Mysterious MCH3601 errors at V4R3M0

[Jon.Paris@xxxxxxxxxx]

 >> how as control passes from one program to the next can one of the programs
in the stack only sometimes corrupt the stack before the first line of
executable code.

Quite simply. The corruption of the pointer to the variable (which is what is
being passed) can have occured some time before the actual call. Take the
following example:

In program A variable XYZ is defined as 20 characters long.

Program A calls program B passing XYZ.  In program B XYZ is defined as 200 long.

In program B the logic says:

  If <condition>
  Eval XYZ = *Blanks
  EndIf

Whenever the condition is true the 180 bytes of memory that follow the "real"
XYZ get 'nuked' - but only when the condition is true.  If that 180 bytes
contains the pointer that is about to be passed ........ boom (but only later
when the call is made).


This is a classic error that can surface when compiling for a new release
because the memory locations in the newly compiled objects can change.  Some of
the code in the original TAATOOLS (from QUSRTOOL) exhibits this problem when
switched to RPG IV.


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