Create and Use Shared Libraries

Building and Using .so Files

Shared libraries let many processes map one physical copy of libc. Compile with -fPIC, link with -shared. Export symbols with default visibility; hide internals. LD_LIBRARY_PATH and rpath control search paths at runtime.

Create and Link Against

Build the shared object first, then link the main program against it. The dynamic linker resolves libfoo.so at startup using DT_NEEDED entries and search paths baked into the executable.

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• SONAME (libfoo.so.1) supports versioned ABI
• nm -D shows dynamic symbols
• -Wl,--export-dynamic exports symbols for dlsym
• ABI stability: do not change struct layouts casually

Connecting to real compilers

Production compilers embed this step inside a longer pipeline. GCC flows through cpp, cc1, assembly, and ld; Clang uses the driver, Sema, LLVM IR passes, and a target backend. LLVM bitcode, JVM bytecode, and WASM are other familiar IRs at the same layer. The exercise isolates one pass so you can test it alone before chaining it to the next stage.

Why for this exercise

You will create and use shared libraries. This exercise requires building a PIC shared object, exporting functions, and linking an executable that calls into the library at runtime.