copy the command_line.
> > 
> > A workaround patch was proposed: http://patchwork.ozlabs.org/patch/673130/
> > some discussion ensued.
> > 
> > A GCC bug was raised: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71709
> > The bug has been fixed in 7.0 and backported to GCC 5 and GCC 6.
> > 
> > At the time of writing GCC 5.4 is the most recent and is affected. GCC
> > 6.3 contains the backported fix, has been tested and appears safe to
> > use.
> > 
> > Heavy-lifting-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
> > Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
> > ---
> >  arch/powerpc/Makefile | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> > index 31286fa7873c..a4b886694391 100644
> > --- a/arch/powerpc/Makefile
> > +++ b/arch/powerpc/Makefile
> > @@ -414,6 +414,15 @@ checkbin:
> >  		echo -n '*** Please use a different binutils version.' ; \
> >  		false ; \
> >  	fi
> > +	@if test "$(cc-version)" = "0504" \
> > +		|| test "$(cc-version)" = "0601" \
> > +		|| test "$(cc-version)" = "0602" ; then \
> > +		echo -n '*** GCC-5.4 6.1 6.2 have a bad -O2 optimisation ' ; \
> > +		echo 'which will cause lost commandline options (at least).' ; \
> > +		echo '*** Please use a different GCC version.' ; \
> > +		false ; \
> > +	fi
> > +
> 
> According to the GCC bug report, this bug applies to powerpc64le
> Why force all targets to not use those versions of GCC ?
> 

True, I'll double check on BE, these days BE does suffer from, "oops I
didn't check that". If it is only LE, I'll add another condition.

Thanks,

Cyril

> Christophe