linux-kernel - [PATCH] m68k: Fix lost column on framebuffer debug console

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Message-ID: <c03e60ce451e4ccdf12830192080be4262b31b89.1741338535.git.fthain@linux-m68k.org>
Date: Fri, 07 Mar 2025 20:08:55 +1100
From: Finn Thain <fthain@...ux-m68k.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: stable@...r.kernel.org,
    linux-m68k@...ts.linux-m68k.org,
    linux-kernel@...r.kernel.org
Subject: [PATCH] m68k: Fix lost column on framebuffer debug console

When long lines are sent to the debug console on the framebuffer, the
right-most column is lost. Fix this by subtracting 1 from the column
count before comparing it with console_struct_cur_column, as the latter
counts from zero.

Linewrap is handled with a recursive call to console_putc, but this
alters the console_struct_cur_row global. Store the old value before
calling console_putc, so the right-most character gets rendered on the
correct line.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@...r.kernel.org
Signed-off-by: Finn Thain <fthain@...ux-m68k.org>
---
 arch/m68k/kernel/head.S | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/m68k/kernel/head.S b/arch/m68k/kernel/head.S
index 852255cf60de..9c60047764d0 100644
--- a/arch/m68k/kernel/head.S
+++ b/arch/m68k/kernel/head.S
@@ -3583,11 +3583,16 @@ L(console_not_home):
 	movel	%a0@(Lconsole_struct_cur_column),%d0
 	addql	#1,%a0@(Lconsole_struct_cur_column)
 	movel	%a0@(Lconsole_struct_num_columns),%d1
+	subil	#1,%d1
 	cmpl	%d1,%d0
 	jcs	1f
-	console_putc	#'\n'	/* recursion is OK! */
+	/*	recursion will alter console_struct so load d1 register first */
+	movel	%a0@(Lconsole_struct_cur_row),%d1
+	console_putc	#'\n'
+	jmp	2f
 1:
 	movel	%a0@(Lconsole_struct_cur_row),%d1
+2:
 
 	/*
 	 *	At this point we make a shift in register usage
-- 
2.45.3