From 45256214ebe3f45cbd4046f6f0eea56ca9ba2faf Mon Sep 17 00:00:00 2001
From: "Pedro F. Giffuni" <pfg@FreeBSD.org>
Date: Tue, 1 Mar 2016 19:15:34 +0000
Subject: [PATCH] mbtowc(3): set errno to EILSEQ if an incomplete character is
 passed.

According to POSIX, The mbtowc() function shall fail if:
[EILSEQ] An invalid character sequence is detected.

Reviewed by:		bapt
Differential Revision:	https://reviews.freebsd.org/D5496

Obtained from:	OpenBSD (Ingo Schwarze)
MFC after:	1 month
---
 lib/libc/locale/mbtowc.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/lib/libc/locale/mbtowc.c b/lib/libc/locale/mbtowc.c
index 70fc19ea3500..376d6cfa5d6d 100644
--- a/lib/libc/locale/mbtowc.c
+++ b/lib/libc/locale/mbtowc.c
@@ -32,6 +32,7 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include <errno.h>
 #include <stdlib.h>
 #include <wchar.h>
 #include "mblocal.h"
@@ -49,9 +50,15 @@ mbtowc_l(wchar_t * __restrict pwc, const char * __restrict s, size_t n, locale_t
 		return (0);
 	}
 	rval = XLOCALE_CTYPE(locale)->__mbrtowc(pwc, s, n, &locale->mbtowc);
-	if (rval == (size_t)-1 || rval == (size_t)-2)
+	switch (rval) {
+	case (size_t)-2:
+		errno = EILSEQ;
+		/* FALLTHROUGH */
+	case (size_t)-1:
 		return (-1);
-	return ((int)rval);
+	default:
+		return ((int)rval);
+	}
 }
 int
 mbtowc(wchar_t * __restrict pwc, const char * __restrict s, size_t n)