[Qemu-devel] [PATCH v2] SGABIOS: fix wrong video attrs for int 10h, ah==13h

[Qemu-devel] [PATCH v2] SGABIOS: fix wrong video attrs for int 10h, ah==13h

[Herbie Robinson]

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.  Also, remove save and restore in set_current_cursor,
because set_cursor_position does it.

Signed-off-by: Herbie Robinson <Herbie.Robinson@stratus.com>
---
Removed incorrect code deletions from set_current_cursor.

 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:
 
 set_cursor_position:
   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
   ret
 
-- 
1.8.3.1

Re: [Qemu-devel] [Qemu-trivial] [PATCH v2] SGABIOS: fix wrong video attrs for int 10h, ah==13h

[Laurent Vivier]

On 09/03/2017 19:48, Herbie Robinson wrote:
> 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.  Also, remove save and restore in set_current_cursor,
> because set_cursor_position does it.
> 
> Signed-off-by: Herbie Robinson <Herbie.Robinson@stratus.com>
> ---
> Removed incorrect code deletions from set_current_cursor.

You should update the commit message too.

Laurent
> 
>  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:
>  
>  set_cursor_position:
>    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
>    ret
>  
>