Hi,

On Thu, 2018-11-29 at 15:25 -0800, Eric Dumazet wrote:

On 11/29/2018 03:00 PM, Paolo Abeni wrote:

quoted

This header define a bunch of helpers that allow avoiding the
retpoline overhead when calling builtin functions via function pointers.
It boils down to explicitly comparing the function pointers to
known builtin functions and eventually invoke directly the latter.

The macro defined here implement the boilerplate for the above schema
and will be used by the next patches.

Suggested-by: Eric Dumazet <Eric Dumazet <edumazet@google.com>

Oops... typo here. For some reasons checkpatch did not catch it.

quoted

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 include/linux/indirect_call_wrapper.h | 77 +++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 include/linux/indirect_call_wrapper.h

diff --git a/include/linux/indirect_call_wrapper.h b/include/linux/indirect_call_wrapper.h
new file mode 100644
index 000000000000..57e82b4a166d
--- /dev/null
+++ b/include/linux/indirect_call_wrapper.h

@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_INDIRECT_CALL_WRAPPER_H
+#define _LINUX_INDIRECT_CALL_WRAPPER_H
+
+#ifdef CONFIG_RETPOLINE
+
+/*
+ * INDIRECT_CALL_$NR - wrapper for indirect calls with $NR known builtin
+ *  @f: function pointer
+ *  @name: base name for builtin functions, see INDIRECT_CALLABLE_DECLARE_$NR
+ *  @__VA_ARGS__: arguments for @f
+ *
+ * Avoid retpoline overhead for known builtin, checking @f vs each of them and
+ * eventually invoking directly the builtin function. Fallback to the indirect
+ * call
+ */
+#define INDIRECT_CALL_1(f, name, ...)					\
+	({								\
+		f == name ## 1 ? name ## 1(__VA_ARGS__) :		\

              likely(f == name ## 1) ? ...

Thank you for the feedback!

I thought about the above, and than I avoided it, because I was not
100% it would fit cases (if any) where we have 2 or more built-in
equally likely.

I guess we can address such cases if and when they will pop-up. I'll do
some more benchmarks with the branch prediction hints, and then if
there are no surprises, I'll add them in v1.

BTW I would like to give the correct attribution here. Does 'Suggested-
by' fit? should I list some other guy @google?

Thanks,

Paols