hangdler.c

是关于页面替换算法的代码模拟

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <setjmp.h>
#include <string.h>


typedef void Sigfunc (int);	/* for signal handlers */

Sigfunc *signal (int signo, Sigfunc * func);
static Sigfunc *Signal (int signo, Sigfunc * func);
static char *get_stack_bottom (void);
static void segfault (int signo);

static sigjmp_buf jmpbuf;
static volatile sig_atomic_t canjump = 0;
static Sigfunc *seg_handler;
static Sigfunc *bus_handler;	/* for xxxBSD */

Sigfunc *
signal (int signo, Sigfunc * func)
{
  struct sigaction act, oact;

  act.sa_handler = func;
  sigemptyset (&act.sa_mask);
  act.sa_flags = 0;
  if (sigaction (signo, &act, &oact) < 0)
    {
      return (SIG_ERR);
    }
  return (oact.sa_handler);
}				/* end of signal */

static Sigfunc *
Signal (int signo, Sigfunc * func)	/* for our signal() funct 
					   ion */
{
  Sigfunc *sigfunc;

  if ((sigfunc = signal (signo, func)) == SIG_ERR)
    {
      exit (EXIT_FAILURE);
    }
  return (sigfunc);
}				/* end of Signal */

static char *
get_stack_bottom (void)
{
  volatile char *c;		/* for autovar, must be volatile */

  seg_handler = Signal (SIGSEGV, segfault);
  bus_handler = Signal (SIGBUS, segfault);
  c = (char *) &c;

  if (sigsetjmp (jmpbuf, 1) != 0)
    {
      Signal (SIGSEGV, seg_handler);
      Signal (SIGBUS, bus_handler);
       printf("demo SIGSEGV:     %p\n", (char *)c);
      return ((char *) c);
    }
  canjump = 1;			/* now sigsetjump() is OK */
  while (1)
    {
      *c = *c;
      c++;
    }
  return (NULL);
}				/* end of get_stack_bottom */

static void
segfault (int signo)
{
  if (canjump == 0)
    {
      return;			/* unexpected signal, ignore */
    }
  canjump = 0;
  siglongjmp (jmpbuf, signo);	/* jump back to main, don't return */
}				/* end of segfault */


/**********************************************************************************/
// ligang's method
static void get_start()
{
  char 	 filename[100];
  char 	 content[1024];
  char 	 stack_bottom[64];
  FILE 	*fp;
  char 	*pcontent, *ptmp;
  int 	 i;
  unsigned long  _ckpt_stack_bottom;
   
  
  
  
  // get the address of stack
  // add by lg

  sprintf(filename,"/proc/%d/stat", getpid());
  fp=fopen(filename,"r");
								
  if (fp==NULL){
    perror("in fopen() of get_start()");
    exit(-1);
  }
  fread(content, 1024, 1, fp);
								
  //the 28th element in the file stat is the address of stack
  pcontent = content;
  for (i=1; i<28; i++) {
    pcontent = strstr(pcontent, " ");
    pcontent = pcontent + 1;
  }
  ptmp 				= strstr(pcontent, " ");
  strncpy(stack_bottom, pcontent, ptmp - pcontent);
  stack_bottom[ptmp - pcontent] = '\0';
  sscanf(stack_bottom, "%lu", &_ckpt_stack_bottom);

								
  fclose(fp);

  printf("/proc/<pid>/stat: %p\n", _ckpt_stack_bottom);

}


/********************************************************************/
// read from /proc/pid/maps
static void getStackFromMaps()
{
  char 	 filename[100];
  char   line[256];
  char 	*tmpline;  
  FILE 	*fp;
  char 	*start, *end;


  sprintf(filename,"/proc/%d/maps", getpid());
  fp = fopen(filename, "r");
								
  if (fp==NULL){
    perror("in fopen() of getStackFromMaps");
    exit(-1);
  }
				/* gets the last line */
  do{
    tmpline = fgets(line, 256, fp);
  } while(tmpline != 0);  

  fclose(fp);
  
  start = strstr(line, "-") + 1;
  end 	= strstr(line, " ");
  *end 	= 0;
  printf("/proc/<pid>/maps: 0x%s\n", start);
}


/*******************************************************************************/
// configure.c

char *ptr;

void
pgfault_handler(sig)
long sig;
{
	fprintf(stderr, "configre SIGSEGV: %p\n", ptr);
	exit(0);
}

void getBottomStack()
{
	
	int stack_dummy;
	
	signal(SIGSEGV, (void(*)(int))pgfault_handler);
	
	ptr = (char *)&stack_dummy;
	
	/* program calls exit(0) from signal handler */
	
	while (1) {
		*ptr = 0;
		ptr += 1;
	}
	
}



/*******************************************************************************/
int main (int argc, char *argv[])
{
   printf("Current Stack Bottom:\n");
  //ligang
   get_start();
   
   //demo another
   get_stack_bottom();

   //read from maps
   getStackFromMaps();
   
   //configure another
   getBottomStack();
  return (EXIT_SUCCESS);
}				/* end of main */