Libraries should be listed last on the compiler's command line, so that
the linker can look for and find still unresolved symbols. The librt
library, required for the shm_* functions, was announced using CFLAGS,
which puts the library *before* the source files, and fails compilation
on my system:
======================
gcc -isystem /src/linux-selftests/usr/include -Wall -lrt test_cachestat.c
  -o /src/linux-selftests/kselftest/cachestat/test_cachestat
/usr/bin/ld: /tmp/cceQWO3u.o: in function `test_cachestat_shmem':
test_cachestat.c:(.text+0x890): undefined reference to `shm_open'
/usr/bin/ld: test_cachestat.c:(.text+0x99c): undefined reference to `shm_unlink'
collect2: error: ld returned 1 exit status
make[4]: *** [../lib.mk:181: /src/linux-selftests/kselftest/cachestat/test_cachestat] Error 1
======================

Announce the library using the LDLIBS variable, which ensures the proper
ordering on the command line.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 tools/testing/selftests/cachestat/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cachestat/Makefile b/tools/testing/selftests/cachestat/Makefile
index fca73aaa7d141..778b54ebb0364 100644
--- a/tools/testing/selftests/cachestat/Makefile
+++ b/tools/testing/selftests/cachestat/Makefile
@@ -3,6 +3,6 @@ TEST_GEN_PROGS := test_cachestat
 
 CFLAGS += $(KHDR_INCLUDES)
 CFLAGS += -Wall
-CFLAGS += -lrt
+LDLIBS += -lrt
 
 include ../lib.mk
-- 
2.25.1

On 8/15/23 09:56, Andre Przywara wrote:
> Libraries should be listed last on the compiler's command line, so that
> the linker can look for and find still unresolved symbols. The librt
> library, required for the shm_* functions, was announced using CFLAGS,
> which puts the library *before* the source files, and fails compilation
> on my system:
> ======================
> gcc -isystem /src/linux-selftests/usr/include -Wall -lrt test_cachestat.c
>    -o /src/linux-selftests/kselftest/cachestat/test_cachestat
> /usr/bin/ld: /tmp/cceQWO3u.o: in function `test_cachestat_shmem':
> test_cachestat.c:(.text+0x890): undefined reference to `shm_open'
> /usr/bin/ld: test_cachestat.c:(.text+0x99c): undefined reference to `shm_unlink'
> collect2: error: ld returned 1 exit status
> make[4]: *** [../lib.mk:181: /src/linux-selftests/kselftest/cachestat/test_cachestat] Error 1
> ======================
> 
> Announce the library using the LDLIBS variable, which ensures the proper
> ordering on the command line.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>   tools/testing/selftests/cachestat/Makefile | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/cachestat/Makefile b/tools/testing/selftests/cachestat/Makefile
> index fca73aaa7d141..778b54ebb0364 100644
> --- a/tools/testing/selftests/cachestat/Makefile
> +++ b/tools/testing/selftests/cachestat/Makefile
> @@ -3,6 +3,6 @@ TEST_GEN_PROGS := test_cachestat
>   
>   CFLAGS += $(KHDR_INCLUDES)
>   CFLAGS += -Wall
> -CFLAGS += -lrt
> +LDLIBS += -lrt
>   
>   include ../lib.mk

Thank you. Applied to linux-kselftest next for Linux 6.6-rc1

thanks,
-- Shuah