Re: [PATCH] Work around for enabling CONFIG_CMDLINE on ppc64le

[Akshay Adiga]

Hi Michael,

Here is the link to the bug raised on launchpad.
https://bugs.launchpad.net/ubuntu/+source/gcc-5/+bug/1628207


On 09/23/2016 09:45 AM, Akshay Adiga wrote:
> Hi Michael,
>
> Anton found this bug and raised it against gcc v7.0 and a fix is 
> available
>  in upstream gcc.
>
>     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71709
>
> Currently, gcc v5.4.0  and v6.1.1 shipped with Ubuntu 16.04 and 16.10  
> respectively,
>  are hitting this problem.
>
> I have also raised bug against Ubuntu for fixing gcc for 16.04.
>
> https://bugzilla.linux.ibm.com/show_bug.cgi?id=146668
>
>
> On 09/22/2016 03:51 PM, Michael Ellerman wrote:
> > Akshay Adiga <akshay.adiga@xxxxxxxxxxxxxxxxxx> writes:
> >
> > > Observed that boot arguments (passed as CONFIG_CMDLINE)  are not being
> > > picked up by kernel while using gcc-ppc64-linux-gnu v5.4.0 and v6.1.1.
> > > While it works as expected with v5.3.1 .
> > >
> > > Found that in init/main.c in  setup_command_line() the pointers 
> > > passed to
> > > strcpy() is messed up.
> > Hi Akshay,
> >
> > Thanks for debugging this.
> >
> > > The problem goes away when compiler optimization is restricted to -O1.
> > > diff --git a/init/main.c b/init/main.c
> > > index a8a58e2..4259c42 100644
> > > --- a/init/main.c
> > > +++ b/init/main.c
> > > @@ -358,7 +358,13 @@ static inline void smp_prepare_cpus(unsigned 
> > > int maxcpus) { }
> > >    * parsing is performed in place, and we should allow a component to
> > >    * store reference of name/value for future reference.
> > >    */
> > > -static void __init setup_command_line(char *command_line)
> > > +static void __init
> > > +#ifdef CONFIG_PPC64
> > > +    #if  GCC_VERSION > 50301
> > > +        __attribute__((optimize("-O1")))
> > > +    #endif
> > > +#endif
> > > +        setup_command_line(char *command_line)
> > >   {
> > >       saved_command_line =
> > >           memblock_virt_alloc(strlen(boot_command_line) + 1, 0);
> > But I can't merge that patch.
> >
> > Our options are one or both of:
> >   - get GCC fixed and backport the fix to the compilers we care about.
> >   - blacklist the broken compiler versions.
> >
> > Is there a GCC bug filed for this?
> >
> > cheers