2017-11-07 12:55:08

by Florian Weimer

[permalink] [raw]
Subject: Re: POWER: Unexpected fault when writing to brk-allocated memory

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

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