Unable to reassign signal handler second time - c

Question

I have a simple code which uses two signal handlers for "Segmentation fault" signal. First one works when signal happens and after longjmp, I do reassigning of handler with second one for that signal. Unfortunately, the flow of code doesn't reach necessary handler and I still get "Segmentation fault".
#include <unistd.h>
#include <sys/syscall.h>
#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <signal.h>
#include <setjmp.h>
int i;
int ci;
jmp_buf m_env_buffer;
jmp_buf max_env_buffer;
void handler(int signum){
printf("sigsegv on i:[%d]", i);
ci = (++i);
longjmp(m_env_buffer,1);
}
void top_handler(int signum){
printf("sigsegv on max i:[%d]", i);
longjmp(max_env_buffer,10);
}
int main(void) {
signal(SIGSEGV, handler);
char * pstart = "loremipsum";
int m_cell = 0;
char m_cell_v;
int point;
point = setjmp(m_env_buffer);
if(point == 0){
for(i=0; ;i--){
m_cell_v = pstart[i];
}
}
//this wasn't invoked
signal(SIGSEGV, top_handler);
point = setjmp(max_env_buffer);
if(point == 0){
for(i=ci; ;i++){
char cur = pstart[i];
if(cur==10)
printf("\n");
printf("%c",cur);
}
}
puts("finish");
return 0;
}

Answer 1

signal() should not be used. It has unreliable semantics. On your system the default action (termination) is performed when the second SIGSEGV is received. The second call to signal() has effectively no effect.
You should use sigaction() instead. In your case you can use the following function instead of signal():
void set_signal (int signum, void (*handler)(int))
{
struct sigaction act;
act.sa_handler = handler;
sigemptyset (&act.sa_mask);
act.sa_flags = SA_NODEFER;
act.sa_restorer = NULL;
sigaction (signum, &act, NULL);
}
In the future, read the documentation at your disposal. A good ressource is the glibc manual. It has a good chapter on signal handling.