To prepare symbolic debugging with WinDbg, the assembly source must be assembled with JWasm's -Zi option. Additionally, the MS linker has to be invoked with option /DEBUG. When WinDbg is launched, it will stop very early, before dlls have been initialized. To make it stop at the application's entry point, enter a "g start" ( or whatever the actual name of the entry point is ).
Screenshots of WinDbg sessions:
WinDbg, debugging a 32-bit Windows console application:
WinDbg, debugging a 64-bit Windows GUI application:
WinDbg, debugging a 64-bit Windows GUI application, with open locals view: