tst-longjmp_chk2: add comments/sanity check

If the longjmp checking code is slightly broken, this code can loop
forever which isn't too helpful.  Add a sanity check to keep that
from happening.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

ChangeLog

@@ -1,3 +1,8 @@
+2014-03-13  Mike Frysinger  <vapier@gentoo.org>
+
+	* debug/tst-longjmp_chk2.c: Update header comment.
+	(stackoverflow_handler): Add comment.  Call assert on pass value.
+
 2014-03-13  Igor Zamyatin  <igor.zamyatin@intel.com>
 
 	* config.h.in (HAVE_AVX512_SUPPORT): New #undef.

debug/tst-longjmp_chk2.c

@@ -1,4 +1,6 @@
-/* Test case mostly written by Paolo Bonzini <pbonzini@redhat.com>.  */
+/* Verify longjmp fortify checking does not reject signal stacks.
+
+   Test case mostly written by Paolo Bonzini <pbonzini@redhat.com>.  */
 #include <assert.h>
 #include <setjmp.h>
 #include <signal.h>
@@ -18,7 +20,10 @@ static void
 stackoverflow_handler (int sig)
 {
   stack_t altstack;
+  /* Sanity check to keep test from looping forever (in case the longjmp
+     chk code is slightly broken).  */
   pass++;
+  assert (pass < 5);
   sigaltstack (NULL, &altstack);
   /* Using printf is not really kosher in signal handlers but we know
      it will work.  */