linux-kernel - Re: [PATCH 3/4] selftests: seccomp: use LDLIBS instead of LDFLAGS

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Date:   Wed, 16 Jan 2019 10:13:59 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Daniel Díaz <daniel.diaz@...aro.org>,
        Shuah Khan <shuah@...nel.org>
Cc:     Fathi Boudra <fathi.boudra@...aro.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] selftests: seccomp: use LDLIBS instead of LDFLAGS

On Wed, Jan 16, 2019 at 9:44 AM Daniel Díaz <daniel.diaz@...aro.org> wrote:
>
> From: Fathi Boudra <fathi.boudra@...aro.org>
>
> seccomp_bpf 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 -Wl,-no-as-needed -Wall
>  -Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed -lpthread seccomp_bpf.c -o
>  /build/tmp-rpb-glibc/work/hikey-linaro-linux/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf
>  /tmp/ccrlR3MW.o: In function `tsync_sibling':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1920: undefined reference to `sem_post'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1920: undefined reference to `sem_post'
>  /tmp/ccrlR3MW.o: In function `TSYNC_setup':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1863: undefined reference to `sem_init'
>  /tmp/ccrlR3MW.o: In function `TSYNC_teardown':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1904: undefined reference to `sem_destroy'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1897: undefined reference to `pthread_kill'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1898: undefined reference to `pthread_cancel'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1899: undefined reference to `pthread_join'
>  /tmp/ccrlR3MW.o: In function `tsync_start_sibling':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /tmp/ccrlR3MW.o: In function `TSYNC_siblings_fail_prctl':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1978: undefined reference to `sem_wait'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1990: undefined reference to `pthread_join'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1992: undefined reference to `pthread_join'
>  /tmp/ccrlR3MW.o: In function `tsync_start_sibling':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /tmp/ccrlR3MW.o: In function `TSYNC_two_siblings_with_ancestor':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2016: undefined reference to `sem_wait'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2032: undefined reference to `pthread_join'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2034: undefined reference to `pthread_join'
>  /tmp/ccrlR3MW.o: In function `tsync_start_sibling':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /tmp/ccrlR3MW.o: In function `TSYNC_two_sibling_want_nnp':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2046: undefined reference to `sem_wait'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2058: undefined reference to `pthread_join'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2060: undefined reference to `pthread_join'
>  /tmp/ccrlR3MW.o: In function `tsync_start_sibling':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /tmp/ccrlR3MW.o: In function `TSYNC_two_siblings_with_no_filter':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2073: undefined reference to `sem_wait'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2098: undefined reference to `pthread_join'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2100: undefined reference to `pthread_join'
>  /tmp/ccrlR3MW.o: In function `tsync_start_sibling':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /tmp/ccrlR3MW.o: In function `TSYNC_two_siblings_with_one_divergence':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2125: undefined reference to `sem_wait'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2143: undefined reference to `pthread_join'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2145: undefined reference to `pthread_join'
>  /tmp/ccrlR3MW.o: In function `tsync_start_sibling':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>  /tmp/ccrlR3MW.o: In function `TSYNC_two_siblings_not_under_filter':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2169: undefined reference to `sem_wait'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2202: undefined reference to `pthread_join'
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:2227: undefined reference to `pthread_join'
>  /tmp/ccrlR3MW.o: In function `tsync_start_sibling':
>  /usr/src/debug/kselftests/4.12-r0/linux-4.12-rc7/tools/testing/selftests/seccomp/seccomp_bpf.c:1941: undefined reference to `pthread_create'
>
> 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: Fathi Boudra <fathi.boudra@...aro.org>

Acked-by: Kees Cook <keescook@...omium.org>

Shuah, can you take this?

-Kees

> ---
>  tools/testing/selftests/seccomp/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/seccomp/Makefile b/tools/testing/selftests/seccomp/Makefile
> index fce7f4ce0692..1760b3e39730 100644
> --- a/tools/testing/selftests/seccomp/Makefile
> +++ b/tools/testing/selftests/seccomp/Makefile
> @@ -9,7 +9,7 @@ BINARIES := seccomp_bpf seccomp_benchmark
>  CFLAGS += -Wl,-no-as-needed -Wall
>
>  seccomp_bpf: seccomp_bpf.c ../kselftest_harness.h
> -       $(CC) $(CFLAGS) $(LDFLAGS) -lpthread $< -o $@
> +       $(CC) $(CFLAGS) $(LDFLAGS) $< -lpthread -o $@
>
>  TEST_PROGS += $(BINARIES)
>  EXTRA_CLEAN := $(BINARIES)
> --
> 2.17.1
>


-- 
Kees Cook