Q29735

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Q29735: LES Instruction Assembles Incorrectly

Article: Q29735
Version(s): 5.10
Operating System: MS-DOS
Flags: ENDUSER | buglist5.10
Last Modified: 23-MAY-1988

The following program demonstrates a problem with the LES
instructions in MASM Version 5.10.
   The first LES instruction (Parm1) assembles correctly, but the
second instruction (Parm2) generates an "immediate mode illegal"
message.
   The only difference between the two instructions is the order of
the arguments. In earlier versions of MASM, they produced identical
code.

   The problem is with the type operator and the way it handles
registers inside brackets ([]). The type operator makes things a
constant on the left of the expression.
   Parm1 works because it handles registers inside brackets
differently. "Type" turns bp into a constant; +10 then turns it back
into an addressing mode.
   However, in Parm2, bp+10 has been turned into an addressing mode,
which is then turned into a constant by "type x". This difference is
demonstrated in the following code:

              .model   small

x             struc
y             dd        ?
x             ends

Parm1         equ       dword ptr [bp+type x+10]
Parm2         equ       dword ptr [bp+10+type x]

              .code

begin:        les       di,Parm1
              les       di,Parm2

              end       begin