Re: C23 thoughts and opinions

On 30/05/2024 16:03, Michael S wrote:

On Thu, 30 May 2024 15:48:39 +0100
bart <bc@freeuk.com> wrote:
 

>
Where do the _binary_logo_bmp_start and ...-size symbols come from?
That is, how do they get into the object file.
>

 objcopy generates names of the symbols from the name of input binary
file. I would think that it is possible to change these symbols to
something else, but I am not sure that it is possible withing the same
invocation of objcopy. It certainly is possible with a second pass.
Lawrence probably can give more authoritative answer.
Or as a last resort you can RTFM.
 

I gave myself the simple task of incorporating the source text of hello.c into a program, and printing it out.
My C program looked like this to start, as an initial test (ignoring declaring the size as an array, unless I had to):
   #include <stdio.h>
   typedef unsigned char byte;
   extern byte _binary_hello_c_start[];
   extern int _binary_hello_c_size;
   int main(void) {
      printf("%d\n", _binary_hello_c_size);
   }
One small matter is those ugly, long identifiers. A bigger one in this case is that I really want that embedded text to be zero terminated; here it's unlikely to be.
However I still have to create the object file with the data. I tried this:
   objcopy -I binary -O pe-x86-64 hello.c hello.obj
The contents looked about right when I looked inside.
Now to build my program. Because my C compiler can't link object files itself, I have to get it to generate an object file for the program, then use an external linker:
   C:\c>mcc -c c.c
   Compiling c.c to c.obj
   C:\c>gcc c.obj hello.obj
   hello.obj: file not recognized: file format not recognized
   collect2.exe: error: ld returned 1 exit status
Unfortunately gcc/ld doesn't recognise the output of objcopy. Even though it accepts the output of mcc which is the same COFF format.
But even if it worked, you can see it would be a bit of a palaver.
Here's how builtin embedding worked using a feature of my older C compiler:
   #include <stdio.h>
   #include <string.h>
   char hello[] = strinclude("hello.c");
   int main(void) {
       printf("hello =\n%s\n", hello);
       printf("strlen(hello) = %zu\n", strlen(hello));
       printf("sizeof(hello) = %zu\n", sizeof(hello));
   }
I build it and run it like this:
   C:\c>bcc c
   Compiling c.c to c.exe
   C:\c>c
   hello =
   #include "stdio.h"
   int main(void) {
       printf("Hello, World!\n");
   }
   strlen(hello) = 70
   sizeof(hello) = 71
   C:\c>dir hello.c
   31/05/2024  13:48                70 hello.c
It just works; no messing about with objcopy parameters; no long unwieldy names; no link errors due to unsupported file formats; no problems with missing terminators for embedded text files imported as strings; no funny ways of getting size info.