does it complain if you just put /debug/debugtype:cv ?
also maybe try and specify a complete path like e:\codejps\myproject\myproject.pdb for the /pdb: argument and see if it likes that.
The vKim like tools shouldnt be too difficult to include, just add (for x64) in your source .asm
#define DBG64LIB "c:\GoAsm\dbg\Debug64.lib"
#define DEBUGEXE "c:\GoAsm\dbg\DbgWin.exe"
#include "c:\GoAsm\dbg\Debug64.a"
modify for where your GoAsm is, for example if its stored in codejps then create a dbg folder, and copy the .a, .lib and dbgwin.exe into it:
#define DBG64LIB "e:\codejps\dbg\Debug64.lib"
#define DEBUGEXE "e:\codejps\dbg\DbgWin.exe"
#include "e:\codejps\dbg\Debug64.a"
For x64 the debug.a (or debug.inc for x86) has all the macros that you use in it.
so for x86 masm i would use stuff like
Invoke MessageBox, hWnd, Addr szMsg, Addr szTitle, MB_OK
PrintDec eax ; shows return value in the DbgWin.exe program that will popup - or if its already running.
for x64 i dont know the specifics and for use with goasm, but i would imagine youll be using PrintQWORD macro's to see returned values
Other useful ones are PrintString, PrintStringByAddr, DumpMem, DbgDump
Maybe worth trying it out, will be 100 x better than messageboxes if you get it working:D