AIX Version 4.3 Differences Guide

Segment Number Use in 64-Bit Mode Use in 32-Bit Mode
4-0xC shmat/mmap shmat/mmap
0xD Loader use Shared libraries
0xE shmat/mmap shmat/mmap
0xF Loader use Shared lib data
0x10-0x6FFFFFFF
Application text, data, Bss,
heap
N/A
0x70000000-0x7FFFFFFF Default shmat/mmap N/A
0x80000000-0x8FFFFFFF Private load N/A
0x90000000-0x9FFFFFFF
Shared library text and
data
N/A
0xA0000000-0xEFFFFFFF Reserved for system use N/A
0xF0000000-0xFFFFFFFF Application stack N/A
The following items give more detail on the use of the various segments in 32-bit
and 64-bit mode:
• Process private data
Segment number 2 continues to contain the process private segment. This
segment is substantially different for 32-bit and 64-bit processes. The process
private segment continues to contain errno, errnop, environ, the top_of_stack
structure, and the exec() arguments. It also contains the user structure,
primary user thread structure, and the primary kernel thread stack.
It does not contain the user thread stack or any user data. The user thread
structures (other than the primary) is moved to the kernel thread stack
segments for both 32-bit and 64-bit processes. The errno, errnop, and environ
locations are different in 32-bit and 64-bit mode. The top_of_stack structure is
reformatted for the 64-bit values for 64-bit processes.
The errno, errnop, environ, the top_of_stack structure, and the exec
arguments (all the user accessible data) are kept in the lowest one megabyte
of this segment and are user-modifiable. All data above this in the segment is
read-protected from user access. The segment table, adspace, and segstate
structures for the process are allocated from a region above the first megabyte
in the segment. The segment table is pinned. The region above these adspace
structures and below the primary kernel thread stack is used for the overflow
heap for the per-process loader heap.
• Executable text area
The text area starts in segment number 16. All segments from the start of the
executable, through, and including, the loader section of the executable, are
mapped in. No segments beyond the segment containing the loader section of
the executable are mapped in the address space. The text segments are
mapped read-only if the underlying file system supports mapping (JFS, NFS,
CD-ROM file system, AFS, and DFS support mapping). Otherwise, the text
section and the loader section are copied to working storage segments.
64-Bit Enablement 35