From: Kirill A. Korinsky <kirill@korins.ky>
Subject: Re: bin/ksh: fix vi mode UTF-8 window display
To: tech@openbsd.org
Date: Sun, 25 Jan 2026 17:27:29 +0100

On Thu, 22 Jan 2026 17:02:59 +0100,
Kirill A. Korinsky <kirill@korins.ky> wrote:
> 
> tech@
> 
> here the last my patch for ksh which address issues with UTF-8 disply logic
> which was discovered by testing of resize terminal.
> 
> It also included a fix for a crush reported by Walter Alejandro Iglesias.
> 
> The vi line editor sizes its window buffers by column count and stops
> rendering at the right edge. With UTF-8 input, a continuation byte can
> land at the edge, producing garbage like "\\xb9<" and misplacing the
> indicator; small-window resizes can also overrun the window buffer.
> 
> Size the window buffers for UTF-8 and allow trailing continuation bytes
> at the right edge. When a trailing UTF-8 byte is present, force the
> indicator to print as a space plus the marker in the usual position.
> 

Here an updated version which also included tests.

Ok?


diff --git bin/ksh/vi.c bin/ksh/vi.c
index 168a9a8ffa5..1121fd43b40 100644
--- bin/ksh/vi.c
+++ bin/ksh/vi.c
@@ -24,6 +24,7 @@
 
 #undef CTRL
 #define	CTRL(x)		((x) & 0x1F)	/* ASCII */
+#define UTF8_MAXBYTES	4
 
 struct edstate {
 	char	*cbuf;		/* main buffer to build the command line */
@@ -1370,7 +1371,7 @@ static int	prompt_trunc;		/* how much of prompt to truncate */
 static int	prompt_skip;		/* how much of prompt to skip */
 static int	winwidth;		/* available column positions */
 static char	*wbuf[2];		/* current & previous window buffer */
-static int	wbuf_len;		/* length of window buffers (x_cols-3)*/
+static int	wbuf_len;		/* length of window buffers */
 static int	win;			/* number of window buffer in use */
 static char	morec;			/* more character at right of window */
 static char	holdbuf[LINE];		/* place to hold last edit buffer */
@@ -1450,6 +1451,7 @@ static void
 calc_winsize(void)
 {
 	const char *p;
+	int newlen;
 
 	cur_col = pwidth = promptlen(prompt, &p);
 	prompt_skip = p - prompt;
@@ -1459,8 +1461,9 @@ calc_winsize(void)
 		pwidth -= prompt_trunc;
 	} else
 		prompt_trunc = 0;
-	if (!wbuf_len || wbuf_len != x_cols - 3) {
-		wbuf_len = x_cols - 3;
+	newlen = (x_cols - 3) * UTF8_MAXBYTES;
+	if (!wbuf_len || wbuf_len != newlen) {
+		wbuf_len = newlen;
 		wbuf[0] = aresize(wbuf[0], wbuf_len, APERM);
 		wbuf[1] = aresize(wbuf[1], wbuf_len, APERM);
 	}
@@ -1881,6 +1884,7 @@ display(char *wb1, char *wb2, int leftside)
 	int	 ncol;	/* display column of the cursor */
 	int	 cnt;	/* remaining display columns to fill */
 	int	 moreright;
+	int	 trailu8;
 	char	 mc;	/* new "more character" at the right of window */
 	unsigned char ch;
 
