Add reallocarray to compat.

Makefile.am

@@ -234,6 +234,9 @@ endif
 if NO_OPENAT
 nodist_tmux_SOURCES += compat/openat.c
 endif
+if NO_REALLOCARRAY
+nodist_tmux_SOURCES += compat/reallocarray.c
+endif
 
 # Install tmux.1 in the right format.
 install-exec-hook:

compat/reallocarray.c

@@ -0,0 +1,40 @@
+/*	$OpenBSD: reallocarray.c,v 1.3 2015/09/13 08:31:47 guenther Exp $	*/
+/*
+ * Copyright (c) 2008 Otto Moerbeek <otto@drijf.net>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+#include <errno.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "tmux.h"
+
+/*
+ * This is sqrt(SIZE_MAX+1), as s1*s2 <= SIZE_MAX
+ * if both s1 < MUL_NO_OVERFLOW and s2 < MUL_NO_OVERFLOW
+ */
+#define MUL_NO_OVERFLOW	((size_t)1 << (sizeof(size_t) * 4))
+
+void *
+reallocarray(void *optr, size_t nmemb, size_t size)
+{
+	if ((nmemb >= MUL_NO_OVERFLOW || size >= MUL_NO_OVERFLOW) &&
+	    nmemb > 0 && SIZE_MAX / nmemb < size) {
+		errno = ENOMEM;
+		return NULL;
+	}
+	return realloc(optr, size * nmemb);
+}

configure.ac

@@ -365,6 +365,13 @@ if test "x$found_openat" = xyes; then
 fi
 AM_CONDITIONAL(NO_OPENAT, [test "x$found_openat" = xno])
 
+# Look for reallocarray, compat/reallocarray.c used if missing.
+AC_CHECK_FUNC(reallocarray, found_reallocarray=yes, found_reallocarray=no)
+if test "x$found_reallocarray" = xyes; then
+	AC_DEFINE(HAVE_REALLOCARRAY)
+fi
+AM_CONDITIONAL(NO_REALLOCARRAY, [test "x$found_reallocarray" = xno])
+
 # Look for getopt. glibc's getopt does not enforce argument order and the ways
 # of making it do so are stupid, so just use our own instead.
 AC_CHECK_FUNC(getopt, found_getopt=yes, found_getopt=no)