ID Number: Q81892
6.00 6.00a | 6.00 6.00a
MS-DOS | OS/2
buglist6.00 buglist6.0a
Summary:
PROBLEM ID: MSM9203003
SYMPTOMS
The Microsoft Macro Assembler (MASM) versions 6.0 and 6.0a
incorrectly assemble the FNENI or FNCLEX coprocessor instructions
if the instructions are used in a procedure declared with the PROC
USES directive. FNENI and FNCLEX used outsize of PROC USES
procedures assemble correctly.
RESOLUTION
Several methods can be used to work around this problem, including:
1. Using FENI or FCLEX instead of FNENI or FNCLEX.
2. Using a PROC without the USES directive.
3. Putting the opcode for FNENI or FNCLEX into the code directly.
The sample code below demonstrates this workaround. This could
also be done by setting up a macro that when invoked puts the
opcode into the code directly.
STATUS
Microsoft has confirmed this to be a problem in MASM versions 6.0
and 6.0a. We are researching this problem and will post new
information here as it becomes available.
More Information:
FENI enables interrupts by clearing the interrupt-enable mask in the
control word. Since the 80287, 80387, and 80486 coprocessors do not
have an interrupt-enable mask, this instruction is recognized but
ignored on these coprocessors. FENI is the wait version and FNENI is
the no-wait version.
FCLEX clears all coprocessor exception flags, the busy flag, and bit 7
in the status word. Bit 7 is the interrupt-request flag on the 8087
and the error-status flag on the 80287, 80387 and 80486 coprocessors.
FCLEX is the wait version and FNCLEX is the no-wait version.
If the following sample code is assembled, the FNENI and FNCLEX
instruction will generate the following code:
pop ax
iretd
pop ax
iret
Sample Code
-----------
; Assemble options needed: none
.MODEL small, c
.STACK
.CODE
.STARTUP
call func
.EXIT
func PROC USES ax
fneni ; This statement generates a pop ax and an iretd.
fnclex ; This statement generates a pop ax and an iret.
DW 0E0DBh ; This defines a FNENI statement.
DW 0E2DBh ; This defines a FNCLEX statement.
ret
func ENDP
END
Additional reference words: 6.00 6.00a