Is there a built in linux utility that I can use to test a newly compiled shared library for external undefined references? Gcc seems to be intelligent enough to check for undefined symbols in my own binary, but if the symbol is a reference to another library gcc does not check at link time. Instead I only get the message when I try to link to my new library from another program.
It seems a little silly to get undefined reference messages in a library when I am compiling a different project so I want to know if I can do a check on all references internal and external when I build the library not when I link to it.
Example error:
make -C UnitTests debug
make[1]: Entering directory `~/projects/Foo/UnitTests`
g++ [ tons of objects ] -L../libbar/bin -lbar -o UnitTests
libbar.so: undefined reference to `DoSomethingFromAnotherLibrary`
collect2: ld returned 1 exit status
make[1]: *** [~/projects/Foo/UnitTests] Error 1
Usually, undefined references are allowed when linking shared objects, but you can make the linker generate an error if there are undefined symbols in the object files that you are linking to create the shared library by supplying -z defs to the linker (or equivalently -Wl,-z,defs in the gcc command that calls the linker).
Related
I would like to be able to connect from my c++ program to a local MySQL instance, but the following minimal file testfile.cpp does not compile and returns undefined references:
#include <mysqlx/xdevapi.h>
using namespace ::mysqlx;
int main()
{
printf("Hello world!\n");
return 0;
}
I suspect to not use the right compile flags. When I use the command
c++ -o test1 -std=c++11 -lmysqlcppconn8 -I /usr/include/mysql-cppconn-8/ testfile.cpp
I am getting the following error messages (translated to English):
/tmp/cc02ZbBr.o: In the function "mysqlx::abi2::r0::string::traits<char>::to_str[abi:cxx11](mysqlx::abi2::r0::string const&)":
testfile.cpp:(.text._ZN6mysqlx4abi22r06string6traitsIcE6to_strB5cxx11ERKS2_[_ZN6mysqlx4abi22r06string6traitsIcE6to_strB5cxx11ERKS2_]+0x2e): undefined reference to "mysqlx::abi2::r0::string::Impl::to_utf8[abi:cxx11](mysqlx::abi2::r0::string const&)"
/tmp/cc02ZbBr.o: In the function "mysqlx::abi2::r0::DbDoc::DbDoc()":
testfile.cpp:(.text._ZN6mysqlx4abi22r05DbDocC2Ev[_ZN6mysqlx4abi22r05DbDocC5Ev]+0x1b): undefined reference to "vtable for mysqlx::abi2::r0::DbDoc"
/tmp/cc02ZbBr.o: In the function "mysqlx::abi2::r0::DbDoc::~DbDoc()":
testfile.cpp:(.text._ZN6mysqlx4abi22r05DbDocD2Ev[_ZN6mysqlx4abi22r05DbDocD5Ev]+0xf): undefined reference to "vtable for mysqlx::abi2::r0::DbDoc"
/tmp/cc02ZbBr.o: In the function "mysqlx::abi2::r0::Value::print(std::ostream&) const":
testfile.cpp:(.text._ZNK6mysqlx4abi22r05Value5printERSo[_ZNK6mysqlx4abi22r05Value5printERSo]+0x88): undefined reference to "mysqlx::abi2::r0::common::Value::print(std::ostream&) const"
/tmp/cc02ZbBr.o:(.data.rel.ro._ZTCN6mysqlx4abi22r05ValueE0_NS1_6common5ValueE[_ZTVN6mysqlx4abi22r05ValueE]+0x18): undefined reference to "typeinfo for mysqlx::abi2::r0::common::Value"
/tmp/cc02ZbBr.o:(.data.rel.ro._ZTCN6mysqlx4abi22r05ValueE0_NS1_6common5ValueE[_ZTVN6mysqlx4abi22r05ValueE]+0x20): undefined reference to "mysqlx::abi2::r0::common::Value::print(std::ostream&) const"
/tmp/cc02ZbBr.o:(.data.rel.ro._ZTIN6mysqlx4abi22r05ValueE[_ZTIN6mysqlx4abi22r05ValueE]+0x28): undefined reference to "typeinfo for mysqlx::abi2::r0::common::Value"
collect2: error: ld returned 1 exit status
The header from this file comes from a sample code on MySQL Connector/C++'s Github.
