[PATCH] selftests/mm: silence unused-result warnings

[Kevin Brodsky <kevin.brodsky@arm.com>]

Switching to -O2 when building the mm tests has the unexpected side
effect of triggering many unused-result warnings on certain distros
like Ubuntu, where GCC is configured so that -O2 implies
-D_FORTIFY_SOURCE.

Explicitly disable FORTIFY_SOURCE to avoid those warnings. This has
no effect on upstream toolchains where FORTIFY_SOURCE is not
implicitly enabled.

Suggested-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---

Hi Andrew,

Could you please take this fixup patch for "selftests/mm: Build with
-O2" in mm-unstable? Ryan found that building the mm kselftests on
Ubuntu yields a bunch of warnings, this patch suppresses them.

Cheers,
- Kevin

Cc: aruna.ramakrishna@oracle.com
Cc: catalin.marinas@arm.com
Cc: dave.hansen@linux.intel.com
Cc: joey.gouly@arm.com
Cc: keith.lucas@oracle.com
Cc: shuah@kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kselftest@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: x86@kernel.org
---
 tools/testing/selftests/mm/Makefile | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index fce194a92cad..d633d6b6a6e1 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -36,6 +36,13 @@ MAKEFLAGS += --no-builtin-rules
 CFLAGS = -Wall -O2 -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES) $(TOOLS_INCLUDES)
 LDLIBS = -lrt -lpthread -lm
 
+# Some distributions (such as Ubuntu) configure GCC so that _FORTIFY_SOURCE is
+# automatically enabled at -O1 or above. This triggers various unused-result
+# warnings where functions such as read() or write() are called and their
+# return value is not checked. Disable _FORTIFY_SOURCE to silence those
+# warnings.
+CFLAGS += -U_FORTIFY_SOURCE
+
 KDIR ?= /lib/modules/$(shell uname -r)/build
 ifneq (,$(wildcard $(KDIR)/Module.symvers))
 ifneq (,$(wildcard $(KDIR)/include/linux/page_frag_cache.h))
-- 
2.47.0