From: Miroslav Benes <mbenes@suse.cz>
Date: Thu, 4 Apr 2019 20:44:11 +0200
Subject: kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled
Git-commit: 43bd3a95c98e1a86b8b55d97f745c224ecff02b9
Patch-mainline: v5.2-rc1
References: bsc#1071995 fate#323487

GCC 9 introduces a new option, -flive-patching. It disables certain
optimizations which could make a compilation unsafe for later live
patching of the running kernel.

The option is used only if CONFIG_LIVEPATCH is enabled and $(CC)
supports it.

Performance impact of the option was measured on three different
Intel machines - two bigger NUMA boxes and one smaller UMA box. Kernel
intensive (IO, scheduling, networking) benchmarks were selected, plus a
set of HPC workloads from NAS Parallel Benchmark. The tests were done on
upstream kernel 5.0-rc8 with openSUSE Leap 15.0 userspace.

The majority of the tests is unaffected. The only significant exception
is the scheduler section which suffers 1-3% degradation.

Evaluated-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 Makefile |    4 ++++
 1 file changed, 4 insertions(+)

--- a/Makefile
+++ b/Makefile
@@ -794,6 +794,10 @@ KBUILD_CFLAGS	+= $(call cc-option,-ffunc
 KBUILD_CFLAGS	+= $(call cc-option,-fdata-sections,)
 endif
 
+ifdef CONFIG_LIVEPATCH
+KBUILD_CFLAGS += $(call cc-option, -flive-patching=inline-clone)
+endif
+
 # arch Makefile may override CC so keep this after arch Makefile is included
 NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
 CHECKFLAGS     += $(NOSTDINC_FLAGS)