[Qemu-devel] [BUG] Displaying VGA framebuffer on SDL does not work correctly

[Stefan Weil]

VGA framebuffer shows very strange behaviour with QEMU's SDL display:

I run qemu with my harddisk which contains a debian grub2 bootloader.
grub2 is configured to display a 1280x1024 png background image
(moreblue-orbit-grub.png resized to my monitor resolution).

i386-softmmu/qemu /dev/sda -enable-kvm

-enable-kvm is just to get more speed (without, it takes longer
to see the bug).

Running like this gives random results: sometimes, the png is shown
correctly, sometimes not.

But you will always get a bad display when you resize the QEMU window
while in grub's boot menu (a screenshot is appended).

git bisect detects this commit:

0bd8246bfec1dfb2eb959f52db535572c0260f4c is first bad commit
commit 0bd8246bfec1dfb2eb959f52db535572c0260f4c
Author: Stefano Stabellini <address@hidden>
Date:   Mon Aug 3 16:14:39 2009 +0100

    vga: do not resize the screen on hw_invalidate

    Hi all,
    currently vga always resizes the screen when vga_hw_invalidate is called
    while this is not required and all the other graphic emulators don't.
    This patch fixes it, making vga invalidate behaviour consistent with the
    other emulated devices.

    Signed-off-by: Stefano Stabellini <address@hidden>
    Signed-off-by: Anthony Liguori <address@hidden>

Reverting it fixes the bug.

As this is already the second bug caused by the same commit
and it is also part of a stable version, I recommend reverting it
(then there is more time to look for a better solution).

Regards,
Stefan Weil