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KHB: Failure-oblivious computing

Posted Jun 29, 2006 17:53 UTC (Thu) by cventers (subscriber, #31465)
In reply to: KHB: Failure-oblivious computing by cventers
Parent article: KHB: Failure-oblivious computing

Silly me, this special syscall even already exists! How about stuffing
this in a SIGSEGV signal handler.

/* Dump some core. */
if (fork() == 0) raise(SIGABRT);

/* Magic to initiate an exception from whatever context we were running
in before our signal handler got called */

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KHB: Failure-oblivious computing

Posted Jun 29, 2006 18:09 UTC (Thu) by cventers (subscriber, #31465) [Link]

I apologize to the readers and editors about the volume of my comments replying to myself, but I think we need a longjmp() that is safe to use as an exit from a signal handler. Then my above code could be:

int handle (int sig)
{
  struct jmp_buf buf;

  if (sig == SIGSEGV) {
     if (fork() == 0) raise(SIGABRT);
     pop_jmp_buf_from_tls_stack(&buf);
     longjmp_after_sig(&buf, sig);
  }
}

...then strategically place:

// Prepare an exception context
if (save_context_in_tls_stack() == SIGSEGV) {
   // operation failed
}

do_something_possibly_unsafe();

// Forget about that context
pop_jmp_buf_from_tls_stack(NULL);

Comments?

KHB: Failure-oblivious computing

Posted Jun 29, 2006 21:34 UTC (Thu) by nix (subscriber, #2304) [Link]

Throwing from certain signal handlers is safe in the presence of -fasynchronous-unwind-tables, but I sort of doubt that SIGSEGV is necessarily one of them (what if, e.g., the unwinder segfaults, something which is not unknown?)

Joe Buck would know for sure, I'd guess. :)