Re: [Qemu-devel] Stack corruption problem with SeaBIOS/gPXE under QEMU

[Avi Kivity <avi@redhat.com>]

On 11/14/2009 09:47 PM, Kevin O'Connor wrote:
> Hi,
>
> On Thu, Nov 12, 2009 at 01:20:58PM +0200, Naphtali Sprei wrote:
>    
>> I've found a problem with the usage of SeaBIOS/gPXE in Qemu.  The
>> scenario is when failing to boot from network and falling back to
>> booting from hard-disk (-boot nc).  The cause of the problem is that
>> both SeaBIOS and gPXE (in it's installation phase) uses same stack
>> area, 0x7c00.  The gPXE code corrupts the SeaBIOS stack, so when
>> gPXE returns to SeaBIOS chaos occurs.
>>
>> Output: "qemu: fatal: Trying to execute code outside RAM or ROM at 0x00000000eb300000"
>>      
> Thanks for reporting this.
>
> We can move the SeaBIOS stack, but it's not clear to me where to move
> it to.  Bochs bios puts the top of the stack at 0x10000, but this
> could potentially conflict with the OS load to 0x7c00.  So, in SeaBIOS
> the top of stack was moved to 0x7c00 to prevent this conflict.
>
> Maybe the gPXE developers know where the bios typically places its
> stack.
>
> However, I'm not sure why gPXE doesn't just use the stack it was
> given, or allocate the stack space it needs with PMM.
>    

Something that is likely related, I am seeing reboot failures in 
seabios's pmm_free.  Immediately after loading gpxe, seabios is in an 
endless loop there, likely due to memory corruption.

This is with -smp 2, rebooting Fedora 9 after installation.

-- 
error compiling committee.c: too many arguments to function