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

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dn. Fri, 4 Aug 2023 16:29:24 +0200, R.Wieser napisał:
> I noticed that you are compiling with the "-ms" switch
> (small memory model), which is incompatible with a COM style
> executable. Try "-mt" (tiny memory model) instead.

"-ms" is the proper switch for compiling object files for COM
executables. In fact, the wcc compiler doesn't even understand -mt.

"-mt" is only a convenience switch for wcl (Watcom's "compile & link"
tool) so it knows that after executing wcc -ms it has to pass the
"SYSTEM COM" option to wlink.

Building a COM itself is well documented and hence easy to achieve. The
problem here is that I was trying to make Open Watcom build a tiny (as
in "very small") COM file by avoiding Watcom's libc and startup code,
ie. passing "OPTION NODEFAULTLIBS" to wlink. Then the COM file indeed
becomes very small, but it also ceases working, as the generated code
seems to expect to be executed within an environment prepared by
Watcom's startup routines.

Most probably my expectations towards Open Watcom were too high. It is
an awesome tool, but it's simply not designed to build minimalist COM
files without major hackery.

Such hackery have been done by Peter Szabo (aka pts). I tested just now
his DOSMC tool, and it compiled this program:

void main(void) {
  static char *hello = "Hello$";
  _asm {
    lea ax, main
    mov ah, 9
    mov dx, hello
    int 0x21
  }
}

Into this:

00000000  E80400            call word 0x7
00000003  B44C              mov ah,0x4c
00000005  CD21              int 0x21
00000007  53                push bx
00000008  51                push cx
00000009  52                push dx
0000000A  56                push si
0000000B  57                push di
0000000C  8D060701          lea ax,[0x107]
00000010  B409              mov ah,0x9
00000012  8B162501          mov dx,[0x125]
00000016  CD21              int 0x21
00000018  5F                pop di
00000019  5E                pop si
0000001A  5A                pop dx
0000001B  59                pop cx
0000001C  5B                pop bx
0000001D  C3                ret
0000001E  48                dec ax
0000001F  656C              gs insb
00000021  6C                insb
00000022  6F                outsw
00000023  2400              and al,0x0
00000025  1E                push ds
00000026  01                db 0x01

Works perfectly, at least on this simple test example.
Too bad DOSMC is a perl Linux-only tool.

https://github.com/pts/dosmc


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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