[RFC PATCH powerpc] Fix compile error of pgtable-ppc64.h

[Li Zhong]

On Fri, 2014-01-17 at 12:27 +0530, Aneesh Kumar K.V wrote:
> Li Zhong <zhong at linux.vnet.ibm.com> writes:
> 
> > It seems that forward declaration couldn't work well with typedef, use
> > struct spinlock directly to avoiding following build errors:
> >
> > In file included from include/linux/spinlock.h:81,
> >                  from include/linux/seqlock.h:35,
> >                  from include/linux/time.h:5,
> >                  from include/uapi/linux/timex.h:56,
> >                  from include/linux/timex.h:56,
> >                  from include/linux/sched.h:17,
> >                  from arch/powerpc/kernel/asm-offsets.c:17:
> > include/linux/spinlock_types.h:76: error: redefinition of typedef 'spinlock_t'
> > /root/linux-next/arch/powerpc/include/asm/pgtable-ppc64.h:563: note: previous declaration of 'spinlock_t' was here
> >
> 
> what compiler version ? I have seen that error in gcc 4.3 and it was
> concluded that it is too old a compiler version to worry about. That
> specific compiler version also gave error for forward declaring struct;

gcc version 4.4.6 20110731 (Red Hat 4.4.6-3) (GCC), and it doesn't
report error after use struct directly. 

> 
> > Signed-off-by: Li Zhong <zhong at linux.vnet.ibm.com>
> > ---
> >  arch/powerpc/include/asm/pgtable-ppc64.h |    6 +++---
> >  1 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/pgtable-ppc64.h b/arch/powerpc/include/asm/pgtable-ppc64.h
> > index d27960c..bc141c9 100644
> > --- a/arch/powerpc/include/asm/pgtable-ppc64.h
> > +++ b/arch/powerpc/include/asm/pgtable-ppc64.h
> > @@ -560,9 +560,9 @@ extern void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
> >  			    pmd_t *pmdp);
> >
> >  #define pmd_move_must_withdraw pmd_move_must_withdraw
> > -typedef struct spinlock spinlock_t;
> > -static inline int pmd_move_must_withdraw(spinlock_t *new_pmd_ptl,
> > -					 spinlock_t *old_pmd_ptl)
> > +struct spinlock;
> > +static inline int pmd_move_must_withdraw(struct spinlock *new_pmd_ptl,
> > +					 struct spinlock *old_pmd_ptl)
> >  {
> >  	/*
> >  	 * Archs like ppc64 use pgtable to store per pmd