Re: [PATCH v2 08/12] powerpc: Don't use 'struct ppc_inst' to reference instruction location

On Tue, Jun 15, 2021 at 12:01 PM Michael Ellerman [off-list ref] wrote:

Christophe Leroy [off-list ref] writes:

quoted

diff --git a/arch/powerpc/include/asm/inst.h b/arch/powerpc/include/asm/inst.h
index 5a0740ebf132..32d318c3b180 100644
--- a/arch/powerpc/include/asm/inst.h
+++ b/arch/powerpc/include/asm/inst.h

@@ -139,7 +139,7 @@ static inline int ppc_inst_len(struct ppc_inst x)
  * Return the address of the next instruction, if the instruction @value was
  * located at @location.
  */
-static inline struct ppc_inst *ppc_inst_next(void *location, struct ppc_inst *value)
+static inline unsigned int *ppc_inst_next(unsigned int *location, unsigned int *value)
 {
      struct ppc_inst tmp;

It's not visible in the diff, but the rest of the function is:

        tmp = ppc_inst_read(value);

        return location + ppc_inst_len(tmp);
}

And so changing the type of location from void * to int * changes the
result of that addition, ie. previously it was in units of bytes, now
it's units of 4 bytes.

To fix it I've kept location as unsigned int *, and added a cast where
we do the addition. That way users of the function just see unsigned int *,
the cast to void * is an implementation detail.

We only have a handful of uses of ppc_inst_len(), so maybe that should
change name and return a result in units of int *. But that can be a
separate change.

quoted

diff --git a/arch/powerpc/platforms/86xx/mpc86xx_smp.c b/arch/powerpc/platforms/86xx/mpc86xx_smp.c
index 87f524e4b09c..302f2a1e0361 100644
--- a/arch/powerpc/platforms/86xx/mpc86xx_smp.c
+++ b/arch/powerpc/platforms/86xx/mpc86xx_smp.c

@@ -83,7 +83,7 @@ smp_86xx_kick_cpu(int nr)
              mdelay(1);

      /* Restore the exception vector */
-     patch_instruction((struct ppc_inst *)vector, ppc_inst(save_vector));
+     patch_instruction(vector, ppc_inst(save_vector));

      local_irq_restore(flags);

There was another usage in here:

        /* Setup fake reset vector to call __secondary_start_mpc86xx. */
        target = (unsigned long) __secondary_start_mpc86xx;
-       patch_branch((struct ppc_inst *)vector, target, BRANCH_SET_LINK);
+       patch_branch(vector, target, BRANCH_SET_LINK);

        /* Kick that CPU */
        smp_86xx_release_core(nr);

I fixed it up.

cheers

fwiw
Reviewed by: Jordan Niethe [off-list ref]