DOCERR: MASM 5.1 Instructions Operand Size Documented Wrong

 Last reviewed: November 3, 1994
Article ID: Q67439
The information in this article applies to:
  • Microsoft Macro Assembler for MS-DOS, versions 5.0, 5.1, and 5.1a
  • Microsoft Macro Assembler for OS/2, versions 5.1 and 5.1a

In the "Microsoft Macro Assembler 5.1 Reference" manual, a number of instructions indicate that their operand size is a mem64 when they should indicate an operand size of mem48. The instructions are documented incorrectly as LGDT, LIDT, LLDT, SGDT, SIDT, and SLDT. These instructions require the FWORD PTR operator and not the QWORD PTR operator. If the QWORD PTR operator is used, the Microsoft Macro Assembler (MASM) will generate the following warning: 

   warning A4057: illegal size for operand
These instructions are privileged 286 and 386 instructions that are used to load and save the protected mode descriptor table registers. These registers are only 6 bytes long, even though descriptor table entries are normally 8 bytes.

Additional reference words: 5.00 5.10 5.10a
KBCategory: kbprg kbdocerr
KBSubcategory: MASMLngIss

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Last reviewed: November 3, 1994
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