FIX: JMP Jumps to the Proc When Using Duplicate Names

MS-DOS           | OS/2

The information in this article applies to:

• Microsoft Macro Assembler for MS-DOS, versions 6.0, 6.0a, and 6.0b
• Microsoft Macro Assembler for OS/2, versions 6.0, 6.0a, and 6.0b

SYMPTOMS

Using the Microsoft Macro Assembler (MASM) versions 6.0, 6.0a or 6.0b, the JMP instruction will jump to the procedure name rather than a local label if the names of the procedure and the local label are identical. After the jump, the procedure begins running rather than the code at the label.

RESOLUTION

To work around the problem, create a local label with a name that is different from the procedure name.

STATUS

Microsoft has confirmed this to be a problem in MASM versions 6.0, 6.0a, and 6.0b. This problem was corrected in MASM for MS-DOS version 6.1.

MORE INFORMATION

The sample code below does not generate a syntax error for the identical procedure name and label name because the label is local to the procedure it is defined in. If the label is defined with a double colon (::) instead of a single colon (:), it becomes a global label and causes the assembler to generate an error. The assembler should generate code that jumps to the local label rather than the procedure.

Sample Code

; Assemble options needed: none

.MODEL small .STACK 4096

.DATA

.CODE

   .startup
   call myproc
   .exit 0

   jmp SHORT mylabel

   ret  ; Should execute this

mylabel PROC

   ret  ; Shouldn't execute this

END