share global variable: interaction between main, lib.a and dll - c

Question

i kept the essential.
caller.exe loads the dll, then calls the function dll_init declared inside the dll.
this last function calls the function "get_ptr" declared in the common library which should return a pointer to the global variable.
the issue is:
whenever caller.exe calls "get_ptr" it returns a valid pointer same as the one which was previously allocated on caller.exe start fine.
whenever the dll thru it function "dll_init" (after bein called by
caller.exe) calls "get_ptr" (knowing that the dll is linked to the
static lib) it return NULL pointer.
what i am missing ?
libcommon.c
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
/***************header****************/
int *get_ptr(void);
int set_ptr(void);
/**********************************/
int *global=NULL;
//extern __declspec(dllimport) int *global; doesnt work
int set_ptr() {
global = (int *) malloc(sizeof(int));
printf("global allocated to %p\n",global);
*global=485; //random value
return 0;
}
int *get_ptr() {
return global;
}
here is compiling commands (makefile simplified):
gcc.exe -c libcommon.c -o libcommon.o -m32
ar r libcommon.a libcommon.o
ranlib libcommon.a
module.c
#include <windows.h>
#include <stdio.h>
#if BUILDING_DLL
#define DLLIMPORT __declspec(dllexport)
#else
#define DLLIMPORT __declspec(dllimport)
#endif
DLLIMPORT int dll_init(void) {
int *ptr=(int *) get_ptr();
puts("dll run");
printf("from dll global: %p\n",ptr);
puts("dll end");
return 0;
}
compiling:
gcc.exe -c module.c -o module.o -m32 -DBUILDING_DLL=1
gcc.exe -shared module.o -o module.dll -static-libgcc -lws2_32 -m32 -s -L"." -lcommon -Wl,--output-def,libmodule.def,--out-implib,libmodule.a,--add-stdcall-alias
caller.c
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
typedef void(voidfunc)(void);
voidfunc *fct_ptr;
int test(int a) {
printf("%d",a++);
}
int main() {
set_ptr();
printf("::%p\n",get_ptr());
/* Load the dll then call dll_init */
HMODULE dllptr = LoadLibrary("module.dll");
if (dllptr != NULL) {
fct_ptr = (voidfunc *) GetProcAddress(dllptr, "dll_init");
puts("loaded");
if (fct_ptr != NULL)
fct_ptr();
FreeLibrary(dllptr);
}
}
compiling:
gcc.exe caller.c -o caller.exe -m32 -static-libgcc -lws2_32 -L. -lcommon -m32

Answer 1

I believe you have 2 different places in memory named global. One is
in caller since you compiled it statically with lcommon. Data is set
there via set_ptr. Second is in module space (for the same reasons),
but you never called set_ptr() there. Check memory address of global
inside dll_init and in main. If they are not the same, you then need
to call set_ptr in your `dll_init``
he's right, i think the common static library linked with both exe and dll was a wrong idea.
the solution is here: .dll Plugin that uses functions defined in the main executable
Any other suggestions are welcome