gcc's fvisibility at compile time or link time

Question

I am trying to limit the ABI of a shared library using the gcc's fvisibility feature. However I am confused what is the correct way to do it.

My makefile organizes the build process in two stages. At the first step all .cpp files are built to object files using some gcc options. Then all the object files are linked together using another set of gcc and ld options. From what I have read fvisibility is relevant to the second step. However this contradicts with the results I observer. If I add fvisibility=hidden to the compile time options the result is as expected, nm -D reporting a much smaller set of exported symbols. On the contrary if I add it to the link time options it does not seem to affect the build.

While looking for an explanation I have compared the object files produced with and without fvisibility. The difference seems to be in the addresses of the symbols inside the object file. However I am not aware how that difference in addresses carries the message to the linker so that it is able to hide the symbols in one of the cases and expose them in the other.

Could anyone please explain to me that. Thank you for your time.

Answer 1

您可能会发现http://gcc.gnu.org/wiki/Visibility非常有用