Re: [Qemu-devel] Standard vga breakage

[Blue Swirl <blauwirbel@gmail.com>]

On Sun, Nov 15, 2009 at 11:21 PM, malc <av1474@comtv.ru> wrote:
> On Sun, 15 Nov 2009, Stefan Weil wrote:
>
>> malc schrieb:
>> > On Sun, 15 Nov 2009, Gleb Natapov wrote:
>
> [..snip..]
>
>>
>> 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

With infinite time and resources, we could construct a fully
bisectable tree with the following properties:
- buggy commits (especially commits that break build or require manual
reconfiguration) are replaced with corrected commits by changing the
history
- no merges, linear history
- compound commits are broken down to simple, atomic versions
- documentation is added by the first commit to reduce the number of commits
- spelling fixes applied by changing history, not as a separate commit
- each commit should still have some relation to some real tree commit