This question on SO seems relevant but the syntax/directories might be outdated. In any case, I do not know how to adjust the answers given there to my situation and location of libraries. Therefore I am asking for help here.
More information:
I'm running Linux Ubuntu 18.04, MySQL version 8.0.19 and have the following files in /usr/lib/x86_64-linux-gnu/
libmysqlcppconn.so
libmysqlcppconn.so.7.8.0.19
libmysqlcppconn.so.7
but I do not know how to refer to them.
In /usr/include/mysql-cppconn-8/ I have the directories jdbc/, mysql/ and mysqlx/.
I installed the following binary packages using the apt package manager: libmysqlcppconn-dev, libmysqlcppconn7, libmysqlcppconn8-1 and libmysqlcppconn8-2 (which is probably overkill but according to the installation guide one has to install quite a few of these libraries).
which mysql returns /usr/bin/mysql
When you compile source files and link binaries with object files and libraries, the order does matter. Shared libraries providing exported symbols must follow object files and other shared libraries importing these symbols. In your case, the shared library must be placed in the end of the c++ command invitation:
c++ -o test1 -std=c++11 -I /usr/include/mysql-cppconn-8/ testfile.cpp -lmysqlcppconn8
The undefined symbols discovered after compiling testfile.cpp will be imported from the following libmysqlcppconn8.so. Linkers doesn't remember exported symbols from prior libraries. For more information read this nice article: Why does the order in which libraries are linked sometimes cause errors in GCC.
I have two projects. Project "vDevice" compiles into "libvDevice.so". This library is then used by the other project "videoViewer", which compiles into a binary "app_videoViewer". These were both working fine before I added a call to avdevice_reigster_all() in one of vDevice's files.
vDevice.so compiles and links with no errors. In the makefile I have -L${FFMPEG_PATH} (where all the libav*.a files are located), and -l avformat, avcodec, avutil, asound, avdevice, and bz2 (in that order).
When I try to make videoViewer now, I get this error:
Linking application app_videoViewer ...
/path/to/lib/libvDevice.so: undefined reference to `avdevice_register_all'
collect2: error: ld returned 1 exit status
For videoViewer I added the same things to the makefile, linking to avformat, avcodec, avutil, asound, avdevice, and bz2, all before vDevice... what am I missing?
I have a simple socket program that I'm trying to compile using g++ running in mingw (both the latest versions) on a Win8 system. I'm getting the common linker errors
undefined reference to `__imp_socket'
undefined reference to `__imp_gethostbyname'
I've tried adding -lws2_32 with no luck; i.e. it still can't find the references. Can someone suggest something else I might be missing?
Here's the full output:
G:\source\kak>g++ -o ./test_client -lws2_32 test_client.C
C:\Users\kenkahn\AppData\Local\Temp\ccDZTr9b.o:test_client.C:(.text+0x4f): undefined reference to `__imp_inet_addr'
C:\Users\kenkahn\AppData\Local\Temp\ccDZTr9b.o:test_client.C:(.text+0x6b): undefined reference to `__imp_socket'
C:\Users\kenkahn\AppData\Local\Temp\ccDZTr9b.o:test_client.C:(.text+0x8b): undefined reference to `__imp_connect'
d:/program files/mingw/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/4.8.1/../../../../x86_64-w64-mingw32/bin/ld.exe: C:\Users\kenkahn\AppData\Local\Temp\ccDZTr9b.o: bad reloc address 0xc in section `.xdata'
collect2.exe: error: ld returned 1 exit status
Try putting the -lws2_32 after the test_client.C parameter. The linker of gcc (ld) is touchy about the order of linkable things, this is probably why it doesn't find your imported functions at link time.
