exporting symbols from executable and linking shared objects question

[Mariusz Woloszyn]

Hi!!

I'm new to the list, but I searched archives looking for a solution and
found nothing.

I have TWO questions, but it's the same problem.

First is -rdynamic swich for gcc. it's used to export symbols for shared
objects and the second is about linking shared objects (.dll) with symbols
declared as external.

Let's see following code:

---main.c---
#include <dlfcn.h>
#include <stdio.h>

int c;

main () {

        int (*foo)();
        void *handler = dlopen ("./foo.so", RTLD_LAZY|RTLD_GLOBAL);
        if (!handler) {
                fputs (dlerror(), stderr);
                printf("\n");
                exit(1);
        }
        foo = dlsym(handler,"foo");

        (*foo)();
        dlclose(handler);
}
---main.c---

and following shared object source:

---foo.c---
//extern int c;

foo () {
        printf("Fooo!\n");
//        printf("c=%i\n",c);
}
---foo.c---

If I compile it under Unix or windows (under Win using attached shell
script -- refering to the documentation) everything is OK. But WHAT I have
to do to get it working with foo looking like this:

---foo.c---
extern int c;

foo () {
        printf("Fooo!\n");
        printf("c=%i\n",c);
}
---foo.c---     


Under Unix I used to compile main:
gcc main.c -o main -ldl -rdynamic
(to export symbols to dynamically dlopened shared objects), and foo:
gcc -shared foo.c -o foo.so

First of all -rdynamic does not work under cygwin and moreover ld fails
linking shared objects with symbols declared as external.

Any suggestions???

Regards,

--
Mariusz Wołoszyn
Internet Security Specialist, Internet Partners
-------------- next part --------------

#! /bin/sh
#  Example Script to compile and link a relocatable DLL
#    Files that make up the DLL = $foo.c  init.cc fixup.c.
#        (init.cc and fixup.c are housekeeping routines needed for the DLL. The actual
#                      library routines are in $foo.c and )
# ***Fill in your path to libcygwin.a here (with no trailing slash)***
LIBPATH=/lib

echo "Compiling" `basename $1 .c`".dll"

foo="`basename $1 .c`"

echo $foo

# Compile source files:
gcc -c $foo.c
gcc -c init.cc
gcc -c fixup.c

# Make .def file:
echo EXPORTS > $foo.def
nm $foo.o  init.o fixup.o | grep '^........ [T] _' | sed 's/[^_]*_//' >> $foo.def

# Link DLL.
ld --base-file $foo.base --dll -o $foo.dll $foo.o  init.o fixup.o \
 $LIBPATH/libcygwin.a /lib/w32api/libkernel32.a -e _dll_entry@12
dlltool --as=as --dllname $foo.dll --def $foo.def --base-file $foo.base --output-exp $foo.exp
ld --base-file $foo.base $foo.exp --dll -o $foo.dll $foo.o  init.o fixup.o  \
  $LIBPATH/libcygwin.a /lib/w32api/libkernel32.a -e _dll_entry@12
dlltool --as=as --dllname $foo.dll --def $foo.def --base-file $foo.base --output-exp $foo.exp
ld $foo.exp --dll -o $foo.dll $foo.o  init.o fixup.o  \
 $LIBPATH/libcygwin.a /lib/w32api/libkernel32.a -e _dll_entry@12

# Build the $foo.a lib to link to:
dlltool --as=as --dllname $foo.dll --def $foo.def --output-lib $foo.a

# Linking with main
#gcc main.c $foo.a -o main.exe