Q66290: Reference to _pgmptr in CRTEXE.OBJ Is Invalid

Article: Q66290
Product(s): See article
Version(s): 6.00 6.00a
Operating System(s): OS/2
Keyword(s): ENDUSER | buglist6.00 | mspl13_c
Last Modified: 24-OCT-1990

Problem:

My program uses _pgmptr to find the pathname of the executable
program. When I change my Build Options to "PM multithreaded EXE
with runtime in DLL," _pgmptr contains all zeros.

Response:

This problem stems from the fact that while _pgmptr exists in
CDLLOBJS.DLL, there is no reference to _pgmptr in CDLLOBJS.DEF and
there is an invalid reference to it in CRTEXE.OBJ. Because of this,
you are unable to access it from your program. The first problem is
easily corrected by adding _pgmptr to the .DEF file. The second is not
possible to correct because Microsoft does not release the source code
to CRTEXE.OBJ.

Workaround
----------

However, there is a workaround if a DLL is used to access _pgmptr.
Fortunately the .OBJ file that links the start-up code into the DLL
does have the correct code to perform the function. The following code
fragment is an example of how this is done:

Code Example
------------

In your main application, prototype a function to take the place of
_pgmptr. For instance:

char *DLLpgmptr(void);          // returns _pgmptr from DLL

The function itself will be defined as follows:

/* foo.c */

extern char *_pgmptr;
char *_export _loadds DLLpgmptr(void);

char *_export _loadds DLLpgmptr(void)
{
        return(_pgmptr);
}

There is also a required .DEF file that may be defined as follows:

; foo.def

LIBRARY FOO INITINSTANCE
PROTMODE
DESCRIPTION    '_pgmptr replacement  function'
HEAPSIZE  8192
STACKSIZE 2048
DATA MULTIPLE

The compile line to make this into a DLL is as follows:

cl /c /MD /Gs /W4 foo.c

The link line is as follows:

link crtdll foo.obj, foo.dll ceexample os2, foo.def;
implib foo.lib f.dll

Move the resulting DLL to your LIBPATH and call DLLpgmptr() wherever
you would normally use _pgmptr, and link the library that results from
running IMPLIB into the final .EXE.

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