I have the problem that as the g++ tries to link the object files I receive the following error:
11:29:13 **** Build of configuration Debug for project daytime ****
make all
'Building target: daytime'
'Invoking: Cross G++ Linker'
g++ -o "daytime" ./tcf/services/daytime.o ./tcf/main/main.o
./tcf/services/daytime.o: In function `command_get_time_of_day':
C:\Users\falkstef\runtime-EclipseApplication\daytime\Debug/../tcf/services/daytime.c:38: undefined reference to `json_read_string'
C:\Users\falkstef\runtime-EclipseApplication\daytime\Debug/../tcf/services/daytime.c:40: undefined reference to `exception'
C:\Users\falkstef\runtime-EclipseApplication\daytime\Debug/../tcf/services/daytime.c:43: undefined reference to `exception'
C:\Users\falkstef\runtime-EclipseApplication\daytime\Debug/../tcf/services/daytime.c:52: undefined reference to `write_stringz'
makefile:46: recipe for target 'daytime' failed
C:\Users\falkstef\runtime-EclipseApplication\daytime\Debug/../tcf/services/daytime.c:54: undefined reference to `write_stringz'
C:\Users\falkstef\runtime-EclipseApplication\daytime\Debug/../tcf/services/daytime.c:56: undefined reference to `write_errno'
C:\Users\falkstef\runtime-EclipseApplication\daytime\Debug/../tcf/services/daytime.c:58: undefined reference to `json_write_string'
./tcf/services/daytime.o: In function `ini_daytime_service':
C:\Users\falkstef\runtime-EclipseApplication\daytime\Debug/../tcf/services/daytime.c:70: undefined reference to `add_command_handler'
collect2.exe: error: ld returned 1 exit status
make: *** [daytime] Error 1
I have no idea why this is the case since e.g. #include <tcf/framework/json.h>is included and found.
Didn't gcc compile the corresponding *.c files such that this linker error occurs?
What is the problem here?
Thank you.
It is not enough to include the header files; you also have to specify the libraries where those functions are defined.
To make the linker find all those methods/classes (json_read_string, write_stringz, exception) you need to reference the library. If e.g. they are contained in a library called libjson.so, you should do:
g++ -ljson -o "daytime" ./tcf/services/daytime.o ./tcf/main/main.o
(or add the library to the project options, if eclipse is managing your make files).
Or if it's another .o file, include that in the compilation (-> or in the project, if eclipse is creating the make file).
Ok, newb question here.
I'm trying to compile simple_xy_wr.f90 -- a netCDF example program -- using gfortran on Ubuntu, and I must be doing something pretty silly; I don't have much experince compiling Fortran.
First, I've got the libnetcdf-dev package installed, which includes files like
/usr/lib/libnetcdf.a
/usr/lib/libnetcdff.a
/usr/include/netcdf.mod
So, I've tried to compile the code with (various command like)
f95 -o xy -I/usr/include/ -L/usr/lib/ -lnetcdff -lnetcdf simple_xy_wr.f90
and I get the following output
/tmp/ccE6g7sr.o: In function `check.1847':
simple_xy_wr.f90:(.text+0x72): undefined reference to `__netcdf_MOD_nf90_strerror'
/tmp/ccE6g7sr.o: In function `MAIN__':
simple_xy_wr.f90:(.text+0x284): undefined reference to `__netcdf_MOD_nf90_create'
simple_xy_wr.f90:(.text+0x2b6): undefined reference to `__netcdf_MOD_nf90_def_dim'
simple_xy_wr.f90:(.text+0x2e8): undefined reference to `__netcdf_MOD_nf90_def_dim'
simple_xy_wr.f90:(.text+0x432): undefined reference to `__netcdf_MOD_nf90_def_var_manydims'
simple_xy_wr.f90:(.text+0x468): undefined reference to `__netcdf_MOD_nf90_enddef'
simple_xy_wr.f90:(.text+0x4aa): undefined reference to `__netcdf_MOD_nf90_put_var_2d_fourbyteint'
simple_xy_wr.f90:(.text+0x4cb): undefined reference to `__netcdf_MOD_nf90_close'
collect2: error: ld returned 1 exit status
I think that I'm including the right libraries. E.g. it seems that __netcdf_MOD_nf90_strerror should be there:
$ nm /usr/lib/libnetcdff.a | grep __netcdf_MOD_nf90_strerror
000000000004a100 T __netcdf_MOD_nf90_strerror
What am I doing wrong?
