Here is a short C file cu.c:
int main(int argc, char **argv) {
(void)argc; (void)argv;
return 0;
}
When I compile it with OpenWatcom to a DOS .com file, the result is almost 3 KiB:
$ owcc -bcom -mcmodel=t -fno-stack-check -Os -s -march=i86 -W -Wall -Wextra -o cu.com cu.c
$ ls -l cu.com
-rwxr-x--- 1 pts pts 2938 Jun 20 19:26 cu.com
The smallest possible DOS .com file which does the same (just exits) is 1 byte long: it contains a single ret instruction (byte 0xc3).
How can I compile my cu.c file (with possibly some modifications, I don't care about argc or argv) to a smaller DOS .com file, without the OpenWatcom C library (libc), preferably less than 100 bytes? I will call DOS API functions (int 0x21) directly from my program, thus I won't need any of the OpenWatcom C library functions.
Please note that COM executables with Open Watcom doesn't answer my question, because the solutions presented there all include the OpenWatcom C library.
I was able to solve it by using format dos com instead of system com in my custom .lnk file. By doing so, the libfile cstart_t.obj in system begin com in link.lnk wasn't used, thus the startup code in the OpenWatcom C library wasn't referenced.
The resulting .com file is only 3 bytes (xor ax, eax; ret), which I'm happy with. To make it actually run, I have to prepare and add my .obj file though which contains ..start: and sets up segments.
I'm still looking for a solution which doesn't need a custom .lnk file.