How to merge multiple .so shared libraries?

The need to merge multiple .so shared libraries typically arises in scenarios where simplifying application dependencies or reducing startup time is desired. Merging reduces the number of shared libraries the dynamic linker must load, optimizing performance. Below are two common methods for merging .so shared libraries.

Method One: Static Linking

1. Static Extraction: First, extract the object files from each .so library and convert them into a static library (.a).

   • Use the ar tool to extract .o files from each .so file: ar -x libexample.so
   • Then use the ar tool to package all .o files into a new static library file: ar -crs libcombined.a *.o

2. Linking at Compile Time: When compiling the final application, link with the newly created static library (instead of the original dynamic libraries).

   • Modify the compilation command to: gcc -o application application.c -L. -lcombined -static

Method Two: Creating a Super Shared Library

1. Using a Linker Script: Create a linker script (e.g., combine.ld) that lists all the .so files to be merged.

   • Use the linker script and ld tool to generate a new .so file: ld -T combine.ld -o libcombined.so

2. Verifying the Merge:

   • Use ldd libcombined.so to verify that all original dependencies are included.
   • Ensure the new .so file contains all required symbols and functionality.

Real-World Example

In one of my projects, I needed to merge several shared libraries provided by third parties, commonly used for image processing, into a single library. Using the static linking method, I first extracted the object files from each library and then packaged them into a single static library. This not only simplified the deployment process but also reduced the complexity of runtime dynamic library lookup. After merging, porting to a new Linux environment became more straightforward, without needing to worry about the presence of specific versions of dynamic libraries.

Important Considerations

• Ensure there are no namespace or symbol conflicts.
• Confirm that all copyright and licensing requirements are still satisfied.
• Perform comprehensive testing to ensure the merged library functions correctly.

By using these methods and considerations, we can effectively merge multiple .so shared libraries, optimizing application deployment and execution efficiency.