Re: [PATCH v3 08/14] powerpc/xmon: Remove store_inst() for patch_instruction()

[Jordan Niethe <jniethe5@gmail.com>]

On Wed, Feb 26, 2020 at 6:04 PM Nicholas Piggin <npiggin@gmail.com> wrote:
>
> Jordan Niethe's on February 26, 2020 2:07 pm:
> > For modifying instructions in xmon, patch_instruction() can serve the
> > same role that store_inst() is performing with the advantage of not
> > being specific to xmon. In some places patch_instruction() is already
> > being using followed by store_inst(). In these cases just remove the
> > store_inst(). Otherwise replace store_inst() with patch_instruction().
> >
> > Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> > ---
> >  arch/powerpc/xmon/xmon.c | 13 ++-----------
> >  1 file changed, 2 insertions(+), 11 deletions(-)
> >
> > diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> > index 897e512c6379..a673cf55641c 100644
> > --- a/arch/powerpc/xmon/xmon.c
> > +++ b/arch/powerpc/xmon/xmon.c
> > @@ -325,11 +325,6 @@ static inline void sync(void)
> >       asm volatile("sync; isync");
> >  }
> >
> > -static inline void store_inst(void *p)
> > -{
> > -     asm volatile ("dcbst 0,%0; sync; icbi 0,%0; isync" : : "r" (p));
> > -}
> > -
> >  static inline void cflush(void *p)
> >  {
> >       asm volatile ("dcbf 0,%0; icbi 0,%0" : : "r" (p));
> > @@ -882,8 +877,7 @@ static struct bpt *new_breakpoint(unsigned long a)
> >       for (bp = bpts; bp < &bpts[NBPTS]; ++bp) {
> >               if (!bp->enabled && atomic_read(&bp->ref_count) == 0) {
> >                       bp->address = a;
> > -                     bp->instr[1] = bpinstr;
> > -                     store_inst(&bp->instr[1]);
> > +                     patch_instruction(&bp->instr[1], bpinstr);
> >                       return bp;
> >               }
> >       }
> > @@ -913,7 +907,7 @@ static void insert_bpts(void)
> >                       bp->enabled = 0;
> >                       continue;
> >               }
> > -             store_inst(&bp->instr[0]);
> > +             patch_instruction(&bp->instr[0], bp->instr[0]);
>
> Hmm that's a bit weird. Can you read instructions into a local variable
> first, do the checks on them, then patch them into their execution
> location?
I agree it is weird, local variables would be better.
>
> Otherwise, good cleanup.
>
> Thanks,
> Nick