how to dynamically increase the stack size of a process

Hi I am trying to implement a process, which increases its available stack dynamically by handling the exception of (overflow/segmentation fault).

I am writing a sample program here, by recursively allocating space on stack and hence growing the stack till it gives a SIGSEGV, I am handling this exception in a handler and increasing the resource limit of the process by using getrlimit and setrlimit, this doesnt seem to work and I cant figure out why, if I try to do the same by programtically generating a SIGSEGV by raise(), I am able to increase the stack size ,here is the code I am using

    #include<unistd.h>
    #include<sys/resource.h>
    #include<stdio.h>
    #include<stdlib.h>
    #include<signal.h>
    #include<sys/time.h>
    void allocate(void);
    void handler(int sig)
    {
    struct rlimit r;
    getrlimit(RLIMIT_STACK,&r);
    r.rlim_cur=r.rlim_cur *5; // increasing stack size five times
    setrlimit(RLIMIT_STACK,&r);
    write(1,"Handler",7);  //to check handler invocation
    //signal(SIGSEGV,SIG_DFL);
    }

    int cntz=0xfff; //for adusting recursion

    int main()
    {
    struct sigaction sa;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags=0;
    sa.sa_handler=handler;
    sigaction(SIGSEGV,&sa,NULL);
    //raise(SIGSEGV);    to raise self signal to increase stack size 
    allocate();
    //getchar();
    exit(1);

    } 

    void allocate()
    {
    char staczzk[5000];  //allocating memory on stack in each 
    recursive call
    cntz--;
    printf("%dn",cntz);
    if (cntz==0)
    return;
    allocate();    //recusrive call
    }

---

Your signal handler will, by default, use the same stack as the rest of the program, and there's no stack space left thanks to all the calls to allocate .

The fix is to use an alternate signal stack. The following is based on your code along with code from the sigaltstack man page:

int main()
{
    struct sigaction sa;
    stack_t ss;

    ss.ss_sp = malloc(SIGSTKSZ);
    if (ss.ss_sp == NULL) { perror("malloc"); exit(1); }
    ss.ss_size = SIGSTKSZ;
    ss.ss_flags = 0;
    if (sigaltstack(&ss, NULL) == -1) { perror("sigaltstack"); exit(1); }

    sigemptyset(&sa.sa_mask);
    sa.sa_flags=SA_ONSTACK;
    sa.sa_handler=handler;
    if(sigaction(SIGSEGV,&sa,NULL)<0) { perror("sigaction"); exit(1); }
    //raise(SIGSEGV);    to raise self signal to increase stack size
    allocate();
    exit(1);
}

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