Re: [PATCH bpf-next 3/5] selftests/bpf: fix test_cpp compilation failure with clang

[Yonghong Song <yhs@fb.com>]

On 4/11/21 3:47 AM, Sedat Dilek wrote:
> On Sat, Apr 10, 2021 at 6:49 PM Yonghong Song <yhs@fb.com> wrote:
>>
>> With clang compiler:
>>    make -j60 LLVM=1 LLVM_IAS=1  <=== compile kernel
>>    make -j60 -C tools/testing/selftests/bpf LLVM=1 LLVM_IAS=1
>> the test_cpp build failed due to the failure:
>>    warning: treating 'c-header' input as 'c++-header' when in C++ mode, this behavior is deprecated [-Wdeprecated]
>>    clang-13: warning: cannot specify -o when generating multiple output files
>>
>> test_cpp compilation flag looks like:
>>    clang++ -g -Og -rdynamic -Wall -I<...> ... \
>>    -Dbpf_prog_load=bpf_prog_test_load -Dbpf_load_program=bpf_test_load_program \
>>    test_cpp.cpp <...>/test_core_extern.skel.h <...>/libbpf.a <...>/test_stub.o \
>>    -lcap -lelf -lz -lrt -lpthread -o <...>/test_cpp
>>
>> The clang++ compiler complains the header file in the command line.
>> Let us remove the header file from the command line which is not intended
>> any way, and this fixed the problem.
>>
>> Signed-off-by: Yonghong Song <yhs@fb.com>
>> ---
>>   tools/testing/selftests/bpf/Makefile | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
>> index 6448c626498f..bbd61cc3889b 100644
>> --- a/tools/testing/selftests/bpf/Makefile
>> +++ b/tools/testing/selftests/bpf/Makefile
>> @@ -481,7 +481,7 @@ $(OUTPUT)/test_verifier: test_verifier.c verifier/tests.h $(BPFOBJ) | $(OUTPUT)
>>   # Make sure we are able to include and link libbpf against c++.
>>   $(OUTPUT)/test_cpp: test_cpp.cpp $(OUTPUT)/test_core_extern.skel.h $(BPFOBJ)
>>          $(call msg,CXX,,$@)
>> -       $(Q)$(CXX) $(CFLAGS) $^ $(LDLIBS) -o $@
>> +       $(Q)$(CXX) $(CFLAGS) test_cpp.cpp $(BPFOBJ) $(LDLIBS) -o $@
>>
>>   # Benchmark runner
>>   $(OUTPUT)/bench_%.o: benchs/bench_%.c bench.h
>> --
>> 2.30.2
>>
> 
> NOTE: bpf-next might be different from my build-environment.
> 
> Yonghong, can you please re-test by adding explicitly CXX=g++ to your make line?
> 
> Here I have:
> 
> $ grep test_cpp make-log_tools-testing-selftests-bpf_clang_clang++.txt
> 1907:clang++ -g -rdynamic -Wall -O2 -DHAVE_GENHDR
> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf
> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/include
> -I/home/dileks/src/linux-kernel/git/include/generated
> -I/home/dileks/src/linux-kernel/git/tools/lib
> -I/home/dileks/src/linux-kernel/git/tools/include
> -I/home/dileks/src/linux-kernel/git/tools/include/uapi
> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf
> -Wno-unused-command-line-argument -Wno-format-security
> -Dbpf_prog_load=bpf_prog_test_load
> -Dbpf_load_program=bpf_test_load_program test_cpp.cpp
> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a
> -lcap -lelf -lz -lrt -lpthread -o
> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_cpp
> 
> This clang++ line does not include <...>/test_core_extern.skel.h ^^^
> 
> $ grep test_core_extern.skel.h
> make-log_tools-testing-selftests-bpf_clang_clang++.txt
> 704:/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/sbin/bpftool
> gen skeleton /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_co
> re_extern.o > /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_core_extern.skel.h
> 1592:/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/sbin/bpftool
> gen skeleton /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/no_alu
> 32/test_core_extern.o >
> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/no_alu32/test_core_extern.skel.h
> 
> Checking test_cpp:
> 
> $ /opt/llvm-toolchain/bin/llvm-objdump-12 -Dr test_cpp | grep extern
> 0000000000417e50 <cmp_externs>:
>   417e54: 75 22                         jne     0x417e78 <cmp_externs+0x28>
>   417e59: 75 10                         jne     0x417e6b <cmp_externs+0x1b>
>   417e61: 75 21                         jne     0x417e84 <cmp_externs+0x34>
>   417e69: 75 1e                         jne     0x417e89 <cmp_externs+0x39>
>   417e87: eb f2                         jmp     0x417e7b <cmp_externs+0x2b>
>   417e8c: eb ed                         jmp     0x417e7b <cmp_externs+0x2b>
> 
> $ /opt/llvm-toolchain/bin/llvm-objdump-12 -Dr test_cpp | grep core_extern
> [ EMPTY ]
> 
> When compiled with g++ in an earlier setup this contained "core_extern".
> 
> With this version of your patchser it breaks *here* when using CXX=g++
> (and uses /usr/bin/ld as linker):
> 
> g++ -g -rdynamic -Wall -O2 -DHAVE_GENHDR
> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf
> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/b
> pf/tools/include -I/home/dileks/src/linux-kernel/git/include/generated
> -I/home/dileks/src/linux-kernel/git/tools/lib
> -I/home/dileks/src/linux-kernel/git/tools/include
> -I/home/dileks/src/linux-kernel/git/tools/include/uapi
> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf
> -Wno-unused-command-line-argument -Wno-format-security
> -Dbpf_prog_load=bpf_prog_test_load
> -Dbpf_load_program=bpf_test_load_program test_cpp.cpp
> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a
> -lcap -lelf -lz -lrt -lpthread -o
> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_cpp
> 
> /usr/bin/ld: /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a(libbpf-in.o):
> relocation R_X86_64_32 against `.rodata.str1.1' ca
> n not be used when making a PIE object; recompile with -fPIE
> collect2: error: ld returned 1 exit status
> make: *** [Makefile:457:
> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_cpp]
> Error 1

