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From: jak <nospam@please.ty>
Newsgroups: comp.lang.c
Subject: Re: C23 thoughts and opinions
Date: Fri, 31 May 2024 21:42:35 +0200
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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.