Using XL Fortran in a 64-bit environment

The 64-bit environment addresses an increasing demand for larger storage requirements and greater processing power. The AIX® operating system provides an environment that allows you to develop and execute programs that exploit 64-bit processors through the use of 64-bit address space and 64-bit integers. XL Fortran only supports applications that target the 64-bit Large Data Type (LDT) Application Binary Interface (ABI). Non-LDT environments, such as AIX version 4, are no longer supported.

To support larger executables that can be fit within a 64-bit address space, a separate, 64-bit object form is used to meet the requirements of 64-bit executables. The binder binds 64-bit objects to create 64-bit executables. Note that objects that are bound together must all be of the same object format. The following scenarios are not permitted and will fail to load, or execute, or both:

A 64-bit object or executable that has references to symbols from a 32-bit library or shared library
A 32-bit object or executable that has references to symbols from a 64-bit library or shared library
A 64-bit executable that attempts to explicitly load a 32-bit module
A 32-bit executable that attempts to explicitly load a 64-bit module
Attempts to run 64-bit applications on 32-bit platforms

On both 64-bit and 32-bit platforms, 32-bit executables will continue to run as they currently do on a 32-bit platform. On 32-bit platforms, 64-bit executables can be generated by specifying the -q64 option.

The XL Fortran compiler mainly provides 64-bit mode support through the -q64 compiler option in conjunction with the -qarch compiler option. This combination determines the bit mode and instruction set for the target architecture. The -q32 and -q64 options take precedence over the setting of the -qarch option. Conflicts between the -q32 and -q64 options are resolved by the "last option wins" rule. Setting -qarch=ppc will ensure future compatibility for applications in 32–bit mode. For 64-bit mode applications, use -qarch=ppc64 to achieve the same effect for all present or future supported 64-bit mode systems. -qarch settings that target a specific architecture, like thepwr5, pwr6, ppc970, or auto settings will be more system-dependent.