Re: [PATCH v4 07/16] powerpc: Introduce functions for instruction nullity and equality

On Mon, Mar 23, 2020 at 5:46 PM Nicholas Piggin [off-list ref] wrote:

Jordan Niethe's on March 20, 2020 3:18 pm:

quoted

In preparation for an instruction data type that can not be directly
used with the '==' operator use functions for checking equality and
nullity.

Signed-off-by: Jordan Niethe <redacted>
---
 arch/powerpc/kernel/optprobes.c      |  2 +-
 arch/powerpc/kernel/trace/ftrace.c   | 33 +++++++++++++++-------------
 arch/powerpc/lib/code-patching.c     | 16 +++++++-------
 arch/powerpc/lib/feature-fixups.c    |  2 +-
 arch/powerpc/lib/test_emulate_step.c |  4 ++--
 arch/powerpc/xmon/xmon.c             |  4 ++--
 6 files changed, 32 insertions(+), 29 deletions(-)

diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
index 1025a7a3b3a8..6027425a85f2 100644
--- a/arch/powerpc/kernel/optprobes.c
+++ b/arch/powerpc/kernel/optprobes.c

@@ -259,7 +259,7 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
                              (unsigned long)emulate_step_addr,
                              BRANCH_SET_LINK);

-     if (!branch_op_callback || !branch_emulate_step)
+     if (ppc_inst_null(branch_op_callback) || ppc_inst_null(branch_emulate_step))

Is an instruction null, or zeroes?

ppc_inst_zero() would probably be clearer.

Oh, most of this comes from create_branch and things. Hmm, would rather
see those functions modified to take a &insn and return an int err.

Good idea.

quoted

@@ -437,7 +438,7 @@ int ftrace_make_nop(struct module *mod,
       * then we had to use a trampoline to make the call.
       * Otherwise just update the call site.
       */
-     if (test_24bit_addr(ip, addr)) {
+     if (!ppc_inst_null(test_24bit_addr(ip, addr))) {
              /* within range */
              old = ftrace_call_replace(ip, addr, 1);
              new = PPC_INST(PPC_INST_NOP);

test_24bit_addr shouldn't be passing a ppc_inst back, but a bool.

True.

Thanks,
Nick