[PATCH 1/2] trace: Use -mcount-record for dynamic ftrace

[Andi Kleen]

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.

So far doesn't use -mcount-nop, which also exists now.

This is needed to make ftrace work with LTO because the
normal record-mcount script doesn't run over the link
time output.

It should also improve build times slightly in the general
case.
Link: http://lkml.kernel.org/r/20171127213423.27218-12-andi@xxxxxxxxxxxxxx

Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
 scripts/Makefile.build | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 42aef001dfdd..fff1452cb76e 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -221,6 +221,11 @@ cmd_modversions_c =								\
 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
@@ -250,6 +255,7 @@ cmd_record_mcount =						\
 		$(sub_cmd_record_mcount)			\
 	fi;
 endif
+endif
 
 define rule_cc_o_c
 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
-- 
2.30.1


--MP_/bXGQGfX8vm3N8i=A7vGCG6X
Content-Type: text/x-patch
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
 filename=0002-tracing-Avoid-calling-cc-option-mrecord-mcount-for-e.patch