Message MCH0601 From strcpy() in C/C++ Called by RPG

This document shows how an RPG program calling a C/C++ program that uses strcpy() could cause an MCH0601.

Problem

The issue manifests as an MCH0601 to and from the end user program.

MCH0601    Escape                  40   02/28/12  11:53:02.720264  PGMNAME    PGMLIB       *STMT    PGMNAME   PGMLIB       *STMT
                                     From module . . . . . . . . :   PARSER
                                     From procedure  . . . . . . :   strcpy__FPcPCc
                                     Statement . . . . . . . . . :   1
                                     To module . . . . . . . . . :   PARSER
                                     To procedure  . . . . . . . :   strcpy__FPcPCc
                                     Statement . . . . . . . . . :   1
                                     Message . . . . :   Space offset X'00058000' or X'0000000000000000' is outside
                                       current limit for object JOBNAME JOBUSER    JOBNUM.

The procedure name shows that they're trying to do a strcpy().

The calling RPG program used the following prototype:

D Fcn1           pr             5i 0 extproc('eval__FPcRr')
D                            65535a
D                                8f

Variable definitions:

D Rtn             s              5i 0 inz(0)
D Str             S          65535A
D Flt             s              8f

And the call:
C                   Eval      Rtn = Fcn1(Str:Flt)

The C/C++ function had the following definition:

short int eval(char *string, long double &result)

The call to strcpy() was embedded several functions deep in the C/C++ code.

Resolution

strcpy() was signalling a message MCH0601 because it tried to address space beyond the end of the string that it was working with. As documented in the ILE C/C++ Runtime Library Functions manual, strcpy() does not perform any sort of length checking on the string that it is working with; it depends on the string being null terminated.

The solution was to change the RPG prototype to ensure that the string being passed to the C/C++ program was null terminated. This can be done by using the OPTIONS(*STRING) keyword on a pointer data type, as shown below:

D Fcn1            pr             5i 0 extproc('eval__FPcRr')
D                                 *   Value Options(*String)
D                                8f