How to dynamically load and call a function in a BPL package - delphi

Question

It seems pretty straightforward but the code below doesn't work.
BPL:
procedure DoSomething();
begin
LogEvent('Did');
end;
exports
DoSomething;
Main EXE:
procedure CallModuleFunc;
var
H: THandle;
P: procedure();
begin
H := LoadPackage('mymod.bpl');
try
if (H <> 0) then
begin
#P := GetProcAddress(H, 'DoSomething');
if Assigned(P) then
P();
end;
finally
UnloadPackage(H);
end;
end;
Now there's no error, the bpl loads successfully with LoadPackage() but GetProcAddress() returns nil. Why? probably because name mangling. I've tried adding stdcall (both exported function and P's declaration) but that didn't solve the problem. I've seen hundreds of examples on the web that it's supposed to be working this way. I even tried GetProcAddress(H, 'DoSomething$qqsv') but it didn't work either. What am I missing here?

Answer 1

After hours of searches and trial and errors, I realized it had to be about something I do or did differently. The problem was that my very first version of mymod.bpl was put into Delphi's default BPL output directory (which had no export, no DoSomething() at all). Then, I had changed the BPL output directory to my project's root source directory, so that I could see the sources and the bpl modules in one place. The exe was not put into where the sources reside as it used to be in Delphi 7, it was under Debug or Release folders. What misdirecting me was that when LoadPackage() cannot find the module in exe's current dir (which was Debug/Release) it looks at Delphi's default package folder (which had the very first and wrong version of the bpl) and loads it, so no error there but also no DoSomething() because it was no longer updated by my module's compile.
I hope this explanation helps someone else who might have a similar issue to figure things out. Thanks to everyone who spared time to read this and written comments.

Answer 2

See below a piece of code.
It's running under Delphi XE3.
// Package declaration
package Package1;
{$R *.res}
{$IFDEF IMPLICITBUILDING This IFDEF should not be used by users}
{$ALIGN 8}
{$ASSERTIONS ON}
{$BOOLEVAL OFF}
{$DEBUGINFO ON}
{$EXTENDEDSYNTAX ON}
{$IMPORTEDDATA ON}
{$IOCHECKS ON}
{$LOCALSYMBOLS ON}
{$LONGSTRINGS ON}
{$OPENSTRINGS ON}
{$OPTIMIZATION OFF}
{$OVERFLOWCHECKS OFF}
{$RANGECHECKS OFF}
{$REFERENCEINFO ON}
{$SAFEDIVIDE OFF}
{$STACKFRAMES ON}
{$TYPEDADDRESS OFF}
{$VARSTRINGCHECKS ON}
{$WRITEABLECONST OFF}
{$MINENUMSIZE 1}
{$IMAGEBASE $400000}
{$DEFINE DEBUG}
{$ENDIF IMPLICITBUILDING}
{$IMPLICITBUILD ON}
requires
rtl,
vcl;
contains
Unit1 in 'Unit1.pas';
end.
The unit Unit1.pas
unit Unit1;
interface
uses Vcl.Forms;
procedure Test(); stdcall;
exports
Test;
implementation
procedure Test();
var F : TForm;
begin
F := TForm.Create(nil);
F.ShowModal;
F.Release;
end;
end.
The Project for testing bpl.
Contains only one Tform with one TButton.
(Package1.bpl is in the same directory of project1.exe)
unit Unit2;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;
type
TForm2 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Déclarations privées }
public
{ Déclarations publiques }
end;
var
Form2: TForm2;
implementation
{$R *.dfm}
procedure TForm2.Button1Click(Sender: TObject);
type
TProcTest = procedure;
var
PackageModule: HModule;
proc : TProcTest;
begin
PackageModule := LoadPackage('Package1.bpl');
if PackageModule <> 0 then
begin
#Proc := GetProcAddress( PackageModule, 'Test' );
if #Proc <> nil then
Proc;
UnloadPackage(PackageModule);
end;
end;
end.

Answer 3

You must have to add stdCall in your declaration.
procedure DoSomething();stdcall;
begin
LogEvent('Did');
end;
exports
DoSomething;