Question

• Modify the program in Figure 8.18 so that the following two conditions are met:
  1. Each child terminates abnormally after attempting to write to a location in the read-only text segment.
  2. The parent prints output that is identical (except for the PIDs) to the following: child 12255 terminated by signal 11: Segmentation fault
  child 12254 terminated by signal 11: Segmentation fault

• Modify your solution to Problem 8.24 so that one (and only one) child installs a Segmentation-fault handler which prints an error message and exits. What is the output of the program after this change?

  /* Figure 8.18 */ #include "csapp.h" #define N 2 int main() int status, i; pid_t pid; /* Parent creates N children */ for (i = 0; i < N; i++) if ((pid = Fork ()) == 0) /* child */ exit(100+i); /* Parent reaps N children in no particular order */ while ((pid = waitpid(-1, &status, 0)) > 0) if (WIFEXITED (status) ) printf("child %d terminated normally with exit status=%d\n", pid, WEXITSTATUS (status)); else printf("child %d terminated abnormally\n", pid) ; /* The normal termination is if there are no more children */ if (errno != ECHILD) unix_error("waitpid error"); exit(0);

Answer 1

Do like and comment if you have any queries.

Note: Used the code given in the question and made modifications

Code to copy:

   #include <stdio.h>
   #include <stdlib.h>
   #include <string.h>
   #include <errno.h>
   #include <unistd.h> /* psignal */
   #include <sys/types.h> /* waitpid */
   #include <sys/wait.h> /* waitpid */

   #define N 2

   int main() {
      
           int status, i;
           pid_t pid[N], ret_pid;

           /* Parent creates N children */
           for(i = 0; i < N; i++) {
                   if((pid[i] = fork()) == 0) { /* child */
                           strcpy("Hello", "World"); /* Writing on read-only location. It creates SIGSEGV */
                           exit(100 + i);
                   }
           }

           /* Parent reaps N children in order */
           i = 0;
           while ((ret_pid = waitpid(pid[i++], &status, 0)) > 0)
           {
                   if(WIFEXITED(status))
                           printf("child %d terminated normally with exit status=%d\n", ret_pid, WEXITSTATUS(status));
                   else if(WIFSIGNALED(status)) { /* Exited with a signal */
                           printf("child %d terminated by signal %d: \n", ret_pid, SIGSEGV);
                           psignal(WTERMSIG(status), NULL);
                   }
                   else
                           printf("child %d terminated abnormally \n", ret_pid);
           }

           /* The only normal termination is if there are no more children */
           if(errno != ECHILD)
                   printf("waitpid error");

           exit(0);
   }

Code Screenshot:

со ја са в #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> /* psignal */ #include <sys/types.h> /* waitpid */ #include <sys/wait.h> /* waitpid */ #define N 2 о н Qint main() { о int status, i; pid_t pid[N], ret_pid; л о со /* Parent creates N children */ for (i = 0; i < N; i++) { if((pid[i] = fork()) == 0) { /* child */ strcpy("Hello", "World"); /* Writing on read-only location. It creates SIGSEGV */ exit (100 + i); со мно

/* Parent reaps N children in order / i = 0; while ((ret_pid = waitpid (pid[i++], &status, 0)) > 0) if (WIFEXITED (status)) printf("child $d terminated normally with exit status=$d\n", ret_pid, WEXITSTATUS (status)); else if (WIFSIGNALED (status)) { /* Exited with a signal */ printf("child $d terminated by signal $d: \n", ret_pid, SIGSEGV); psignal (WTERMSIG (status), NULL); else printf("child $d terminated abnormally \n", ret_pid); / /* The only normal termination is if there are no more children if (errno != ECHILD) printf("waitpid error"); exit(0);

Output Screenshot:

} clang-7 -pthread -lm -o main main.c } ./main child 64 terminated by signal 11: Segmentation fault child 65 terminated by signal 11: Segmentation fault