TNS/R Native Application Migration Guide

Developing a Migration Strategy

TNS/R Native Application Migration Guide—523745-001

2-7

Eliminating Compatibility Traps

In most cases, data misalignment in data objects and reference misalignment in

pointers cause traps. To eliminate compatibility traps caused by data misalignment in

data objects, specify a FIELDALIGN SHARED2 pragma or directive for the misaligned

data object.

By default, the native compilers generate code for pointer dereferencing operations

that expects the pointer to contain an address that satisfies the alignment requirements

of the data object being pointed to. For example, a 4-byte object should have an

address which is a multiple of four. If the data object is at an address that does not

satisfy its alignment requirements, a compatibility trap occurs. To avoid this

compatibility trap, specify a REFALIGNED 2 on the pointer to the object. This directs

the native compilers to generate code that assumes the dereferenced object is not

properly aligned and compensates for the improper alignment. While REFALIGNED 2

always generates a few extra instructions for each dereferencing operation, a

compatibility trap results in hundreds of additional instructions.

These directives and pragmas ensure that compatibility traps do not occur. For

additional information on data alignment, see:

•

C/C++ Programmer’s Guide

•

pTAL Conversion Guide