selftests: centralize -D_GNU_SOURCE= to CFLAGS in lib.mk

Centralize the _GNU_SOURCE definition to CFLAGS in lib.mk.  Remove
redundant defines from Makefiles that import lib.mk.  Convert any usage of
"#define _GNU_SOURCE 1" to "#define _GNU_SOURCE".

This uses the form "-D_GNU_SOURCE=", which is equivalent to
"#define _GNU_SOURCE".

Otherwise using "-D_GNU_SOURCE" is equivalent to "-D_GNU_SOURCE=1" and
"#define _GNU_SOURCE 1", which is less commonly seen in source code and
would require many changes in selftests to avoid redefinition warnings.

Link: https://lkml.kernel.org/r/20240625223454.1586259-2-edliaw@google.comSigned-off-by: Edward Liaw <edliaw@google.com>
Suggested-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: André Almeida <andrealmeid@igalia.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kees Cook <kees@kernel.org>
Cc: Kevin Tian <kevin.tian@intel.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Reinette Chatre <reinette.chatre@intel.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/exec/Makefile

 # SPDX-License-Identifier: GPL-2.0
 CFLAGS = -Wall
 CFLAGS += -Wno-nonnull
-CFLAGS += -D_GNU_SOURCE
 
 TEST_PROGS := binfmt_script.py
 TEST_GEN_PROGS := execveat load_address_4096 load_address_2097152 load_address_16777216 non-regular

tools/testing/selftests/futex/functional/Makefile

 # 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 -pthread $(INCLUDES) $(KHDR_INCLUDES)
 LDLIBS := -lpthread -lrt
 
 LOCAL_HDRS := \

tools/testing/selftests/intel_pstate/Makefile

 # SPDX-License-Identifier: GPL-2.0
-CFLAGS := $(CFLAGS) -Wall -D_GNU_SOURCE
+CFLAGS := $(CFLAGS) -Wall
 LDLIBS += -lm
 
 ARCH ?= $(shell uname -m 2>/dev/null || echo not)

tools/testing/selftests/iommu/Makefile

@@ -2,8 +2,6 @@
 CFLAGS += -Wall -O2 -Wno-unused-function
 CFLAGS += $(KHDR_INCLUDES)
 
-CFLAGS += -D_GNU_SOURCE
-
 TEST_GEN_PROGS :=
 TEST_GEN_PROGS += iommufd
 TEST_GEN_PROGS += iommufd_fail_nth

tools/testing/selftests/kvm/Makefile

@@ -231,7 +231,7 @@ LINUX_TOOL_ARCH_INCLUDE = $(top_srcdir)/tools/arch/$(ARCH)/include
 endif
 CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
 	-Wno-gnu-variable-sized-type-not-at-end -MD -MP -DCONFIG_64BIT \
-	-D_GNU_SOURCE -fno-builtin-memcmp -fno-builtin-memcpy \
+	-fno-builtin-memcmp -fno-builtin-memcpy \
 	-fno-builtin-memset -fno-builtin-strnlen \
 	-fno-stack-protector -fno-PIE -I$(LINUX_TOOL_INCLUDE) \
 	-I$(LINUX_TOOL_ARCH_INCLUDE) -I$(LINUX_HDR_PATH) -Iinclude \

tools/testing/selftests/lib.mk

@@ -188,6 +188,9 @@ endef
 clean: $(if $(TEST_GEN_MODS_DIR),clean_mods_dir)
 	$(CLEAN)
 
+# Build with _GNU_SOURCE by default
+CFLAGS += -D_GNU_SOURCE=
+
 # Enables to extend CFLAGS and LDFLAGS from command line, e.g.
 # make USERCFLAGS=-Werror USERLDFLAGS=-static
 CFLAGS += $(USERCFLAGS)

tools/testing/selftests/mm/thuge-gen.c

@@ -13,7 +13,7 @@
    sudo ipcs | awk '$1 == "0x00000000" {print $2}' | xargs -n1 sudo ipcrm -m
    (warning this will remove all if someone else uses them) */
 
-#define _GNU_SOURCE 1
+#define _GNU_SOURCE
 #include <sys/mman.h>
 #include <linux/mman.h>
 #include <stdlib.h>

tools/testing/selftests/net/Makefile

 # SPDX-License-Identifier: GPL-2.0
 # Makefile for net selftests
 
-CFLAGS =  -Wall -Wl,--no-as-needed -O2 -g
+CFLAGS +=  -Wall -Wl,--no-as-needed -O2 -g
 CFLAGS += -I../../../../usr/include/ $(KHDR_INCLUDES)
 # Additional include paths needed by kselftest.h
 CFLAGS += -I../

tools/testing/selftests/net/tcp_ao/Makefile

@@ -26,7 +26,7 @@ LIB	:= $(LIBDIR)/libaotst.a
 LDLIBS	+= $(LIB) -pthread
 LIBDEPS	:= lib/aolib.h Makefile
 
-CFLAGS	:= -Wall -O2 -g -D_GNU_SOURCE -fno-strict-aliasing
+CFLAGS	+= -Wall -O2 -g -fno-strict-aliasing
 CFLAGS	+= $(KHDR_INCLUDES)
 CFLAGS	+= -iquote ./lib/ -I ../../../../include/
 

tools/testing/selftests/proc/Makefile

 # SPDX-License-Identifier: GPL-2.0-only
 CFLAGS += -Wall -O2 -Wno-unused-function
-CFLAGS += -D_GNU_SOURCE
 LDFLAGS += -pthread
 
 TEST_GEN_PROGS :=

tools/testing/selftests/resctrl/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
-CFLAGS = -g -Wall -O2 -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE
+CFLAGS = -g -Wall -O2 -D_FORTIFY_SOURCE=2
 CFLAGS += $(KHDR_INCLUDES)
 
 TEST_GEN_PROGS := resctrl_tests

tools/testing/selftests/ring-buffer/Makefile

 # SPDX-License-Identifier: GPL-2.0
 CFLAGS += -Wl,-no-as-needed -Wall
 CFLAGS += $(KHDR_INCLUDES)
-CFLAGS += -D_GNU_SOURCE
 
 TEST_GEN_PROGS = map_test
 

tools/testing/selftests/riscv/mm/Makefile

@@ -3,7 +3,7 @@
 # Originally tools/testing/arm64/abi/Makefile
 
 # Additional include paths needed by kselftest.h and local headers
-CFLAGS += -D_GNU_SOURCE -std=gnu99 -I.
+CFLAGS += -std=gnu99 -I.
 
 TEST_GEN_FILES := mmap_default mmap_bottomup
 

tools/testing/selftests/sgx/Makefile

@@ -12,7 +12,7 @@ OBJCOPY := $(CROSS_COMPILE)objcopy
 endif
 
 INCLUDES := -I$(top_srcdir)/tools/include
-HOST_CFLAGS := -Wall -Werror -g $(INCLUDES) -fPIC
+HOST_CFLAGS := -Wall -Werror -g $(INCLUDES) -fPIC $(CFLAGS)
 HOST_LDFLAGS := -z noexecstack -lcrypto
 ENCL_CFLAGS += -Wall -Werror -static-pie -nostdlib -ffreestanding -fPIE \
 	       -fno-stack-protector -mrdrnd $(INCLUDES)

tools/testing/selftests/tmpfs/Makefile

 # SPDX-License-Identifier: GPL-2.0-only
 CFLAGS += -Wall -O2
-CFLAGS += -D_GNU_SOURCE
 
 TEST_GEN_PROGS :=
 TEST_GEN_PROGS += bug-link-o-tmpfile