AIX Version 4.3 Differences Guide

Depending on the execution environment of the executable and the targeted
XCOFF format, the following combinations exist:
• 32-bit program manipulating 32-bit XCOFF files.
A 32-bit program that manipulates 32-bit XCOFF files will require no change to
continue to do so with the new header files.
Note: Since the types of some fields are being changed from long to int, code
that takes the address of such a field will result in a compiler warning when
compiled in ANSI mode.
• 32-bit program manipulating 64-bit XCOFF files.
An existing 32-bit program that manipulates 32-bit XCOFF files can be
recompiled to manipulate 64-bit XCOFF files by defining the symbol
__XCOFF64__. Some code changes will be necessary, but the changes with
respect to the file format will be limited to cases where 32-bit XCOFF and
64-bit XCOFF use different constructs. In particular, n_name will not be
defined in struct syment, and use of struct auxent will require changes since
auxiliary symbols are redefined.
• 64-bit program manipulating 32-bit XCOFF files.
An existing 32-bit program that processes 32-bit XCOFF files can be
recompiled to a 64-bit program without change (with respect to the XCOFF
definition) with two exceptions:
• Pointers in the existing XCOFF files will be defined as ints in 64-bit mode.
• Existing header files use preprocessor macro definitions in some cases.
These same macros may no longer exist when compiling in 64-bit mode, so
incidental use of the macros may require a code change.
3.2.3.3 Incomplete aouthdr Structure
Non-executable XCOFF files do not require a full-size auxiliary header. Current
practice defines a short 32-bit auxiliary header that is generated by the compiler
or the linker when the output file is not an executable. A short 64-bit auxiliary
header will not be required by this definition. Applications examining
non-executables must examine f_opthdr in the XCOFF header to determine how
much of the auxiliary header is in the file.
There will be no auxiliary header used for non-executable 64-bit XCOFF files.
Applications needing the fields from the auxiliary header for non-executable
64-bit XCOFF files should use the information in the section headers to generate
these values. The fields where this may be necessary are text, data, and BSS
sizes.
3.2.3.4 XCOFF Magic Number
The calling conventions for 32-bit mode and 64-bit mode are different in detail
because one saves 32-bit General Purpose Registers (GPRs) onto the stack
frame, and the other saves 64-bit GPRs. Calling from a program of one mode to a
subroutine of the other mode is not supported. The linkage editor ld refuses a
request to link programs of differing execution mode.
Because of this, a new magic number has been introduced for 64-bit execution
mode. The primary purpose of the XCOFF magic number is to identify the
associated Application Binary Interface (ABI), which implies a hardware system
48 AIX Version 4.3 Differences Guide