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From: bart <bc@freeuk.com>
Newsgroups: comp.lang.c
Subject: Re: C23 thoughts and opinions
Date: Sun, 2 Jun 2024 00:39:39 +0100
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On 01/06/2024 23:11, Michael S wrote:
> On Fri, 31 May 2024 22:15:54 +0100
> bart <bc@freeuk.com> wrote:
> 
>> If I run this:
>>
>>       printf("%p\n", &_binary_hello_c_start);
>>       printf("%p\n", &_binary_hello_c_end);
>>       printf("%p\n", &_binary_hello_c_size);
>>
>> I get:
>>
>>       00007ff6ef252010
>>       00007ff6ef252056
>>       00007ff5af240046
>>
>> I can see that the first two can be subtracted to give the sizes of
>> the data, which is 70 or 0x46. 0x46 is the last byte of the address
>> of _size, so what's happening there? What's with the crap in bits
>> 16-47?
>>
> 
> It looks like ASLR. I don't see it because I test on Win7.
> 

I understand those are high-loading addresses. I was asking what they 
were doing as part of the size.

Apparently, that size value is wrongly relocated by some versions of 
gcc-ld. Since allocations work on 64KB blocks, that explains why the 
bottom 16 bits are unaffected.

So such a size value could still be used for objects up 64KB-1, but it 
sounds dodgy.