linux-kernel - [PATCH] Use -mcount-record for dynamic ftrace

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Date:   Tue,  1 Nov 2016 19:27:27 -0700
From:   Andi Kleen <andi@...stfloor.org>
To:     rostedt@...dmis.org
Cc:     linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH] Use -mcount-record for dynamic ftrace

From: Andi Kleen <ak@...ux.intel.com>

gcc 5 supports a new -mcount-record option to generate ftrace
tables directly. This avoids the need to run record_mcount
manually.

Use this option when available.

It also has a -mcount-nop option to generate the mcount calls
as nops. So far that is not implemented, but it could be used
to optimize patching at boot up.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 scripts/Makefile.build | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index de46ab03f063..2d7467076411 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -212,6 +212,11 @@ cmd_modversions =								\
 endif
 
 ifdef CONFIG_FTRACE_MCOUNT_RECORD
+# gcc 5 supports generating the mcount tables directly
+ifneq ($(call cc-option,-mrecord-mcount,y),y)
+  KBUILD_CFLAGS += -mrecord-mcount
+else
+# else do it all manually
 ifdef BUILD_C_RECORDMCOUNT
 ifeq ("$(origin RECORDMCOUNT_WARN)", "command line")
   RECORDMCOUNT_FLAGS = -w
@@ -241,6 +246,7 @@ cmd_record_mcount =						\
 		$(sub_cmd_record_mcount)			\
 	fi;
 endif
+endif
 
 ifdef CONFIG_STACK_VALIDATION
 ifneq ($(SKIP_STACK_VALIDATION),1)
-- 
2.5.5