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Date: Thu, 08 Jul 2010 13:52:41 +0200
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: Re: [Xenomai-help] native: A 32k stack is not always a 'reasonable'
 size
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To: Philippe Gerum <rpm@xenomai.org>
Cc: xenomai-help <xenomai@xenomai.org>

Philippe Gerum wrote:
> On Thu, 2010-07-08 at 11:35 +0200, Gilles Chanteperdrix wrote:
>> +       down_read(&mm->mmap_sem);
>> +       if (find_vma(mm, addr) == find_vma(mm, regs->ARM_sp))
>> +               printk(KERN_INFO "FCSE: process %u(%s) probably overflowed stack
>>  at 0x%08lx.\n",
>> +                      current->pid, current->comm, regs->ARM_pc);
>> +       up_read(&mm->mmap_sem);
>>
> 
> My understanding is that such code detects faulty references within the
> _valid_ address space, typically when hitting a page guard area. But I
> guess that this won't work when treading on stack memory outside of the
> address space, e.g. below the red zone for instance, isn't it? AFAIU,
> those things may happen when the heading space of preposterously large
> stack-based objects are addressed.

We only get the case where addr and sp are both in the guard page, or
both in a memory mapping hole. We can improve a bit by trying:

	if (!find_vma(mm, regs->ARM_sp) ||
		find_vma(mm, addr) == find_vma(mm, regs->ARM_sp))

We will also catch the case where addr is in the guard page, whereas sp
is in a memory mapping hole. But as I said in the other mail I just
sent, this will only work on machines with holes between thread stacks.

-- 
					    Gilles.