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?
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.
Here is detailed explanation of why either repeating libraries or using --start/--end-group is required in this situation.
You can normally specify a library more than once to get around this kind of problem, e.g.
$ gcc ... -lsupport -lcpu -lsupport ...
来源：https://stackoverflow.com/questions/4802624/linking-libraries-that-contain-circular-references-in-gcc