#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <signal.h>
#include <setjmp.h>

// Global flag and jump buffer for recovery
static jmp_buf env_buffer;
static volatile int enable_handler = 0;

void segfault_handler(int signal_num) {
  if (enable_handler == 1) {
    longjmp(env_buffer, 1);
  } else {
    printf("Segmentation Fault :(");
    exit(signal_num);
  }
}
#define IMPL_TRY_DEREF(type) \
  int tryDereference(type* pointer, type* output) { \
  if(setjmp(env_buffer) == 0) {\
    enable_handler = 1;\
    *output = *pointer;\
    enable_handler = 0;\
    return 1;\
    } else {\
      enable_handler = 0;\
  return 0;\
    }\
  }
IMPL_TRY_DEREF(uint8_t)

void printMem(uint8_t* location) {
  uint8_t value;
  if(tryDereference(location, &value)) {
    printf("%p: 0x%02x\n", location, value);
  }
  else {
    printf("%p: SEGFAULT\n", location);
  }
}


uint8_t* flipBit(uint8_t* data, int bit) {
  return (uint8_t*)((1<<bit) ^ (uintptr_t)data);
}
uint32_t nBits() {
  //NOTE: Just use UINTPTR_MAX
  uint32_t n = 0;
  for(uintptr_t p = 1;p > 0; p<<=1) ++n;
  return n;
}

int main(int argc, char *argv[])
{
  signal(SIGSEGV, segfault_handler);
  uint32_t nbits = nBits();
  printf("Using %u bit addresses\n", nbits);

  uint8_t a = 0x55;
  uint8_t* var = &a;
  printMem(var-1);
  printMem(var);
  printMem(var+1);
  for (uint32_t i = 0; i < nbits; ++i) {
    //printf("flipping bit %u\n", i);
    printMem(flipBit(var, i));
  }

  return EXIT_SUCCESS;
}