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Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library

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dn. Tue, 1 Aug 2023 18:38:45 +0700, JJ napisał:
> > void main(void) {
> >   static char *hello = "Hello$";
> >   _asm {
> >     mov ah, 9
> >     mov dx, hello
> >     int 0x21
> >   }
> > }  
> 
> The `hello` from `mov dx, hello` in assembly's perspective, means the
> content of the variable. Not its address.

Sure, but the variable at hand is a pointer, so what I am effectively
interested in is where it points to (ie. its content). The variable
itself acts only as a convenient label.

> > FORMAT DOS COM
> > FILE test.obj
> > OPTION NODEFAULTLIBS
> > NAME TEST.COM
> > OPTION START=main_  
> 
> I'm not familiar with Watcom linker, but the linker user's guide says
> to use these:
> 
>   system   com

Yes, and the program I posted does work all right when linked as
"system com", but a side effect of "system com" is that it forces the
import of watcom's startup code and symbols. "format dos com" does not
(but yields a non-working binary where I have to fix addresses by hand
with a hex editor).

> If you disassembed a binary using a blind disassembler (which don't
> know binary file format, and platform), all file bytes will be
> treated as code, and will start at zero or at disassembler
> application's predefined address.

This is a COM file, so it's raw code. The only data here is the "hello"
string, but it's placed at the end of the binary so it's easy to spot.

> Also check the compiled binary. Make sure it doesn't start with "MZ",

I posted the exact, full content of the binary. It's a COM file, no MZ.

Earlier today I stumbled upon an interesting stackoverflow discussion,
where Peter Szabo was trying to achieve something very similar to what
I am doing now, and Michael Petch provided some deep insight into the
matter:
https://stackoverflow.com/questions/62473231/small-model-dos-exe-compiled-and-linked-by-openwatcom-crashes

My understanding is that wlink needs the startup code to figure out how
to lay out the program's memory. Things seem to be much more convoluted
than I expected, even for building a simple COM image.

Peter Szabo ended up creating a specialized tool to solve the problem:
https://github.com/pts/dosmc/blob/master/dosmc.dir/dosmc.pl

This is not a road I am willing to take, since I was simply (naively,
perhaps) looking for a way of building minimalist COM files using the C
language, hoping that Open Watcom would be able to do so, if properly
instructed. I think now that I might be using the wrong tool for the
job.

Mateusz

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[OpenWatcom] building a COM file without pulling in the Watcom standard library Mateusz Viste <mateusz@x.invalid> - 2023-07-31 17:28 +0200
  Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library JJ <jj4public@outlook.com> - 2023-08-01 18:38 +0700
    Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library Mateusz Viste <mateusz@x.invalid> - 2023-08-01 14:50 +0200
      Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library T. Ment <t.ment@protocol.invalid> - 2023-08-01 15:23 +0100
  Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library "Alexei A. Frounze" <alexfrunews@gmail.com> - 2023-08-02 20:28 -0700
    Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library Mateusz Viste <mateusz@x.invalid> - 2023-08-03 10:21 +0200
      Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library "Alexei A. Frounze" <alexfrunews@gmail.com> - 2023-08-03 19:41 -0700
        Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library Mateusz Viste <mateusz@x.invalid> - 2023-08-04 14:03 +0200
  Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library "R.Wieser" <address@is.invalid> - 2023-08-03 10:39 +0200
    Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library Mateusz Viste <mateusz@x.invalid> - 2023-08-03 12:07 +0200
      Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library "R.Wieser" <address@is.invalid> - 2023-08-03 14:35 +0200
      Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library "R.Wieser" <address@is.invalid> - 2023-08-04 08:31 +0200
        Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library Mateusz Viste <mateusz@x.invalid> - 2023-08-04 14:03 +0200
          Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library "R.Wieser" <address@is.invalid> - 2023-08-04 16:29 +0200
            Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library Mateusz Viste <mateusz@x.invalid> - 2023-08-04 16:56 +0200
              Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library "R.Wieser" <address@is.invalid> - 2023-08-04 19:02 +0200
                Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library Mateusz Viste <mateusz@x.invalid> - 2023-08-04 21:18 +0200
  Re: [OpenWatcom] building a COM file without pulling in the Watcom standard library Mateusz Viste <mateusz@x.invalid> - 2023-11-10 00:19 +0100

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