objtool: Fix gcov check for older versions of GCC

Objtool tries to silence 'unreachable instruction' warnings when it
detects gcov is enabled, because gcov produces a lot of unreachable
instructions and they don't really matter.

However, the 0-day bot is still reporting some unreachable instruction
warnings with CONFIG_GCOV_KERNEL=y on GCC 4.6.4.

As it turns out, objtool's gcov detection doesn't work with older
versions of GCC because they don't create a bunch of symbols with the
'gcov.' prefix like newer versions of GCC do.

Move the gcov check out of objtool and instead just create a new
'--no-unreachable' flag which can be passed in by the kernel Makefile
when CONFIG_GCOV_KERNEL is defined.

Also rename the 'nofp' variable to 'no_fp' for consistency with the new
'no_unreachable' variable.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 9cfffb116887 ("objtool: Skip all "unreachable instruction" warnings for gcov kernels")
Link: http://lkml.kernel.org/r/c243dc78eb2ffdabb6e927844dea39b6033cd395.1500939244.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index eedf089b1495..57254f5b2779 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -29,7 +29,7 @@
 #include "builtin.h"
 #include "check.h"
 
-bool nofp;
+bool no_fp, no_unreachable;
 
 static const char * const check_usage[] = {
 	"objtool check [<options>] file.o",
@@ -37,7 +37,8 @@ static const char * const check_usage[] = {
 };
 
 const struct option check_options[] = {
-	OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
+	OPT_BOOLEAN('f', "no-fp", &no_fp, "Skip frame pointer validation"),
+	OPT_BOOLEAN('u', "no-unreachable", &no_unreachable, "Skip 'unreachable instruction' warnings"),
 	OPT_END(),
 };
 
@@ -52,5 +53,5 @@ int cmd_check(int argc, const char **argv)
 
 	objname = argv[0];
 
-	return check(objname, nofp, false);
+	return check(objname, no_fp, no_unreachable, false);
 }