I cannot reproduce the issue with g++ with bpf-next, my command line is

g++ -g -Og -rdynamic -Wall 
-I/home/yhs/work/bpf-next/tools/testing/selftests/bpf 
-I/home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/include 
-I/home/yhs/work/bpf-next/include/generated 
-I/home/yhs/work/bpf-next/tools/lib 
-I/home/yhs/work/bpf-next/tools/include 
-I/home/yhs/work/bpf-next/tools/include/uapi 
-I/home/yhs/work/bpf-next/tools/testing/selftests/bpf 
-Wno-unused-command-line-argument -Wno-format-security 
-Dbpf_prog_load=bpf_prog_test_load 
-Dbpf_load_program=bpf_test_load_program test_cpp.cpp 
/home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a 
-lcap -lelf -lz -lrt -lpthread -o 
/home/yhs/work/bpf-next/tools/testing/selftests/bpf/test_cpp

I modified to
g++ -g -rdynamic -Wall -O2 -DHAVE_GENHDR 
-I/home/yhs/work/bpf-next/tools/testing/selftests/bpf ...
and cannot reproduce the issue.
The macro HAVE_GENHDR is only effect for test_verifier.


Could you try to run the above g++ command by adding 
test_core_extern.skel.h back, something like

 > g++ -g -rdynamic -Wall -O2 -DHAVE_GENHDR
 > -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf
 > -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/b
 > pf/tools/include -I/home/dileks/src/linux-kernel/git/include/generated
 > -I/home/dileks/src/linux-kernel/git/tools/lib
 > -I/home/dileks/src/linux-kernel/git/tools/include
 > -I/home/dileks/src/linux-kernel/git/tools/include/uapi
 > -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf
 > -Wno-unused-command-line-argument -Wno-format-security
 > -Dbpf_prog_load=bpf_prog_test_load
 > -Dbpf_load_program=bpf_test_load_program test_cpp.cpp
 > test_core_extern.skel.h
 > 
/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a
 > -lcap -lelf -lz -lrt -lpthread -o
 > /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_cpp

The issue could be somewhere else?

> 
> $ grep test_cpp ../make-log_tools-testing-selftests-bpf_clang_g++.txt
> | grep test_core_extern.skel.h
> [ EMPTY ]
> 
> As said I do NOT use bpf-next.
> 
> - Sedat -
> 
> 
> 
> - Sedat -
>