Re: C23 thoughts and opinions

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.