10.1 Building modules to dlopen

On some operating systems, a program symbol must be specially declared in order to be dynamically resolved with the dlsym (or equivalent) function. Libtool provides the ‘-export-dynamic’ and ‘-module’ link flags (see section Link mode), for you to make that declaration. You need to use these flags if you are linking an application program that dlopens other modules or a libtool library that will also be dlopened.

For example, if we wanted to build a shared library, ‘hello’, that would later be dlopened by an application, we would add ‘-module’ to the other link flags:

burger$ libtool --mode=link gcc -module -o hello.la foo.lo \
                hello.lo -rpath /usr/local/lib -lm
burger$

If symbols from your executable are needed to satisfy unresolved references in a library you want to dlopen you will have to use the flag ‘-export-dynamic’. You should use ‘-export-dynamic’ while linking the executable that calls dlopen:

burger$ libtool --mode=link gcc -export-dynamic -o helldl main.o
burger$

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