Re: [Qemu-devel] [SeaBIOS] [BUG] Windows 7 fails to start with new vgabios binaries

[Kevin O'Connor <kevin@koconnor.net>]

On Tue, Dec 10, 2013 at 04:55:36AM -0500, Gal Hammer wrote:
> Kevin,
> 
> The patch was verified and it solves the problem on Windows 7 official release as well.

Thanks.

I pushed this patch to seabios git master.

-Kevin


> 
> ----- Original Message -----
> From: "Kevin O'Connor" <kevin@koconnor.net>
> To: "Gerd Hoffmann" <kraxel@redhat.com>
> Cc: "Gal Hammer" <ghammer@redhat.com>, "seabios" <seabios@seabios.org>, qemu-devel@nongnu.org, "Julian Pidancet" <julian.pidancet@gmail.com>
> Sent: Tuesday, December 10, 2013 12:12:51 AM
> Subject: Re: [SeaBIOS] [BUG] Windows 7 fails to start with new vgabios binaries
> 
> On Mon, Dec 09, 2013 at 10:57:25AM -0500, Kevin O'Connor wrote:
> > On Mon, Dec 09, 2013 at 02:20:59PM +0100, Gerd Hoffmann wrote:
> > > On Mo, 2013-12-09 at 14:18 +0200, Gal Hammer wrote:
> > > > A Windows 7 (32-bit) VM running with QXL device fails to start with the 
> > > > new updated vgabios binaries (commit 
> > > Tracked down to the new vgabios stack switching.  With
> > > CONFIG_VGA_ALLOCATE_EXTRA_STACK=n everything is fine again.
> > 
> > Ughh.  WinXP doesn't have the problem, but I can also reproduce on
> > Win7 beta.
> > 
> > I'll change the default for CONFIG_VGA_ALLOCATE_EXTRA_STACK to off.
> 
> I tracked this down further.  The problem is the Windows x86 emulator
> doesn't correctly handle memory accesses relative to the %esp
> register.  Julian reported this some time back and we worked around it
> then.  However, the recent "extra stack" assembler code inserted a few
> of these instructions.
> 
> I think the proper fix is to leave CONFIG_VGA_ALLOCATE_EXTRA_STACK on
> and use slightly different assembler so as not to aggravate win7.
> 
> I tested the seabios patch below and my win7 beta now boots okay.
> 
> -Kevin
> 
> 
> --- a/vgasrc/vgaentry.S
> +++ b/vgasrc/vgaentry.S
> @@ -97,12 +97,9 @@ entry_10_extrastack:
>          movl %ecx, BREGS_ecx(%eax)
>          movw %es, BREGS_es(%eax)
>          movl %esp, BREGS_size+0(%eax)
> -        movzwl %sp, %esp
>          movw %ss, BREGS_size+4(%eax)
> -        movl (%esp), %edx
> -        movl %edx, BREGS_code(%eax)
> -        movw 4(%esp), %dx
> -        movw %dx, BREGS_flags(%eax)
> +        popl BREGS_code(%eax)
> +        popw BREGS_flags(%eax)
>  
>          movw %ds, %dx           // Setup %ss/%esp and call function
>          movw %dx, %ss