linux-kernel - [PATCH 2/3] vt: coherence validation code for the unicode screen buffer

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Date:   Tue, 17 Jul 2018 21:02:41 -0400
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Adam Borowski <kilobyte@...band.pl>,
        Dave Mielke <Dave@...lke.cc>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        linux-kernel@...r.kernel.org, linux-console@...r.kernel.org
Subject: [PATCH 2/3] vt: coherence validation code for the unicode screen buffer

Make sure the unicode screen buffer matches the video screen content.
This is provided for debugging convenience and disabled by default.

Signed-off-by: Nicolas Pitre <nico@...aro.org>
---
 drivers/tty/vt/vt.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 03e79f7787..331f175265 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -328,6 +328,8 @@ void schedule_console_callback(void)
 #define get_vc_uniscr(vc) vc->vc_uni_screen
 #endif
 
+#define VC_UNI_SCREEN_DEBUG 0
+
 typedef uint32_t char32_t;
 
 /*
@@ -571,6 +573,42 @@ void vc_uniscr_copy_line(struct vc_data *vc, void *dest, int viewed,
 	}
 }
 
+/* this is for validation and debugging only */
+static void vc_uniscr_debug_check(struct vc_data *vc)
+{
+	struct uni_screen *uniscr = get_vc_uniscr(vc);
+	unsigned short *p;
+	int x, y, mask;
+
+	if (!VC_UNI_SCREEN_DEBUG || !uniscr)
+		return;
+
+	WARN_CONSOLE_UNLOCKED();
+
+	/*
+	 * Make sure our unicode screen translates into the same glyphs
+	 * as the actual screen. This is brutal indeed.
+	 */
+	p = (unsigned short *)vc->vc_origin;
+	mask = vc->vc_hi_font_mask | 0xff;
+	for (y = 0; y < vc->vc_rows; y++) {
+		char32_t *line = uniscr->lines[y];
+		for (x = 0; x < vc->vc_cols; x++) {
+			u16 glyph = scr_readw(p++) & mask;
+			char32_t uc = line[x];
+			int tc = conv_uni_to_pc(vc, uc);
+			if (tc == -4)
+				tc = conv_uni_to_pc(vc, 0xfffd);
+			if (tc == -4)
+				tc = conv_uni_to_pc(vc, '?');
+			if (tc != glyph)
+				pr_err_ratelimited(
+					"%s: mismatch at %d,%d: glyph=%#x tc=%#x\n",
+					__func__, x, y, glyph, tc);
+		}
+	}
+}
+
 
 static void con_scroll(struct vc_data *vc, unsigned int t, unsigned int b,
 		enum con_scroll dir, unsigned int nr)
@@ -2719,6 +2757,7 @@ static int do_con_write(struct tty_struct *tty, const unsigned char *buf, int co
 		do_con_trol(tty, vc, orig);
 	}
 	con_flush(vc, draw_from, draw_to, &draw_x);
+	vc_uniscr_debug_check(vc);
 	console_conditional_schedule();
 	console_unlock();
 	notify_update(vc);
-- 
2.17.1