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

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Date:	Sun, 12 Apr 2015 17:54:27 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	rostedt@...dmis.org
Cc:	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
	mmarek@...e.cz, 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 01df30a..f258e9b 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -210,6 +210,11 @@ cmd_modversions =								\
 	fi;
 endif
 
+# gcc 5 supports generating the mcount tables directly
+ifneq ($(call cc-option,-mrecord-mcount,y),y)
+KBUILD_CFLAGS += -mrecord-mcount
+else
+# else do it all manually
 ifdef CONFIG_FTRACE_MCOUNT_RECORD
 ifdef BUILD_C_RECORDMCOUNT
 ifeq ("$(origin RECORDMCOUNT_WARN)", "command line")
@@ -240,6 +245,7 @@ cmd_record_mcount =						\
 		$(sub_cmd_record_mcount)			\
 	fi;
 endif
+endif
 
 define rule_cc_o_c
 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
-- 
2.3.3

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