It's slightly better to set _GNU_SOURCE in the source code, but if one must do it via the compiler invocation, then the best way to do so is this:
$(CC) -D_GNU_SOURCE=
...because otherwise, if this form is used:
$(CC) -D_GNU_SOURCE
...then that leads the compiler to set a value, as if you had passed in:
$(CC) -D_GNU_SOURCE=1
That, in turn, leads to warnings under both gcc and clang, like this:
futex_requeue_pi.c:20: warning: "_GNU_SOURCE" redefined
Fix this by using the "-D_GNU_SOURCE=" form.
Signed-off-by: John Hubbard jhubbard@nvidia.com --- tools/testing/selftests/futex/functional/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/testing/selftests/futex/functional/Makefile b/tools/testing/selftests/futex/functional/Makefile index a392d0917b4e..994fa3468f17 100644 --- a/tools/testing/selftests/futex/functional/Makefile +++ b/tools/testing/selftests/futex/functional/Makefile @@ -1,6 +1,6 @@ # SPDX-License-Identifier: GPL-2.0 INCLUDES := -I../include -I../../ $(KHDR_INCLUDES) -CFLAGS := $(CFLAGS) -g -O2 -Wall -D_GNU_SOURCE -pthread $(INCLUDES) $(KHDR_INCLUDES) +CFLAGS := $(CFLAGS) -g -O2 -Wall -D_GNU_SOURCE= -pthread $(INCLUDES) $(KHDR_INCLUDES) LDLIBS := -lpthread -lrt
LOCAL_HDRS := \