How to make an executable shared library with lazarus on linux ?
lazarus / 32-Linux

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njlgg · 2017-12-19 01:11

On linux,some special shared libraries can be dynamically loaded by
other applications, and they can also be executed . There are some
ways of creating such kind of "Executable Library" with C or C++.
      Now the question is:Is it possible and how to make an
"Executable Library" with Lazarus on linux?

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Phil · 2017-12-19 01:14

Quote from: njlgg on December 19, 2017, 02:11:02 am      On linux,some
special shared libraries can be dynamically loaded by other
applications, and they can also be executed . There are some ways of
creating such kind of "Executable Library" with C or C++.
      Now the question is:Is it possible and how to make an
"Executable Library" with Lazarus on linux?

https://macpgmr.github.io/MacXPlatform/PascalDynLibs.html

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njlgg · 2017-12-19 02:02

This article is mainly about compiling a shared library and how to
inter-act with other languages.It does not get the key point of the
question.
Let me introduce the key point  by some pieces of source code on
windows.
*************project source begin**********
program libTest;

{$mode objfpc}{$H+}

uses
  {$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  {$ENDIF}{$ENDIF}
  Interfaces, // this includes the LCL widgetset
  Forms, main
  { you can add units after this };

{$R *.res}

exports
  sayHello;

begin
  RequireDerivedFormResource:=True;
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.
*************project source end**********

*************unit source begin**********
....
function sayHello(msg:String):String;export;stdcall;
begin
   result:='this is from libTest';
end;

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
type
  sayHello = function(msg:String): String;stdcall;
var
  MyLib: TLibHandle = dynlibs.NilHandle;
  FsayHello:sayHello;
begin
   //Please note here that we use Loadlibrary to load the program
itself as a library
    MyLib := LoadLibrary(forms.Application.ExeName);
    FsayHello:=sayHello( GetProcedureAddress(MyLib,'sayHello') );
    ShowMessage( FsayHello('njlgg'));
end;
......
*************unit source end**********

NOTE the project type is "program",not "library",the program exports a
function "sayHello",and we  use Loadlibrary to load the program itself
as a library in the unit code.

On windows,it works as expected,but on linux,if we define the project
type as "program",we get an executable file,we can't load an
executable as library ,or on the other hand ,if we define the project
type as "library",we get a shared library,it can inter-act with other
languages correctly ,but we can't run the library seperately like an
executable program.

So the key point is How to make an "Executable Library" on linux.

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Phil · 2017-12-19 03:05

Quote from: njlgg on December 19, 2017, 03:02:03 amNOTE the project
type is "program",not "library",the program exports a function
"sayHello",and we  use Loadlibrary to load the program itself as a
library in the unit code.

On windows,it works as expected,but on linux,if we define the project
type as "program",we get an executable file,we can't load an
executable as library ,or on the other hand ,if we define the project
type as "library",we get a shared library,it can inter-act with other
languages correctly ,but we can't run the library seperately like an
executable program.

So the key point is How to make an "Executable Library" on linux.

That works fine here on both Windows and Linux (Ubuntu). On Mac I get
a compile error, so it's not a universal thing:

/Users/phil/Tools/laztests/testexeclib/project1.lpr(15,1) Warning:
(3186) Use of unsupported feature!
/Users/phil/Tools/laztests/testexeclib/project1.lpr(15,1) Fatal:
(2003) Syntax error, "BEGIN" expected but "EXPORTS" found

Not sure why you would want a program executable that could also be
loaded as a dynamic library. I would separate out the non-UI code and
put it in a dynamic library and leave the UI code in the program.

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njlgg · 2017-12-19 04:58

Quote from: Phil on December 19, 2017, 04:05:30 am
That works fine here on both Windows and Linux (Ubuntu). On Mac I get
a compile error, so it's not a universal thing:


    MyLib := LoadLibrary(forms.Application.ExeName);
    FsayHello:=sayHello( GetProcedureAddress(MyLib,'sayHello') );
    ShowMessage( FsayHello('njlgg'));

    The above code does work fine on Linux(Ubuntu),but it's a special
occasion.

    Mylib:=LoadLibrary(forms.Application.ExeName) will always get a
value "0",that means the executable program not really been loaded as
library .So if you try to load the executable program as library in
another program,not within itself , error occurs while processing
GetProcedureAddress(MyLib,'sayHello').
    if we try to load the executable program as library from java code
like this:

     static {
         System.load("/home/njlgg/MyDevelop/SoLibraryTest/libTest");
    }
  
   We will get an error:cannot dynamically load executable. The
problem is not solved yet.

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Thaddy · 2017-12-19 08:17

If you do not specify PIC there is no chance that is works on Linux.
Library code *must* be relocatable.

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njlgg · 2017-12-19 09:07

Quote from: Thaddy on December 19, 2017, 09:17:14 amIf you do not
specify PIC there is no chance that is works on Linux. Library code
*must* be relocatable.

I specify -fpic in Project options->compiler options->custom
options,but it doesn't work.Besides, another opition -cd (create also
dynamic library is displayed "not supported").Is that the reason a
program can't be also compiled into a dynamic library?

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Чебурашка · 2022-08-24 14:39

Hello,
for what I understand, the OP question has not been answered yet.

Is is possible with fpc to get a linux shared library that is also
executable?

gcc allows this with the options "-fPIC" "-pie" according to this post
https://unix.stackexchange.com/questions/223385/why-and-how-are-some-
shared-libraries-runnable-as-though-they-are-executables

Thanks

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Fred vS · 2022-08-24 15:01

Quote from: tt on August 24, 2022, 04:39:56 pmHello,
for what I understand, the OP question has not been answered yet.

Is is possible with fpc to get a linux shared library that is also
executable?

gcc allows this with the options "-fPIC" "-pie" according to this post
https://unix.stackexchange.com/questions/223385/why-and-how-are-some-
shared-libraries-runnable-as-though-they-are-executables

Thanks

Hello.

You may "hardening" your executable that will be transformed into a
library runnable.
Just add those parameters for compilation:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i -Cg -k-pie
-znowhttps://wiki.freepascal.org/hardening