gcov: add gcov profiling infrastructure

Enable the use of GCC's coverage testing tool gcov [1] with the Linux
kernel.  gcov may be useful for:

 * debugging (has this code been reached at all?)
 * test improvement (how do I change my test to cover these lines?)
 * minimizing kernel configurations (do I need this option if the
   associated code is never run?)

The profiling patch incorporates the following changes:

 * change kbuild to include profiling flags
 * provide functions needed by profiling code
 * present profiling data as files in debugfs

Note that on some architectures, enabling gcc's profiling option
"-fprofile-arcs" for the entire kernel may trigger compile/link/
run-time problems, some of which are caused by toolchain bugs and
others which require adjustment of architecture code.

For this reason profiling the entire kernel is initially restricted
to those architectures for which it is known to work without changes.
This restriction can be lifted once an architecture has been tested
and found compatible with gcc's profiling. Profiling of single files
or directories is still available on all platforms (see config help
text).

[1] http://gcc.gnu.org/onlinedocs/gcc/Gcov.html

Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Li Wei <W.Li@Sun.COM>
Cc: Michael Ellerman <michaele@au1.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Heiko Carstens <heicars2@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <mschwid2@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/Makefile b/Makefile
index ea63667617f3..46e1c9d03d51 100644
--- a/Makefile
+++ b/Makefile
@@ -330,6 +330,7 @@ AFLAGS_MODULE   = $(MODFLAGS)
 LDFLAGS_MODULE  =
 CFLAGS_KERNEL   =
 AFLAGS_KERNEL   =
+CFLAGS_GCOV     = -fprofile-arcs -ftest-coverage
 
 
 # Use LINUXINCLUDE when you must reference the include/ directory.
@@ -356,7 +357,7 @@ export CPP AR NM STRIP OBJCOPY OBJDUMP MAKE AWK GENKSYMS PERL UTS_MACHINE
 export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
-export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
+export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_GCOV
 export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
 
 # When compiling out-of-tree modules, put MODVERDIR in the module
@@ -1216,8 +1217,8 @@ clean: archclean $(clean-dirs)
                 \( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
                 -o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
                 -o -name '*.symtypes' -o -name 'modules.order' \
-                -o -name 'Module.markers' -o -name '.tmp_*.o.*' \) \
-                -type f -print | xargs rm -f
+                -o -name 'Module.markers' -o -name '.tmp_*.o.*' \
+                -o -name '*.gcno' \) -type f -print | xargs rm -f
 
 # mrproper - Delete all generated files, including .config
 #
@@ -1421,8 +1422,8 @@ clean: $(clean-dirs)
         $(call cmd,rmfiles)
         @find $(KBUILD_EXTMOD) $(RCS_FIND_IGNORE) \
                 \( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
-                -o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \) \
-                -type f -print | xargs rm -f
+                -o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
+                -o -name '*.gcno' \) -type f -print | xargs rm -f
 
 help:
         @echo  '  Building external modules.'