Dynamic Libraries

Doug Hardie bc979 at lafn.org
Wed Mar 7 20:37:17 UTC 2012

On 7 March 2012, at 01:40, Volodymyr Kostyrko wrote:

> Doug Hardie wrote:
>> I have encountered something that I do not understand.  Everything works fine.  Basically I have a bunch of user modules (low level) that are built into a dynamic library.  If I write top level code that calls modules in that library, everything works just fine on i386 and AMD64.  However, the application involved has another library of modules.  Some of them call modules in the low level library.  The top level code call modules in both libraries.  Often when it calls a module in the mid level library, that module calls several modules in the low level library.
>> All this works just fine on i386.  However, when I compile everything on AMD64 I get an error message that says the lower level library needs to be compiled with fPIC.  If I add that to the Makefile for the lower level library and rebuild everything, it all works again.  I don't understand why the fPIC is required for AMD64.
>> Also, how do I tell if the lower level library is being dynamically linked at run time, or being directly incorporated into the mid level library or top level application?  Since both of these libraries are quite large, and they are in use by a number of top level applications, I want just one copy to exist in physical memory.
> This sounds exactly like compiling with clang through ccache. There are issues with clang and ccache cooperation. Actually the one you may hit is libtool detecting implicit fPIC requirement when running clang through ccache.

The Makefile specifies GCC and its FreeBSD 8.0.  I don't believe clang was in that soon, but I may be wrong.  How can I check that?  Where is clang?  I have installed 9.0 on another system but haven't had time to try that out yet.

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