mr4th-dynamic-linking/win32_before_main/win32_before_main.c

// this specific section contains before-main function pointers
// this pragma ensures the compilation unit will generate this section
#pragma section(".CRT$XCU", read)

// declare the "before main" function
static void run_before_main_func(void);

// set the before-main execution function pointer
__declspec(allocate(".CRT$XCU"))
__pragma(comment(linker,"/include:run_before_main_ptr"))
void (*run_before_main_ptr)(void) = run_before_main_func;

// define the "before main" function
int x = 0;
static void run_before_main_func(void){
  x = 100;
}

// main
#include <stdio.h>
int main(){
  printf("x = %d\n", x);
  return(0);
}


#if 0
// wrapped in a macro:

#define BEFORE_MAIN(n) static void n(void);    \
__declspec(allocate(".CRT$XCU"))              \
__pragma(comment(linker,"/include:" #n "__")) \
void (*n##__)(void) = n;                      \
static void n(void)

BEFORE_MAIN(before_main_rule){
  // do work here
}

#endif