[Qemu-devel] [Bug 922076] [NEW] doesn't clear screen on boot

[Askar Safin]

Public bug reported:

When I start Linux in Qemu via "qemu -kernel /vmlinuz ...", opens Qemu
window, it shows message "Starting Seabios (version 0.5.1-2010...)", and
then Linux writes messages like "Loading, please wait..." on top of
previous message!

For example, I can see "Loading, please wait...on 0.5.1-2010...)"

So, Qemu doesn't clean screan before booting OS.

Moreover, when I start Linux via "qemu /disk-image", Qemu shows
"Starting Seabios (version 0.5.1-2010...)", then switches to graphical
mode, shows GRUB, then switches back to text mode and shows "Starting
Seabios" again! And again Linux prints messages on top of Seabios
messages, and we see a mix of symbols on screen.

Also, I found another bug! I am learning now to write kernels. And I see
that operator "*(char *)0xb8000 = 0" in C code of kernel doesn't clean
first charaster of screen in Qemu in "-curses" mode! If I want to real
clean this charaster, I must type "*(char *)0xb8000 = ' '".

I attach a kernel (x86, multiboot) with this bug. Just type "make" (you
need gcc) and "qemu -curses -kernel kernel". You will see that screen is
not cleared, but kernel tries to clean it. If you change 0 to ' ', all
will work!

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/922076

Title:
  doesn't clear screen on boot

Status in QEMU:
  New

Bug description:
  When I start Linux in Qemu via "qemu -kernel /vmlinuz ...", opens Qemu
  window, it shows message "Starting Seabios (version 0.5.1-2010...)",
  and then Linux writes messages like "Loading, please wait..." on top
  of previous message!

  For example, I can see "Loading, please wait...on 0.5.1-2010...)"

  So, Qemu doesn't clean screan before booting OS.

  Moreover, when I start Linux via "qemu /disk-image", Qemu shows
  "Starting Seabios (version 0.5.1-2010...)", then switches to graphical
  mode, shows GRUB, then switches back to text mode and shows "Starting
  Seabios" again! And again Linux prints messages on top of Seabios
  messages, and we see a mix of symbols on screen.

  Also, I found another bug! I am learning now to write kernels. And I
  see that operator "*(char *)0xb8000 = 0" in C code of kernel doesn't
  clean first charaster of screen in Qemu in "-curses" mode! If I want
  to real clean this charaster, I must type "*(char *)0xb8000 = ' '".

  I attach a kernel (x86, multiboot) with this bug. Just type "make"
  (you need gcc) and "qemu -curses -kernel kernel". You will see that
  screen is not cleared, but kernel tries to clean it. If you change 0
  to ' ', all will work!

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