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Re: [Qemu-devel] Standard vga breakage

From: malc
Subject: Re: [Qemu-devel] Standard vga breakage
Date: Mon, 16 Nov 2009 00:21:17 +0300 (MSK)

On Sun, 15 Nov 2009, Stefan Weil wrote:

> malc schrieb:
> > On Sun, 15 Nov 2009, Gleb Natapov wrote:


> Here is a summary of my analysis of this problem:
> Graphics mode memory (ram 0xe0000000 ...) is not mapped
> in QEMU address space (which results in unassigned
> memory writes) for standard pci vga (-vga std), so users
> don't get vga display output with grub (in graphical mode),
> debian installer (in graphical mode) or similar boot software.
> This happens for PC system emulation using SeaBIOS.
> It won't happen when using Bochs BIOS.
> Other system emulations which can run standard pci vga
> seem to suffer from the same problem: when I run mips
> malta using -vga std, it won't display anything on the vga
> screen (it works with cirrus pci vga).
> Malta has no vga bios, so the error might be in QEMU's
> vga code (hw/vga-pci.c). Maybe wrong initial PCI mappings?
> Maybe this has always be wrong (which would explain why
> git bisect does not work).

git bisect doesn't work because most of the time:

a. Compilation fails
b. Compilation succeeds but qemu segfaults before even trying to
   execute any guest code

> pci_vga_init() is called by sun4u, ppc_prep, ppc_oldworld,
> ppc_newworld, pc and mips, so all these emulations
> share the same potential problem.
> Bochs BIOS and PC Linux obviously fix the problem.
> Regards,
> Stefan


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