trace: Use -mcount-record for dynamic ftrace

commit 96f60dfa5819a065bfdd2f2ba0df7d9cbce7f4dd upstream.

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@firstfloor.org
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 3edc9c04cb468204bf576cfa7ffcd3b6e385eb06..b13aaf280183ae982b5da0bc529080bc9646fda9 100644 (file)
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -224,6 +224,11 @@ 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
@@ -274,6 +279,7 @@ endif
 ifdef CONFIG_RETPOLINE
   objtool_args += --retpoline
 endif
+endif
 
 
 ifdef CONFIG_MODVERSIONS