为什么信号处理程序进入无限循环？ - SIGSEGV

Question

Any idea why the signal handler goes to infinite loop?

Here is the code. Please help me.

enter code here
 9 void SIGSEGV_handler(int signal)
10 {
11  printf("Segmentation fault caught....\n");
12  printf("Value of instance variable: i = %d\n\n", i);
13 } 
16 
17 int main()
18 {
19  char *mallocPtr, *callocPtr, *reallocPtr, *memalignPtr, *vallocPtr;
20  struct sigaction sa;
21 
22  sa.sa_handler=SIGSEGV_handler;
23  sigaction(SIGSEGV, &sa, NULL);
24 
37 
38  printf("The segmentation fault handler will be entered for i = 3, 4, 5 and 6\n");
39 
40 
41  for(i=0; i<7; i++)
42   {
43    printf("i = %d\n",i);
44 
45    mallocPtr=(char*)malloc(3);
46    printf("Malloc address : %x\n",mallocPtr);
47    strcpy(mallocPtr, "Hhvhgvghsvxhvshxv");
48    puts(mallocPtr);

Answer 1

The default action for SIGSEGV is to terminate your process. But you install a handler and override this:

/* Does nothing to "fix" what was wrong with the faulting
 * instruction.
 */
void SIGSEGV_handler(int signal)
{
    printf("Segmentation fault caught....\n");
    printf("Value of instance variable: i = %d\n\n", i);
}

So for every instruction that triggers a sigsegv, this handler is called and the instruction is restarted . But your handler did nothing to fix what was wrong in the first place with the faulting instruction.

In conclusion, when the instruction is restarted, it will fault again. And again, and again and... you get the idea.

Answer 2

http://pubs.opengroup.org/onlinepubs/009604599/functions/xsh_chap02_04.html#tag_02_04

The behavior of a process is undefined after it returns normally from a signal-catching function for a SIGBUS, SIGFPE, SIGILL, or SIGSEGV signal that was not generated by kill(), sigqueue(), or raise().