[Qemu-devel] uvesafb doesn't work with seabios

[Qemu-devel] uvesafb doesn't work with seabios

[Bernhard Walle]

Hello,

I'm using QEmu 2.0.0 on a Linux host (x86-64) with a quite special
target system that uses uvesafb ('video=uvesafb:1024x768-32'). I get
following errors in the target system:

    uvesafb: Getting mode info block for mode 0x2 failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0x3 failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0x4 failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0x5 failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0x6 failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0x7 failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0xd failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0xe failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0xf failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0x10 failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0x11 failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0x12 failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0x13 failed (eax=0x4f01, err=1)
    uvesafb: Getting mode info block for mode 0x6a failed (eax=0x4f01, err=1)
    uvesafb: vbe_init() failed with -22
    uvesafb: probe of uvesafb.0 failed with error -22

With QEmu 1.6, it worked. I bisected that down to following commit:

    commit 6eefccc0bb9c34051b1e21880fc3a1c1c8686edd
    Author: Gerd Hoffmann <kraxel@redhat.com>
    Date:   Mon Dec 2 13:01:20 2013 +0100

    roms: update vgabios binaries

And indeed, when I switch 'vgabios-stdvga.bin' to the old variant, it works.

What can I do to track down the problem? I tried to build the svga bios
inside the QEMU tree, but I didn't succeed. Building it in the current
seabios git tree worked, but I got a different error...


Regards,
Bernhard

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Kevin O'Connor]

On Fri, May 09, 2014 at 05:06:21PM +0200, Bernhard Walle wrote:
> Hello,
> 
> I'm using QEmu 2.0.0 on a Linux host (x86-64) with a quite special
> target system that uses uvesafb ('video=uvesafb:1024x768-32'). I get
> following errors in the target system:
> 
>     uvesafb: Getting mode info block for mode 0x2 failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0x3 failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0x4 failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0x5 failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0x6 failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0x7 failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0xd failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0xe failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0xf failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0x10 failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0x11 failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0x12 failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0x13 failed (eax=0x4f01, err=1)
>     uvesafb: Getting mode info block for mode 0x6a failed (eax=0x4f01, err=1)
>     uvesafb: vbe_init() failed with -22
>     uvesafb: probe of uvesafb.0 failed with error -22
> 
> With QEmu 1.6, it worked. I bisected that down to following commit:
> 
>     commit 6eefccc0bb9c34051b1e21880fc3a1c1c8686edd
>     Author: Gerd Hoffmann <kraxel@redhat.com>
>     Date:   Mon Dec 2 13:01:20 2013 +0100
> 
>     roms: update vgabios binaries
> 
> And indeed, when I switch 'vgabios-stdvga.bin' to the old variant, it works.
> 
> What can I do to track down the problem? I tried to build the svga bios
> inside the QEMU tree, but I didn't succeed. Building it in the current
> seabios git tree worked, but I got a different error...

Can you run the original SeaVGABIOS image and provide the output with
the following added to the qemu command line:

-chardev stdio,id=seabios -device isa-debugcon,iobase=0x402,chardev=seabios

Also, it looks like uvesafb can call x86emu.  Older versions of x86emu
are known to not emulate some instructions properly, and it has caused
problems for SeaVGABIOS.  The most recent version of SeaVGABIOS from
SeaBIOS git has additional checks for this - can you grab the seabios
git, set CONFIG_DEBUG_LEVEL to 8, build SeaVGABIOS (set
CONFIG_VGA_BOCHS), and post the logs from both Linux and QEMU with the
above options?

-Kevin

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Bernhard Walle]

Am 10.05.14 17:07, schrieb Kevin O'Connor:
> 
> Can you run the original SeaVGABIOS image and provide the output with
> the following added to the qemu command line:
> 
> -chardev stdio,id=seabios -device isa-debugcon,iobase=0x402,chardev=seabios

Since it's quite much debugging info, I uploaded it to
http://bwalle.de/tmp/debugoutput-unmodified

Basically it's

  set VGA mode 12
  set VGA mode 3
  VBE mode info request: 100
  VBE mode info request: 101
  ...
  VBE mode info request: 6a
  set VGA mode 3
  VBE mode info request: 100

> Also, it looks like uvesafb can call x86emu.  Older versions of x86emu
> are known to not emulate some instructions properly, and it has caused
> problems for SeaVGABIOS.  The most recent version of SeaVGABIOS from
> SeaBIOS git has additional checks for this - can you grab the seabios
> git, set CONFIG_DEBUG_LEVEL to 8, build SeaVGABIOS (set
> CONFIG_VGA_BOCHS), and post the logs from both Linux and QEMU with the
> above options?

It doesn't change the result (that it doesn't work). It only makes the
kernel failing much faster and of course there's much more debugging
output: http://bwalle.de/tmp/debugoutput (250k).


