/***************************
 * Buffer aligné et protegé
 */

#define LEN (8*4096)
#include <malloc.h>
#include <sys/mman.h>

int main() {
  ...

  buffer = memalign(4096, LEN);
  if (!buffer) {
    printf("failed to malloc\n");
    exit(-1);
  }
  printf("buffer = %p\n", buffer);

  ret = mprotect(buffer, LEN, PROT_NONE);
  if (ret < 0) {
    printf("failed to mprotect\n");
    exit(-1);
  }





/**********************
 * Traitant de SIGSEGV
 */

#define _GNU_SOURCE /* a garder TOUT EN HAUT du fichier */

#include <ucontext.h>
#include <signal.h>

void segv_handler(int sig, siginfo_t *info, void *_context)
{
  ucontext_t *context = _context;
  int write = (context->uc_mcontext.gregs[REG_ERR] & 2);
#ifdef __x86_64__
  void *addr = (void *)(context->uc_mcontext.gregs[REG_CR2]);
#elif __i386__
  void *addr = (void *)(context->uc_mcontext.cr2);
#else
#error Architecture non supportée
#endif
  ...




int main()
{
  ...

  struct sigaction act;
  int ret;

  act.sa_flags = SA_SIGINFO;
  act.sa_sigaction = segv_handler;
  sigaction(SIGSEGV, &act, NULL);





/**********************
 * Attributs des pages
 */

enum status {
  INVALID,
  READONLY,
  READWRITE,
};

struct pageattr {
  void * address;
  enum status status;
  int owner;
}




/*********************************************
 * 4 tubes, 8 entrées, pour le cas symétrique
 */

static int fd_outreq;	/* where I send my requests to the other process */
static int fd_inresp;	/* where I receive the other process responses to my requests */
static int fd_inreq;	/* where I receive requests from the other process */
static int fd_outresp;	/* where I send responses to the other process requests */

int main()
{
  ...
  int pipes[8];

  ret = pipe(&pipes[0]); /* first pipe to send requests from first process */
  if (ret < 0) {
    perror("pipe1");
    exit(-1);
  }
  ret = pipe(&pipes[2]); /* second pipe to recv responses to first process requests */
  if (ret < 0) {
    perror("pipe2");
    exit(-1);
  }
  ret = pipe(&pipes[4]); /* third pipe to send requests from second process */
  if (ret < 0) {
    perror("pipe3");
    exit(-1);
  }
  ret = pipe(&pipes[6]); /* fourth pipe to recv responses to second process requests */
  if (ret < 0) {
    perror("pipe4");
    exit(-1);
  }

  pid = fork();
  if (pid) {
    /* pere */
    close(pipes[0]);
    fd_outreq = pipes[1];
    fd_inresp = pipes[2];
    close(pipes[3]);
    fd_inreq = pipes[4];
    close(pipes[5]);
    close(pipes[6]);
    fd_outresp = pipes[7];
    ...

  } else {
    /* fils */
    fd_inreq = pipes[0];
    close(pipes[1]);
    close(pipes[2]);
    fd_outresp = pipes[3];
    close(pipes[4]);
    fd_outreq = pipes[5];
    fd_inresp = pipes[6];
    close(pipes[7]);
    ...

  }