[fpc-devel] Problems linking FPC-built library into C program on linux x86_64

[Michael Van Canneyt]

On Thu, 25 May 2006, Dominique Leducq wrote:

> On Wed, 24 May 2006 15:40:27 +0200
> Dominique Leducq <dleducq at magellan-ing.fr> wrote:
>
>> On Wed, 24 May 2006 11:49:03 +0200 (CEST)
>> Michael Van Canneyt <michael at freepascal.org> wrote:
>>
>>>
>>>
>>> On Wed, 24 May 2006, Dominique Leducq wrote:
>>>
>>>> Hi again,
>>>>
>>>> I still don't succeed in linking Free Pascal compiled code with a C program.
>>>>
>>>> When linking with the shared library built by fpc, I have problems with undefined symbols, which are defined in the loaders.
>>>>
>>>> $ gcc -o test_shared test2.o -L. -lsoTest3
>>>> ./libsoTest3.so: undefined reference to `__stkptr'
>>>> ./libsoTest3.so: undefined reference to `_haltproc'
>>>> ./libsoTest3.so: undefined reference to `operatingsystem_parameter_argc'
>>>> ./libsoTest3.so: undefined reference to `operatingsystem_parameter_argv'
>>>> collect2: ld returned 1 exit status
>>>>
>>>> When linking in the loader prt0.o too, there are symbol conflicts with /usr/lib/crt1.o (_start, __data_start) if I call ld through gcc.
>>>>
>>>> $ gcc -o test_shared test2.o prt0.o -L. -lsoTest3
>>>> prt0.o: In function `_start':
>>>> (.text+0x0): multiple definition of `_start'
>>>> /usr/lib/gcc/x86_64-linux-gnu/4.0.3/../../../../lib64/crt1.o:../sysdeps/x86_64/elf/start.S:65: first defined here
>>>> prt0.o: In function `data_start':
>>>> (.data+0x0): multiple definition of `__data_start'
>>>> /usr/lib/gcc/x86_64-linux-gnu/4.0.3/../../../../lib64/crt1.o:(.data+0x0): first defined here
>>>> collect2: ld returned 1 exit status
>>>>
>>>>
>>>> Exactly the same happens when linking statically.
>>>>
>>>>
>>>>  If I call ld directly, linking succeeds, but the main() of the C program never gets called...
>>>>
>>>> However, according to the FPC Programmer's Guide, "using a pascal library from a C program" (12.4) seems to be supported...
>>>>
>>>> Do I miss something ?
>>>
>>> That statement means that you can create a separate library,
>>> which can be called from a C program.
>>>
>>
>> That is actually what I want to do. How can I achieve this ? I followed the steps in the Programmer Guide, to no avail.
>>
>
> OK, I've done it with this little trick :
>
> $ gcc -c test3.c
> $ gcc -o test3 test3.o dummy.o -L. -lsoTest5
>
> with the source of dummy.c:
>
> #define NULL (void *)0
>
> long operatingsystem_parameter_argc = 0;
> char **operatingsystem_parameter_argv = NULL;
> char **operatingsystem_parameter_envp = NULL;
> void *__stkptr = NULL;
>
>
> void _haltproc(long e)
> {
>  return;
> }
>
> When calling a library function that do no IO (only arithmetics on the parameters), it works.
> When doing simple IO (writeLn), it doesn't: I see calls to handleerror_frame, get_frame, get_caller_frame, get_caller_addr, break_error... when debugging, following calls to write_text_pchar_as_array and IOcheck

Add a call to FPC_INITIALIZEUNITS before calling any FPC routines, and
it should work fine.

Michael.