On Monday 21 November 2005 17:38, Rob Landley wrote:
> On Monday 21 November 2005 08:58, Jeff Dike wrote:
> > On Sat, Nov 19, 2005 at 02:11:50PM +0100, Joel Palmius wrote:
> > >   * SKAS0 mode, crash:
>
> ...
>
> > > Kernel panic - not syncing: copy_context_skas0 : failed to wait for
> > > SIGUSR1/SIGTRAP, pid = 11008, n = 11008, errno = 0, status = 0xb7f
> >
> > Can you send a disassembly of stub_clone_handler?
> >
> >     Jeff
>
> I'll see this crash and raise you.  I just tried vanilla 2.6.15-rc2, and
> although it booted to a shell it crashed with the first command I ran. 
> (This is my x86 laptop, built under ubuntu with gcc 3.3.5).  Dump and
> dissassemblies follow.

Ok, below is the likely failure point.

From reading the code, I guess that this register is EIP, and that the 
disassembly is on not relocated code (the last 3 digits match):

12 - bfffe08d

>  8113080:       55                      push   %ebp
>  8113081:       89 c5                   mov    %eax,%ebp
>  8113083:       b8 c0 00 00 00          mov    $0xc0,%eax
>  8113088:       cd 80                   int    $0x80
>  811308a:       5d                      pop    %ebp
By memory we have remapped the stack
>  811308b:       89 c7                   mov    %eax,%edi

Ok, this instruction seems the failing one. However, I really wonder why it 
should fail - there is no "normal" reason for the failure, at least for what 
I see.

What makes me think is: the kernel doesn't accept stack faults below $esp - 32 
- that's called "a bug" by sources. This shouldn't be considered as a stack, 
but who knows.

>  811308d:       89 7d 18                mov    %edi,0x18(%ebp)

>  8113090:       cc                      int3
The below can be considered random crap - we stop here.

>  8113091:       8b 5c 24 04             mov    0x4(%esp),%ebx
>  8113095:       8b 74 24 08             mov    0x8(%esp),%esi
>  8113099:       8b 7c 24 0c             mov    0xc(%esp),%edi
>  811309d:       8b 6c 24 10             mov    0x10(%esp),%ebp
>  81130a1:       83 c4 14                add    $0x14,%esp
>  81130a4:       c3                      ret


> 081130b0 <stub_segv_handler>:
This one looks ok from _this_ point of view.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade





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