Regards,
Bernhard

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Kevin O'Connor]

On Sun, May 11, 2014 at 01:42:57PM +0200, Bernhard Walle wrote:
> Am 10.05.14 17:07, schrieb Kevin O'Connor:
> > Also, it looks like uvesafb can call x86emu.  Older versions of x86emu
> > are known to not emulate some instructions properly, and it has caused
> > problems for SeaVGABIOS.  The most recent version of SeaVGABIOS from
> > SeaBIOS git has additional checks for this - can you grab the seabios
> > git, set CONFIG_DEBUG_LEVEL to 8, build SeaVGABIOS (set
> > CONFIG_VGA_BOCHS), and post the logs from both Linux and QEMU with the
> > above options?
> 
> It doesn't change the result (that it doesn't work). It only makes the
> kernel failing much faster and of course there's much more debugging
> output: http://bwalle.de/tmp/debugoutput (250k).

Were there any Linux or userspace messages with the above?

-Kevin

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Bernhard Walle]

Am 2014-05-11 14:37, schrieb Kevin O'Connor:
> On Sun, May 11, 2014 at 01:42:57PM +0200, Bernhard Walle wrote:
>> Am 10.05.14 17:07, schrieb Kevin O'Connor:
>> > Also, it looks like uvesafb can call x86emu.  Older versions of x86emu
>> > are known to not emulate some instructions properly, and it has caused
>> > problems for SeaVGABIOS.  The most recent version of SeaVGABIOS from
>> > SeaBIOS git has additional checks for this - can you grab the seabios
>> > git, set CONFIG_DEBUG_LEVEL to 8, build SeaVGABIOS (set
>> > CONFIG_VGA_BOCHS), and post the logs from both Linux and QEMU with the
>> > above options?
>> 
>> It doesn't change the result (that it doesn't work). It only makes the
>> kernel failing much faster and of course there's much more debugging
>> output: http://bwalle.de/tmp/debugoutput (250k).
> 
> Were there any Linux or userspace messages with the above?


Yes:

   uvesafb: Getting VBE info block failed (eax=0x1d2, err=0)
   uvesafb: vbe_init() failed with -22
   uvesafb: probe of uvesafb.0 failed with error -22



Regards,
Bernhard

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Kevin O'Connor]

On Sun, May 11, 2014 at 04:19:55PM +0200, Bernhard Walle wrote:
> Am 2014-05-11 14:37, schrieb Kevin O'Connor:
> >On Sun, May 11, 2014 at 01:42:57PM +0200, Bernhard Walle wrote:
> >>Am 10.05.14 17:07, schrieb Kevin O'Connor:
> >>> Also, it looks like uvesafb can call x86emu.  Older versions of x86emu
> >>> are known to not emulate some instructions properly, and it has caused
> >>> problems for SeaVGABIOS.  The most recent version of SeaVGABIOS from
> >>> SeaBIOS git has additional checks for this - can you grab the seabios
> >>> git, set CONFIG_DEBUG_LEVEL to 8, build SeaVGABIOS (set
> >>> CONFIG_VGA_BOCHS), and post the logs from both Linux and QEMU with the
> >>> above options?
> >>
> >>It doesn't change the result (that it doesn't work). It only makes the
> >>kernel failing much faster and of course there's much more debugging
> >>output: http://bwalle.de/tmp/debugoutput (250k).
> >
> >Were there any Linux or userspace messages with the above?
> 
> 
> Yes:
> 
>   uvesafb: Getting VBE info block failed (eax=0x1d2, err=0)
>   uvesafb: vbe_init() failed with -22
>   uvesafb: probe of uvesafb.0 failed with error -22

It does look like the x86emu issue.  You can try applying the
SeaVGABIOS patch below to confirm it.

-Kevin


--- a/vgasrc/vgaentry.S
+++ b/vgasrc/vgaentry.S
@@ -47,7 +47,14 @@ _rom_header_signature:
 
         // Force a fault if found to be running on broken x86emu versions.
         DECLFUNC x86emu_fault
+msg:    .ascii "SeaVGABIOS: x86emu leal trap!\n"
 x86emu_fault:
+#if CONFIG_DEBUG_IO
+        movw %cs:DebugOutputPort, %dx
+        movl $30, %ecx
+        movl $msg, %esi
+        rep outsb %cs:(%esi), (%dx)
+#endif
 1:      hlt
         jmp 1b
 

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Bernhard Walle]

Am 2014-05-12 07:29, schrieb Kevin O'Connor:
> 
> It does look like the x86emu issue.  You can try applying the
> SeaVGABIOS patch below to confirm it.

The output doesn't appear. But I'm sure that I copied the correct files
because modifications of other strings worked.

