> The instruction at "0x00018084" referenced memory at "0x00018084". The
> memory could not be "read".

> Gottfried Hegmanns

> You need three files, hello.c and helloos2.def. Cut these from between the
'=='
> lines, then
> run the command, then test it with testhello.cmd

> ================ hello.c ======================
> #include <stdlib.h>
> #include <stdio.h>
> #include <os2emx.h>
> #define PVERSION "0.0"
> #define OK 0
> #define INVALID_CALL 40

> /* This routine returns a string 'Hello world: ' plus the first argument
*/

> /*
*/

> ULONG helloWorld(PCSZ name, LONG argc, const RXSTRING *argv,
>                     PCSZ queuename, PRXSTRING retstr)
> {
>   char *argv0;
>   retstr->strlength = 0;
>   if (argc != 1) return(INVALID_CALL);
>   strcpy(retstr->strptr, "Hello world: ");
>   argv0 = RXSTRPTR(argv[0]);
>   strcat(retstr->strptr, argv0);
>   retstr->strlength = strlen(retstr->strptr);
>   return(OK);
> }

> /* Routines to register these functions
*/

> /*
*/

> /* Returns the version of this program.
*/

> /* If one parameter is given, it prints out the version string.
*/

> /* Calling this function with more than one parameter causes "Incorrect
call  */

> /* to routine".
*/

> static void regfun (PCSZ name)
> {
>   RexxRegisterFunctionDll (name, "HELLOOS2", name);
> }

> /* This function will register all other functions
*/

> /*
*/

> ULONG helloLoadFuncs (PCSZ name, LONG argc, const RXSTRING *argv,
>                         PCSZ queuename, PRXSTRING retstr)
> {
>   int rc;
>   char *vs = PVERSION;
>   if (argc > 1) return INVALID_CALL;
>   regfun("helloWorld");
>   printf("helloLoadFuncs: helloos2.dll Library loaded\n");
>   MAKERXSTRING(*retstr, vs, strlen(vs));
>   return(OK);
> }
> ===================================================
> ============ helloos2.def =========================
> LIBRARY HELLOOS2 INITINSTANCE
> DESCRIPTION 'test rexx external function dll with gcc+emx under OS/2'
> DATA
>    MULTIPLE NONSHARED
> EXPORTS
>   HELLOWORLD             = helloWorld
>   HELLOLOADFUNCS         = helloLoadFuncs
> ===================================================
> =============== the command =======================
> gcc -Zmap -Zdll -Zomf -Zso -Zsys -Zlinker /map -s -O  \
>                   -o helloos2.dll hello.c helloos2.def
> ===================================================
> ============= testhello.cmd ==========================
> /**/
> call RxFuncAdd 'helloLoadFuncs', "helloos2", 'helloLoadFuncs'
> xx = helloLoadFuncs(1)
> say 'library version <'xx'> sucessfully loaded'
> answer = helloWorld("*** This is an argument ***")
> say answer
> ===================================================

> There is a problem in your code that causes Regina to crash. The line:
>   MAKERXSTRING(*retstr, vs, strlen(vs));
> in helloLoadFuncs() should be replaced with the following two lines:
>   strcpy( retstr->strptr, vs);
>   retstr->strlength = strlen(vs);

> The reason is that by default Regina provides a 256 character RXSTRING in
which
> you can deposit your return code from the external function. If you need
to return
> a value longer than 256 characters, you must allocate an RXSTRING strptr
of suitable
> length and populate the allocated memory.

> When the external function returns to Regina, it checks to see if the
address of the
> pointer supplied to the external function is the same as the one coming
back. If not,
> it assumes that the memory has been allocated and free's it.

> In your code, the pointers are different, but the memory you are passing
back is a
> constant, and when Regina tries to free it; it crashes.
> The OS/2 Rexx manual should explain this requirement (the Object Rexx one
does, and I
> hope the Regina manual also does).

> I guess that the reason it works under OS/2 is that freeing up a constant
memory address
> may not cause problems until later in the execution of the code (and you
may get away with
> it forever!)

> Cheers, Mark
> --------------------------------------------------------------------------
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