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[Qemu-trivial] [PATCH v3] SGABIOS: fix wrong video attrs for int 10h, ah

From: Herbie Robinson
Subject: [Qemu-trivial] [PATCH v3] SGABIOS: fix wrong video attrs for int 10h, ah==13h
Date: Fri, 10 Mar 2017 10:54:55 -0500

Fix Bug #1670509: wrong video attrs for int 10h, ah==13h
The subroutine set_cursor_position is trashing %bx.
Unfortunately, %bl contains the video attribute for write_string.

The fix saves %bx in the function prolog and restores it in
the epilog. 

Signed-off-by: Herbie Robinson <address@hidden>
Removed incorrect code deletions from set_current_cursor.
Removed explanation of same from the commit message.

BTW, I didn't see any test cases for this code, but if they exist
and somebody points me at them, I should be able to generate a 
very small qcow2 file that demonstrates the problem.

 sgabios.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sgabios.S b/sgabios.S
index 275d063..96c4e23 100644
--- a/sgabios.S
+++ b/sgabios.S
@@ -1728,6 +1728,7 @@ write_string_tail:
   pushw %ax
+  pushw %bx
   pushw %ds
   pushw $BDA_SEG
   popw %ds                             /* ds = 0x40 */
@@ -1738,6 +1739,7 @@ set_cursor_position:
   movw %ax, %bx                        /* bx = cursor save offset */
   movw %dx, (%bx)                      /* save new cursor value */
   popw %ds
+  popw %bx
   popw %ax

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