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: greeter.ads ``` package Greeter is procedure Hello; end Greeter; ``` greeter.adb ``` with Ada.Text_IO; use Ada.Text_IO; package body Greeter is procedure Hello is begin Put_Line ("Hello, world!"); end Hello; end Greeter; ``` And compile them into a shared object like this: ``` gnatmake -z -fPIC greeter.adb gcc -shared -o libgreeter.so greeter.o ``` This compiles fine. `nm` shows the following symbols: ``` $ nm -D libgreeter.so w _Jv_RegisterClasses 0000000000201028 A __bss_start w __cxa_finalize w __gmon_start__ U __gnat_eh_personality 0000000000201028 A _edata 0000000000201038 A _end 00000000000006a8 T _fini 0000000000000520 T _init U ada__text_io__put_line__2 0000000000201018 D greeter_E 000000000000063c T greeter__hello ``` Now I try to load that shared object in Perl: ``` #!/usr/bin/env perl use 5.014; use strict; use warnings; #BEGIN…

Accepted Answer

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_name`init` and library_name`final` - 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 <stdio.h>

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
```

Loading Ada shared objects in Perl with DynaLoader.pm

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