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Q47826: Default for NODATA When Using the _export Keyword |
/pubs/pc/reference/microsoft/kb/Q47826/ |
Article: Q47826
Version(s): 5.01.21 | 5.01.21
Operating System: MS-DOS | OS/2
Flags: ENDUSER | buglist5.10.21 buglist5.02 fixlist5.03
Last Modified: 21-AUG-1989
Question:
What is the default for NODATA when using the _export keyword? The
_export keyword is used to mark functions in DLLs for export. It
appears that for real-mode windows, for normal applications, _export
does not use NODATA. However, for DLLs (also for real-mode windows)
_export marks the function NODATA. How does the keyword _export mark
functions (NODATA or not).
Response:
The default as issued by the compiler is not NODATA, i.e., the
exported routine is assumed to use the shared data segment.
Unfortunately, the linker has a problem that causes it to mistakenly
assume NODATA for all exports declared from the .OBJ file.
Microsoft has confirmed this to be a problem with LINK Version 5.01.21
and 5.02. The problem was corrected in LINK Version 5.03 and later.
In OS/2 this should not make any difference. In Windows, the program
loader looks for the -Gw sequence in the prolog of the exported entry
and replaces it with a sequence to load DS. The _loadds keyword will
generate the load-DS sequence in the first place.
In any case, a workaround is to not use the _export keyword and
declare the routine in EXPORTS in the .DEF file.