Re: cygwin.rules - Enabling shared libXt finally?

["Ralf Habacker" <Ralf dot Habacker at freenet dot de>]

Hi all,

>
>What we would need is a startup function which replaces pointers to the
>importlib _XtInherit to the pointer of _XtInherit from the dll.
>
>func reloc_addr[] = { .... };
>unsigned reloc_addr_size = ...;
>__startup_relocate(void) {
>    unsigned i;
>    func real_func = dlsym("cygXt.dll", "_XtInherit");
>    for (i = 0; i < reloc_addr_size; i++)
>        *(reloc_addr[i]) = real_func;
>}
>
>This must be added to libXt.dll.a and the linker must fill the reloc_addr
>array.

I've found some time to take a look at this problem and it seems as I've got
a solution, which is documented below.
Could you please give this a try ?

cheers
Ralf


/*
/*
 * The Symbol _XtInherit is used in two different manners. First it could be
used as a
 * generric function and second as an absolute address reference, which will
be used to
 * check the initialisation process of several other libraries. Because of
this the symbol
 * must be accessable by all client dll's and applications.
 * In unix environments this is no problem, because the used shared
libraries format (elf)
 * supports this immediatly.
 * Under Windows this isn't true, because a functions address in a dll is
different from
 * the same function in another dll or applications. The used Portable
Executable
 * File adds a code stub to each client to provide the exported symbol name.
This stub
 * uses an indirect pointer to get the original symbol address, to which is
then jumped to,
 * like this example shows:
 *
 * --- client ---                                     --- dll ----
 *  ...
 *  call foo
 *
 * foo: jmp (*_imp_foo)               ---->           foo: ....
 *      nop
 *      nop
 *
 * _imp_foo: .long <index of foo in dll export table, is set to the real
address
 *                  by the runtime linker>
 *
 * Now it is clear why the clients symbol foo isn't the same as in the dll
and we can think
 * about how to deal which this two above mentioned requirements, to export
this symbol to
 * all clients and to allow calling this symbol as a function.
 * The solution I've used exports the symbol _XtInherit as data symbol,
because globale data
 * symbols are exported to all clients. But how to deal with the second
requirement, that
 * this symbol should be used as function ? The Trick is to build a little
code stub in the
 * data section in the exact manner as above explained. This is done with
the assembler code
 * below.
 *
 * References:
 * msdn          http://msdn.microsoft.com/msdnmag/issues/02/02/PE/PE.asp
 * cygwin-xfree: http://www.cygwin.com/ml/cygwin-xfree/2003-10/msg00000.html
 */

Attachment: libtest-1.tar.gz2
Description: Binary data

Attachment: lib_xt.patch
Description: Binary data