ID Number: Q73752
6.00 | 6.00
MS-DOS | OS/2
buglist6.00
Summary:
In certain situations, the Microsoft Macro Assembler (MASM) version
6.0 will not detect an overflow condition when initializing structure
elements. This will most likely occur when the MASM 5.1 compatibility
option is used (that is, /Zm on the command line, OPTION M510 in the
source code, or when using the MASM driver) and the initialized type
is of word size. In cases where the error is not generated but should
be, the specified initialization value, modulo the maximum size for
the type, is used as the value of the variable.
More Information:
In the sample code below, a structure is declared without initializing
the elements in the structure. Later, another structure is declared
that contains the first structure and it initializes the structure to
a value that will create an overflow condition. This error is not
caught by the assembler.
In the second case, a data item is allocated for the first structure
and initialized to a value that would be an overflow. Again, the
assembler does not generate an error if assembled with MASM 5.1
compatibility.
In the third case, a structure is declared and initialized at the same
time. In this instance, MASM will generate the following error if an
overflow condition exists.
error A2071: initializer magnitude too large for specified size
In this particular example, a number in the range of 65536 (010000h)
to 65663 (01007fh) will not be caught by the assembler if decimal
notation is used. If hex notation is used, the assembler will catch
the error.
To work around this, either avoid using the MASM 5.1 compatibility
options or use hex notation when initializing variables.
Microsoft has confirmed this to be a problem in MASM version 6.0. We
are researching this problem and will post new information here as it
becomes available.
Sample Code
-----------
; Assemble options needed: /Zm /Fl
.MODEL small
OPTION M510
Struc1 struc
StrucWord dw ?
Struc1 ends
Struc2 struc
foo Struc1 {65536} ; Should generate A2071 Error
Struc2 ends
Struc3 struc
StrucWord2 dw 65536 ; Does generate A2071 Error
Struc3 ends
.DATA
test1 Struc1 {65536} ; Should generate A2071 Error
test2 Struc2 { }
test3 Struc3 { } ; Does generate A2071 Error
END
end