FIX: MASM 6.0 May Generate Wrong Listing for CMPXCHG (79835)

SYMPTOMS

When using the Microsoft Macro Assembler (MASM) to generate a listing file for an assembler source file that contains a CMPXCHG instruction, errors may occur in that listing. A colon is appended to bytes of values 26h, 2Eh, 36h, and 3Eh when they appear in an instruction. For example, the following are generated:

   0000  0F B0 26: 00 00              cmpxchg data1, ah
   0005  0F B0 2E: 00 00              cmpxchg data1, ch
   000A  0F B0 36: 00 00              cmpxchg data1, dh
   000F  0F B0 3E: 00 00              cmpxchg data1, bh
				

instead of the following:

   0000  0F B0 26 0000  R             cmpxchg data1, ah
   0005  0F B0 2E 0000  R             cmpxchg data1, ch
   000A  0F B0 36 0000  R             cmpxchg data1, dh
   000F  0F B0 3E 0000  R             cmpxchg data1, bh
				

In addition, the address of a memory location is not always shown; instead, a series of disjoint zero bytes appear. For example, the following is generated:

   0014  0F B0 16 00 00               cmpxchg data2, dl
				

instead of the following:

   0014  0F B0 16 0100  R             cmpxchg data2, dl
				

Note that this also occurs in the first example. Finally, extra trailing bytes may be placed in the listing file. For example, the following is generated:

   0019  67& 0F B1 94 73 00000200  R  cmpxchg data3[ebx+2*esi],dx
         00 00 00 09
				

instead of the following:

   0019  67& 0F B1 94 73 00000200  R  cmpxchg data3[ebx+2*esi],dx
				

; Assemble options needed: /c /Fl

.MODEL small
.486
.STACK 4096

.DATA
data1 DB 100h DUP ('x')
data2 DB 100h DUP ('y')
data3 DW 100h DUP (1)

.CODE
start:
     cmpxchg data1, ah
     cmpxchg data1, ch
     cmpxchg data1, dh
     cmpxchg data1, bh
     cmpxchg data2, dl
     cmpxchg data3[ebx+2*esi],dx
END start