Frequently Asked Questions

• Using masm and Debug
• DOS help.
  • MASM32 won't work at home
• Assemble and execute a program.
• Debug a program.
• Programming
• Relative Jump Out of Range
• Illegal Memory Reference
• Unexpected end of file encountered
• Macro Locals

DOS help

Basic commands - The following are the basic DOS commands needed for this class.

• Masm32 won't work at home - We'll assume that you've installed masm32 using the default location. DOS needs the PATH with the location of masm32. To make sure that we have the correct location:
• 16-bit programs used in HW1-3,
  • Open Command Prompt.
• Type exactly:
  •  PATH=\masm32\bin;%PATH%
• Type:
  • ml
• You should get a window that looks like below.

usage: ML [ options ] filelist [ /link linkoptions] Run "ML /help" or "ML /?" for more info

• 32-bit programs used HW4 and later. At home you'll need to download and assemble io.asm as listed in the following steps.
  • Visual Studio 6.0
    1. Locate the directory where C++ is installed, probably C:\Program Files\Microsoft Visual Studio\VC98\Bin.
    2. Copy the  file from C:\Program Files\Microsoft Visual Studio\VC98\Bin\vcvars32.batto the directory with the assembler program.
    3. In the directory where vcvars32.bat copied, type exactly: 
       • vcvars32                           See below for ERROR about ENVIRONMENT SPACE .
       • PATH=%PATH%;\masm32\bin
       • ml
       • You should get a window that looks like below:

4. Assemble io.asm
   • Download io.asm
   • ml /c /coff io.asm 

• Visual Studio .NET

1. Locate the .NET directory, probably:
   • C:\Program Files\Microsoft Visual Studio .NET\Vc7\Bin
2. Copy C:\Program Files\Microsoft Visual Studio .NET\Vc7\Bin\vcvars32.bat to the directory with the assembler program.
3. In the directory where vcvars32.bat was copied, type exactly: 
   • vcvars32                           See below for ERROR about ENVIRONMENT SPACE .
   • PATH=%PATH%;\masm32\bin
   • ml
   • You should get a window that looks like below:

4. Assemble io.asm
   • Download io.asm
   • ml /c /coff io.asm 

• ENVIRONMENT SPACE Error - On Windows 98 systems, the VC++ path may require more memory than available. Try entering the following and repeating Step 3 above:
  • path=.
• Assembling - To assemble a 32-bit program named Helloworld.asm enter:
  • ml /coff /Zi /Fl HelloWorld.asm /link io.obj /subsystem:console

• CD - Displays the name of or changes the current directory.
 
CD [drive:][path]
CD[..]
  ..   Specifies that you want to change to the parent directory.


Type CD drive: to display the current directory in the specified drive. Example: CD C:
Type CD without parameters to display the current drive and directory. Example: CD
Type CD path to change to a new directory. Example to change to the top directory: CD \

• DIR - Displays a list of files and subdirectories in a directory.
 
DIR [drive:][path][filename] [/P] [/W] [/A[[:]attributes]]
  [/O[[:]sortorder]] [/S] [/B] [/L] [/V] [/4]

  [drive:][path][filename]
              Specifies drive, directory, and/or files to list.
              (Could be enhanced file specification or multiple filespecs.)
  /P          Pauses after each screenful of information.
  /W          Uses wide list format.
  /A          Displays files with specified attributes.
  attributes   D  Directories                R  Read-only files
               H  Hidden files               A  Files ready for archiving
               S  System files               -  Prefix meaning not
  /O          List by files in sorted order.
  sortorder    N  By name (alphabetic)       S  By size (smallest first)
               E  By extension (alphabetic)  D  By date & time (earliest first)
               G  Group directories first    -  Prefix to reverse order
               A  By Last Access Date (earliest first)
  /S          Displays files in specified directory and all subdirectories.
  /B          Uses bare format (no heading information or summary).
  /L          Uses lowercase.
  /V          Verbose mode.
  /4          Displays year with 4 digits (ignored if /V also given).

Switches may be preset in the DIRCMD environment variable.  Override
preset switches by prefixing any switch with - (hyphen)--for example, /-W.
 

• MD - Creates a directory.

 
MD [drive:]path

Type MD path to create a new directory path. Example to create a new directory named C335 at the top of the directory tree:
    MD \C335

• ML - Assembles a program, generates error list, and produces an object file for linking. To assemble the program HW1.ASM enter:

ml /Fl HW1.ASM
• LINK - Links the object file with optional libraries functions into an executable program. To link HW1.OBJ (assuming that it uses no external library functions):
 
LINK /v HW1

• Debug - Runs the Debugger (described below) to execute an executable Assembly program while watching the internal operation of the CPU and memory. To debug the HW1 program:
 
debug HW1.exe

Assembler

2.    Assemble - Windows 95/98 run MS-DOS by Start | Programs | MS-DOS.
       Or , , .

To assemble the Hw1.Asm program at IUS enter:

v:\common\user\c335\assembler                Do once for DOS mappings.
ml /Fl hw1.asm                               Do each time program changed.

