linking object files and linking static libraries containing these files

Hello Stack Overflow Community,

i am working on a c project to interleave multiple c programs into one binary, which can run the interleaved programs as treads or forks for benchmarking purposes.

Therefore i run make in each program folder of the desired programs and prelink all .o files with "ld -r" to one new .o file. After that i add a specific named function to each of these "big" .o files, which does nothing but run the main() of each program and providing the argc and argv. Then i use objcopy to localize every global Symbol except the unknown ones and the one of my specific function which shall run the main(). At last i link these manipulated .o files together with my program which runs the specific named functions as threads, or forks or after another.

Now to my Question/Problem: I ran into a problem with static libs. I was using ffmpeg for testing, and it builds static libs such as libavcodc and libavutil and so on. Unfortunately, "ld -r" does not link .a files. So i tried to extract these libs with ar -x and then link the extracted .o files in the way mentioned above to the "big" new .o file. But i did not work because libavcodec and libavutil both include the file ff_inverse.o. That is obviously not a pro开发者_开发百科blem when i just build ffmpeg, which will link these static libraries. But still, both libraries include it, so there must be a machanism which makes the choice, which ff_inverse.o to use and to link. So my Question: How does this work? Where is the difference?

The way ld does it with normal linking is to prioritize the libraries. Libraries listed first in the command line are linked in first, and only if symbols still are unresolved does it move on to the next library. When linking static libraries, it ignores the name of each .o file, because the name is unnecessary, only the exported symbols are necessary. You may want to emulate that behavior, by extracting libraries in a sorted order.