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From: Victor Porton <porton@narod.ru>
Newsgroups: comp.lang.ada
Subject: Re: Allocators design flaw
Date: Sat, 14 Oct 2017 19:42:50 +0300
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Date: 2017-10-14T19:42:50+03:00
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Dmitry A. Kazakov wrote:

> On 2017-10-14 17:18, Victor Porton wrote:
>> Dmitry A. Kazakov wrote:
>> 
>>> On 2017-10-14 16:03, Victor Porton wrote:
>>>> Dmitry A. Kazakov wrote:
>>>>
>>>>> When freed use the stored offset to
>                  ^^^^^^^^^^^^^^^^^^^^^^^^
>>>>> get the original address.
>       ^^^^^^^^^^^^^^^^^^^^^^^^
> 
>>>> As far as I understand, it will not work, because the C library I am
>>>> writing bindings for may try to free an object allocated by me (or I my
>>>> need to free an object allocated by the library).
>>>
>>> The last sentence describes freeing memory, i.e. for Deallocate.
>> 
>> I again state that we need the C function *_free() to free memory. But it
>> is impossible in your scenario, because you change the pointer to point
>> to another byte of memory.
> 
> Re-read the last sentence of my response.

No Dmitry, you don't understand me.

We may pass the allocated address to a C function.

1. This C function may need to get some data from the struct. In this case 
we need to pass into C the shifted address.

2. This C function may call *_free() with the address of the struct. In this 
case we need to pass into C the original allocation address.

Thus the same address we pass into a C function is both original and 
shifted. This is a clear contradiction.

-- 
Victor Porton - http://portonvictor.org