How do I compile DDS code into a shared library in Linux?

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How do I compile DDS code into a shared library in Linux?

Is it possible to compile RTI DDS code into a shared library, like a .so, and call it from another application? It would be nice if someone already done it with Eclipse, and post the instruction here on the forum. Or is there a makefile that RTI have that can compile DDS example code into the shared library? Please help. Thanks

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Hi Joseph,

I assume that you want to create a shared library with the code generated by rtiddsgen so that you can link it against other applications. If that is the case, you can do the following:

First, generate an example makefile. In this case we are using C++ and the architecture is x64Linux3gcc4.8.2, but this applies to any other platform.

$ rtiddsgen -language C++ -example x64Linux3gcc4.8.2 hello.idl

This should have generated a makefile called makefile_hello_x64Linux3gcc4.8.2. We are going to make a copy of the original makefile and call it makefile_hello_x64Linux3gcc4.8.2.original, that way you can compare the changes to the original file. 

$ cp makefile_hello_x64Linux3gcc4.8.2 makefile_hello_x64Linux3gcc4.8.2.original

From now on we will editing makefile_hello_x64Linux3gcc4.8.2. In that makefile will find that we are actually building two executables: hello_publisher and hello_subscriber. We are now going to make some changes to link those executables against a shared library that we are going to create and that will contain all the type plugins generated by rtiddsgen. To do so modify the makefile as follows:

  1. Add -fPIC to your compiler flags.
     COMPILER_FLAGS = -m64 -Wall -fPIC
    
  2. Declare a variable called SHARED_LIB where you will name your shared library (e.g., libhello.so).
     EXEC          = hello_subscriber hello_publisher
    SHARED_LIB    = libhello.so
    
  3. Create a new target in the makefile called objs/$(TARGET_ARCH)/$(SHARED_LIB)
     objs/$(TARGET_ARCH)/$(SHARED_LIB): $(COMMONOBJS)                                                                                                                               
            $(LINKER) $(LINKER_FLAGS) -shared -o $@ $(COMMONOBJS) $(LIBS)                                                                                                
    
  4. Add the new target to the dependencies of  $(TARGET_ARCH):
     # We actually stick the objects in a sub directory to keep your directory clean.                                                                                               
    $(TARGET_ARCH) : $(DIRECTORIES) $(COMMONOBJS) \                                                                                                                                
            objs/$(TARGET_ARCH)/$(SHARED_LIB) \                                                                                                                                    
            $(EXEC:%=objs/$(TARGET_ARCH)/%.o) \                                                                                                                                    
            $(EXEC:%=objs/$(TARGET_ARCH)/%)                                                                                                                           
    
  5. Modify the objs/$(TARGET_ARCH)/% target to use the new shared library instead of the orignial common object files:
     objs/$(TARGET_ARCH)/% : objs/$(TARGET_ARCH)/$(SHARED_LIB)                                                                                                                      
            $(LINKER) $(LINKER_FLAGS) -o $@ $@.o \                                                                                                                               
            objs/$(TARGET_ARCH)/$(SHARED_LIB) $(LIBS)                                                                                                                           
    

Once you have done those changes, you can run the makefile as follows. You will find the library and executables you have created under objs/$(TARGET_ARCH):

$ make -f makefile_hello_x64Linux3gcc4.8.2
$ ls objs/x64Linux3gcc4.8.2/
hello.o helloPlugin.o hello_publisher hello_publisher.o hello_subscriber hello_subscriber.o helloSupport.o libhello.so
$ ldd objs/x64Linux3gcc4.8.2/hello_publisher
	linux-vdso.so.1 =>  (0x00007fffde1ab000)
	objs/x64Linux3gcc4.8.2/libhello.so (0x00007fb24e117000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fb24deef000)
	libnsl.so.1 => /lib/x86_64-linux-gnu/libnsl.so.1 (0x00007fb24dcd5000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fb24dab8000)
	librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007fb24d8b0000)
	libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007fb24d52d000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fb24d224000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fb24ce5b000)
	libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fb24cc44000)
	/lib64/ld-linux-x86-64.so.2 (0x0000560240da3000)

Please, let me know if this is what you were looking for or you have doubts on how to make the appropriate changes in your makefile. I think it is probably better to do these changes at the makefile level, so that you can compile both from Eclipse and from the command line.

