check if we were previously on a signal stack before restoring.

OS X fails to restore the old signal stack because the signal stack is
not enabled by default. This causes sigaltstack(2) to fail with ENOMEM
as ss_size is 0, < MINSIGSTCKSZ.

ok jsing@

1 files changed, 3 insertions, 2 deletions

diff --git a/src/regress/lib/libc/explicit_bzero/explicit_bzero.c b/src/regress/lib/libc/explicit_bzero/explicit_bzero.c
index b4b6c9e559..d78c4d6054 100644
--- a/src/regress/lib/libc/explicit_bzero/explicit_bzero.c
+++ b/src/regress/lib/libc/explicit_bzero/explicit_bzero.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: explicit_bzero.c,v 1.1 2014/06/12 22:01:55 matthew Exp $      */
+/*      $OpenBSD: explicit_bzero.c,v 1.2 2014/07/09 14:26:59 bcook Exp $        */
 /*
  * Copyright (c) 2014 Google Inc.
  *
@@ -67,7 +67,8 @@ call_on_stack(void (*fn)(int), void *stack, size_t stacklen)
 
         /* Restore the original signal action, stack, and mask. */
         ASSERT_EQ(0, sigaction(SIGUSR1, &oldsigact, NULL));
-        ASSERT_EQ(0, sigaltstack(&oldsigstk, NULL));
+        if (oldsigstk.ss_flags & SA_ONSTACK)
+                ASSERT_EQ(0, sigaltstack(&oldsigstk, NULL));
         ASSERT_EQ(0, sigprocmask(SIG_SETMASK, &oldsigset, NULL));
 }