(FWIW, a few relevant references I've looked at are below.
undefined reference using netcdf library
Compiling problems with gfortran and NETCDF
Compiling and Running Fortran Programs - a basic guide
)
Ordering of object files and archives on the linker command line is very important on Unix systems since the default linker behaviour is to search for symbol definitions only in archives that follow the object file or archive, where an unresolved reference was found, referred to single pass linking.
This means that if your code references __netcdf_MOD_nf90_strerror, then the archive that contains the definition of this symbol (libnetcdff.a) must appear after the list of object files from your program. libnetcdff.a itself references symbols from the C library libnetcdf.a, hence it must be linked after libnetcdff.a. So the correct link order is:
/tmp/ccE6g7sr.o libnetcdff.a libnetcdf.a
where /tmp/ccE6g7sr.o is the temporary object file that the assembler produces from the compiled source file. The correct command line to compile your code is then:
f95 -o xy -I/usr/include/ simple_xy_wr.f90 -lnetcdff -lnetcdf
In this case the linker is not called directly, rather the compiler does it. GCC compilers pass all link-related things in the same order to an intermediate utility called collect2 which then calls the actual linker ld.
Note that if shared object versions of the netCDF library archives are also present (i.e. there are libnetcdff.so and libnetcdf.so), then the linker would prefer them to the static archives (unless static linking is enabled with the -static option) and the final link phase would be handled to the run-time link editor (RTLD) (/lib64/ld-linux-x86-64.so.2 on Ubuntu). In this case the same command line as in your question would actually succeed without link errors, despite the fact that both libraries are positioned before the code that references them, as the missing symbol references would be resolved by the RTLD while it is loading the executable file.
In Ubuntu 12.10, the order of the libraries is the trick (as Hristo suggested):
angelv#palas:~$ gfortran -o xy -I/usr/include/ -L/usr/lib/ -lnetcdf -lnetcdff simple_xy_wr.f90
/tmp/ccj95anF.o: In function `check.1847':
simple_xy_wr.f90:(.text+0x72): undefined reference to `__netcdf_MOD_nf90_strerror'
/tmp/ccj95anF.o: In function `MAIN__':
simple_xy_wr.f90:(.text+0x284): undefined reference to `__netcdf_MOD_nf90_create'
simple_xy_wr.f90:(.text+0x2b6): undefined reference to `__netcdf_MOD_nf90_def_dim'
simple_xy_wr.f90:(.text+0x2e8): undefined reference to `__netcdf_MOD_nf90_def_dim'
simple_xy_wr.f90:(.text+0x432): undefined reference to `__netcdf_MOD_nf90_def_var_manydims'
simple_xy_wr.f90:(.text+0x468): undefined reference to `__netcdf_MOD_nf90_enddef'
simple_xy_wr.f90:(.text+0x4aa): undefined reference to `__netcdf_MOD_nf90_put_var_2d_fourbyteint'
simple_xy_wr.f90:(.text+0x4cb): undefined reference to `__netcdf_MOD_nf90_close'
collect2: error: ld returned 1 exit status
angelv#palas:~$ gfortran -o xy -I/usr/include/ simple_xy_wr.f90 -L/usr/lib/ -lnetcdf -lnetcdff
angelv#palas:~$ ./xy
0 12 24 36
*** SUCCESS writing example file simple_xy.nc!