Relocatable Object Module Format (OMF) Specification
Relocatable Object Module Format (OMF) Specification
Relocatable Object Module Format (OMF) Specification
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<strong>Relocatable</strong> <strong>Object</strong> <strong>Module</strong> <strong>Format</strong><br />
88H WKEXT—Weak Extern Record (Comment Class A8)<br />
Description<br />
This record marks a set of external names as "weak," and for every weak extern, the record associates another<br />
external name to use as the default resolution.<br />
History<br />
This comment class and subtype is a Microsoft extension added for Microsoft Basic version 7.0. There is no<br />
construct in Microsoft Basic that produces it, but the record type is manually inserted into Microsoft Basic library<br />
modules.<br />
The first user-accessible construct to produce a weak extern was added for Microsoft MASM version 6.0.<br />
See the following "Notes" section for details on how and why this record is used in Microsoft’s Basic and MASM.<br />
Record <strong>Format</strong><br />
The subrecord format is:<br />
1 1 or 2 1 or 2<br />
A8 Weak EXTDEF Default Resolution<br />
Index<br />
EXTDEF Index<br />
<br />
The Weak EXTDEF Index field is the 1- or 2-byte index to the EXTDEF of the extern that is weak.<br />
The Default Resolution EXTDEF Index field is the 1- or 2-byte index to the EXTDEF of the extern that will be used<br />
to resolve the extern if no "stronger" link is found to resolve it.<br />
Notes<br />
There are two ways to cancel the "weakness" of a weak extern; both result in the extern becoming a<br />
"strong" extern (the same as an EXTDEF). They are:<br />
• If a PUBDEF for the weak extern is linked in<br />
• If an EXTDEF for the weak extern is found in another module (including libraries)<br />
If a weak extern becomes strong, then it must be resolved with a matching PUBDEF, just like a regular<br />
EXTDEF. If a weak extern has not become strong by the end of the linking process, then the default<br />
resolution is used.<br />
If two weak externs for the same symbol in different modules have differing default resolutions, many<br />
linkers will emit a warning.<br />
Weak externs do not query libraries for resolution; if an extern is still weak when libraries are searched,<br />
it stays weak and gets the default resolution. However, if a library module is linked in for other reasons<br />
(say, to resolve strong externs) and there are EXTDEFs for symbols that were weak, the symbols<br />
become strong.<br />
Tool Interface Standards (TIS) <strong>OMF</strong> <strong>Specification</strong>, Version 1.1 23
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