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Subject: Re: [PATCH 3/4] selftests: seccomp: use LDLIBS instead of LDFLAGS
To:     Kees Cook <keescook@chromium.org>,
        =?UTF-8?Q?Daniel_D=c3=adaz?= <daniel.diaz@linaro.org>
Cc:     Fathi Boudra <fathi.boudra@linaro.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Will Drewry <wad@chromium.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        shuah <shuah@kernel.org>
References: <20190116174320.14938-1-daniel.diaz@linaro.org>
 <20190116174320.14938-3-daniel.diaz@linaro.org>
 <CAGXu5j+1tOvB0jHk=kCxfhTg-PEPjCHp2TQb++wZsGxJCcQxng@mail.gmail.com>
From:   shuah <shuah@kernel.org>
Message-ID: <dfe6e14f-ccf4-80ef-7bdd-23d7d2698bb8@kernel.org>
Date:   Wed, 16 Jan 2019 11:26:13 -0700
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On 1/16/19 11:13 AM, Kees Cook wrote:
> On Wed, Jan 16, 2019 at 9:44 AM Daniel Díaz <daniel.diaz@linaro.org> wrote:
>>
>> From: Fathi Boudra <fathi.boudra@linaro.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@linaro.org>
> 

Thanks for the patch.

> Acked-by: Kees Cook <keescook@chromium.org>
> 
> Shuah, can you take this?
> 

Thanks for Ack. I will get this in for 5.0-rc3 or rc4.

thanks,
-- Shuah