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Asked: 2026-05-16T08:37:22+00:00

I have created a .c file which is being converted to a .o file

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I have created a .c file which is being converted to a .o file along with around 300 other .c files and included in a .a static library. This library, along with many others is being used to create a .so dynamic library. On analyzing both the .a and the .so file with nm, I found that for some reason the symbols defined in the .c file are present in the .a file but not in the .so file. I can think of no reason this should happen. Can somebody please help me out here? The steps used to create the two binaries are:

gcc -fvisibility=hidden -c foo.c -o foo.c.o
ar cr libbar.a foo.c.o ...
gcc -fvisibility=hidden -fPIC -o libfinal.so libbar.a x.o y.a ...

The reason I have specified visibility hidden here is that I want to expose only a few selected symbols. To expose the symbols from foo.c I have specified the visibility attribute so that the functions signatures in the header foo.h look like:

extern int _____attribute_____ ((visibility (“default”))) func();

EDIT: The command nm libbar.a | grep Ctx gives:

000023c5 T CtxAcquireBitmap
000026e9 T CtxAcquireArray
00001e77 T CtxCallMethod

However, nm libfinal.so | grep Ctx does not show anything.

UPDATE: Found another post which discusses the uses of the --whole-archive option. Also, stumbled across the --export-dynamicoption which apparently tells the linker to retain unreferenced symbols. Investigating further.

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1 Answer

  1. Editorial Team

    Creating a dummy reference for the required symbols in my main file did not solve the problem. The referenced symbols appeared in the binary dump (obtained using nm) with a U (= undefined) marker. I managed to solve the problem by linking the object file directly when creating the .so file instead of including it in the .a library first. As these functions were marked extern they were included in the .so even though they were not being referenced within the library. Had they not been marked extern, they would not have been included just like sylvainulg said.

    Thanks to Dmitry for pointing out the --whole-archive option. I did not know that such an option exists.

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