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From: bart <bc@freeuk.com>
Newsgroups: comp.lang.c
Subject: Re: C23 thoughts and opinions
Date: Fri, 31 May 2024 22:15:54 +0100
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On 31/05/2024 19:36, Scott Lurndal wrote:
> bart <bc@freeuk.com> writes:
>> On 31/05/2024 15:34, Michael S wrote:
>>> On Fri, 31 May 2024 15:04:46 +0100
>>> bart <bc@freeuk.com> wrote:
> 
>> Instead of one compiler, here I used two compilers, a tool 'objcopy'
>> (which bizarrely needs to generate ELF format files) and lots of extra
>> ugly code. I also need to disregard whatever the hell _binary_..._size does.
> 
> $ objcopy -I binary -O elf64-x86-64 main.cpp /tmp/test.o
> 
> $ objdump -x /tmp/test.o
> 
> /tmp/test.o:     file format elf64-little
> /tmp/test.o
> architecture: UNKNOWN!, flags 0x00000010:
> HAS_SYMS
> start address 0x0000000000000000
> 
> Sections:
> Idx Name          Size      VMA               LMA               File off  Algn
>    0 .data         000030e2  0000000000000000  0000000000000000  00000040  2**0
>                    CONTENTS, ALLOC, LOAD, DATA
> SYMBOL TABLE:
> 0000000000000000 l    d  .data  0000000000000000 .data
> 0000000000000000 g       .data  0000000000000000 _binary_main_cpp_start
> 00000000000030e2 g       .data  0000000000000000 _binary_main_cpp_end
> 00000000000030e2 g       *ABS*  0000000000000000 _binary_main_cpp_size
> 
> $ ls -l main.cpp
> -rw-rw-r--. 1 scott scott 12514 May  9  2022 main.cpp
> $ printf '%u\n' $(( 0x30e2 ))
> 12514
> 
> The value of the symbol _binary_main_cpp_size is the
> number of bytes in the file.
> 
> (in other words,
> 
>       _binary_main_cpp_size = _binary_main_cpp_end - _binary_main_cpp_start
> 
> )
> 
> In C code:
> 
> extern uint8_t _binary_main_cpp_size;
> 
> const size_t embed_size = &_binary_main_cpp_size;

Did you see the output from my version of Michael S's program? The size 
is just an address. If I do what you do:

   extern unsigned char _binary_hello_c_size;

.....
   size_t size = &_binary_hello_c_size;
   printf("size: %zu\n", size);

It produces:

   size: 140697695027270

Little of this seems to work, sorry. You guys keep saying, do this, do 
that, no do it that way, go RTFM, but nobody has shown a complete 
program that correctly shows the -size symbol to be giving anything 
meaningful.

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?

I can extract the size using:

    printf("%d\n", (unsigned short)&_binary_hello_c_size);

But something is not right. I've also asked what is the point of the 
-size symbol if you can just do -end - -start, but nobody has explained.