Regards,
Bernhard

> 
> -Kevin
> 
> 
> --- a/vgasrc/vgaentry.S
> +++ b/vgasrc/vgaentry.S
> @@ -47,7 +47,14 @@ _rom_header_signature:
> 
>          // Force a fault if found to be running on broken x86emu 
> versions.
>          DECLFUNC x86emu_fault
> +msg:    .ascii "SeaVGABIOS: x86emu leal trap!\n"
>  x86emu_fault:
> +#if CONFIG_DEBUG_IO
> +        movw %cs:DebugOutputPort, %dx
> +        movl $30, %ecx
> +        movl $msg, %esi
> +        rep outsb %cs:(%esi), (%dx)
> +#endif
>  1:      hlt
>          jmp 1b

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Kevin O'Connor]

On Mon, May 12, 2014 at 08:53:53PM +0200, Bernhard Walle wrote:
> Am 2014-05-12 07:29, schrieb Kevin O'Connor:
> >
> >It does look like the x86emu issue.  You can try applying the
> >SeaVGABIOS patch below to confirm it.
> 
> The output doesn't appear. But I'm sure that I copied the correct files
> because modifications of other strings worked.

Heh - old versions of x86emu apparently don't support "rep outsb"
either.  Can you test the patch below instead?

-Kevin


--- a/vgasrc/vgaentry.S
+++ b/vgasrc/vgaentry.S
@@ -47,7 +47,17 @@ _rom_header_signature:
 
         // Force a fault if found to be running on broken x86emu versions.
         DECLFUNC x86emu_fault
+msg:    .ascii "SeaVGABIOS: x86emu leal trap!\n"
 x86emu_fault:
+#if CONFIG_DEBUG_IO
+        movw %cs:DebugOutputPort, %dx
+        movw $msg, %si
+1:      movb %cs:(%si), %al
+        outb %al, (%dx)
+        incw %si
+        cmpw $x86emu_fault, %si
+        jl 1b
+#endif
 1:      hlt
         jmp 1b
 

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Bernhard Walle]

Hi,

* Kevin O'Connor <kevin@koconnor.net> [2014-05-12 22:07]:
> On Mon, May 12, 2014 at 08:53:53PM +0200, Bernhard Walle wrote:
> > Am 2014-05-12 07:29, schrieb Kevin O'Connor:
> > >
> > >It does look like the x86emu issue.  You can try applying the
> > >SeaVGABIOS patch below to confirm it.
> > 
> > The output doesn't appear. But I'm sure that I copied the correct files
> > because modifications of other strings worked.
> 
> Heh - old versions of x86emu apparently don't support "rep outsb"
> either.  Can you test the patch below instead?

Okay, the output appears. So that means that I should update
v86d (the x86emu lib included there is okay?)?


Regards,
Bernhard

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Bernhard Walle]

Am 2014-05-13 07:52, schrieb Bernhard Walle:
> Hi,
> 
> * Kevin O'Connor <kevin@koconnor.net> [2014-05-12 22:07]:
>> On Mon, May 12, 2014 at 08:53:53PM +0200, Bernhard Walle wrote:
>> > Am 2014-05-12 07:29, schrieb Kevin O'Connor:
>> > >
>> > >It does look like the x86emu issue.  You can try applying the
>> > >SeaVGABIOS patch below to confirm it.
>> >
>> > The output doesn't appear. But I'm sure that I copied the correct files
>> > because modifications of other strings worked.
>> 
>> Heh - old versions of x86emu apparently don't support "rep outsb"
>> either.  Can you test the patch below instead?
> 
> Okay, the output appears. So that means that I should update
> v86d (the x86emu lib included there is okay?)?

I already have the latest version of x86d from
https://github.com/mjanusz/v86d/commits/master.


Regards,
Bernhard

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Kevin O'Connor]

On Tue, May 13, 2014 at 11:20:11AM +0200, Bernhard Walle wrote:
> Am 2014-05-13 07:52, schrieb Bernhard Walle:
> >* Kevin O'Connor <kevin@koconnor.net> [2014-05-12 22:07]:
> >>On Mon, May 12, 2014 at 08:53:53PM +0200, Bernhard Walle wrote:
> >>> Am 2014-05-12 07:29, schrieb Kevin O'Connor:
> >>> >
> >>> >It does look like the x86emu issue.  You can try applying the
> >>> >SeaVGABIOS patch below to confirm it.
> >>>
> >>> The output doesn't appear. But I'm sure that I copied the correct files
> >>> because modifications of other strings worked.
> >>
> >>Heh - old versions of x86emu apparently don't support "rep outsb"
> >>either.  Can you test the patch below instead?
> >
> >Okay, the output appears. So that means that I should update
> >v86d (the x86emu lib included there is okay?)?
> 
> I already have the latest version of x86d from
> https://github.com/mjanusz/v86d/commits/master.

Thanks for running further tests.

