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Subject: Re: POWER: Unexpected fault when writing to brk-allocated memory
To: "Kirill A. Shutemov" <kirill@shutemov.name>,
        Nicholas Piggin <npiggin@gmail.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
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From: Florian Weimer <fweimer@redhat.com>
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Date: Tue, 7 Nov 2017 12:26:12 +0100
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On 11/07/2017 12:15 PM, Kirill A. Shutemov wrote:

>> First of all, using addr and MAP_FIXED to develop our heuristic can
>> never really give unchanged ABI. It's an in-band signal. brk() is a
>> good example that steadily keeps incrementing address, so depending
>> on malloc usage and address space randomization, you will get a brk()
>> that ends exactly at 128T, then the next one will be >
>> DEFAULT_MAP_WINDOW, and it will switch you to 56 bit address space.
> 
> No, it won't. You will hit stack first.

That's not actually true on POWER in some cases.  See the process maps I 
posted here:

   <https://marc.info/?l=linuxppc-embedded&m=150988538106263&w=2>

Thanks,
Florian