XL Fortran Enterprise Edition for AIX : User's Guide - IBM

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 pointers 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, statically or shared, must all be of the same object format. The
following scenarios are not permitted and will fail to load, or execute, or both:
v A 64-bit object or executable that has references to symbols from a 32-bit library
or shared library
v A 32-bit object or executable that has references to symbols from a 64-bit library
or shared library
v A 64-bit executable that attempts to explicitly load a 32-bit module
v A 32-bit executable that attempts to explicitly load a 64-bit module
v 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.
The XL Fortran compiler mainly provides 64-bit mode support through the
compiler option -q64 in conjunction with the compiler option -qarch. 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.
The -q64 option will win over a 32-bit mode only -qarch setting, and the compiler
will upgrade the -qarch setting to something that will handle 64-bit mode.
Conflicts between the -q32 and -q64 options are resolved by the ″last option wins″
rule. Setting -qarch=com 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 the 603, 604, rs64a, rs64b, rs64c, pwr3, pwr4, pwr5,
ppc970, and auto settings will be more system-dependent.
64-Bit Large Data Type Support
The 64-bit Large Data Type (LDT) Application Binary Interface (ABI), or 64-bit LDT
ABI, increases scalability for 64-bit applications, while maintaining binary
compatibility for existing 32-bit applications. To accomplish this, some
system-derived types are increased from 32-bits to 64-bits. In addition, a new 64-bit
magic number is being introduced in the XCOFF definition to identify object code
files using the new 64-bit ABI.
The AIX 4.3 64-bit, non-LDT, ABI is no longer supported on AIX 5.1. Object code
files with the old 64-bit magic number will not link, load, or execute. Pre-AIX 5.1
64-bit applications must be recomplied in order to execute them on AIX 5.1. Binary
compatibility will be preserved for 32-bit objects generated on all earlier levels of
AIX, regardless of LDT support.
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