Re: C23 thoughts and opinions

bart ha scritto:

On 31/05/2024 15:34, Michael S wrote:

On Fri, 31 May 2024 15:04:46 +0100
bart <bc@freeuk.com> wrote:

 

Can you show the full program and the full process?

>
test_objcopy.c:
#include <stdio.h>
>
int data1[42] = { 1,2,3 ,4,5};
extern unsigned char _binary_test_bi_start[];
extern unsigned char _binary_test_bi_end[];
extern unsigned char _binary_test_bi_size[];
>
extern unsigned char _binary_bin_to_list_c_start[];
extern unsigned char _binary_bin_to_list_c_end[];
extern unsigned char _binary_bin_to_list_c_size[];
>
int main()
{
   printf("%-40s %p %zd\n", "_binary_test_bi_start",
     _binary_test_bi_start, (size_t)_binary_test_bi_start);
   printf("%-40s %p %zd\n", "_binary_test_bi_end",
     _binary_test_bi_end, (size_t)_binary_test_bi_end);
   printf("%-40s %p %zd\n", "_binary_test_bi_size",
     _binary_test_bi_size, (size_t)_binary_test_bi_size);
   printf("%-40s %p %zd\n", "_binary_bin_to_list_c_start",
     _binary_bin_to_list_c_start, (size_t)_binary_bin_to_list_c_start);
   printf("%-40s %p %zd\n", "_binary_bin_to_list_c_end",
     _binary_bin_to_list_c_end, (size_t)_binary_bin_to_list_c_end);
   printf("%-40s %p %zd\n", "_binary_bin_to_list_c_size",
     _binary_bin_to_list_c_size, (size_t)_binary_bin_to_list_c_size);
   return 0;
}
>
Test files: test.bi and bin_to_list_c.
Conversion to ojects:
objcopy -I binary -O elf64-x86-64 test.bi test_bi.o
objcopy -I binary -O elf64-x86-64 bin_to_list.c test_c.o
>
Compilation:
gcc -s -Wall -Oz test_objcopy.c test_bi.o test_c.o

 OK, thanks. But I forget to ask what results you got from running the program. Because if I try your code, using hello.c and hello.exe as test binary/source data, I get this output:
 _binary_test_bi_start                    00007ff6497620e0 140695771160800
_binary_test_bi_end                      00007ff649762ae0 140695771163360
_binary_test_bi_size                     00007ff509750a00 140690402380288
_binary_bin_to_list_c_start              00007ff649762ae0 140695771163360
_binary_bin_to_list_c_end                00007ff649762b26 140695771163430
_binary_bin_to_list_c_size               00007ff509750046 140690402377798
 The sizes should have been 2560 and 70 respectively; those values are bit bigger than that.
 However I see that you also have start and end addresses, which sounds a much better way of determining the size. (In that case, what are those *size symbols for?).
 So I can put together a working test:
 ---------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 extern unsigned char _binary_hello_c_start[];
extern unsigned char _binary_hello_c_end[];
 char* makestr(char* start, char* end) {
     int length = end-start;
     char* s = malloc(length+1);
     memcpy(s, start, length);
     *(s+length) = 0;
     return s;
}
 int main() {
     char* str = makestr(_binary_hello_c_start, _binary_hello_c_end);
      printf("Hello = \n%s", str);
}
---------------------------------
 I can build it like this:
 ---------------------------------
C:\c>mcc -c c
Compiling c.c to c.obj
 C:\c>objcopy -I binary -O elf64-x86-64 hello.c hello.obj
 C:\c>gcc c.c hello.obj
---------------------------------
 And run it like this:
---------------------------------
C:\c>a
Hello =
#include "stdio.h"
 int main(void) {
     printf("Hello, World!\n");
}
---------------------------------
 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.
 But it works.
  

You could use the pe-x86-64 format instead of the elf64-x86-64 to reduce
the size of the object.