Re: 2.6.12-rc1 breaks dosemu

[Arjan van de Ven]

On Sat, 2005-03-26 at 15:28 +0100, Arjan van de Ven wrote:
> On Sat, 2005-03-26 at 14:49 +0100, Arnd Bergmann wrote:
> > On SÃnnavend 26 MÃrz 2005 09:18, Bart Oldeman wrote:
> > > On Sat, 26 Mar 2005, Arjan van de Ven wrote:
> > > 
> > > > > eip: 0x000069ee  esp: 0xbfdbffcc  eflags: 0x00010246
> > > >
> > > > hmm interesting. Can you check if at the time of the crash, the esp is
> > > > actually inside the stack vma? If it's not, I wonder what dosemu does to
> > > > get its stack pointer outside the vma... (and on which side of the vma
> > > > it is)
> > 
> > The esp value is always slightly below the stack vma and above ld.so.
> > Running it a few times gives 
> > 
> > stack VMA         crash esp
> > bfc8f000-bfca4000 bfc5ffcc  
> 
> the esp is 0x2F034/192564 bytes below the stack vma. That is a lot! I
> vaguely remember linux having a limit to how much below the stack vma it
> will allow accesses to auto-grow the stack, but I forgot what that limit
> actually was. I wonder if dosemu is somehow getting away with assuming a
> certain alignment by accident and then being inside the kernel grow
> limit, while with randomisation the alignment is only 4Kb and somehow a
> bigger-than-expected auto-grow is needed.

hmm I just read back your first mail and it seems the actual memory
access isn't to the stack at all but to 0xffffff8e
sounds like dosemu had an internal underflow somewhere...


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