ID Number: Q81327
5.00 5.10 5.10a 6.00 6.00a 6.00b | 5.00 5.10 5.10a 6.00 6.00a 6.00b
MS-DOS | OS/2
Summary:
Microsoft Macro Assembler (MASM) versions 5.1 and 6.0 and Microsoft
QuickAssembler versions 2.01 and 2.51 place several restrictions on
the placement of EXTRN and EXTERN statements. The assembler also
makes assumptions on where the declarations are placed.
Because of these assumptions, the code may assemble correctly, but
cause the following link errors:
Warning: L4004 Possible fixup overflow at <addr> in segment <name>
-or-
Error L2002: fixup overflow at <addr> in segment <name>
More Information:
Here are the rules you should follow when declaring externals:
1. If you know which segment defines an external symbol, put the
EXTRN statement in that segment.
2. NEAR code labels (including procedures) must be declared in
the code segment from which they are accessed.
3. If you know the group but not the segment, position the EXTRN
statement outside any segment and reference the variable with
the group name. For example, if var1 is in DGROUP, you would
reference the variable as
mov DGROUP:var1, 10
4. If you know nothing about the location of an external
variable, put the EXTRN statement outside any segment. You can
use the SEG directive to access the external variable like
this:
mov ax, SEG var1
mov es, ax
mov ax, es:var1
5. If the symbol is an absolute symbol or a far code label, you
can declare it external anywhere in the source code.
While following these rules will help to avoid L2002 and L4004 fixup
overflow errors, the above rules are not absolute. Using groups,
ASSUME statements, and .MODELS you can often work around these errors.
EXTERN is the MASM 6.0 version of EXTRN. For more information about
EXTERN see pageS 222 to 224 of the MASM version 6.0 Programmer's
Guide. For more information on EXTRN see pageS 161 to 163 of the MASM
version 5.1 Programmer's Guide, or pages 169 to 171 of the Microsoft
QuickAssembler's Programer's Guide.
Additional reference words: 5.00 5.10 5.10a 6.00 6.00a 6.00b