Unable to start xserver

[Andreas Mohr]

Hi,

On Tue, Jul 03, 2012 at 09:07:40AM -0700, xorg-request at lists.x.org wrote:
> Date: Tue, 3 Jul 2012 14:08:57 +0200
> From: Abhishek Gupta <abhishek.ismdhn at gmail.com>

> Hi,
> 
> I was trying to run xserver on l4linux which is paravirtualised liux
> running on top of l4
> 
> using vesa frame buffer (l4 is running on kvm) and virtual machine
> hangs with a black screen.
> 
> 
> When I tried to debug it using gdb, it displays
> 0xb6ee9b28 in SetResetBIOSVars (pInt=0x820f5a0, set=<value optimized out>)
> at ../../../../hw/xfree86/int10/helper_exec.c:686
> 
> this code is from the xserver 1.7.7
> 
> static void
> SetResetBIOSVars(xf86Int10InfoPtr pInt, Bool set)
> {
>     int pagesize = getpagesize();
>     unsigned char* base = xf86MapVidMem(pInt->scrnIndex,
> VIDMEM_MMIO, 0, pagesize);
>     int i;
> 
>     if (set) {
> for (i = BIOS_SCRATCH_OFF; i < BIOS_SCRATCH_END; i++)
>     MEM_WW(pInt, i, *(base + i));
>     } else {
> for (i = BIOS_SCRATCH_OFF; i < BIOS_SCRATCH_END; i++)
>               /*line 685*/
>     *(base + i) = MEM_RW(pInt, i);    /*line 686*/ //This line of code
> is not working
> 
>     }
> 
>     xf86UnMapVidMem(pInt->scrnIndex,base,pagesize);
> }
> I changed the DEFAULT_INT10 from x86emu to vm86 but then also xserver
> stops at exactly same Macro.
> 
> Is there any driver which I can use that doesn't uses int10 to set the
> video mode?

I'm not qualified to indicate this, sorry.

> Also what could be the possible reasons that xserver is showing
> segmentation fault while running MEM_RW macro??

You should have listed a disas around EIP register
(i.e. info reg, disas $eip-0x40 $eip+0x40 or some such).
That way one would be able to gather more details of what's
failing (possibly base address NULL, ...).

HTH,

Andreas Mohr