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 42aef001dfdd73f8fd4970a1c8fd45cf27fbf8c6..fff1452cb76e1b39129b0569f8b6c2b2ab20d83a 100644 (file)
--- 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)                         \