Unfortunately, I don't know enough about v86d or x86emu to really help
here.  I do know that the version of x86emu that ships with Xorg was
updated several years back and no longer has trouble with the leal
instruction.

As background, the root of the problem is that SeaVGABIOS is compiled
with gcc, and gcc can emit the "leal" instruction.  The old "lgpl VGA
BIOS" uses a really old compiler (bcc) which doesn't emit that x86
instruction.  The x86emu code does not properly emulate "leal" (as
near as I can tell it treats it as a "leaw" instead), which leads to
all sorts of bizarre behavior when it tries to interpret the code.
This type of issue has occurred for a bunch of instructions (on both
x86emu and on an emulator Windows uses) and we've worked around it in
SeaVGABIOS with a combination of gcc compiler flags and by post
processing gcc's assembler to remove some troublesome instructions.
Unfortunately, I don't know of any way to convince gcc to not emit the
"leal" instruction and the instruction appears too complex to readily
patch out of the assembler.

So, my advice would be to either avoid x86emu (eg, maybe by trying the
vm86 mode of v86d, or maybe by not using uvesafb), try compiling v86d
with a newer version of x86emu, or stick with the "lgpl VGA BIOS".

-Kevin

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Gerhard Wiesinger]

On 13.05.2014 17:41, Kevin O'Connor wrote:
>  The x86emu code does not properly emulate "leal" (as near as I can 
> tell it treats it as a "leaw" instead), which leads to all sorts of 
> bizarre behavior when it tries to interpret the code. This type of 
> issue has occurred for a bunch of instructions (on both x86emu and on 
> an emulator Windows uses) and we've worked around it in SeaVGABIOS 
> with a combination of gcc compiler flags and by post processing gcc's 
> assembler to remove some troublesome instructions. Unfortunately, I 
> don't know of any way to convince gcc to not emit the "leal" 
> instruction and the instruction appears too complex to readily patch 
> out of the assembler.

Can't that wrong behaviour of "leal" instruction be fixed in qemu?

Ciao,
Gerhard

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Kevin O'Connor]

On Tue, May 13, 2014 at 08:08:41PM +0200, Gerhard Wiesinger wrote:
> On 13.05.2014 17:41, Kevin O'Connor wrote:
> > The x86emu code does not properly emulate "leal" (as near as I can tell
> >it treats it as a "leaw" instead), which leads to all sorts of bizarre
> >behavior when it tries to interpret the code. This type of issue has
> >occurred for a bunch of instructions (on both x86emu and on an emulator
> >Windows uses) and we've worked around it in SeaVGABIOS with a combination
> >of gcc compiler flags and by post processing gcc's assembler to remove
> >some troublesome instructions. Unfortunately, I don't know of any way to
> >convince gcc to not emit the "leal" instruction and the instruction
> >appears too complex to readily patch out of the assembler.
> 
> Can't that wrong behaviour of "leal" instruction be fixed in qemu?

QEMU doesn't have any issue with leal.  x86emu is a separate program
that implements a (partial) x86 interpretter.

The issue being reported is when QEMU runs a guest which uses x86emu
to interpret SeaVGABIOS - QEMU is correctly emulating what a real
machine would do (random faults) and thus it can't be fixed in QEMU
itself.

-Kevin

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Bernhard Walle]

Am 13.05.14 17:41, schrieb Kevin O'Connor:
> 
> So, my advice would be to either avoid x86emu (eg, maybe by trying the
> vm86 mode of v86d, or maybe by not using uvesafb), try compiling v86d
> with a newer version of x86emu, or stick with the "lgpl VGA BIOS".

Unfortunately I cannot use vm86 mode because it's a x86-64 image (and I
really want to avoid kernel patches that seem to provide vm86 on 64 bit
kernels).

However, I took the step to update the x86emu code from X.org. That
seems to work! At least with my test VM that is based on Arch Linux.
I'll try the original Gentoo-based VM tomorrow.

For the meanwhile, I uploaded my patch at
https://bitbucket.org/bwalle/v86d/commits/all. Maybe someone else can
use it.

I'll try to push the fix to the original v86d repo, but the project seem
to be a bit unmaintained. Unfortunately, there seem to be three
independent versions of x86emu out there that even have different APIs
(luckily the X.org copy still has the same API as the "original" x86emu).

Thanks for your advise and debugging help!



Regards,
Bernhard

Re: [Qemu-devel] uvesafb doesn't work with seabios

[Bernhard Walle]

Am 13.05.14 21:48, schrieb Bernhard Walle:
> However, I took the step to update the x86emu code from X.org. That
> seems to work! At least with my test VM that is based on Arch Linux.
> I'll try the original Gentoo-based VM tomorrow.

That worked, too. :)

I sent a pull request via https://github.com/bwalle/v86d to
https://github.com/mjanusz/v86d.

Regards,
Bernhard