#define _GNU_SOURCE /* Required for 'constructor' attribute (GNU extension) */
#define _POSIX_C_SOURCE  /* Required for sigsetmp/siglongjmp */
#ifdef LONGJMP
# include <setjmp.h>
#else
# include <ucontext.h>
#endif
#ifdef LONGJMP
#include <setjmp.h>
#else
#endif
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int, char *[]);
// The 'context' variable includes the register values to be saved and restored
#ifdef LONGJMP
sigjmp_buf context;
#else
ucontext_t context;
#endif

void signal_handler(int signal) {
  // We use siglongjmp()/setcontext; sigsetjump()/setcontext saved the context
  //   outside of any signal handler.  So, when we call siglongjmp(),
  //   any pending ^C will immediately take effect.
#ifdef LONGJMP
  siglongjmp(context, 1);
#else
  setcontext(&context);
#endif 
}

#ifdef LOOKUP_MAIN_SYMBOL
typedef void *(*main_ptr_t)(char *, char *[]);
void *get_main_address(char *target) {
  char command[100];
  long unsigned int main_address;
  snprintf(command, sizeof command, "nm %s | grep ' main$'", target);
  FILE *cmd = popen(command, "r");
  fscanf(cmd, "%x", (void *)&main_address);
  return (void *)main_address;
}
#endif

void __attribute__((constructor))
my_constructor() {
  signal(SIGINT, &signal_handler);

  fprintf(stderr, "*************************************\n"
                  "***  We are running, using test5. ***\n"
                  "*************************************\n");

#ifdef LONGJMP
  if (sigsetjmp(context, 1) != 0) { // if returning from siglongjmp (restart)()
    printf("\n\n*** RESTARTING ***\n");
    return;
  }
#else
  static int is_restart; // static local variables are stored in data segment
  is_restart = 0;
  getcontext(&context);
  if (is_restart == 1) { // if returning from setcontext()
    printf("\n\n*** RESTARTING ***\n");
    is_restart = 0;
    return;
  }
  // Saving the memory segments must be done _after_ setting 'is_restart = 1'
  // Then, when we return from setcontext() into getcontext(),
  //   is_restart will restore the correct value of '1' from the data segment.
  is_restart = 1;
#endif

  fprintf(stderr, "*** What integer should we test? ");
  fflush(stdout);
  char buf[100] = {'\0'};  // null characters at end of string
  read(0, buf, sizeof(buf)-1);
  char *argv[] = {"UNKNOWN", "12345", NULL};
  argv[0] = getenv("TARGET");
  argv[1] = buf;
#ifdef LOOKUP_MAIN_SYMBOL
  // If the target was cmopiled with -rdynamic in 'gcc', then we don't
  //   need this code.  If we didn't use -rdynamic, then this code would
  //   find the address of 'main()' by more obscure means.
  main_ptr_t = get_main_address(getenv("TARGET"));
  (*main_ptr_t)(argv[/* argc */ 2, argv);
#endif
  // This assumes that our target was compiled with the -rdynamic to gcc.
  // Otherwise, we would define LOOKUP_MAIN_SYMBOL in this code.
#ifndef LOOKUP_MAIN_SYMBOL
  main(/* argc */ 2, argv);
#endif
  // The constructor exits now.  Otherwise, if it returns, then the linker
  // will then call 'main()' in the normal way.
  exit(0);
}