DllMain/DllMainCRTStartup does not execute in DLL - dll

Question

The initialization code in a DLL build with gnat is not running automatically when imported. I did a MCVE that consists on:
division.ads
with System;
with Interfaces.C;
package Division is
--Neither of these work
procedure DllMainCRTStartup ;
pragma Export (StdCall, DllMainCRTStartup , "DllMainCRTStartup"); --Edited as noticed by Brian
-- procedure DllMain
-- pragma Export (StdCall, DllMain , "DllMain ");
function Div (A : in INTEGER; B : in INTEGER) return INTEGER;
pragma Export (C, Div, "MyDivision");
-- --If I put this, it does not compile... maybe a wrong linkage option set?
-- procedure AdaInit;
-- pragma Import (C, AdaInit, "adainit");
end Division;
division.adb
with text_io;
package body Division is
procedure DllMainCRTStartup is begin --DllMain or DllMainCRTStartup
text_io.put("INIT CODE YEAH!!!*************!"); --This does not execute :(
--AdaInit;
end DllMainCRTStartup ;
function Div(A : in INTEGER; B : in INTEGER) return INTEGER is
X : INTEGER := A/B;
begin
return X;
end Div;
end Division;
and the gpr:
library project Proj_Name is
for Library_Name use "math";
for Object_Dir use "obj";
for Source_Dirs use ("src");
for Library_Dir use "lib";
for Library_Interface use ("Division");
for Library_Kind use "dynamic";
for Library_Options use ("-LC:\GNAT\2015\lib\gcc\i686-pc-mingw32\4.9.3\adalib",
"-LC:\GNAT\2015\lib\gcc\i686-pc-mingw32\4.9.3\adalib\libgnat");
end Proj_Name;
I am testing the dll from python, with ctypes. I import it with ctypes.CDLL and I'm able to use MyDivision. However, the init code does not run when importing the dll, as the text_io is not executed.
On the other hand, if I add the AdaInit procedure to the code I get something like this when compiling:
undefined reference to `adainit'
Thank you very much!

Answer 1

I’m not sure how you know that the initialization code isn’t being run?
I’m running on macOS, but the Ada aspects should be similar. I wrote this package spec/body as a simpler version of yours:
package Division is
function Div (A : in INTEGER; B : in INTEGER) return INTEGER;
pragma Export (C, Div, "MyDivision");
end Division;
with Ada.Text_IO;
package body Division is
function Div(A : in INTEGER; B : in INTEGER) return INTEGER is
X : INTEGER := A/B;
begin
return X;
end Div;
procedure Test_For_Elaboration is
begin
Ada.Text_IO.Put_Line ("hello world!");
end Test_For_Elaboration;
begin
Test_For_Elaboration;
end Division;
with this simpler GPR
library project Proj_Name is
for Library_Name use "math";
for Object_Dir use "obj";
for Source_Dirs use ("src");
for Library_Dir use "lib";
for Library_Interface use ("Division");
for Library_Kind use "dynamic";
end Proj_Name;
and tested with this C code:
#include <stdio.h>
extern int MyDivision(int, int);
int main()
{
printf("42 / 2 => %d\n", MyDivision(42, 2));
return 0;
}
and the result was
$ ./caller
hello world!
42 / 2 => 21
so clearly, for me, library elaboration was called without my having to do anything.
The reason is that you specified Library_Interface in your project file, which means you’re building a stand-alone library, which
is a library that contains the necessary code to elaborate the Ada units that are included in the library. A stand-alone library is a convenient way to add an Ada subsystem to a more global system whose main is not in Ada since it makes the elaboration of the Ada part mostly transparent.
You can specify a stand-alone dynamic library which is not automatically initialized, using
for Library_Auto_Init use "false";
in which case you need to call the library’s initialization procedure yourself; it's called {library-name}init (in your case, mathinit). But then you need to call it from your main program; it’d need to be declared, in C
extern void mathinit();