@@ -1892,8 +1896,11 @@ display(char *wb1, char *wb2, int leftside)
 	ncol = col = 0;
 	cur = es->winleft;
 	moreright = 0;
+	trailu8 = 0;
 	twb1 = wb1;
-	while (col < winwidth && cur < es->linelen) {
+	while (cur < es->linelen &&
+	    (col < winwidth ||
+	    (col == winwidth && isu8cont(es->cbuf[cur])))) {
 		if (cur == es->cursor && leftside)
 			ncol = col + pwidth;
 		if ((ch = es->cbuf[cur]) == '\t') {
@@ -1909,7 +1916,8 @@ display(char *wb1, char *wb2, int leftside)
 				}
 				ch &= 0x7f;
 			}
-			if (col < winwidth) {
+			if (col < winwidth ||
+			    (col == winwidth && isu8cont(ch))) {
 				if (ch < ' ' || ch == 0x7f) {
 					*twb1++ = '^';
 					if (++col < winwidth) {
@@ -1917,6 +1925,8 @@ display(char *wb1, char *wb2, int leftside)
 						col++;
 					}
 				} else {
+					if (col == winwidth && isu8cont(ch))
+						trailu8 = 1;
 					*twb1++ = ch;
 					if (col == 0 || !isu8cont(ch))
 						col++;
@@ -2009,8 +2019,10 @@ display(char *wb1, char *wb2, int leftside)
 		mc = '>';
 	else
 		mc = ' ';
-	if (mc != morec) {
-		ed_mov_opt(pwidth + winwidth + 1, wb1);
+	if (mc != morec || trailu8) {
+		ed_mov_opt(pwidth + winwidth, wb1);
+		x_putc(' ');
+		cur_col++;
 		x_putc(mc);
 		cur_col++;
 		morec = mc;
diff --git regress/bin/ksh/edit/vi.sh regress/bin/ksh/edit/vi.sh
index b32c9f7a566..187417c7fe4 100644
--- regress/bin/ksh/edit/vi.sh
+++ regress/bin/ksh/edit/vi.sh
@@ -225,3 +225,35 @@ testseq "aaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbccccccccccccccccccccc
 	" # aaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbccccccccccccccccccccccc\r # bbbbbbbbbbbbbcccccccccccccccccccccccc                                      <\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\bc\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\baaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbcccccccccccccccccccccccc >\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b"
 testseq "aaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbccccccccccccccccccccccccc\0033hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh\000RS81" \
 	" # aaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbccccccccccccccccccccccc\r # bbbbbbbbbbbbbcccccccccccccccccccccccc                                      <\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\bc\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\baaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbcccccccccccccccccccccccc >\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\r\033[J # aaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbccccccccccccccccccccccccc >\r # "
+
+# ASCII window indicator at left edge
+testseq "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbb" \
+	" # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbb\r # aaaaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbb                                      <\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b"
+
+# UTF-8 window indicator at left edge
+testseq "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\0303\0266bbbbbbbbb" \
+	" # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\0303\0266bbbbbbbb\r # aaaaaaaaaaaaaaaaaaaaaaaaaaa\0303\0266bbbbbbbbb                                      <\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b"
+
+# ASCII window indicator at right edge
+testseq "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabb\00330" \
+	" # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b                                      <\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\bbb\b\baaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa >\r # "
+
+# UTF-8 window indicator at right edge
+testseq "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\0303\0266b\00330" \
+	" # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b                                      <\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\0303\0266b\b\baaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa >\r # "
+
+# ASCII window indicator on both sides
+testseq "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\003340h" \
+	" # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b                                      <\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\baaaaaabbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\r # aaaaaabbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb                                    \b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\r # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbbb +\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b"
+
+# UTF-8 window indicator on both sides
+testseq "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\0303\0266bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\003340h" \
+	" # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b                                      <\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\baaaaaa\0303\0266bbbbbbbbbbbbbbbbbbbbbbbbbbbbb\r # aaaaaa\0303\0266bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb                                    \b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\r # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\0303\0266bbbbbbbbbbbbbbbbbbbbbbbbbb +\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b"
+
+# ASCII redraw at right edge
+testseq "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabb\00330\0022" \
+	" # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b                                      <\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\bbb\b\baaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa >\r # \r\r\n # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa >\r # "
+
+# UTF-8 redraw at right edge
+testseq "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\0303\0266b\00330\0022" \
+	" # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b                                      <\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\0303\0266b\b\baaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa >\r # \r\r\n # aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa >\r # "
-- 
2.52.0