4.   Link - The assembly generates an object code corresponding to the assembly source instructions.
                 Link the object code of Hw1.Obj into an executable module named Hw1.Exe by entering:

link hw1.obj,,,,,

debug hw1

Debugging

• Starting Debugger - debug filename.exe - where filename is the name of an executable file (i.e. has an exe extension).

The debugger will display a command prompt of a '-'. The five commands needed are:

1. u - Unassemble the machine code. Lists the mnemonic that correspond to the machine code. ADD AX, +06 corresponds to 83C006 machine code.

   u 12C0:0000 BBBF12 MOV BX,12BF 12C0:0003 8EDB MOV DS,BX 12C0:0005 A10000 MOV AX,[0000] 12C0:0008 83C006 ADD AX,+06 12C0:000B 2B060400 SUB AX,[0004] 12C0:000F BA3412 MOV DX,1234 12C0:0012 F7260200 MUL WORD PTR [0002] 12C0:0016 A30600 MOV [0006],AX 12C0:0019 B44C MOV AH,4C 12C0:001B CD21 INT 21 12C0:001D C3 RET 12C0:001E BFB2E8 MOV DI,E8B2

2. r - Register view. Displays the registers and next instruction to execute.

   r AX=0000 BX=0000 CX=002D DX=0000 SP=00FE BP=0000 SI=0000 DI=000 DS=12AF ES=12AF SS=12C2 CS=12C0 IP=0000 NV UP EI PL NZ NA PO NC 12C0:0000 BBBF12 MOV BX,12BF

3. p - Proceed by executing the next one or more instructions. The registers and next instruction to execute are displayed.

   p2 AX=0000 BX=12BF CX=002D DX=0000 SP=00FE BP=0000 SI=0000 DI=0000 DS=12AF ES=12AF SS=12C2 CS=12C0 IP=0003 NV UP EI PL NZ NA PO NC 12C0:0003 8EDB MOV DS,BX AX=0000 BX=12BF CX=002D DX=0000 SP=00FE BP=0000 SI=0000 DI=0000 DS=12BF ES=12AF SS=12C2 CS=12C0 IP=0005 NV UP EI PL NZ NA PO NC 12C0:0005 A10000 MOV AX,[0000] DS:0000=0064

4. d - Dump memory. The d ds:0 command dumps memory pointed to by the DS register. Memory containing the program data variables has been dumped, variable S has been located and underlined in the following example. 

   d ds:0 S 12BF:0000 64 00 08 00 01 00 00 00-00 00 00 00 00 00 00 00 d............... 12BF:0010 BB BF 12 8E DB A1 00 00-83 C0 06 2B 06 04 00 BA ...........+.... 12BF:0020 34 12 F7 26 02 00 A3 06-00 B4 4C CD 21 C3 BF B2 4..&......L.!... 12BF:0030 E8 B4 2A CD 21 98 51 52-8B F0 D1 E6 03 F0 8B CE ..*.!.QR........ 12BF:0040 A1 12 83 B6 03 57 E8 A9-25 5F 03 F1 B9 03 00 F3 .....W..%_...... 12BF:0050 A4 B0 00 AA 5A 59 C3 8A-D0 32 F6 B8 23 65 CD 21 ....ZY...2..#e.! 12BF:0060 C3 80 3E 27 D3 00 75 72-8B 36 D7 E2 32 D2 AC 0A ..>'..ur.6..2... 12BF:0070 C0 74 26 3C 2A 75 0F F6-C2 02 74 05 80 CA 01 EB .t&<*u....t.....

5. g - Go execute program. Starts execution at the next instruction. The following executes through the last instruction Int 21h which terminates the program.

   g Program terminated normally

Programming

**Error** for.asm(13) Relative jump out of range by 0018h bytes

do:                                ; do {
        :                                   :
        :                                   :

while:    Cmp    Ax, 5             : } while( Ax != 5 );
          Jne    do
endwhile:

1. Reduce the number of between the do: label and Jne conditional. This may not always be practical.
2. Complement the logic of the conditional and use an unconditional branch to the distant target label, for example:

while:    Cmp    Ax, 5
          Je     endwhile
          Jmp    do
endwhile:

3. Keep the logic of the conditional but branch to an intermediate label that branches unconditionally to the distant target label, for example:

while:    Cmp    Ax, 5
          Jne    intermediate
          Jmp    endwhile
intermediate:
          Jmp    do
endwhile:

**Error** hw4.ASM(50) Illegal memory reference

Mov    AB, BA

Mov    Ax, BA
Mov    AB, Ax
 

*Warning* hw4.ASM(86) Open procedure: MAIN
*Warning* hw4.ASM(86) Open segment: CODE
**Fatal** hw4.ASM(86) Unexpected end of file encountered
 
• Missing labels - Common mistake is missing labels in the program. Note that a label must have a : following. For example:
while   Cmp    Ax, 5                does NOT define a label while but:

while:   Cmp   Ax, 5                DOES define a label while.
 

• Missing MACRO ENDM - Each macro needs an ENDM.
• Missing ENDIF - A conditional starts with IF and must end with ENDIF. Don't confuse with a label IF: which has a colon at the end.

Macro locals need to be defined immediately after the start of the macro. For example:

.Sample    Macro    N
                Local      L
                Ifb          <&N>
                               exitm
                Endif
                    :
                    :
endm