Re: Fun trick

On 1/9/2025 8:01 AM, hb0815 wrote:

On 1/9/25 02:00, Arne Vajhøj wrote:

Hmmm.
>
It works in C, but it does not seem to work in
any other language (tested with Pascal and Fortran).
...
I assume the difference relates to user code main not being
the real program entry.

 So, make it a main entry.
 This is on Alpha. It should work on IA64 and x86. I don't have access to any of the latter systems. If this does not work on these systems, I know how to make it work, anyway.
 $ gdiff -ub lib.pas-orig lib.pas

$ gdiff -ub lib.for-orig lib.for

For those that do not speak diffish:
$ type prg.c
#include <stdio.h>
extern void say();
int main(int argc, char *argv[])
{
     say();
     return 0;
}
$ type lib.c
#include <stdio.h>
void say()
{
     printf("Hi\n");
}
int main()
{
     printf("This is a shareable image to link against not run\n");
     return 0;
}
$ cc lib
$ link/share=libshr lib + sys$input/opt
symbol_vector=(say=procedure)
$
$ define/nolog libshr sys$disk:[]libshr
$ cc prg
$ link prg + sys$input/opt
libshr/share
$
$ run prg
Hi
$ run libshr
This is a shareable image to link against not run
$ type prg.pas
program prg(input,output);
[external]
procedure say; external;
begin
    say;
end.
$ type lib.pas
program lib(input, output);
[global]
procedure say;
begin
    writeln('Hi');
end;
begin
    writeln('This is a shareable image to link against not run');
end.
$ pas lib
$ link/share=libshr lib + sys$input/opt
symbol_vector=(say=procedure)
$
$ define/nolog libshr sys$disk:[]libshr
$ pas prg
$ link prg + sys$input/opt
libshr/share
$
$ run prg
Hi
$ run libshr
This is a shareable image to link against not run
$ type prg.for
       program prg
       call say
       end
$ type lib.for
       program lib
       write(*,*) 'This is a shareable image to link against not run'
       end
c
       subroutine say
       write(*,*) 'Hi'
       end
$ for lib
$ link/share=libshr lib + sys$input/opt
symbol_vector=(say=procedure)
$
$ define/nolog libshr sys$disk:[]libshr
$ for prg
$ link prg + sys$input/opt
libshr/share
$
$ run prg
Hi
$ run libshr
This is a shareable image to link against not run
So I think the conclusion must be that one should
not think the traditional grouping:
* executable image
* shareable image
but instead:
* image with transfer address
* image with symbol vector
* image with both transfer address and symbol vector
:-)
I believe that is rare for native code.
But common for non-native code.
$ type prg.py
import lib
if __name__ == '__main__':
     lib.say()
$ type lib.py
def say():
     print('Hi')
if __name__ == '__main__':
     print('This is a library not a program')
$ python prg.py
Hi
$ python lib.py
This is a library not a program
$ type Prg.java
public class Prg {
     public static void main(String[] args) {
         Lib.say();
     }
}
$ type Lib.java
public class Lib {
     public static void say() {
         System.out.println("Hi");
     }
     public static void main(String[] args) throws Exception {
         System.out.println("This is a library not a program");
     }
}
$ javac Prg.java Lib.java
$ java Prg
Hi
$ java Lib
This is a library not a program
Arne