Linking Libraries that contain circular references

问题:

I am trying to link an application with multiple static libraries in GCC.

There are two libraries that cause problems. Libsupport provides a terminal for the application. It relies on libcpu to provide a serial link, timing and syncronisation. Libcpu relies on libsupport to provide queueing for serial data and more.

If I specify libsupport first when linking libcpu cannot be linked with the queue functions. Is I specify libcpu first lib support can not link the serial link (and more) functions.

It looks like GCC parses a library only once and discard any unused objects.

Can I ask gcc to parse libraries multiple times or to include all objects?

回答1:

gcc ... -lsupport -lcpu -lsupport -lcpu

-> Each mention of a library will cause resolution of libraries that came before it (but not necessarily ones specified afterwards), which is why you may need to specify more "-lsupport -lcpu" in future.

Alternatively, try --start-group -lsupport -lcpu --end-group once.

回答2:

Here is detailed explanation of why either repeating libraries or using --start/--end-group is required in this situation.

回答3:

You can normally specify a library more than once to get around this kind of problem, e.g.

$ gcc ... -lsupport -lcpu -lsupport ...