Long ago, malloc internally had two kinds of failures, warnings and errors.

The 'A' option elevated warnings to errors, and has been the default for some
time. Then warnings were effectively eliminated in favor of everything
being an error, but then the 'a' flag turned real errors into warnings!
Remove the 'a' option entirely. You shouldn't have used it anyway.
ok tb tdeval

src/lib/libc/stdlib/malloc.3

@@ -30,9 +30,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: malloc.3,v 1.91 2015/09/14 13:08:01 schwarze Exp $
+.\"	$OpenBSD: malloc.3,v 1.92 2016/01/06 17:57:22 tedu Exp $
 .\"
-.Dd $Mdocdate: September 14 2015 $
+.Dd $Mdocdate: January 6 2016 $
 .Dt MALLOC 3
 .Os
 .Sh NAME
@@ -345,10 +345,7 @@ or
 detect an error condition,
 a message will be printed to file descriptor
 2 (not using stdio).
-Errors will result in the process being aborted,
-unless the
-.Cm a
-option has been specified.
+Errors will result in the process being aborted.
 .Pp
 Here is a brief description of the error messages and what they mean:
 .Bl -tag -width Ds

src/lib/libc/stdlib/malloc.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: malloc.c,v 1.179 2015/12/30 06:04:39 tedu Exp $	*/
+/*	$OpenBSD: malloc.c,v 1.180 2016/01/06 17:57:22 tedu Exp $	*/
 /*
  * Copyright (c) 2008, 2010, 2011 Otto Moerbeek <otto@drijf.net>
  * Copyright (c) 2012 Matthew Dempsky <matthew@openbsd.org>
@@ -177,7 +177,6 @@ struct chunk_info {
 
 struct malloc_readonly {
 	struct dir_info *malloc_pool;	/* Main bookkeeping information */
-	int	malloc_abort;		/* abort() on error */
 	int	malloc_freenow;		/* Free quickly - disable chunk rnd */
 	int	malloc_freeunmap;	/* mprotect free pages PROT_NONE? */
 	int	malloc_hint;		/* call madvice on free pages?  */
@@ -280,8 +279,8 @@ wrterror(char *msg, void *p)
 #endif /* MALLOC_STATS */
 
 	errno = saved_errno;
-	if (mopts.malloc_abort)
-		abort();
+
+	abort();
 }
 
 static void
@@ -485,7 +484,6 @@ omalloc_init(struct dir_info **dp)
 	/*
 	 * Default options
 	 */
-	mopts.malloc_abort = 1;
 	mopts.malloc_junk = 1;
 	mopts.malloc_move = 1;
 	mopts.malloc_cache = MALLOC_DEFAULT_CACHE;
@@ -523,10 +521,8 @@ omalloc_init(struct dir_info **dp)
 				mopts.malloc_cache >>= 1;
 				break;
 			case 'a':
-				mopts.malloc_abort = 0;
-				break;
 			case 'A':
-				mopts.malloc_abort = 1;
+				/* ignored */
 				break;
 			case 'c':
 				mopts.malloc_canaries = 0;