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Asked: 2026-06-10T01:47:09+00:00

I have a question regarding an article of JNI at http://java.sun.com/developer/onlineTraining/Programming/JDCBook/jniexamp.html . gcc -o

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I have a question regarding an article of JNI at http://java.sun.com/developer/onlineTraining/Programming/JDCBook/jniexamp.html.

gcc  -o libnativelib.so -shared -Wl,-soname,libnative.so  
     -I/export/home/jdk1.2/include 
     -I/export/home/jdk1.2/include/linux nativelib.c  
     -static -lc

I guess I am still a little confused with the function of ‘-o libnativelib.so’ and ‘-Wl,-soname,libnative.so’.

‘-o libnativelib.so’ specify the name of output file of gcc to be libnativelib.so. From what i understand it is the library name to load from JAVA side as shown in the article:

  static {
    System.loadLibrary("nativelib");
  }

So what’s the use of ‘-Wl,-soname,libnative.so’?

I found following info on ld option manual:

-soname=name

When creating an ELF shared object, set the internal DT_SONAME field to the specified name. When an executable is linked with a shared object which has a DT_SONAME field, then when the executable is run the dynamic linker will attempt to load the shared object specified by the DT_SONAME field rather than the using the file name given to the linker.

So what does it mean? When final executable is run, linker will attempt to load ?? rather than ?? in the name of ??

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1 Answer

  1. Editorial Team

    This is useful for a system, where one library can be present under several names, for example: libz.so, libz.so.1, libz.so.1.2.3. All these libraries are symlinks to one file, and DT_SONAME inside it points to “libz.so.1”. When you link your code against libz.so, it will record dependency on “libz.so.1” in the executable file. And when your file is executed on another system, which contains, say, libz.so.1.2.5, it will still work, because it will look for libz.so.1. But if the destination system will have much newer version, like libz.2.3.4, it will fail, because libz.so.2, but not libz.so.1 will be present.

    DT_SONAME field is used only by linker. When you use System.loadLibrary(), the file name is specified by you, and the value of this option is not used. If you want, you can implement a similar versioning scheme for you libnative, to ensure that you java code always load a compatible version.

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