Re: [PATCH 4/8] s390/entry: workaround llvm's IAS limitations

[Heiko Carstens]

On Wed, May 11, 2022 at 10:30:05AM -0700, Nathan Chancellor wrote:
> Hi Heiko,
> 
> On Wed, May 11, 2022 at 02:05:28PM +0200, Heiko Carstens wrote:
> > llvm's integrated assembler cannot handle immediate values which are
> > calculated with two local labels:
> > 
> > <instantiation>:3:13: error: invalid operand for instruction
> >  clgfi %r14,.Lsie_done - .Lsie_gmap
> > 
> > Workaround this by adding clang specific code which reads the specific
> > value from memory. Since this code is within the hot paths of the kernel
> > and adds an additional memory reference, keep the original code, and add
> > ifdef'ed code.
> > 
> > Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
> > ---
> >  arch/s390/kernel/entry.S | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
> > index e1664b45090f..ff7a75078e93 100644
> > --- a/arch/s390/kernel/entry.S
> > +++ b/arch/s390/kernel/entry.S
> > @@ -171,8 +171,19 @@ _LPP_OFFSET	= __LC_LPP
> >  	.macro OUTSIDE reg,start,end,outside_label
> >  	larl	%r14,\start
> >  	slgrk	%r14,\reg,%r14
> > +#ifdef CONFIG_CC_IS_CLANG
> 
> I intend to put this series through my build and boot test matrix later
> today but one fly by comment in the meantime. Should this be
> CONFIG_AS_IS_LLVM if this is an integrated assembler limitation, rather
> than a clang one?

Yes, that makes a lot of sense. Considering that I will drop the
previous patch within this series, the new version looks like: