Index: cddl/contrib/opensolaris/tools/ctf/cvt/ctf.c
===================================================================
--- cddl/contrib/opensolaris/tools/ctf/cvt/ctf.c
+++ cddl/contrib/opensolaris/tools/ctf/cvt/ctf.c
@@ -1205,7 +1205,7 @@
 			tdp->t_fndef = xcalloc(sizeof (fndef_t));
 			tdp->t_fndef->fn_ret = tdarr[ctt->ctt_type];
 
-			v = (void *) (dptr + (sizeof (ushort_t) * (vlen - 1)));
+			v = (void *) (dptr + (ptrdiff_t)(sizeof (ushort_t) * (vlen - 1)));
 			if (vlen > 0 && *(ushort_t *)v == 0)
 				tdp->t_fndef->fn_vargs = 1;
 
Index: cddl/contrib/opensolaris/tools/ctf/cvt/hash.c
===================================================================
--- cddl/contrib/opensolaris/tools/ctf/cvt/hash.c
+++ cddl/contrib/opensolaris/tools/ctf/cvt/hash.c
@@ -76,7 +76,7 @@
 {
 	const char *c;
 	ulong_t g;
-	int h = 0;
+	unsigned h = 0;
 
 	for (c = name; *c; c++) {
 		h = (h << 4) + *c;
Index: contrib/elftoolchain/libdwarf/_libdwarf.h
===================================================================
--- contrib/elftoolchain/libdwarf/_libdwarf.h
+++ contrib/elftoolchain/libdwarf/_libdwarf.h
@@ -36,6 +36,7 @@
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdint.h>
 #include <string.h>
 #include <gelf.h>
 #include "dwarf.h"
Index: contrib/elftoolchain/libdwarf/libdwarf_rw.c
===================================================================
--- contrib/elftoolchain/libdwarf/libdwarf_rw.c
+++ contrib/elftoolchain/libdwarf/libdwarf_rw.c
@@ -290,7 +290,7 @@
 	} while ((b & 0x80) != 0);
 
 	if (shift < 64 && (b & 0x40) != 0)
-		ret |= (-1 << shift);
+		ret |= (UINT64_MAX << shift);
 
 	return (ret);
 }
@@ -353,7 +353,7 @@
 
 	do {
 		b = *src++;
-		ret |= ((b & 0x7f) << shift);
+		ret |= ((uint64_t)(b & 0x7f) << shift);
 		(*offsetp)++;
 		shift += 7;
 	} while ((b & 0x80) != 0);
Index: usr.bin/sort/Makefile
===================================================================
--- usr.bin/sort/Makefile
+++ usr.bin/sort/Makefile
@@ -3,8 +3,8 @@
 .include <src.opts.mk>
 
 PROG=	sort
-
 SRCS=	bwstring.c coll.c file.c mem.c radixsort.c sort.c vsort.c
+CSTD=	c11
 
 sort.1: sort.1.in
 	sed ${MAN_SUB} ${.ALLSRC} >${.TARGET}
Index: usr.bin/sort/bwstring.h
===================================================================
--- usr.bin/sort/bwstring.h
+++ usr.bin/sort/bwstring.h
@@ -50,12 +50,26 @@
  */
 struct bwstring
 {
-	size_t				len;
-	union
-	{
-		wchar_t		wstr[0];
-		unsigned char	cstr[0];
-	}				data;
+	/*
+	 * FIXME: this is really ugly, but the easiest way to silence UBSAN's
+	 * array-bounds warning without changing any of the other code. It's
+	 * needed because we can't defined flexible array members inside unions
+	 * (unless they are wrapped inside a struct) and UBSAN complains if we
+	 * use the [0] workaround.
+	 */
+	union {
+		size_t len;
+		union {
+			struct {
+				size_t wlen;
+				wchar_t wstr[];
+			};
+			struct {
+				size_t clen;
+				unsigned char cstr[];
+			};
+		} data;
+	};
 };
 
 struct reader_buffer