This document describes how to change to the large address-space model, which may be required for some applications that manipulate large amounts of data. This document applies to all levels of AIX.
The AIX and product documentation library is also available:
http://www.rs6000.ibm.com/resource/aix_resource/Pubs/index.html
Your computer divides the address space into sixteen equally sized segments of 256MB. When a program is loaded, by default, a single segment is allocated to program text (executable instructions) and a second segment is allocated to program data (heap, stack, and user block).
This arrangement is sufficient for most applications. However, applications that manipulate large amounts of data may require more than one segment for program data. Such allocation is facilitated with the large address-space model, which is described in InfoExplorer in the article "Large Program Support Overview". For AIX Version 4.3, check the product documentation for additional information.
When an application is compiled, the loader stores the maximum data-segment size in the executable file. This value may be changed with the two scripts in the following section. These two scripts modify the executable file header and cause the executable to use the large address-space model.
Create the file, maxdata, and carefully enter the script text given below. Put the file in the system directory where local commands are stored. This directory must be in the $PATH environment variable for the commands to be found. Make the file executable with the chmod command. Enter chmod 555 maxdata.
This is the maxdata script: ---this is beginning of script-- do not put this line in script--------------
#! /bin/ksh
# This script modifies 32-bit XCOFF variable o_maxdata (+4C).
# This script CANNOT be use on a 64-bit XCOFF executable.
# This script MUST be run on the REAL executable, you CANNOT run
# this script on a symbolic link.
# See "AIX: General Programming Concepts, Writing and Debugging Pgms."
# To find the current maxdata setting for an executable
# run the command dump -ov executable look for the maxDATA entry
# on the last line.
# This script requires exactly two parameters?
# 1st parm is name of executable
# 2nd parm is maxdata unit
# maxdata units are:
# 0 = 256mb
# 1 = 256mb
# 2 = 512mb
# 3 = 768mb
# 4 = 1024mb-1gb
# 5 = 1280mb
# 6 = 1536mb
# 7 = 1792mb
# 8 = 2048mb-2gb-max size for 32bit software/hardware
#
if [[ $# -ne 2 ]]
then
print 'usage: "maxdata XCOFF [0-8]"' ;
print '\tThe second parameter (maxdata size) specifies units of 256M.' ;
print '\ie: "maxdata /bin/xldb 4" sets /bin/xldb maxdata to 1G.' ;
exit ;
fi
# first parm a 32-bit xcoff?
file $1 | grep -q 'executable (RISC System/6000) or object module' ;
if [[ $? -ne 0 ]]
then
print "$1 isn't a readable 32-bit XCOFF file." ;
exit ;
fi
# ... and writable?
if [[ ! -w $1 ]]
then
print "$1 isn't a writable and executable file." ;
exit ;
fi
# second parm equals 0,1,2,...,8 ?
case ${2:-4} in
[0-8] ) typeset -i8 d=${2:-4}*16 ;
typeset -i10 m=${2:-4}*256 ;;
* ) print 'The second parameter has to be an integer [0-8].' ;
exit 1 ;;
esac
# Do it:
print -n "$1 o_maxdata before: " ; od -HAx -N4 -j76 $1 | head -1 ;
eval "print -n '\\0'${d#*#}'\\0\\0\\0' |
dd of=$1 bs=4 count=1 seek=19 conv=notrunc 2>/dev/null" ;
print -n "$1 o_maxdata after: " ; od -HAx -N4 -j76 $1 | head -1 ;
print "Maxdata in $1 now set to ${m}M." ;
----this is the end of the script -- do not put this line in script-----
Before using the maxdata script, you should check the current size of the executable. Enter the following command:
dump -ov executable-name
This should produce output similar to:
executable-name:
***Object Module Header***
# Sections Symbol Ptr # Symbols Opt Hdr Len Flags
4 0x00000000 0 72 0x1007
Flags=( RELFLG EXEC LNNO DYNLOAD )
Timestamp = "Jun 09 20:51:49 1999"
Magic = 0x1df (32-bit XCOFF)
***Optional Header***
Tsize Dsize Bsize Tstart Dstart
0x00005cc4 0x000009a4 0x00000984 0x10000100 0x00000000
SNloader SNentry SNtext SNtoc SNdata
0x0004 0x0002 0x0001 0x0002 0x0002
TXTalign DATAalign TOC vstamp entry
0x0005 0x0003 0x00000898 0x0001 0x00000878
maxSTACK maxDATA SNbss magic modtype
0x00000000 0x00000000 0x0003 0x010b 1L
Check the second entry in the last line (maxDATA) this field shows the current size of the program. You can look at the maxdata script for a descript of maxDATA units.
You MUST have read and write authority to the executable to use the maxdata script.
Using the above output as an example, to increase from 0 maxDATA units to 4 (1gb) enter the command:
maxdata executable-name 4
You should see output similar to:
executable-name o_maxdata before: 0000000 00000000
executable-name o_maxdata after: 0000000 40000000
Maxdata in executable-name now set to 1024M.
To set the executable back to 0 maxDATA units enter the command:
maxdata executable-name 0
You should see output similar to:
executable-name o_maxdata before: 0000000 40000000
executable-name o_maxdata after: 0000000 00000000
Maxdata in executable-name now set to 0M.
You should always use dump -ov executable-name to confirm the change.
[ Doc Ref: 90605208414730 Publish Date: Feb. 06, 2001 4FAX Ref: 2942 ]