Thanks,
Fernando.

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Thanks Fernando. I didn't expect to get a quick answer, but you did. Thanks again, and it works perfect.

Just little mispell on line 64 "LIKER" should be "LINKER"

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That is great! I have just fixed line 64, thanks for pointing that out.

Best,
Fernando.

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And I am trying to model your makefile to do a static library, but no luck. Would you be kind and show me how to compile and build a static library also? Thanks Fernando.

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Hi Joseph,

If you want to create a static library as well you will need to use the ar archiver. Plese, modify your makefile as follows:

  1. Declare your archiver:
    ifndef ARCHIVER                                                                                                                                                                                                    
    ARCHIVER = ar                                                                                                                                                                                                      
    endif                                                                                                                                                                                                              
    
  2. Declare the name of your static library:
    STATIC_LIB    = libhello.a
  3. Create a new target to create the static library.
    objs/$(TARGET_ARCH)/$(STATIC_LIB): $(COMMONOBJS)                                                                                                                                                                   
            $(ARCHIVER) rcs $@ $(COMMONOBJS)
    
  4. Add the new target to the list of dependencies for $(TARGET_ARCH):
    # We actually stick the objects in a sub directory to keep your directory clean.                                                                                                                                   
    $(TARGET_ARCH) : $(DIRECTORIES) $(COMMONOBJS) \                                                                                                                                                                    
            objs/$(TARGET_ARCH)/$(SHARED_LIB) \                                                                                                                                                                        
            objs/$(TARGET_ARCH)/$(STATIC_LIB) \                                                                                                                                                                        
            $(EXEC:%=objs/$(TARGET_ARCH)/%.o) \                                                                                                                                                                        
            $(EXEC:%=objs/$(TARGET_ARCH)/%)                                                                                                                                                                            
    
  5. Optionally modify the way you build your executables to link against the new static library:
    objs/$(TARGET_ARCH)/% : objs/$(TARGET_ARCH)/$(SHARED_LIB)                                                                                                                                                          
            $(LINKER) $(LINKER_FLAGS)   -o $@ $@.o \                                                                                                                                                                   
            objs/$(TARGET_ARCH)/$(STATIC_LIB) $(LIBS)                                                                                                                                                                  
    

Please, let me know if this solves your issue.

Thanks,
Fernando 

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Yes sir. That solves it. Thank you, thank you.

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Fernando,

If I use this static library (libhello.a) to link into another application, do I need to set any RTI DDS compiler/linker flags in that application at all? Just link the library, and specify the path, and add the include file? I am not sure why I can't call the function inside the lib. Do you have any suggestion? Thanks

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Hello Mr Fernando

I have incorporated the changes as given by you. But i am getting errors like publisher.o file not found etc. while i am running my makefile. 

Kindly help.

 

 

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Hi Shikha,

Are you modifying the makefile generated by rtiddsgen? Could you post makefile so that we can help you figure out the problem?

Thanks,
Fernando.

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Hello Fernando,

I am trying to create shared library( static and dynamic) . I am getting the below error. Also attached the makefile

/usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/crt1.o: In function `_start':
(.text+0x24): undefined reference to `main'
collect2: error: ld returned 1 exit status
make: *** [makefile_SimulatorIDL_x64Linux4gcc7.3.0:105: objs/x64Linux4gcc7.3.0/libRTISimulator.so] Error 1
[paras@localhost RTI_SIM]$ vi makefile_SimulatorIDL_x64Linux4gcc7.3.0

 

 

Regards

Chand