How to determine inter-library dependencies?

Question

My project consists of a couple of static libraries, which are linked together in a final step. Now I have the problem, that the link order of the library is important (othe

Answer 1

If you truly have a circular dependency chain of static libraries (and this is not clear from your paste; you show only a non-circular dependency), there are two options:

1. Remove the circular dependency somehow; for example, you could make sure libcommon does not reference symbols in libpthardware.
2. Extract the individual .o files from the .a library, and link them directly. Then link order no longer matters.

In the case of 2., you may find it helpful to use partial linking rather than creating static libraries. On systems using GNU bintools, this can be done by invoking something like:

ld -r -o libfoo.o foo.o bar.o

The effect of this is to combine foo.o and bar.o into a single .o file. The order does not matter. You can then simply reference libfoo.o as a normal object file in your final link step.

Note that doing this may interfere with the linker's ability to discard unreferenced portions of the static library (normally this is done at the level of .o files within the .a, I believe). If you're using all or most of these libraries, this is probably not a problem. However, if code memory is an issue, you may want to look into automatically discarding unused code at the function level. If you do this, pass --gc-sections and -s only at the final link stage (and avoid doing so if you need to debug!). Also, static linking with system libraries does not seem to be necessary with modern gcc.