Seg fault in Fibonacci fork program??

[fussbol12]

I cannot find what is giving me the segfault in my code...I used printf statements to check for errors....anyon e see the problem??

#include <stdio.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <unistd.h> //required for fork
#include <stdlib.h>

int main(int argc, char *argv[]) {

int fib[75];
int i;
pid_t pid = fork(); //fork and save pid
siginfo_t siginfo; //this will save info on signals from traced process
int waitval = 0; //value returned by wait. used to see if child ended

if(argc != 2){
printf("Please enter a valid integer.\n");
exit(1);
}

if(*argv[2] < 0){
printf("Please enter an integer greater than 0.\n");
}

if(*argv[2] == 0){
printf("0\n");
exit(1);
}

if(*argv[2] == 1){
printf("1\n");
exit(1);
}

if(pid == 0){ //child

ptrace(PTRACE_T RACEME, 0, NULL, NULL); //tell parent to trace child

for(i = 0; i < *argv[2]; i++)
*argv[i] = *argv[i-1] + *argv[i-2];

for(i = 1; i < *argv[2]; i++)
printf("%10d\n" , *argv[2]);

execvp("ls", NULL);
}
else{
wait(&waitval); //wait for signal from child
while(1){
ptrace(PTRACE_G ETSIGINFO, pid, NULL, &siginfo); //get siginfo from child
printf("Signal number: %d\n", siginfo.si_sign o); //print siginfo

if(WIFEXITED(wa itval)) //quit loop if the signal returned from wait
break; //was child exiting
ptrace(PTRACE_C ONT, pid, NULL, NULL); //tell child to continue
wait(&waitval); }} //wait again for next signal


return 0;}

[donbock]

It would have been a lot easier to read your program if you used CODE tags. It would also help if you told us where in the program the Seg Fault occurred.

It looks like your intent is for the child process to do all the computations and for the parent process to simply wait til the child is done (although that execvp call looks tricky). It isn't obvious to me what benefit you gain from the parent process in that case.

1. You should add comments explaining what the command line arguments are; and what the output should look like when the program works.
2. If you want a single process to do all the computations, then you should start by writing that process first (don't use fork). You can add fork later.
3. On the other hand, there might be a more fruitful way to use multiple processes. What is your algorithm for computing the fibonacci sequence? Try stating the procedure in English first (not C). (It wouldn't be a bad idea to enshrine those words as comments in your program.)
4. Take a close look at your code. You aren't using all of your variables (hint).
5. What do you expect the execvp() call to do?

Cheers,
donbock

[donbock]

There are two basic techniques for implementing repetition in software: iteration and recursion. The typical way to achieve recursion is to nest a series of self-referential function calls. I suppose another way to achieve the same end is a cascade of forked child processes.

Cheers,
donbock

[JosAH]

for(i = 0; i < *argv[2]; i++)
    *argv[i] = *argv[i-1] + *argv[i-2];
 

Check what happens when i == 0 or i == 1; your array index is out of bounds.
Another thing is that argv[i] points to a character sequence, not ints.

kind regards,

Jos

[song846079]

siginfo_t siginfo; //this will save info on signals from traced process
siginfo should be static