Loading Ada shared objects in Perl with DynaLoader.pm

Question

Long time listener, first time caller. I\'m aware this is a somewhat obscure question, and don\'t expect too much. :-)

I have the following Ada files:

gr

Answer 1

I can't help with the Perl side (you require 5.14, Mac OS X has 5.12, Debian 6 has 5.10). That said, I can help with building the library for a C main and direct linking ...

The GNAT build process is sufficiently complicated that there are two tools to support it, gnatmake and gprbuild. It’s likely (writing at September 2015) that gnatmake will lose the ability to build libraries, so gprbuild is the better option.

I think you need a stand-alone library project (that is, one with the initialization and finalization operations that control Ada elaboration; if you don't initialize the Ada library, you'll get SEGVs or other bad behaviours). You'll find the lowdown on building one here.

The greeter.gpr I wrote is

project Greeter is
   for Library_Name use "greeter";
   for Library_Kind use "relocatable";
   for Library_Dir use "lib";
   for Library_Interface use ("greeter");
   for Library_Auto_Init use "true"; -- the default, I think
   for Object_Dir use ".build"; -- to keep temp objects out of the way
end Greeter;

The Library_Name attribute controls the name of the library; libgreeter.dylib on Mac OS X, libgreeter.so on Linux.

The Library_Kind attribute could alternatively be "static", in which case the name would be libgreeter.a. However, stand-alone libraries must be relocatable.

The Library_Dir attribute, which you have to supply (with the two above) to make a library at all, controls where the library is created; in this case, in lib/.

You have to supply the Library_Interface attribute to make it a stand-alone library and generate the initialization and finalization operations that control Ada elaboration. They're called library_nameinit and library_namefinal - here, greeterinit, greeterfinal.

If Library_Auto_Init is "false" you have to call the initialization and finalization operations yourself, if "true", they're managed automagically.

OK, build the library by

gprbuild -p -P greeter

(-p says "create any needed output directories", -P specifies the project file).

I built greeter.c

#include 

extern void greeter_hello();

int main()
{
  greeter__hello();
  return 0;
}

using

$ gcc greeter.c -o greeter -L lib -l greeter

and run (on Linux) using

$ LD_LIBRARY_PATH=./lib ./greeter