simple DOS EXE works but DOS COM crashes

[LowLevelMahn]

using: https://github.com/open-watcom/open-watcom-v2/releases/tag/Current-build, Last updated 2022-02-20 01:50:29

hello.c

#include <stdio.h>
void main()
{
  printf("hello\n");
}

build.bat

set WATCOM=%tools_dir%\open-watcom-2_0-c-win-x64
set WATCOM_BIN=%watcom%\binnt64
set INCLUDE=%watcom%\h
set PATH=%WATCOM_BIN%;%PATH%
set wcc_exe=%watcom_bin%\wcc.exe
set wlink_exe=%watcom_bin%\wlink.exe

%wcc_exe% hello.c
%wlink_exe% name hello.com system dos com file { hello.obj }

gives

Open Watcom C x86 16-bit Optimizing Compiler
Version 2.0 beta Feb 20 2022 00:59:21 (64-bit)
Copyright (c) 2002-2022 The Open Watcom Contributors. All Rights Reserved.
Portions Copyright (c) 1984-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See http://www.openwatcom.org/ for details.
hello.c: 8 lines, included 813, 0 warnings, 0 errors
Code size: 17
Open Watcom Linker Version 2.0 beta Feb 20 2022 00:55:27 (64-bit)
Copyright (c) 2002-2022 The Open Watcom Contributors. All Rights Reserved.
Portions Copyright (c) 1985-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See http://www.openwatcom.org/ for details.
loading object files
searching libraries
creating a DOS .COM executable
Warning! W1019: file clibs.lib(cstart): segment relocation at 0000:00a9
Warning! W1019: file clibs.lib(cstart): segment relocation at 0000:0135
Warning! W1019: file clibs.lib(cstart): segment relocation at 0000:021a
Warning! W1019: file clibs.lib(cstart): segment relocation at 0000:02fd
Warning! W1087: stack segment ignored in .COM file

and the COM file crashes

works when creating a exe with system dos

[jmalak]

Sorry, it is not a problem with OW.
COM format is special DOS format with single segment only.
See documentation Creating a Tiny Memory Model Application .

[LowLevelMahn]

thanks

wlink name hello.com system dos com file { %WATCOM%\lib286\dos\cstart_t.obj hello.obj }

creates a non-crashing hello.com

question: why does system dos com not implicitly add cstart_t.obj as first obj file?

[jmalak]

Read documentation carefully there is option -ms for compilation sources and linker command is also different, uses system com.
The right commands in your build.bat (which do all what you expect) are

%wcc_exe% hello.c -ms
%wlink_exe% name hello.com system com file { hello.obj }

against yours

%wcc_exe% hello.c
%wlink_exe% name hello.com system dos com file { hello.obj }

For cross-compilation you should add -bt=dos option for compilers too.
Your compiler command should looks like
%wcc_exe% hello.c -bt=dos -ms

If you don't specify -bt=dos option then implicit value is taken, by example if you compile on OS/2 then implicit equivalent of -bt=os2 is used not -bt=dos. It is good practice to specify -bt=... option on command line then command is cross-compile save.

[LowLevelMahn]

Thank your clearing that up - there are so many options and combination that sometimes/or partially work - trial & error isn't really a good strategie here :)

[jmalak]

Take into account that OW is cross-compiler by nature against Microsoft compilers or GCC which works by default for single target.
You need not to use too many option but you should always specify 3 things explicitly, even if it is defined implicitly for host system:

• compiler target -bt=... option (implicit is host system)
• compiler memory model -m... option (implicit is -ml for 16-bit, -mf or -ms for 32-bit, depend on target)
• linker target executable format system .... directive (implicit is host system for 32-bit and system dos is for 16-bit if host is 32-bit only, by example Linux host)

[LowLevelMahn]

thanks for the info