Re: Fun trick

On 1/8/2025 5:31 PM, hb0815 wrote:

On 1/8/25 23:20, Arne Vajhøj wrote:

On 1/8/2025 5:11 PM, hb0815 wrote:

On 1/8/25 02:58, Arne Vajhøj wrote:

During some troubleshooting over at VSI forum hb told me that
running a shareable image will execute LIB$INITIALIZE
functions.
>
That made me write this:

>
Yeah, but ... You do not need init code for this.

>
Oh.
>
Can one get a transfer address into a shareable image?

$ ty s.c
#include <stdio.h>
static int firstFunctionInThisModuleBecomesTheEntryPoint () {
   printf ("It's the shareable, stupid!\n");
   return 1;
}
int foo () {
   printf ("This is %s\n", __func__);
   return 1;
}
$ cc s/stand=rel
$ link/share s,tt:/opt ! symbol_v=(foo=proc)
symbol_v=(foo=proc)
  Exit
$ r s
It's the shareable, stupid!

Hmmm.
It works in C, but it does not seem to work in
any other language (tested with Pascal and Fortran).
$ type prg.c
#include <stdio.h>
extern void say();
int main(int argc, char *argv[])
{
     say();
     return 0;
}
$ type lib.c
#include <stdio.h>
int ooops()
{
     printf("This is a shareable image to link against not run\n");
     return 1;
}
void say()
{
     printf("Hi\n");
}
$ 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
[inherit('sys$library:starlet')]
module lib(input, output);
[global]
procedure ooops;
begin
    writeln('This is a shareable image to link against not run');
    $exit(ss$_normal);
end;
[global]
procedure say;
begin
    writeln('Hi');
end;
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
%DCL-E-NOTFR, no transfer address
$ type prg.for
       program prg
       call say
       end
$ type lib.for
       subroutine ooops
       include '($ssdef)'
       write(*,*) 'This is a shareable image to link against not run'
       call sys$exit(ss$_normal)
       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
%DCL-E-NOTFR, no transfer address
I assume the difference relates to user code main not being
the real program entry.
Arne