如何捕捉SIGBUS错误？

Question

I am trying to catch the error on read only memory but unable to do it? If i handle the error then it program can continue or only option is exit/abort?

 #include<iostream> #include <stdlib.h> #include <signal.h> #include <stdio.h> #include <unistd.h> #include <string.h> char * F00() { char *s2="ab"; return s2; } void InvalidMem() { (F00())[0]='l'; } void termination_handler (int signum) { fprintf(stderr,"BUS error"); } int main(int argc, char **argv) { signal (SIGBUS, termination_handler); InvalidMem(); for(int i = 0; i < 10; ++i) std::cout<<" L " ; return 0; } 

Answer 1

SIGBUS means you are accessing an unaligned address, SIGSEGV means you are accessing an address you are "not supposed to" (either invalid address, or writing to read-only memory - in some cases memory can be write-only, and a read from such memory would then result in SIGSEGV too).

Since the processor doesn't really know how what state it is in when you end up in the signal handler, it is typically not possible to just continue from the signal handler itself in these cases. Instead, the typical approach is to use setjmp and longjmp to "recover to a known point". This may be the "main loop" of your code, or some error recovery point.

So, something like this:

 jmp_buf reset;

 int termination_handler(int signum)
 {
     longjmp(reset, 1);
 }

 int main()
 {
    if (setjmp(reset) != 0)
    {
        printf("We got back from signal handler")
        ...
    }
    signal (SIGBUS, termination_handler);
    ...
    return 0;
 }

It should be noted that you can get into some serious trouble if you actually "keep going" after execution errors like bus fault or address fault - consider for example:

// At global level:
  some_lock lock;

// in some function. 
  ....
  lock->take();
  some code that crashes;
  lock->release();

So, now the lock is held, and never released... Code will probably hang next time you need to take the lock...