9

I'm not a frequent user of Linux and I think I did something wrong.

This is the code for a test dynamic library ".so" I'm generating.

class InternalClass
{
public:
    int Function(){ return 10; }
};

extern "C"
{
    int WrapperFunctionSimple() { return 10; }
    void WrapperCreateInstance() {InternalClass* item = new InternalClass(); delete item; }
}

The compilation fails with the following error:

g++ -Wall -fexceptions -O2  -c /home/lidia/compartida/TestLibrary/TestLibrary/main.cpp -o obj/Release/main.o
g++ -shared  obj/Release/main.o  -o bin/Release/libTestLibrary.so -s  
/usr/lib64/gcc/x86_64-suse-linux/7/../../../../x86_64-suse-linux/bin/ld: obj/Release/main.o: warning: relocation against `_Znwm@@GLIBCXX_3.4' in read-only section `.text'
/usr/lib64/gcc/x86_64-suse-linux/7/../../../../x86_64-suse-linux/bin/ld: obj/Release/main.o: relocation R_X86_64_PC32 against symbol `_Znwm@@GLIBCXX_3.4' can not be used when making a shared object; recompile with -fPIC
/usr/lib64/gcc/x86_64-suse-linux/7/../../../../x86_64-suse-linux/bin/ld: final link failed: bad value
collect2: error: ld returned 1 exit status

I tried with -fPIC as suggested and it compiles. But when using this library, It cannot be loaded when I add that last function:

void WrapperCreateInstance() {InternalClass* item = new InternalClass(); delete item; }

The problem is using the InternalClass, without this function everything works.

I'm using VirtualBox. I installed OpenSUSE 64bit, the app that uses the library is also 64bit. In another linux distribution (Mint), with exactly the same project and settings (without fPIC), it can be compiled. When I use that library (.so) it works in SUSE.

I'm also using :

  • gcc (SUSE Linux) 7.5.0
  • g++ (SUSE Linux) 7.5.0
  • My IDE is Code::Blocks 20 (last version). Settings are empty except for the -m64 flag.

What am I doing wrong? This seems like something advanced Linux users could help me understand.

EDIT: To add more information, this can compile in Ubuntu with the same settings. Not in SUSE

Darkgaze
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  • What does "It cannot be loaded" mean? – Sam Varshavchik Dec 22 '20 at 12:00
  • @SamVarshavchik It means that I get a DllImportException ( I use it from c# ), but it says the library cannot be loaded in the debug log. No more information returned – Darkgaze Dec 22 '20 at 13:13
  • I've tried reproducing the loading issue (used `-fPIC`) but a simple `dlopen` on the resulting shared library works. Please post what error you get from `dlerror()`, maybe try loading it from a C program first instead of C# – dyp Dec 03 '21 at 11:39

2 Answers2

1

To me it happened, if one library (A) depends on another one (B) and library A was linked before library B. The solution is to link library B first and then A.

nee6AGag
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0

It happened to me when I used GCC to compile a CPP file. So for C++ files use g++ only, and obviously not GCC, which is meant for c files.

Yugank Singh
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