kbuild/recordmcount: Add RECORDMCOUNT_WARN to warn about mcount callers

When mcount is called in a section that ftrace will not modify it into
a nop, we want to warn about this. But not warn about this always. Now
if the user builds the kernel with the option RECORDMCOUNT_WARN=1 then
the build will warn about mcount callers that are ignored and will just
waste execution time.

Acked-by: Michal Marek <mmarek@suse.cz>
Cc: linux-kbuild@vger.kernel.org
Link: http://lkml.kernel.org/r/20110421023738.714956282@goodmis.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 5 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 41ea6fbec55a..e7d01adaf692 100644
--- a/Makefile
+++ b/Makefile
@@ -1268,6 +1268,7 @@ help:
         @echo  '  make C=1   [targets] Check all c source with $$CHECK (sparse by default)'
         @echo  '  make C=2   [targets] Force check of all c source with $$CHECK'
         @echo  '  make W=1   [targets] Enable extra gcc checks'
+        @echo  '  make RECORDMCOUNT_WARN=1 [targets] Warn about ignored mcount sections'
         @echo  ''
         @echo  'Execute "make" or "make all" to build all targets marked with [*] '
         @echo  'For further info see the ./README file'
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 7d3f9036eee2..6165622c3e29 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -244,13 +244,16 @@ endif
 
 ifdef CONFIG_FTRACE_MCOUNT_RECORD
 ifdef BUILD_C_RECORDMCOUNT
+ifeq ("$(origin RECORDMCOUNT_WARN)", "command line")
+  RECORDMCOUNT_FLAGS = -w
+endif
 # Due to recursion, we must skip empty.o.
 # The empty.o file is created in the make process in order to determine
 #  the target endianness and word size. It is made before all other C
 #  files, including recordmcount.
 sub_cmd_record_mcount =                                 \
         if [ $(@) != "scripts/mod/empty.o" ]; then      \
-                $(objtree)/scripts/recordmcount "$(@)"; \
+                $(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) "$(@)";   \
         fi;
 recordmcount_source := $(srctree)/scripts/recordmcount.c \
                     $(srctree)/scripts/recordmcount.h