From: Fathi Boudra <fathi.boudra@xxxxxxxxxx> posix_timers fails to build due to undefined reference errors: aarch64-linaro-linux-gcc --sysroot=/build/tmp-rpb-glibc/sysroots/hikey -O2 -pipe -g -feliminate-unused-debug-types -O3 -Wl,-no-as-needed -Wall -DKTEST -Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed -lrt -lpthread posix_timers.c -o /build/tmp-rpb-glibc/work/hikey-linaro-linux/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/timers/posix_timers /tmp/cc1FTZzT.o: In function `check_timer_create': /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/timers/posix_timers.c:157: undefined reference to `timer_create' /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/timers/posix_timers.c:170: undefined reference to `timer_settime' collect2: error: ld returned 1 exit status It's GNU Make and linker specific. The default Makefile rule looks like: $(CC) $(CFLAGS) $(LDFLAGS) $@ $^ $(LDLIBS) When linking is done by gcc itself, no issue, but when it needs to be passed to proper ld, only LDLIBS follows and then ld cannot know what libs to link with. More detail: https://www.gnu.org/software/make/manual/html_node/Implicit-Variables.html LDFLAGS Extra flags to give to compilers when they are supposed to invoke the linker, ‘ld’, such as -L. Libraries (-lfoo) should be added to the LDLIBS variable instead. LDLIBS Library flags or names given to compilers when they are supposed to invoke the linker, ‘ld’. LOADLIBES is a deprecated (but still supported) alternative to LDLIBS. Non-library linker flags, such as -L, should go in the LDFLAGS variable. https://lkml.org/lkml/2010/2/10/362 tools/perf: libraries must come after objects Link order matters, use LDLIBS instead of LDFLAGS to properly link against libpthread. Signed-off-by: Denys Dmytriyenko <denys@xxxxxx> Signed-off-by: Fathi Boudra <fathi.boudra@xxxxxxxxxx> --- tools/testing/selftests/timers/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/testing/selftests/timers/Makefile b/tools/testing/selftests/timers/Makefile index c02683cfb6c9..7656c7ce79d9 100644 --- a/tools/testing/selftests/timers/Makefile +++ b/tools/testing/selftests/timers/Makefile @@ -1,6 +1,6 @@ # SPDX-License-Identifier: GPL-2.0 CFLAGS += -O3 -Wl,-no-as-needed -Wall -LDFLAGS += -lrt -lpthread -lm +LDLIBS += -lrt -lpthread -lm # these are all "safe" tests that don't modify # system time or require escalated privileges -- 2.17.1
