Re: [Qemu-devel] Where is vga-rom mapped in guest system memory?

[Jaeyong Yoo]

> -----Original Message-----
> From: address@hidden [mailto:qemu-
> address@hidden On Behalf Of Laszlo
> Ersek
> Sent: Wednesday, May 14, 2014 7:56 PM
> To: Jaeyong Yoo; address@hidden
> Subject: Re: [Qemu-devel] Where is vga-rom mapped in guest system memory?
> 
> On 05/14/14 06:01, Jaeyong Yoo wrote:
> >> -----Original Message-----
> >> From: address@hidden
> >> [mailto:qemu-
> >> address@hidden On Behalf Of Laszlo
> >> Ersek
> >> Sent: Tuesday, May 13, 2014 10:55 PM
> >> To: address@hidden; address@hidden
> >> Subject: Re: [Qemu-devel] Where is vga-rom mapped in guest system
> memory?
> >>
> >> On 05/13/14 14:58, Jaeyong Yoo wrote:
> >>> Hello qemu!
> >>>
> >>>
> >>>
> >>> I am currently writing a vga device emulator and need to debug vga-
> bios.
> >>>
> >>> What I want is to set break-point on the entry of vga-bios and for
> >>> this,
> >>>
> >>> I'm reading qemu source around pci device and rom-related memory
> >>> regions
> >>>
> >>> to find out where should I set break point. And, sadly, got stuck.
> >>>
> >>>
> >>>
> >>> Could you give me any advice about the memory-mapped address of
> >>> vga-rom or
> >>>
> >>> any pointers?
> >>
> >> Some.
> >>
> >> The vgabios binary is loaded from the file identified by the "romfile"
> >> property of the VGA card that you select. For example,
> >>
> >>   -device qxl-vga,romfile=...
> >>
> >> or
> >>
> >>   -vga qxl \
> >>   -global qxl-vga.romfile=...
> >>
> >> Of course the property has a default value for each VGA card. See the
> >>
> >>   k->romfile = ...
> >>
> >> assignments in:
> >> - cirrus_vga_class_init() -- vgabios-cirrus.bin
> >> - qxl_primary_class_init() -- vgabios-qxl.bin
> >> - vga_class_init() -- vgabios-stdvga.bin
> >>
> >> I think the oprom is loaded in
> >>
> >> pci_qdev_init() [hw/pci/pci.c]
> >>   pci_add_option_rom()
> >>
> >> The vgabios oprom is shadowed from ROM (pci address space) to RAM by
> >> the SeaBIOS initialization code, and then POSTed:
> >>
> >> handle_post() [src/post.c]
> >>   make_bios_writable() [src/fw/shadow.c]
> >>     make_bios_writable_intel()
> >>       __make_bios_writable_intel() -- shadows vgabios in C segment too
> >>   dopost() [src/post.c]
> >>     maininit()
> >>       vgarom_setup() [src/optionroms.c]
> >>         init_pcirom()
> >>           init_optionrom()
> >>             callrom()
> >>               __callrom()
> >>                 _rom_header_entry [vgasrc/vgaentry.S]
> >>                   vga_post() [vgasrc/vgainit.c]
> >>
> >> You can instrument vga_post() in the SeaBIOS source
> >> [vgasrc/vgainit.c], rebuild the vgabios binary, and load this binary
> >> with the video card's romfile=... property on the qemu command line.
> >
> > Thanks for the answer. It is the exact code-path that I was looking
> > for :-)
> >
> > I have one follow-up question.
> > It looks like seabios (bios.bin) includes the vgabios (such as
> > vga_post functions). And this bios.bin is not loaded as
> > vgabios-stdvga.bin (the one that you mentioned in vga_class_init). I'm
> > not clearly understanding the difference between vgabios inside bios.bin
> and vgabios-stdvga.bin.
> > Could you tell me the difference?
> 
> bios.bin and vgabios.bin are separate build outputs of SeaBIOS. If you run
> "make menuconfig" in the seabios directory and browse the options, it
> should become clearer. (The build system should be discussed on the
> seabios list, the maintainers can help you more than I can.)
> 
> I recommend to study the following SRPM:
> 
> https://www.kraxel.org/repos/jenkins/seabios/seabios.git-1.7.4-
> 93.b113.g6ad7b5b.src.rpm
> 
> the SPEC file should help (see the do_build() function and the various
> build config files).

Thanks for the answer, Laszlo.

I built the seabios in qemu and try to see the debug message of seabios.
So, I checked the "Serial port debugging" option in Debugging section with the 
serial port base address 0x3f8. (Is this the correct value?)
And, launch qemu with option "-serial stdio" but I don’t see any messages from
seabios. If I want to see the debug message of seabios to the output console,
what am I missing?

My full command for launching qemu is the following:
$ sudo x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 1024 -vga vmware 
-serial stdio ~/data/qemu-images/ubuntu-13.04-desktop.img


Thanks,
Jaeyong