Handling Abnormally Large .so Files After Modifying Build Configuration Parameters

#harmonyos #ndkbuild #dynamiclinking #sofilesizeoptimization

Read the original article：Handling Abnormally Large .so Files After Modifying Build Configuration Parameters

Problem Description

After adding the parameter "arguments": "-v -DOHOS_STL=c++_static" in the module-level build configuration, the .so file size increased abnormally instead of decreasing.
Originally, this modification was intended to remove the dependency on libc++_shared.so, but it unexpectedly caused the .so file to grow significantly.

Background Knowledge

Shared Object (.so) Linking Methods:

Static Linking:
- The library code is compiled directly into the executable or .so file.
- Use the -static option or specify the absolute path of the library file during compilation.
- Advantages: The resulting binary is self-contained and does not depend on external libraries.
- Disadvantages: Each binary includes its own copy of the library, resulting in a much larger .so file and wasted storage space.
Dynamic Linking:
- The program dynamically loads .so libraries at runtime using functions such as dlopen().
- Advantages: Enables flexible runtime loading, reduces binary size, and allows shared usage across applications.
- Disadvantages: Requires managing library dependencies and ensuring library paths are correct.
Symbol Table in .so Files:
- Records information about functions and variables in the shared library (e.g., names, addresses, and sizes).
- Useful for debugging and crash analysis.
- Stripping symbol tables can significantly reduce .so file size.

Analysis Conclusion

When -DOHOS_STL=c++_static is used, the standard C++ library (libc++) is linked statically into your .so file.
This means all the standard library symbols are compiled directly into the .so, leading to a large size increase.
The original shared linking mode (c++_shared) only referenced the shared library dynamically, keeping the .so smaller.

Solution

To reduce .so file size after static linking changes, apply the following optimizations:

1.Set Build Type to Release
Remove debugging information by adding:

   -DCMAKE_BUILD_TYPE=Release

2.Strip Symbol Table
Remove symbol table information to reduce file size by adding:

   cppFlags: "-s"

3.Use Shared Linking Instead of Static Linking
Revert to using shared linking if not strictly required:

   -DOHOS_STL=c++_shared

4.Enable Compiler Optimization for Size
Use -Os or -Oz to optimize for smaller binaries:

   cppFlags: "-Os"
   // or
   cppFlags: "-Oz"

Recommended Configuration Example

"externalNativeOptions": {
  "path": "./src/main/cpp/CMakeLists.txt",
  "arguments": "-DOHOS_STL=c++_shared -DCMAKE_BUILD_TYPE=Release",
  "cppFlags": "-s -Os"
}

This configuration:

Builds in Release mode.
Strips debugging and symbol information.
Uses shared STL linking to prevent library duplication.
Applies size optimization for minimal .so output.

Verification Result

Not applicable — this issue concerns build configuration and file size optimization rather than runtime behavior.
Applicable to NDK-based HarmonyOS native module builds.
Compatible with Release build types only.
Must recompile the project after modifying CMake arguments for changes to take effect.