[libcxx-dev] Is the C++ filesystem object file installed via LLVM's APT repository missing symbols?

Mon Apr 1 16:01:27 PDT 2019

On Mon, Apr 1, 2019 at 9:46 AM TheAspiringHacker via libcxx-dev <
libcxx-dev at lists.llvm.org> wrote:

> Hello,
>
> I have downloaded LLVM and Clang 8 from the APT repository (deb
> http://apt.llvm.org/xenial/ llvm-toolchain-xenial-8 main). When I compile
> and link
>
> #include <filesystem>
>
> namespace fs = std::filesystem;
>
> int main()
> {
>     fs::path wd = fs::current_path();
>     return 0;
> }
>
> with clang-8 -std=c++17 -stdlib=libc++ -lc++ -lc++abi -lc++fs test.cpp -v
>
> I get the output:
>
> clang version 8.0.0-svn356034-1~exp1~20190313094121.53
> (branches/release_80)
> Target: x86_64-pc-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
> Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/5
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/x86_64-linux-gnu/5.5.0
> Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/6
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/x86_64-linux-gnu/6.5.0
> Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/x86_64-linux-gnu/7.4.0
> Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/8
> Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
> Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
> Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
> Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
> Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
> Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.4.0
> Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
> Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/5.5.0
> Candidate multilib: .;@m64
> Selected multilib: .;@m64
> "/usr/lib/llvm-8/bin/clang" -cc1 -triple x86_64-pc-linux-gnu -emit-obj
> -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names
> -main-file-name test.cpp -mrelocation-model static -mthread-model posix
> -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases
> -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info
> -debugger-tuning=gdb -v -resource-dir /usr/lib/llvm-8/lib/clang/8.0.0
> -internal-isystem /usr/lib/llvm-8/bin/../include/c++/v1 -internal-isystem
> /usr/include/clang/8.0.0/include/ -internal-isystem /usr/local/include
> -internal-isystem /usr/lib/llvm-8/lib/clang/8.0.0/include
> -internal-externc-isystem /usr/include/x86_64-linux-gnu
> -internal-externc-isystem /include -internal-externc-isystem /usr/include
> -std=c++17 -fdeprecated-macro -fdebug-compilation-dir /home/<username>
> -ferror-limit 19 -fmessage-length 0 -fobjc-runtime=gcc -fcxx-exceptions
> -fexceptions -fdiagnostics-show-option -o /tmp/test-b088e9.o -x c++
> test.cpp -faddrsig
> clang -cc1 version 8.0.0 based upon LLVM 8.0.0 default target
> x86_64-pc-linux-gnu
> ignoring nonexistent directory "/include"
> ignoring duplicate directory "/usr/include/clang/8.0.0/include"
> #include "..." search starts here:
> #include <...> search starts here:
> /usr/lib/llvm-8/bin/../include/c++/v1
> /usr/include/clang/8.0.0/include
> /usr/local/include
> /usr/include/x86_64-linux-gnu
> /usr/include
> End of search list.
> "/usr/bin/ld" --hash-style=both --build-id --eh-frame-hdr -m elf_x86_64
> -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out
> /usr/bin/../lib/gcc/x86_64-linux-gnu/5.5.0/../../../x86_64-linux-gnu/crt1.o
> /usr/bin/../lib/gcc/x86_64-linux-gnu/5.5.0/../../../x86_64-linux-gnu/crti.o
> /usr/bin/../lib/gcc/x86_64-linux-gnu/5.5.0/crtbegin.o
> -L/usr/bin/../lib/gcc/x86_64-linux-gnu/5.5.0
> -L/usr/bin/../lib/gcc/x86_64-linux-gnu/5.5.0/../../../x86_64-linux-gnu
> -L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu
> -L/usr/bin/../lib/gcc/x86_64-linux-gnu/5.5.0/../../..
> -L/usr/lib/llvm-8/bin/../lib -L/lib -L/usr/lib -lc++ -lc++abi -lc++fs
> /tmp/test-b088e9.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc
> --as-needed -lgcc_s --no-as-needed
> /usr/bin/../lib/gcc/x86_64-linux-gnu/5.5.0/crtend.o
> /usr/bin/../lib/gcc/x86_64-linux-gnu/5.5.0/../../../x86_64-linux-gnu/crtn.o
> /tmp/test-b088e9.o: In function
> `std::__1::__fs::filesystem::current_path()':
> test.cpp:(.text._ZNSt3__14__fs10filesystem12current_pathEv[_ZNSt3__14__fs10filesystem12current_pathEv]+0x14):
> undefined reference to
> `std::__1::__fs::filesystem::__current_path(std::__1::error_code*)'
> clang: error: linker command failed with exit code 1 (use -v to see
> invocation)
>
>
> I ran:
>
> nm -C /usr/lib/llvm-8/lib/libc++fs.a | fgrep
> 'std::__1::__fs::filesystem::__current_path'
>
> and got:
>
> 0000000000002540 T
> std::__1::__fs::filesystem::__current_path(std::__1::error_code*)
> 0000000000002880 T
> std::__1::__fs::filesystem::__current_path(std::__1::__fs::filesystem::path
> const&, std::__1::error_code*)
>
> It seems that the `current_path` functions, as defined in the libc++fs.a
> file that I installed, do not match the overloads as documented at
> https://en.cppreference.com/w/cpp/filesystem/current_path or specified in
> the filesystem header file of libc++. According to
> http://libcxx.llvm.org/ts1z_status.html, as of June 17, 2016, the
> filesystem library is complete. For comparison, the APT repository was last
> updated on March 27, 2019.
>
> I do not know if perhaps I made a mistake in linking the code or
> installing the library. https://libcxx.llvm.org/ directed me to ask here
> if I'm not sure whether I found a bug.
>
> Is this an issue with the files I downloaded from the APT repository, or
> is it my own mistake?
>

Your invocation of Clang puts -lc++fs before the source file that depends
on it.
You need to put the source file before the libraries. Ex:

 clang-8 -std=c++17 -stdlib=libc++ test.cpp -lc++fs -v

>
> Thanks,
> TAH
>
>
> _______________________________________________
> libcxx-dev mailing list
> libcxx-dev at lists.llvm.org
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>
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